Phase evolution in Inconel718 / Al / Inconel718 couples obtained by TLPB

MARIANA POLISERPI; REQUENA GUILLERMO; PERE BARRIOVERO VILA; POLETTI CECILIA; BOERI ROBERTO; SOMMADOSSI SILVANA

Valdivia

Congreso; 19° CONGRESO INTERNACIONAL DE METALURGIA Y MATERIALES CONAMET/SAM 2019; 2019

Facultad de Ingeniería de la Universidad Austral de Chile

High temperature welding is a complex research field that requires the optimization of the bonding process and the investigation of phase transformation during its manufacture. Ni based superalloys and Al-Ni intermetallics still present some challenges related to their joining process. Inconel 718 is one of the most used superalloys in high temperature environments by the aerospace and power generation industries, due to the excellent high temperature properties obtained through the combination of solid solution and precipitation strengthening mechanisms. Because of its microstructural complexity, some difficulties arise when these alloys are subjected to brazing, fusion welding and diffusion welding techniques. In this context, the Transient Liquid Phase Bonding (TLPB), is an attractive alternative developed by Paulonis et al. [1]. Although there are several publications on TLPB, the fundamental mechanisms of the diffusion-reaction processes for commercial alloys, its microstructural evolution and the effects of the joining process on the technological properties are still unclear. Thorough knowledge of equilibrium phase diagrams and kinetics are required to understand their thermal stability and phase formation sequence during this process. Recent investigations show that it is feasible to use TLPB to obtain defects-free and reduced thickness joints in superalloys and Al-Ni intermetallics [2-4]. TLPB was used to bond a Ni-based superalloy using pure Al as filler metal. The bonded area developed as a set of layers. Figure 1 shows a typical TLPB interconnection zone. Previously, a first approach in phase identification of the interconnection zone by means of SEM-EDS EBSD was done. A biphasic layer of Cr, Nb, Fe-rich phases was identified next to the substrate due to nickel outward diffusion from the superalloy and a layer of coarse AlNi grains with secondary phases at grain boundary towards the centre of the interconnection zone, Figure 1. Splitting of AlNi phase previously observed in binary couples [4], was also observed.The aim of this work is to study the kinetics of phase transformation in INC718 / Al / INC718 couples bonded by TLPB. The evolution of phase formation will be followed at 1000°C by tracking markers positions at different bonding times. In addition, transmission time-resolved analysis using in situ high energy synchrotron X-ray diffraction (λ = 0.124 Å) was carried out. Preliminary results indicate that AlNi phase develops at very short times. Splitting may appear as two peaks, that change intensity over time due to Ni diffusion from substrate and the development of Al-poor AlNi layer in the interconnection zone, Figure 2.