Showing papers in "Powder Metallurgy in 2011"
TL;DR: In this paper, the sources of interstitial contamination when processing titanium powders by compaction, isostatic pressing, powder injection molding (PIM), and innovative foaming processes are reviewed, focusing specifically on oxygen.
Abstract: 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.
83 citations
TL;DR: In this paper, a set of low cost beta alloys with the composition Ti-7Fe, processed by conventional powder metallurgy (PM), 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.
Abstract: 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.
65 citations
TL;DR: In this paper, the characteristics of the powders, sintering behavior and final properties of the parts indicate that the master alloy approach leads to better compressibility than the prealloyed powders and, therefore, to lower dimensional change during sinter.
Abstract: The use and development of titanium and titanium alloys have been strongly correlated to high technology industries where costs are not the most important aspect. Titanium could see its market grow by the application of lower cost and more efficient processing methods such as powder metallurgy. This work deals with the characterisation of two types of powders: commercial prealloyed powder and powder produced from master alloy combining mechanical milling and conventional blending to adjust the particle size. The characteristics of the powders, sintering behaviour and final properties of the parts indicate that the master alloy approach leads to better compressibility than the prealloyed powders and, therefore, to lower dimensional change during sintering. The most important result is that it is possible to obtain Ti alloys with properties similar to or better than alloys from prealloyed powders and to obtain homogeneous microstructures, which allows the composition to be adjusted to requirements.
37 citations
TL;DR: In this paper, the authors describe the properties of titanium powders produced via the hydride-dehydride process with reference to the markets that they serve, based on more than 20 years of operating experience at Reading Alloys.
Abstract: 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.
34 citations
TL;DR: In this article, the authors analyzed the influence of process parameters (compaction pressure, metal grain size range and spacer volume) on porosity morphology and distribution and bending strength.
Abstract: Porous titanium specimens have been produced by means of the space holder method. Titanium grade 3 (TiCP3) has been used as material and ammonium bicarbonate as spacer. Process parameters (compaction pressure, metal grain size range and spacer volume) influence on porosity morphology and distribution and bending strength has been analysed. The results denote an important loss of strength when comparing samples sintered without and with spacer. On the other hand, a higher bending strength was observed in the porous samples with a smaller size of ammonium bicarbonate particles. Finally, the evolution of bending strength with the compaction pressure depends on the spacer volume, having a direct dependency for reduced amounts and inverse for higher contents.
31 citations
TL;DR: In this article, commercial V-4 tool steel powders were classified by sifting, which was previously the matrix, and fine TiC powder was used as an additive to produce a new material with high hardness and wear resistance, via powder metallurgy and a sintering process.
Abstract: In this study, commercial VANADIS 4 (V-4) tool steel powders were classified by sifting, which was previously the matrix, and fine TiC powder was used as an additive to produce a new material with high hardness and wear resistance, via powder metallurgy and a sintering process. Experimental results showed that the transverse rupture strength of the original V-4 steel powder was 678·5 MPa and was enhanced to 868·6 MPa below 25 μm, after the addition of 35 wt-%TiC powders through sintering at 1400°C. In addition, the hardness increased to 86·2 HRA, transverse rupture strength reached 1059·3 MPa and porosity decreased to 1·2% of the V-4 steel powders (below 25 μm) added with 35 wt-%TiC after sintered at 1400°C and annealed at 850°C, followed by quenching at 1030°C and tempering at 200°C.
25 citations
TL;DR: In this paper, a modified Heckel equation was used to study the compressibility of a nanostructured Al-5AlN composite powder synthesized via high energy ball milling for various times.
Abstract: Compressibility of a nanostructured Al–5AlN composite powder synthesised via high energy ball milling for various times was studied by means of a modified Heckel equation. Since workhardening and morphological changes take place by milling evolution, the compressibility was consequently affected. Strengthening of composite compacts was influenced by milling and compaction processes, i.e. strength of compacts increased at longer milling times and higher compaction pressures. It was found that, at the initial stages of milling and higher compaction pressures, the strengthening was mostly affected from compaction process, whereas the milling strengthening fraction was near to unity at lower compaction pressures as well as prolonged milling. Nevertheless, a sharp increase in milling strengthening fraction of unreinforced Al occurred at intermediate milling times. The rate of strengthening induced by milling raised at higher compaction pressures.
