title: Local strain evolution due to athermal γ→ε martensitic transformation in biomedical CoCrMo alloys.
abstract: Locally developed strains caused by athermal γ face-centered cubic (fcc)→ε hexagonal close-packed (hcp) martensitic transformation were investigated for the γ matrix of Ni-free Co-29Cr-6Mo (wt%) alloys prepared with or without added nitrogen. Electron-backscatter-diffraction-(EBSD)-based strain analysis revealed that in addition to ε-martensite interiors, the N-free alloy that had a duplex microstructure consisting of the γ matrix and athermal ε-martensite plates showed larger magnitudes of both elastic and plastic strains in the γ phase matrix than the N-doped counterpart that did not have a ε-martensite phase. Transmission electron microscopy (TEM) results indicated that the ε-martensite microplates were aggregates of thin ε-layers, which were formed by three different {111}γ〈112¯〉γ Shockley partial dislocations in accordance with a previously proposed mechanism (Putaux and Chevalier, 1996) that canceled the shear strains of the individual variants. The plastic strains are believed to have originated from the martensitic transformation itself, and the activity of dislocations is believed to be the origin of the transformation. We have revealed that the elastic strains in the γ matrix originate from interactions among the ε-martensite phase, extended dislocations, and/or thin ε-layers. The dislocations highly dissociated into stacking faults, making stress relaxation at intersections difficult and further introducing local strain evolution.
authors.affiliation: Institute for Materials Research, Tohoku University, 2-1-1 Katahira, Aoba-ku, Sendai 980-8577, Japan. Electronic address: k_yamanaka@imr.tohoku.ac.jp.
authors.forename: Kenta
authors.initials: K
authors.lastname: Yamanaka
authors.affiliation: Department of Materials and Environmental Engineering, Sendai National College of Technology, 48 Nodayama, Medeshima-Shiote, Natori 981-1239, Japan.
authors.forename: Manami
authors.initials: M
authors.lastname: Mori
authors.affiliation: Institute for Materials Research, Tohoku University, 2-1-1 Katahira, Aoba-ku, Sendai 980-8577, Japan.
authors.forename: Yuichiro
authors.initials: Y
authors.lastname: Koizumi
authors.affiliation: Institute for Materials Research, Tohoku University, 2-1-1 Katahira, Aoba-ku, Sendai 980-8577, Japan.
authors.forename: Akihiko
authors.initials: A
authors.lastname: Chiba
mesh_terms: D000497:Alloys / Q000737:chemistry*; D001672:Biocompatible Materials / Q000737:chemistry*; D002857:Chromium / Q000737:chemistry; D003035:Cobalt / Q000737:chemistry; D003722:Dental Alloys / Q000737:chemistry*; D004548:Elasticity; D008422:Materials Testing; D008982:Molybdenum / Q000737:chemistry; D013314:Stress, Mechanical; D013696:Temperature
chemical_list: D000497:Alloys; D001672:Biocompatible Materials; D003722:Dental Alloys; D002857:Chromium; C093824:Martensite; D003035:Cobalt; D008982:Molybdenum
keywords: Biomedical CoCrMo alloys; Electron backscatter diffraction (EBSD); Local strain distribution; Martensitic transformation; Transmission electron microscopy (TEM)