Research On Process,Microstructures And Strengthening Of Metallic Material Matrix Via Phase Compositing For Laser Additive Manufacturing

The materials used in selective laser melting(SLM)are mainly metal materials.The mechanical properties of SLM metal parts can be improved by the adjustment of process parameters.Another important strengthening technology is the phase regulation by introducing ceramic strengthening phase.Metal matrix composites(MMCs)can be fabricated by SLM.In this paper,nano-ceramic particles were introduced into the metal materials.Two kinds of metal matrix composite parts,V8C7/316L stainless steel and TiN/FeCoCrNiMn high-entropy alloys(HEA),were successfully fabricated by SLM process.The microstructure of the SLM samples under different process parameters was characterized,and the mechanical properties of the samples were tested.The evolution mechanism of the phase and microstructure was revealed,and the strengthening mechanism of mechanical properties was highlighted.This paper mainly works from the following aspects:(1)V8C7/316L and TiN/FeCoCrNiMn mixed powders were prepared by ball milling method,and the ceramic particles were uniformly dispersed in the metal powders.By changing the laser power,scanning speed and scanning spacing,the effects of different SLM process parameters on the density and microstructure of the samples were studied,and optimized process window were obtained.The results show that the relative density of the samples can be increased by increasing the laser energy density in a certain range.(2)The microstructures of V8C7/316L stainless steel and TiN/FeCoCrNiMn HEA were studied by XRD,FE-SEM,EDS,EBSD and other detection methods.It could be observed that the V8C7 particles decomposed during the rapid melting of the SLM process,and precipitated into various VC.metastable phases in the 316L matrix during the subsequent rapid solidification process.The VCx metastable phases were mainly distributed in the 316L matrix grain boundary and its substructure interface.TiN particles can also achieve a uniform dispersion distribution in the HEA matrix after SLM.The introduction of nanometer or submicron ceramic particles was helpful for the metal matrix grains to form ultra-fine near-equal crystals during rapid laser melting-solidification process.(3)The mechanical tensile tests were carried out on the V8C7/316L and TiN/FeCoCrNiMn HEA samples respectively.Compared with the mechanical properties of the original alloy prepared by SLM,it could be observed that the introduction of ceramic particles had obvious strengthening effect on the SLM metal matrix.Combined with the microstructure evolution mechanism of V8C7/316L and TiN/FeCoCrNiMn HEA,and the distribution rule of ceramic reinforcing particles in the metal matrix,the strengthening mechanism of SLM forming metal matrix composites was clarified.The research results in this paper can provide theoretical support for the material design,process regulation and performance enhancement of SLM formed MMCs.