Showing papers in "Powder Metallurgy in 2015"
TL;DR: In this paper, the authors explored the process window for selecting electron beam melting (EBM) for Ti-6Al-4V with varying beam current and scan speed in a wide range and characterized the EBM specimens by their density, porosity size, chemical composition, microstructure, hardness and tensile strength.
Abstract: Selective electron beam melting (EBM) is a powder-bed based additive manufacturing technique for the fabrication of dense metallic parts. As a free-form deposition process EBM offers a high degree of freedom in design and a highly efficient utilization of material. For a widespread industrial application the achievable build rate is a critical factor. In this paper the process window for Ti-6Al-4V is explored by varying beam current and scan speed in a wide range. The EBM specimens were characterized by their density, porosity size and distribution, chemical composition, microstructure, hardness and tensile strength. Key findings include: (1) the minimum line energy necessary to achieve full density, (2) parameter sets for increased build rates at full density, and (3) formation of α'-martensite at high scan rates.
54 citations
TL;DR: In this paper, the PM-SLM material was mechanically tested in the as SLM state as well as in the SLM+HIP state and it was found that the mechanical properties of the PM material did not reach the level of the fatigue strength of as cast matrices.
Abstract: The Co-based alloy ASTM (Co – 28.5 wt.-% Cr – 6.3 wt.-% Mo) is widely used for medical implants, e.g. knee prostheses, and is commonly processed by investment casting. Selective laser (SLM) melting is supposed to be an efficient alternative for the production of individually designed knee implants regarding production time and production costs. The mechanical properties, in particular the fatigue strength, of the material have been studied in different states of the material. The mechanical properties of investment casted ASTM F75 and PM-SLM produced ASTM F75 were investigated. The focus in this study was on the PM-SLM material, the specimens were initially produced by selective laser melting and a part of the specimens were further processed by hot isostatic pressing (HIP). The PM-SLM material was mechanically tested in the as-SLM state as well as in the SLM+HIP state. It was found that the mechanical properties of the as-SLM material did not reach the level of the fatigue strength of as cast mat...
38 citations
TL;DR: In this article, the effect of process variables on liquid phase sintering of prealloyed brass powder was evaluated using response surface methodology based on central composite rotatable design.
Abstract: The present study focuses on modelling, optimisation and experimental investigation into properties and microstructure of supersolidus liquid phase sintered Cu–28Zn brass from prealloyed powder. The experiments are designed using response surface methodology based on central composite rotatable design to evaluate the effect of process variables on liquid phase sintering of prealloyed brass powder. Three variables namely temperature, time and atmosphere were changed during sintering. The mathematical equations were derived to predict densification and impact energy using second order regression analysis. The optimum condition was predicted when the sintering variables were set at about 876uC, 43 min and N2 atmosphere. Selecting optimum sintering parameters is an important factor for achieving improved properties and relatively homogeneous microstructure. Gravitational force has a detrimental influence on homogeneity which is reflected by a graded structure that is formed especially at higher sintering temperature and extended time. Also structural coarsening occurs at higher sintering temperatures and longer times. It is concluded that both gravitational effect and structural coarsening should be considered in manufacturing of Cu–28Zn alloy parts. Furthermore, a combination of modelling and experimental investigation provide a new concept for better understanding and analysing the sintering process of brass and related structures.
32 citations
TL;DR: In this article, the hardness and bend strength of diamond tool matrix materials prepared from partially pre-alloyed Fe-Cu powders and from elemental powder mixes of equivalent composition has been compared.
Abstract: The hardness and bend strength of diamond tool matrix materials prepared from partially pre-alloyed Fe–Cu powders and from elemental powder mixes of equivalent composition has been compared. After sintering at 890oC, the hardness of the partially pre-alloyed powder matrix was 81.72 HRB, 9.3% higher than that of the mixed powders matrix; sintering at 870oC gave the highest bend strength (634.85 MPa), 11.6% higher than that of the mixed powders matrix. The improved homogeneity of alloy elements distribution achieved in the matrix by pre-alloying was shown generally to increase the hardness and strength. The cutting performance of diamond tool segments prepared with the pre-alloyed matrix material met standard requirements; overall, the pre-alloyed material is felt to offer significant manufacturing and performance benefits.
31 citations
TL;DR: In this article, the microwave assisted bidirectional rapid sintering technique followed by hot extrusion was used to synthesize magnesium-based composite materials, and the properties of various Mg-MMCs containing nanosized ceramic/metal particles, synthesized using this techniq...
