Powder Metallurgy

Titanium powders produced via the hydride–dehydride process are described with reference to the markets that they serve, on the basis of more than 20 years of operating experience at Reading Alloys. Raw material selection and downstream finishing play important roles in determining key characteristics of the finished powder. Resultant chemistry, morphology and particle size distributions are discussed.

The effect of interstitials on the mechanical properties of cast and wrought titanium alloys has been extensively reported but less information is available on the effect of contamination during PM processing. The sources of interstitial contamination when processing titanium powders by compaction, isostatic pressing, powder injection moulding (PIM) and innovative foaming processes are reviewed, focusing specifically on oxygen. The initial powder characteristics (surface area, size), process parameters (time, temperature) and environment (atmosphere, binder, support) may all have significant impact on the final interstitial content. It is, therefore, important to identify and control the sources of contamination by interstitials. A case study on PIM is provided to illustrate the relative contribution of the different sources.

R&D efforts at CSIRO, Australia, into the production of ‘lower cost’ titanium powders are complemented by a strong, downstream PM programme. One of these efforts has focused on the direct powder rolling of commercially pure (cp) titanium powder with a view to the continuous production of fully dense strip. Considerable research is also being undertaken to produce titanium alloy strip, initially from the Ti–6Al–4V alloy, using this process. An experimental design approach has been employed to establish key parameters, maximise the process window and meet property specifications. Demonstration of a proof-of-system at pilot scale is well advanced and the focus is now shifting to seeking industrial engagement with a view to collaboration, technology transfer and commercialisation of the technology. The current status of the technology is surveyed including aspects of the associated market trends and commercial feasibility.

Warm hooker extrusions of sintered powder metallurgical preforms of steel were investigated at different temperatures ranging from room temperature to 773 K in steps of 100 K for strains of 0·87, 1·0, 1·14 and 1·3. The resident densities for extrusion were chosen from the formability limit diagrams generated at different temperatures, which demarcates the safe zone from fail zone. Microstructure characterisations vide pore closure revealed the possibility of deformation and warm working assisted sintering of preforms extruded at warm working temperatures. The rate of force/stroke (dF/dS) and ratio of actual force to theoretical force called correction factor φ for different temperatures were evaluated to substantiate the deformation and warm working assisted sintering. Hardness data of the extruded samples were measured to determine the densification. The extruded samples were analysed for the surface roughness along their length and the optimum temperature for extruding steel preforms for better properties were identified.

The focus of the current study was to evaluate and quantify the effects of particle reinforcements and lubricants on the die wear during compaction of Al matrix composites. A new wear model was developed and combined with experiments to quantify die wear using automatic die compaction experiments. The influences of the reinforcement particle type and content, as well as the premixed lubricant content, are presented and discussed.

In this study, a series of Co–Cr–Mo alloys with varying Cr contents were produced by powder metallurgy technique, and the effects of Cr content on microstructure and abrasive wear behaviour were studied. Seven different powder compositions having 15–35 wt-%Cr were used in the experiments. Homogeneously blended powders were cold compacted in a 120 kN single action press. The sintering process was carried out at 1200°C for 60 min in an argon atmosphere. The effects of Cr on the microstructure and abrasion wear performance of the produced powder metallurgy alloys were investigated using SEM, energy dispersive spectroscopy and abrasion wear tests. Abrasive wear resistances were observed to have been increasing up to 27·5 wt-%Cr addition and decreasing subsequently.

In this work ultrafine and nanocrystalline WC–Co mixtures were obtained by low energy milling in planetary ball mill. The effect of the processing conditions on the reduction and distribution of the grain sizes and the internal strains level were studied. The characterisation of the powder mixtures was performed by means of scanning and transmission electron microscopy and X-ray diffraction analysis. Observations through SEM and TEM images showed a particle size below 100 nm, after milling. The X-ray diffraction profile analysis revealed a WC phase refined to a crystallite size of 19 nm.

The mixtures obtained have been consolidated and mechanical and microstructurally characterised. The results show improvements in resistant behaviour of the material consolidated from nanocrystalline powders, in spite of the grain growth experienced during the sintering. The best results were found for the material obtained by wet milling during 100 h, which presents values of hardness higher than 1800 HV.

