Ti-6Al-4V合金の高温疲労強度に及ぼすショットピーニングの影響(<特集>疲労)

概要

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(1)The fatigue strength of the unpeened specimens of Ti-6Al-4V alloy was found to be 490 MPa, 430 MPa, 410 MPa and 440 MPa at 20℃, 250℃, 350℃ and 450℃, respectively. The respective values for the shot peened specimens were 620 MPa, 520 MPa, 440 MPa and 260 MPa. The fatigue strength was definitely increased by shot peening at 20℃, 250℃ and 350℃, and the increments were about 27%, 21% and 7%, respectively. The fatigue strength, however, was remarkably decreased by shot peening at 450℃, and its decrement reached about 41%. (2)The fatigue strength of the specimen shot-peened and then electro-polished was 470 MPa at 450℃. The fatigue strength greatly increased from 260 MPa to 470 MPa after polishing. The value of 470 MPa is comparable to 460 MPa of the fatigue strength of the unpeened specimen. The decrease in fatigue strength due to shot peening at 450℃ may be explained as follows. The compressive residual stress in the near-surface region induced by shot peening disappear during fatigue cycling at 450℃, but the great surface roughness due to shot peening still remains, which reduce the fatigue strength of the shot peened specimen.
1996-01-15