Research On Microstructure And Properties Of 316L Stainless Steel Fabricateded By Selective Laser Melting

Selective laser melting(SLM),as a promising additive manufacturing technology,has been widely used in manufacturing.Compared with traditional casting,components with complex shapes can be directly processed by SLM,without the need to design and manufacture molds,and parts fabricated by SLM will maintain good mechanical properties.316L stainless steel(SS)has broad prospects in aerospace,petrochemical and other fields due to its excellent corrosion resistance,ductility,biocompatibility,low price and structural stability,and has been the first material used in SLM process.However,its low strength,serious intergranular corrosion,low surface hardness and poor wear resistance hinder its engineering application.Therefore,in order to improve its service life under complex working conditions,it is urgent to improve its performance.In recent years,metal powder particle reinforced stainless steel composites have been widely used in various industries because of their high strength,high stiffness,excellent corrosion resistance and wear resistance.However,the traditional smelting and casting technology is difficult to improve the severe microstructure segregation caused by additive segregation.At the same time,the mechanical,corrosion resistance and friction and wear properties of the parts prepared by casting methods are lower than those of parts fabricatd by SLM.Therefore,considering the advantages of SLM forming,it is used to manufacture metal particle reinforced 316L SS composites.Firstly,in order to improve the strength and corrosion resistance of 316L SS performance different mass fraction(3%and 10%)of tungsten(W)particles were added to 316L SS powder respectively and then they would be processed with a SLM equipment.Compared with the pure 316L SS,after adding W,the strength of the samples and corrosion resistance had been improved.Among of them,the Yield strength(YS)of 10 wt%W/316L SS samples increased from 627 MPa to 980 MPa,and it had good elongation(19%).The YS of 3wt%W/316L SS samples increased by 5%and the original elongation was maintained.In addition,3 wt%W on corrosion resistance of the most significant ascension,the corrosion current density from 10.1 ?Acm-2 to 3.36 ?Acm-2,at the same time,the charge transfer resistance increased by 30 times.Generally,the lower the corrosion current density and the higher the charge transfer resistance,the better the corrosion resistance.But the gorrosion resistance was not positively related to the content of W,due to excessive heavy metal element W would lead to ferrite formed in the substrate,which would be the starting point of corrosion resulting in local corrosion deterioration.The increase in strength and the change in corrosion resistance could be attributed to the microstructure changes caused by the introduction of W particles.Secondly,Nb/316L SS composites were prepared to improve the intergranular corrosion of 316L SS and reduce its susceptibility to sensitization.The results showed that the electrochemical corrosion properties of the samples were improved after adding Nb particles.The corrosion potential(Ecorr)changed from-288 mV to-191 mV.The corrosion current density(Icorr)decreased from 1.23 ?Acm-2 to 0.78 ?Acm-2.The pitting potential also increased by 140 mV.The surface charge transfer resistance increased.The DOS value of grain boundary sensitization index decreased from 0.242 to 0.097,and the lower the value,the smaller the sensitization tendency.Nb had affinity with C,which inhibited the formation of Cr and C compounds.The phenomenon of local Cr deficiency would be improved.In addition,the introduction of Nb led to an increase in the frequency of high angle grain boundaries(HAGBs),which meant that the total grain boundary length decreases.Compared with the interior of the grain,the energy at the grain boundary was higher,where the atom was in an unstable state leading to the initial position of corrosion.Therefore,the decrease of the grain boundary length contributed to the improvement of its corrosion resistance.Moreover,Nb promoted the formation of surface passivation film and increased the proportion of inner passivation film(Cr,Mo,Nb and other oxides),which led to a large charge transfer resistance and prevented further corrosion of substrate by corrosive media such as Cl-through surface passivation filmFinally,the effects of different WC contents(0.5%,1.5%,3%)on the surface hardness and wear property were investigated.The results showed that the surface hardness was positively correlated with WC contents,increasing from 221 HV to 269 HV.The coefficient of friction(COF)has negative correlation with the WC contents,from 0.78 to 0.16.Therefore,WC could significantly improve the surface performance.The causes of the properties change were analyzed by the microstructure and the wear morphology.With the increase of WC contents,the grain size decreased successively,and the surface hardness increased.The higher the hardness,the better wear performance.In addition,the proportion of low angle grain boundary(LAGBs)increased,which led to the dislocation density increasing.Then,the ability to resist deformation would increase,which contributed to the change of wear mode from abrasive wear to adhesive wear.All the samples showed two wear modes,abrasive wear and adhesive wear.The abrasive path surface of the sample containing 3wt%WC was relatively flat and shallow,which represented a lower wear rate,consistenting with the lower COF,indicating the best wear performance.