Study On Laser Absorptivity And Selective Laser Melting Forming Of Copper And Copper Alloy Powder

Copper alloy has excellent thermal conductivity and electrical conductivity,and is an ideal cooling wall material for the combustion chamber of liquid rocket engine.The high degree of freedom design of selective laser melting technology can easily and quickly realize the high-precision forming of complex parts,which provides a new way to optimize the structural design of the combustion chamber of aerospace engines.However,since most SLM(selective laser melting)equipment currently uses infrared lasers and copper and copper alloys have a low energy absorptivity for infrared lasers,which seriously affects the structure and performance of SLM formed copper alloys.This article investigated the influence of powder particle size,alloying,surface modification,and surface oxidation treatment on the laser absorptivity of the powder in order to improve the structure and performance of copper and copper alloys after SLM forming.Explored the ways to improve the density and mechanical,thermal and electrical properties of SLM copper and copper alloys.The experimental results shows that the particle size of copper powder has a certain effect on the laser absorptivity.Among the pure copper powders with three particle sizes of 5-35?m,15-35?m,and 40-160?m,the laser absorptivity of 5-35?m copper powder is higher,15-35?m followed,40-160?m copper powder has the lowest laser absorptivity.In the same 15-53?m particle size range,compared with pure copper powder,the laser absorptivity of Copper powder with 0.8%mass fraction of Cr is higher.Surface modification has a greater impact on the laser absorptivity of copper and Cu-0.8wt%Cr powders.The laser absorptivity of the powder has been significantly improved after adding nano-TiC to the copper powder.The higher the quality powder added with nano-TiC,the greater laser absorptivity of the copper and Cu-0.8wt%Cr powders.Oxidation treatment of copper powder will increase its laser absorptivity.The higher oxidation treatment temperature,the greater laser absorptivity of copper powder,but the oxygen content in the powder was also increased.The SLM forming experiment results of three pure copper powders under the same process conditions show that 15-53?m copper powder formed samples have better performance.The experimental results of selective laser melting forming of copper and copper alloy powder before and after nano-TiC modification show that under the same conditions,the density of the Cu-0.8wt%Cr alloy sample is higher than that of the pure copper sample.After adding 0.2%mass fraction of nano-TiC modified,the density and mechanical properties of the formed samples are further improved.Under the parameter combination of 320W laser power and 600mm/s scanning speed,the density of Cu-0.8wt%Cr and Cu-0.8wt%Cr+0.2wt%TiC samples formed by SLM are 97.6%and 99.7%,tensile strength is 198.5Mpa and 225.9Mpa,Brinell hardness is 85.3HB and 98.1HB,thermal conductivity is 97.4W?m^-1?k^-1 and82.6W?m^-1?k^-1,electrical conductivity is 27.8%IACS and 23.6%IACS,respectively.It shows that adding 0.2wt%nano-TiC modification significantly improves the mechanical properties of the sample,but makes the thermal and electrical conductivity decrease slightly.