Microscopic Investigation of High-Temperature Oxidation of hcp-ZrAl 2
- PDF / 3,513,605 Bytes
- 15 Pages / 439.37 x 666.142 pts Page_size
- 49 Downloads / 243 Views
Microscopic Investigation of High‑Temperature Oxidation of hcp‑ZrAl2 Zhangping Hu1 · Yifei Xu1 · Zongqing Ma1 · Chong Li1 · Yuan Huang1 · Yongchang Liu1 · Zumin Wang1 Received: 29 November 2019 / Revised: 5 August 2020 © Springer Science+Business Media, LLC, part of Springer Nature 2020
Abstract The high-temperature oxidation of ZrAl2 upon exposure to pure O2 at 800–950 °C was studied in terms of the oxidation kinetics and the formation mechanism of the oxide layer. The alloy followed parabolic oxidation kinetics, and the activation energy of oxidation was 239 ± 14 kJ/mol. During the early stages of oxidation below 850 °C, a single-layer oxide formed due to the crystallization of the initially formed amorphous oxide layer. A multilayer oxide structure developed at higher temperatures, due to the slightly higher affinity of oxygen for Zr than for Al and the oxidation-induced compositional changes. Keywords Thermal oxidation · Zr–Al alloys · Multilayer oxide · Oxidation kinetics
Introduction The surficial oxide layers are inevitably formed on the in-service functional and structural materials, which intensively determines their surface-related properties, such as corrosion resistance, catalytic activity, friction, wear and long-term reliability [1–4]. The compositions and microstructures of the oxide layers are governed by many factors, such as oxidation conditions (including temperature, time and oxygen partial pressure [5]), atomic structure and composition of the parent alloys [6]. Zr-M (M = Al, Sn, Mo and Nb) binary alloys possess good physical properties, such as good high-temperature creep resistances and low thermal expansion coefficients [7–13], and thus are widely used as fuel cladding materials for pressurized-water reactor [14, 15] and hydrogen absorbing agents [16]. Among the Zr–M binary alloy family, Zr–Al alloys attract intensive attentions due to their excellent * Chong Li [email protected] * Zumin Wang [email protected] 1
School of Materials Science and Engineering, Tianjin University, Tianjin 300350, China
13
Vol.:(0123456789)
Oxidation of Metals
physical properties, such as high thermal conductivity, high hardness and superelastic properties [17–22]. ZrAl2 alloy has the highest bulk modulus, shear modulus and Young’s modulus among the various Zr–Al intermetallic phases [23, 24], as shown in the phase diagram of Zr–Al binary system (Fig. 1) [25]. The atomic structure of ZrAl2 is similar to the topologically close-packed (TCP) M gZn2 (Laves phase) [26], which can result in a good high-temperature stability. Therefore, ZrAl2 is a promising high-temperature structural material, for example, in thermonuclear reactors [26, 27]. The thermal oxidation of Z rAl2 alloys in the temperature range of 350–750 °C has been studied [6, 28]. Synchronous oxidation of Zr and Al in the Z rAl2 alloy results in the formation of amorphous ( Zr0.33Al0.67)O1.66 oxide layers with a thickness of tens of nanometers to several micrometers. The amorphous Zr–Al–O oxide with a stoichiometric composition
Data Loading...