Abstract: Magnesium (with density, ρ = 1.74 g cc− 1) being ∼35% lighter than aluminium and ∼75% lighter than steel is an attractive and a viable candidate for the fabrication of lightweight structures. Being the designers' choice for weight critical applications, extensive research efforts are underway into the development of magnesium metal matrix composites (Mg-MMCs) through various cost effective fabrication technologies. In recent years, there has been a progressive advancement in utilising the microwave energy to consolidate powder materials, and the present study accentuates the use of energy efficient and environment friendly microwave sintering process to synthesise magnesium based composite materials. The processing advantages of the innovative and cost effective microwave assisted bidirectional rapid sintering technique followed by hot extrusion are first briefly introduced. Subsequently, the properties of various Mg-MMCs containing nanosized ceramic/metal particles, synthesised using this techniq...
25 citations
TL;DR: In this paper, the effect of cold compaction pressure and spacer agent type on the cell morphology was investigated by scanning electron microscopy (SEM) and optical stereo microscopy.
Abstract: Cell shape plays a crucial role on mechanical properties of titanium foam as scaffold in bone tissue engineering. In the present research, titanium foam was prepared using space holder technique. Sodium chloride and ammonium bicarbonate were utilised as spacer agent separately. The effect of cold compaction pressure and spacer agent type on the cell morphology was investigated by scanning electron microscopy (SEM) and optical stereo microscopy. Image analysing technique was performed to evaluate the microscopic images quantitatively. Exact salt leaching time was introduced by a new approach using electrical conductivity measurement. True and apparent porosities and compressive mechanical properties of the synthesised foams were evaluated. Finally, the superior spacer agent and appropriate cold compaction pressure were determined. It was shown that sodium chloride, due to maintaining its morphology during cold compaction pressure and absence of chemical side effects on titanium, is the superior spa...
24 citations
TL;DR: In this paper, the effects of temperature and particle size on the spark plasma sintering (SPS) response of two prealloyed aluminium powders atomised from wrought alloys AA 2024 and AA 7075 were assessed.
Abstract: The central objective of this research was to assess the effects of temperature and particle size on the spark plasma sintering (SPS) response of two prealloyed aluminium powders atomised from wrought alloys AA 2024 and AA 7075. A SPS temperature of 400°C was found to yield fully dense specimens of both alloys with hardness values that were comparable to the starting wrought ingot materials. Such samples also exhibited appreciably lower concentrations of residual oxygen and hydrogen when compared to those present in the raw powders. Degassing experiments completed through thermogravimetric analyser (TGA)–gas chromatography (GC)–mass spectrometry (MS) indicated that the release of CO2 and adsorbed/chemisorbed H2O were responsible for the enhanced purity of the SPS products. Particle size was also a factor of influence with the most favourable results for density and minimised O/H concentrations achieved with particles ≧180 μm in diameter.
22 citations
TL;DR: In this article, hot quasi-static pressing and dynamic compaction of Al7075-B4C composite powder are studied and the results showed that the increase of B4C content improved the hardness of the compacts but did not improve the compressive strength.
Abstract: Hot quasi-static pressing and dynamic compaction of Al7075–B4C composite powder are studied in this work. Micron sized Al7075 and B4C particles were milled to obtain uniform dispersion of B4C reinforcing phase. Samples with relative densities up to 97.5, 99 and 100% were fabricated using gas gun, drop hammer and hot quasi-statically compactions respectively. The results showed that the increase of B4C content improved the hardness of the compacts but did not improve the compressive strength in the samples compacted by the gas gun. However, the ductility of the samples was reduced significantly. The samples compacted using the drop hammer and under hot quasi-static loading experienced ∼25 and 11% enhancement in the compressive strength respectively. The investigation indicated that the dynamic compaction using the gas gun was more successful if it is performed after quasi-static pre-compaction and under warm compaction process. It was concluded that the quasi-static pressing is the best fabrication techniq...
21 citations
TL;DR: In this paper, the effects of Al content and porosity on the mechanical properties of porous Fe-Al intermetallics, particularly at high temperatures, were determined using scanning electron microscopy, X-ray diffraction and mechanical properties testing.
