Study On Process Technology Of Laser Cladding Nickel-based Alloy Powder For High-speed Trains Brake Disc

As a key part of the high-speed train braking system,brake disc need to transform a large number of kinetic energy into heat when braking.High temperature friction and a large amount of heat transfer is the direct cause of leading to wear and thermal fatigue damage of the brake disc.Therefore,the comprehensive performance of the brake disc is very demanding.Due to the limitations of casting process,cast steel brake disc is easy to appear casting defects in the production,so it is difficult to ensure the use of a large number of brake disc.Therefore,in this study,the coating with the thickness of 5~10 mm was prepared on the surface of cast steel with good casting properties and good toughness by the method of laser cladding deposition combined with casting technology.Firstly,the effect of laser power on the microstructure and properties of nickel-based alloy powder coating was studied.And the effects of V and Ti added in the initial powder on the microstructure and properties of nickel-based alloy coating were studied.The results show that on condition that other technological parameters keep unchanged,with the increase of laser power.The microstructure of the cladding layer becomes fine and then coarsening,and the microhardness increases first and then decreases.The hardness increases gradually along the direction away from the surface,and the hardness reaches the peak near the heat affected zone.After adding V and Ti,the grain size of the cladding layer is refined,the hardness is improved,and the effect of Ti powder is more obvious than V.Under the present conditions,the appropriate laser power and the addition of Ti powder content were 1 000 W and 1%.Secondly,on the basis of nickel-based alloy powder with the addition of 1% Ti,the variation of microhardness of the cladding layer of the four kinds of alloy powder with different B and Si contents were studied by adding 1% B and Si elements in turn.The results show that with the increase of the content of B and Si,the hardness increases gradually,and the microhardness of cladding layer increases by about 30 HV with the average increase of 1% B and 1% Si.The hardness of cladding layer which added 3.5% B and 4.5% Si is highest,up to 320 HV.Then,WC particles were added into the nickel-based alloy powder,and the content of B powder and Si powder were reduced properly.And the microstructure and microhardness of four different kinds of WC,B,Si alloy powders' cladding layers were studied.The results show that the microstructure of cladding layer with the increase of the content of WC,there are more and more cellular dendrite in the tissue,and a lot of disordered dendrite.And a large number of W and C were obtained due to the thermal decomposition of WC,which combined with Ti,Cr and other elements to become new strengthening phases,and the hardness has been greatly improved because of these phases enriched in dendrites.Four kinds of powders cladding layers' hardness are higher than that of the base metal.With the increase of the content of WC,more and more cracks and slag inclusions in the cladding layers.Under the conditions of this study,the optimum contents of the three powders were: WC powder 10%,B powder2.5%,Si powder 2.5%.Finally,the friction and wear properties of nickel-based alloy powder coating with different contents of WC,B and Si were studied.The results show that with the increase of the content of WC,the amount of wear of the coatings decrease first and then increase.When the content of WC is 10%,the cladding layer of wear rate is the lowest,which has the best wear resistance,and the result is consistent with microstructure observation,microhardness,and formability.