Microstructure and Mechanical Characterization Study in the IN718/BNi-2/316L Joint by Transient Liquid Phase Bonding Process

Abstract

In this research, the relationship among TLP bonding microstructures, mechanical properties and fracture mechanism of IN 718 / BNi-2 /AISI 316L joint was studied. In the first step, by changing TLP variables e.g. time and bonding temperature in the range 30-60 min and 950-1050 0 C respectively, characteristics of each type of microstructures including formation of destructive phases and homogeneity of microstructures were studied. In the second step, in order to investigate the mechanical properties and their fracture surface morphology, hardness and shear tests were accomplished. In the next stage, based on diffusion behavior of alloying elements, the relationship among microstructure, mechanical properties and fracture mechanism was studied. Results show that microstructures of bonding region were classified in three types. Type I: solid state bonding microstructure, Type II: Athermalisothermal solidification microstructure, and Type III: isothermal solidification microstructure. It was observed that for each specific microstructure, there is one fracture mechanism or there are more that are dimples fracture resulting from precipitations within matrix, quasi-cleavage fracture resulting from dual microstructure of eutecticisothermal solidification and dimple-tearing fracture resulting from tiny precipitations within bonding region.

Effect of Bonding Temperature on Microstructure and Mechanical Properties of Dissimilar Joint Between Inconel 617 and Stainless Steel 310

“…It can be deduced that the fracture surface of the bond fabricated at 1040 °C was completely brittle and the level of cup and cone structure increases by increasing the bonding temperature. This brittle fracture is related to the increasing amount of intermetallic compounds at higher bonding temperatures, as reported previously [20].…”

“…The bonding time and temperatures were selected according to previous studies [6,14,20] and our preliminary trials.…”

“…It is well documented that the isothermal solidification process and the formation of brittle intermetallic compounds are two controlling factors for strength of the joints [20]. The lower shear strength of the TLP bond prepared at 1100 °C can be attributed to the formation of the more intermetallic compounds such as Fe-Ni, FeNi 3 , AlNi 3 , and Al-Ti-Ni (Figs.…”

“…Also, it can be deduced that all boron was not consumed in the bonds. This behaviour can be related to non-isothermal solidification at temperatures below eutectic temperature and incomplete isothermal solidification [20]. EDS results of the Ni and Cr revealed that the amount of these elements was decreased in the interlayer by increasing the bonding temperature.…”

“…ASZ is accompanied by non-isothermal solidification. The formation of some eutectic micro-constituents is the main occurrence in this region [20]. DAZ is a region with secondary phase precipitates that are formed due to diffusion of melting point depressants (MPD) elements into the base metals [8].…”