Ti6Al4V alloy is widely used as a system material in high temperature and high pressure environments in various industrial fields and is difficult to mechanically machine. Thus, high temperature processing methods such as hot forging, rolling, and hot forming are usually applied. Among various methods for deriving optimal molding conditions during high-temperature processing, the dynamic material model suggests energy dissipation efficiency according to the flow stress of the material. However, the energy dissipation efficiency merely numerically represents the change in flow stress, not the metallurgical behavior of the material. Therefore, it is necessary to understand the difference in energy dissipation efficiency in relation to the high-temperature deformation mechanism. In this study, high temperature compression tests were performed on the Ti6Al4V alloy. The temperature range was set at 800°C³1200°C at intervals of 50°C, and the strain rate was set at 1 © 10 0 /sec³1 © 10 ¹3 /sec at intervals of 10 ¹1 /sec. Based on the results of the experiments, flow stress and processing maps were derived, and the high temperature plastic deformation behaviors of Ti6Al4V alloy were analyzed in correlation with the microstructural changes and mechanical properties according to temperature and strain rate. And the prior beta grain size according to the difference in energy dissipation efficiency was explained for each condition.

Ti-6Al-4V alloys are used in various industrial fields such as aircraft parts due to its excellent specific strength and mechanical properties. A high-temperature forming technology has been applied because it is difficult to process complex shapes. During the high-temperature forming process, the microstructure changes significantly due to temperature, strain rate, reduction ratio, and other process variables, and mechanical properties of high-temperature molded products are changed accordingly. Therefore, in this study, a high-temperature compression test was performed on AMS4928, which is one of Ti-6Al-4V alloys used as a material for aircraft parts, and the severe plastic deformation and dead zone were confirmed in connection with the processing map. The changes in microstructure were comparatively analyzed. In addition, it was confirmed that there was a difference in formability due to grain refinement by dynamic recrystallization, and optimal high-temperature forming conditions were derived by linking and analyzing the formability and microstructural factors.

General austenitic stainless steel has a problem with intergranular corrosion due to volatilizing chromium, which forms chromium carbide in a high temperature environment. By adding titanium as an alloying element, STS 321 stainless steel has excellent creep resistance and intergranular corrosion resistance at high temperatures, because the formation of chromium carbide is suppressed. It is important to find the optimal process conditions for STS 321 stainless steel used in the aerospace field, because high temperature processing is mainly applied, and defects or inhomogeneity of materials that occur during high temperature processing lowers the yield of products. In this study, to investigate the effect of the initial microstructure on the high-temperature deformation behavior of STS 321 stainless steel, a high-temperature compression test was performed on two types of STS321 alloys with different initial microstructures. The temperature range was set at 50°C intervals from 800°C to 1100°C, and the strain rate was set at 10^-1/sec intervals from 1 × 100/ sec to 1 × 10^-3/sec. Based on the experimental results, the thermal activation energy, which differed depending on differences in the initial microstructure, was calculated. In addition, by deriving flow stress and processing maps, the difference in energy dissipation efficiency depending on temperature and strain rate was explained, along with the initial microstructure and high-temperature deformation mechanism.