This work deals with the possibility of hydrometallurgical treatment electric arc furnace (EAF) dust using dilute sulphuric acid solutions. The origin of the EAF dust sample was Železiarne Podbrezová a.s., Slovakia. Zinc content in the dust was 17.05 % and zinc was present both as zincite ZnO and zinc ferrite ZnFe2O4. The effect of temperature, acid concentration and leaching time on zinc, iron and calcium extraction into the solution was investigated in order to optimize leaching parameters. The leaching experiments were carried out in temperature range within 20 and 95°C in aqueous solutions of sulphuric acid with concentrations of 0.05, 0.1, 0.25, 0.5 and 1 M. The maximum zinc extraction of 95 % was achieved in 1 M H2SO4 at 80°C after 90 minutes of leaching, while the iron extraction under the same conditions was 66 %. The main objective of this study was to find out conditions at which the maximum amount of zinc passes into the solution while iron remais in the solid residue. Following conditions were specified as optimum: 0.1 M H 2S0 4, 60 °C. The zinc extraction under the given conditions was 65 %, while iron extraction was around 5 %.
Cooling is one of the critical points during aluminum casting. Improper cooling leads to a structure which isn't homogenous, full of internal and surface defects. It is necessary to know the boundary conditions (heat transfer coefficient or heat flux) for cooling optimization. The boundary conditions for different types of cooling are obtained from experiments.
This article is focused on the cooling of vertical surfaces of aluminum by flat water jets. The sample initial temperature was close to the liquid state. The sample was cooled while in a vertical position by a flat water jet which hit the upper part of the cooling surface, and then the water flow down along the surface. The temperatures were recorded during the experiment by a set of thermocouples which were installed inside the sample. Thermocouples were placed closed to the cooled surface at different heights. The moving horizontal Leidenfrost front between nucleate and film boiling could be observed during the experiment. This front moved downward along the sample surface.
The aim of this work is to evaluate the boundary conditions for described measurements. The evaluation held due to the solution of the 2D inverse task, similar to Beck’s sequential methods. The computation procedure was modified to be able to deal with the moving Leidenfrost front between low and height cooling intensities. Results are presented in a form of heat transfer coefficients as a function of position and temperature.
Two twin-roll cast strips prepared from EN AW 3003 aluminium alloys with
and without an addition of zirconium were processed by constrained groove
pressing. The evolution of microstructure during annealing was studied and
related to mechanical properties. In accordance with numerical
calculations a distribution of microhardness, which reflects the
distribution of imposed strain, is inhomogeneously scattered along the
width of strips. Microhardnes measurements were used for the mapping of
mechanical properties. Light optical microscopy and electron back-scatter
difraction have proven that inhomogeneity in mechanical properties is
always linked with inhomogeneities in the microstructure.
Rapid solidification (RS) combined with following plastic consolidation of RS powders or flakes are considered as a valuable commercial method for the production of a wide range of metallic materials having fine-grained structures. This technique is particularly convenient for aluminum based alloys with additions of transition metals (TM), where fine intermetallic particles are the main hardening mechanism responsible for high mechanical properties.
In this work, rapid solidification of Al-TM (TM: Fe, Ni, Mn) alloys, combined with following mechanical consolidation of RS flakes was used to produced highly-refined structure of the materials. RS flakes were produced by spray deposition of the molten alloy on the rotating water-cooled copper roll. The preliminary consolidation of the RS-flakes was performed utilizing vacuum
compression at∼620 K and 100-tonn press. The as-compressed billets were then extruded at ~670K using extrusion ratio λ=19. The mechanical properties of as-extruded alloys were examined under compression between 300K – 873K. It was found that as extruded RS materials exhibit higher strength in comparison to conventional, as cast and extruded alloy. The results suggest that rapid solidification combined with hot extrusion give rise to enhancement of mechanical properties of Al-TM alloys. Received results will be discussed in relation to the structure features as studied by SEM and TEM.
High strength aluminum alloys are commonly used as structural materials, particularly in the areas of industry where high specific strength is required. It has been already recognized that among all wrought aluminum alloys, precipitation strengthened 2xxx and 7xxx series alloys exhibit the highest mechanical properties. However, it is also known that those alloys suffer from poor corrosion resistance. Contrary, 5xxx series are characterized by excellent corrosion resistance properties and moderate strength. It is known that mechanical properties of Al-Mg system can be effectively increased by the plastic working or structure refinement.
