scispace - formally typeset
Search or ask a question

Showing papers in "Powder Metallurgy in 2009"


Journal ArticleDOI
TL;DR: In this article, the microstructural and mechanical properties of injection molded Ti-6Al-4V parts were described, and the results showed that they can be sintered to a maximum 99% of theoretical density.
Abstract: This paper describes the microstructural and mechanical properties of injection moulded Ti–6Al–4V parts. Ti–6Al–4V powder was injection moulded with wax based binder. The critical powder loading for injection moulding was 67·5 vol.-% for feedstock. Binder debinding was performed with solvent and thermal method. After debinding the samples were sintered at different temperatures and times in vacuum atmosphere (10−4 torr). Metallographic studies were conducted to determine to extend densification and the corresponding microstructural changes. The results show that Ti–6Al–4V powder could be sintered to a maximum 99% of theoretical density. Maximum ultimate tensile strength and hardness were obtained 704 MPa and 38·6 HRC at 1275°C for 10 h.

33 citations


Journal ArticleDOI
I. A. MacAskill1, A. D. P. LaDepha1, J. Milligan1, J. J. Fulton1, D. P. Bishop1 
TL;DR: In this paper, the effects of hot and cold swaging on the density and mechanical properties of a commercial Alumix 431D powder metallurgy alloy known as alumix431D were investigated.
Abstract: The objective of this work was to investigate the effects of hot and cold swaging on the density and mechanical properties of a commercial Al–Zn–Mg–Cu powder metallurgy alloy known as Alumix 431D. To do so, as sintered samples of the PM alloy were swaged under a variety of conditions and characterised. For comparison purposes, equivalent characterisation tests were completed on the chemically similar wrought alloy 7075-T6. Cold swaging was moderately successful provided the as sintered billets were annealed or solutionised before densification. Here, modest improvements in density and tensile properties were noted. Hot swaging proved to be a more effective approach. Optimal properties were achieved when samples were preheated to 470 ± 10°C. When processed in this manner, a density of 99·6% of theoretical was realised while the tensile and fatigue properties exceeded those of the wrought 7075-T6 alloy tested for comparison purposes.

28 citations


Journal ArticleDOI
TL;DR: In this article, the effect of reinforcement content and sintering temperature on the densification and microstructural development of Al6061/SiC composite materials during sinteration was studied.
Abstract: The aim of the present work is to study the effect of reinforcement content and sintering temperature on the densification and microstructural development during sintering of Al6061/SiC composite c...

25 citations


Journal ArticleDOI
TL;DR: In this article, the morphological, microstructural and mechanical properties changes during nanosized alumina increment to Al powder were studied, and the results showed that the strength, ductility and hardness were increased by increasing the reinforcement nanoparticles weight percentage.
Abstract: Aluminium based metal matrix composites produced by powder metallurgy are used in the aerospace and automobile industries because of their high strength, light weight, etc. The properties may become much better when nanosized reinforcements are used. In this research, the morphological, microstructural and mechanical properties changes during nanosized alumina increment to Al powder were studied. Because nanosized particles are extremely prone to agglomeration, all of the samples have been milled for 12 h by a planetary ball mill. The process was conducted for Al–(0–20) wt‐%Al2O3 powders to explore the role of reinforcement nanoparticles on the microstructure and mechanical properties. The results showed that the strength, ductility and hardness were increased by increasing the reinforcement nanoparticles weight percentage. Also, addition of hard particles accelerated the milling process, leading to faster work hardening rate and fracture of the aluminium powder.

24 citations


Journal ArticleDOI
TL;DR: The suitability of nickel as an alloying element in titanium alloys produced using the blended elemental powder metallurgy approach has been explored in this paper, where it was shown that nickel initially accelerates sintering, providing greater densification at lower temperature than observed for unalloyed titanium.
Abstract: The suitability of nickel as an alloying element in titanium alloys produced using the blended elemental powder metallurgy approach has been explored. Nickel initially accelerates sintering, providing greater densification at lower temperature than observed for unalloyed titanium. However, it provides only a minor improvement in the density achieved after long sintering times or at high solid state sintering temperatures. Swelling is observed under liquid phase sintering conditions. The highest density was achieved by sintering at just below the solidus temperature. Nickel also accelerates the Ostwald ripening of the pore structure and the conversion of open porosity into closed porosity.

