Creep and oxidation kinetics at 1100°C of nickel-base alloys reinforced by hafnium carbides

Abstract

The mechanical reinforcement of polycrystalline alloys at elevated temperature may be achieved by HfC carbides. Generally such alloys must be also resistant against oxidation by hot gases and corrosion by molten substances. Polycrystalline chromium-rich nickel-based alloys represent a good solution for answering these requirements about the high temperature chemical resistance. Unfortunately they tend to be rather mechanically weak at high temperature compared to γ/γ' single crystals. In this work a new family of alloys, combining a chromium-rich nickel-based matrix and an interdendritic HfC carbide network, is studied. Two equiaxed cast alloys were elaborated by classical foundry and the obtained microstructures were examined. Two types of high temperature properties were characterized at 1100°C, creep resistance and oxidation kinetic. The microstructures of the two alloys are composed of a dendritic austenitic matrix and of script-like eutectic carbides which are recognized to be very favorable for high strength at high temperature. Creep tests proved this potential benefit by showing that these alloys are much more resistant than usual cast polycrystalline nickel-based alloys. The base made of nickel and the 25 wt.% content in chromium allow obtaining a chromia-forming behavior leading to good resistance against oxidation in hot air.

Effects of Initial δ Phase on Creep Behaviors and Fracture Characteristics of a Nickel‐Based Superalloy

“…Bao et al discussed the creep crack growth rates and fracture features of FGH97 superalloy in the service temperature. Berthod and Conrath studied the creep and oxidation kinetics of nickel‐base alloys reinforced by HF carbides at 1100 °C. Giorgetti et al observed the microstructural change of rené N4 superalloy during creep and aging at high temperatures.…”

Effect of NbC Addition on the High-Temperature Oxidation Resistance of Co- and Ni-Based Chromium-Rich Alloys

“…After heat treatment, niobium and chromium carbides have adopted a more circular shape; they get fragmented in order to reduce their matrix/carbide interfacial energy, a classical phenomenon. The obtained microstructures can be compared to the ones of as-cast ternary alloys earlier studied: Ni-25Cr-0.5 [9] and Co-25Cr-0.5C [16] (in wt.%), which can play the role of Nb-free references. In these ternary alloys, only chromium carbides were present.…”

“…The Nb-free Ni-based alloy [9] has a chromia-forming behavior at 1100°C since only the Cr 2 O 3 layer is formed hence the mass gain is low. This chromia layer protected the alloy from oxidation by acting as diffusion barrier to O and Ni, which avoided the formation of NiO and NiCr 2 O 4 .…”

“…This was recently done with conventionally cast chromium-rich cobalt-based [6], iron-based [7] and nickel-based [8] alloys strengthened by eutectic HfC carbides. These new model alloys displayed interesting mechanical properties at temperatures as high as 1100°C [9] and even 1200°C [10]. Beside TaC and HfC, other MC carbides may be considered, involving metals not so expensive as tantalum and hafnium in particular.…”

Microstructures and hardness of as-cast {C, Ta or Ti or Hf of Zr}-containing Cr-rich Niobium-based alloys candidate for uses at elevated temperatures

“…This is, for instance, what was recently done with conventionally cast chromium-rich cobalt-based [9,10] , iron-based [11] and nickel-based [12] alloys strengthened by eutectic HfC carbides. Such alloys, taking back the commonly used base elements of the current superalloys, and in which chromium / tungsten or tantalum carbides are replaced by exotic but much more stable carbides, showed very interesting mechanical properties at temperatures as high as 1100°C [13] and even 1200°C [14] .…”