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Abstract

The welding metallurgy of Thermo-Span alloy has been evaluated and compared with that of two common superalloys, alloy 909 and alloy 718. The solidification behaviour and fusion zone hot cracking tendency were evaluated using differential thermal analysis and varestraint testing. Gleeble thermal cycle simulations were used to assess the hot ductility of the alloy during weld thermal cycles. Solidification microstructures were characterised by optical and electron microscopy. Differential thermal analysis indicated that melting of wrought Thermo-Span initiates at ternperatures near 1265°C and continues to ∼1413°C. In a manner similar to that of alloy 909, Thermo-Span solidifies with the formation of primary austenite followed by a terminal eutecticlike constituent near 1225°C. Varestraint testing indicates that the hot cracking tendency of Thermo-Span is similar to that of alloys 718 and 909. Hot ductility testing revealed that Thermo-Span displays ductilities on heating and cooling similar to those of alloy 909 and other nickel based superalloys. Solidification microsegregation patterns were determined by electron probe microanalysis, and the terminal solidification phases were identified by analytical electron microscopy and backscattered electron Kikuchi patterns to be an austenite–Laves eutecticlike constituent.

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Solidification and welding metallurgy of Thermo-Span alloy

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