Research On Microstructure And Mechanical Properties Of Iron-based Materials Fabricated By Indirect Additive Manufacturing

At present,the research on indirect additive manufacturing techniques for metals,such as binder jetting（3DP）,fused deposition modelling（FDM）,and powder extrusion printing（PEP）,is still in the very early stage of trial and feasibility exploration.Quite a lot of in-depth research needs to be done as soon as possible for feedstock metal powder properties,printing-debinding-sintering-heat treatment processes,and microstructure and mechanical properties.In addition,few comparative studies on various indirect additive manufacturing techniques have been reported in previous study.Taking 316 L stainless steel as a typical iron-based material,and employing binder jetting（3DP）and powder extrusion printing（PEP）as the main additive manufacturing techniques,this paper systematically made the comparative research between 3DP and PEP of iron-based materials on printing process,technique features of printing-debinding-sintering-heat treatment post sintering,densification mechanism,and microstructure evolution,and constructed the process specification for printing,debinding,and sintering.In this study,the particle size range of 316 L stainless steel suitable for 3DP and PEP processes has been determined,and the organic binder mainly based on PW and MW has been successfully developed for PEP process.And therefore,two kinds of feedstock pellet with different particle sizes of 316 L stainless steel have been prepared.The relative density of3 DP and PEP processed 316 L stainless steel has exceeded 98% upon sintering process.It was found that the initial powder particle size has an significant effect on the final austenite grain size and mechanical properties of 3DP and PEP processed 316 L stainless steel.The comparative study between 3DP and PEP process on 316 L stainless steel shows that the particle size range of metal powder suitable for PEP is significantly larger than that of 3DP.Compared with PEP,3DP has a longer printing cycle and 3DP green parts need to be solidified for a long time after printing,but more samples can be processed at a time.PEP has a shorter printing cycle,but it is difficult for PEP to print more samples at a time.The debinding time of 3DP green parts is significantly less than that of PEP ones.The microstructure and mechanical properties of sintered 3DP and PEP parts from the same 316 L stainless steel powder are similar,and the tensile strength of sintered 3DP and PEP parts is higher than that of the traditionally processed ones but lower than that of selective laser melting（SLM）processed ones.However,the process cost is lower and the fabrication efficiency is higher for 3DP and PEP as compared with those for SLM,so both 3DP and PEP techniques have good commercial application prospect.