21 citations
TL;DR: In this paper, the development of NiAl-matrix composite and its production by reactive sintering powder metallurgy was devoted to the development and production by NiAl−Al2O3 composites, and various types of reinforcement (aluminium oxide, silicon and tungsten carbides, titanium silicide) were tested.
Abstract: 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.
19 citations
TL;DR: In this article, the die compaction and sintering response of an atomised Al-6061 alloy powder containing Mg and Si produced by rapid solidification is described.
Abstract: 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.
19 citations
TL;DR: In this article, the microstructure and phase transformations in the powder during milling were examined as a function of milling time and heat treatment, and the phases of the product were evaluated by X-ray diffraction technique.
Abstract: 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 TiCx after 2 h milling and nanocrytalline AlFe3 and TiCx after 5 h milling. The increase in the milling time resulted in the formation of AlFe3Cx. By heat treatment of the body after 20 h milling at 1000°C, AlFe3Cx disappeared, showing that this phase is unstable.
18 citations
TL;DR: In this paper, the role of iron and zirconium powder additions in the fabrication of powder-in-moulded composite components was discussed. But the role and performance of the powder injection molding process was not investigated.
Abstract: 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
TL;DR: In this paper, a microstructure characterisation of cast, extruded and micrometre sized particles was conducted for various alloy compositions and the effects of electrode rotation speed on the particle size distribution, particle shape and crystal structure were investigated.
Abstract: A microstructure characterisation of Ti–6Al–4V is conducted for cast, extruded and micrometre sized particles. The plasma rotating electrode process is used to produce spherical Ti–6Al–4V powders from an alloy electrode. The process parameters and their impact on the material properties are described. The effects of electrode rotation speed on the particle size distribution, particle shape and crystal structure are investigated in detail. Optical microscopy and scanning electron microscopy are used for microstructural characterisation. The analysis shows that cast and extruded Ti–6Al–4V alloys have equiaxial α and α+β phase structures, while plasma rotating electrode processed powder from the same alloy compositions has an acicular or martensitic (α) structure. The microstructure scale depends on the particle size. Microhardness measurements are used to assess mechanical property dependence on the microstructure of this alloy. The rapidly cooled alloy particles have much higher hardness than cast ...
TL;DR: In this article, the current status of the technology is surveyed including aspects of the associated market trends and commercial feasibility, and the focus is now shifting to seeking industrial engagement with a view to collaboration, technology transfer and commercialisation of the technologies.
Abstract: 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
TL;DR: In this paper, a detailed investigation of the properties in dependence on the processing route is performed, and the results show that the resulting corrosion and wear resistance depend not only on the processed method, but also on the incorporated hard phases in combination with the manufacturing method.
Abstract: 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, ...
TL;DR: Aluminium (Al) silicon alloy fly ash composites were developed using powder metallurgy technique as mentioned in this paper, and various properties of the Al alloy fly-ash composites are studied and compared with that of base alloy.
Abstract: Aluminium (Al) silicon alloy fly ash composites were developed using powder metallurgy technique. Aluminium silicon alloy powder was homogenously mixed with various weight percentages of fly ash (5–15%) and uniaxially cold pressed at pressures ranging between 200 and 515 MPa, and the green specimens were sintered at temperatures between 575 and 625°C. The various properties of the Al alloy fly ash composites were studied and compared with that of base alloy. The density of Al alloy fly ash composites was lower than that of the base alloy. The sintered density of the Al alloy fly ash composites and Al alloy slightly decreased when compared to green density. The hardness of the Al alloy fly ash composites was higher than that of base alloy and it increased with the increase in weight percentage of fly ash content upto 12 wt-%. Compressive strength of the composites was lower than that of base alloy and it decreased with increasing weight percentage of fly ash. The electrical resistivity and corrosio...
TL;DR: In this article, the dependence of microstructure of in situ titanium aluminide and silicide composites on chemical composition and conditions of reactive sintering was studied, and it was found that the rate of reaction time increases with growing silicon content.
