In the past the treatment of industrial residues from copper, lead or zinc industry focused in the majority of cases only on the recovery of one target metal. Mostly it is the focal metal produced in the industry the residue arises from. With this, valuable accompanying elements were often disregarded. Especially in copper, zinc and lead industry minor metals, like the group of precious metals but also others like indium or germanium, are interesting side-elements occurring in the concentrates next to the base metal itself. Although a recovery of these elements is partly considered in the base metal production, the presence in the corresponding residues in regard to their recycling is unvalued in a lot of processes until today. This offers the chance in future recycling concepts that these minor elements, like for instance silver, can contribute to the overall economic feasibility of potential new processes, even though they occur in significant lower amount as the base metal in the tailings, dusts, sludge or dusts of the corresponding industry. For example the annually produced and mainly land filled amount of leach residues from zinc industry contains roughly 500 tons silver next to other valuable elements, like zinc or lead. Thus, this paper tries to answer the question how recycling of such residues can contribute to the supply of minor elements, especially at the example of silver.
An important scientific and utilitarian challenge is to provide repeatability of the chemical composition in volume of billets, which guarantee the uniform yield stress during hot metal forming processes. During real billet manufacturing processes the segregation of chemical composition is observed. It depends on the type of alloy, solidification process conditions, and technological factors. This segregation can occur in the microscale (microsegregation) or in the macroscale (macrosegregation). The microsegregation can be reduced by the homogenisation but macrosegregation is an indelible defect. An effective way to reduce macrosegregation is electromagnetic stirring of liquid metal before solidification. The effectiveness of this mixing depends on the position of the stirring coil in relation to the solidification area.
The paper presents the impact of selected continuous casting process parameters (casting speed, cooling medium flow in the primary cooling) on the alloying elements macrosegregation in the billets. Additionally macrostructures of billets were reported and electrical conductivity of material as an alternative measure of the alloying elements content was done. The distribution of alloying elements on the billet diameter shows a maximum set asymmetrically relative to the axis of the billet (horizontal casting). Variation of the silicon content is greater than for the magnesium. Changing the conditions of the mould primary cooling – increase the flow of cooling medium results in a decrease of solidification zone distance from the mixing coil and causes mainly the reduction of magnesium macrosegregation.
Fe is a detrimental impurity element in recycled, secondary Al-Si alloys. It causes decrease of castability and promotes crack initiation due to formation of primary, Fe containing, intermetallic phases e.g. β-(Al,Si)5,5Fe. The Fe content in Al-Si-alloy melts can be remarkably reduced by removal of these phases above the solidus temperature of the alloys. For success of Fe removal, it is crucial how much Fe is bond by primary crystallites. Therefore, the chemical composition is as important as conditioning of the melts regarding morphology and volume fraction of the primary crystallites.
Within the present study, the effect of Mn and Cr on primary intermetallic phase formation was investigated in AlSi7.1at%(Fe+M)1.5at% with M = Cr, Mn produced by arc melting from pure elements. The optimum melt conditioning temperature was determined by Thermo-Calc calculations in combination with differential thermal analysis as 620°C. The melts were treated for 2 h in alumina crucibles under Ar atmosphere and quenched. The microstructure was scrutinized using scanning electron microscopy including energy dispersive X-ray spectroscopy to measure chemical compositions and electron backscatter diffraction analysis for correct phase identification.
In Mn-containing alloys and in Cr-containing alloys with 0.6at% Cr or less, the primary crystallites consist of α-(Al,Si)19(Fe,M)4. At higher Cr contents, α-Al13Cr4Si4 and β-Al9Cr3Si form additionally. All these phases form large massive polyhedral crystallites which are advantageous for filtration. Thus, the Fe content in the residual melt could be reduced to about 30% of the original Fe content. Simultaneously, considerably less Cr than Mn would remains in the melt.
The given study deals with advantages and disadvantages of aluminum alloys application for oil and gas extraction. Aluminum alloy applications in drilling pipe, tapered and casing tubing as well as in raisers to extract hydrocarbons have been widely known for a long time. Aluminum alloys application in pipe manufacturing has proved its advantages compared to conventional steel pipes; despite this application in steel pipe manufacturing aluminum pipes have remained in narrow and limited utilization. These limits result from certain aluminum alloys drawbacks such as low hardness causing increased pipe wear and limited corrosion resistance under different conditions. In spite of the disadvantages, structural aluminum alloys, have proved to have certain advantages, e.g. hydrogen-sulfide corrosion resistance, low temperature properties stability and, finally, huge strength-to-weight ratio. Unfortunately, the disadvantages still prevail especially in conventional drilling. Currently petrochemical industry is becoming more sophisticated in field development conditions: super deep wells, complicated well space trajectory and sea bed developments, thus resulting in drilling costs increase. As a result, the limitation and obstacles to apply aluminum alloys in the petrochemical industry have been brought for reconsideration.
