Microstructure and Mechanical Properties of W-High Entropy Alloy Composite by Hot Swaging

To improve the mechanical properties of a sintered WHA using high entropy alloy as the matrix (W-HEA), investigations were carried out to apply deformation strengthening method of hot swaging on the W-HEA. The W-HEA samples were swaged around 1300°C with the 10%, 15% and 20% of reduction in area. The results show that the strength and hardness of the W-HEA composite increased with the increasing degree of deformation. And the aspect ratio of tungsten grains increases along the axial direction in the swaged alloys. The hardness of W-HEA with a 20% reduction in area reaches 448 HV, and the dynamic compression yield strength is about 1911 MPa. After hot swaging, the hardness and strength of the W-HEA are greatly improved compared with the sintered W-HEA.

Feasibility study of a novel method for production of glassy reinforced composite Al–Ni60Nb40 of powder thixoforging

In the present study, the semisolid forming has been proved to be effective in fabricating amorphous reinforced aluminum matrix composite of high quality with appreciable mechanical properties. In other words, the Ni60Nb40 glassy reinforcement in 520.0 aluminum matrix composite was successfully fabricated via powder thixoforging without altering the glassy nature. Most prior studies are focused on solid state (powder metallurgy). Subsequently, the use of glassy particles with high crystallization temperatures provides processing the composite at higher temperatures. Considering the powder thixoforming benefits, we open a door to another way of manufacturing high-efficient amorphous reinforced metal matrix composite with brilliant mechanical properties. In monolithic matrix, the alloy produced via powder thixoforging hardness and compression yield strength reached 223(HV) and 747 MPa compared to as cast condition increase of 116% and 228%, respectively. Additionally, this significant mechanical strength was combined with a brilliant fracture strain of 40%. Moreover, the 30 vol.% glassy reinforced composite possess hardness, compression yield strength, and fracture strain of 311(HV), 875 MPa, and 13%, respectively. All produced specimens reached near full density over 99% relative density, leading to a considerable combination of superior strength and ductility. Significantly, the SYS of powder thixoforging samples significantly increased from 89 kN m kg−1 for as cast condition to 290, 238, 220, and 199 kN m kg−1 for the monolithic and amorphous reinforced Al matrix composites of 12, 20 and 30 vol.%.

Split Bar Hopkinson with Springs Striker Bar Launcher

Research on the dynamic strength of various materials such as metallic materials, polymers, concrete has been done by many researchers. The Split Hopkinson Bar method is still used to produce a high strain rate. In this method, a striker bar is usually launched using pressurized gas. However, high security system is required to prevent leakage as the operating pressure is very high. Avoiding the use of high-pressure gas, in this study, a mechanical system of springs used to propel the Striker Bar. By varying the spring deflection of 1 cm to 8 cm, a linear Striker Bar velocity from 2.17 m/s until 19.45 m/s is obtained. Aluminum alloy Al-2024 has been tested with this tool and it is found that at the maximum Striker Bar velocity, strain rate on the material can be reach 1132 s-1, and dynamic compression yield strength increase 56% from quasi-static compression yield strength.

Microstructural Evolution of a New Aerospace 7XXX Alloy during Retrogression and Re-Ageing Treatment

RRA treatment was applied to a high-Zn, 7XXX alloy under development for aerospace applications. Microstructure of the alloy is studied at different stages of the 3-step ageing process, by Transmission Electron Microscopy, in order to understand the corresponding evolution of mechanical and corrosion properties. The Compression Yield Strength at the end of the high temperature step was found higher than at the end of the 1st step, contrary to the conventional RRA treatment. After re-ageing, the final CYS turned out significantly higher than at the T6 temper of the alloy, while the material remained sensitive to exfoliation corrosion.