Research On Microstructure Optimization And Performance Control Technique Of CoCrMoCu Alloy Formed By Selective Laser Melting

CoCrMo alloy has excellent biocompatibility,high surface strength and other advantages.It is widely used in dental restorations,bone implants and other medical fields.However,there are still problems,such as structural failure caused by bacterial infection in its clinical application.CoCrMo-xCu antimicrobial alloy manufactured by laser-selective melting is mainly used for medical implants.This paper takes the engineering application as the background to study the influence of Cu content on the forming process,tissue state and mechanical properties of CoCrMo-xCu,elucidate the influence law of sampling direction on the microstructure and properties of exposed surface,and determine the influence of various heat treatment systems on the non-equilibrium solidification organization and properties.The main contents and results of the full text are as follows:（1）The optimization of SLM process parameters can effectively improve the key properties of the printer,such as forming ability,density,micro-hardness and so on.Analyzing the forming quality of SLM printing parts,optimizing the forming process of CoCrMo alloy,by changing the laser power and scanning speed.Studying the effect of laser energy density on macro-forming,Surface roughness,density and microhardness.When the laser energy density is high or low,the printing parts have some forming problems,such as the decrease of density and microhardness,the increase of roughness.Combine the various performances to determine the optimal parameters are:the scanning speed is 800 mm/s,the density is 97.02%,the microhardness is 383.6 HV.（2）Cu alloying changed the phase composition and microstructure,improved its corrosion resistance,but decreased its tensile properties,microhardness and wear resistance.The rapid solidification microstructure of CoCrMo consists ofγphase and a small amount ofεphase.As the Cu content increased from 0%to 4.5%,the volume fraction ofγphase decreases,but theεphase component increases.Meanwhile,the microhardness,wear resistance,strength and elongation decreased linearly,but corrosion resistance increased.（3）The sample direction affects the grain morphology and microstructure of the exposed surface of CoCrMo-xCu.The elongation and corrosion resistance increase and the strength decreases with the increase of sample angle.The sampling direction was determined by the angle between the normal line of the exposed surface and the deposition direction.With the increasing of the sampling angle,the morphology of the exposed surface gradually changed from the overlapped structure in the same layer to the“Fish scale”structure.The microstructural characteristics changed from honeycomb cellular structure,in the cross section of columnar crystal to parallel cellular structure in the longitudinal section of columnar crystal.When the angle increases,the dendrite spacing increases and the proportion of interfaces decreases.The difference of heat experience results in the change of phase composition of the exposed surface,which has moreγphase than that of the exposed surface at 0°.With the increase of the angle between the sampling direction,the small melting area makes the heating more uniform,but the micropores of the sediment accumulate.The results show that the strength,corrosion resistance and the microhardness of the alloy decreases,the elongation and element diffusivity increases with the increase of the sampling angle.（4）The heat treatment system is optimized to improve the microstructure uniformity of the formed parts,effectively improve corrosion resistance,tensile properties,micro-hardness,wear resistance.The CoCrMo-xCu alloy was treated by homogenization heat treatment and laser remelting transient heat treatment respectively.After homogenization heat treatment,the lapped structure of cladding channel in the same layer disappears,different size grains andεmartensite structure appear.At the same time,εphase proportion increases,and carbide M₂₃C₆precipitates during aging treatment.The solution-aging treatment can improve the homogeneity of the alloy and precipitate the strengthening phase,improve the microhardness,tensile properties and wear resistance after laser remelting.The microstructure and phase composition have no significant changes,but the mechanical properties and corrosion resistance are greatly improved with the increase of density and the decrease of internal defects.