The results of alloying systems Al-Cu-Mg and Al-Zn-Mg-Cu application in real field developments and basic problems those companies faced with contact corrosion in condition corrosive mediums and high temperatures possible. Results received, the examples verifying aluminum alloys D16T and 1953T1 temperature stability in range temperature 200-250 0C at both short-term on 3-10 minutes and long-term operation until 1000 hours near 150 0C in the well environment have been presented. The testing results pilot micro arc oxidation of surface treatment of near-to-fastener pipe area, current treatment isolated contact between aluminum pipe and steel joint to avoid negative impact on contact corrosion have been provided. These data have proved the feasibility of D16T and 1953T1 alloys pipes compared to steel pipes. The aluminum alloys corrosion stability under the real operation conditions has been proved. The obtained results verified the aluminum alloy advantages compared to steel prefabricated pipes. The provided examples illustrated possible techniques to minimize aluminum alloys drawbacks and eliminate imaginary obstacles for further implementing light alloy pipes in the petrochemical industry.
Steel-aluminum wires, despite their common use, show insufficient operational properties for current needs. Their main disadvantages are high mass and maximum operating temperature limit that guarantees the stability of mechanical properties at 80°C, which more and more often proves to be insufficient. Current trends in the overhead electrical power engineering in the area of wire materials, include e.g. the improvement of aluminum alloys for electrical purposes, development of composite cores in place of steel in bimetallic conductors and overall improvement of mechanical, electrical and operational properties of the wires. Alloying pure aluminum with other elements results in an inevitable decrease of its electrical conductivity, but at the same time it creates the possibility for the mechanical and operating properties improvement.
The article presents the research results on drawing process for the new aluminum based alloys with the addition of zirconium, silver and molybdenum. Technical aluminum grade enriched with a modifier was used as a reference material. This paper presents an analysis of the properties of the produced wires dedicated for electrical applications. Wires were obtained in a laboratory continuous casting process with various process parameters.
This paper was produced as part of INNOTECH II project financed by the National Research and Development Centre.
The solidification defects like shrinkage cavity, porosity can be minimized by designing an appropriate feeding system ensuring directional solidification in the casting. Gating and feeding system values varies according to geometry of component. Riser should provide sufficient amount of capacity to provide required amount of molten metal and should solidify at the last after solidifying casting. In this paper, the values shrinkage porosities for various riser heights had been calculated and from that optimal riser height is selected. Similarly the effect of riser heights on yield was also studied. By this optimal design a pattern was prepared by using 3D printing with FDM technique with Polylactic acid (PLA) material.
Using nanoparticles as reinforcement for aluminum matrix composites allows significantly increase mechanical and operational properties of details. However, input of exogenous nanoparticles into the aluminum melts is associated with significant technological difficulties caused by their agglomeration and poor wettability with liquid aluminum. For these reasons, it is ineffective to use traditional liquid phase methods of composites production (stir casting, etc.) for synthesis of aluminum matrix nanocomposites. One of solutions is the input of exogenous nanoparticles in metal melts within mechanically activated and compacted mixture of reaction-active powder precursors.
Within designated approach was developed liquid-phase technological process of production of aluminum matrix nanocomposites of the system Al-Al3Ti-TiB2-Al2O3, including mechanical activation of titanium and boron powders with alumina nanoparticles in planetary ball mill, compacting the mixture and entering the preforms into matrix melt, holding of composite melt for components interaction, stirring and pouring. Selection of reinforcing components based on thermodynamic analysis of interphase interaction processes in considered system. The effect of temperature and time parameters of technological process of aluminum matrix nanocomposites manufacturing and thermal conditions of composite melt crystallization on structure formation and phase composition of cast samples are studied. Adding of nanoparticles leads to decrease in the mean size of intermetallic compounds and changes their morphology to a more compact and also improves the uniformity of their distribution in the structure of cast material. X-ray phase analysis confirms the formation of target endogenous reinforcing phases and retention of exogenous nanoparticles in conditions of liquid-phase technology of nanocomposites production.
Twin-roll cast Al-Mg-Sc alloy was processed by equal-channel angular pressing in order to produce ultrafine-grained structure. During the subsequent heat treatment new grains formed via recrystallization. The process was influenced by presence of Al3Sc precipitates. The microstructure was studied by the means of scanning electron microscopy, electron back-scatter diffraction and transmission electron microscopy.
One of the basic operational hazards of overhead conductors is fatigue damage.
