Laser Cladding Authigenic Titanium Diboride Ceramic Coating

A new method that In-situ laser surface cladding of ceramic layer combining laser cladding technique and in-situ metal-matrix composite producing technique has been studied in this paper.In-situ TiBi ceramic coating on Al-Si alloy substrate has been successfully obtained.According to the heat transfer feature during the melting process of laser cladding,the model of the heat transfer was eatablished,and the calculated results were agreed with the experimental ones quite well.The results show that,in laser cladding process,the metal substrate will absorb heat energy about 3 times to that of cladding layer so the energy absorbed by substrate can not be neglected simply.According to stantard Gibbs energy for possible reactions of laser coatings as a function of temperature,the tendency of thermodynamics for possible formed phase were analyzed. The reason why TiB2 can be formed optimally were explained.At the same time,the mechanisms among titanium and boron were testified.The results show that in proper processing method,titanium is molten firstly because of its relative lower melting point. TiBi is generated on the surface of boron.Further produced TiB2 depends on titanium's diffusion.The solidification behavior and the microstructures of the cladding layers were studied,which indicates that the solidification in molten areas accords with the crystallization regular pattern.Nucleating starts firstly interface between the molten area and substrate.Then crystal grows according to the direction of heat flow to form large dendrites.At last the solid-liquid interface comes into the cladding zone little dendrites are created.The TiB2 particles homogeneously distribute in cldding coatings.The effect of laser beam parameters such as laser power and laser translation speed on the microstructure and the performance of cladding layers is also discussed, which indicates that laser translation speed influenced the microstructure and the performance more intensively than to laser power. So laser translation should be paid more attention during laser cladding process.The hardness was measured from coating to substrate.It's easy to see that the value of the hardness was the highest on the coating layers,that of the substrate was the lowest.The multi-pass laser cladding are investigated.The overlapping coefficient is defined in theory.The good experimental results was got when coefficient equals 0.2. What's more,the distribution of hardness both from coating to coating and from molten area molten area exhibited a periodicity corresponding to the changes of microstructure throughout the coating layer and molten area.