Effects of Surface Modifications on Rotating Bending Fatigue of Ni-Al Bronze Alloy

Abstract

Surface modifications, including laser surface melting (LSM) and micro-shot peening (MSP), were applied to improve the fatigue performance of the Ni-Al bronze (NAB) alloy. LSM could homogenize the NAB into a uniform microstructure with refined columnar grains in the laser-melted zone but introduced residual tensile stress (RTS). The bombardment and generated heat induced by MSP could not entirely remove the granular kappa II precipitates and lamellar kappa III phase in the peened zone of the shot-peened sample (NSP sample) but introduced residual compressive stress (RCS) into the NSP sample under the peening intensity of this work. The results of fatigue tests revealed that the LSM sample had the poorest fatigue performance, but the NSP sample showed the best fatigue performance among the tested samples. The fatigue limit of the NAB alloy was about 325 MPa; meanwhile, the fatigue performance of the LSP (LSM + MSP) sample was equivalent to or a little better than that of the NAB alloy (NBM sample). The RTS and aligned columnar grains accounted for the degraded fatigue resistance of the LSM sample. By contrast, the high RCS and the refined structure were responsible for the improved fatigue strength/life of the NSP sample relative to that of the other samples. The fatigue limit of the NSP sample was as high as 450 MPa. However, the increase in fatigue strength of the NSP sample occurred in service life regions above 3 x 105 cycles.