Fatigue damage is caused by defects of the structure (inclusions, micro-ruptures or hollows, created as a result of the technological process) as well as superficial defects, which are a consequence of surface processing procedures. Hard temper wires are commonly used as part of overhead conductors (about 90% strain hardening). In theory, they should also have a higher fatigue resistance threshold than soft temper wires. This research aims at conducting an experimental evaluation of the influence of the temper of EN AW 1370 and Cu-ETP wires on their fatigue resistance.
In this article, there are results of the research into fatigue resistance of various levels strain hardening wires. On the basis of the results of the research, Wohler’s curves have been designed. This describes the correlation between tension in the function of cycle numbers and material fatigue. An evaluation of fatigue fractures of wires, with the use of the scanning microscopy technique has been made as well.
In this study, the effect of Ti addition on phase formation, microstructure, and hardness of Al1.5CoCrFeMoNiTix (x=0-0.6) high entropy alloys (HEAs) were investigated. The Al1.5CoCrFeMoNiTix HEAs were synthesized by vacuum arc melting in argon atmosphere from high purity elements. The effects of the addition of the Ti on the phase formation, microstructure and hardness of HEAs were investigated by X-ray diffraction (XRD), scanning electron microscopy (SEM), and Vickers hardness tests. The major phases in both Al1.5CoCrFeMoNi and Al1.5CoCrFeMoNiTix alloys were identified as body-centered cubic (BCC), ordered BCC (B2) and sigma (). The results show that the addition of Ti element can improve the Vickers hardness of the based alloys. The hardness values of the alloys increase when the Ti content increases from 0.1 to 0.5 and peak (869 HV) at a Ti content of 0.5. The effects of Ti additions on microstructure of the base Al1.5CoCrFeMoNi HEAs were discussed.
In this work, the effects of Fe particles weight percent (from 5 to 14%) and changing the tool rotation direction in each pass were studied on the microstructure evolution and mechanical properties of the in-situ Al/intermetallic composites produced by 1 to 3 passes friction stir processing (FSP) with ~10 µm Fe particles. Optical and scanning electron microscopes were used for investigation of the composites homogeneity, formation of Al/Fe intermetallic compounds and fracture surfaces. Tensile and microhardness tests were also carried out in order to explore the mechanical properties of the produced composites. The results showed that changing the tool rotation direction in each pass reduced the asymmetrical distribution of the reinforcing particles and led to better dispersion of Fe particles due to overlapping of the advancing and retreating sides in the samples. Higher amount of Al5Fe2 and Al3Fe intermetallic compounds were also formed in the composites produced by changing the tool rotation direction. Increase in the particles weight percent refined the composite grains (from ~35 m in the sample processed without particles to ~6 m in the composite included 14 weight percent of particles). Tensile test results indicated that changing the tool rotation direction in each pass resulted in higher values of ultimate tensile strength (UTS). In addition, enhancement of the reinforcing particles increased UTS of the composite up to ~60% due to finer grain structure as well as the higher load bearing capacity of the reinforcing particles compared to aluminum matrix.
Magnesium alloy and its composites are lightest metal based structural materials with strong potential in wide spectrum of industrial applications including automobile and aerospace and electronics industries. In this work, Mg-3%Al alloys were reinforced by graphene nano-plates using powder metallurgy technique including microwave sintering and hot extrusion. Graphene nano-plates were synthesised using modified Hummer’s method. Raman test and FESEM analyses were carried out to confirm the formation of graphene nano-plates. The powders of Mg and 3%Al were mixed with graphene nano-plates. The microstructural characterization of the bulk composite revealed a reasonably uniform distribution of the graphene nano-plates in the matrix. The EDX results showed the presence of aluminium in the composite, while XRD result revealed that the aluminium powder completely dissolve and makes a solid solution of Mg. The microhardness test were performed with a Vickers hardness testing machine (Model: MTR3/50-50/NI). The measurements were made on samples with a 100-g load applied by the indenter for 20 s. The tests were repeated in five different regions to get the average value of Vickers hardness. To study the sliding contact behaviour, micro-scratch test was carried out using MTR3/50-50/NI instrument supplied by MICROTEST S.A, Spain. The indentation force, 9.8 N, was applied to the polished samples in order to get an initial penetration. An attempt is made to correlate the microstructural characteristics with the mechanical/tribological response of the monolithic and composite samples.
