Research On Microstructure And Properties Of Co-based Alloy Coatings Prepared On H13 Steal

At present,mould technology has been become an important symbol to measure the level of a country's product manufacturing.Mould life is not only the important factor that affecting product quality,machining efficiency and cost,but also an important guide to measure the level of manufacturing.Thermal fatigue is a leading failure of hot working die steels.According to statistics,60～70%die failure are caused by thermal fatigue of hot working die.So there have great national economic significance to raising the service life of hot work die by surface strengthening technology.Co-based alloy coatings are prepared on H13 steel by laser cladding and vacuum fusion sintering technology.Microstructure,Microhardness of the coatings have been tested using optical microscope,scanning electron microscope(SEM,including EDS microanalysis),X-ray diffraction instrument(XRD)and microhardness tester.The interracial bonding and thermal fatigue properties of coatings were studied.The experiment results showed that the microstructure of single track laser cladding Co-based alloy coating include the cladding,combined and heat-affected area.When increasing the laser scanning speed or decreasing the laser power the microstructure of laser cladding coating become finer.With the experiment,the optimal laser cladding parameters have been obtained.In multi-track laser cladding coating there have no planar crystal in interface,because the temperature of substrate raised leading to the temperature gradient in interface decrease,so it can't form chilled layer.The vacuum fusion sintering coating has compact structure and coarse microstructure.In interface,there happen the element diffusion;by diffusion reaction a good diffuse combination interface was formed.The results showed that there are primary phasesγ-Co,Cr₂₃C₆ and Ni_2.9Cr_0.7Fe_0.36in the laser cladding coating.Co, Cr₇C₃ and Ni_2.9Cr_0.7Fe_0.36phases are shown in vacuum fusion sintering coating.The laser lading coating has higher surface microhardness than vacuum fusion sintering coating.When increasing the laser scanning speed or decreasing the laser power the microhardness of laser cladding coating increased.Because of the burning of alloy elements in surface,the microhardness in surface is a little lower than subsurface.The microhardness of multi-track laser cladding coating is lower than single track laser cladding coating.Thermal fatigue is a leading failure of hot working die steels.The experiment results showed that laser cladding coating has the most excellent thermal fatigue property.The laser cladding coating suffers the most thermal cycling times before appear macroscopic thermal fatigue crack,and the crack width is the least,the crack width is 14um.H13 steal without surface treatment has the poorest thermal fatigue property.The Co-based alloy coating has high thermal stability,so the descend range of microhardness is small after thermal cycling.But the descend range of H13 steel is large.After thermal cycling,microcracks will generate encircle the massive eutectic compound of vacuum fusion sintering coating,spalling and become pit lastly.