Fabrication and characterization of high-strength refractory AlMo$_{0.5}$NbTa$_{0.5}$TiZr and AlMo$_{0.5}$Nb(TaW)$_{0.5}$TiZr High Entropy Alloy

Abstract

Different from conventional alloys composed of one main element with addition of minor elements, High Entropy Alloys (HEAs) consist of 5-13 metallic elements with equi- or near equi-atomic ratio. Due to the characteristics of the high entropy alloys: High mixing entropy, severe lattice distortion because of atomic size difference, sluggish diffusion rate, and cocktail effect, HEAs exhibit excellent mechanical properties and attract a wide spread attention. Therefore, a variety of the research of new HEA systems have been conducted. The fabricate process of refractory HEAs is mainly focused on arc-melting and casting process which has following problems: inhomogeneous microstructure because of segregation of alloy elements, grain coarsening during the cooling. In this study, powder metallurgical process (PM) was applied to fabricate the refractory HEAs to homogenize the microstructure and enhance the mechanical properties. Here, two refractory HEA system of AlMo$_{0.5}$NbTa$_{0.5}$TiZr and AlMo$_{0.5}$Nb(TaW)$_{0.5}$TiZr was produced and characterized. AlMo$_(0.5)$NbTa$_(0.5)$TiZr HEA is known for its excellent mechanical property at room temperature, low density, but low elongation at room temperature, low strength at temperature higher than 1000$^\circ C$ with expensive cost of raw materials. To reduce the contaminations during the mechanical alloying, minimum time of mechanical alloying was conducted. HEA bulks were prepared by spark plasma sintering. Different sintering temperatures were employed to compare the properties. The mechanical properties of fabricated bulk specimen were evaluated by Vickers hardness test and compressive test. Consequently, it was obvious that the HEAs fabricated by powder metallurgical process exhibit enhanced mechanical properties than those of arc-melting and casting process. Addition of W effectively improved mechanical properties at elevated temperature. Based on this study of fabricating refractory HEAs by powder metallurgical process, it is expected to develop further research to find new refractory high entropy alloys and improve the mechanical properties by grain growth.