In situ TiB₂ and TiC particulates reinforced steel matrix composites have been fabricated using cheap ferrotitanium and boron carbide powders by spark plasma sintering (SPS) technique. The sintering behaviour and the formation mechanism of the composite were studied. The results show that when the composite was sintered at 1050°C for 5 min, the maximum relative density and hardness of the composite are 99·2% and 83·8 HRA respectively. The phase evolution of the composite during sintering indicates that the TiB₂ and TiC reinforcements were formed in situ as follows: first, the solid/solid interface reaction between Fe₂Ti and B₄C, resulting in the formation of a small amount of TiB₂ and TiC below 950°C; second, the solid–liquid solution precipitation reaction in the Fe–Ti–B–C system, resulting in the formation of the main TiB₂ and TiC reinforcements at ∼1000°C.

The selective laser melting of a metallic/inorganic blended powder system consisting of 316L stainless steel powder and NH₄HCO₃ powder was performed. The SEM characterisation showed the formation of a honeycomb-like porous structure possessing unusually micrometre scaled pores (∼2 to ∼5 μm), with the addition of 4·0 wt-%NH₄HCO₃ powder using a high laser power of 800 W. The EDX and XRD analyses testified that the obtained porous structure was stainless steel with high chemical purity. The developing mechanism of such a novel microcellular structure under various processing conditions was addressed. It shows that the cooperative action between bubbles escaping kinetics and metallic matrix solidification kinetics, accounts for the formation of the honeycomb porous configuration. The effects of component ratio and main processing parameters on the development of porous structures were also assessed.

A mixture of ferrotitanium, nickel powders and sucrose was heated with an intention of carbonising the sucrose. The tiny ferrotitanium, nickel particles are bound by the carbon obtained from pyrolysis of the sucrose to form a unique structure of Fe–Ti–Ni–C composite powder for reactive thermal spraying. The carbon is a reactive constituent as well as the binder in the composite powder. TiC/Fe–Ni cermet coating was prepared by reactive plasma spraying of this powder. A mass of TiC particles were in situ synthesised and uniformly distributed in the Fe–Ni alloy matrix without residuals of raw materials in the coating. The coating is consisted of two different areas: one is the composite area, where lots of spherical fine TiC particles (100–500 nm) are homogeneously distributed within the Fe–Ni alloy matrix; the other is a small fraction of TiC accumulation. The volume fraction of composite area is >87%.

Present investigation is aimed at developing duplex stainless steels through powder metallurgy route and study the effect of sintering atmospheres on density, mechanical properties and microstructures. Duplex stainless steel composition was prepared from the mixture of 316L and 430L alloyed powders. The powders were mixed in a pot mill for 12 h and compacted at a pressure of 560 MPa. The green compacts were sintered at 1350°C in four different atmospheres such as nitrogen, argon, hydrogen and partial vacuum. Sintered duplex stainless steels were subjected to density measurement, metallography examinations and tensile testing. Duplex stainless steel sintered in partial vacuum showed highest densification of 96% theoretical, tensile strength and ferrite content, when compared with stainless steels sintered in other three atmospheres. Microstructure of stainless steels sintered in argon, hydrogen and partial vacuum showed the bi-phase structure. SEM fractographs of the stainless steels sintered in partial vacuum and hydrogen revealed completely ductile mode of failure.

This work studies a set of low cost beta alloys with the composition Ti–7Fe, processed by conventional powder metallurgy (PM). The materials were prepared by conventional blending of elemental Ti hydride–dehydride powder with three different Fe powder additions: water atomised Fe, Fe carbonyl and master alloy Fe–25Ti. The optimal sintering behaviour and the best mechanical properties were attained with the use of Fe carbonyl powder, which reached a sintered density of up to 93% of the theoretical density, with UTS values of 800 MPa in the ‘as sintered’ condition. Coarse water atomised powder particles promoted reactive sintering, and coarse porosity was found due to the coalescence of Kirkendall porosity and by the pores generated during the exothermic reaction between Ti and Fe. The addition of Fe–25Ti produced brittle materials, as its low purity (91·5%) was found to be unsuitable for formulating Ti alloys.

Highly porous (70%) and large pore sized Ti–Al alloys with low thermal conductivity were successfully fabricated by reactive infiltration of Al in porous Ti preform. The porousTi–Al alloy has a single phase structure of γ-TiAl, and the average pore size is ∼100 μm. The formation mechanism of the porous structure was discussed. The thermal conductivity was determined by the laser flash method, and the effect of porosity on the thermal conductivity was studied. The thermal conductivity of the porous Ti–Al alloy is about 1/3 of the bulk alloy. The results show that the porous Ti–Al alloys have good bending strength.