Abstract: The effects of Al content and porosity on the mechanical properties of porous Fe–Al intermetallics, particularly at high temperatures, were determined using scanning electron microscopy, X-ray diffraction and mechanical properties testing. Results show that the optimal mechanical properties are achieved at 20 to 30 wt-%Al content. The tensile and bend strengths decrease with increasing Al content at 35 to 60 wt-%Al content. The quantitative relationship between porosity and strength for porous Fe–Al intermetallics can be described as σb = 181(1−θ)3.3. The strength of porous Fe–Al intermetallics increases at medium temperature with the increase in temperature from room temperature. The maximum tensile strength (50.2 MPa) is achieved at 600°C, which is almost 36.8% higher than that at room temperature.
20 citations
TL;DR: In this article, the Selective Laser Melting (SLM) technology was used to manufacture flat specimens from Inconel 718 powder, and the flat specimens were encapsulated by means of Cathodic Arc Deposition (Arc-PVD) and High Velocity Oxygen Fuel Spraying (HVOF) to seal open pores.
Abstract: In this study, the Selective Laser Melting (SLM) technology was used to manufacture flat specimens from Inconel 718 powder. The SLM process parameters have a major impact on the microstructure as well as on the mechanical properties of the fabricated specimens. Despite using optimized processing parameters, defects like pores cannot be completely avoided. These pores act as stress raisers and lead to premature crack initiation under cyclic loading, eventually reducing the fatigue strength of the material. Hot Isostatic Pressing (HIP) offers the possibility to eliminate the porosity and thus to increase the fatigue performance of the material. HIP combines high pressure and high temperature to produce materials with superior properties. Unfortunately, open porosity, i.e. open pores on the surface, can prevent full densification. In the present work, SLM flat specimens were encapsulated by means of Cathodic Arc Deposition (Arc-PVD) and High Velocity Oxygen Fuel Spraying (HVOF) to seal open pores. For this p...
20 citations
TL;DR: In this paper, a macroscopic visualisation of Zn evaporation has been achieved using a copper substrate placed within the gas stream near the sample, which revealed the formation of nanocrystalline ZnO.
Abstract: The formation of a liquid phase during sintering of prealloyed Cu–28Zn powder is potentially attractive for densification, but the effect of gravity results in graded densification which tends to result in heterogeneous cross-sections. The formation of a necklace structure along grain boundaries due to the accumulation of liquid phase with high Zn content, especially at higher temperatures, is also of interest. Evaporation of zinc is another essential feature to consider, since loss of Zn during sintering can influence strongly the mechanical properties of brass products. A macroscopic visualisation of Zn evaporation has been achieved using a copper substrate placed within the gas stream near the sample. FEGSEM observation and XRD analysis of the deposited white mass revealed the formation of nanocrystalline ZnO as a consequence of Zn evaporation. It is proposed that this method could usefully show the evaporation of other alloying elements during sintering of similar alloys.
TL;DR: In this article, the role of compaction and sintering parameters on pore structure, cell wall integrity and compressive properties of foams was investigated, and the results show that compressive yield strength and modulus of elasticity decrease with porosity and a good compatibility with Gibson-Ashby model of cellular solids is discovered.
Abstract: Open-cell Zn foams with 74–92% porosity were fabricated by space holder technique, including compacting spherical carbamide granules coated with Zn powders followed by leaching the space holder and sintering. The role of compaction and sintering parameters on pore structure, cell wall integrity and compressive properties of foams was investigated. The results show that compressive yield strength and modulus of elasticity decrease with porosity and a good compatibility with Gibson–Ashby model of cellular solids is discovered. The optimum structure and mechanical properties of Zn foams are achieved by compaction at 300 MPa and sintering for 2 h at 410°C.
TL;DR: In this article, an orthogonal experiment scheme was employed to study the influences of forming pressure, sintering temperature and holding time and Cu content on microstructure, hardness and electrical resistivity of the Cu/Invar composites prepared by the powder metallurgy (PM) technique.
Abstract: An orthogonal experiment scheme was employed to study the influences of forming pressure, sintering temperature and holding time and Cu content on microstructure, hardness and electrical resistivity of the Cu/Invar composites prepared by the powder metallurgy (PM) technique. The interdiffusion of the Fe, Ni and Cu atoms of the composites during sintering was also investigated. The results show that the Invar alloy is distributed continuously in the composites, when the Cu content is 30 wt-% and below; when the Cu content is 40 wt-% and above, a continuous net structure of Cu forms. Properties, especially the electrical and thermal conductivities, depend on the relative density and atom interdiffusion of the Cu/Invar composites. Taking the electrical resistivity of the composites as index, the optimum processing parameters are: forming pressure of 600 MPa, sintering temperature of 1000°C, holding time of 60 min and Cu content of 50 wt-%.
