Research On Invar36/Ni60 Composite Coatings By High Frequency Induction Cladding

At present,laser cladding and plasma cladding,which are commonly used in the field of die surface strengthening,can not reducing the thermal expansion coefficient of the die while improve the mechanical properties of the die surface.To solve this problem,the high frequency induction cladding technology was used to prepare different proportions of Invar36/Ni60 composite coatings on the surface of 45 Steel.By comparing the methods of high frequency induction cladding of Invar 36/Ni60 composite coating,it was found that the success rate of adding Invar 36 powders in the coating was higher than that of inserting Invar 36 wires,and the defects were less.Some process parameters were optimized by orthogonal test and the optimum process parameters were as follows:preheating time 2 s,induction heating power supply 41 k W,workpiece speed 15 r/min,weight ratio of sodium silicate to mixed powder 3:100.The temperature field of induction cladding was analyzed by ANSYS software.It could be found that the highest temperature of Invar36/Ni60 composite coating appeared near the surface of the substrate.Current density and power frequency were the main factors affecting the temperature field of the coating.Increasing the content of Invar36 could decrease the coating temperature slightly and increase the temperature difference between inside and outside of the coating.Combined with experimental research and simulation data,it could be obtained that the maximum temperature in the coating should be controlled at 1430-1600?to avoid overmelting and unmelting.Under the optimum heating time,the larger the current density,the more prone to cracks,the bigger the thermal impact zone of the substrate in the y direction.The following results were found by optical microscopy,electron probe and X-ray diffraction.Elements diffused between coatings and substrates,forming a firm metallurgical combination.The phase distribution of the coatings was that floral Cr B,Cr B2 precipitates and block Cr7C3 and Cr23C6precipitates were uniformly distributed on the iron-nickel solid solute Fe Ni3.The influence of Invar36content on thermal expansion coefficient of the coatings was analyzed by thermomechanical analyzer.And it was found that the thermal expansion coefficient of the coating could be significantly reduced by adding Invar36 to Ni60.At 100?the thermal expansion coefficient of the coating containing 30%Invar36decreased by 9.42%compared to the coating with only Ni60,and decreased by 7.85%at 200?.The micro-hardness distribution of the coating were measured.It was found that the microhardness of Ni60coating was about 800HV_0.3,adding Invar36 would reduce the hardness of the coating,but proper addition of Invar36 could still meet the hardness requirements of the die.It was found by electrochemical corrosion test that the addition of a small amount of Invar36 did not change the corrosion resistance of the coating.The above research provides a new process method of high frequency induction cladding Invar36/Ni60 composite coatings,and establishes an effective numerical model of temperature field,provides reliable experimental data,which can be used in the field of die repair,surface strengthening and manufacturing.