Amorphous Zr₅₀Al₁₅Ni₁₀Cu₂₅ alloy powders were fabricated by mechanical alloying technique with commercially pure element powders. The effects of small amount of C, Si₃N₄ and SiC powders addition on the thermal stability and crystallisation behaviour of the Zr₅₀Al₁₅Ni₁₀Cu₂₅ amorphous alloy were investigated. The blended powders were compacted into bars by oil hydraulic press, and were sintered in argon atmosphere at different temperatures and pressures. The samples before and after sintering were characterised by X-ray diffraction, scanning electron microscopy, differential scanning calorimetry and electron tensile testing machine. The results demonstrated that a proper addition of Si₃N₄ powders to the amorphous matrix can improve the thermal stability of the matrix. Suitable additives can help to improve the density and mechanical properties of the matrix in sintering process.

In the present work, Distaloy AE powder metallurgy (PM) steel, in as-sintered state are experienced under uniaxial fatigue tests in a range of tensile mean stresses. Microstructural investigations reveal that for tensile mean stress, pores are widened and easily linked up by cracks. Moreover, with obtained fatigue results, well-known fatigue failure criteria, such as Goodman, Gerber and Morrow, are employed to the experimental data. The result shows that the experimental data for Distaloy AE porous sintered steel are well suited to these criteria especially in the case of Morrow and Gerber failure criteria. Furthermore, the alteration of samples length versus cycles shows the cyclic hardening behaviour for this diffusion-bonded PM steel. It seems that this concept is a reason for increasing the fatigue property of diffusion-bonded steels in comparison with other PM Steels.

C_f/SiC was successfully joined to TC4 with Ag–Cu–Ti–SiC mixed powders. Microstructures of the brazed joint were investigated by SEM, EDS and XRD. The mechanical properties of the brazed joints were measured by mechanical testing machine. The results showed that the performed joints have dense bonding layers reinforced by residual SiC and reaction products from reaction of SiC and Ti in the bonding layers. These composite brazing layers relaxed the thermal stress of the joint effectively. These characteristics were beneficial to the joint, of which the shear strengths were remarkably higher than the optimal shear strengths of the joint brazed with Ag–Cu–Ti.

Ternary carbides of titanium and aluminium were prepared via mechanical alloying and following heat treatment. Effects of the starting materials, milling time and heat treating temperature were investigated. In order to study the structural and morphological evolutions of the ball milled and annealed powders, X-ray diffraction (XRD) and scanning electron microscopy (SEM) were used. Results showed that the ball milling of TiO–Al–C as starting materials was unsuccessful for the synthesis of Ti₃AlC₂. On the other hand, ball milling of the elemental powders for shorter milling times led to the activation of powders and after longer milling times, Ti–TiC nanocomposite was obtained. Also, during the annealing of the 6 h milled sample, Ti₃AlC₂–Ti₄Al₂C₂ nanocomposite was synthesised. At the end of milling, a very fine microstructure with narrow size distribution and spheroid particles was procured.

FeAl–TiC nanocomposite was successfully synthesised by the ball milling of Fe, Al, Ti and graphite powder mixture. The structural and morphological evolutions of the powders were studied by X-ray diffraction and scanning electron microscopy respectively. Results show that reactions forming of FeAl and TiC began after 6 h of milling and completed after 12 h of milling. The minimum mean grain size and maximum microstrain values of FeAl were 5·5 nm and 1·8% at the end of milling. Maximum microhardness value of the 12 h milled and annealed powder was 8·75 GPa. Scanning electron microscopy images and particle size measurement showed that very fine spheroid particles (3·4 μm) were prepared at the end of milling.

In this study, a powder mixture was prepared by adding 1–3 wt-% of FeMo, FeTi and Co powders to the austenitic stainless steel powders and samples were produced by the powder metallurgy method. Attempts were made to establish correlations between the microstructure, hardness, toughness, and abrasive wear values of these samples. Wear resistance of the materials was measured by a two body pin-on-disk wear tester. SiC abrasive papers of 65 μm and 177 μm sizes were used as the abrasive media. Wear tests were performed at the loads of 10, 20, and 30 N at room temperature. They showed that the softer, base austenitic stainless steel exhibited higher mass loss than the alloyed samples. Furthermore, the abrasive wear resistance of the base austenitic stainless steel composites increased with increasing FeTi, FeMo,Co content. The wear rate with the 177 μm SiC abrasive paper increased more than that with the 65 μm SiC abrasive paper.