22 citations


Journal ArticleDOI
TL;DR: In this article, the compaction and sintering conditions required for avoidance of swelling and development of very coarse pores during liquid phase Sintering of mixed elemental titanium powder metallurgy alloys are described with reference to the titanium-nickel binary system.
Abstract: The compaction and sintering conditions required for avoidance of swelling and development of very coarse pores during liquid phase sintering of mixed elemental titanium powder metallurgy alloys are described with reference to the titanium–nickel binary system. Swelling is minimised by using low compaction pressure or short sintering time. Swelling appears to require the presence of persistent liquid and closed pores. Gas pressure within closed pores is the probable mechanism of swelling.

21 citations


Journal ArticleDOI
TL;DR: In this article, Fe-Al-Si alloys were prepared by reactive sintering and the contents of silicon and aluminium ranged between 0.30 and 10.40% respectively.
Abstract: In this work, Fe–Al–Si alloys were prepared by reactive sintering. The contents of silicon and aluminium ranged between 0–30 wt‐% and 10–40 wt‐% respectively. Aluminium, silicon and AlSi30 master alloy powders prepared by mechanical machining and/or milling and commercial powder of high purity iron were used for sintering. Powders were blended and pressed at room temperature. Sintering was carried out at 950°C for 60 min. Compact low porosity products without unreacted components were prepared, if a powder mixture contained 15–20 wt‐% of silicon and 20–25 wt‐% of aluminium. It was shown that these materials contain two phases (Al2FeSi and AlFeSi). Hardness of the alloys increased with growing silicon content, while the increase in aluminium content reduced the hardness.

19 citations


Journal ArticleDOI
TL;DR: In this article, the authors describe steps in the process of developing a Ti-Ni-Sn alloy, able to be sintered to near full density at a sintering temperature as low as 1100°C without requiring unusually fine powder or high compaction pressure.
Abstract: Few Ti alloys have been designed for ease of sintering. This paper considers the design of alloys for processing using the mixed elemental technique, in which powders are mixed, cold pressed in a die to near net shape and sintered under vacuum at high temperature. The authors describe steps in the process of developing a Ti–Ni–Sn alloy, able to be sintered to near full density at a sintering temperature as low as 1100°C without requiring unusually fine powder or high compaction pressure. Higher sintering temperature allows the Ni content of the alloy to be reduced, but swelling of the alloy probably imposes an upper limit on practical sintering temperature. The increase in green density, and hence sintered density, conferred by Sn in Ti–Sn alloys, and the increase in sintered density due to the high diffusivity of Ni in Ti–Ni alloys, are combined in Ti–Ni–Sn alloys.

17 citations


Journal ArticleDOI
TL;DR: In this article, the effect of the nanometric reinforcement particles on the mechanical milling (MA) process of the soft matrix was studied by scanning electron microscopy, X-ray diffraction (XRD), transmission electron microscope, laser particle size analyser and standard metallographic techniques.
Abstract: This paper presents experimental results on the synthesis of nanostructured aluminium matrix nanocomposite powders by comilling of nanoscaled SiC and Al2O3 particles and micrometric aluminium powder. The effect of the nanometric reinforcement particles on the mechanical milling (MA) process of the soft matrix was studied by scanning electron microscopy, X-ray diffraction (XRD), transmission electron microscopy, laser particle size analyser and standard metallographic techniques. It was found that at the early stage of milling, the nanoparticles are smeared on the surface of the aluminium powder and thus do not significantly contribute in the MA process. As the milling continues, the hard nanoparticles are distributed throughout the matrix and enhance the work hardening rate of the soft material. This leads to premature occurrence of the fracture process, so the steady state condition is attained in a shorter milling time compared with the unreinforced aluminium. It was shown that the structural ev...

15 citations


Journal ArticleDOI
TL;DR: The strength and failure of TiC-based cermets under monotonously increasing and cyclic loading conditions were investigated in this paper, where it was shown that the failure of the carbide composite is preceded by local plastic strain taking place in its both phases in the ductile binder and in the brittle carbide phase.
Abstract: The strength and failure of TiC based cermets (designed for metalforming) under monotonously increasing and cyclic loading conditions were investigated. Comparative trials with an ordinary WC hardmetal (widely used in metalforming) complemented with XRD studies were performed. It is shown that the failure of the carbide composite is preceded by local plastic strain taking place in its both phases in the ductile binder and in the brittle carbide phase. Under cyclic loading conditions the plasticity of carbide composites decreases. The intensity in decrease depends on alloy composition.

