| Mold is a tool for making molded articles and has become an important part of manufacturing.It has a great variety,such as stamping mold,plastic mold,die casting mold,glass mold,etc.Its application is also very wide.During the process of serving,the mold will be affected by high temperature,high pressure,alternating thermal stress and so on,in particular,the friction between the mold forming parts and products.These factors can cause the failure or failure of mold parts,especially the molding parts.How to repair the mold,improve the wear resistance of mold,and extend the service life of mold is an important research topic in the field of mold.In this paper,plasma spray welding technology is used as the means,45 steel,H13 hot work mold steel and HT250 gray cast iron are selected as the base material.Nickel-based alloy powders Ni45 A and Ni60 B are used to prepare for spray samples,and the spray samples are 45 steel-Ni45 A,45 steel-Ni60 B,H13-Ni45 A and HT250-Ni45 A.The technical parameters of plasma spray welding,the combination of spray welding powder and substrate,microstructure,the mechanical properties and friction and wear properties of the samples were studied.The main research contents and conclusions are as follows:1.The microstructure of the plasma sprayed layers show that the microstructure of the spray welding layer of 45 steel-Ni45 A and 45 steel-Ni60 B is mainly composed of cellular crystal and dendrite.The microstructure of the spray welding layer of H13-Ni45 A and HT250-Ni45 A is mainly composed of cellular crystal and columnar crystal.EDS analysis found that the alloying elements interdiffuse between the spray welding layers and the substrates.Spray welding layers and substrates form a clear binding area.SEM analysis found that there are white and gray phases in each spray welding layer.There are also black phases in spray welding layers of 45 steel-Ni60 B and HT250-Ni45 A.XRD analysis shows that the microstructure of spray welding layers contain rich Ni gamma-Ni,FeNi3 matrix phase and M7C3(Cr7C3,(Cr,Fe)7C3),M23C6(Cr23C6,(Cr,Fe)23C6)hard phase.(Cr,Fe)7C3?(Cr,Fe)23C6 are carbides that contain Fe atoms which based on Cr7C3 and Cr23C6 respectively.The white phase is predominantly a compound containing Ni,Fe,the gray phase is mainly the carbide of M7C3,and the black phase is mainly the carbide of M23C6.2.The study on the mechanical properties shows that the microhardness of the spray welding layers by plasma spray is significantly higher than that of the substrates.The microhardness of Ni60 B spray welding layer is higher than that of Ni45 A spraying welding layers.The fine M23C6 and M7C3 carbides can improve the tensile strength and yield strength.3.The study on the properties of friction and wear of the plasma sprayed layers shows that,with the time of friction and wear and load increasing,the spray welding layers' friction coefficient of 45 steel-Ni45 A and 45 steel-Ni60 B reduce,and the wear volume increase.Thespray welding layers' friction coefficient of 45 steel-Ni45 A can reach 0.15,and 45steel-Ni60 B can reach 0.11,which is significantly lower than that of 45 steel substrate(about0.7).In the early stage of the friction and wear,a small amount of adhesive particles appear on the coating wear surface of the spray welding layer of 45 steel-Ni45 A,and the coating wear surface of the spray welding layer of 45 steel-Ni60 B is slight wear and tear.The main wear mechanism is adhesive wear.With the time of friction and wear and load increasing,wear pits appear on the coating wear surface of 45 steel-Ni45 A,and furrows and even larger pits appear on the coating wear surface of 45 steel-Ni60 B.The main wear mechanism are the abrasive wear and delamination wear.4.The study on this paper shows that it is feasible to repair mold materials by spray welding layers prepared by Ni45 A and Ni60 B alloy powders on the surface of 45 steel,H13 and HT250.The spray welding layers and substrates can achieve metallurgical bonding. |
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