Journal of Welding Science

In this research, the effect of bonding temperature on the microstructure and mechanical properties of Inconel 939 super alloy by transient liquid phase bonding method. For this purpose, the middle layer of MBF20 with a thickness of 50 microns and three temperatures of 1060 °C, 1120 °C, 1180 °C and a time of 45 minutes have been used. In order to evaluate the microstructure, a scanning electron microscope equipped with an elemental analysis system has been used. Vickers hardness test and shear strength test have been used to evaluate the mechanical properties. The research findings showed that with increasing temperature from 1060 °C to 1120 °C, the width of the athermal solidification zonedecreased from 38µm to 35µm and with increasing temperature at 1180 °C, the athermal solidification zone was completely removed and isothermal solidification zone was replaced. In addition, with increasing temperature, the hardness in the joint center decreases and the shear strength increases.

This study aimed to investigate the effect of diffusion welding parameters on the microstructural characteristics and mechanical properties of the dissimilar joint between AISI 418 stainless steel and Inconel 738 superalloy using Ni interlayer with a thickness of 50 µm. The experiments were performed in a vacuum furnace at three temperatures of 1000, 1050 and 1150 °C for 45, 60, 75 and 90 min under the pressure of 5 MPa.The results show that voids and non-bonded areas are seen in the samples that were bonded at a lower temperature (1000 °C). By increasing the joining temperature from 1000 °C to 1050 °C, all micro discontinuities have disappeared, which shows that the microplastic deformation of roughness has improved. Then, by increasing the temperature to 1150 °C,non-bonded areas are observed in the joint due to the reduction of pressure on the contact surfaces. When pure nickel is used as an interlayer, intermetallic compounds of
γ' [Ni3(Al, Ti)] are formed in the γ matrix phase on the side of Inconel 738 superalloy while compounds of FeNi3 and γ (γFe, Ni) are formed on the side of AISI 418 stainless steel. According to the results of line scan analysis, the slope and penetration of elements in Inconel 738 superalloy is lower than AISI 418 stainless steel , which indicates less penetration in Inconel 738 superalloy. In the sample welded at the temperature of 1050 °C and the time of  90 Min, the penetration value of the nickel interlayer in AISI 418 stainless steel  and Inconel 738 superalloy was 40 µm and 35 µm, respectively. By comparing the maximum hardness, it can be concluded that the joint at the temperature of 1050 °C and the time of 90 Min has a lower maximum hardness than other samples. Therefore, it has better joint characteristics than other samples in terms of intermetallic compounds. The highest value of shear strength was obtained at the temperature of 1050 °C and the time of 90 Min, which is equal to 270 MPa.