Indentation study of titanium, zirconium, and hafnium hydrides
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1043-T09-11
Indentation study of titanium, zirconium, and hafnium hydrides Masato Ito, Shunichiro Nishioka, Hiroaki Muta, Ken Kurosaki, Masayoshi Uno, and Shinsuke Yamanaka Division of Sustainable Energy and Environmental Engineering, Graduate School of Engineering, Osaka University, 2-1 Yamada-oka, Suita, Osaka, 565-0871, Japan ABSTRACT The mechanical properties of titanium, zirconium, and hafnium hydrides were evaluated by indentation tests in the present study. Single-phase bulk specimens of titanium, zirconium, and hafnium hydrides with a fluorite type structure were produced using a Sieverts’ apparatus. The indentation hardness values of titanium and hafnium hydrides were lower than those of the pure metals and drastically decreased with increasing hydrogen content. The hardness of zirconium hydride was higher than that of pure zirconium and slightly depended on hydrogen content. The hardness of the hydrides decreased with increasing maximum indentation load, which has been referred to as indentation size effect. The dependences of hardness on the indentation depth for the hydrides were found to obey the Nix–Gao model. The indentation size effects for the hydrides were significantly smaller than those for the pure metals.
INTRODUCTION Metal hydrides, especially titanium, zirconium, and hafnium hydrides, are important materials for developments of the nuclear power systems from the following points of view: - Titanium and its alloys have been extensively utilized and are expected to be used in steam condenser tubes, irradiation targets for transmuting radioactive wastes, and overpacks for geological disposal of high-level radioactive wastes because of their high chemical durability and strength. However, titanium alloys are hydrogenated due to corrosion, followed by the production of titanium hydrides. The precipitations of the hydrides are known to adversely affect the mechanical properties of the alloys. Therefore, in order to verify the mechanism for the degradation of the integrity of the titanium alloys, it is essential to study the mechanical properties of titanium hydride. - Zirconium alloys have been widely used in the fuel cladding of nuclear reactors. In recent years, hydrogen behavior has been examined in detail to achieve the extended burn-up of nuclear fuels. Zirconium alloys absorb a part of hydrogen generated by a corrosion reaction during operation, which then form zirconium hydrides. This causes problems such as embrittlement. On the contrary, actinide–zirconium hydrides are expected to be used as fuel targets for the transmutation of minor actinides. The targets are polyphasic materials containing the zirconium hydride that is considered to play important role for controlling their hydrogen dissociation pressure. Therefore, it is important to evaluate the characteristics of zirconium hydride. - Since hydrogen can moderate the fast neutrons and the hafnium has superior absorptive property of the thermal neutron, hafnium hydride can efficiently absorb fast neutrons. Therefore, hafnium hydride i
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