Nowadays, metallic biomaterials are widely utilized in various applications in medicine, including joint replacements, stents, fixation devices for fractured bones, scaffolds for repair of bone defects, dental implants and other. Four main groups of alloys are currently used in these applications - titanium alloys, stainless steels, cobalt alloys and noble metal alloys. All these materials are highly corrosion resistant, relatively inert in the human body, therefore, suitable for implants with permanent functions. But, some medical applications, such as stents to restore blood vessels of oesophageus, screws, plates or wires for fixations of fractured bones, require only temporary functions. After tissue healing, the implant is not further needed and, in many cases, should be removed by the second surgery causing high inconvenience for patients. In this paper, a novel class of biodegradable metallic materials is discussed. Biodegradable metallic implants progressively degrade in the human body and they are replaced by healing tissue. No second surgery is needed which improves the quality of medical care. Biodegradable metallic materials are subjects of extensive research at the University of Chemistry and Technology in Prague (UCT). In the paper, recent achievements in this field at UCT are summarized.
In surgery, besides the joint replacements that need permanent prosthesis implantation in the human body, there are many other clinical cases, such as bone fracture, cardiovascular diseases, in which the temporary implant materials are needed. The fixation or mechanical support are there temporarily needed during the healing process of the injured or pathological tissue, and after that, the implants accomplish their mission have no longer function in human body. In this case, biodegradable materials are the optimal choice as these materials do their job while healing and a new tissue forming occur and degrade in the human body thereafter. Amorphous alloys based on magnesium and calcium are nowadays a very perspective group of metallic glasses. We have developed composition series of completely new (not published) ternary Ca-Mg-Au biodegradable alloys with attractive properties in terms of possible future applications (density and elastic modulus comparable to human bones, wide supercooled liquid region etc.). Although the rate of their degradation in physiological solutions is still too fast, these ternary alloys will serve as precursors for design of future highly alloyed systems with tuned dissociation rate in human body.
Three kinds of aluminum alloys based on Al-Zn-Mg system and doped with Ca, Ni and Ce were studied. Determination of hot tearing tendency, phase composition and structure formation investigation were conducted. Alloying with the elements of Ca, Ni, Ce group is effective to increase casting properties that is better than those of a commercial A206 alloy. The structure after slow cooling during sand mold casting contains mainly needle like Al3Fe. But after permanent mold casting the iron containing phases are only ternary phases Al10CaFe2, Al9FeNi and Al10CeFe2. Most of Zn and Mg content are in aluminum solid solution as a result of casting that cause of appropriate mechanical properties under as-cast state. Moreover the high content of iron can allow us to include new alloys into the recycled type which means the opportunity to be produced using low grade aluminum or can scrap.
Alloys with increased configurational entropy are new group of materials with very broad range of possible properties, but their application potential is currently limited because of complicated and inefficient manufacturing processes used mainly on laboratory scale. Paper presents the results of preliminary research aimed on manufacturing castings made of medium entropy alloys (MEA) by industry scale casting technologies. The main aim of the presented research was to determine the influence of melting and casting conditions on the solidification process of selected Al-based MEA’s. The alloys were poured into sample moulds made of material with heat transfer coefficient similar to those used in industrial scale manufacturing processes. Furthermore, the pattern used in the mould preparation was designed to create zones of varied heat dissipation rates and thus solidification rate. Solidification process was characterized by use of thermal-derivative analysis and differential scanning calorimetry. The structure in as-cast state and chemical composition in micro-areas were investigated using SEM microscopy and EDS analysis.
Gas porosity is one of the most common casting defect in die cast parts and it has an undeniable effect on strength, leakage and heat treatability. Reducing and even preventing porosity level can be achieved by the integrative design of mold, vacuum system and optimized process parameters. Applying semi-solid processing also helps to improve quality; not only by preventing defects but also modifying microstructure to have stronger products. In semi-solid casting, generated globular primary phases cause reduction in apparent viscosity under increased shear stress in thixotropic behaviour. This leads to planar flow instead of turbulent, which helps reducing air entrapment during injection and mold filling. In this study, GISS (Gas Induced Semi-Solid) adapted high pressure die casting technique is used for producing AlSi9Cu3 alloy die cast parts. The effects of semi-solid processing temperature, rheo-casting time, changeover position and fast shot velocity are investigated on microstructural changes and porosity levels by using Taguchi method. Radiographic analysis is used for non-destructive testing for determining porosity state. Optic and field emission scanning electron microscope (FE-SEM) are used for microstructural and morphological characterization. Energy-dispersive X-ray spectroscopy (EDS) is also applied for chemical analyses of the phases involved. As results, fast shot velocity and rheo-casting time are found to be the most effective parameters on the porosity level and globular microstructure, by increased shear stress.