15 citations


Journal ArticleDOI
TL;DR: In this article, the sintered properties of cylindrical tensile specimens green machined are compared to those machined after sintering, and the results show that the tensile properties of components machined in their green state are identical to those of components manufactured after the sinter.
Abstract: With the increasing demand for sinter hardened powder metallurgy components, there is a growing need to solve the poor machining behaviour that characterises them. Approaches based on green machining appear promising to extend tool life and reduce machining costs. The present study deals with the sintered properties of cylindrical tensile specimens green machined. Results show that tensile properties of components machined in their green state are identical to those of components machined after sintering.

Journal ArticleDOI
TL;DR: In this article, X-ray diffraction investigations revealed the presence of W2C intermetallic phase in sintered composites produced from both wet and dry milled W-1C powders.
Abstract: Tungsten based W–1C and W–2B4C–1C (wt-%) powders synthesised by mechanical alloying (MA) for milling durations of 10, 20 and 30 h, in wet (ethanol) and dry conditions, were characterised. X-ray fluorescence spectroscopy investigations revealed Co contamination which increased with increasing milling time during wet milling. X-ray diffraction investigations revealed the presence of W and WC phases in all powders, Co3C intermetallic in the wet milled W–1C powders and W2B intermetallic phase in both wet and dry milled W–2B4C–1C powders. As blended and MA processed powders were consolidated into green compacts by uniaxial cold pressing at 500 MPa and solid phase sintered at 1680°C under hydrogen and argon atmospheres for 1 h. X-ray diffraction investigations revealed the presence of W2C intermetallic phase in sintered composites produced from both wet and dry milled W–1C powders and the W2B intermetallic phase in sintered material from the wet milled W–2B4C–1C powder. Sintered composites from wet mill...

Journal ArticleDOI
TL;DR: In this paper, the effects of the Al content on the pore properties of resultant porous Fe-Al alloys were systematically studied and it was found that the volume expansion, the open porosity and the permeability can be manipulated by varying the al content and their maximum values are reached at Fe-45 wt-%Al.
Abstract: Porous Fe-Al alloys with the nominal composition ranging from Fe-20 wt-%Al to Fe-60 wt-%Al have been fabricated by Fe and Al elemental powder reactive synthesis. The effects of the Al content on the pore properties of resultant porous Fe-Al alloys were systematically studied. It has been found that the volume expansion, the open porosity and the permeability can be manipulated by varying the Al content and that their maximum values are reached at Fe-45 wt-%Al. Their mechanical properties suggest that they are strong enough for the filtration applications.

Journal ArticleDOI
TL;DR: In this paper, the authors determined, using a statistical method, optimal models which define viscosity as a function of three parameters: shear rate, temperature and solid loading for low-viscosity feedstocks.
Abstract: Powder injection moulding (PIM) carried out with the use of low viscosity feedstocks offers numerous benefits for manufacturing small complex shape parts. Unlike typical high pressure metal injection moulding (HPIM) viscous feedstocks, soft tooling can be employed for prototyping and small volume manufacturing. Compared to HPIM, there are very few studies on the rheology of low viscosity feedstocks. The objective of this paper is to clearly determine, using a statistical method, optimal models which define viscosity as a function of three parameters: shear rate, temperature and solid loading for low viscosity feedstocks. With the statistical method employed, it was found that the models of Herschel–Bulkley, Arrhenius, and Maron and Pierce can be used respectively to effectively model each of the three parameters stated previously. Moreover, the combination of these three models in one global model is proposed to predict the combined effect of the three parameters on low viscosity PIM feedstocks.

