Effect of 1 at.% nitrogen addition on the creep resistance of two phase TiAl alloy

Abstract

The effect of the 1 at.% nitrogen addition on the lamellar Ti-48.5Al-1.5Mo (at.%) alloy was investigated at the creep test conditions of temperature range from 750 to 850 degrees C under constant stress ranging from 150 to 250 MPa in air. Effect of N addition on the minimum creep rate depends on stress level. In 200 and 250 MPa, N reduced the minimum creep rate significantly, however, gave no effect in 150 MPa. It was also observed that the N addition significantly enhanced the creep resistance in primary regime. Precipitate hardening of p-phase (TI,AIN) and solute hardening of nitrogen atoms may be responsible for this beneficial effect. While creep fracture of mother alloy occurred by secondary crack, N addition alloy fractured by cavity formation. We considered the controlling process of the minimum creep rate at 150 MPa stress level to be identical for the mother alloy and N addition alloy, and the nitrides and nitrogen atoms give little effect on the rate controlling process. (C) 1999 Elsevier Science S.A. All rights reserved.