In this work, results of RS-PC (rapid solidification followed by plastic consolidation) material preparation route in application to the commercial AA5083 alloy are presented. For comparison, conventionally cast and extruded AA5083 alloy was studied as well. It was found that in as-extruded condition RS-PC material exhibits 50% higher yield strength (YS=310 MPa) with respect to conventionally prepared alloy (YS = 200 MPa). Further increase of strength was obtained by cold rolling. Such high mechanical properties of RS-PC alloys were found to be a consequence/were attributed to of highly refined structure with an average grain size below 1um. Received results suggest than RS-PC 5083 aluminum alloy, can be considered as high strength material comparable to precipitation strengthened 2xxx series aluminum alloys.
According to Hall-Petch relationship there is correspondence between structure refinement and yield strength increase. Application of rapid solidification (RS) as well as sever plastic deformation (SPD) techniques gives an opportunity for further increase/enhancement of strength in precipitation hardened aluminum alloys. In the present work, rapid solidification of 6061 aluminum alloy, combined with following plastic consolidation was performed. RS materials were produced by melt-spinning and gas atomization processes, while plastic consolidation was performed utilizing by hot extrusion. For comparison purposes cast and extruded materials was produced as well. Optimal T6 heat treatment procedures were applied to all types of tested alloys. It has been shown that each kind of alloy have similar response to heat treatment.
It was found that the strength of RS 6061 alloys is mainly controlled by precipitation strengthening; no additional strengthening mechanism such as grain strengthening contributes to the overall mechanical properties.
Amorphous Al90-xNi10MMx (MM: Mischmetal; x=2-8) alloys were prepared by melt spinning and their thermal stability, glass forming ability and mechanism of crystallization were studied. The effect of MM content on the crystallization process was elaborated by thermal analysis. The apparent activation energy of the first crystallization stage increased from 137±5 kJ/mol for Al88Ni10MM2 to 387±12 kJ/mol for Al83Ni10MM7, indicating higher thermal stability of the amorphous alloys containing higher MM concentrations. A change in the crystallization mechanism from diffusion control with zero nucleation rate (for MM=2 at. %) to nucleation and growth mechanism with increasing nucleation barrier (for MM=7at. %) was also noticed. Moreover, the Al-Ni alloys containing up to 4 at.% MM exhibited nanocrystallization without clear glass transition temperature while at higher MM concentrations, the alloys showed a glassy state having a glass transition temperature with higher thermal stability.
The microstructure and mechanical properties of powder metallurgical Al7075 alloy modified by the addition of 1 wt. % Zr were studied. The gas atomized powder was consolidated by spark plasma sintering (SPS) to a fully dense compact. The powder particles of the typical size below 50 m had a cellular to columnar or equiaxed dendritic microstructure (the size in the order of m) with a large fraction of intermetallic phases at the boundaries. During the sintering (at 500 °C for 3 min) the grain structure remained nearly unchanged. Optical microscopy revealed a bimodal microstructure. The grain size remained unchanged during annealing at even 500 °C for 10 hours. The microhardness of the SPS compact material was 150 HV. The annealing at 500 °C for 10 hours resulted in a decrease of microhardness to 110 HV. Natural aging at room temperature gradually enhances microhardness to its initial value. Tensile tests performed on natural aged samples at room temperature revealed a brittle behaviour. Ductility of 15 % was found at 500 °C. Both the measurements of the strain rate sensitivity parameter m and results of light microscopy revealed the operation of grain boundary sliding.
Exova Plzeň tests the load control fatigue test according to the required specifications due to the quality control on rolled aluminium sheets and plates.
Although the machining process is described in specifications in a very detailed way, the first test results were approximately 10 % lower than expected. Some comparative tests met the requirements while some others did not. At first the program was focused on the final step of sample machining, i.e. polishing. Based on consulting other Exova laboratories, West Bohemian University and some producers for turning tool tips, the range of appropriate residual stress was determined.
At the beginning of the program it was incorrectly expected that the compression residual stress is caused by polishing; now it has emerged that it is caused especially by turning. Next steps were focused on the testing of different types of commercially available tool tips and their geometry. These tests didn’t bring satisfactory results. It led to the first tests of our tool tip modification. In 2011 we started cooperating with the company HOFMEISTER Inc. who is capable to machine tool tips by laser technology.
CTU developed a method of residual stress measurement for our round aluminium samples. At least one sample was machined by each modified tool tip and analysed by CTU subsequently.
The current results indicate satisfactory progress in reaching the required residual stress. The repeatability of production and the life time of tool tips are still to be verified.