TL;DR: Porous Ti59.38Nb26.6Zr8.7Fe5.32 alloys with high strength and low modulus were successfully fabricated by space holder method through adding ammonium hydrogen carbonate (NH4HCO3) as discussed by the authors.
Abstract: Porous Ti59.38Nb26.6Zr8.7Fe5.32 (wt-%, referred to as TNZF) alloys with high strength and low modulus were successfully fabricated by space holder method through adding ammonium hydrogen carbonate (NH4HCO3). Results show that the fabricated porous TNZF alloys are of β type titanium alloy with adjustable pore characteristics and mechanical properties. Varied amount of NH4HCO3 exerts significant effects on phase constituents, pore characteristics and mechanical properties of the porous alloys. Fracture mechanism of the porous alloys, which is different from the typical brittle fracture as a result of high porosity, exhibits transgranular fracture accompanied with cleavage steps. Strain increased even under low stress during the compressive deformation, demonstrating that the porous alloys possess certain ductility. The porous TNZF alloys with a porosity of 39–53%, an average pore size of 300–800 μm and a compressive modulus of 7–16 GPa and a compressive strength of 117–204 MPa can well meet the requ...
TL;DR: In this article, Fraunhofer IFAM Dresden uses 3D screen printing, a modified screen printing process based on a powder-binder mixture which is printed layer-by-layer to the desired shape followed by debinding and a conventional sintering step.
Abstract: For the production of complex shaped titanium parts huge advances have been made by powder metallurgy (P/M) during the last years. However, when it comes to miniaturized parts with intricate inner structures like closed channels without entrapped powder and high aspect ratios conventional P/M methods are stretched to their limits. To remedy this shortcoming, Fraunhofer IFAM Dresden uses 3D screen printing, a modified screen printing process based on a powder-binder mixture which is printed layer-by-layer to the desired shape followed by debinding and a conventional sintering step. Especially for small parts a productivity of several million parts per year is achievable. The objective of this work is to demonstrate the possibility to manufacture complex designs based on titanium including thin walls down to 120 μm. Therefore, pre-alloyed gas atomized Ti-6Al-4V powder was used. Analysis of part accuracy, resulting porosity, impurity level and mechanical properties were performed.
TL;DR: In this article, the development of multilayered polymeric/metallic materials by a PM route employing spark plasma sintering (SPS) has been explored, where the aim is to produce composites that join a polymer with a metal for structural applications.
Abstract: The development of multilayered polymeric/metallic materials by a PM route employing spark plasma sintering (SPS) has been explored. The aim is to produce composites that join a polymer with a metal for structural applications. In a first approach, the consolidation of polyimide-based composites by SPS was studied. For temperatures as low as 350°C, homogeneous mechanical properties were achieved in compression tests. In a second set of experiments, multilayered polyimide/aluminium composites were consolidated by SPS. These polymer-based composites could be used as an interlayer material to join effectively polyimide and aluminium.
TL;DR: In this paper, a porous titanium based composite has been developed by powder metallurgy route using cenosphere and sodium chloride (NaCl) as space holders and the effect of particle size and sintering parameters on density, microstructure, wear and corrosion resistance has been studied.
Abstract: In the present study, porous titanium based composite has been developed by powder metallurgy route using cenosphere and sodium chloride (NaCl) as space holders. The effect of cenosphere particle size and sintering parameters on density, microstructure, wear and corrosion resistance has been studied. The microstructure of the composite consists of uniform distribution of cenosphere in α-Ti matrix with the presence of few TiO2 and SiO2 phases. The density of the composites varies from 1331 to 1812 kg m− 3. The kinetics and mechanism of fretting wear against hardened steel ball (at an oscillation frequency of 10 Hz) as a function of applied load (5 and 10 N) have been studied. There is a significant reduction in coefficient of friction in porous composite as compared to that of pure titanium. There is improvement in corrosion resistance in porous titanium composites as compared to as received titanium in 3.56 wt-% NaCl solution.
TL;DR: In this article, the use of the small punch test (SPT) to mechanically characterise in a direct way the final sintered products was explained in this research work and the regressions to determine the tensile mechanical properties of the aforementioned products were also developed.
