Research On Preparation And Properties Of Gradient WC Enhanced NiCrBSi Alloy Coating By Vacuum Brazing

WC-NiCrBSi alloy coating was made by vacuum brazing technology and flexible metal cloth.It has many advantages,such as compact coating,no cracks,pores,the coating and substrate metallurgical bonding,vacuum atmosphere,no oxidation,decarburization and other pollution impurities,smooth coating surface.It also can modify the application with a variety of surface structure.Ceramic/Metal gradient material coating on one side has the advantages of high wear resistance,high hardness and high temperature resistance,and the other side has the advantages of high toughness and high strength.Therefore,the combination of brazing technology and ceramic gradient material coating will have great application value.In this paper,the gradient WC ceramic reinforced NiCrBSi alloy coating was prepared by vacuum brazing.The main contents and results are as follows:The flexible metal cloth forming experiments were carried out.The study found that WC flexible metal cloth can be formed when mWC:mPTFE changed in the range of 10-150.When the mass ratio is less than 10,the metal elastic cloth has low quality.When mWC:mPTFE larger than 150,the metal cloth has low strength and easily rot.The WC metal cloth were tested by tensile testing machine.The cloth was made by four fold rolling times.The study found that when the mass ratio is less than 10,the metal cloth fracture strain is small.When the mass ratio increases in the range of 10-50,the fracture strain increases.When the mass ratio is greater than 50,the fracture strain decreased significantly.The tensile and wear properties of uniform WC enhanced NiCrBSi alloy coatings were tested under different brazing temperature and holding time.It was found that when the holding time is 15min and the brazing temperature is in the range of 1000-1100?,the least wear loss is 11.1 mg at 1080?.When the brazing temperature is 1080? and the holding time is in the range of 5-30min,the tensile property increases at first and then decreases with the increase of temperature.When the holding time is 10min,the coating bonding strength is best up to 230MPa.By adjusting the volume ratio of WC particles and NiCrBSi alloy powder in the metal cloth,the WC was graded in the different layers of metal cloth.Based on a large number of experiments and optimization of brazing process parameters,four kinds of gradient WC reinforced NiCrBSi alloy coatings were obtained.The wear properties of four kinds gradient slope coatings were tested.The coating gradient slope effects on the microstructure,hardness,friction and wear properties were studied.The wear resistance of the coating increases with the increase of the coating gradient slope.When the coating gradient slope is small,the wear failure mechanism of the coating is abrasive wear.When the gradient slope is large,the coating is fatigue wear failure.The tensile properties of four kinds gradient slope coatings and coating/substrate samples were studied.The whole process of the coating/substrate specimen surface crack from the initiation to full penetration was observed by in-situ tensile test.It was found that the crack was formed in the vicinity of the WC particles and the stress concentration.With the increase of the coating gradient slope,the fracture strain of the coating/substrate increases,the number of the through cracks increases slightly.The coating fracture strain decreased and the tensile strength reduced with the increase of the gradient slope.The coating is brittle fracture.