In this study, TiB2 particles were employed to improve the microstructure of A206 alloy and therefore, to increase the yield strength and tensile strength of this kind of alloy. In-situ TiB2 particles were obtained by direct reaction among K2TiF6, KBF4 and Al melt at 800-850°C. Microstructure examination shows that the size of in-situ formed TiB2 particles was about 1µm, and interestingly, with addition of in-situ TiB2 particles, the coarse eutectic phase of Al2Cu was refined completely. More important, the yield strength and the tensile strength of TiB2/A206 are increased by 140MPa, 100MPa than that of A206 alloy. The value of 490MPa and 535MPa is for yield strength and tensile strength of TiB2/A206 respectively. Besides, the yield strength and tensile strength are 488MPa and 533MPa respectively for TiB2/A206 alloy after remelting and casting. This verifies that the improvement of mechanical properties of such kind of material possesses stability and reliability.
In this study ultrafine grain structure evolution during high pressure torsion of commercial alloy AA6082 at increased temperature is investigated. Two different initial structural states of the alloy were prepared by thermal treatment. The progress in structure refinement in dependence on the shear strain level was investigated in thin foils by TEM. The impact of different amount of strain introduced was analysed with respect to increased temperature. The microhardness results measured across the HPT deformed disc pointed out to data scattering. The microstructure analyses results confirmed that ultrafine grain structure was already formed in deformed disc upon the first turn was finished, regardless the initial structure state of the alloy. The heterogeneity in ufg structure development across the deformed discs was observed in thin foils, supporting by microhardness results scattering. By increasing strain level (value), applying increasing number of turns (N 2, 4, 6), more effectively homogenized ufg microstructure was observed across the deformed discs. The effect of increased deformation temperature became evident and dynamic recrystallization then modified locally received ufg structure. The retardation in growth of the new grains and higher thermal stability of ufg structure was then observed across, when two step thermal treatment of alloy, introducing quenching a d ageing was executed prior sample deformation. The strength measurement results, yielded from tensile tests, showed that the effect of structure strengthening was degraded by local recrystallization of deformed structure. The results received at torque measurement versus the time then showed, the torque required to deform the sample was increasing until the first turn and then kept stable or even decreases.
Twin-roll cast aluminium alloy from AA3003 series was subjected to several passes of asymmetrical rolling at room temperature, which gradually led to grain elongation and refinement. This process is more effective in grain refinement than conventional cold-rolling.
During subsequent annealing at elevated temperatures the deformed grains were replaced by new ones via recrystallization, which started near the surfaces of the foils. The higher was the imposed deformation by rolling, the earlier was the onset of recrystallization. The rolling direction was still apparent after recrystallization.
The main objective of severe plastic deformation methods is to obtain material with ultra-fine grained microstructure. Large deformations introduced during SPD processes leads to extensive refinement of initial coarse microstructure which has significant influence on overall mechanical properties of such material.
In this work both microstructure and mechanical properties of 413.0 aluminum alloy combined techniques of plastic consolidation and ECAP have been studied. Metal chips obtained from machining process have been pre-compacted into a form of cylindrical billet and then extruded at elevated temperature into a form of longitudinal square profiles with cross section of 10 x 10 mm. Structural observations revealed that at this stage of experiment effective refinement of the structural components was observed. Particularly, silicon and iron based intermetallics were fragmented into fine particles with an average size of 2µm.Second part of the experiment included ECAP deformation, which consists of multiple passes through the 90° die. Mechanical properties were determined by uniaxial tensile tests and microhardness measurements. Structural observations did not reveal any significant changes in particles size and morphology, which suggest that ECAP procedure does not provide further refinement of the brittle phases. Increase of mechanical properties was attributed to the work hardening of the aluminum matrix.
This paper deals with influence of microstructure of magnesium alloy AZ91 on its mechanical properties. Tensile characteristics and microstructures of cast and extruded alloy, and both of these alloys after equal channel angular pressing (ECAP) were compared. It was found that in this case tensile properties are not determined only by grain size but another aspect has an important role because the highest values of yield and tensile strength are achieved for extruded alloy despite its higher average grain size compared to both ECAPed alloys. Compared to this, microhardness seems to be related only to grain size.
Severe plastic deformation techniques are now widely used for grain
refinement of different polycrystalline materials. Grain refinement of
magnesium alloys sheets is under the huge interest since magnesium
alloys are the lightest structural materials used in a variety of
applications. Twin-roll casting is a technique which allows production
of high quality thin magnesium alloys strips with enhanced
microstructure. However, further treatment using severe plastic
deformation technique or annealing is required to improve mechanical
properties of strips. Equal channel angular pressing is a very
effective tool for grain refinement of magnesium alloys. In the
present study the effect of annealing on the resulting microstructure of
twin-roll cast AZ31 magnesium alloy strip after equal channel angular
pressing is studied. Also the influence of the strip orientation during
processing is considered. Light and scanning electron microscopy were used for microstructure observations. The evolution of mechanical properties was investigated using Vickers microhardness measurements.