FeAl–Al₂O₃ nanocomposite powder was synthesised under different conditions of milling and annealing. The structure, morphology and microstructure of the milled powders were monitored by the X-ray diffraction (XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM) respectively. Results showed that the formation of FeAl and Al₂O₃ took place in explosive mode during milling with the cup speed of 600 rev min⁻¹. However, at the cup speed of 500 rev min⁻¹, FeAl and Al₂O₃ were synthesised only during annealing. Formation of the FeAl and Al₂O₃ was completed after 120, 270 and 360 min of milling at the ball to powder weight ratios (BPRs) of 5∶1, 15∶1 and 10∶1 respectively. Maximum microhardness of 8·8 GPa was obtained in the 270 min milled sample with the BPR of 15∶1 and cup speed of 600 rev min⁻¹. Mean grain size of 30 nm was calculated in the annealed FeAl that was in consistent with TEM results.

This study elucidates the effects of key injection moulding and sintering factors on the dimensions and mechanical properties of 316L stainless steel metal injection moulded compact. Sintered parts of optimal quality can be produced by properly setting the process parameters. Taguchi method and principal component analysis are performed initially to elucidate and optimise the key control factors that affect the qualities of metal injection moulded compact. Next, a feasible process window is tested by observing the powder and binder distribution of green parts, for various control factors of injection moulding. Experimental findings show that, first, a proper injection speed facilitates mould filling during injection moulding and so improving the quality of sintered parts; second, temperature critically determines the rate of dimensional shrinkage, density and hardness of sintered parts; Third, optimal parameters setting can efficiently improve the quality of 316L metal injection moulded compact.

This work was devoted to the development of NiAl–matrix composite and its production by reactive sintering powder metallurgy. Various types of reinforcement (aluminium oxide, silicon and tungsten carbides, titanium silicide) were tested. The best chemical compatibility and the highest hardness and wear resistance were achieved by Al₂O₃ fibres. Electroless nickel plating pretreatment of Al₂O₃ fibres improves both distribution of fibres and hardness of the composite. However, it strongly reduces the wear resistance, probably due to phosphorus content in the nickel coating. In situ formation of NiAl–Al₂O₃ composites by reactive sintering of a pressed powder mixture of Ni, Al and NiO was unsuccessful. Only a small amount of cubic γ-Al₂O₃ was detected after reactive sintering and hence no significant hardness increase was observed.

Performance improvement that can be achieved by Cu infiltration is quantified in this paper. Tensile and fatigue properties of a Fe–2·0Cu–0·7C powder metallurgy steel were compared to the same alloy infiltrated with 8 wt-%Cu. Microstructural characterisation, using optical and electron microscopies, was carried out to understand the effect of Cu infiltration on mechanical properties. Cu infiltration improves the ultimate tensile strength by 40% by increasing the load bearing structure, decreasing the stress concentrations associated to open porosity and increasing the hardness of the steel matrix. Fractographic observations show the evidence of stress transmission from the sinternecks to the steel particles due to infiltrated Cu. The beneficial effect of Cu infiltration is less pronounced for the fatigue properties as the endurance limit is increased by 10%. This lower improvement is explained by crack initiating at the Cu/steel matrix interface.

Tungsten based composites such as W/Cu have successfully been used in high temperature environments. In order to reduce the weight and improve their erosion resistance, W/ZrC composite has already been developed via displacive compensation of porosity method by Dickerson et al. The aim of this work was to investigate the effect of preform porosity on the composition of final composite. For this purpose, a mixture of tungsten carbide powder and PVA was cold isostatic pressed to make a porous tungsten carbide preform. The porous perform was debinded for 14·4×10³ s at 673 K and sintered for 14·4×10³ s at 1673 K. The sintered perform was then infiltrated by molten Zr₂Cu at 1573 K for 25·2×10³ s. The cross-section of infiltrated specimens was studied using scanning electron microscopy equipped with an energy dispersive spectroscope analyser as well as X-ray diffraction. The results indicated that the amount of tungsten and zirconium carbide phases in final composite increased as the porosity of WC preform increased. The relative density of W/ZrC composite reduced with increasing initial porosity of sintered preform.