Journal ArticleDOI
TL;DR: In this article, the effect of various process parameters such as atomising pressure, deposition distance, melt superheat and melt delivery tube diameter on porosity of the spray-deposition thin aluminium strip was reported and explained.
Abstract: A characteristic feature of the spray deposited metal strip is that it contains porosity. The present paper has reported and explained the effect of various process parameters such as atomising pressure, deposition distance, melt superheat and melt delivery tube diameter on porosity of the spray deposited thin aluminium strip. Porosity of the spray deposited aluminium strip greatly depends not only on the liquid fraction present on the substrate, but also on the thermal condition through the substrate. It has been shown that there are several types of porosity present in the strip, namely interstitial, mechanically entrapped gas, intersplat boundary, solidification shrinkage and porosity due to hydrogen evolution. The mechanism of their formation has been discussed. An increase in the initial temperature of the substrate lowers the porosity content in the spray deposited aluminium strip.

Journal ArticleDOI
TL;DR: The phase distribution of a candidate cold work tool steel consisting of a stainless steel matrix with fine, well distributed niobium carbide precipitates is reported and compared with equilibrium calculations as mentioned in this paper.
Abstract: To increase the wear resistance of tool steels, high contents of super-hard MC type carbides formed by Ti, V or Nb are desirable. Unfortunately, these carbides precipitate primarily from the melt at high temperatures. Thus, atomising such steels is not feasible with current technology because carbides precipitating in the melt may clog the nozzle. This problem can be avoided by atomising a melt that contains high amounts of carbide forming elements but no carbon. Subsequently the powder is mixed with graphite to provide the carbon necessary to form carbides and for the hardenability of the matrix. During hipping, graphite dissolves and the carbon is distributed evenly in the material. The phase distribution of a candidate cold work tool steel consisting of a stainless steel matrix with fine, well distributed niobium carbide precipitates is reported and compared with equilibrium calculations.

Journal ArticleDOI
TL;DR: Uniformity is an important quality attribute of products manufactured via the powder route, such as structural powder metallurgy (PM) parts, ceramics, hardmetals, magnets, detergents, pharmaceutical tablets, etc.
Abstract: Uniformity is an important quality attribute of products manufactured via the powder route, such as structural powder metallurgy (PM) parts, ceramics, hardmetals, magnets, detergents, pharmaceutical tablets, etc. Uniformity can be regarded in terms of weight, composition and structure variations from part to part or within a compact and can be traced, in a good number of cases, to die fill.

Journal ArticleDOI
G. L. Hao1, Q. P. Xu, F.S. Han1, W. D. Li, S. M. Bai 
TL;DR: The well distributed open cellular porous copper was fabricated by present powder metallurgy technique based on space holder method, depending on the volume fraction and size of the space holding p... as discussed by the authors.
Abstract: The well distributed open cellular porous copper was fabricated by present powder metallurgy technique based on space holder method, Depending on the volume fraction and size of the space holding p...

Journal ArticleDOI
TL;DR: In this paper, the sintering response of pure tin is assessed and correlated with microstructure and tensile behaviour following extrusion, and the results revealed that energy efficient microwave sintered samples exhibit superior combination of microstructures and tensiles properties when compared to unsintered and conventionally sintering samples.
Abstract: In the present study, sintering response of pure tin is assessed and correlated with microstructure and tensile behaviour following extrusion. This study was undertaken as there is no information in public domain on tin which is emerging as an interconnect material in its nearly pure forms. Benchmarking was carried out with unsintered tin as the recrystallisation temperature of tin is much lower than ambient temperature. Results revealed that energy efficient microwave sintered samples exhibit superior combination of microstructure and tensile properties when compared to unsintered and conventionally sintered samples.

Journal ArticleDOI
TL;DR: The grey iron microstructure Fe-2C-2Si powder-based compact is tailored by different kinds of in situ and post sintering processing as discussed by the authors, which can be achieved by combining thermodynamic and kinetics modelling of micro-structure development with Sintering and controlled heat treatment experiments of tensile test specimens die compacted at 600 MPa.
Abstract: The grey iron microstructure Fe–2C–2Si powder based compact is tailored by different kinds of in situ and post sintering processing. This has been achieved by combining thermodynamic and kinetics modelling of microstructure development with sintering and controlled heat treatment experiments of tensile test specimens die compacted at 600 MPa. Applying optimised sintering conditions led to a grey iron like microstructure with 95% relative sintered density. Sinter hardening the compacts led to 500 MPa in yield strength and 600 MPa in ultimate tensile strength in combination with ductile fracture. Quenched and tempered condition showed the same strength values, but combined with brittle fracture due to martensitic structure. Pore rounding and partial pore filling by graphite were obtained by austenising isothermal hold during the cooling of the sintering cycle.

