| In recent years,the process of customized manufacture is speeding up with the development of additive manufacturing,Selective laser melting(SLM)is a representative technology in the field of metal additive manufacturing.The parts with complex structure,good property and high precision can be manufactured rapidly by SLM.Cobalt chromium alloy has excellent wear resistance,corrosion resistance and biocompatibility,and is widely used in manufacturing in the field of medical and implant denture and joints.In this study,the dental cobalt chromium alloy powder is used to manufacture some parts by SLM.The microstructure and mechanical properties of the specimen were studied by changing the process parameters.The main contents include the following aspects:(1)The influence of SLM process parameters on the geometry of the sample molten pool is studied.By designing single-factor experiments,the laser power,scanning speed,and scanning line spacing in the SLM process were changed respectively,and the weld pool width(w)and depth(h)of the samples under different processes were measured.It can be seen that: w and h are positively correlated with the laser power.When the laser power is 300 W,w and h are 189 μm and 64 μm,respectively;w and h are negatively correlated with the laser power,when the laser power is 700 mm/s,w and h is 122 μm and 61 μm,respectively;the remelting zone within the layer increases significantly as the scan line spacing increases.(2)SLM process parameters were optimized.Multifactor experimental was designed by changing the SLM process of laser power,scanning speed and line spacing.The density,tensile properties and molding efficiency of samples under each process were tested and the optimized process parameters were found based on these three aspects so that the density exceeded 99% and tensile properties exceed the ASTM F75 medical standard(tensile strength> 625 MPa,yield strength> 520 MPa,elongation> 8%)as the conditions,the highest molding process parameters are: laser power(P)= 200 W,scan speed(v)= 1100 mm/s,scan line spacing(h)= 0.06 mm.(3)The microstructure of SLM sample was analyzed.The microstructure of the SLM samples were analyzed.The specific subgrain structure and the epitaxial growth phenomenon were found via observing the microstructure of SLM specimens.The columnar epitaxial growth phenomenon can be effectively suppressed when the inter-layer rotation angle is 67°,the chaos degree of the grain direction increased of which grain growth inside the melt pool.This research can provide theoretical basis for the formation and process optimization of SLM formed cobalt chromium alloy,and it is of great significance to the practical application of selective laser melting in various fields. |