In this study, two kinds of Cr and Si powders were mixed ingredients in set proportions (Cr/Si = 50∶50 in weight percentage), and different vacuum sintering temperatures were used to achieve the optimal densification process. The specimens used in this investigation have common microstructures of hardness, XRD, transverse rupture strength and resistivity of the Cr50–Si50 targets. The microstructure shows that the porosity tends to decrease as sintering temperature increases. Conversely, hardness and transverse rupture strength increase as sintering temperature increases. These results agree with the variation in porosity. Additionally, the resistivity tends to decrease with increasing sintering temperature. It should be correlated with the microstructure of Cr50–Si50 targets, increasing the density of CrSi₂ could significantly decrease the resistance. Meanwhile, the resistivity decreases and conductivity increases as the neighbours are closer together, which also results from the decreasing porosity.

The effect of austenitisation temperature on austenite transformations on 0·7%C Astaloy CrL steel was studied by dilatometry. The steel has a good hardenability, forming martensite at most of the austenitisation temperatures and cooling rates investigated. Only on cooling from 1073 K, austenite transforms into bainite completely at 3 K s⁻¹ and partially at 12·5 K s⁻¹. The effect of austenitisation temperature on the prior austenitic grain size is quite poor because of the pinning effect of pores. The martensite start temperature M_s increases slightly with the austenitisation temperature up to 1173 K and decreases at 1523 K. This trend is due to the presence of nanometric carbides (Cr₂₃C₆), which were detected at TEM. They dissolve almost completely in austenite at 1523 K only, increasing the stability of austenite against the martensitic transformation. The effect of temperature in the range from 1073 K up to 1523 K is poor. As a consequence, the microstructural characteristics of hardened steels are very similar.

Powder materials are widely used in journal bearings since they provide a good tribological performance with journal bearings. These bearings are self-lubricated and can be used in places where no lubricating is possible. In this study, tribological and mechanical properties of copper based CuSn10, ferrous based Fe–graphite and copper+ferrous based CuSnFe–graphite bearings manufactured by powder metallurgy method have been determined and compared. Wear tests were carried out at 20 N load and 1500 rev min⁻¹ every 30 min for 2·5 h using radial journal bearing wear test rig. Hardness, tensile, compressive, bending and radial fracture mechanical tests of these bearing materials were carried out. As a result, tribological and mechanical properties improved in CuSnFe–C bearings.

A process based on powder metallurgy approach was developed to produce open celled aluminium foam. In the preparation of foam specimens, the Al powder and the NaCl (leaching agent) were dry mixed together in order to prepare a homogeneous mixture. The blended mixture was then subjected to pressure assisted sintering in which a pressure beyond atmospheric level is externally applied to the specimen during high frequency induction heated sintering. The embedded leaching agent was then dissolved in order to leave behind an open celled Al with the same chemical composition as that of the original Al powder. The final material is highly porous and has an interconnected porosity network. The structure of the resulting material has three levels of porosity (i.e. main cells, windows and microporosity). The X-ray diffraction analysis shows that, as the content of NaCl is increased to the volume fraction of 60%, no traces of NaCl presents in the foam.

Complex aluminium alloy components fabricated by powder metallurgy (P/M) offer the promise of a low cost and high strength-to-weight ratio, which meets the demands of the automotive sector. This paper describes the die compaction and sintering response of an atomised Al-6061 alloy powder containing Mg and Si produced by rapid solidification. A design of experiments is used involving three levels for each of the die compaction pressure, sintering temperature, peak temperature hold time and heating rate. Three trials were used to obtain the optimum press sinter processing conditions. Besides the mechanical properties, phase transformation and microstructure are investigated. Supplemental insight is gained through thermogravimetric analysis, differential scanning calorimetry and SEM with energy dispersive spectroscopy. Analysis of variation is used to quantify the contribution of each design variable to the mechanical properties.

This study aims to compare the effect of Al₂O₃ nanoparticle additions on the densification and mechanical properties of the injection moulded 316L stainless steels. The 316L stainless steel and Al₂O₃ nanoparticles were dry mixed and moulded using a wax based binder. The critical powder loading for injection moulding were 60 vol.-% for all samples. Debinding process was performed in solvent using thermal method. After the debinding process, the samples were sintered at 1405°C for 60 and 120 min under vacuum. Metallographic examination was conducted to determine the extend of densification and the corresponding microstructural changes. The sintered samples were characterised by measuring tensile strength, hardness and wear behaviour. Wear loss was determined for all the samples after wear testing. All the powders, fracture surfaces of moulded and sintered samples were examined using scanning electron microscope. The sintered density of straight as well as Al₂O₃ nanoparticles reinforced injection moulded 316L stainless steels increases with the increase in sintering time. The additions of Al₂O₃ nanoparticles improve the hardness and wear resistance with the increase of sintering time.