Abstract: Powder metallurgy is a manufacturing technology widely used, especially in the automotive sector. In order to assure the quality of these components different conventional tests are employed directly on the final product, but in order to mechanically characterise the sintered material, standard mechanical tests can only be performed onto samples compacted and sintered in controlled conditions similar to the ones used in the real production. The final mechanical properties of these products after compacting and sintering are the input needed to define and analyze new geometries and products. The use of the small punch test (SPT) to mechanically characterise in a direct way the final sintered products was explained in this research work and the regressions to determine the tensile mechanical properties of the aforementioned products were also developed.
TL;DR: In this article, a new type of Mg-8Al-1Sn (AT81) magnesium matrix composites reinforced with different volume fractions (5, 10, 15, 20, 25 and 30 vol.-%) of SiC particles (average size of 10 μm) was fabricated by powder metallurgy.
Abstract: The new type of Mg–8Al–1Sn (AT81) magnesium matrix composites reinforced with different volume fractions (5, 10, 15, 20, 25 and 30 vol.-%) of SiC particles (average size of 10 μm) was fabricated by powder metallurgy. With the increasing volume fraction of SiC particles (SiCp), the particles gradually show more homogeneous distribution. Compared with the AT81 alloy, the yield strength (YS) and ultimate compressive strength of the SiCp/AT81 composites are improved simultaneously. With the increasing SiCp from 0 to 30 vol.-%, the YS and ultimate compressive strength increase from 69 to 239 MPa and 286 to 385 MPa respectively, while the corresponding fracture strain (e) decreases from 19·3 to 4·8%. The improvement of the YS and ultimate compressive strength of the SiCp/AT81 composites benefits from the more homogeneous microstructure due to the increase in the SiC particles.
TL;DR: In this article, PM 316L based composite materials reinforced with SiC and emery powders in amounts of 5, 10 and 15 vol.-% were produced by uniaxial pressing at 700 MPa.
Abstract: In this work, PM 316L based composite materials reinforced with SiC and emery powders in amounts of 5, 10 and 15 vol.-% were produced. The mixed powders were compacted by uniaxial pressing at 700 MPa and processed at 1160 and 1250°C for 1 h by means of conventional sintering and microwave sintering. The sintering atmospheres were Ar/H2 95/5% for conventional sintering and Ar/H2 90/10% for microwave sintering. Mechanical properties were evaluated with transverse rupture strength (TRS) tests. Densities and porosities were determined using Archimedes method. Sintered samples were characterised by optical microscopy and SEM. All of the composite materials had lower TRS values compared with 316L base material. Among all compositions, 5 vol.-% emery powder reinforced 316L alloy composite samples exhibited the most favourable mechanical and physical properties. The 10 vol.-%SiC containing composite samples also had acceptable properties. Moreover, microwave sintering yields better mechanical and physical...
TL;DR: In this article, the role of sintering variables in realising the complicated effects on densification and microstructure of prealloyed brass powder compacts is examined.
Abstract: Coarsening of the grains and pores during sintering has a pronouncedly negative effect on the densification of prealloyed brass powder compacts. This investigation examines the role of sintering variables in realising the complicated effects on densification and microstructure. Experiments were designed to model and evaluate the effect of sintering parameters such as temperature, time and furnace atmosphere on densification, grain and pore intercept as well as pore number. The study of microstructures suggests that there is a good correlation between grain and pore intercepts. It is concluded that pore coarsening is a result of supersolidus liquid phase sintering of Cu28Zn powder, and it can retard densification, which is in acceptable agreement with the experimental data.
TL;DR: In this article, the effect of three carbon sources (synthetic graphite, natural graphite and carbon black) on microstructure and inter-particle neck development in Cr-alloyed PM steels was analyzed.
Abstract: Modern water-atomised steel powder grades are characterised by the presence of two types of surface oxides: a thin iron oxide layer, covering more than 90% of the powder surface, and more thermodynamically stable particulate oxides. The development of inter-particle necks and carbon dissolution in the iron matrix both require efficient removal of the iron oxide layer. Hence, carbon reactivity strongly affects the surface oxide reduction that determines inter-particle neck development and carbon dissolution, and so microstructure development. An analysis is presented of the effect of three carbon sources – synthetic graphite, natural graphite and carbon black – on microstructure and inter-particle neck development in Cr-alloyed PM steels. Metallographic and fractographic studies indicate that the most significant property of the carbon sources affecting reactivity is the carbon powder size. Carbon black shows the highest reactivity at elevated temperatures but is fully inert at temperatures below 9...
