Study On The Preparation And Brazing Performances Of The Ni-Cu-P Electroless Film Deposited On YG8 Cermet

Cermet has been one kind of material which has high hardness and wear resistance, good red-hardness and chemical stability, in which YG8 cermet is most widely applied to many industrial fields, such as the mechanical processing, geological exploration and mining etc. Because of the high cost and poor toughness, processed into complex shape of cutting tools or drill is difficult, YG8 cemented carbide is often brazed together with steel which toughness is good. The thermal expansion coefficient between YG8 hard alloy and steel is large, causing high stress in the weld seam, resulting in many failure behaviors such as hole, crack and fracture easily, impacting on the working life of tools seriously. To strengthen the bonding strength of weld joint and improve the brazing performance, an alloy transition layer has been prepared by electroless plating on the surface of YG8 cermet.The electroless plating pretreatment of YG8 cemented carbides mainly involved surface cleaning, roughening, sensitization and activation. In this paper, to get a optimal pretreatment project, the influence of thiourea and BTA cleaner on the Co emergence of YG8 cermet when washing in aqua regia, and the effect of activation scheme on the morphology and properties of coating was researched by trying plating.Ni-Cu-P alloy film was deposited on the surface of YG8 cemented carbides via ternary electroless plating, and impact of the PH value, concentration of the copper sulfate (Ni/Cu atomic ratio in plating solution) and plating temperature on the coating structure and properties were mainly discussed. According to the results of advance experiment, the influence of plating on the brazing performance of YG8 alloy was checked further through solder spreading and test of shear strength, eventually obtaining optimal process.Research results show that thiourea can remit the emergence of Co of YG8 cemented carbide when cleaning in aqua regia, the depth of area taken off Co is only 1-2μm when the concentration of thiourea is lmol/L, but the BTA accelerate the corrosion rate on the contrary. The catalytic core formed on the surface of hard alloy via the activation scheme including roughening, sensitization and activation, making the alloy coating deposited smoothly. The structure and performance of coating were affected by the pH value, the concentration of copper sulfate and plating temperature, the optimal processing parameters of plating is:the pH value 11, the concentration of copper sulfate 1.25g/L, when the Ni/Cu atomic ratio in plating solution is 5:1, and plating temperature 90℃, when the structure of coating was uniform and close, the invasive with solder is good, and the shear strength of welding reaches 480MPa, improving the brazing performance of YG8 cermet effectively.