Magnesium alloys are studied for their low density and good mechanical properties. They find application in the automotive and aviation industry. Magnesium is biocompatible and non-toxic element with properties similar to bone tissue, so it can be also used as material for biodegradable implants. In such case, high demands on mechanical and corrosion properties are required. Therefore, properties of pure magnesium need to be improved by alloying. One of the alloying systems is known as WZ (Mg-Y-Zn) series. Yttrium and zinc forms intermetallic phases with magnesium which increase mechanical properties. Properties of this alloy may also be altered by suitable heat treatment or thermomechanical processing. Present contribution is focused on preparation and characterization of the Mg-2Y-1Zn alloy by extrusion. Microstructure, mechanical properties, hardness and corrosion properties are studied and compared with the as-cast material.
The recrystallization process of Mg-Ce alloy after high-pressure torsion (HPT) was investigated using differential scanning calorimetry (DSC) technique. The DSC results show that the recrystallization peak temperature increases with increasing the heating rate which confirms that recrystallization is thermally activated and kinetically controlled. The recrystallized volume fraction, the rate of recrystallization, the transformation function and the kinetic parameters (activation energy and Avrami exponent) for Mg-Ce alloy were estimated using several analytical approaches.
Intensive efforts have been recently made for the production and processing of Mg-based light structural alloys, which would provide the utilization in the automotive and aerospace engineering, medical implants and equipment, power generation system, etc. This interest is growing due to their special mechanical properties. Three magnesium alloys containing neodymium (Nd) and/or yttrium (W) were investigated to evaluate the potential improvement of mechanical properties. The mechanical strength of the alloys was evaluated by compression deformation tests in the extrusion direction (ED) and in the transverse direction (TD). Acoustic emission technique was concurrently applied to investigate activity of particular deformation mechanisms. During deformation tests was observed different shape of the deformation curves in ED and TD direction, which indicate diverse behavior due to unique texture of material. Microstructure observations, processed by scanning electron microscope (SEM) with EBSD camera, in addition demonstrate a relation between the microstructure and an activation various deformation mechanisms. The highest yield strength of samples which contents the highest amount of rare earths WN43, as compared with N2 and W4 samples, indicated that mechanical properties of magnesium alloys is dependent on chemical composition of rare earths.
In this study, effect of indium (In) addition on microstructure and mechanical properties of AM60 magnesium alloys was investigated. In additions were made by 0.2, 0.5 and 1 wt%. Alloys were produced by conventional gravity casting in a steel mould. A homogenization treatment at 350 °C for 24 h was performed after the casting processes. Homogenized samples were 1 pass hot-rolled by 40% thickness reduction at 350 °C. The results showed that the average grain size of as-cast and hot-rolled AM60 alloys decreased with In addition. SEM analysis revealed that In addition led to formation of tiny Mg-In binary second phases at triple junctions. Tensile strength of as-cast AM60 alloy increased with increasing amount of In up to 0.5 wt% above which it decreased. However, after hot-rolling process, AM60 alloy containing 0.2 wt% In showed the best tensile properties. These improvements was attributed to the refinement of microstructure and dispersion strengthening by Mg-In intermetallic phases.
Electron beam welding offers many advantages over other methods of fusion welding. High current density of electron beam is one of the advantages. Energy delivered on the surface of welded components allows rapid melting and evaporation of base materials. It is possible to weld materials with the different thermophysical properties under condition of appropriately adjustment of process parameters. One of the examples is welding of aluminium and titanium alloys, which provides suitable combination of physical and mechanical properties, especially for aerospace and automotive industry. Fusion welding of these materials is associated with formation of intermetallic phases during mixing of basic materials and subsequent solidification and cooling of weldment. In this work was evaluated influence of welding speed, oscillating frequency, beam focus and offset of electron beam on the structure and integrity of welded joints. The resulting weld joints were evaluated by using light and electron microscopy. Type of intermetallic phases observed in the welds was determined by EDS analysis. Estimation of mechanical properties was carried out on the base of measurement of microhardness profile across weld joints.
The improvement of the tribological behavior of the titanium alloys used for hard implants requires the application of different treatments (heat treatment and electron beam surface modification (EBSM) by scanning electron beam) that homogenize the bulk and surface structure as compared with the as-received material. In view of analyzing the influence of the applied vacuum heat treatment Vickers hardness measurements in three mutually perpendicular planes of the Ti-5Al-4V samples in as-received, quenched and quenched and aged condition are used for determining the plane for scratch test analysis and application of the EBSM afterwards. The aim of this study is to reveal the changes in the mechanical properties (hardness, coefficient of friction (μ) and tangential force (Ft)) at progressive loading of the normal force (Fn) up to pre-defined maximal value. The scratch results compare the heat treated and EBSM samples in different conditions in the rolling and normal directions of testing. Such studies will be useful for further examinations of the alloy.
