In order to make full use of the advantages of TLP and solid state diffusion welding for combination of these two processes

it was necessary to study the liquefaction law of base metal at the joint interface. DD407 nickelbased single crystal superalloy was joined by intermediate layer alloy of BNi9 with 3.5% B. The variations of width of joint and liquefied base metal as process parameters were investigated. Results were as follow: With the increase of welding temperature and the holding time

the width of the liquefaction zone increased. When welding with interlayer in thickness of 150μm at temperature of 1100℃ and holding time of 5min

the width of liquefied base metal reached 65.8μm. The effect of the thickness of interlayer on the liquefaction of the base metal was relatively higher due to the increase of B contents. The liquefying procedure of base metal was summarized as follow: interacted region of base metal were liquefied by diffusion of melting point depressing element of B

which resulted in the increase of the liquefied area width. But the content decrease of B element in the interlayer gave rise of isothermal solidification

which ceased the further liquefaction

thus the action of surface cleaning was affected in some content.