Rumu Halder Banerjee¹, Ashok Arya¹, Srikumar Banerjee¹; ¹Bhabha Atomic Research Centre; Homi Bhabha National Institute

The ordering and clustering tendencies in alloys are often manifested either in the formation of superlattice structures with symmetry elements which are a subset of those of the parent structure or in the development of concentration modulations along specific crystallographic directions. A simultaneous or sequential operation of clustering and ordering processes may lead to formation of ordered particles aligned along elastically soft directions. This has been previously demonstrated based on first principles thermodynamic calculations, in the Al-Li and Ni-Mo systems, identifying the temperature-concentration-domains over which different sequences of transformations operate. A summary of these studies will be presented. The addition of Cr in Ni-Mo alloys changes the relative stabilities of the competing superlattice structures – a factor which determines the constituent phases in commercial Hastelloys. Phase stabilities in the Ni-rich side of the ternary Ni-Mo-Cr system will be discussed for illustrating the influence of ternary addition in the phase evolution process.