Original paper(Vol.45 No.1 pp.43)
Effect of shot peening on fatigue strength of Ti-6Al-4V alloy at elevated temperatures
Kato Yozo; Takafuji Shinzaburo; Kiriyama Masaki
Abstract:(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 degree, 250 degree, 350 degree and 450 degree, 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 degree, 250 degree and 350 degree, and the increments were about 27%, 21% and 7%, respectively. The fatigue strength, however, was remarkably decreased by shot peening at 450 degree, and its decrement reached about 41%.
(2) The fatigue strength of the specimen shot-peened and then electro-polished was 470 MPa at 450 degree. 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 degree may be explained as follows. The compressive residual stress in the near-surface region induced by shot peening disappear during fatigue cycling at 450 degree, but the great surface roughness due to shot peening still remains, which reduce the fatigue strength of the shot peened specimen.
Key Words:fatigue strength, Ti-6Al-4V alloy, shot peening, elevated temperature, residual stress