Harmonic structure design of Co-Cr-Mo alloy with outstanding mechanical properties. Choncharoen Sawangrat 1,a , Osamu Yamaguchi 1,b , Sanjay Kumar Vajpai 2,c and Kei Ameyama 3,d 1 Graduate school of Integrated Science and Engineering, Ritsumeikan University, Japan 2 Ritsumeikan Global Innovation Research Organization, Ritsumeikan University, Japan 3 Faculty of Science and Engineering, Ritsumeikan University, Japan a choncharoen@gmail.com, b rm0011xh@ed.ritsumei.ac.jp, c vajpaisk@gmail.com, d ameyama@se.ritsumei.ac.jp Keywords: mechanical milling, Co-Cr-Mo alloys, mechanical properties, harmonic structure. 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 nano-sized 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 ÐujgnnÑ. cpf *kk+ vjg eqctug itckpgf tgikqpu ecnngf ÐeqtgÑ0 Vjg ÐujgnnÑ cpf vjg ÐeqtgÑ eqttgurqpf vq 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 au ÐJctoqpke UvtwevwtgÑ0 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. Introduction Co-Cr-Mo alloy is widely used as structural and functional material due to its excellent wear resistance, corrosion resistance, and biocompatibility [1]. However, the areas of application of conventional coarse-grained (CG) Co-Cr-Mo alloys are often restricted because of their relatively low strength. Grain refinement via Severe Plastic Deformation (SPD) processing is an attractive way to improve the strength of metallic materials [2]. Although grain refinement via SPD leads to a significant improvement in the strength, the fine-grained structure exhibit poor ductility. Therefore, it is a necessity to develop a microstructural design wherein high strength and excellent ductility can be achieved at the same time. Recently, it has been demonstrated that a reasonable balance between strength and ductility can be achieved through a novel microstructural design, called ÐHarmonic structureÑ. The concept of Harmonic structure design has been successfully in materials such as pure Ti, Ti-6Al-4V and SUS316L [3,4,5]. Therefore, in the present paper, attempt has been made to apply the concept of Harmonic structure design to Co-Cr-Mo alloy to achieve improved mechanical properties. Cfxcpegf Ocvgtkcnu Tgugctej Xqn0 ;5; *4236+ rr 82/89 Æ *4236+ Vtcpu Vgej Rwdnkecvkqpu. Uykv¦gtncpf fqk<320624:1yyy0uekgpvkhke0pgv1COT0;5;082 Cnn tkijvu tgugtxgf0 Pq rctv qh eqpvgpvu qh vjku rcrgt oc{ dg tgrtqfwegf qt vtcpuokvvgf kp cp{ hqto qt d{ cp{ ogcpu ykvjqwv vjg ytkvvgp rgtokuukqp qh VVR. yyy0vvr0pgv0 *KF< 3:204903;;098/48126136.39<28<28+