TL;DR: In this paper, a differential scanning calorimetry (DSC) method was developed capable of measuring the rate of in situ alloying during Al-V master alloy (MA) sintering of Ti6Al4V based on monitoring the characteristics of the β-α phase transformation during cooling from the Sintering temperature.
Abstract: A differential scanning calorimetry (DSC) method was developed capable of measuring the rate of in situ alloying during Al–V master alloy (MA) sintering of Ti6Al4V based on monitoring the characteristics of the β–α phase transformation during cooling from the sintering temperature. The beta transus temperature and transformation temperature range both decreased with increasing sintering time, while the enthalpy of transformation increased. Supporting microstructural analysis confirmed that this change in the β–α phase transformation behaviour was due to interdiffusion of Ti, Al and V between the MA particle and CP-Ti matrix and the progressive dissolution of the MA particles. The majority of in situ alloying and MA dissolution occurred within one hour, while 3 h of sintering was required to achieve a level of homogenisation similar to that measured for a wrought Ti6Al4V sample. The use of finer MA particles resulted in more rapid and complete homogenisation.
TL;DR: In this article, a powder injection molding route was used to process Ti matrix composites for full densification at 1300°C for 2 h in vacuum. But the critical powder loading for injection moldings was 55 vol.-% for all samples and the debinding was performed using solvent and thermal methods.
Abstract: Titanium (Ti) matrix composites based on Ti and reinforced with TiN, TiC and TiCN particles, were processed following a powder injection molding route: mixing, preparation of feedstock, moulding, debinding and sintering for full densification. The Ti and ceramic powders were dry mixed and molded using a wax based binder. The critical powder loading for injection molding was 55 vol.-% for all samples. Binder debinding was performed using solvent and thermal methods. Following the debinding stage, the samples were sintered for full densification at 1300°C for 2 h in vacuum. Metallographic studies were conducted to investigate densification and the corresponding microstructural changes. The sintered samples were characterized by measuring tensile strength, elongation and hardness. All powders and fracture surfaces of sintered samples were also examined using scanning electron microscope techniques. The sintered densities of injection molded Ti and composites samples were changed with increasing amoun...
TL;DR: In this article, an electrically insulating inorganic coating applied to iron particles targeting fabrication of soft magnetic composite (SMC) for low to medium frequency applications is presented. But, the coating is not suitable for low-to medium-frequency applications.
Abstract: Achieving high density with soft magnetic composite (SMC) materials requires compaction pressures exceeding 700 MPa; resulting in significant work hardening of the iron powder particles, increasing the DC magnetic coercive force along with a corresponding increase in the hysteresis loss portion of the total core loss. Annealing the as-compacted component at temperatures at or above 650°C reduces the coercive DC force and tends to decrease the AC core losses provided that the insulation layer is stable during the annealing cycle. Detailed in this paper are preliminary results utilising a novel electrically insulating inorganic coating applied to iron particles targeting fabrication of SMCs for low to medium frequency applications. This novel coating uniformly covers the iron powder and can withstand a curing temperature ≥650°C (≥1200°F). Various curing temperatures and processing conditions were evaluated and will be discussed in terms of mechanical properties as well as magnetic performance. This new mate...
TL;DR: In this paper, the concept of a sintered soft magnetic composite (SSC) was introduced, which is a combination of a soft magnet and soft magnetic composites, and a high temperature heat treatment (sintering) was used to create a Fe-Si based bulk material with a microstructure of Si rich, highly insulating ferromagnetic particle boundary phases by a high-temperature heat treatment.
Abstract: The present paper introduces a new concept of a sintered soft magnetic composite (SSC): a combination of a sintered soft magnet and soft magnetic composite. The approach is to create a Fe–Si based bulk material with a microstructure of Si rich, highly insulating ferromagnetic particle boundary phases by a high temperature heat treatment (sintering). The concept is realised via a powder metallurgical route, starting from an initial mixture of iron, silicon and copper. Silicon forms a graded boundary phase around the iron particles. Copper is added to reduce the melting point of the silicon and to ensure a uniform wetting of the silicon-rich layer around the iron particles. A systematic composition range of such sintered materials are evaluated as to magnetic and mechanical properties. The best material composition found has 96 wt-% iron+3 wt-% silicon+1 wt-% copper with the optimum sintering parameters of 1050 to 1100°C for 30 min in a nitrogen atmosphere.
