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In the present research, two different compositions of submicron-structured cobalt (800 ± 45 nm) and chromium (700 ± 50 nm) powders are mixed to fabricate Co-50 mass% Cr alloys by the vacuum hot-press sintering technique. This study imposes various hot-press sintering temperatures (1150, 1200, 1250 and 1300°C) and pressures (20, 30, 40 and 50 MPa) while maintaining the sintering time at 1 h, respectively. The experimental results show that the optimum parameters of hot-press sintered Co-50 mass% Cr alloys are 1200°C at 50 MPa for 1 h. Meanwhile, the sintered density reaches 7.73 g cm−3, the closed porosity decreases to 0.31%, and the hardness and transverse rupture strength values increase to 80.6 ± 0.3 HRA and 1052.9 ± 17.5 MPa, respectively. Grain growth is not obviously generated after 1200°C hot-press sintering at 50 MPa for 1 h. Consequently, the optimal solid-phase sintering process effectively improved hot-press sintered Co-50 mass% Cr alloys, which resulted in the good properties. [ABSTRACT FROM AUTHOR]

In this study,in situ50 vol.-% TiCx/2014Al composites with different C/Ti molar ratios (0.6, 0.7, 0.8, 0.9 and 1) were successfully produced by the method of combustion synthesis and hot press consolidation. The microstructure and the mechanical properties of the composites were investigated. Microstructure characterisation of the TiCx/2014Al composites showed relatively uniform distribution of the TiCxparticles with the particle size in the range of 200–900 nm. With the increase of the C/Ti molar ratio, the yield strength (σ0.2) and the ultimate compression strength (σUCS) increased first then decreased, and the fracture strain (εf) increased. Theσ0.2,σUCSand the abrasive wear resistance of the 50 vol.-% TiCx/2014Al composites reached the highest value when the value of the C/Ti molar ratio comes to 0.8. Theσ0.2,σUCSandεfof the 50 vol.-% TiCx/2014Al composites with the C/Ti molar ratio of 0.8 are 1094 MPa, 1454 and 6.13%, respectively. [ABSTRACT FROM PUBLISHER]

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. [ABSTRACT FROM AUTHOR]

Alloys with composition of Ta-10 wt.% W and Ta-10 wt.% W-6 wt.% Al, respectively, were prepared by the hot-press sintering process. The oxidation behaviour at 900°C and 1000°C was studied. The oxidation weight gain curves of the Ta–10%W alloy followed the linear law and the final oxidation product was Ta2O5 solid solution. Meanwhile, due to the addition of Al, the oxidation weight gain curves of the Ta–10%W–6%Al alloy followed the parabolic law. The final oxidation products at 900°C formed a dense outer layer Al2O3 and an inner layer. However, after being oxidised at 1000°C, the oxidation products included Al2O3, AlTaO4 and Ta22W4O67. Since the dense Al2O3 oxide film was consumed by the generation of AlTaO4, the inward diffusion of oxygen cannot be prevented. The oxidation resistance degraded at 1000°C. The addition of Al significantly improved the oxidation resistance of the Ta-W-based alloy system. [ABSTRACT FROM AUTHOR]

The objective of the present work was to determine the suitability of a new iron-based Mn–Cu–Sn matrix alloy for the manufacture of diamond-impregnated tool components. A number of specimens were consolidated by the hot press route from ball-milled powders. Density, microstructural features, phase composition, bending properties and hardness were evaluated. The results revealed excellent mechanical properties, includingσ0.2 > 850 MPa in 3-point bending and HK0.5 > 300. A commercial Co-WC reference matrix alloy was also produced for comparison purposes. Diamond-impregnated specimens with different matrices were tested for wear rate on abrasive sandstone using a test rig specially designed to simulate tool application conditions. The tests that involved 3- and 2-body abrasion ranked the alloys in different orders. Statistical analysis showed that the wear rate of diamond-impregnated composites was mainly affected by diamond concentration, but statistically significant contribution of the matrix resistance to 3-body abrasion was also found. [ABSTRACT FROM PUBLISHER]

Effects of TiB2/TiCx ratios on compression properties and abrasive wear resistance of 50 vol.-% (TiB2–TiCx)/Al–Cu composites fabricated via the combustion synthesis (CS) method assisted with hot press from the Al–Ti–B4C system were studied. With decrease in the TiB2/TiCx ratio from 3:1 to 1:3, the shape of TiB2 changed from platelike to clubbed while the size of TiCx particles increased, which directly led to different mechanical properties. The 50 vol.-% (TiB2–TiCx)/Al–Cu composite with the TiB2/TiCx ratio of 2:1 exhibited good compression strength without sacrificing the fracture strain, while the composite possessed the highest abrasive wear resistance when the TiB2/TiCx ratio was 3:1. The appropriate TiB2/TiCx ratio was recommended to be 2:1 in this research. [ABSTRACT FROM AUTHOR]

