Influence of mechanical surface treatments on fatigue strength of commercial purity titanium

Abstract

A comparative study of two mechanical surface treatments of shot peening (SP) and cold rolling (CR) on fatigue strength of commercial purity titanium has been conducted. The treated surface was characterized by using transmission electron microscopy (TEM), X-ray diffraction (XRD), and surface roughness measurements. Experimental result shows that SP and CR increased the fatigue strength of commercial purity titanium, and moreover, the following results were obtained: (1) The improvement of fatigue strength is related to the formation of deformation twins in strengthened layer. Before or after fatigue, the samples strengthened by SP or CR not only have twin shape and number change, but also have twin interactions in the SP and twin-grain boundary interactions in the CR. (2) XRD measurement demonstrated that SP leads to surface compressive residual stress are much higher than those after CR. Surface compressive residual stress has higher relaxation in the SP than in the CR condition during cyclic loading, then the surface compressive residual stress has the same values after fatigue deformation. (3) Surface roughness resulting from SP is ten times of CR.