Effect of High Temperature on Microstructure and Hardness of Ti-6Al-4Dy Alloy by High Energy Ball Milling and Spark Plasma Sintering

In this study, Ti-6wt%Al-4wt%Dy and Ti-6wt%Al-4wt%V were prepared by high energy ball milling and spark plasma sintering(SPS). A high energy ball milling was conducted in an argon atmosphere at 800rpm for 3h to produce alloy powders. Subsequently, the obtained powders were consolidated by SPS at 1373K for 15min under 50MPa in vacuum. The sintered bodies of Ti-6Al-4Dy and Ti-6Al-4V both had an approximate density of 99%, with grain sizes of 6μm and 2.6μm, respectively. In Ti-6Al-4Dy, secondary phases such as Ti3Al, Al3Dy, and Ti4Al20Dy were confirmed by XRD and TEM. In Ti-6Al-4V, only the alpha phase of Ti was confirmed. At temperature ranging from 300K to 1173K, the micro hardness of both Ti-6Al-4Dy and Ti-6Al-4V alloys decreased with increasing temperature, and the Ti-6Al-4V was harder at all temperatures. XRD analysis of Ti-6Al-4Dy and Ti-6Al-4V revealed no discernible changes in peaks after high temperature hardness test. However, the grain size increased from 6 to 10μm and 2.6 to 3.4μm in Ti-6Al-4Dy and Ti-6Al-4V alloys, respectively. It was concluded that this difference in grain size was the main reason for the hardness decreased at high temperature.