Abstract: Cast-steel shot peening was employed on directionally solidified alloy DZ125 to analyze the fatigue property,surface residual stress and microhardness profile under various shot peening intensity and coverage conditions.The results show that with the increase of shot peening intensity,the estimated median fatigue life increases gradually.At high intensity,the estimated median fatigue life at 700 ℃/500 MPa is 2 times that of the original specimen.Moreover,with the increase of surface coverage,the estimated median fatigue life increases first and then stabilizes,and when the coverage reaches 400%,the estimated median fatigue life is stable.When the shot peening intensity is high and at the coverage rate of 400%,the fatigue limit is 480 MPa,which is 20% higher than the original value (400 MPa).Residual stress and microstructure strengthening mechanism are the strengthening factors of shot peening for DZ125 alloy.With the increase of shot peening intensity,the residual compressive stress decreases slightly,but it is still obviously larger than the original state.When the shot peening intensity is high and at the coverage rate of 400%,the surface hardness field of DZ125 alloy exceeds 200 μm in depth,and the surface hardness is 37% higher than that of the matrix (430 HV0.1).When the actual load at the notch is greater than the yield strength,the residual stress and hardness are relaxed obviously during fatigue process;the surface residual stress of the fractured specimen decreases by 54% and the surface hardness decreases by 14% after 700 ℃/600 MPa/1.5×10⁵ cycles.

Key words: DZ125 alloy, shot peening intensity, surface coverage, fatigue, stress relaxation