Effect of Thermochemical Treatment in Regulated Gas Media on the Thermal Resistance of Zr1%Nb Alloy
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EFFECT OF THERMOCHEMICAL TREATMENT IN REGULATED GAS MEDIA ON THE THERMAL RESISTANCE OF Zr1%Nb ALLOY V. M. Fedirko,1, 2 O. H. Luk’yanenko,1 V. S. Trush,1 P. I. Stoev,3 and M. A. Tykhonovs’kyi3
UDC 620.197.5: [669.296: 621.785.062]
We perform experimental investigation of the oxidation of Zr1%Nb zirconium alloy after preliminary thermochemical treatment of ring specimens made of the pipe of a fuel element. It is shown that the preliminary nitriding protects Zr1%Nb alloy against the oxidation in air ( T = 550°C, τ = 100 h) to a greater extent than the preliminary treatment in regulated oxygen-containing media. Keywords: zirconium alloy, thermochemical treatment, oxidation, mass increment, subsurface layer, hardness.
Due to the combination of unique physicomechanical properties with small cross-section of absorption of thermal neutrons, zirconium and its alloys are extensively used in nuclear engineering, which makes them noncompetitive structural materials for operation in the active zone of thermal-neutron reactors [1, 2]. At the same time, the action of some factors significantly decreases the possibility of their application. In particular, the service properties of zirconium are strongly affected by an interstitial element, i.e., by oxygen. It easily reacts with zirconium and participates in all processes running in the material under various conditions, including thermal, radiation, and mechanical processes. However, the data on the influence of oxygen dissolved in the subsurface layer of the metal remain poor and contradictory [3, 4]. The thermochemical treatment (TCT) is one of the efficient methods of control over the structure and characteristics of the subsurface layers of metals capable of improvement of various physicomechanical characteristics of the materials [5]. Therefore, it is reasonable to clarify the influence of subsurface layers enriched with interstitial elements on the properties of the pipes made of Zr1%Nb alloy and intended for fuel elements, in particular, in the course of oxidation. The aim of the present work is to study the process of oxidation of the pipes of fuel elements made of Zr1%Nb alloy in air at a temperature of 550°C for 100 h after the thermochemical treatment in regulated oxygen- and nitrogen-containing media. Material and Method As an object of investigations, we chose a pipe of the fuel element made of Zr1%Nb alloy in Ukraine [6]. In order to determine the increment of mass after the thermochemical treatment and oxidation, we performed durometric investigations by using specimens in the form of rings cut out from the pipe of fuel element (Fig. 1). 1 2 3
Karpenko Physicomechanical Institute, Ukrainian National Academy of Sciences, Lviv, Ukraine. Corresponding author; e-mail: [email protected].
Institute of Solid State Physics, Materials Science, and Technologies, “KhFTI” NSC, Ukrainian National Academy of Science, Kharkiv, Ukraine. Translated from Fizyko-Khimichna Mekhanika Materialiv, Vol. 52, No. 2, pp. 61–66, March–April, 2016. Original article submitted November 27,
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