High-Temperature Oxidation Behavior of Refractory High-Entropy Alloys: Effect of Alloy Composition

Abstract

The high temperature oxidation behavior of a new family of refractory high entropy alloys (HEAs) with compositions of W-Mo-Cr-Ti-Al, Nb-Mo-Cr-Ti-Al and Ta-Mo-Cr-Ti-Al was studied at 1000°C and 1100°C. Based on these equimolar starting compositions, the main incentive of this study was to select the most promising alloy system whose properties may then be successively improved. Despite the high amount of refractory elements, all HEAs studied here showed good oxidation resistance at least during 48h of air exposure at 1000°C and 1100°C. Moderate values of mass gain and complex oxidation kinetics were observed for the W-and Nb-containing HEAs. These alloys formed inhomogeneous oxide scales possessing regions with thick and porous layers as well as areas revealing quite thin oxide scales due to the formation of discontinuous Cr-and Al-rich scales. The most promising behavior, though, was shown by the alloy Ta-Mo-Cr-Ti-Al which followed the parabolic rate law for oxide growth due to the formation of a thin and compact Al-rich layer.

Contribution of Lattice Distortion to Solid Solution Strengthening in a Series of Refractory High Entropy Alloys

“…The alloy exhibits a reasonable high temperature strength. Furthermore, the capability of increasing oxidation resistance by adding Cr and Al has been verified for the present and related alloys [15][16][17][18].…”

Simulations of oxidation of metal nanoparticles with a grain boundary inside

“…[3][4][5][6][7][8][9][10][11]). Nowadays, this area is still open for research (see, e.g., recent experiments [12][13][14][15][16] and models [17][18][19][20][21][22][23][24][25]) due to its complexity related to (i) generation of the electric field between the metal-oxide and oxide-gas interfaces, (ii) stress (or lattice strain) arising due to the lattice expansion during oxide formation, (iii) numerous defects in the oxide structure and their evolution, e.g., via grain growth, and (iv) defects, e.g., grain boundaries and dislocations in the metal phase.…”

High-temperature oxidation behaviour of AlxFeCrCoNi and AlTiVCr compositionally complex alloys

“…While CCAs exhibit sufficiently high melting points and phase stability for demanding applications, they however remain dependent on the formation of a reliable protective oxide scale for continuity of usage, which is no different to "traditional" Fe-and Ni-base alloys. At present, there is insufficient knowledge regarding high-temperature oxidation behaviour of CCAs more generally, with relatively few studies reported such properties [8][9][10][11][12][13][14][15][16][17][18][19][20][21][22]. A literature survey of the limited research within the context of oxidation of CCAs at temperatures ranging from 500 to 1200°C is provided in Table 1.…”

“…An appraisal of the literature (Table 1 and Fig. 1) reveals that (i) the high-temperature oxidation of only a very limited number of CCAs have, to date, been studied, with the majority of studies focusing on either the CoCrFeNiX (X = Al, Mn, Si) [6,10,11] or MoCrTiAlY (Y = W, Nb, Ta) [14] systems, (ii) the two essential alloying elements, Cr [9] and Al [10], positively influence the oxidation properties of CCAs, and (iii) the surface oxide forming on CCAs containing Mn [10,16] and Cu [21] are prone to failure e.g. cracking and spallation, due to the formation of Mn-rich oxides.…”