The growing field of aluminium powder metallurgy (PM) brings promise to an economical and environmental demand for the production of high strength, light weight aluminium engine components. In an effort to further enhance the mechanical properties of these alloys, the effects of hot upset forging sintered compacts were studied. This article details findings on the hot compression response of these alloys, modelling of this flow behaviour, and its effects on final density and microstructure. Two aluminium–silicon based PM alloys were used for comparison. One alloy was a hypereutectic blend known as Alumix-231 (Al–15Si–2·5Cu–0·5Mg) and the second was an experimental hypoeutectic system (Al–6Si–4·5Cu–0·5Mg). Using a Gleeble 1500D thermomechanical simulator, sintered cylinders of the alloys were upset forged at various temperatures and strain rates, and the resulting stress–strain trends were studied. The constitutive equations of hot deformation were used to model peak flow stresses for each alloy when forged between 360 and 480°C, using strain rates of 0·005–5·0 s⁻¹. Both alloys benefited from hot deformation within the ranges studied. The experimental alloy achieved an average density of 99·6% (±0·2%) while the commercial alloy achieved 98·3% (±0·6%) of its theoretical density. It was found that the experimentally obtained peak flow stresses for each material studied could be very closely approximated using the semi-empirical Zener–Hollomon models.

Metal powder slurries were prepared by adding 316L stainless steel powder to a methylcellulose solution. The highly viscous solution, in combination with high particle loadings, hindered powder sedimentation. The efficacy of a dispersant to produce low viscosity slurry was assessed by measuring the torque required to stir the suspension, compared to that needed to stir the base solution under the same conditions. These measurements were in reasonable agreement with data from viscometry, indicating a dispersant addition of 1·5 wt-% (based on the mass of the powder added) was sufficient to reduce the viscosity to that for the base cellulose solution. Slurries containing 45 vol.-% of 316L powder in a 2 wt-% methylcellulose solution, to which a minimum of 1·5 wt-% dispersant had been added, had a viscosity of roughly 0·5 Pa s and is deemed suitable for the production of metal foams via dipping or by mechanical whisking methods.

The aim of this work was to study the structure and particle size of copper based composite materials reinforced with a high content (15–35 wt-%) of silicon carbide and prepared by mechanical alloying in the high energy planetary mill. Raw materials consisted of grinded copper chips with a size of <5000 μm and reinforcing particles with an initial size of 10 μm. Duration of milling was 20–80 min. It was shown that the formation of Cu–(15–25 wt-%)SiC composites occurred successfully. With an increase in the silicon carbide content of above 25 wt-% (48 vol.-%), the efficiency of mechanical alloying was decreased. The average size of composite particles was ∼20 μm.

Al foams were produced by applying a powder metallurgy route. Foam expansion, cell structures and foam stability of foamed samples were investigated. The results show that larger expansion and more homogeneous cell structures were achieved due to the presence of 1·0 wt-%Mg addition. Mg addition results in the formation of spinel particles through the reaction between Mg powder and alumina on Al powder. Spinel particles show good wetting with Al melt and are fully embedded into Plateau borders and cell walls. The liquid is tightly trapped within cell walls and Plateau borders in the presence of spinel particles, preventing cell walls from thinning further and improving foam stability significantly.

The excellent properties of Ti have resulted in its generalised use for bone implants. However, Ti is very stiff in comparison with human cortical bone, and this creates problems of bone weakening and loosening of the implant. This article discusses the mechanical properties (flexural and compressive strength, and stiffness) of porous Ti–6Al–4V specimens developed using the space holder method. These properties are examined relative to the production process parameters: compacting pressure and sintering time, as well as temperature, and the addition of spacer and its particle size. It is seen that when spacer is added, compressive strength decreases with the application of compacting pressure and that these are the most influential parameters. The developed pieces show a closed and unconnected porosity. Small additions of spacer (25 vol.-%) reduce stiffness to around half of that shown by the solid material, and the resulting pieces are strong enough to be used as bone substitute.

New type of water jet cooled rotating disc atomisation unit was designed and constructed. The raw material was melted in graphite crucible with high frequency induction heating, and atomisation was performed in high purity argon gas atmosphere. Cu–10Sn alloy was atomised to investigate the effect of production parameters, such as disc speed, disc surface condition, liquid metal flowrate, disc fin number and superheat of liquid metal with respect to mean particle size and powder yield rate. The produced powders appeared spherical, rounded, ligamentous, irregular and flaky, depending on particle size. The mean particle size of produced powders was in the range of 100–250 μm with 65–85% powder yield rate depending of atomisation parameters. The ZrO₂ material coated disc with four fins gave the finer mean particle size and higher powder yield rate in comparison with uncoated disc with two fins.