Aluminium Chloride (AlCl3) is highly reactive and corrosive. It is classified as Lewis Acid and will always be ready to share a pair of electrons. So if positively charged ions are introduced in the system containing AlCl3, then it would be possible to reduce AlCl3, without resorting to electrolysis. For a reductant, dry ammonia (NH3) is to be converted to NH4+ ions. For this, it is proposed to use Alpha (α) radiations. Alpha (α) particles are nothing but Helium (He) nucleus, having two protons (+) and two neutrons. These α-particles can convert dry ammonia (NH3) in to NH4+ ions in an ionization chamber.
The NH4+ ions thus produced are passed in to a Reaction Chamber, along with the aluminium chloride vapours produced by carbo-chlorination of Bauxite. Since NH4+ ions & AlCl3 are in gaseous form, they will require a medium to react with each other. Therefore, the reaction is proposed to be carried out in the medium of molten aluminium & molten salt bath of KCl & NaCl (similar to the ones used in electrolysis of AlCl3) at a temperature of 1000°K. The reaction occurring in the reaction chamber can be given as:
AlCl3 + 3NH4+ -------→ At 1000°K (in molten Al) -------→ Al(l) + {NH4Cl} (g)
The NH4Cl formed in the process being in gaseous state will be taken out of the reactor, where it will be trapped to regenerate NH3 & Cl2. Removal of NH4Cl would also ensure that the reaction is proceeds in the right direction.
Thus, the process uses medium of molten aluminium to produce aluminium. The use of molten aluminium covered with molten salt bath also ensures a more +ve ∆S for the reaction
The paper determines the influence of presence of various manganese content (0.2; 0.4 and 0.6 wt%) on the course of the crystallisation process, mechanical properties and structure of alloy AlSi10Mg. Recycled secondary materials with elevated content of iron were used to prepare the cast of this silumin. It was found that about 0.6 wt% of Mn causes the disappearance of the adverse, brittle phase β-Al5FeSi in favour of phase α-Al15(FeMn)3Si2, which crystallises in the form of evenly distributed in the metallic matrix of solution α (Al) with concentrated precipitations sized approximately 7-8 µm. The change of the adverse morphology of brittle eutectics containing Fe causes a slight increase of mechanical properties without the decrease of plasticity of alloys Al-Si-Mg-Mn used mainly as gravity die casting or pressure die casting. Manganese is therefore a “morphological corrector” of phase β in favour of privileged precipitations of α-Al15(FeMn)3Si2. Taking into account the economic aspects and ecological conditions it seems reasonable to apply manganese in order to increase the presence of secondary Al alloys rather than the primary elements.
Imposing large plastic deformation by SPD processes such as ECAP, HPT, ARB etc. in a relatively simple way enables to obtain material with high grain refinement. In result significant change in both strength and plastic properties can be observed. However, this hardening effect is highly thermal sensitive and even small increase in temperature can initiate structure recovery processes. In the following paper thermal stability of aluminum chips (AA1050, AA3103, AA5083) after machining has been examined. By identifying moment of structure recovery optimal conditions for plastic consolidation could be determined.
The issues which appears at fusion welding of 6082 T6 aluminum alloy are connected with hot cracking (solidification and liquation crackings), porosity and over aging of a portion from heat-affected zone (HAZ). Relatively high thermal expansion and the wide range solidification temperature of the Al alloy are the main causes of susceptibility to welding cracking. Moreover, over aging phenomenon of a portion from HAZ, due to the welding thermal cycle is manifested by the decrease in hardness and mechanical strength of the welded joint. The main objective followed by this paper is to restore the microstructure and the mechanical properties of the pulsed MIG welded joints made from 5 mm thickness sheets by applying a post weld heat treatment of solution quenching followed by artificial aging.
