Effect of Ni content on solidification cracking susceptibility of Inconel 706 Ni-base superalloy

Abstract

Summary Inconel 706 Ni-base superalloy has been developed on the basis of Inconel 718 to confer the economic advantage of Ni content saving. The modified alloy has much the same high strength, high ductility and high-temperature oxidation resistance as Inconel 718, while having a slightly higher hot-cracking susceptibility. The hot-cracking susceptibility of Inconel 706, however, has not yet been investigated in any great detail. The trans-varestraint test was conducted to determine the solidification cracking susceptibility of Inconel 706 depending on the base metal Ni content. Three types of Ni-base alloys with an Ni content of 44, 55, and 65mass%Ni were used. The fracture surfaces of the trans-varestraint test specimens show the typical dendrite structure. Quantitative analysis of the cracks reveals that the solidification crack length and the temperature range in which hot-cracking occurs (brittle temperature range (BTR)) decreases with an increasing Ni content. Calculation of the liquidus and solidus temperatures of the alloys by thermocalc data also shows that the solidification temperature range decreases with an increasing Ni content. Based on these results, it is concluded that improvement of the solidification cracking susceptibility with an increasing Ni content is due to a decrease in the solidification temperature range of the alloys.