In this work, combustion synthesis of ferrotitanium–Al–C powder mixtures with different compositions was carried out to synthesise Fe–Al/TiC composites. Differential thermal analysis was performed on the precursor powder from ambient temperature to 1673 K at a heating rate of 30 K min⁻¹. Phase development and structural changes were investigated by X-ray diffraction technique and scanning electron microscopy. The results showed that no trace of TiAl_x (x = 1, 3) was formed in all samples, and the reaction of (Ti–Fe)–Al–C system took place in the following two steps: first, molten Al and Fe reacted exothermically to form Fe–Al intermetallic compound. Second, the produced heat melted the ferrotitanium with lower Fe content and resulted in a liquid containing Ti, Fe, Al and C. TiC formed in all samples, but depending on the Al content, different phases containing FeAl₂, FeAl, Fe₃Al, Fe₃AlC_x and α-Fe formed as phases of matrix. The mixture with the lower Al content gave out a higher combustion temperature.

The criterion to control self-propagation high temperature synthesis for the fabrication of porous Ti–Al intermetallics was established from the prereaction model and the thermal balance condition. The criterion equation reflecting the relation between the solid reaction layer thickness correlation parameter and the ignition temperature was deduced to be p³ = C₁/(T_ad−T₀)+C₂, according to which the near net shaping synthesis of porous Ti–Al intermetallics was realised, which was significantly important for the industrial productions and applications of this high performance novel porous material. The slight difference between theoretical predictions and experimental data was analysed according to the model analysis.

The aims of this work were to produce nanocrystalline powder by mechanical alloying of FeTi₂–Al–C powder mixture in a high energy ball mill and to study the phase transformation that took place during 20 h milling time. The microstructure and the phase transformations in the powder during milling were examined as a function of milling time and heat treatment. The phases of the product were evaluated by X-ray diffraction technique. The microstructural evolution during mechanical alloying was analysed using SEM. The results obtained showed that high energy ball milling, as performed in this work, led to the formation of a bcc phase identified as Fe(Al) solid solution and TiC_x after 2 h milling and nanocrytalline AlFe₃ and TiC_x after 5 h milling. The increase in the milling time resulted in the formation of AlFe₃C_x. By heat treatment of the body after 20 h milling at 1000°C, AlFe3C_x disappeared, showing that this phase is unstable.

Using a combination of mixed elemental powders and TiB₂, a series of Ti–Ni and Ti–Ni–B alloys were optimised for sintering by varying the nickel and boron contents, the particle size of the elemental powders and the compaction pressure. The sintering temperature was maintained at 1200°C to limit the costs of a potential commercial sintering operation. For Ti–Ni alloys, a density of 99% was attained in Ti–7Ni made using fine Ti and Ni powders sintered in the solid state, and from liquid phase sintering of Ti–8Ni made using coarser powders. Porosity was almost eliminated from Ti–7Ni–xB alloys made by adding 1–3%TiB₂ to the coarser Ti and Ni powders. The action of TiB₂ as a sintering aid is possibly owing to a combination of the formation of a small amount of liquid at the sintering temperature and the restriction of grain growth owing to the presence of TiB particles.

Powder injection moulding is a maturing technology that has proven most useful for the production of complex metallic and ceramic components of modest sizes. Considering the inevitable demand for cost effectiveness in automotive applications, components manufactured from low cost sponge titanium (Ti) powder currently reflect the most advantageous economics among the available Ti powders. This paper describes the net shape fabrication of Ti components and considers the role of iron and zirconium powder additions. Sintering cycle optimisation relied on differential scanning calorimetry to identify a cycle in the 1275–1300°C range for 1–2 h. The sintered material was characterised using tensile and hardness testing and microscopic examinations. The influence of test conditions on densification, microstructure and mechanical properties was analysed.

This paper describes the microstructural and mechanical properties of injection moulded aluminium powder. Gas atomised aluminium powder was injection moulded with wax based binder. The critical powder loading for injection moulding was 62·5 vol.-% for feedstock. Binder debinding was performed in solvent and thermal method. After debinding, the samples were sintered at different temperatures and times in high purity N₂. Metallographic studies were conducted to determine the extent of densification and the corresponding microstructural changes. The results show that gas atomised aluminium powder could be sintered to a maximum 96·2% of theoretical density. Maximum density, tensile strength and hardness were obtained when sintered at 650°C for 60 min.