Copper and aluminum are both widely applicable in a variety of industrial and commercial branches, from automotive to electrotechnics and laminated materials and clad composites are innovative and perspective solutions for various applications. This study deals with the investigation of structure development via internal stress analyses, grains size observation, and residual stress analyses within Al-Cu clad composites rotary swaged at room temperature and at 250 °C by optical and electron microscopy, EBSD analyses and microhardness measurements. The swaged composites were also subjected to post-process heat treatment - annealing at 350 °C for 30 minutes. The results showed that intermetallic phases developed at the interfaces especially when subjected to higher temperatures (warm swaging and annealing). On the other hand, these treatments resulted in a significant decrease in the residual stress, which was also influenced substantially by sub-structure development (grain refinement). The analyses were supplemented with microhardness measurements, the results of which were in accordance with the results of substructure development.
Development and study of metal-matrix composites (MMCs) is a challenging and up-to-date task in the field of materials science. This study aims to contribute to the growing area of research on MMCs by using the stir-casting technique and mechanical alloying to combine AA2024 alloy matrix with nanosized SiCp. The effect of thermomechanical treatment - rolling and extrusion/compacting - on the mechanical properties of MMCs have been shown. The objective of this research is to provide a better understanding of the effect of nano- and microsized reinforcements on the mechanical characteristics and microstructural changes during high-temperature uniaxial tensile testing of AA2024/SiCp. The maximum engineering strain (250-270%) was reached with SiCp (2 vol. %) reinforcements at a low strain rate of 10−4 s−1 at 490 C. The confirmation of the increase in the strain (up to 50%, twice higher than in AA2024) was observed in AA2024/SiCp deformed at a high strain rate of 10−1 s−1 at 490 C. The tested material experienced dynamic grain growth. High ductility is explained by the presence of fine SiCp inclusions and high density of Alx(Mn,Fe)ySi nanoparticles in the matrix, which restrain grain boundary movement.
In the present work Al4Cu-SiC composites were fabricated in a rigid die on a single-action compaction press and then sintered under the nitrogen atmosphere. The SiC (< 2 µm) content was 5 and 10 wt%. An attempt has been made to study the mechanical and tribological properties of fabricated materials. The microstructure of composite materials was analyzed with scanning electron microscopy (SEM) and X-ray diffraction (XRD). The obtained results indicated that introduction the ceramic particles into Al4Cu matrix resulted in an increase of most mechanical properties compared to the matrix material. However, the tribological properties were higher for unreinforced Al4Cu matrix than for composites with the addition of SiC.
Biodegradable implants are effective because of no revision surgery is needed for further implant removing. It was known that the Mg-Zn-Ca-(Mn) alloys are promising for biodegradable applications because of high biocompatibility and enough mechanical properties. The influence of hot extrusion at different temperatures on the microstructure and mechanical properties in longitudinal and transverse direction with respect to the deformation axis of four Mg-Zn-Ca-(Mn) alloys was studied in this research. It was established that for low hot extrusion temperatures the large non-recrystallized elongated grains surrounded by fine grains are typical. With increasing of hot extrusion temperature, the fully recrystallized fine uniform grains were observed. The grain size after extrusion change from 1.5 to 6.2 μm and the upper limit relates to hot extrusion at high temperatures. It was demonstrated that higher ultimate tensile strength, higher yield strength and lower elongation is typical for low hot extrusion temperatures and vice versa. The mechanical properties are higher in longitudinal direction and the best its combination was observed for MgZn4Ca0.5 alloy.
Magnesium alloy Mg-4Y-3Nd was prepared by spark plasma sintering technique. The gas-atomized powder was sintered at temperatures in the range of 400-500 °C and holding time up to 10 minutes. The effect of sintering parameters, particularly sintering temperature and holding time, on the microstructure and corrosion resistance was investigated. The effect of sintering on the microstructure was investigated by scanning electron microscopy. Mechanical strength was investigated by microhardness measurements and corrosion properties were studied by linear polarization method. The results show that the sintering conditions seem to have only a minor effect on the final microhardness in the investigated temperature range. However, the increase in the sintering temperature caused recrystallization and grain growth accompanied by dissolution and reprecipitation of secondary phases particles. Due to these microstructural changes, the corrosion resistance was improved.
The gas-atomized powder prepared from AE42 magnesium alloy was mechanically milled at various conditions. The effect of milling on the size, morphology and particle microstructure was investigated. It was shown that dry milling at room temperature in argon atmosphere leads to significant refinement of the powder, but the negative effect of cold-welding was observed despite the addition of the process control agent. On the other hand, wet milling in ethanol suppressed the cold-welding and resulted in a significant change of particles morphology from spherical-like to flake-like. The microstructure of powder particles was severely refined, but further investigation by transmission electron microscopy is needed. In addition, it was shown that the continuous oxide layer present on the gas-atomized particles was successfully disrupted by the mechanical milling.
