Boron Enhanced Complex Concentrated Silicides – New pathway for designing and optimizing ultra-high temperature intermetallic composite materials

Abstract

Refractory Metal Intermetallic Composites and Refractory Complex Concentrated Alloys have been identified as promising candidates for ultra-high-temperature applications that exceed the limits of superalloys. However, designing and developing new materials with the proper density for aerospace applications is a significant challenge. For this reason, new refractory metal-based materials are in continuous development. This study introduces a new class of materials known as Boron-Enhanced Complex Concentrated Silicides (BECCSs). By providing a balance between density and high-temperature performance, these materials with their density-optimized refractory metal silicide-borides have the potential to revolutionize high-temperature applications. Utilizing a quaternary MoNbTaW equiatomic alloy (ρ = 13.73 gcm−3) as a starting point and a computer-aided alloy modeling tool, seven alloy compositions were designed in a multi-step process aimed at lowering the material density. Through the introduction of Ti, Si, and/or B, the microstructure was transformed from a BCC solid solution to a multiphase structure comprised of silicides and borides. The proposed redesign of the alloy led to a significant reduction in density, even to 5.44 gcm−3. All seven alloys were produced by using a laboratory arc melter, and their microstructure and room-temperature mechanical properties were analyzed using SEM, EDS, EBSD, and micro-indentation. The results of structural characterization allowed us to identify specific phase constituents, and it was established that a transition from BCC solid solutions to silicides/borides-based alloys results in a substantial increase in hardness, even above 1600 H V (17 GPa).

Keywords

• Refractory high entropy alloys
• Silicides
• Borides
• Materials design
• Materials characterization