Advanced microstructural characterisation of cast ATI 718Plus®—effect of homogenisation heat treatments on secondary phases and repair welding behaviour

Artikel i vetenskaplig tidskrift, 2020

The influence of base metal conditions on the weld cracking behaviour of castATI 718Plus® is investigated by comparing 4 h and
24 h dwell time pseudo-hip homogenisation heat treatments at 1120, 1160 and 1190 °C with the as-cast microstructure. Scanning
electron microscopy (SEM), X-ray diffraction (XRD) on electrolytically extracted powder and transmission electron microscopy
(TEM) were used to identify Nb-rich secondary phases in interdendritic areas as the C14 Laves phase and Nb(Ti) MC-type
carbides. All homogenisation heat treatments but the 1120 °C 4-h condition dissolve the Laves phase. A repair welding operation
was simulated by linear groove multi-pass manual gas tungsten arc welding (GTAW). The Laves phase containing microstructures
resulted in lower total crack length for heat affected zone cracking. Constitutional liquation of Nb(Ti) MC-type carbides is
observed as a liquation mechanism in Laves-free microstructure, while thick liquid film formation due to the Laves eutectic
melting could reduce the formation of weld cracks in microstructures containing the Laves phase.