The report presents results of the analyses of biocompatible WE 43 Mg-based alloy processed by friction stir processing (FSP) at two different rotational speeds of 400 rpm, and 1200 rpm. The structures were observed by scanning electron microscopy (SEM), electron backscattered diffraction (EBSD). Observations were primarily focused on characterizations of grains and textures; supplementary testing of mechanical properties was performed via tensile tests. The results of low angle grain boundaries fractions and grain sizes showed that both the processing methods led to significant grain refinement and recrystallization, the average grain diameter within the 1200 rpm sample was less than 2 µm. Texture observations showed slight tendencies of the grains to align in the {0001}〈101 ̅0〉 and {0001}〈112 ̅0〉 preferential orientations, however, the maximum intensities were only about two times random. Supplementary tensile tests confirmed the positive effects of FSP on structures and properties of both the samples.
Two experimental magnesium alloys containing neodymium and zinc (Mg-5Nd-1Zn and Mg-1Nd-1Zn) were processed by severe plastic deformation (SPD) method - equal channel angular pressing (ECAP). The effect of SPD processing on the microstructure was studied by light microscopy (LM) and scanning electron microscopy (SEM) including electron backscatter diffraction (EBSD). A significant grain refinement was observed after 8 passes of ECAP in both alloys resulting in homogenous ultra-fine grained condition. Microstructure evolution significant affected mechanical properties, which were studied by microhardness measurements and compression deformation tests. Both yield compression strength σ0.2 and microhardness significantly increased after ECAP when compared to the extruded or as-cast counterparts.
Superplastic behavior of ultrafine-grained (UFG) magnesium alloy Mg-4Y-3RE (wt%) prepared by equal channel angular pressing (ECAP) was investigated at high strain rates. Eight passes through ECAP resulted in grain refinement down to ~340 nm and formation of a high volume fraction of fine secondary phase particles located at the grain boundaries and triple-points. Dense distribution and high thermal stability of these particles provided excellent thermal stability of the UFG microstructure even at high temperatures. The microstructure of the material was investigated by transmission electron microscopy. Superplastic behavior was investigated in the temperature range of 350-450 °C and strain rate range of 10-2 s-1 - 10-1 s-1. The results revealed high strain rate superplasticity in the investigated material. Deformation to fracture exceeded 1000 % for several deformation conditions, even at the strain rate of 10-1 s-1.
Advanced in-situ and ex-situ methods were used to reveal active deformation mechanisms during deformation of magnesium alloy with a strong texture. Three sets of samples were prepared from the rolled sheet of commercial AZ31 alloy with respect to its strong basal texture - normal direction (ND), rolling direction (RD) and 45° between RD and ND, and were deformed in both compression and tension. The signal of acoustic emission (AE) was measured concurrently during the deformation. Electron backscattered diffraction (EBSD) was used to study the microstructure after the selected stages of the deformation. It is shown that the extension twinning played an important role during the plastic deformation in the samples having favorably oriented basal texture component, whereas in the unfavorably oriented samples, the role of twinning was marginal. Pronounced activation of twinning only in some samples caused a considerable variation in the deformation behavior and AE response. A consistent link between the energy and amplitudes of the AE signal and the microstructure changes investigated by EBSD was established.
Metastable titanium alloys that attain pure beta (bcc) phase upon quenching have attracted much attention in the last 2 decades due to desired combination of properties: high strength, low Young’s modulus and content of purely biocompatible elements. Very high strength (over 1000 MPa) of alloys with composition Ti-Nb-Zr-Ta-O is achieved by relatively large amount of interstitial oxygen (0.7 wt.%) and Young’s modulus can be tuned by content of beta stabilizing elements (26 - 35 % of Nb, 0 - 6 % of Ta and 7 % of Zr).
Cold swaging is very convenient method of working this type of alloys as no oxidation occurs in contrast to hot working. Six studied alloys with various amount of Nb/Ta could be cold swaged from cast condition up to 70% of area reduction. Subsequent annealing was performed at 800°C - 1200°C for 2, 5, 15 and 30 min. Scanning electron microscopy together with electron back-scatter diffraction was used for microstructural characterization and microhardness measurements were used to determine homogeneity of deformation stored in cold swaged conditions.
