Application of Harmonic Structure Design to Biomedical Co–Cr–Mo Alloy for Improved Mechanical Properties

Abstract

Harmonic structure is a recently introduced concept for material microstructure design. It is essentially a bimodal microstructure in which deliberately introduced structural heterogeneity has a specific order: interconnected network of ultra-fine grained (UFG) regions, called "shell area", and coarse-grained regions called "core area". Such microstructural features dictate a unique set of properties to the Harmonic-structured materials. The present paper deals with the application of harmonic structure design to biomedical CoCrMo alloys for improved mechanical properties. In the present work, it has been demonstrated that full density CoCrMo alloy compacts with harmonic structure can be successfully prepared by controlled mechanical milling followed by spark plasma sintering of the pre-alloyed powders at 1323 K for 3.6 ks. Sintered compacts exhibited an excellent combination of strength and ductility. Moreover, it has been also shown that the mechanical properties depend strongly on the volume fraction of the inter-connected three-dimensional network of fine-grained regions, i.e., shell volume fraction. In addition, the plastic deformation of harmonic structure CoCrMo alloy also led to ¡-FCC to ¾-HCP allotropic transformation. Therefore, the application of harmonic structure design leads to the new generation microstructure of biomedical CoCrMo alloys, which demonstrates outstanding mechanical properties compared to conventional materials.

Application of Al-Si Semi-Solid Reaction for Fabricating Harmonic Structured Al Based Alloy

“…It appears that the plastic deformation is only limited to the surface of the powder particles. Similar morphological observations have been reported also in literature 9,12,13) . Moreover, it is also noticed that the Si particles have fragmented to signi cantly smaller particle size after mechanical milling.…”

“…Recently, Ameyama and co-workers have proposed a microstructural design to improve mechanical properties by obtaining both high strength and high ductility in metallic materials, through the formation of so-called harmonic structured material [1][2][3][4][5][6][7][8][9][10][11][12][13] . Essentially, it is an exquisite heterogeneous microstructural design, consisting of bimodal grain size distribution, in which ductile coarse grained regions (termed as core ) are enclosed in a continuously connected three-dimensional networks regions with high strength ultra-ne grained structure, known as shell .…”

Three-dimensionally gradient harmonic structure design: an integrated approach for high performance structural materials

“…To deal with the above-mentioned issues of controlled heterogeneous microstructure, Ameyama et al proposed an integrated approach to prepare bulk materials with a controlled and unique heterogeneous microstructure, called 'harmonic structure' (HS), with bimodal grain size distribution. [15][16][17][18][19][20][21][22][23][24][25] A schematic diagram illustrating the HS design is shown in Figure 1. The HS is a heterogeneous microstructure with a specific spatial distribution of fine and coarse grains, that is, the CG areas ('core') embedded in the matrix of three-dimensional continuously connected network ('shell') of fine-grained (FG) areas.…”

“…It has also been demonstrated that the shell/core fraction can be successfully controlled by controlling milling time and number of milling passes in BM process and JM process, respectively. [19][20][21][22] The milled bimodal powders are consolidated at elevated temperatures to prepare bulk materials. Recently, spark plasma sintering (SPS) has been used extensively for the consolidation due to rapid sintering together with avoidance of deformation induced texture during consolidation process.…”

Influence of alloying elements on the mechanical properties of a cobalt-based alloy produced with powder metallurgy

“…Cobalt endoprostheses are non-magnetic, have suitable mechanical properties, corrosion resistance to the body fluids and also a good biocompatibility with the body´s environment. [2][3][4] The mechanical properties of cobalt-based alloys, and of the other metallic materials, are primarily dependent on the chemical composition, microstructure and their manufacturing processes. 5 Pure cobalt exists in two allotropic modifications.…”