Additive layer manufacturing (ALM) is a revolutionary method of production which has allowed the building of novel structures that cannot be produced through traditional means. Many ALM methods exist, however Electron Beam Melting (EBM) is one such ALM method that can produce metallic parts. Despite the ability for EBM to produce parts that are comparable to traditionally produced parts, studies on EBM lattices report large variations in mechanical properties.
This study uses non-stochastic lattices with a diamond structure, built using EBM with Ti6Al4V. Static and a dynamic tests are used to compare the mechanical properties of as built lattices, with lattices that have been post processed using hot isostatic pressing (HIP), to quantify differences in mechanical properties.
Obtaining of an appropriate implant material requires a detailed analysis of the effect of the applied surface treatments. In the particular study the Ti-5Al-4V alloy is vacuum heat treated and electron beam surface modified (EBSM) by scanning electron beam and its surface characteristics are revealed by modern topographic and metallographic analysis. The studies provide an essential insight into the change of the surface characteristics – topography and surface roughness, as well as the transformations of the structure caused by the vacuum heat treatment (quenching and aging) and the subsequent EBSM. The results from the surface roughness, SEM, AFM and profilometry analysis after different parameters of EBSM of as-received, quenched and quenched and aged Ti-5Al-4V alloy are compared. The examination results are indicative of the alloy ability to modify into the desired structure, appropriate for biomedical applications.
This research work was focused on the application of powder metallurgy technology to the production of high-quality products from Ti-6Al-4V alloy (Ti-6-4). This alloy presenttly is most widely used titanium alloy, accounting for more than 50% of all titanium tonnage in the world. The aerospace industry accounts for more of 80% of this usage. Other large applications of this alloy can be found in automotive, marine, and chemical industries as well as medicine. The common way to produce structural parts from Ti-6-4 alloy is hot forging. At present, the stock for forging is commonly manufactured from cast material. An attractive alternative for producing such billets can be powder metallurgy technology (P/M). The processing of compacts makes it possible to reduce the cost of production and leads to obtaining very good quality of the microstructure and properties. It is also very important, that this process can be realised using commercial processing lines for forming the cast stock, without modifications.
The proposed procedures of development and verification of the parameters of deformation of Ti-6Al-4V alloy compacts in open-die forging process were presented and discussed. As the material under investigation, compacts obtained from elemental powders were applied. The compacts were nearly free from porosity, which was confirmed by metallographic examination as well as computed tomography non-destructive tests. The numerical modeling of hot forming of the selected forging was performed based on the finite element method (FEM), with application of QForm 2D/3D commercial software. Various combinations of forging conditions were selected and simulated, however, the range of parameters was in accordance with possibilities and limitations of the industrial line, specified at the initial stage of the research work. Basing on the results of the numerical modeling, appropriate conditions of hot open die forging of the selected part were determined. The results of modeling were verified in the trials conducted in industrial conditions. The quality of the product was estimated by the examinations of the microstructure as well as hardness measurements. It was found, that forging of billet, manufactured with application of the proposed powder metallurgy technology, leads to obtaining a defect-free Ti-6Al-4V alloy part.
Direct Metal Laser Sintering (DMLS), one of Additive Manufacturing technologies, produces layer-by-layer geometrically complex components from metal powders, such as nickel alloys, titanium alloys, aluminium alloys, etc. using a high power concentrated laser beam. The material structure created by this technology is influenced by process parameters and build orientation. The process is characterized by localized high heat inputs during very short interaction times leading to the formation of very fine structures but also to the generation of internal stresses. Therefore, the DMLS parts are heat treated to decrease or completely remove residual stresses. The DMLS manufacturing process examined here was characterized by a 400 W laser power and 60 µm layer thickness applied to a fine Ti6Al4V powder. Plane bending fatigue testing was performed on three sets of special miniature specimens prepared according to three different build orientations. A cyclic bending stress was applied to the smooth flat surface of the specimens. The surface was tested in the as-build state and in the polished state to reduce roughness of the as-build surface. The fatigue behaviour of DMLS Ti6Al4V was found to be influenced by the build orientation. Fatigue specimens with polished surfaces showed better fatigue properties compared to the as-build specimens.