Very strong texture [110] emerges during cold swaging and the deformation is stored in the material in the form of bands with high density of lattice defects. Upon annealing below beta transus temperature, these bands serve as preferential nucleation sites for alpha phase precipitation. During annealing at higher temperatures, recrystallization and recovery processes are detected. At 900°C, recrystallization occurs at the bands and recovery processes prevail in bands-free area. From 1000°C higher, homogenous recrystallization is the prevailing effect. There is also rather weak effect of composition (Nb and Ta content) on the recrystallized fraction at 900°C: the less Nb and Ta, the higher the recrystallized fraction.
In-situ TiAl-based matrix composites reinforced with ceramic particles can improve the deficiency of lightweight TiAl-based alloys at high temperatures and facilitate their industrial applications using well-known and widely applied processing technologies. Carbide particles show a significant role in toughening and reinforcing of TiAl-based matrix composites. Among various techniques applied for processing of in-situ composites, precise casting is of large industrial interest for the production of complex shaped components such as turbocharger wheels or turbine blades. This paper reviews developments in cast in-situ TiAl-based matrix composites reinforced with carbide particles concentrating on the last four years and drawing examples from the three most widely researched systems with near γ(TiAl), duplex and fully lamellar α2(Ti3Al) + γ(TiAl) matrices. The effect of processing techniques on microstructure and high temperature mechanical properties of designed composite systems is presented and discussed.
Analytical and numerical analyses of room temperature compressive deformation behavior of cast in-situ composites with the chemical compositions Ti-44.6Al-7.9Nb-3.6C-0.7Mo and Ti-44.9Al-7.5Nb-4.9C-0.6Mo-0.1B (at%) were performed. The microstructural evaluation was carried out by scanning electron microscopy (SEM) and SEM in back scattered electron (BSE) mode. The uniaxial room temperature compression tests were carried out at an initial strain rate of 1x10−4 s−1 up to a true strain of 15 %. The finite element analysis (FEA) of local equivalent strains supported by quantitative microstructural analysis indicates that the mean length of major axis of fragmented primary carbide particles decreases with increasing local equivalent strain in the compression specimens. The observed differences in compressive work hardening behavior are related to the initial non-uniform deformation, cracking of the primary carbide particles, propagation of cracks in the intermetallic matrix and finally to disintegration of the compressive specimens.
Samples of in-situ TiAl-based matrix composite reinforced with Ti2AlC particles were prepared by vacuum induction melting of a charge with a nominal composition Ti-47Al-5Nb-1C-0.2B (at%) in graphite crucibles and centrifugal casting into a graphite mould. The as-cast samples were subjected to hot isostatic pressing (HIP) and multi-step heat treatments. High temperature compression tests at 1000 °C were carried out on the heat-treated in-situ composite with an optimised microstructure. During compressive deformation, the work hardening is the predominant mechanism at small strains due to an increment of dislocation density in the in-situ composite. At higher strains, dynamic recovery and recrystallization act as main softening mechanisms and exceed the work hardening, which leads to a decrease of the compressive flow stress with increasing strain. The creep deformation curves exhibit a primary creep stage, which is followed by a tertiary creep stage at temperatures ranging from 800 to 900 °C and applied stresses ranging from 150 to 250 MPa. The high temperature creep resistance of the studied in-situ composite is superior compared with that of some TiAl-based alloys with fully lamellar, nearly lamellar, convoluted and pseudo-duplex microstructures at a temperature of 800 °C and applied stress of 200 MPa.
The effect of Al content on morphology, chemical composition, nanohardness and elastic modulus of primary (Ti,Nb)2AlC particles was investigated in in-situ composites with nominal composition Ti-xAl-8Nb-1Mo-0.1B-3.7C (at%), where x ranged from 38 to 45 at%. The in-situ composites were prepared by vacuum induction melting in the graphite crucibles and consecutive tilt casting into a graphite mould. Microstructural analyses show that the microstructure of the composites consists of irregular shaped, plate-like and regular shaped primary carbide particles which are relatively homogeneously distributed in the multiphase intermetallic matrix. The particles consist of (Ti,Nb)2AlC phase with small amount of (Ti,Nb)C phase in the cores of some coarse irregular shaped ones. The Al content has no effect on the measured volume fraction of the particles, but affects their morphology. The shape factor of the particles increases with increasing Al content. The size of the coarse irregular shaped particles decreases with increasing Al content. The solubility of Nb in (Ti,Nb)2AlC phase is not affected by the Al content and reaches only (0.78 ± 0.06) of the average Nb content in the composites. Mo dissolves predominantly in the matrix. The variation of the Al content in the composites has no significant effect on nanohardness and elastic modulus of (Ti,Nb)2AlC particles.
