Chemical, Physical, and Mechanical Properties and Microstructures of Laser-Sintered Co-25Cr-5Mo-5W (SP2) and W-Free Co-28Cr-6Mo Alloys for Dental Applications

Yoshimitsu Okazaki; Akira Ishino; Shizuo Higuchi

doi:10.3390/ma12244039

Chemical, Physical, and Mechanical Properties and Microstructures of Laser-Sintered Co-25Cr-5Mo-5W (SP2) and W-Free Co-28Cr-6Mo Alloys for Dental Applications

Materials (Basel). 2019 Dec 4;12(24):4039. doi: 10.3390/ma12244039.

Authors

Yoshimitsu Okazaki¹, Akira Ishino², Shizuo Higuchi³

Affiliations

¹ National Institute of Advanced Industrial Science and Technology, 1-1 Higashi 1-chome, Tsukuba, Ibaraki 305-8566, Japan.
² IDS Co., Ltd., 3-5-4 Hongo, Bunkyo-ku, Tokyo 113-0033, Japan.
³ Graduate School of Oral Health Sciences, Osaka Dental University, 1-4-4 Makinohonmachi, Hirakata City, Osaka 573-1144, Japan.

Abstract

We examined the chemical, physical, and mechanical properties and microstructures of laser-sintered Co-25Cr-5Mo-5W (SP2) and W-free Co-28Cr-6Mo alloys. The tensile and fatigue properties of the laser-sintered Co-Cr-Mo alloys were extremely superior to those of dental-cast alloys. The ultimate tensile strength (σ_UTS) and total elongation (T.E.) were close to those of hot-forged Co-28Cr-6Mo alloys. The fatigue strengths (σ_FS) at 10⁷ cycles of the 90°-, 45°-, and 0°-direction-built Co-28Cr-6Mo alloys were ~500, ~560, and ~600 MPa, respectively. The ratio σ_FS /σ_UTS was ~0.4. These superior mechanical properties were attributed to the fine π-phase particles in the grains and grain boundaries of the fine face-centered cubic (fcc) matrix formed owing to the rapid solidification. The chemical composition of 20-times-laser-sintered Co-Cr-Mo alloy without the virgin powder added was approximately the same as that of the alloy laser-sintered with the virgin powder. σ_FS of the 90°-direction-built alloys after laser sintering 20 times was also ~500 MPa. σ_UTS of hot-forged Co-28Cr-6Mo alloys decreased with increasing annealing temperature, whereas T.E. increased. For the Co-Cr-Mo alloys annealed at 1000 to 1150 °C for 30 min after laser sintering, the rates of decrease in σ_UTS were small. σ_FS/σ_UTS increased to near those of annealed Co-28Cr-6Mo alloys after hot forging. The durability of clasps fabricated by laser sintering was superior to that of dental-cast clasps.

Keywords: cobalt–chromium–molybdenum alloys; dental prostheses; fatigue property; laser sintering; microstructure; physical property; tensile property.