Study On The Preparation Process And Properties Of Spherical Mo Metal Particle Enhanced Stainless Steel

Particle reinforced metal matrix composite(PRMMCs)is a new material made of pure metal or alloy as matrix,with high strength and high modulus second phase particles as reinforcement.The traditional method is difficult to achieve the direct molding of complex parts,and the addition of enhanced particles leads to the cutting performance difference of PRMMCs and the alloy,which brings difficulties to the final processing of the parts.Laser selective melting(Selective Laser Melting,SLM)combines the advantages of rapid laser solidification and powder metallurgy,and shows great advantages in the preparation of complex structures and PRMMCs.Based on the selective laser melting(SLM)process,Mo/316 L stainless steel composites(MPR-SSCs)were successfully prepared by adding spherical metal Mo particles with high melting point and low laser absorption rate to 316 L stainless steel powder as reinforcements,using the difference in laser absorption rate and melting point of different metal powders.Firstly,SLM-2Mo/316 L was taken as the research object,and its forming parameters such as laser power,scanning speed and scanning distance were adjusted to obtain MPR-SSCs with the highest density.Secondly,under the optimal process parameter window,the effects of the addition of Mo particles(0,2 wt%,6 wt%)with different mass fractions on the microstructure,mechanical properties,corrosion resistance and friction and wear properties of MPR-SSCs materials were systematically studied,and the main conclusions obtained were as follows:When the laser power is 230 W,the scanning speed is 730 mm / s,the scanning spacing is 0.10 mm,and the powder layer thickness is 40 μm,the formed MPR-SSCs have the highest density.In the laser scanning stage and melt pool stage,Mo particles remain in the solid phase state,suspended in the SLM melt tank solvent plays the role of "cold iron",bringing greater cooling rate and overcooling,changing the temperature field distribution in the melt pool,and has a significant impact on the solidification behavior and organization of the matrix.After forming,Mo particles form a unique spherical metal-like enhancer in the matrix,and their deformable particle characteristics and spherical morphology with low stress concentration are beneficial to achieve the enhanced and toughening effect.When the amount of Mo particles added is 2wt%,the austenite grains are significantly refined,and the columnar crystals growing along the heat flow direction change to isoaxial,the cell and stripe microstructure in the grains change to the slender "acne spot" substructure.Compared with SLM-316 L prepared with the same process parameters,the hardness increased by 12.1%(from 209.1 HV to234.3HV),the tensile strength increased by 9.7%(from 660 MPa to 724MPa),and the fracture elongation was also improved.When the amount of Mo particles added is 6wt%,with the consolidation of some Mo elements and under the austenite bypass effect caused by fast coagulation,its single austenite phase matrix changed into a matrix dominated by high temperature δ ferrite and part of austenite residue.At this time,the hardness of MPR-SSCs increased to 304.7 HV,an increase of 45.7%.The yield strength reached 952 MPa,which was further increased by 44.2%,and the elongation at break was 21%,which still maintained good plasticity.Different from the addition of Mo elements in the form of alloying,the additional Mo elements added to MPR-SSCs materials are mostly aggregated in the form of pure metal particles,because the pure Mo particle reinforcement itself has good corrosion resistance,and the small diffusion of Mo content in the Mo content in the matrix around the Mo particles increases the thickness of the passivation film,and the corrosion resistance of MPR-SSCs is improved.And with the increase of Mo particle content,the corrosion resistance of MPR-SSCs is better;In addition,due to the well-distributed high-hardness spherical Mo particles and the metal-metal interface between the 316 L matrix,the Mo particles are not easy to fall off during the wear process,avoiding stress concentration and plastic deformation of the matrix,and the wear resistance of MPR-SSCs is improved.And with the increase of Mo particle content,the better the wear resistance of MPR-SSCs.