Composition Design Of Ni-base Superalloys Based On The Cluster-plus-glue-atom Model

The Nickel-base superalloys find extensive applications in diverse areas such as aeronautics and astonautics, power plants, transportation, oil equipment and biomedical implants due to their superior high-temperature strength, ultimate tensile strength and toughness, substantial resistance to high-temperature creep and fatigue, excellent tolerance in severe operating environments of corrosion and oxidation as well as high level of alloying and stability. Therefore the development of Nickel-base superalloys with high performances is quite critical to enhance the defense power and industrial level of a nation.However, there are as many as over ten elements in the Nickel-base superalloys making the composition design quite complicated. In this paper, the structural model "Cluster-plus-glue-atoms" proposed in the long-term research of composition rules of metallic alloys and quasicrystals was applied to interpretate and to design the Nickel-base superallos. The basic cluster formula derived from the Ni-Cr binary phase diagram was set as [Cr-Ni12]Cr3, where [Cr-Ni12] cluster stands for a Cr-centered cuboctahedron surrounded by12Ni atoms in FCC lattice and three Cr atoms represent glue atoms. The site occupation of each alloying element in the cluster model is determined by its enthalpy of mixing with base Ni, thus a general cluster formula [(Al/Ti/Nb)-(Ni/Fe/Co)12](Cr/Al)3is generated.The designed alloy series were prepared into alloy rods by copper mould suction cast method and then heat-treated at1373K for2h followed by air cooling. Then a series of tests were conducted including OM, XRD and TEM determining the structure of designed alloys and Vickemess test, tensile test sat room temperature, electrochemical tests and hot corrosion tests evaluating their performance. Principal results are as follows.1) γ’ precipitation was subjected to the additions of various alloying elements:the alloys with one Al atom in cluster formula had extremely fine γ’ particles precipitated in the y matrix,[(Al1/3Ti1/3Nb1/3)-(Ni10Fe2)]Cr3with the substitution of Ti and Nb for Al in equal proportion had larger γ’precipitation in scales of nanometers, and in the [Al-(Ni10Fe2)](Cr2Al) alloy with two Al atoms, a lot of γ’ particles grew up to a size range of40-60nm.2) Among the designd alloys,[(Al1/3Ti1/3Nb1/3)-(Ni10Fe2)]Cr3and [Al-(Ni10Fe2)](Cr2Al) reached the highest hardness of2.8GPa, which was greatly improved as compared to the binary systems while Reference In718had a relatively low hardness of1.82GPa in the same condition.[(Al1/3Ti1/3Nb1/3)-(Ni10Fe2)]Cr3showed out the highest tensile strength σ0.2= 533.7MPa, σb=783.5MPa, as well as a good ducticity ψ=41.5%, ε=21.6%in the tensile test at RT.3)[Al-(Ni10Fe2)]Cr3and [Al-(Ni9Fe2Co)]Cr3possessed the best corrosion resistance in3.5wt.%NaCl solution among designed alloys, with Ecorr at-0.283V and-0.273V respectively and Icorr～0.44μA·cm-2. For a20-hour hot corrosion test in25%NaCl+75%molten salts at1173K, the average corrosion rate for [(Al1/3Ti1/3Nb1/3)-(Ni10Fe2)]Cr3was0.406g·cm-3·h-1, which was comparable to that of Reference In718alloy.