The effect of PVD coatings on the tensile strength and low-cycle fatigue resistance of stainless steel and titanium alloys

Abstract

PVD coatings applied to components form hard, stronger layers and generate high residual compressive stresses that limit the plastic deformation in surface layers of the base metal thus increasing its tensile strength and resistance to fatigue loading. The purpose of this paper is to experimentally determine the influence of the deposition of 2 to 16.5-μm-thick PVD coatings of TiN, Cr, (Cr+TiN), (TiC)N, (TiAl)N onto specimens of stainless steel 321 and titanium alloys of types MILT-81556A and (10-2-3; 4966) on their tensile strength and low-cycle fatigue resistance when the development of large elastic–plastic strains takes place. The tensile and low-cycle fatigue tests were conducted under conditions of axial zero-to-tension cycle of the stress-controlled loading on flat 1- to 1.5-mm-thick specimens in the initial state (uncoated specimens) and after application of a PVD coating, including those after pretensioning or after cyclic prestraining in the low-cycle fatigue range. The deposition of PVD coatings is found to enhance the characteristics of tensile strength and low-cycle fatigue resistance in the quasi-static fracture range. The deposition of PVD coatings on specimens cyclically prestrained to the values of 53–86% of the number of cycles to fracture, changes the cyclic properties of the material and predetermines the fatigue fracture mode only.