In this study, nanoporous high-entropy alloys (HEAs) were fabricated by chemically de-alloying aluminium atoms in mechanically alloyed HEAs. In addition, the effect of alloy composition, compositional uniformity, and porosity of the HEA precursors on the pore structures of the final HEA foams was investigated. Aluminium was successfully de-alloyed only for Ni-free HEAs because of the low mixing enthalpy of Ni and Al. For HEAs containing pre-existing microscale pores, aluminium atoms were readily de-alloyed because the pores opened pathways for NaOH, thereby resulting in hierarchical micro-nanoporous structures in the final foams. For denser HEAs with better compositional uniformity, homogeneous nanoporous structures were revealed in the final foams. [ABSTRACT FROM AUTHOR]

This work fabricated CoMoNiTa3 medium-entropy alloys using the vacuum hot pressing process of powder metallurgy technology. Micron-grade cobalt (6.3 μm), molybdenum (13.2 μm), nickel (2.4 μm) and tantalum powders (25.0 μm) were combined using ball milling. The experiments utilised various hot pressing temperatures (1000, 1050, 1100, and 1150 °C) and hot pressing pressures (20, 35, and 50 MPa) to identify the optimal parameters for CoMoNiTa3 alloys, while simultaneously investigating the differences in microstructures. The experimental results reveal that the optimal hot pressing parameters of this alloy were 1100 °C at 50 MPa for 1 h. The sintering density was enhanced to 9.65 ± 0.01 g cm−3, while the hardness, transverse rupture strength, and flexural modulus reached 85.5 ± 0.1 HRA, 1370.3 ± 90.1 MPa and 168.6 ± 12.7 GPa, respectively. Moreover, the electrical conductivity was 6.53 ± 0.13 × 104 S cm−1. Furthermore, the electron probe microanalyser, electron backscatter diffraction, and transmission electron microscopy results confirmed the face-centred cubic solid solution, Ni3Ta, and μ phases of the CoMoNiTa3 structure, and no preferred grain orientation was found. [ABSTRACT FROM AUTHOR]

An analytical densification model describing the final stages of hot pressing and sintering has been developed and found to be consistent with empirical findings. The behaviour of composite powders for the matrices of diamond tools has been studied under hot pressing conditions. Differential scanning calorimetry was used to determine the heat capacity at constant pressure Cp of pure Co, 663Cu, and composite iron- and cobalt based powders (also containing WC, Ni and 663Cu). The relationship between Cp and composite densification has been analysed, and it has been found that optimised rare earth additions to the iron based composite powders can produce Cp characteristics close or equivalent to that of pure Co powders. This modified composite powder has been used to hot press diamond drill and saw bits that show good properties. Employing a densification regime guided by the dynamic model has been found radically to improve stability in service (bend strength, hardness, impact, ductility and porosity). [ABSTRACT FROM AUTHOR]

In the present work, the effect of Al content (0, 3, 5, 10, 15 wt-%) on the microstructure, mechanical and wear properties of Cu was systematically studied. Interestingly, the core–shell microstructure was observed in the Cu–Al alloys or Al bronzes with different layers of α-Cu, and intermetallic phases. The Cu–Al alloys displayed good compressive yield strength of 174–653 MPa, in particular, the Cu samples with Al (upto 10 wt-%) did not show fracture upto strain of 40%. Abrasion wear was the predominant wear mechanism in pure Cu and Cu–Al alloys after sliding against SiC. The Al addition to Cu drastically decreased the wear rate (198 ×10−3 to 3.8 ×10−3 mm3 N–1m–1) of Cu–Al alloys. The present work demonstrates the advantage of the addition of (5–10 wt-%) Al to Cu in achieving good combination of mechanical and wear properties of Cu–Al alloys. [ABSTRACT FROM AUTHOR]

In this study, copper powders with dendritic morphology were produced by the electrolysis method, and then silver coating was applied to these powders by an electroless coating method. The bulk samples were fabricated by hot pressing method using different ratios of copper and silver-plated copper powders. The results showed that the electroless silver coating layer provided a strong bond at the particle boundaries of the samples, significantly improving the physical and mechanical properties of the materials. Accordingly, the hardness, tensile strength, electrical and thermal conductivity values of the samples produced from silver-plated dendritic copper particles were determined to be approximately 98 HB, 185 MPa, 102 IACS% and 402 W mK−1, respectively. In addition, the oxidation resistance of the sample produced from completely silver-coated copper powders is 4 times higher than that of pure copper. [ABSTRACT FROM AUTHOR]

