The Role of Oxygen Uptake and Scale Formation on the Embrittlement of Vanadium Alloys

Abstract

Vanadium alloys are of interest in fusion energy systems, however, their environmental durability is a major concern. Specimens of V-4Cr-4Ti were exposed to air and oxygen (10 5 Pa), low pressure (10 −3 −10 −6 Pa) oxygen and high purity He environments (10 5 −10 1 Pa) at 500−700 • C in order to characterize the surface oxide, determine oxidation kinetics and quantify effects on mechanical properties at 25 and 600 • C. At low oxygen pressures (P O 2 10 −5 Pa), linear reaction kinetics were measured for exposures up to 2000 hr and the data were used to develop a mathematical expression for the oxidation rate as a function of temperature and oxygen pressure. At higher pressures, linear-parabolic reaction kinetics were associated with high oxygen uptake and the formation of an external oxide layer. Room-temperature and 600 • C tensile ductility was reduced by these exposures, but specimens which formed an external oxide were found to retain some tensile ductility after exposure. However, similar specimens with an external oxide that were subsequently annealed for 2000 hr at 700 • C became severely embrittled demonstrating that a surface oxide will not prevent degradation of this refractory alloy. Exposures in He were performed to determine the effect of total gas pressure on oxygen uptake.

Oxidation Behavior of ODS Fe?Cr Alloys

“…Vanadium alloys are susceptible to environmental embrittlement by oxygen and hydrogen, and to low temperature radiation embrittlement. [6][7][8][9] SiC composites have limitations typically associated with ceramics of fabrication and lack of engineering design data. 10 Ferritic steels are limited in temperature (≈550 • C) due to creep strength.…”

Initial characterization of V–4Cr–4Ti and MHD coatings exposed to flowing Li

“…Fig. 3 shows results from room temperature tensile tests of specimens from the hot and cold legs as well as average values for unexposed specimens from the same specimen batch which have similar properties to prior studies [21][22][23]. The 0.2% yield and ultimate tensile strengths increased in specimens as the exposure temperature decreased, Fig.…”

Design strategies for new oxidation-resistant high temperature alloys

“…The high solubility of O in Nb (and V and Ta) means that a surface oxide acts as a source of O rather than a protective layer. This was demonstrated for V-4Cr-4Ti alloys, where a ductile specimen with a surface oxide was embrittled by annealing at 700°C in a quartz ampoule (Pint and DiStefano, 2005). The surface oxide layer dissolved into the V alloy substrate due to the lack of thermodynamic equilibrium in this metaloxide system.…”