Phase Transformations in TLPB Process for Inconel-718/Al and Ni/Al

M. POLISERPI; R. BUZOLIN; R. BOERI; C. POLETTI; S. SOMMADOSSI

Singapur

Conferencia; CALPHAD XLVIII International Conference on Computer Coupling of Phase Diagrams and Thermochemistry; 2019

Singapore University of Technology and Design

Phase transformations in TLPB process for Inconel-718/Al and Ni/AlM. Poliserpi1, R. Buzolin3, R. Boeri2, C. Poletti3, S. Sommadossi11 Materials Division, IITCI CONICET-UNCo, 8300 Neuquén, Argentina2 Metallurgy Division, INTEMA CONICET-UNMdP, 7608 Mar del Plata, Argentina3 Institute of Materials Science, Joining and Forming, TU-Graz, , 8010 Graz, Austriae-mail address of corresponding author: ssommadossi@comahue-conicet.gob.arKey words: Transient Liquid Phase Bonding, INCONEL, SEM/EDS-EBSD, phase transformation AbstractHigh temperature welds are a complex research field that requires the optimization of bonding process and investigation of phase transformation during its fabrication. Ni based superalloys and Al-Ni intermetallics, belong to those materials which still represent some challenges related to joining process. Inconel 718 is one of the most used superalloy in high temperature environment such as aerospace and power generation industry, due to the combination of solid solution and precipitation strengthening mechanisms. Because of its microstructural complexity, some difficulties arise when they are subject to brazing, fusion welding and diffusion welding techniques. In this context, the transient liquid phase bonding, TLPB, or diffusion brazing is an attractive alternative. TLPB was developed by Paulonis et al. and emerged from those problems during conventional welding processes. TLPB involves four main stages: melding of filler metal, substrate dissolution, isothermal solidification and homogenization if the connexion zone [1]. Although there are several publications on TLPB, fundamental mechanisms of diffusion-reaction processes for commercial alloys, microstructure evolution and the effects of the joining process on technological properties are still unclear. Knowledge of equilibrium phase diagrams, kinetics and diffusion are required to understand phase transformations, 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]. The aim of this work is to study the interconnetion zone of Inc718 / Al / Inc718 couples bonded by TLPB at 800-1100ºC, focus in the phase stability by means of SEM-EDS/EBSD and in-situ analysis using synchrotron X-ray source. Composition and nano and micro-hardness profiles were obtained. Additionally, phase evolution in the interconnection zone was monitored by changes in layers width and grain size. Cr,Nb,Fe-rich phases were identified next to the base material due to nickel outward diffusion from base metal and a thick AlNi layer and secondary phases in grain boundary towards joint centreline. Spheroidal nano-precipitates were found inside the large AlNi grains. References [1] Cook, G. O., et al. (2011). ?Overview of transient liquid phase and partial transient liquid phase bonding?, J. Mater.Sci., 46.16 (2011): 5305-5323. [2] Pouranvari, M., et al. ?Microstructure evolution mechanism during post-bond heat treatment of transient liquid phase bonded wrought IN718 superalloy: an approach to fabricate boride-free joints?, J. Alloys and Compounds, 723 (2017): 84-91.[3] Tumminello, S., et al. ?Growth kinetics of intermetallic phases in transient liquid phase bonding process (TLPB) in Al/Ni system?, Defect and Diffusion Forum, 323 (2012):465-470. [4] Urrutia et al. ?Characterization of Al?Ni intermetallics around 30?60 at% Al for TLPB application?, CALPHAD, 44 (2014): 108?113 Figure 1. TLPB microstructure of Inc718/Al at 1000°C.Biographical Note Dr.rer.nat. Silvana SOMMADOSSI was born in Neuquén, Patagonia, Argentina in 1973. She got her PhD in 2002 at Stuttgart Univ./Max-Planck-Institute working on joining technologies and lead-free solders and worked as postdoc at IPA-Fraunhofer till 2004 on surface engineering in Germany. She returned to homeland to work as professor and researcher at Comahue National University and CONICET. Now she is director of the Institute for Technology and Engineering Sciences Research (IITCI) CONICET-UNCo and continuing working in joining technologies and phase transformations and diffusion phenomena.