HIGH-ENTROPY METAL DIBORIDES: A NEW CLASS OF ULTRAHIGH TEMPERATURE CERAMICS

摘要

Several equimolar, five-component, metal diborides were fabricated via high-energy ball milling and spark plasma sintering [Scientific Reports 6:37946 (2016)] or conventional pressure-less sintering. Most compositions synthesized, e.g., (Hf_(0.2)Zr_(0.2)Ta_(0.2)Nb_(0.2)Ti_(0.2)B2, (Hf_(0.2)Zr_(0.2)Ta_(0.2)Mo_(0.2)Ti_(0.2)B_2 and several others, processed single solid-solution phases of the hexagonal AIB2 structure, while a few other compositions yielded two or more boride phases. These materials represent a new type of ultra-high temperature ceramic (UHTC) as well as a new class of high-entropy materials that possess a non-cubic (hexagonal) and layered (quasi-2D) crystal structure (Fig. 1). A density functional theory (DFT) based partial occupation method was implemented within the AFLOW to calculate energy distributions that were used to construct a descriptor to predict the formation and stability of these high-entropy materials. DFT based modeling of charge disorder and lattice distortions have also been conducted. Results from the most recent on-going studies of processing optimization, mechanical testing, and oxidation measurements of these high-entropy metal diborides will also be presented and discussed.