Journal ArticleDOI
TL;DR: In this article, conditions of comparable microstructure and compressive behaviours of powder metallurgy (PM) Ti-46Al (Cr,Nb,W,B) alloy prepared by hot isostatic pressing (HIP) and pseudo-HIP technology were discussed.
Abstract: The present work discusses conditions of comparable microstructure and compressive behaviours of powder metallurgy (PM) Ti–46Al–(Cr,Nb,W,B) (at.‐%) alloy prepared by hot isostatic pressing (HIP) and pseudo‐HIP technology respectively. A PM route based on pseudo‐HIP of alloy powder prepared by plasma rotating electrode process was used for the rapid fabrication of high quality TiAl alloys. The pseudo‐hipped alloy shows a fine grained microstructure which is significantly finer than that of the hipped alloy consolidated under similar conditions. The pseudo‐hipped alloy exhibits more excellent compression properties than that of the hipped alloy at elevated temperatures. By using the kinetic rate equation, the stress exponent n and the apparent activation energy Q are determined and discussed respectively. The influence of microstructure on the flow behaviour during the total hot compressive deformation was studied. The role of submicrocrystalline forming and dynamic recrystallisation due to mechanical twinn...

Journal ArticleDOI
TL;DR: In this paper, the tensile and axial fatigue properties of sintered hardened Fe-1·5Mo-2Cu-0·5C at three density levels (6·8, 7·0 and 7·2 g cm-3) have been studied.
Abstract: In the present work the tensile and axial fatigue behaviour of sintered hardened Fe–1·5Mo–2Cu–0·5C at three density levels (6·8, 7·0 and 7·2 g cm–3) have been studied. The materials were tested under the as sintered condition, and after tempering at 180 and at 240°C. The results show that steels under the as sintered condition posses a high hardness but a brittle tensile deformation and fracture behaviour. Tempering at 180 and 250°C induces the disappearance of brittleness and tensile fracture is thus ductile although very localised at the necks. Fatigue strength is determined by the resistance of the materials to the internal damage evolution due to the nucleation of small cracks at the pores edges, and their coalescence into a long crack. Tempering induces an increase in the fatigue resistance. The greatest fatigue strength at 2 × 106 cycles is displayed by the steel with a density of 7·2 g cm–3 and tempered at 180°C.

Journal ArticleDOI
TL;DR: In this article, a porous NiTi shape memory alloy was fabricated by self-propagating high temperature synthesis and the effects of solution treatment under load applied on the microstructure were investigated.
Abstract: Porous NiTi shape memory alloy was fabricated by self-propagating high temperature synthesis. Effects of solution treatment under load applied on the microstructure were investigated. The densities of the phases changed insignificantly with solution treatment but the intermetallic phases such as Ti2Ni, Ni4Ti3 and Ni3Ti2 disappeared and the density of B2(NiTi) phase increased with the load applied during solution treatment. Consequently, porous NiTi SMA with ideal pore characteristics, high chemical homogeneity and high strength for hard tissue implants was obtained.

Journal ArticleDOI
TL;DR: In this article, an adequate sintering assembly was designed and studied, in order to achieve desired levels of mechanical properties, different Ti powders (either pure Ti or Ti hydride) were tested as metal matrix.
Abstract: The attractive physical and mechanical properties that can be obtained with Ti metal matrix composites (Ti-MMCs), such as high specific modulus, strength or wear resistance have been documented extensively. Interest in MMCs for use in the automotive industries, aerospace, and other structural applications has increased over the past 25 years as a result of several processing routes being developed and availability of reinforcements. Additionally, Ti powder metallurgy offers the possibility of creating net shape or near net shape parts without the material loss and cost associated with machining intricate components from wrought stock material, Ti being notoriously difficult to machine. This work focuses on research of a suitable Ti based metal matrix which will be reinforced by particles. First an adequate sintering assembly was designed and studied. Next, in order to achieve desired levels of mechanical properties, different Ti powders (either pure Ti or Ti hydride) were tested as metal matrix. T...