The fracture initiation and propagation was studied in a novel in-situ Ti-44.5Al-8Nb-4.8C-0.8Mo-0.1B (at%) composite reinforced with carbide particles. The composite was prepared by vacuum induction melting in graphite crucibles and precise casting into graphite mould. The as-cast samples were subjected to hot isostatic pressing and stabilisation annealing. The phase composition of the test specimens was characterised by X-ray diffraction analysis and transmission electron microscopy. The fracture of the composite was studied by scanning electron microscopy (SEM) and SEM in backscattered mode (BSEM). The coarse primary carbide particles are found to be effective obstacles to propagation of cracks initiated in the TiAl matrix during room-temperature three point bending test. The propagation of fracture in the in-situ composite includes crack arrest by carbide particles, crack deflection, delamination on the matrix-carbide interfaces and extraction of some carbide reinforcements from the TiAl matrix.
The influence of severe plastic deformation on ongoing phase transformations in metastable β-Ti alloy Ti15Mo was investigated in-situ during linear heating by electrical resistance and complemented by ex-situ microstructure observations using transmission electron microscopy. Several non-monotonic regions in the temperature dependence of electrical resistance were identified and associated with corresponding phase transitions, namely the reversible diffusionless shuffle transformation of athermal ω phase, followed first by diffusion controlled growth of isothermal ω phase and subsequently its continuous dissolution. Formation of α phase at high temperature is associated with increase of the electrical resistance. The influence of severe plastic deformation on the phase transformations sequence is discussed in detail. For ex-situ microstructural observations different conditions were selected based on electrical resistance measurement. It was revealed, that lattice defects introduced by severe plastic deformation strongly influence the phase transitions during heating of the alloy.
We performed continuous casting of Cu-9Al alloy, following microstructure characterization and computational simulation. Numerical simulation was done on the two scales: within the thermo-mechanical model on the macro scale and the phase-field approach on the mesoscopic scale. In the experimental part of this work, Cu-9Al bars were obtained by the continuous casting (CC) process which was subsequently analyzed by optical, scanning electron microscopy, and energy-dispersive X-ray spectroscopy. For the precise quantitative description, a full coupled thermo-mechanical model of the casting process was implemented. Within this model, we successfully numerically simulated time-dependent temperature and solid fraction fields within standard macro phenomenological models. The obtained fields were used as input for a mesoscale multi-phase-field model of the constrained dendrite growth into the undercooled melt. Simulations of dendrite structure were compared with the experimental findings and thoroughly analyzed. Two scale simulation frame work has been identified as a useful tool for quantitative prediction of dendrite morphology and CC process optimization.
The present work is focused on the study of high temperature low cycle fatigue behaviour of Inconel 713LC produced by a vibratory investment casting (VIC) in as-cast conditions and in the condition after heat treatment (HT) consisting of hot isostatic pressing (HIP) followed by precipitation hardening. Low cycle fatigue tests were carried out on cylindrical specimens in symmetrical push-pull cycle under strain control with constant total strain amplitude and strain rate at 800 °C in air. Hardening/softening curves and fatigue life curves of both materials were assessed and compared with data of Inconel 713LC produced by a conventional investment casting (CIC). Cyclic hardening can be observed in the high amplitude domain while saturated stress response is apparent for low amplitude cycling for all material batches. Data presented in Basquin representation show an increase in fatigue life of both VIC batches compared to the CIC batch, however, no effect of HT on fatigue life of Inconel 713LC produced by VIC was observed. In contrast, the heat treated Inconel 713LC demonstrates slightly higher fatigue life in Coffin-Manson representation. The microstructure of both superalloys was studied by means of scanning electron microscopy (SEM). The microstructure of superalloy is characterized by dendritic grains with casting defects. It comprises the γ matrix, cubic γ´ precipitates, eutectics and carbides. The effect of the VIC and HT on fatigue performance and microstructure of Inconel 713LC is discussed.