Currently, copper alloy castings are increasingly applied in various industrial branches. Their production is relatively expensive and technically difficult. Their utilization is associated with high thermal conductivity and corrosion resistance. For the foundry industry are used both known group of copper alloys - bronzes and brasses. Bronzes are used for manufacturing of highly stressed components e.g. wreaths gears, worm gears, the housing, saddles of pumps, valves for high pressure. Brasses are used for the production of gear wheels, special nuts, bearing housings, parts of pumps, valves, and have good resistance to seawater. Currently electric conductive copper begins exceptionally be used for the manufacture of special, very small castings. Therefore, copper and its alloys retain long historic role since the time of Eneolith (about 7000 years BC) to the present. Currently at our workplace (the Department of Engineering Technology - Technical University of Liberec) we are engaged in metallurgical research on copper and its alloys, especially crystallization. This research was never widely performed in the Czech Republic (even in times of Czechoslovakia) was due to the demanding technologies of copper alloy castings. And also because for the melting of alloys must be provided with the necessary melting facilities. This paper contains a description of the crystallization of copper alloys and their equilibrium diagrams, experimental casting of selected copper alloys, melt metallurgical preparation and metallographic evaluation of the structure of castings.
The shape memory alloys based on the ternary system Cu - Al - Ni are able to produce a memory effect at high temperatures. However, if the material undergoes an accidental overheating, a transformation process leads to progressive loss of its characteristics. In the present work, we present the effects of heating rate between 450 and 580 °C on the structural transformations of austenite after cooling to room temperature.
Cu60Zr30Ti10 at. % bulk metallic glass was prepared by suction casting technique with the final diameter of 3,3 mm and the length of 26 mm. Amorphous ribbon of the width of 35 μm with same composition was prepared by melt – spinning technique. Preparation of the materials was performed under Argon atmosphere, chemical composition was verified by Scanning Electon Microscopy (SEM). Thermal stability of the ingot as well as the ribbon was investigated by Differential Scanning Calorimetry (DSC) – we measured and compared thermal stability parameters such as glass transition temperature, crystallisation temperature and subsequent supercooled liquid region of both materials. Amorphous character of prepared materials was validated by X-Ray Diffraction (XRD) and it was identified phase composition and phase evolution of the material after annealing.
Alloys which have the gold as principal constituent have been the subject of research since a long time, because of their very particular properties and of their vast scopes of application and especially the Au-Cu and Au-Cu-Ag systems. and as it is well known that the mechanical properties have a direct report with the order-disorder transformation as well as with the composition of the alloy, therefore, it is important to know the effect of the existence and the concentration of the silver-in the Au-Cu system- on the ordering and disordering process of this system, so for that we have used the dilatometry, the differential scanning calorimetry (DSC) for the thermal analyzes and the micro-hardness measure for the mechanical study. The thermal analyze of samples which having the atomic compositions: Au-39%Cu, Au-35%Cu-25%Ag, Au-5%Cu-43%Ag and Au-8%Cu-56%Ag have shown that the increase of Ag's concentration leads for an acceleration of the ordering reactions and a stabilization of the ordered phase AuCuI , thus, a deceleration of the disordering reaction. We note, also the appearances of several new reactions at a high temperatures.
In this work, an Zn-1.6Mg alloy was studied. The alloy composition was chosen according to the results of our previous work, which was focused on the research of biodegradable materials. The mechanical properties of such cast alloy are similar to the characteristics of human bones. Moreover, the Zn-1.6Mg alloy satisfies the requirements of biocompatibility. These facts determine the alloy for use in medicine as a suitable material for temporary implants.
The alloy was studied in three different stages of processing: a cast form, an extruded form, and finally a rapidly solidified alloy prepared by melt-spinning with the following hot extrusion. The main aim was to prepare Zn-1.6Mg alloy with fine structure which ensures the improvement of mechanical properties. Microstructure was evaluated by optical and electron microscopy, mechanical properties (compressive strength, hardness) were measured and corrosion rate was evaluated in model physiological solution.
Zn and Zn-based alloys attract interest due to an ability to protect steel surface against corrosion. Thin surface layer of a protective zinc alloy is usually prepared by hot dip galvanizing and acts as a barrier against a corrosive environment or as a sacrificial anode in case the bare steel surface is exposed.
Ability of zinc to protect steel surface against corrosion can be further increased by addition of alloying elements such as for example Al and Mg. These could be added in different amounts leading to a several-fold increase in corrosion resistance. Further elements are therefore studied in order to understand their effect on corrosion behavior and other properties such as for example ductility, hardness, wear resistance, etc.