One of the most common titanium alloys for aerospace industry is Ti-6Al-4V (usually designed as Ti-64), which is used for manufacturing aero-engine components, such as fan discs, compressor discs, blades and stators. At temperatures exceeding 480°C, titanium alloys generally oxidize and form a hard and brittle layer enriched with oxygen, which is called alpha case. This layer has negative effects on several mechanical properties, lowering the tensile ductility and the fatigue resistance. Therefore, any alpha-case formed on titanium alloys during manufacturing processes, such as heat treatments, must be removed before the final part is mounted in the engine. In addition, long time exposure at elevated temperatures during engine operation could lead to formation of alpha-case on actual parts. Consequently, knowledge and understanding on the kinetics of alpha-case formation is an important question. In the present study, cyclic thermal treatments were performed in air on a Ti-64 alloy, at 500 and 700 ºC up to 500 hours, and compared with similar treatments carried on in isothermal oxidation conditions. The evolution of the surface oxidation and alpha-case formation was analyzed by metallographic techniques and x-ray diffraction, together with a detailed analysis of the microstructure by using Scanning Electron Microscopy (SEM) and Focus Ions Beam (FIB). Results point out that cyclic thermal treatments induce a strong increase of the oxide formed at 500 ºC compared to isothermal treatments, while at 700 ºC thermal stress caused by cyclic treatments promotes the fracture of the oxide layer after the first 20 hours.
Titanium alloys composed of non-toxic elements such as Nb, Ta, Zr, Mo and Sn with lower modulus of elasticity, greater strength and greater corrosion resistance. The primary objective of this work was to produce biocompatible titanium alloys from elemental powders such as Nb and Sn by high energy ball milling/mechanical alloying. Mechanical alloying experiments were carried out at room temperature in a Spex™ 8000D Mixer/Mill to produce titanium alloys with different compositions. After the milling the powders were consolidated at room temperature using a uniaxial press and sintered at elevated temperatures. In this work, niobium was chosen as the β stabilizer and tin as the reducer of the elastic modulus. X-ray diffraction and electron microscope techniques were used to investigate the phase transformation and alloying kinetics as a function of alloying compositions. This research was supported by Necmettin Erbakan University - BAP under grant number 151219009.
The second generation nickel-based superalloy MAR-M247 offer a satisfying combination of fatigue and creep properties and oxidation and corrosion resistance that is required for application at elevated temperatures in hostile environments. The microstructure consists mainly of face centred cubic γ matrix and ordered γ´ strengthening precipitates (L12 type). The present work focuses on low cycle fatigue (LCF) behaviour of polycrystalline nickel-based superalloy MAR-M247 at high temperature. LCF tests were conducted on cylindrical specimens in symmetrical push-pull cycle under strain control with constant total strain amplitude and strain rate at 700 °C in ambient air. Plastic strain amplitude vs. stress amplitude and stress amplitude vs. the number of cycles to failure were plotted and compared with data obtained on Inconel 713LC. Special attention is paid to the investigation of crack initiation in MAR-M247 during low cycle fatigue. Crack initiation sites were studied by means of scanning electron microscopy (SEM) in dual beam microscope TESCAN LYRA 3 XMU FESEM equipped with focus ion beam (FIB). Specimens’ surface observations revealed the formation of pronounced surface relief indicating localisation of plastic deformation. TEM observation confirmed localisation of cyclic plastic deformation in persistent slip bands along {111} slip planes. Fractographic analysis revealed fatigue crack initiation sites. Fatigue crack propagation in stage I was typical of smooth facets up to 500 μm long.
The effect of chemical composition on hot tearing susceptibility of a polycrystalline industrial gas turbine blade during casting process has been investigated. Five master melts from two different nickel base superalloys by nearly similar chemical composition have been used for this purpose. The results show that in IN738-LC alloy, hot tear sensitivity has a direct relation with Zr content, but in Rene80 the amount of Zr, doesn’t have any obvious effect on the hot tearing susceptibility of alloy. It could be related to lower HSC parameter in Rene80 alloy in comparison with that in IN738LC. Besides the amount of Cr and Al which are the most segregating elements next to eutectic phase, in the IN738LC are higher than that in Rene80 alloy.
In this paper, were determined the effects of cutting speed, cutting tool and feed rate on cutting forces and surface roughness based on Taguchi experimental design. Tree different cutting cemented carpide tools were used in experiments as K313, KCU10 and KCU25. Main cutting force, Fz is considered to be cutting force as a criterion. In the experiments, depending on the tool material, lowest main cutting force 369.76 N at 75 m/min with KCU10 and lowest average surface roughness (0.424 μm) at 90 m/min with KCU25 cementid carpide tool was found. While feed rate (68.84%) and cutting tool (19.85%) has higher effect on the cutting force, cutting tool (90.18%) and cutting speed (3.96%) has shown higher effect on average surface roughness. In the cutting force turning tests KCU10 and in the surface roughness turning tests, KCU25 cutting tool has shown better performance than the other cutting tools. The effects of machining parameters were determined using Taguchi L27 orthogonal array. Optimal cutting conditions were determined using the signal-to-noise (S/N) ratio which is calculated for average surface roughness and cutting force according to the "the smaller is better" approach. Using results of analysis of variance (ANOVA) and signal-to–noise (S/N) ratio, effects of parameters on both average surface roughness and cutting forces were statistically investigated.
