Fatigue damage assessment of SUS316L using EBSD and PALS measurements

Abstract

Kernel averaging misorientation (KAM) measurements and positron annihilation lifetime spectroscopy (PALS) were conducted to investigate the damage introduced by the tensile and fatigue testing of type 316L stainless steel. The fatigue tests were carried out at room temperature and at 550 °C under the strain controlled mode with total strain amounts, Δε of 0.4% and 1.5%. A number of different samples were prepared by interrupting the fatigue test at various ratios of fatigue cycle time to fatigue lifetime. Both KAM and PALS analyses indicated increasing damage as increasing misorientation average or number of vacancies with increasing strains in tensile- and fatigue-tested samples. Dislocations play an important role in the evolution of damage as they produce vacancies and form dislocation structures. In the fatigue test at high temperature, accelerated dislocation relaxation encourages formation of dislocation structures that result in an early increase in misorientation. Under the same conditions, the positron lifetime rather decreased because of the migration of defects at early stages of fatigue and rapidly increased at fracture. We observed different responses to mechanical straining that can be useful for evaluation of damage in 316L stainless steel.