The aim of this paper is characterization of a ternary alloy Zn-1.6wt.%Al-1.6wt.%Mg which is further modified with addition of tin in a rage from 0, 0.5, 1, 2, 3 wt.%. Prepared by melting of elements with 4N purity under a Zincogen 318 flux layer in a ceramic crucible all compositions were left to solidify by air cooling outside a melting furnace. Structure analysis of as-cast alloys was carried out with a help of light microscopy (LM), scanning electron microscopy (SEM), x-ray diffraction (xrd) and differential scanning calorimetry (DSC) and led to the identification of following phases: Zn reach solid solution, Al reach solid solution, Zn2Mg and Mg2Sn. Furthermore, XRD was used to identify corrosion products which were formed during exposure of alloys in a salt spray chamber.
With every tonne of pig iron being produced, over 10kg of flue dust is generated. Direct recycling of this material is unacceptable mainly due to its high zinc content. This waste often ends up on landfills, which is not ideal because of its heavy metal content and fine-grained character. There are several pyrometallurgical methods for recycling this type of material, but due to high energy consumption and low zinc content it is not ideal choice. On the other hand, hydrometallurgy is suitable for low zinc content with possibility of selective leaching. In this work, leaching of the dust with sulfuric acid was observed. Thermodynamic and kinetic aspects of zinc leaching were studied. Experiments were carried out under atmospheric pressure and effect of acid concentration and temperature was investigated. The goal was to set the conditions for maximum zinc leaching while minimum amount of iron is transferred into solution. Ideal conditions for selective leaching were achieved using 50°C and 1 - 0,5M sulfuric acid solution. Higher temperature and concentration caused higher iron leaching ratio. With optimal conditions, iron recovery was in the range 5 – 10 %, while all of the zinc was leached out. Solid residue, obtained by this method is relatively zinc-free and can be reused in blast furnace process.
The beta titanium alloys are widely used for hard tissue replacements due to their properties (e.g. high strength, low Young’s modulus or biocompatibility). Mechanical properties are dependent on microstructure which can be controlled through suitable thermo-mechanical treatment. The effect of cold rolling on texture evolution and mechanical properties has been studied in this paper. Hot forged, solution treated (850°C/0.5h/water quenched) Ti-35Nb-6Ta alloy has been cold rolled with thickness reduction 40, 60 and 80 and 90%. The texture evolution has been studied by using X-ray diffraction analysis and EBSD analysis. The {100}<110> texture is dominant for all studied specimens and became more distinct with increasing thickness reduction. Another texture evolution from {211}<110> to {111}<112> was observed with increasing thickness reduction. The tensile strength increased with thickness reduction from 600 to 830 MPa. On the other hand elongation decreased from 32 to 9%. The Young’s modulus value has been determined within range of 43 to 55 GPa.
TiAl alloys with high Nb content are subject of extensive research with the aim to develop material for applications demanding low density, good corrosion resistance and high strength at elevated temperatures. Disadvantage of broad using of TiAl alloys for parts of vehicle's engines or in aeronautics is in restricted workability, machinability and low fracture toughness especially at room temperature. One way to improve properties of the cast structure of TiAl alloy is the tailoring the microstructure by modification of chemical composition. For this purpose 5 types of TiAl alloys with 7% of Nb were prepared having variable content of Mo and/or C. Addition of Mo and/or C resulted generally in three types of microstructure (fully lamellar, nearly lamellar or mixed structure with higher amount of domains without lamellar colonies) and different phase composition. Presence of colonies consisting of thin lamellae of and 2 phases was characteristic for all alloys. Lamellar grains/colonies were sometimes complemented by gamma and sometimes also by beta phase at the grain boundaries. Mo and Nb are elements supporting formation of beta phase while C suppresses the occurrence of this phase. Variable microstructure and phase composition resulted in scatter of mechanical behaviour. The most promising tensile properties at both room and elevated temperature were observed for two materials: alloy doped with 2% of Mo having the mixed microstructure containing beta phase and alloy doped with 0.5% of C with NL microstructure without beta phase. 2Mo alloy exhibited reasonably good ductility (plastic deformation at fracture at 750°C was approx. 0.4%) while 0.5C alloy reached the highest tensile strength (approx. 630 MPa at 750°C). Also low cycle fatigue behaviour of these two materials was the best of all five materials under investigation. The fatigue deformation characteristics were better in case of 2Mo alloy while 0.5C alloy exhibited higher cyclic stresses. Fracture mechanisms were determined using fractographic analysis after test termination. The major fracture mode of all alloys was trans-lamellar. Occasionally also inter-lamellar fracture was observed and related to rather low mechanical properties (in case of alloy doped with 0.2 %C).
