Welding metallurgy of alloy HR-160 (R)

The solidification behavior and resultant solidification cracking susceptib ility of autogenous gas tungsten are fusion welds in Alloy HR-160(R) was in vestigated by Varestraint testing, differential thermal analysis and variou s microstructural characterization techniques. The alloy exhibited a liquid us temperature of 1387 degrees C and initiated solidification by a primary L --> gamma reaction in which Ni, Si and Ti segregated to the interdendriti c liquid and cosegregated to the gamma dendrite cores. Chromium exhibited n o preference for segregation to the solid or liquid phase during solidifica tion. Solidification terminated at approximate to 1162 degrees C by a eutec tic-type L --> [gamma+ (Ni,Co)(16)(Ti,Cr)(6)Si-7] reaction. The (Ni,Co)(16) (Ti,Cr)(6)Si-7 phase is found to be analogous to the G phase that forms in the Ni-Ti-Si and Co-Ti-Si ternary systems, and similarities are found betwe en the solidification behavior of this commercial multicomponent alloy and the simple Ni-Si and Ni-Ti binary systems. Reasonable agreement is obtained between the calculated and measured volume percent of the [gamma+(Ni,Co)(1 6)(Ti,Cr)(6)Si-7] eutectic-type constituent with the Scheil equation using experimentally determined k values for Si and Ti from electron microprobe d ata. The alloy exhibited a very high susceptibility to solidification crack ing in the Varestraint test. This is attributed to a large solidification t emperature range of 225 degrees C and the presence of 2-5 vol-% solute-rich interdendritic liquid that preferentially wets the grain boundaries and in terdendritic regions.