Micro hot embossing is a well-established technology to produce polymer microdevices and parts. This technology on metal powder/binder feedstocks is an innovator challenge that fits into the sustainable circular economy, being excellent for small series production of precision metallic parts. The powder hot embossing technology is integrated into processes denominated SDS (shaping, debinding, and sintering). This study presents the feasibility of replicating the die features into metallic parts by comparing two binders (Lc and M1). A new binder involves optimising critical parameters during hot embossing to ensure the replication of microdetails and the quality of metallic parts. Comparing the two binders, Lc contributes to the best precision of geometric details, and M1 improves surface quality. The study shows that hot powder embossing is a promising process to manufacture metallic parts with high precision and high-quality geometrical features on a microscale. [ABSTRACT FROM AUTHOR]

This study fabricated Ni–35Mo–15Cr alloys by the vacuum hot pressing technique. The experiments utilised various hot pressing temperatures (1050°C, 1100°C, 1150°C, and 1200°C) and pressures (20, 35, and 50 MPa) to determine the optimal parameters for Ni–35Mo–15Cr alloys. The experimental result showed that the optimal hot pressing parameters of this alloy were 1150°C at 35 MPa for 1 h. Among them, the sintering density reached 8.92 g·cm−3, and the hardness and TRS increased to 77.1 HRA and 1218.2 MPa, respectively; while, the electrical conductivity was 7.08 × 103 S cm−1 and the polarisation resistance was 294.65 Ω·cm2. Furthermore, the TEM observation identified the HCP structures of the Mo2C that precipitated in the Ni–35Mo–15Cr alloys, and the [02 2 ¯ 1] and [01 1 ¯ 2] crystal axis of Mo2C can be found. Overall, the properties of Ni–35Mo–15Cr alloys were effectively improved through the hot pressing process. [ABSTRACT FROM AUTHOR]

To improve low hardness and poor corrosion resistance of the Fe-based alloys, Fe–Ti–Al–B–Si–C–P–Cr novel alloy was prepared using mechanical alloying and spark plasma sintering (SPS). Two types of mills, including of high-energy planetary (HEP) and SPEX(S) ball mills (BM) were used to reach the solid solution. Mechanical alloying by the HEP route led to the formation of the Fe(α) phase after 60 h, while its milling after 15 h by high-energy SPEX mill led to the formation of the Fe(α) solid solution. After sintering of as-milled powders by SPS, the composite of Fe (α)/nanocrystalline was obtained. The micro-hardness of the HEP–SPS and the S–SPS samples obtained about 689.5 ± 0.15 and 2068.5 ± 0.18 HV0.3, respectively. The lowest corrosion current density and the highest polarization resistance were related to the HEP–SPS sample and was calculated to be 0.51 µA/cm2 and 41.668 KHz/cm2, respectively. [ABSTRACT FROM AUTHOR]

Different approaches to take advantage of powder metallurgy in the manufacturing of diamond-impregnated components were studied. Three different powders were used as starting materials; two pre-alloyed powders, based on Fe–Cu and Fe–Cu–Sn systems, and one pre-mixed Fe-based powder. Different manufacturing routes as a strategy to obtain tailored mechanical properties were studied, with the influence of alloying elements such as graphite, iron phosphide and Mn–Ni–B master alloy to reinforce the iron-based powders. Both uncoated and coated commercial synthetic diamonds were introduced in the systems to analyse the surface reactions that depend on both metallic matrix and processing parameters. Hardness values from 88 to 105 HRB were obtained with a wide range of transverse rupture strength values from 1250 to 1640 MPa. An appropriate combination of metallic matrix, alloying elements and processing parameters makes the materials analysed here suitable powders for the manufacturing of diamond-impregnated tools. [ABSTRACT FROM AUTHOR]

Precipitation hardenable metastable-beta type Ti–Nb–Cu alloy was produced by powder metallurgy for implant applications. Specimens were sintered, quenched and aged in a single-step process to enhance the mechanical properties. Sinter-aging combines the sintering, quenching and aging in a single step. This process reduces the cost of operation. Although, there are studies about the aging or sinter-hardening of titanium, there is no study on the sinter-aging of the titanium or any other metals. The effects of process parameters (sintering temperature, cooling rate and aging) on the mechanical properties were investigated. Young's modulus and strength values were enhanced with increasing sintering temperature and cooling rate. Strength and elastic modulus values were increased with increasing aging temperature. Increasing Cu content lowered the corrosion potential and increased the current density. Metal release values are not higher than the reference levels in the body. [ABSTRACT FROM AUTHOR]

