Ultrasonic impact peening for the surface properties’ management

It is demonstrated that the ultrasonic impact peening (UIP) technique is a beneficial method for essential increase in the fatigue durability of metallic materials due to the surface nanocrystallization and hardening process provided for severe plastic deformation of surface via multiple impacts of high velocity impact pins. Nano-scale grain structures were obtained in the surface layers of stainless steel, low carbon steel weld and different titanium alloys using developed equipment for the UIP. Both the surface nanostructure and compressive residual stresses are shown to attribute to the essential hardness increase. It is revealed experimentally using profilometry that new modification of the UIP apparatus providing high velocity “sliding” impacts leads to marked diminution of the surface roughness, which is another important factor affecting to the fatigue cracks initiation process. The two-dimensional finite element model is used to simulate the indent formation process during single impaction. The solid steel pin and the Al alloy plate are modeled as a rigid material and an elasto-plastic material, respectively. It is shown that the surface roughness magnitude depends on the correlation of the vertical and lateral load components.