Study On The Liquefaction Law Of DD407 Nickel Based Single Crystal During TLP Bonding

Nickel-based single crystal superalloy has excellent comprehensive properties at high temperature and has been used as the main material for turbine blade of aero-engine. For the fabrication of single crystal complex blade, the casting technique becomes very difficult, which necessarily involves the connection problem of single crystal material. At present, the commonly used methods are high temperature brazing and transient liquid phase(TLP) diffusion bonding. The performance of solder joints is difficult to meet the requirements of the aviation industry for higher performance. The residue of the melting-point depressant elements in the TLP connection joint affects high temperature properties. In order to get better performance of the joint, the transition liquid phase assisted solid state bonding technique is proposed. The study of liquefaction law of the base material is the premise of the realization of the technology.In this paper, the welding experiment of DD407 nickel-based single crystal superalloy was carried out by using transient liquid phase(TLP) diffusion bonding technology, with BNi9 and BNi5 as interlayers. The influence of process parameters on the width of liquefaction zone was analyzed by studying the morphology of the cross section of the base material under different process parameters. At the same time, the characteristics of the interfacial structure and composition distribution under different conditions were studied. By comparative analysis of the effect of the above two kinds of interlayers on the liquefaction of base material, the law of base material liquefaction was analyzed.The welding experiment of DD407 nickel-based single crystal superalloy was carried out by using TLP diffusion bonding technology, with BNi9 as an interlayer. Results show that the liquefaction width of the base material can increase with the increase of heating temperature. The liquid width of base material reaches the maximum value of 60.7μm at 1150℃. High heating temperature makes the liquid phase quickly occur isothermal solidification. The increase of the holding time increases the liquefaction width of the base material. When the holding time is 1min, the maximum liquefaction degree of the base material is acquired. The greater the thickness of the interlayer, the greater the liquefaction width of the base material. The thickness of the interlayer has less effect on the liquid width of base metal than the heating temperature and the holding time. The microstructure of the interface is mainly composed of the reaction liquid layer and the solid solution of the middle layer.The welding experiment of DD407 nickel-based single crystal superalloy was carried out by using TLP diffusion bonding technology, with BNi5 as an interlayer. The surface liquefaction law of the base material under process parameters shows that the increase of temperature will promote the liquefaction of the base material. When the temperature rises to 1160℃, the liquid width of the base material is 28.5um, and the liquid interface between the base material and the interlayer is smooth. The liquid width of base material increases with the increase of the thickness of the interlayer. When the thickness of the interlayer is 150 um, the liquid width of the base material acquires a maximum value of 55.5um.By comparative analysis of the effect of the two kinds of interlayers on the surface liquefaction of base material, we can see that the effect of BNi9 on the liquefaction of the base metal is better than that of BNi5. The former has obvious interfacial reaction layer, and the latter has obvious strengthening phase residue region. The liquefaction mechanism of BNi9 is that the diffusion of melting-point element B to the base material makes the melting point of the diffusion zone decrease, then the base material is liquefied. The liquefaction mechanism of BNi5 is that the interaction of Si in the middle layer and base metal forms low melting point eutectic, which makes the base material liquefied. By the comprehensive analysis of the surface liquefaction law of DD407 nickel base single crystal, we can see that the main influencing factors are types of melting-point depressant element, heating temperature, holding time, amount of interlayer material, etc.