Laser Cladding Technology Of Mixed Materials Of Ti,Cu Powder And Stellite6 Alloy For Titanium Brake Disc

Train lightweight is the development direction of high-speed train.The current use of iron-based brake disc is heavy and brake disc is one of important lightweight components.If titanium brake disc is applied,it will effectively achieve the goal of train lightweight,because titanium alloy has the characteristics of high strength and low density.But the wear resistance of titanium alloy is not well to meet the service requirements of high wear resistance of brake disc.In this paper,Wear resistant cladding layers of different chemical composition were prepared by means of technological research and mixing of different composition through laser cladding technology with pure Ti and Stellite6 alloy as materials.The cladding layers included 10%Stellite6-90%Ti,20%Stellite6-80%Ti and 30%Stellite6-70%Ti.And then 5%or 10%Cu were added to the 30%Stellite6-70%Ti powder to decrease microcrack defect of cladding layer.The microstructures and phases of Ti-Stellite6 and Ti-Stellite6-Cu cladding layers were analyzed by optical microscope,energy dispersive spectrometer,scanning electron microscope and X-ray diffractometer.The hardness of the cladding layers,the shear performance of the cladding layers,bonding performance of cladding layers to matrix,and the friction and wear performance of the cladding layers were analyzed and evaluated by hardness test,micro shear test,friction and wear test.The single-pass cladding process study showed that improper process parameters could easily cause porosity and other defects.The process parameters had a significant effect on the forming geometry parameters.The influence of scanning speed on clad height and contact angle was greater than that of laser power,and both of them had the compared similar effect on the remelt depth.With the increase of Stellite6 content,the microhardness of Ti-Stellite6 cladding layers increased.In general,when the scanning speed was 100mm/min and laser power was 1200 W,all Ti-Stellite6 cladding layers with different chemical composition were well formed.The main phases of 10%Stellite6-90%Ti cladding layer prepared by optimum technology parameters wereβ-Ti andα-Ti;The main phase of 20%Stellite6-80%Ti cladding layer wasβ-Ti;The main phases of 30%Stellite6-70%Ti cladding layer wereβ-Ti,Ti₂Co,TiCo,TiCo₂ and TiC.When 5%Cu or 10%Cu were added in 30%Stellite6-70%Ti powder,the microcrack defect of 30%Stellite6-70%Ti cladding layer was significantly decreased and generated TiCu and Ti₂Cu.With the increase of Stellite6 content,the microhardness of cladding layer increased gradually,up to 486 HV₁（30%Stellite6-70%Ti）.But addition of excessive Cu（such as 10%Cu）would reduce the hardness of the cladding layer.With the increase of Stellite6 content,the shear strength and press-in ratio of the cladding layers and interfaces were decreased,and the fracture modes gradually changed from mixed fracture to cleavage brittle fracture.Cu element had little effect on changing shear performance.The friction coefficients of different Ti-Stellite6 and Ti-Stellite6-Cu cladding layers were lower than that of TC4.And addition of excessive Cu（such as 10%Cu）would greatly reduce the friction coefficient.The wear weight loss of different Ti-Stellite6 and Ti-Stellite6-Cu cladding layers were lower than that of TC4.When the mass ratio of Stellite6to Ti was 3:7,the wear resistance of the cladding layers were the best,and the wear weight loss only accounted for about 3.2%of that of TC4.Cu had little effect on changing weight loss.The wear mechanism of all cladding layers and TC4 was mainly abrasive wear,accompanied by adhesive wear and oxidation wear.Considering the forming quality,hardness and wear resistance of different cladding layers,it could be known that28.5%Stellite6-66.5%Ti-5%Cu was the best powder ratio at present.The average hardness of the cladding layer was 479 HV₁,and the wear weight loss accounted for 3.5%of that of TC4.