Harmonic Structure Design of Co-Cr-Mo Alloy with Outstanding Mechanical Properties

Abstract

Co-Cr-Mo alloy powders were subjected to controlled mechanical milling at room temperature under Ar atmosphere to fabricate bimodal microstructure in the MM powders, having nanosized grains in the surface region and micron-sized coarse grains in the center of the milled powders. Subsequently, the MM powder was compacted by spark-plasma sintering (SPS) process. The sintered compacts indicated two structure areas: (i) ultra-fine grained (UFG) regions, called shell, and (ii) the coarse grained regions called core. The shell and the core correspond to the surface and center of the MM powders, respectively. The shell regions established a continuous three dimensional network of high strength ultra-fine grained regions, which surrounded the discrete coarse grained ductile regions. Such a microstructure is referred as Harmonic Structure. The sintered Co-Cr-Mo alloy compacts exhibited outstanding mechanical properties. The yield strength increased from 605 to 635 MPa, and ultimate tensile strength increased from 1201 to 1283 MPa. Moreover, the elongation was maintained more or less same as that of coarse grained compacts. Therefore, the harmonic structure design leads to the new generation microstructure of Co-Cr-Mo alloy, which demonstrates outstanding mechanical properties, i.e. superior strength and excellent ductility as compared to conventional materials. Keywords: mechanical milling, Co-Cr-Mo alloys, mechanical properties, harmonic structure.