The effect of Tungsten (W), Tantalum (Ta) and simultaneous addition of Germanium (Ge) and Silicon... more The effect of Tungsten (W), Tantalum (Ta) and simultaneous addition of Germanium (Ge) and Silicon (Si) on the microstructure evolution, tensile and creep properties of the near-alpha alloy Ti-5.7Al-3.9Sn-3.7Zr-0.7Nb-0.5Mo-0.35Si-0.05C have been investigated at high temperatures up to 650°C. Microstructural characterizations following solution treatment at 1050°C for 2 hours with oil quenching and aging treatment at 700°C for 2 hours followed by air cooling, highlighted that the additions of refractory elements such as W and Ta led to a decrease of both the volume fraction of the primary alpha phase (ap) and its average size. Tensile tests performed up to 650°C revealed a significant improvement in tensile strength with additions of W and Ta, even though a decrease of ductility has been also detected. Creep tests carried out at 600°C under a constant stress of 200 MPa pointed out that, refractory elements, Ge and Si have a beneficial effect on both primary and steady-state creep stra...
The effects of Al content on the microstructures and the mechanic properties of complex brass (Cu... more The effects of Al content on the microstructures and the mechanic properties of complex brass (Cu-22.7Zn-Al-1.0Ni) in as-cast, hot-rolled and cold rolled strip were investigated. The results show that Al is able to significantly reduce the size of α phase and increase the area of β-phase. With the increase of Al content, α phase transforms from block to strip shape and distributes more uniform, and the tensile strength and hardness is improved, however, the elongation is decreased. With the addition of 3.0% Al in the alloy, the hardness and tensile strength of cold-rolled plate with the thickness of 0.2 mm can reach up to the peak, 255HV and 820MPa. The proper deformation processing and heat treatment will induce that the hardness and tensile strength of 0.2mm thick cold-rolled plate are 20.3% and 7.9% than that of 0.4mm thick cold-rolled plate, respectively.
In the context of research of lighter and/or stronger high temperature materials in order to impr... more In the context of research of lighter and/or stronger high temperature materials in order to improve aeroengines, the present work shows an example of a powder metallurgy (PM) manufacturing route for TiAl alloys that could be used for low pressure turbine (LPT) blades processing. In this frame, two different alloys, Ti-47Al-1Fe-1Zr-1Mo-0.2Si (at.%) FZM and Ti-43.5Al-4Nb-1Mo-0.1B (at.%) TNM-B1, were gas-atomized into powders, extruded, heat-treated and mechanically tested.
Separate effects of 0.3 at% Si and 0.2 at% C additions have been investigated on the Ti–43.5Al–1M... more Separate effects of 0.3 at% Si and 0.2 at% C additions have been investigated on the Ti–43.5Al–1Mo–4Nb–0.1B alloy. Both elements appear to stabilise the γ phase. Si addition induces an increase in both γ-lamellar and γ-grain volume fractions. A heterogeneous distribution of primary and secondary silicides is observed in Al-rich regions of the microstructure, but silicon appears to be mainly in solid solution in the lamellar structure. The solid solution effect of silicon in the more plastically deformable β phase is probably very limited because of the high volume fraction of α2 in this alloy. This may explain the lack of beneficial effect of 0.3 at% of silicon on both tensile and creep properties. Carbon appears to stabilise the γ phase through an increase in γ-grain volume fraction and is found to be in solid solution in the lamellar structure. Our results suggest a very strong solid solution effect of carbon, since addition as low as 0.16 at% leads to an increase in yield strength at room and high temperature, a reduction in the secondary creep rate and a longer creep life.
A scanning method based on diffusion couples has been set up to experimentally explore phase diag... more A scanning method based on diffusion couples has been set up to experimentally explore phase diagrams and to observe the stable phases in quinary alloys. This method enables to realize a fast, experimental and reliable scanning of composition and then determine promising alloy compositions for potential structural application. Aiming at developing promising refractory complex concentrated alloys (RCCAs), the method was applied on the Ti-Nb-Al-Si system with an initial two phase, body-centered cubic (bcc) + orthorhombic (O), microstructure and focuses on the effect of Mo, Ta, V and Zr additions on this microstructure. The evolution of the orthorhombic phase fraction according to the content of additional elements was quantified, as well as the maximum concentration of those elements in order to stabilize the duplex microstructure, and maintain it above 800 • C. In such framework, it appears that Mo, Ta and V show the most promising effects on the Ti-Nb-Al-Si system. The comparisons between experimental results and calculated phase diagrams using current thermodynamic database showed that these calculations applied to RCCAs are good qualitative tools but are not accurate enough to be used as predictive means.
