DESIGN OF CUBIC Ni-BASED ALLOYS FOR USE AS COATING IN PETROCHEMICAL INDUSTRY – A FIRST PRINCIPLES APPROACH

Abstract

This work presents the structural stability and mechanical properties of ordered face-centred cubic (FCC) Ni-Cr binary and ternary alloys. The effects of alloying on these properties have been evaluated using the first principles density functional theory (DFT) within generalised gradient approximation (GGA). The calculated heats of formation show that the introduction of third elements (Al, Ti, Mo, Sn) improved the thermodynamic stability of the usually unstable L12 Ni3Cr phase. Unsurprisingly, ternary alloys that yielded higher mechanical properties were those alloyed with Al and Ti owing to their ability to form a very stable L12 phase with Ni. Therefore, the theoretical technique has been successfully employed to identify promising high-strength cubic Ni-based ternary intermetallic alloys that can be used as coatings.

Effect of heat-treatment on corrosion performance of Ni and Ni-Cr-based alloys

“…However, it seems the high temperature heat resistance takes priority over corrosion resistance in the development of these alloys. This excellent heat resistance is attributed to high content of refractory elements (with brittle character), which also promotes formation of undesired sigma (σ) Ni2Cr phase with a low coefficient of thermal expansion (CTE) compared to the austenitic matrix [13]. Consequently, resulting CTE mismatch has potential to become a crack-initiation point during shutdown cycles, thus causing material failure.…”

“…Thus in the current work, the alloys designed using density-functional-theory (DFT) based computational materials modelling software described elsewhere [13] were experimentally manufactured, heat-treated, characterized and tested under corrosion environment. Since the alloy 800 used as a substrate material for construction of reformers in petrochemical plants [14] has an austenitic structure, the suitable coating material needs also to be of face-centred cubic (FCC) crystal structure such as Ni-Cr-X (Cu, Fe) complex corrosion-resistant alloys that are mechanically stable at both low and high temperatures.…”

Improving mechanical properties of Ni electrode through alloying and heat treatment

“…Thus, Ni alloys containing Cr display a corrosion resistance in oxidising media. Furthermore, the addition of Cr to Ni has been shown to enhance mechanical properties such as the tensile strength associated with the stiffness of the materials [9]. Furthermore, the addition of molybdenum (Mo) and copper (Cu) is known to enhance the corrosion resistance of nickel in reducing media [7].…”

“…The choice of Cr composition that is retained in the austenite phase even at lower temperatures is guided by the binary Ni-Cr phase diagram shown in Figure 1 [11]. The actual Cr composition of 18 atomic percent (at.%) used in this work has previously been predicted using first-principles calculations [9]. To further increase strength, the FCC transition metal, which is a non-carbide former, Cu, is added to form a ternary alloy [12].…”

First-principles study of binary austenitic Ni-Cu alloys

“…Nickel (Ni) forms as a base for a wide range of Ni alloys used in numerous engineering applications due to their good mechanical properties and excellent corrosion resistance in various environments [1][2][3]. This performance is owed to the fact that Ni has the ability to dissolve high concentrations of alloying elements in comparison to other metals and still maintain good metallurgical stability [4].…”