Deformation behavior of Zr 3 Al-Nb alloys II: Indentation creep studies
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I.
INTRODUCTION
THE hardness has been recognized as a simple and reliable means of determining the mechanical behavior of materials. Because of the ease and speed with which it can be conducted, an indentation hardness test was used to assess the mechanical properties of ductile metals to brittle ceramics.[1] The hardness is related to the physical and mechanical properties of the materials such as thermal conductivity, electrical resistivity, yield and ultimate tensile strength, fatigue strength, creep, and rupture properties.[2–6] The microindentation technique for measuring hardness has several advantages over the conventional method of measuring the strength of material. The material requirement in the case of the microindentation technique is very small. Unlike in the case of the conventional tensile testing method, where a separate sample is required for each temperature, in the microindentation technique, a number of tests at different temperatures can be carried out on the same sample. Therefore, microindentation can provide a quick assessment of the mechanical properties of materials as a function of temperature. In search of a material with better high-temperature properties, which can be used as structural material for pressurized heavy water reactors (PHWRs), Schulson et al.[7,8] have proposed Zr3Al-based alloys. Zr3Al has an ordered fcc structure (Cu3Au type; L12 structure) and a relatively low absorption cross section for thermal neutrons, a reasonably high melting point, and a moderate density. However, due to some inherent problems, Zr3Al-based materials have not been used for structural applications in PHWR.[9] It has been thought that ternary additions with niobium to Zr3Al could improve these shortcomings, and therefore, systematic work on Zr3Al-Nb R. TEWARI, Postdoctoral Fellow, is with the Department of Chemical and Materials Engineering, University of Cincinnati, Cincinnati, OH 45221. Contact e-mail: [email protected] G.K. DEY, Scientific Officer (H), Materials Science Division, T.R.G. KUTTY, Scientific Officer (G), and A.K. SENGUPTA, Scientific Officer (H), Radiometallurgy Division, and S. BANERJEE, Director, Materials Group, are with Bhabha Atomic Research Centre, Mumbai 400 085, India. N. PRABHU, Associate Professor, is with the Indian Institute of Technology–Bombay, Mumbai 400 076, India. Manuscript submitted June 7, 2002. METALLURGICAL AND MATERIALS TRANSACTIONS A
alloys was initiated in our laboratory. In our previous articles,[10] we demonstrated that the addition of Nb improves the hightemperature deformability of the alloy and identified the optimum temperature range for hot working of the Zr3Al-Nb alloys. Liquidus temperatures and elastic constants such as shear modulus, Young’s modulus, etc. of the preceding alloys were also determined.[10] The objective of the present study is to determine the hightemperature creep properties of the Zr3Al-Nb alloys. In this study, attempts were made to determine the operative creep mechanisms in different temperature regions by using hardnes
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