Effect of niobium and austenitizing temperature on the microstructures and properties of spray-deposited AISI M3:2 high speed steel

The microstructure and properties of niobium-containing AISI M3:2 high speed steels (HSSs) fabricated by spray forming and traditional casting have been investigated. The results show that fine and uniformly-distributed grains without macrosegregation appeared in the as-deposited HSSs that differ from those of as-cast HSSs. Nb mostly appears in primary MC carbides, whereas it contributes less to the formation of M6C carbides. The high stabilization of Nb-rich MC carbides can pin the grain boundaries during high-temperature austenitizing process, thus conferring a fine grains and raising the content of dissolved alloying elements. Enhanced precipitation strengthening and fine dispersion of NbC carbides throughout the matrix contribute to the high hardness and red hardness of Nb-containing HSS.

Thermal Expansion Behavior of Co-Spray Formed Al-20Si/7075 Bimetallic Gradient Alloy

Bimetallic gradient alloys have attracted research attention recently due to their potential applications in the aerospace and automobile industries. In this study, Al-20Si/7075 bimetallic gradient alloys were successfully manufactured by co-spray forming and the roll process. We investigated the thermal expansion behavior of the gradient alloy. It was found that the coefficients of thermal expansion increased with silicon content and increased temperature, reaching the highest point at 573 K, after which they decreased on account of the relaxation of residual thermal stress and the silicon desolvation from the supersaturated aluminum phase. The measured thermal expansion coefficient can be roughly predicted through the traditional theoretical models. Our results revealed the thermal expansion behavior of Al-20Si/7075 bimetallic gradient alloys and would improve the development of new type aluminum–silicon alloy for electronic packaging.

Study on Hot Deformation Behavior of Spray-Forming and Nano-Sized Al–Cu–Mg Alloy

Spray-forming Al–Cu–Mg alloy was compressed to 70% deformation at 300–450 °C and strain rates of 0.01–10.00 s−1 on a Gleeble-3180 system. The microstructures of the hot deformed, sprayforming, nano-sized Al–Cu–Mg alloys were studied through electron backscatter diffraction. Constitutive equation and parameter Z were established to describe the deformation behavior of the alloy at high temperature, and the Q value was 155.67 KJ·mol−1. 3D power dissipation and processing maps were analyzed under strain values of 0.3, 0.6, 0.9, and 1.2. When the strain was increased from 0.6 to 0.9, the processing performance changed remarkably. Dynamic recovery occurred at low temperature and high strain rate, whereas dynamic recrystallization took place at increased temperature and low strain rate. The region in 400–450 °C and 0.01 s−1–0.08 s−1 exhibited an improved processing performance.