In this study, the two types of high-strength low-alloy steels were melted and cast in a vacuum induction furnace. Phase transition temperature of HSLA steel was calculated by JMatPro software. The calculation results show that the two different types of HSLA steels which have equal phase proportions of ferrite and austenite at a temperature of approximately 820 and 800 °C in HSLA-I and HSLA-II, respectively. In addition, the effect of chemical composition on the microstructure and mechanical properties of steels were studied. The results indicate that the ultimate tensile stress value of HSLA-II samples was greater than the HSLA-I samples by about 35%, and the yield stress and breaking strength value of HSLA-II were higher than HSLA-I as well.

In the scope of refractory material processed by spark plasma sintering development for structural applications in the core of future combustion chamber, Mo-TiC alloys and Mo-TiC-Cr alloys were sintered at 1700°C with a pressure of 30 MPa. Powders of Mo, TiC and Cr were prepared by planetary ball mill in an argon atmosphere. In this dissertation, the structure, element and phase composition of alloys were investigated. The Mo-TiC alloys showed obvious intergranular brittle fracture. The fracture mode of Mo-TiC-Cr alloys, however, was changed to mixed intergranular and transgranular fracture. The obtained results demonstrated that, compared with the peaks of Mo and Mo2C from Mo-TiC, the peaks of Mo and Mo2C from Mo-TiC-Cr were deflected to the right, due to the addition of chromium forming a solid solution. The results of isothermal oxidation tests at 1200°C in air revealed that the chromium compound on the surface of the oxide layer increases and the pores decreases with the increase of oxidation time for Mo-TiC-Cr alloys. The pores of surface of the Mo-TiC alloys were less and smaller than the Mo-TiC-Cr.

Effects of alloying elements (i.e., variable content of Mo and C) on the microstructure and compression properties of four types of experimental material based on TiAl-based alloy containing 8 at.% Nb were investigated. The specimens were prepared by vacuum noncollapsable melting technology and followed by a homogenization treatment with air cooling. The compression properties at room and at elevated temperature were evaluated in laboratory air. The results demonstrate that the inter-lamellar space of the alloy decreased with the addition of the Cr and Mo alloying elements. Cr acts a better role in grain refinement, while Mo enhances the content of γ phase in the alloys. The addition of Cr/Mo elements improves the elastic modulus of the material, but reduces the breaking strength due to the absence of the dislocation region found in non-Cr / Mo alloys that resist cracking. The concentrated distribution of γ phase at grain boundaries hinders recrystallization and the tendency of grain orientation.

This paper aims to research the high-temperature oxidation behavior of TiC/Mo composite. Adding 5 wt.% TiC, Mo-based composite was prepared by Spark Plasma Sintering. The composite was oxidized at different temperatures (400°C, 600°C, 800°C, 1000°C and 1200°C) and times (5 min, 10 min, 20 min, 30 min and 60 min). When oxidation was at 400-1000°C for 20 minutes, the degree of oxidation intensifies with the increase of temperature, and TiO2 was observed at 1000°C. While the temperature was 1200°C, the oxidation rate gradually decreased with the increase of time. The result shows that the formation of TiO2 can inhibit the oxidation process.