Constant industrial demand for alloys with increased mechanical properties has led to the development of high-entropy and multiprincipal element alloys. These class of alloys have been shown to exceed the mechanical properties of some commercial alloys due to their multicomponent mixtures and tendency for simple phase formation. Developing new materials that can overcome the strength-ductility trade-off has been one of the overarching themes of metals research. These classes of alloys are headed in the direction of being the next superalloys due to their unique microstructures and characteristics.
Researchers in Prof. Reza Abbaschian’s High-Pressure High-Temperature Materials Processing Laboratory (HPHT Lab) have developed a new multiprincipal element alloy (MPEA) consisting of near equal parts Co, Cr, Cu, Mn, and Ti that combines strength and fracture toughness due to its hard intermetallic microstructure encapsulated in a Cu-rich matrix (Fig. 1). HPHT Lab refers to this alloy as Chromantium. Additional alloying elements such as iron, carbon, boron, magnesium, or any of the rare earth elements may be added to this mixture to achieve similar microstructure and properties. Refining the amounts of the elements in the composition leads to a more uniform microstructure shown in Figure 2.
Unlike most commercial alloys, Chromantium has primary dendrites that have Hexagonal Close Packed (HCP) crystalline structure. As such, these extremely hard dendrites are embedded in a softer cubic Cu-rich matrix. The Vickers hardness values of the dendrites is 1000 HV, while the softer matrix is around 460 HV. The overall hardness encompassing both regions is 480 HV. While precise conversion from HV to Rockwell C is not available, the above numbers show hardness values in excess of 68 HRC for dendrites and around 46 HRC for the matrix. Direct measurement of HRC for the as-cast microstructure of the refined material composition in Fig. 2 has bulk Rockwell hardness of 43 HRC. For comparison, H13 tool steel has hardness ranging from 360 HV to 490 HV depending on composition and heat treatment.
These extreme hardness values make Chromantium desirable for applications that require hard materials and good wear properties.
Fig. 1 Dendritic microstructure of equiatomic CoCrCuMnTi
Fig. 2 Dendritic microstructure of refined Chromantium displaying a much more uniform microstructure when compared to the equiatomic composition in Fig. 1.