Effects of oxygen and hydrogen at low pressure on the mechanical properties of V-Cr-Ti alloys

Exposure of V-Cr-Ti alloys to low oxygen partial pressures;It high temperat ure results in oxygen absorption and internal oxidation. Characterization o f a V-4Cr-4Ti alloy after oxidation at 500 degreesC revealed a microstructu re with ultrafine oxide precipitates in the matrix and along grain boundari es. Heat treatment at 950 degreesC following oxidation resulted in large Ti Ox precipitates in the matrix and grain boundaries. Tensile ductility was r educed by exposure to low-pressure oxygen under the temperature and pressur e conditions. However, heat treatment at 950 degreesC following oxidation w as generally effective in recovering ductility irrespective of initial anne aling treatment or grain size. Without increases in oxygen, >500 wppm hydro gen was required to cause significant decreases in tensile elongation. When oxygen was added either during or prior to hydrogen exposure, significant embrittlement occurred with 100 wppm hydrogen. Because of this synergism wi th hydrogen, oxygen pick-up remains a major concern for V-Cr-Ti alloys in f usion reactor applications. (C) 2000 Elsevier Science B.V. All rights reser ved.