The microstructure of initial Nd-Fe-B alloy has the substantial effect on the processing and the hysteretic properties of sintered Nd-Fe-B-based magnets. This work is aimed at the structural characterization of the strip-cast Nd-Fe-B alloy, which will be used as the matrix alloy for the preparation of magnets with variable set of functional parameters via the application of REM hydrides or hydrogenated REM compounds added to the powder mixture and using processes of grain boundary diffusion and grain boundary structuring. The microstructure, phase composition and distribution of Nd in the structural components of the strip-cast alloy were investigated by SEM/EDX, DTA and XRD methods. The nucleation region in the contact area between the cooling wheel and melt and radially grown Nd2Fe14B dendritic structure was observed. Individual dendrite arms are characterized by different crystal orientations and a thickness of 2 to 5 µm. In the interdendritic regions, the R-rich phase with a variable ratio of Nd/Fe is present. In this region, the NdFe4B4 compound was also identified as the minority phase. The X-ray elemental map showed the increased boron content in this phase. Major diffraction peaks in the XRD patterns could be indexed to either Nd2Fe14B or Nd-based phases. According to DTA data obtaining upon heating, the first peak is recorded in the temperature range of 693 to 731 °C which is probably related to the decomposition of NdFe4B4 phase. Other peak in a range of from 980 to 1061 °C is related to the melting of Nd-rich phases.
In this article, La and Sm ions doped BaCo2-W-Type hexaferrite (BaCo2LaxSmxFe(16-x)O27) Nanopowders (where x = 0.2, 0.5, 1.0 and 1.5 molar ratios) have been synthesized using tartaric precursor technique with different annealing temperatures from 1000 to 1350 °C, based on low cost starting materials. As a consequence, the effect of synthesis conditions on the crystal structure, crystallite size, microstructure and magnetic properties was studied using X-ray diffraction (XRD), scanning electron microscopy (SEM) and vibrating sample magnetometer (VSM). The results confirmed that well crystalline La and Sm co-doped BaCo2-W-Type hexaferrite phase was formed for Ba:Co molar ratio equal 1.1:2.1 at different annealing temperatures from 1000 °C to 1350 oC for 2 h. In all cases, crystalline size of La and Sm co-doped BaCo2-W-Type hexaferrite was in the nano-range and increased with increasing annealing temperature. However, the crystalline size of BaCo2-W-Type hexaferrite co-doped with x= 1.0 (BaCo2La1.0Sm1.0Fe15O27) was lower than that of pure BaCo2-W-Type hexaferrite. Meanwhile, the morphology and microstructure of W-Type hexaferrite nanopowders was highly depends on the conditions under which they were formed. In all cases, homogeneous grains were observed in the specimens. Homogeneous grains and relatively larger were observed at high annealing temperatures. Meanwhile, Magnetic properties will be determined using a vibrating sample magnetometer (VSM). The measurements will conducted at room temperature in a maximum applied field of 20 kOe. From the obtained hysteresis loops, the saturation magnetization (Ms), remanance magnetization (Mr) and coercivity (Hc) will determined.
The influence of different sintering conditions (sintering temperature and time) on the structure and properties of the investigated tungsten heavy alloy (THA) consisting of tungsten, cobalt, and nickel was evaluated within this study. The samples for sintering were prepared by powder metallurgy techniques (powder mixing followed by isostatic compression), the microstructures were investigated via optical and scanning electron microscopy, and the mechanical properties were investigated by tensile testing. The first part of the experiment was focused on finding the critical temperature to acquire the required microstructure, while the second part was focused on comparison of two selected sintering periods in order to acquire the best possible combination of mechanical and structure properties. The highest hardness reached up to 500 HV for the sample sintered at 1 500 °C, however, increasing the sintering temperature to 1 525 °C even increased the ultimate tensile strength which exceeded 1 000 MPa. This sample also consisted of the smallest agglomerates.
ACKNOWLEDGEMENTS: The authors acknowledge the financial support of the FV40286 TRIO programme by Ministry of Industry and Trade.
