Strain-Induced Martensitic Transformation and Texture Evolution in Cold-Rolled Co–Cr Alloys

Abstract

Co–Cr alloys have been used in biomedical purposes such as stents and artificial hip joints. However, the difficulty of plastic deformation limits the application of the alloys. During the deformation, Co–Cr alloys often exhibit strain-induced martensitic transformation (SIMT), which is a possible reason for the low formability. The distinct increase in dislocation density in the matrix phase may also result in early fractures. Since these microstructural evolutions accompany the textural evolution, it is crucial to understand the relationship among the SIMT, the increase in dislocations, and the texture evolution. To characterize those at the same time, we conducted time-of-flight neutron diffraction experiments at iMATERIA beamline at the Japan Proton Accelerator Research Complex (J-PARC) Materials and Life Science Experimental Facility (MLF), Ibaraki, Japan. The cold-rolled sheets of Co–29Cr–6Mo (CCM) and Co–20Cr–15W–10Ni (CCWN) alloys were investigated in this study. As expected from the different stacking fault energies, the SIMT progressed more rapidly in the CCM alloy. The dislocation densities of the matrix phases of the CCM and CCWN alloys increased similarly with an increase in the rolling reduction. These results suggest that the difference in deformability between the CCM and CCWN alloys originate not from the strain hardening of the matrix phase but from the growth behaviors of the martensitic phase.

Keywords

• Co–Cr alloy
• strain-induced martensite transformation
• neutron diffraction
• iMATERIA
• texture
• phase fraction
• dislocation density
• CMWP method