In Ni rich Ni–Ti alloys, various phases such as hexagonal TiNi3, cubic Ti2Ni and rhombohedral Ti3Ni4 appear during heat treatment. The presence of these precipitates affects the shape memory effect and superelasticity in an important manner. In this paper we present a study of the phase evolution during annealing of the Ni–48at.%Ti shape memory alloy elaborated by self-propagating high-temperature synthesis (SHS). Morphology and crystallography of the phases were examined by means of light metallography (LM), scanning electron microscopy (SEM), electron back-scattering diffraction (EBSD), neutron diffraction, differential thermal analysis (DTA), transmission electron microscopy (TEM) and energy dispersive X-ray spectroscopy (EDS). Besides the phases mentioned in the literature, a Ni-rich phase having a cubic symmetry was found. This phase develops from Ti3Ni4 particles during slow (furnace) cooling from the temperature of 1000 °C. Its particles have the form of thin platelets coherent with the B2 matrix. The orientation relation is either cube-to-cube or [115]B2 || [111]P and (552)B2 || (121)P.
One bi-layer Ni-Ti thin films with chemical compositions of Ni50.8Ti49.2 / Ni45Ti50Cu5 (numbers indicate at.%) determined by energy dispersive X-ray spectroscopy was deposited on Si substrates using RF magnetron sputtering. The structures and transformation temperatures of annealed thin films at 500oC for 1h were studied using grazing incidence X-ray diffraction (GIXRD) and differential scanning calorimetry (DSC), respectively. Nanoindentation was used to characterize the mechanical properties.
The DSC and X-ray diffraction results indicated the bi-layer was composed of austenitic and martensitic thin films. The bi-layer thin film exhibited a combined pseudo elastic behavior and shape memory effect at the same time similar to the austenitic and martensitic thin films, respectively. The combination of pseudo elastic with shape memory effect produces a two-way shape memory effect with a reduced hysteresis in the bi-layers.
Viscoplasticity and crystal plasticity have been used to model cyclic deformation of nickel-based superalloys at elevated temperature. Model parameters were determined from strain-controlled cyclic test data, with consideration of strain rate effects. Model simulations are in good agreement with the experimental results for stress-strain loops, cyclic hardening behaviour and stress relaxation behaviour during the hold periods at the maximum and minimum strain levels. The models were also applied to study crack-tip deformation under fatigue, which showed the accumulation of permanent deformation at the crack tip due to plasticity-induced strain ratcheting behaviour. The strain accumulation was subsequently utilized as a criterion to predict crack propagation in standard specimens using the finite element method, in comparison with experimental results. In addition, discrete dislocation dynamics has been attempted to model monotonic and cyclic deformation of single crystal superalloy, focusing on the interaction of dislocation dynamics with material underlying microstructure. Furthermore, finite element analyses of oxygen penetration along grain boundaries have been carried out to quantify the fatigue-oxidation damage and calibrate the diffusion parameters based on FIB measurements of internal oxidation. A sequentially coupled mechanical-diffusion analysis was adopted to account for the effects of deformation on diffusion during fatigue loading. Prediction of oxidation-assisted crack growth has been carried out from finite element analyses of oxygen diffusion near a fatigue crack tip. The predictions compared well with the experimental results for triangular and dwell loading waveforms, with significant improvement achieved over those predicted from the mechanical model alone.
This Project has an aim to evaluate and investigate the effect of heat treatment conditions on microstructural refurbishment in cast nickel base superalloy, grade MGA 1400. This cast nickel base superalloy used as turbine blade material. The evaluated reheat treatment programs consist of solution treatment at 1125◦C, 1150◦C and 1175◦C for 2, 4 and 6 hours then following with primary aging at 925◦C for 2 hours and secondary aging at 845◦C for 25 hours respectively. All reheat treated microstructures were examined and analyzed by SEM and image analysis program, namely, “ImageJ”. From all obtained results, it was found that the most proper solution treatment is at temperature of 1125◦C for 2 hours to provide the most uniform microstructural characteristics, which consist of the uniform distribution of very dense gamma prime particles precipitating in the matrix. This microstructure also provides the highest area fraction of gamma prime phase and the most proper average size of the gamma prime particles.