TL;DR: In this paper, a simple, low cost, eco-friendly PM method has been developed to prepare MAX phase foams from commercial Ti2AlC powder, using crystalline carbohydrate as space holder.
Abstract: There have been few systematic studies of the fabrication and properties of porous MAX phase microstructures despite the potential applications of these materials. A simple, low cost, eco-friendly PM method has been developed to prepare MAX phase foams from commercial Ti2AlC powder, using crystalline carbohydrate as space holder. This method involves: mixing Ti2AlC powder with crystalline carbohydrate, pressing to form a green body, removal of the space holder and sintering. Compaction was achieved by uniaxial pressing (UP) and cold isostatic pressing (CIP). Control of porosity was achieved by varying the particle size (three ranges between 250 and 1000 μm), and volume fractions (20, 40 and 60%) of space holder. The foams were characterised and the porosity compared with the expected values. Optimal conditions for this novel processing technique were established with the aim of controlling the final microstructures and properties of the Ti2AlC foams.
TL;DR: In this paper, the effects of annealing temperature and time on microstructure evolution and mechanical properties of Ti-6Al-4V titanium alloy prepared using powder hot isostatic pressing were investigated.
Abstract: The effects of annealing temperature and annealing time on microstructure evolution and mechanical properties of Ti–6Al–4V titanium alloy prepared using powder hot isostatic pressing were investigated. The results showed that when annealing temperature was < 1173 K, the globularisation of primary α was observed, and the morphology of secondary α changed from acicular shapes to acicular and continuous lathy grains. Scanning electron microscopy fracture surface showed that the fracture mechanism changed from transcrystalline dimple type to a mixture of transcrystalline and intercrystalline dimple types with increasing annealing temperature. The tensile strength and elongation varied with the temperature in an opposite trend. However, they varied similarly with increasing annealing time. Microhardness was sensitive to the annealing time, resulting into a maximum microhardness of 396.95 HV at 1173 K for 3 h.
TL;DR: In this paper, a novel technique for synthesis of in situ titanium diborides and nitrides reinforced steel matrix composite (TiB2-TiN/Fe) was put forward.
Abstract: A novel technique for synthesis of in situ titanium diborides and nitrides reinforced steel matrix composite (TiB2–TiN/Fe) was put forward. In situ TiB2–TiN/Fe composite was synthesised by spark plasma sintering of mechanically mixed ferrotitanium and boron nitride (BN) powders. The phase evolution during sintering indicates that the TiB2–TiN reinforcements are formed in situ as follows: first step, the solid/solid interface reaction between ferrotitanium and BN, resulting in the formation of a small amount of TiB2 and TiN below 1000°C; second step, the solid–liquid solution precipitation reaction in the Fe–Ti–B–N system, resulting in most of TiB2 and TiN reinforcement formation at ∼1100°C. The microstructure investigation reveals that utrafine TiB2 and TiN reinforcements with a size of ∼1 μm are homogeneously distributed in the Fe matrix.
TL;DR: In this article, dual phase nanosized (TiB2−Ti5Si3)/TiAl composites were successfully fabricated using in situ method of combustion synthesis and hot press consolidation.
Abstract: The dual phase nanosized (TiB2–Ti5Si3)/TiAl composites were successfully fabricated using in situ method of combustion synthesis and hot press consolidation. The effects of proportions of the in situ dual phase nanoparticles (TiB2 and Ti5Si3) on microstructures and compression properties of the composites were investigated. Compared with the monophase TiB2 and Ti5Si3 particles, dual phase TiB2–Ti5Si3 particles exhibit more obvious grain refinement effect. The grain size of TiAl alloy was refined from ∼66 to ∼12 μm with the the generation of dual phase TiB2–Ti5Si3 particles. Moreover, the TiAl matrix composites reinforced with dual phase nanosized TiB2–Ti5Si3 particles exhibit better comprehensive compression properties. When TiB2:Ti5Si3 = 2:1[Σ(TiB2 + Ti5Si3) = 4 vol.-%], the TiAl matrix composite has a high true fraction strain of 26.1%, a true yield strength of 761 MPa and an ultimate compression strength of 1647 MPa.