Effect of boron and phosphorus on HAZ microfissuring of Allvac 718 Plus superalloy

Abstract

Heat affected zone (HAZ) microfissuring was investigated in electron beam welds of two Allvac 718 PLUS (718 Plus) alloys with different boron and phosphorus contents. Two preweld solution heat treatments were used and microfissuring susceptibility was evaluated by measuring the HAZ crack lengths in both alloys after bead on plate welding. The segregation behaviour of boron and phosphorus was studied before and after welding by secondary ion mass spectrometry (SIMS). Hot ductility behaviour of the alloys in the standard solution preweld heat treatment was also examined. The results of crack measurements, segregation studies and hot ductility tests correlated well with each other. It was observed that besides constitutional liquation of Nb rich MC type carbides, segregation of B and P largely influenced the microfissuring susceptibility of the alloy. Heat affected zone microfissuring increased with an increase in BzP concentrations and with an increase in the preweld solution heat treatment temperature. Segregation behaviour of B and P and its contribution to microfissuring in Allvac 718 Plus alloy were discussed.

Effects of Boron on the Microstructure, Ductility-dip-cracking, and Tensile Properties for NiCrFe-7 Weld Metal

“…The segregation of boron at GBs would cause GB embrittlement and deteriorate hot ductility of a nickel based alloy [41,48] , making them more susceptible to DDC. The general effect of increasing boron concentration at GB is to increase DDC tendency, with boron having a highly significant effect, in contrast to the minor influence of C [34] .…”

“…Chaturvedi [41] found nonequilibrium segregation of boron could not be suppressed by water quenching. Karlsson and Norden [42] have measured GB boron levels of up to 18 at.% in stainless steel using an atom probe.…”

“…Special metal corporation (SMC) added boron to FM-52M to reduce the tendency for DDC [46] . Several works in superalloys found that the addition of boron would cause heat-affected zone (HAZ) microfissuring [36,41,47] . The boron addition affects the wetting characteristics along the GBs and lowers the solidification temperature, increasing HAZ liquation cracking susceptibility.…”

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

“…High homogenisation heat treatments and their associated cooling cycles have been found to create an environment where non-equilibrium boron segregation can occur at grain boundaries in Alloy 718 and ATI 718Plus ® [14,15]. This in turn can lead to local melting point suppression and the formation of liquid during subsequent high temperature exposure.…”

Weldability of Ni-Based Superalloys Waspaloy® and Haynes® 282® - A Study Performed with Varestraint Testing

“…Therefore, differences of these elements are assumed to be less important. When considering the phosphorous content of 0.004 wt.% in Waspaloy®, which is double compared with that of Haynes® 282® and the boron content of 0.006 wt.% compared with 0.004 wt.%, respectively, the weldability is generally accepted to be worse for Waspaloy® [7,[25][26][27][28] . The element segregation of melting point depressants like boron and phosphorous, can reduce the melting point of the grain boundaries.…”