Abstract: In this work, the dependence of microstructure of in situ titanium aluminide and silicide composites on chemical composition and conditions of reactive sintering was studied. It was found that the rate of reactive sintering process increases with growing silicon content. In addition, heating rate strongly affects the structure of Ti–Al–Si alloys with lower content of silicon represented by TiAl23Si10 alloy. The structure consisting of homogeneously distributed Ti5Si3 particles in TiAl matrix can be obtained by rapid heating over 250 K min−1 in this material. TiAl15Si15 alloy forms the desired two phase TiAl–Ti5Si3 structure when a heating rate of at least 10 K min−1 and temperature over 750°C are applied. Replacement of aluminium and silicon powders by Al–Si alloy positively affects the reactive sintering process. The structure of these materials can be refined by milling of Al–Si master alloy powder to the <100 μm fraction, reducing the size of Ti5Si3 particles and porosity significantly.
TL;DR: In this paper, a 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.
Abstract: 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/(Tad−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.
TL;DR: In this paper, the effects of hot upset forging sintered compacts were studied and the constitutive equations of hot deformation were used to model peak flow stresses for each alloy.
Abstract: 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 wh...
TL;DR: In this paper, a brazed CF/SiC was successfully joined to TC4 with Ag-Cu-Ti-SiC mixed powders and the results showed that the performed joints have dense bonding layers reinforced by residual SiC and reaction products from reaction of SiC in the bonding layers.
Abstract: Cf/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.
TL;DR: In this article, the effect of nickel-rich areas (NRAs) on powder metal steel parts was investigated using X-ray energy dispersive spectrometry and electron diffraction.
Abstract: Nickel is an often used alloying element in powder metal steel to achieve high hardenability. However, when nickel is added, the slow diffusion rate between iron and nickel leads to the formation of nickel rich areas (NRAs). Two steel alloys were studied: a Fe–6·4Ni–0·7Mo–0·7C with standard sized nickel powder additions and a Fe–2·4Ni–0·7Mo–0·7C with a finer sized nickel powder. Microstructural characterisation of the parts revealed that sufficient hardenability was achieved for both materials, but that NRAs were observed when standard sized nickel is used. X-ray energy dispersive spectrometry and electron diffraction show that the NRAs are composed of martensite and austenite under rapid cooling conditions. Three-point bending fatigue tests were carried out on both alloys to evaluate the effect of these soft austenitic areas on the fatigue properties of powder metal steel parts. The analysis of the endurance limit results shows that NRAs are not a governing factor.
TL;DR: In this article, the authors examined the mechanical properties of porous Ti-6Al-4V specimens developed using the space holder method and found that when spacer is added, compressive strength decreases with the application of compacting pressure and that these are the most influential parameters.
Abstract: 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.
TL;DR: In this paper, two approaches were used to obtain Al-20TiB2 (wt-%) nanocomposite powder in situ using mechanical alloying (MA) using X-ray diffractometry and scanning electron microscopy (SEM).
Abstract: Production of in situ Al–TiB2 nanocomposite powder was studied using mechanical alloying (MA). Two approaches were used to obtain Al–20TiB2 (wt-%) nanocomposite powder. In the first approach the synthesis of Al–20TiB2 (wt-%) was investigated by ball milling an elemental Al–Ti–B powder mixture. The second approach involved a double step milling procedure to achieve an Al–20TiB2 (wt-%) composite powder. The microstructure of as milled powder particles was investigated by X-ray diffractometry (XRD) and scanning electron microscopy (SEM). The thermal behaviour of MA powders was studied by differential scanning calorimetry (DSC). From these studies it was possible to conclude that TiB2 can be formed in situ using the second approach without the production of undesirable phases; however, the first approach tends to form an undesirable Al3Ti intermetallic phase in addition to the TiB2 ceramic reinforcement.
TL;DR: In this article, the effect of the processing conditions on the reduction and distribution of the grain sizes and the internal strains level were studied by means of scanning and transmission electron microscopy and X-ray diffraction analysis.
Abstract: 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.
TL;DR: In this article, the effect of sintering atmospheres on density, mechanical properties and microstructures of duplex stainless steels was investigated. And the results showed that duplex steels sintered in partial vacuum showed the highest densification of 96% theoretical, tensile strength and ferrite content.
Abstract: 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 pa...
