Influence of Shot Peening on the Isothermal Fatigue Behavior of the Gamma Titanium Aluminide Ti-48Al-2Cr-2Nb at 750 °C

Abstract

One possibility to improve the fatigue life and strength of metallic materials is shot peening. However, at elevated temperatures, the induced residual stresses may relax. To investigate the influence of shot peening on high-temperature fatigue behavior, isothermal fatigue tests were conducted on shot-peened and untreated samples of gamma TiAl 48-2-2 at 750 °C in air. The shot-peened material was characterized using EBSD, microhardness, and residual stress analyses. Shot peening leads to a significant increase in surface hardness and high compressive residual stresses near the surface. Both effects may have a positive influence on lifetime. However, it also leads to surface notches and tensile residual stresses in the bulk material with a negative impact on cyclic lifetime. During fully reversed uniaxial tension-compression fatigue tests (R = −1) at a stress amplitude of 260 MPa, the positive effects dominate, and the fatigue lifetime increases. At a lower stress amplitude of 230 MPa, the negative effect of internal tensile residual stresses dominates, and the lifetime decreases. Shot peening leads to a transition from surface to volume crack initiation if the surface is not damaged by the shots.

Archives of Metallurgy and Materials

“…that reported shot peening leads to high compressive residual stresses and increased surface hardness of the specimens due to work hardening. Stress-free annealing at 750 _C for 8 h reduces both effects; however, they are still significant [25].…”

Laser shock peening: a promising tool for enhancing the aeroengine materials’ surface properties

“…To attain better surface properties, several surface modification techniques are available such as shot peening [34,35], laser shock peening (LSP) [19,20,23,36], deep rolling [30,37,38], ultrasonic peening [39], water jet peening [40] and low plasticity burnishing (LPB) [41] or a combination of these are used by industry to enhance the surface properties to enhance the resistance against surface originated failures [42,43]. Among these techniques, shot peening has been commercially used in the aerospace industry for past decades due to its advantages, such as robust and economical, induced compressive residual stress on the surface and near-surface work hardening [41,[44][45][46][47]. However, it damages the surface by imposing a high degree of roughness, also the induced CRS are not thermally stable (CRS relaxation rate increases when exposed to high temperature; this might be due to the high cold work during the shot peening process) [48] which leads to the probability of accelerating the failure and also requires frequent maintenance.…”