Abstract
Alloy 718 is a nickel-based superalloy which consists of an FCC solid solution of Ni, Fe, and Cr strengthened with γ″ precipitates. The composition of the alloy is shown in Table 1. It has excellent high temperature mechanical properties and oxidation resistance. However, Alloy 718 is susceptible to hot cracking in weld heat affected zones (HAZ) as a result of the formation of intergranular liquid. This metastable grain boundary liquid may be due to “constitutional liquation” of second phase particles, known as constitutional liquid film migration (CLFM). Radhakrishnan and Thompson report that CLFM can occur in situ in the weld HAZ of alloy 718 as a result of constitutional liquation.Constitutional liquation can be described in terms of a binary alloy with a phase diagram such as theone shown in Figure 1. If an alloy of composition C° is rapidly heated above theeutectic temperature, TE, to temperature T, the AB particles will not have sufficient time to dissolve, as dictated by equilibrium.
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