Generally, the rejuvenation heat treatment of degraded turbine blades, which were made of cast nickel based superalloy, Grade Inconel 738, usually consist of solution treatment condition with temperature range of 1125ºC- 1205ºC for 3 hours and then following with double aging processes, which include primary aging at 1055ºC for 1 hour and secondary aging at 845ºC for 24 hours. However, in practical working conditions of reheat treatment processed, the possible change of temperature during solution treatment can be obtained by error or malfunction of heating furnace, which usually provides the temperature dropping down. To simulate this effect, the dropping temperature during solution treatment was chosen to decrease till the level of 845ºC, which usually happens in practices then immediately heating up again to solution temperature level. The various selected temperature dropping programs were performed during solution treatment. The maximum number of temperature droppings during the single solution treatment is up to 3 times. From the received results, it was found that the effect of temperature dropping during solution treatment has extremely influenced on the final rejuvenated microstructures.
Cast polycrystalline superalloy MAR-M 247 has been thoroughly studied under high cycle fatigue loading. Investigated alloy was available in several batches cast under different conditions and also into different types of molds. Fully reversed (R = -1) fatigue testing was conducted by resonant pulsator in stress control regime at temperatures 650 and 800 °C. Significant differences in fatigue life time were observed among various batches. Obtained fatigue test results are showing the effect of the distribution and size of defects, average grain size and also experimental temperature. Fractured surface of tested specimens underwent fractographic analysis by light and electron microscopy. Typical features of fracture surfaces for the experimental temperatures were closely studied and main deformation mechanisms were described. In most cases, the shrinkage pores were places of the fatigue crack initiation at both temperatures. Advanced electron microscopy techniques like electron back-scattered diffraction (EBSD) and focused ion beam (FIB) revealed significant localization of cyclic plastic deformation into slip planes in favourable oriented grains. The localization of cyclic plastic deformation partly diminished with increased experimental temperature.
The aim of the work was to determine the microstructure effect on the tribological properties of the Monel K-500 alloy. The supersaturation temperature of 1150oC was selected in such a way so that it would exceed the solution temperature of the carbides present in the Monel K-500 alloy by less than 10oC. For the annealing temperature assumed in this way, the annealing time was assumed to be 1 h, 2 h and 4 h. Ageing at the temperature of 595oC for 8 h was also performed, followed by cooling at the rate of 0,2oC/min down to the temperature of 480oC. Further cooling was continued in air. The evaluation of the test results was based on hardness measurements, a friction test as well as a stereological evaluation of the grain. It was stated that the hardness is not a factor which determines the tribological wear resistance of the Monel K-500 alloy. The deciding factor for the tribological wear resistance are the dominant wear mechanisms. The Monel K-500 alloy exhibits a higher wear resistance in the supersaturated state than the aged state after supersaturation. The grain growth seems to result in a reduction of wear and an increase of the friction coefficient in the case of samples aged after supersaturation.
The microstructures of two nickel based alloys (Ni-Cr-Al-C and Ni-Cr-Nb-Al-C) containing chromium and chromium plus niobium carbides were investigated. These alloys unlike commercially available nickel based superalloys contain high volume fraction of carbides to obtain high wear resistance. Moreover aluminum addition enables precipitation hardening of the nickel based matrix. Scanning electron microscopy (SEM) including energy-dispersive X-ray spectroscopy (EDX) and X-ray diffraction (XRD) studies were carried out with particular attention to phase composition of materials. Solution treatment and aging was applied to improve retention of carbides within matrix during wear as well as to improve high temperature strength.
High-quality compacts were prepared using the spark plasma sintering (SPS) method from powders of similar composition Fe-Al-Zr-B. The properties of the sintered compacts are strongly dependent on the morphology and properties of the feedstock powder. The first powder was obtained by ball milling of the as cast alloy and the second was prepared by atomization under argon atmosphere. The morphology and structure of the two powders are compared and mechanical properties and microstructure of compacts prepared under the same conditions of the SPS procedure are discussed. The milled powder has an irregular morphology and shape of the polycrystalline particles, which have a completely disordered BCC structure with considerable internal stresses, high concentration of structural defects and the presence of aluminum oxide. The atomized powder particles are nearly spherical, polycrystalline with ordered B2 structure, with no significant signs of internal stresses and oxidation. Microhardness of particles of both powders was measured and compared with the microhardness of compact materials, the results of compression tests of compacts at room temperature were compared and discussed.
