Study On Fatigue Crack Growth Of 316L Stainless Steel By Selective Laser Melting (SLM)

Selective Laser Melting(SLM)is a technique in which metal powder is completely melted under the action of the heat of the laser beam and solidified by cooling.The essence is welding,so there must be pores in the process.This paper mainly studied the fatigue crack growth performance of 316 L prepared by SLM,and provided ideas and basic data accumulation for the actual production of SLM 316 L parts.The research had strong engineering practical value.To study 316 L sample under different process parameters of the difference of the fatigue crack propagation performance exists in this paper,through the energy density in a different direction,different process parameters for the preparation of the various conditions of 316 L,room temperature tensile and compact tension specimen,and with the aid of optical microscope,scanning electron microscopy(SEM)and a series of experimental tools to measure vickers hardness,density,microstructure examination and fracture morphology and related parameters.Instron hydraulic servo fatigue testing machine was used to conduct unidirectional tensile test and fatigue crack propagation test on 316 L stainless steel samples prepared by SLM.The experimental results showed that the porosity first increases and then decreases with the increase of the forming Angle,but the surface hardness is independent of the forming Angle.SLM forming Angle has no obvious influence on fatigue crack growth rate,and SLM forming energy density has obvious influence on fatigue crack growth rate.As energy density increases,crack growth rate first increases and then decreases.There are two morphologies of fatigue crack propagation fractures formed in SLM horizontal direction and vertical direction.At the stage of steady crack growth,the fracture presents fluvial striation,accompanied by cleavage steps and secondary cracks,and presents brittle transgranular fracture characteristics.At the stage of rapid instable crack propagation,the fracture has a large number of dimples and is characterized by ductile fracture.This experimental study can better guide the actual production and manufacture of 316 L SLM,so as to obtain SLM products more in line with the expectations.In this paper,the effects of process parameters(forming angle and energy density)on the fatigue crack growth performance of 316 L prepared by SLM were studied.By comparing various mechanical parameters,the fatigue of 316 L samples prepared under different parameters was analyzed systematically.There are differences in crack propagation performance.However,due to the limitations of experimental conditions and experimental time,only some process parameters are selected as research objects.The processing parameters can be further subdivided in order to further understand the influence of process parameters on the fatigue crack growth performance of SLM molded parts.