Powder metallurgy allows for the rapid, automated and efficient production of many different types of automotive components. However, a drawback is the limited selection of readily available light alloy blends. Owing to the wide spread use of aluminium–silicon casting alloys for existing components it is logical to develop aluminium–silicon PM options. Therefore, an experimental hypoeutectic aluminium–silicon alloy was chosen for study and an optimum processing route developed. Tests were performed to determine the green strength and density as a function of compaction pressure. Sintering conditions were optimised based on sintered density, hardness and dimensional changes. Metallography, differential scanning calorimetry and energy dispersive X-ray spectroscopy analysis provided insight into post-sinter furnace cooling and heat treatment parameters. An appropriate T6 heat treatment was developed and samples were tested in tension. The alloy was able to achieve a high sintered density approaching 98% and a yield strength of 232 MPa under the T6 condition.

Effects of the milling time, annealing temperature and vial rotation speed were investigated on the formation of MoSi₂–CrSi₂ nanocomposite powder. X-ray diffraction was used to characterise the milled and annealed powders. The morphological and microstructural evolutions were studied by scanning electron microscopy and transmission electron microscopy. Results showed that this composite formed after 20 h of milling with mechanically induced self-sustaining reaction mechanism at the cup speed of 640 rev min⁻¹. On the other hand, this composite was partially synthesised after 50 h of milling with the gradual mode at the cup speed of 540 rev min⁻¹. Low temperature polymorph of MoSi₂ and CrSi₂ were obtained after annealing at 1000°C at both speeds. The mean grain size <25 nm was procured for MoSi₂–CrSi₂ composite at both speeds on the basis of peak profile analysis and transmission electron microscopy. This composite maintained its nanocrystalline nature after annealing.

In the present study, crystallisation behaviours of the Al₈₀Fe₁₀Ti₁₀ amorphous phase (prepared by mechanical alloying) has been investigated using X-ray diffraction and differential thermal analysis techniques. It was found that Al₈₀Fe₁₀Ti₁₀ amorphous phase exhibits one-stage crystallisation on heating [amorphous to Al₁₃Fe₄, Al(Fe,Ti) and Al₅Fe₂ intermetallic phases]. The activation energies for crystallisation of Al₈₀Fe₁₀Ti₁₀ amorphous phase were determined as 326, 322, 351 and 301 kJ mol⁻¹ by means of the Kissinger–Akahira–Sunose, Flynn–Wall–Ozawa, Friedman and Afify equations respectively. Kinetic parameters such as Avarmi exponent or reaction order n and frequency factor K_o were also discussed. The reaction orders obtained for the crystallisation was ∼2·03, suggesting that a diffusion controlled crystallisation process with a decreasing nucleation rate was the crystallisation mechanism. The deduced K_o value for crystallisation peak was calculated to be 6·75×10¹⁰ s⁻¹.

A multilayer back propagation learning algorithm was used as an artificial neural network tool to predict the mechanical properties of porous NiTi shape memory alloys fabricated by press/sintering of the mixed powders. Effects of green porosity, sintering time and the ratio of the average Ti to Ni particle sizes on properties of the product were investigated. Hardness and tensile strength of the compacts were determined by hardness Rockwell B method and shear punch test. Three-fourths of 36 pairs of experimental data were used for training the network within the toolbox of the MATLAB software. Porosity, sintering time and particle size ratios were defined as the input variables of the model. Ultimate strength and hardness were the outputs of the model. Results indicated that seven neurons in the hidden layer yielded the minimum normal error. The modelling outcomes confirmed the feasibility of the model and its good correlation with the experimental information.

Many industrial applications, e.g. processing of polymers, suffer from high costs caused by corrosion and wear. Particularly the combination of both increases the requirements for the materials used. Corrosion resistant cold work steels were developed to withstand the combined attack. Resistance is achieved by a sufficient content of chromium in the metal matrix and by carbides dispersed in a martensitic matrix. A further gain in wear resistance is possible by adding hard phases to the steel to produce a particulate reinforced metal matrix composite (MMC). The common consolidation process for such MMCs is hot isostatic pressing, but they can also be processed by solid state or liquid phase sintering. This work focuses on detailed investigations of the properties in dependence on the processing route. The results show that the resulting corrosion and wear resistance depend not only on the processing method, but also on the incorporated hard phases in combination with the manufacturing method. In addition, the unreinforced metal matrices were compared to the MMC.