The ever-increasing demand for weight reduction of manufactured parts is leading to the replacement of steel with light metals such as aluminum and magnesium. However, light metals are at times unable to withstand high tribological, thermal or mechanical loads. This leads to an application of metal-matrix-composites (MMC) that possess the advantages of light metals (low weight and high ductility), as well as the characteristics of the reinforcing phase (high hardness, high strength and good wear resistance). To manufacture the MMC components, metal powders were shaped in a pressing process and further densified during a subsequent sintering phase. The residual porosity within the produced parts can be reduced by means of a subsequent sinterforging operation. In this paper, cylindrical partially particle-reinforced specimens, with a radially layered structure, were manufactured by two-sided powder pressing and sintering. A subsequent forging operation was carried out to eliminate the minimal porosity. Different process parameters (forming temperature, true strain and dilation rate) were varied to investigate their effects on the density and structural bonding of the partially particle-reinforced material system. Therefore, the sinterforging process upsetting was carried out. Subsequently, the particle-reinforced parts were characterised by metallographic analysis and hardness measurements. The results show that cracks and defects in the layer system of partially particle-reinforced powder compacts can be repaired using sinter forging.
We live in the age when humanity finds itself on the edge of energy crisis, fossil fuels are consumed and our energy consumption rises every year. One solution would be to obtain energy from renewable sources and to minimize the losses of energy produced, e.g. reuse the waste heat. Thermoelectric materials can convert heat directly and reversibly into electricity and allow therefore to use waste thermal energy more efficiently. Their benefits include the absence of moving parts, quiet operation, reliability, durability, and the fact that they do not produce any polluting emissions, so we can use them in a wide range of applications and they are also attractive from an environmental point of view. Half-Heusler alloys belong to one of the most promising thermoelectric materials composed of relatively non-toxic and abundant elements, with highest ZT = 1.5 at 700 K for Zr0.25Hf0.25Ti0.5Ni1Sn0.998Sb0.002 at% alloy. In our study we try to improve the thermoelectric performance of this alloy by doping it with semiconducting dispersion phase - β-FeSi2, which should reduce the thermal conductivity of the origin alloy. Since thermal conductivity depends to large extent on the propagation of phonons we have investigated how the nanostructuring of the samples by means of ball milling and doping impact the phonon behavior. For this purpose we have conducted inelastic neutron scattering experiments using the time-of flight spectrometer NEAT at Helmholtz Zentrum Berlin. In this paper are presented results of our study demonstrating the effect of phonon suppression by nanostructuring and doping in thermoelectric half-Heusler alloys.
Today, the demand for platinum is constantly growing. It is related to its use as a catalyst mainly in the production of cars. Car production has been increased year by year, consequently the used catalytic converters is the biggest problem. On the one hand, it is a waste, on the other it is also a source of valuable and precious metals. Thus, the automotive catalytic converter is treated hydrometallurgically and pyrometallurgically to recover valuable metals. However, this process is not so easy. After obtaining solutions containing precious metals from hydrometallurgical methods or alloys of the metal collector with PGM (Platinum Group Metals) from pyrometallurgical methods there should be separation and purification of PGM. These processes are difficult and complicated due to their resistance to chemicals attack and the ability to create many chemical compounds. The article presents and discusses the possible methods of separation and purification of platinum and PGM (e.g. liquid-liquid extraction, adsorption, ion exchange).
An efficient technology is currently being searched for the processing of electric arc furnace (EAF) steelmaking dust obtained at the Ural steelmaking plants. In this study, the hydrometallurgical processing of electric arc furnace dusts after Wealz process was investigated on a laboratory scale under normal temperature and pressure conditions. The Waelz-fume is the following chemical composition: 61 wt% Zn, 10 wt% Cl, 6 wt% Pb, 1 wt% Fe, 1 wt% K. The most optimal for hydrometallurgical processing are ammonia solutions, which allow to transfer zinc into the solution while lead and iron ought to remain as a solid residue. During the process complicated chemical reactions proceed with the zinc complex compounds formation resulting from the interaction between Zn2+, Cl- ions and NH3 ligands depending on the pH value. Therefore, this method does not require the introduction of additional purification stages from chlorine and fluorine ions, which make processing difficult, since their accumulation can lead to difficulty in stripping cathode zinc.
The zinc behavior under the influence of ammonium chloride with ammonium as the leaching agents was discussed. Based on the obtained data plots were built and the dependence between the ratio liquid-solid (L/S), ammonium chloride and ammonium concentration were investigated. Optimal leaching parameters were determined. The possibility of zinc electroextraction from the ammonium solutions with obtained cathode zinc was studied.