Modeling and characterization of MoNbTiW refractory multi-principal element alloy

Abstract

Refractory multi-principal element alloys (RMPEAs) have great potential for high temperature applications such as aerospace propulsion systems, terrestrial gas turbines, and nuclear reactors. However, such applications are limited due to the brittleness presented by RMPEAs at room temperature. In this work, an alloy with refractory elements is produced and characterized. These elements are Mo and W, and Nb and Ti exhibiting high melting points and high elastic moduli, respectively. CALPHAD simulations are used to determine phase stability. With this, a stable BCC-A2 phase between 730ºC and 2180ºC is attained. Results from the evolutionary search coupled with the Debye model also indicate the stability of the BCC-A2 phase above 1276 C. The X-ray diffraction pattern of the as-cast alloy suggests a single BCC-A2 phase. Energy dispersive spectroscopy mapping reveals a microstructure of a single BCC-A2 phase with Ti segregation. The mechanical characterization indicates a Vickers hardness of 5.58 GPa, a compressive yield strength of 1080 MPa, a fracture strength of 1300 MPa associated with a strain of 5.9%. This induces to good ductility combined with high mechanical strength at room temperature. These results, therefore, indicate that the MoNbTiW alloy has promise properties for high temperature applications.