TL;DR: In this paper, the authors used thermodynamic models to predict liquid phase amounts for Fe −0·85Mo −(0·4−0·6)Si −(1·2−1·4)C in the temperature range of 1285−1300°C and such powder mixes were pressed and liquid phase sintered.
Abstract: Thermo-Calc modelling was employed to predict liquid phase amounts for Fe–0·85Mo–(0·4–0·6)Si–(1·2–1·4)C in the temperature range of 1285–1300°C and such powder mixes were pressed and liquid phase sintered. In high C steels, carbide networks form at the prior particle boundaries, leading to brittleness, unless the steel is heat treated. To assist the break-up of these continuous carbide networks, 0·4–0·6% silicon, in the form of silicon carbide, was added. After solution of processing problems associated with the formation of CO gas in the early part of the sintering cycle, and hence large porosity, densities in excess of 7·75 g cc−1 were attained. A spheroidising treatment resulted in microstructures having the potential of producing components, which are both tough and suitable for sizing to improve dimensional tolerance. Yield strengths up to 410 MPa, fracture strengths up to 950 MPa and strains up to 16% were attained.
TL;DR: In this paper, a nanostructural solid solution of Cu-Cr was prepared by the mechanical alloying process and the mixtures were subsequently compacted and sintered at 450, 600 and 750°C for half an hour.
Abstract: A nanostructural solid solution of Cu–Cr was prepared by the mechanical alloying process. Three mixtures of Cu powders with 1, 3 and 6 wt-%Cr powders were milled under 250 rev min−1 for different milling times of 4, 12, 48 and 96 h. The mixtures were subsequently compacted and sintered at 450, 600 and 750°C for half an hour. Milled powder mixtures were examined by X-ray diffraction technique, which showed the presence of nanoscale crystallites in the samples and the decrease of lattice parameter of Cu crystals. Sintered powders were investigated by optical microscope and their hardnesses were measured by microhardness. Results showed increasing trends in hardness of the compacted powder mixtures with increasing milling time. Sintering temperature had also evident effects on the behaviour of powder mixtures. As sintering temperature increased, microhardness increased and a peak appeared then a decreasing trend was observed.
TL;DR: In this article, combustion synthesis of ferrotitanium-Al-C powder mixtures with different compositions was carried out to synthesise Fe-Al/TiC composites, and the phase development and structural changes were investigated by X-ray diffraction technique and scanning electron microscopy.
Abstract: 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 TiAlx (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, Fe3AlCx and α-Fe formed as phases of matrix. The mixture with the lower Al content gave out a higher combustion temperature.
TL;DR: In this article, the effect of Al2O3 nanoparticle additions on the densification and mechanical properties of the injection moulded 316L stainless steels was compared. And the sintered samples were characterised by measuring tensile strength, hardness and wear behaviour.
Abstract: 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 mou...
TL;DR: In this paper, the selective laser melting of a metallic/inorganic blended powder system consisting of 316L stainless steel powder and NH4HCO3 powder was performed, and the formation of a honeycomb-like porous structure possessing unusually micrometre scaled pores (∼2 to ∼5 μm).
Abstract: 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.
TL;DR: In this article, a powder metallurgy route consisting of preparing powder preforms from premixed Cu, Al and Ni powders by cold compaction, stepwise sintering in the range 873-1273 K, followed by unsheathed multipass hot rolling at 1273 K in a protective atmosphere.
Abstract: Cu–Al–Ni shape memory alloy strips were successfully prepared by a powder metallurgy route consisting of preparing powder preforms from premixed Cu, Al and Ni powders by cold compaction, stepwise sintering in the range 873–1273 K, followed by unsheathed multipass hot rolling at 1273 K in protective atmosphere. The densification behaviour of the sintered powder preforms during hot rolling has been discussed. Homogenisation of the hot rolled strips was carried out at 1173 K for 4 h. It has been shown that the finished Cu–Al–Ni alloy strip consisted of self-accommodated plates ofβ' and γ' martensites together with a small amount of nanocrystalline Cu9Al4 phase. The finished hot rolled Cu–Al–Ni strips had fracture strength of 476 MPa, coupled with 2·5% elongation. The shape memory tests showed almost 100% recovery after 10 thermomechanical cycles in the hot rolled strips at 1 and 2% applied prestrain.