This study evaluates fatigue properties of copper (Cu) alloy Cu7,2Ni21,8Si1Cr produced by selective laser melting technology (SLM). This technology belongs to additive manufacturing or 3D printing technologies and allows to produce metal parts with complicated shapes in short production time and without the need to use expensive molds or large material waste. As the SLM technology is still under intensive research, the production process is not optimized for wide range of materials (most of studies were focused on titanium or aluminum alloys). Low quality of SLM materials is mainly connected with production defects caused by big temperature gradients during production.
The SLM material is subjected to fatigue bending tests, which are supplemented by acoustic emission (AE) measurement and fractography analysis. By AE is possible to analyze fatigue behavior in detail and determine different fatigue stages and mechanism of crack propagation. After verification experiments, it is also possible to predict the remaining fatigue life. All results are compared with fatigue properties of conventionally produced Cu alloy AMPCOLOY® 944 (Cu7Ni2Si1Cr) using standard S-N curves. The fatigue life of SLM material is slightly worse than we can observe in conventionally produced materials and AE results suggest that there is different mechanism of crack propagation. As expected, the fractography study shows there is big amount of production defects (mainly pores) in SLM material and the crack origins are located near them.
Observed in recent years - trends in the search for novel materials with unconventional properties arise from the constantly growing needs of the economy. An example of such a material is graphene, which in recent years has revolutionized the market and create opportunities to develop new composites based on graphene. Work on the creation of composite copper - graphene have been taken to improve the - first of all - the electrical conductivity of materials, but also strength and other performance properties. Are now being made various attempts to synthesize graphene and copper, among others, using electro-deposition processes, casting processes and the processes of consolidation of powders. It is suspected that the increase in electrical conductivity can be obtained in the case of the structure that is targeted. One in which graphene layers are arranged in the direction of conduction of electric current. Certainly, to obtain such a structure facilitates the process of continuous casting, and further processing the rods in the process of drawing further directs structure.
The microstructure and mechanical properties of a powder metallurgical AlZrTi alloy was studied. Fine powder with a typical size below 50 um was prepared by gas atomization. The smallest powder particles with a diameter below 10 um exhibited a segregation free microstructure. Larger droplets were found to contain intermetallic particles rich in Ti and Zr. The gas atomized powder was consolidated by spark plasma sintering (SPS) at various temperatures ranging from 450 to 550°C. During SPS the materials microstructure remained nearly unchanged. All SPS samples exhibited a microhardness of around 90HV. The annealing (1h, 500°C) of the sample sintered at the highest temperature (550°C) resulted in a decrease of microhardness to 75 HV as a result of changes in the phase composition. Natural aging at room temperature does not altered this value. The sintered samples exhibited a fine grain size between 2 and 3 um. Annealing at 500°C does not led to grain coarsening.
Niobium silicide-based alloys have a potential application in gas turbine blades, promising significant improvements when compared to Ni-based alloys. This is due to the higher temperature capability that they present and significant lower density and good mechanical properties, conferred by the presence of reinforcing ceramic phases, such as Nb5Si3 and/or Nb3Si, embedded in a ductile solid solution phase, Nbss. The combination of these properties would allow the manufacturing of lighter engines able to run at higher temperatures, increasing their efficiency.
A better understanding of the microstructure evolution is therefore required in order to follow the formation and change of phases from the solidification to the heat treatment stages. This study focuses on the analysis of the solidification behavior of a multi-component Nb-18Si-24Ti-5Cr-5Al-2Mo alloy under rapid freezing produced via laser additive manufacturing processing (LAM) posteriorly heat treated at 1200ºC.
The additions of elements such as Cr, Al, and Mo have proved to impact significantly in the evolution of phases expected under equilibrium, and because of that a thermo-calculation analysis provides a more precise prediction of the solidification path for this alloy, which will be compared to that obtained under rapid freezing conditions. This will then lead to an investigation of the changes in microstructure observed after heat treatment.
Bulk metallic glass and their composites are unique new materials which have superior mechanical and structural properties as compared to existing conventional materials. Owing to this, they are potential candidates for tomorrow’s structural applications. However, they suffer from disadvantages of poor ductility and little or no toughness which render them brittle and they manifest catastrophic failure on the application of force. In present study, an effort has been made to overcome this pitfall. A controlled amount of carefully selected inoculants are introduced into alloys during melting and casting stage. This results in preferential in-situ heterogeneous nucleation and growth of ductile phase dendrites in glassy matrix during rapid cooling under vacuum. Effect of type, size and quantity of inoculants is studied by change in number density, size and distribution of ductile phase dendrites. Effect of cooling rate was studied by observing phase development across a wedge shape casting. Optical and scanning electron microscopic (SEM) studies confirmed effectivity of inoculants in preferentially causing an increase in nucleation sites and their dispersion all over matrix in a certain area. This results in development of fine structure which causes increase in ductility and toughness. Two types of hypo and hyper eutectic systems (Zr65Cu15Al10Ni10 and Zr47.5Cu45.5Al5Co2) were studied with ZrC and ZrN inoculants.