The effect of Tungsten (W), Tantalum (Ta) and simultaneous addition of Germanium (Ge) and Silicon... more The effect of Tungsten (W), Tantalum (Ta) and simultaneous addition of Germanium (Ge) and Silicon (Si) on the microstructure evolution, tensile and creep properties of the near-alpha alloy Ti-5.7Al-3.9Sn-3.7Zr-0.7Nb-0.5Mo-0.35Si-0.05C have been investigated at high temperatures up to 650°C. Microstructural characterizations following solution treatment at 1050°C for 2 hours with oil quenching and aging treatment at 700°C for 2 hours followed by air cooling, highlighted that the additions of refractory elements such as W and Ta led to a decrease of both the volume fraction of the primary alpha phase (ap) and its average size. Tensile tests performed up to 650°C revealed a significant improvement in tensile strength with additions of W and Ta, even though a decrease of ductility has been also detected. Creep tests carried out at 600°C under a constant stress of 200 MPa pointed out that, refractory elements, Ge and Si have a beneficial effect on both primary and steady-state creep stra...
The effects of Al content on the microstructures and the mechanic properties of complex brass (Cu... more The effects of Al content on the microstructures and the mechanic properties of complex brass (Cu-22.7Zn-Al-1.0Ni) in as-cast, hot-rolled and cold rolled strip were investigated. The results show that Al is able to significantly reduce the size of α phase and increase the area of β-phase. With the increase of Al content, α phase transforms from block to strip shape and distributes more uniform, and the tensile strength and hardness is improved, however, the elongation is decreased. With the addition of 3.0% Al in the alloy, the hardness and tensile strength of cold-rolled plate with the thickness of 0.2 mm can reach up to the peak, 255HV and 820MPa. The proper deformation processing and heat treatment will induce that the hardness and tensile strength of 0.2mm thick cold-rolled plate are 20.3% and 7.9% than that of 0.4mm thick cold-rolled plate, respectively.
In the context of research of lighter and/or stronger high temperature materials in order to impr... more In the context of research of lighter and/or stronger high temperature materials in order to improve aeroengines, the present work shows an example of a powder metallurgy (PM) manufacturing route for TiAl alloys that could be used for low pressure turbine (LPT) blades processing. In this frame, two different alloys, Ti-47Al-1Fe-1Zr-1Mo-0.2Si (at.%) FZM and Ti-43.5Al-4Nb-1Mo-0.1B (at.%) TNM-B1, were gas-atomized into powders, extruded, heat-treated and mechanically tested.
Separate effects of 0.3 at% Si and 0.2 at% C additions have been investigated on the Ti–43.5Al–1M... more Separate effects of 0.3 at% Si and 0.2 at% C additions have been investigated on the Ti–43.5Al–1Mo–4Nb–0.1B alloy. Both elements appear to stabilise the γ phase. Si addition induces an increase in both γ-lamellar and γ-grain volume fractions. A heterogeneous distribution of primary and secondary silicides is observed in Al-rich regions of the microstructure, but silicon appears to be mainly in solid solution in the lamellar structure. The solid solution effect of silicon in the more plastically deformable β phase is probably very limited because of the high volume fraction of α2 in this alloy. This may explain the lack of beneficial effect of 0.3 at% of silicon on both tensile and creep properties. Carbon appears to stabilise the γ phase through an increase in γ-grain volume fraction and is found to be in solid solution in the lamellar structure. Our results suggest a very strong solid solution effect of carbon, since addition as low as 0.16 at% leads to an increase in yield strength at room and high temperature, a reduction in the secondary creep rate and a longer creep life.
A scanning method based on diffusion couples has been set up to experimentally explore phase diag... more A scanning method based on diffusion couples has been set up to experimentally explore phase diagrams and to observe the stable phases in quinary alloys. This method enables to realize a fast, experimental and reliable scanning of composition and then determine promising alloy compositions for potential structural application. Aiming at developing promising refractory complex concentrated alloys (RCCAs), the method was applied on the Ti-Nb-Al-Si system with an initial two phase, body-centered cubic (bcc) + orthorhombic (O), microstructure and focuses on the effect of Mo, Ta, V and Zr additions on this microstructure. The evolution of the orthorhombic phase fraction according to the content of additional elements was quantified, as well as the maximum concentration of those elements in order to stabilize the duplex microstructure, and maintain it above 800 • C. In such framework, it appears that Mo, Ta and V show the most promising effects on the Ti-Nb-Al-Si system. The comparisons between experimental results and calculated phase diagrams using current thermodynamic database showed that these calculations applied to RCCAs are good qualitative tools but are not accurate enough to be used as predictive means.
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