In situ TiB2 and TiC reinforced copper matrix composites with tailored heterogeneous structure were fabricated via high-energy ball milling of Cu, TiH2 and B4C powders followed by hot pressing. The microstructures of both ball-milled powders and hot-pressed composites were compared. Although the dislocation density of Cu matrix was changed after hot pressing, the mode of distribution of ceramic phases in the Cu matrix was noted to transmit from the ball-milled powders to hot-pressed composites in case of the TiH2 particles synthesised by the in situ reactions. The structural inheritance between the ball-milled powders and hot-pressed composites could be used to control microstructural features and thus to tune properties. The hot-pressed TiB2–TiC/Cu composites with tailored heterogeneous structure exhibited better performance than those of homogeneous counterparts. [ABSTRACT FROM AUTHOR]

Effects of carbon sources, i.e. carbon nanotubes (CNTs), graphite, carbon black (C-black), on synthesised TiCx size, shape and compressive properties of in situ 40–60 vol.-% TiCx/2009Al composites were investigated. When CNTs and C-black were used, the synthesised TiCx with particle sizes of 0.08–1 and 0.9–5 µm, respectively, was spherical or nearly spherical in shape, while graphite was used, the synthesised TiCx with particles sizes of 0.2–2 µm was octahedral or spherical in shape. The yield strength (σ0.2), ultimate compression strength (σUCS) and hardness of TiCx/2009Al composites all increased with increasing TiCx content, while the plastic strain (ε) decreased. The σ0.2, σUCS, ε and hardness of 60 vol.-% TiCx/2009Al composites fabricated by using CNTs were 722 MPa, 946 MPa, 3.2% and 260 ± 10 Hv, respectively. The strength increase of the composites resulted from finer-sized TiCx particles with spherical shape. [ABSTRACT FROM AUTHOR]

Biomedical Mg-matrixin situcomposites were fabricated from Mg and ZnO powder via ball mixing and spark plasma sintering. XRD analysis indicated thatin situreactions occurred during sintering process producing MgO, Zn and Mg–Zn intermetallic compounds. The formation ofin situproducts strongly contributed to the enhancement of the strength and the ductility of the fabricated composites compared with pure Mg. Specifically, the highest strength at 380 MPa was observed in the Mg-20 wt-% ZnO composite, and the highest failure strain at 12.9% was achieved in the Mg-5 wt-% composite compared with the 156 MPa strength and the 10.2% failure strain of pure Mg. In addition, the strengths of as-produced composites are as double as that of cortical bones. With these superior mechanical properties, the fabricated composites are considered as very potential candidate for biomedical load-bearing applications. [ABSTRACT FROM PUBLISHER]

The effect of quenching conditions on phase transformation characteristics and microstructural features of Cu–Al–Ni–Ti shape memory alloys (SMAs) have been studied. The alloys were synthesised via conventional powder metallurgy process using elemental metal powders. Four different quenching techniques, such as (a) two-step quenching, first to 100°C and then to 0°C; (b) two-step quenching, initially to 40°C and later to 0°C; (c) direct quenching to 40°C and (d) direct quenching to 0°C, were used. The microstructural features and phase transformations that the alloys had undergone were studied using FE-SEM and XRD techniques. The martensitic phase transformation analyses were carried out by differential scanning calorimeter while the mechanical properties were studied by microhardness and flexural bending tests. The results obtained clearly indicate that the quenching routes followed have a remarkable influence on the properties of Cu-based SMAs. [ABSTRACT FROM PUBLISHER]

In this study, two different compositions of submicrometre copper and chromium powders were mixed and the Cr50Cu50 alloys were fabricated via the powder metallurgy technique. The research imposed various hot pressing pressures, while the temperature was maintained at 1050°C for 1 h, respectively. The experimental results showed that the Saint Venant's effect obviously appeared in 1050°C, 48 MPa, 1 h hot pressing Cr50Cu50 alloys, which led to differences in the surface and internal hardness of the specimens. As a result, the optimal parameters of hot pressing of Cr50Cu50 alloys were 1050°C, 36 MPa for 1 h possessing the highest transverse rupture strength value (921.69 MPa). Moreover, the surface hardness increased to HV0.2221.78 (HRB 95.4), the relative density reached 97.15% and apparent porosity decreased to 0.10%, respectively. Furthermore, the resistivity decreased to 5.28 × 10−6 Ω cm, and ICAS was enhanced to 32.65% after the optimal procedure. [ABSTRACT FROM PUBLISHER]