Study On Brazing Mechanism And Parameters During Joining K24and GH648Superalloys

To meet the engineering requirement of joining the engine turbine guide,brazing of K24and GH68superalloys was investigated in this paper. This researchcontains three parts: first, brazing of K24and GH648superalloys using commercialBNi68CrWB filler alloy powder, characterizing the microstructure and mechanicalproperties of the brazed joints by changing the temperature,the brazing time and thegap size. Second, brazing of K24and GH648superalloys using Ni-Cr-Si-B-W filleralloy powder (being prepared by ball-milling method), characterizing themicrostructure and mechanical properties of the brazed joints by changing thecomposition. Finally, exploring the reaction mechanism of the brazing process.K24and GH648could be successfully brazed by using BNi68CrWB brazingfiller alloy. Typical microstructure of the joint was divided into three characteristiczones: eutectic zone, isothermal solidification zone and diffusion zone. This studyalso investigates the effect of brazing parameters on the microstructure and themechanical behavior of the joints. The eutectic zone can be increased by setting aexcessive brazing temperature,and it is harmful to the joint. A bigger gap size willincreasing the solder volume and the diffusion distance,and it brought a adverseeffect on homogenization. Increasing the holding time can promote the elementdiffusion, and obtain a homogeneous solid solution joint.Ni-Cr-Si-B-W filler alloy powder with seven kinds of composition wereprepared by ball-milling method and were used to braze the K24and GH648superalloys. The effect of B, Si and W elements on the microstructure of the jointswas investigated on the basis of microstructure evolution and the mechanicalproperties of the joints. Appropriate incorporation of B, Si in the brazing alloy canreduce its melting point, however, if the content of B or Si in the brazing alloyexcesses a certain degree, the forming of eutectic zone and diffusion region isenhanced remarkably. Besides, the high-temperature tensile shear strength of thejoints can be effectively improved by adding W to the brazing alloy, however, toomuch W will increase the amount of WB intermetallic compound in the joint, thusdeteriorating the high-temperature tensile shear strength of the joint.The brazing process was simplified and divided into four processes: heatingprocess, dissolving process, isothermal solidification process and cooling process.Each process was dominated by the diffusion of B element.