Journal ArticleDOI
TL;DR: In this paper, a hot powder forging (HPMF) technique was used to fuse the friction elements and the steel container, which happens to become the backing plate of the brake pad assembly.
Abstract: Heavy duty metalloceramic brake pads are currently manufactured by compacting and sintering the metal powder mixture containing about 20–30% non‐metallic constituents. This technology suffers from certain limitations such as poor density, weak joining of backing plates with friction material layers, large consumption of hydrogen gas during processing, etc. etc. In order to overcome these limitations, new technology based on ‘hot powder forging’ has been developed in the present investigation. This technique offers efficient diffusion bonding between friction elements and the steel container which happens to become the backing plate of the brake pad assembly. The brake pads developed through this technology have been tested for military aircrafts namely AN‐32 and MIG‐27. It has been observed that the pads made through this technology are superior in performance in comparison with the pads made by sintering technology. Furthermore, the chemistry employed in the present technology is much simpler. Th...

Journal ArticleDOI
TL;DR: In this paper, the authors examined the sintering of Ti-Ni alloys by means of dilatometry of mixed elemental powders and found that higher sintered density was achieved due to a combination of lower heating rate and lower residual pressure.
Abstract: In earlier work the authors examined the sintering of Ti-Ni alloys by means of dilatometry of mixed elemental powders. Some notable differences were observed when heat treatments were carried out using a vacuum tube furnace rather than the dilatometer: higher sintered density was achieved due to a combination of lower heating rate and lower residual pressure, and swelling during liquid phase sintering was greatly reduced. This observation is consistent with the idea that gas pressure within closed pores causes swelling during liquid phase sintering and retardation of shrinkage in solid state sintering. In addition to the results of measurements of density and open and closed porosity as a function of Ni content and sintering temperature, macrographs and optical micrographs of the sintered compacts are presented, and the effects of heating rate and compaction pressure are described.

Journal ArticleDOI
TL;DR: In this paper, the machinability analysis of sintered metals filled with a Machinability Enhancer was carried out in different drilling conditions, in which the cutting parameters involved in the study were: rotating velocity, feedrate and coating of the tool.
Abstract: The aim of this paper is the machinability analysis, in different drilling conditions, of sintered metals filled with a machinability enhancer. The cutting parameters involved in the study are: rotating velocity, feedrate and coating of the tool. To reduce the number of experimental tests required, a 2k–1 fractional design of experiment with three two level factors and two replications for each run was employed. The experimental design was repeated for three sintered metals with different hardnesses or densities. The obtained results show new insight into the machining mechanism of sintered material and into the influence of the cutting parameters on the machining forces.

Journal ArticleDOI
TL;DR: In this article, a non-destructive test that relies on silicon rubber to transcribe the inner surface profile of the compaction die was developed to measure tool wear and tool surface quality during the die compaction process.
Abstract: A new methodology was developed to observe and measure tool wear and tool surface quality during the die compaction process. The newly developed method is a non-destructive test that relies on silicon rubber to transcribe the inner surface profile of the compaction die. After verification of the method, aluminium and iron alloy powders were compacted to quantify tool wear and tool surface quality with two die materials, tungsten carbide and tool steel. The tool surface quality was quantified by recording surface roughness of the die replicas on a surface profilometer.

Journal ArticleDOI
TL;DR: In this paper, two different porous iron compacts of porosities 21 and 46% were chosen for the present investigation as metal compacts with moderate porosity (10-70%).
Abstract: Experimental design technique was used in this investigation to illustrate the relationship between the porosity degree as well as its morphology on the mechanical properties and the wear resistance of iron metal compacts. Two different porous iron compacts of porosities 21 and 46% were chosen for the present investigation as metal compacts of moderate porosity (10–70%). The results indicated that the 2N factorial design technique could be used in evaluating the wear resistance of the iron compacts dependent on the percentage of porosity. It has been indicated that the increase in porosity is largely affected the wear behaviour of such porous metals. However, the stress–strain relationship of these metals is largely dependent on the degree of porosity. Since the compacts poses lower porosity (21%) provides distinct stages of elastic plastic behaviour, the compacts having higher porosity (46%) exhibit identified ultimate strength point.

Journal ArticleDOI
TL;DR: In this paper, a high speed digital analysis technique was used to study the atomisation plume of a superheated sample of Ni-Al in a close coupled gas atomiser.
Abstract: A high speed digital analysis technique has been used to study the atomisation plume of a superheated sample of Ni–Al in a close coupled gas atomiser. The atomisation, incorporating a generic melt ...