Detailed studies of the phase composition, microstructure and magnetic properties of alni alloy subjected to melt spinning and subsequent isothermal aging at Tann = 500-780oC for 10 min are reported. Microcrystalline Fe2NiAl alloy with the nominal composition Fe51.1Ni23.5Al23.7Si1.7 was prepared by melt-spinning with a copper-wheel speed V=40 m/s. As-prepared ribbons have soft magnetic properties (Hc = 6 Oe). As the Tann increases from 500 to 700oC, Hc increases from 10 to 250 Oe; after aging at 780oC coercive force decreases to Hc = 120 Oe. Transmission electron microscopy (TEM) investigations of the decomposition of the solid solution (β2 → β + β2) during aging have revealed several types of decomposition products. As-prepared ribbons have fine zone structure and antiphase domains (AFDs) inside grains which boundaries were decorated by decomposition products. Aging at 500-600oC led to the coarsening of zone structure inside grains and to the appearance of discontinuous precipitates (DP) (β + β2 → β’ + β’2) at grain boundaries which forms the lamellar microstructure consisting of alternating lamellas of β’ and β’2 phases. Aging at higher than 700oC causes the formation of modulated microstructure inside grains and coarsening of DP products. The periodic modulated structure ensures the coercive force Нc = 250 Oe. The development of DP and SD during the aging at 700-780 oC leads to β’- phases core formation inset in continuous network of β’2 phase. The coarsening of the magnetic β phase causes the change of the magnetization mechanism from single-domain to multi-domain process may be the reason of the decrease of coercive force to Hc = 120 Oe after aging at 780oC.
The influence of different consolidation procedures on compaction of Al powders was evaluated. Powder preparation procedures consisted of selection of particle size distribution, cold isostatic pressing (CIP), and vacuum sintering. Processing parameters investigated included the number of compression steps and compression pressure and sintering temperature and time. Densities of the samples after compression and also after sintering were measured and compared. The overall oxygen content was analysed using scanning electron microscopy. Phase composition was determined using X-ray. Microhardness measurements were performed to evaluate the degree of compaction. Double-step CIP at 200+300 MPa and subsequent sintering at 500°C for 60 min produced the best combination of properties from consolidation of Al particles. Of the particle size ranges studies, those with diameters between 20 and 45 μm produced the best results. Aluminum oxide was present in the structure after all the processing treatments.
In our today, research-development studies required for production of organic brake pads have become fast because asbestos in brake pads have negative effects on human health and damages to the environment. This study focuses to develop to non-asbestos high performance of brake pads reinforced with organic materials such as Hazelnut and Walnut shell dusts eco-friendly. The friction-wear behavior of brake pads produced was tested on a “Brake Pad Friction Equipment” designed according to the actual test conditions. Twenty-four friction dusts were utilized as fillers, reinforcements, binders and abrasives in mixture of organic brake pads produced. The 3.5 wt. % and 7 wt. % content of hazelnut and walnut were added to mixtures of the brake pad as friction modifier material. The mixtures of brake pad prepared were hot-pressed to metal molds under temperature of 155±5 ºC and pressure range of 20-22.5 MPa at 6 minutes. The pressed brake pads were freely held within a furnace which has air-circulation in temperature from 300 ºC to 150 ºC at 10 hours. The performance of brake pads was determined by the test equipment in terms of parameters including speed, temperature, pressure, and friction coefficient. Microstructure examinations, density, surface roughness and hardness of brake pads prepared were also discussed. The results indicated that organic dusts of hazelnut/walnut shell can reduce specific wear rate and provide stable friction coefficient. From this, it can be concluded that new type brake pads of non-asbestos organic-based dusts can be effectively replacement for asbestos in brake pad production.
It is demonstrated that the formation of the plane crystallization front in the process of the directional controlled solidification of castings of solid solution alloys with the crystallization range does not allow to manufacture homogeneous through the length single crystals at any growing parameters. The only possible way of obtaining single crystal ingots without zone segregation is to destroy the plane crystallization front and to create the transition liquid-solid cellular or dendrite structure. It allows to substitute the formation of the zone macrosegregation for the dendrite microsegregation. This method assures that after short-term homogenizing the resulting single crystals of multi-component alloys are homogeneous.
In the work the results of the structural perfection of the single crystals with the diameter 24 mm of the Ticonal 9 (35% Co – 14,5 % Ni – 7 % Al – 4 % Cu – 5 % Ti – Fe the rest) alloy at the growing rates (R) from 0.1 to 9 mm/min with the constant temperature gradient 10 deg/mm are given. It is demonstrated that the size of the blocks decreases from 2.3 mm at R = 0.1 mm/min to 1 mm at R = 9 mm/min at the simultaneous increase of the disalignment from 1.8 deg to 7.8 deg accordingly. The investigation of the working parameters (magnetic properties) of the samples of the ingots obtained at different growing rates has shown that the samples grown at the high rates (5 – 9 mm/min), i.e. the samples with the most imperfect structure, have the highest magnetic properties (HcB, Br, (BH)max). Theoretical and experimental investigations carried out in the present work allowed to explain this contradiction and give recommendations regarding the conditions of manufacturing single crystal ingots of solid solution alloys.