Abstract:Influences of gap size and cyclic-thermal-shock treatment on the mechanical properties of transient liquid phase (TLP) bonded IN-738LC superalloy were investigated. For this purpose, TLP bonding of IN-738LC superalloy was carried out in a vacuum furnace using powdered AMS 4777 as the filler metal. The results showed that isothermal solidified zone (ISZ) consisted of Ni solid-solution and the distribution of alloying elements was homogeneous. High hardness of HV 409 and high shear strength of 506 MPa were observed in 40 μm gap sample. Alloying elements formed γ′ precipitates and the solid-solution in the ISZ. Hardness and shear strength of bonds were reduced with increasing the gap size (in range of 40-120 μm). The fractured surfaces of complete isothermal solidified bonds showed dimpled rupture, but athermal solidified bonds showed cleavage fracture surface. 10, 20, 30 and 40 thermal-shock cycles were applied to 80 μm gap samples, respectively. The shear strength of the bond was measured to be 268 MPa after the 40th thermal-shock cycle. The sample with gap size of 80 μm was failed due to crack nucleation on faying surface at 45th thermal-shock cycle. The amount of the produced brittleness due to quenching the samples in water bath was attributed to the number of thermal-shock cycles.

Key words: IN-738 superalloy; TLP bonding; mechanical properties; cyclic-thermal-shock treatment; shear strength