Nowadays, powder metallurgy (PM) is used in many industrial applications. Conventional PM processes, such as cold pressing and sintering are used frequently in series production due to nearly waste-free use of initial materials and limited or no requirements on further processing by machining. However, these simple processes do not bring significant improvement of mechanical properties and also keep relatively high levels of residual porosity. In production of highly demanding materials, such as high-strength alloys, intermetallics or special composites, modern methods of powder metallurgy are under rapid development. Among powder metallurgy techniques used for powder production, mechanical alloying, which allows for the production of nanocrystalline alloys and intermetallics, composites or oxide dispersion strengthened (ODS) materials, plays very important role. Among the sintering methods, Spark Plasma Sintering (SPS) process became a leading tool because of extremely short sintering times, as well as reduced sintering temperature. Thanks to these facts, the unique properties of nanocrystalline powders can be preserved. Currently, there exist interesting variants of SPS, such as High Pressure SPS and hybrid devices combining SPS and induction heating. In production of intermetallics, there is also a possibility to use the Self-propagating High-temperature Synthesis (SHS) process. In these processes of reaction synthesis, energy is supplied to the compressed mixture of pure metallic powders or other precursors by heating or by electric discharge. In this paper, the application of the above described methods are presented on aluminium alloys, titanium- and iron-based intermetallics and aluminide-ceramics composites.
High entropy alloys (HEAs) are described for multicomponent alloys containing five to three major elements in the at equimolar or near-equimolar compositions and tend to form solid solution structure or amorphous phase. In this study, it was investigated fabrication of high entropy alloy containing wt.%25 Fe-wt.%25 Co-wt.%25 Cr-wt.%15 Ni-wt.%10 Al via Electric Current Activated (Assisted) Sintering (ECAS) process and effect of heat treatment (annealing) on sintering samples. Heat treatments were performed in open atmospheric furnace at 900, 1000°C for 10 hours. Microstructures of sintered and heat treated samples were investigated by optic and scanning electron microscopes, phases in samples were analyzed by XRD and their hardness was measured by Vickers hardness tester ranged from 291 to 977 HV.
The present paper describes producing alumina ceramic matrix composites reinforced with nickel at ratios of 1% to 7% by weight and their resultant mechanical and electromagnetic properties. In this study powder metallurgy method was used and samples obtained at 1440°C for 1h in graphite powder. Argon atmosphere has widely used to produce metallic particulate reinforced ceramic based composites to prevent oxidation risk of metallic particulate. However, in this study using a graphite powder it can be easily sintered bulk materials in a ceramic pot. The firing shrinkage of sintered test materials ranged from 20.14 to 21.19 %. Uniform distribution of ductile nickel particles in the matrix was characterized by SEM microscopy and the presence of nickel and alumina phases were confirmed by EDS and XRD analysis. It was found that the fracture toughness of test materials increased with the nickel content. From 3.0 to 7.05 MPa.m1/2. A slightly decreasing for hardness values also detected. Hardness and fracture toughness was determined using Vickers indentation technique with applying, 0.98 and 98 N load respectively. Electromagnetic transmission, reflection and absorption properties of nickel particle reinforced alumina composites were investigated in the in the wide range high frequencies of 12.4–18 GHz (Ku band). The experimental results indicate that in addition to increasing the mechanical properties electromagnetic characteristics of the composite has been preserved.
From year to year the demand for rare earth metals is getting growing. Majority of these metals find application in permanent magnets, lamp phosphors, catalyst and rechargeable batteries. The production of metals i0 2016 was 126 000 tones and China was the leading producer (84%). In the last years China limited the supplies of these products; therefore it is really important to be more absorbed in recycling of spent products containing rare earth metals. Today the researcher focus on recycling of rare earth metals from their three applications: permanent magnets, nickel metal hydride batteries and lamp phosphors. The article presents review of available methods of recovery the rare earth metals but only from the fluorescent lamps (monochrome and trichromatic phosphors – red, blue and green). Mentioned methods based mainly on hydrometallurgical processes such as leaching, some pyrometallurgical, electrometallurgical and biohydrometallurgical approaches were also discussed.