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

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 r ange from 750 to 850 degrees C under constant stress ranging from 150 to 25 0 MPa in air. Effect of N addition on the minimum creep rate depends on str ess level. In 200 and 250 MPa, N reduced the minimum creep rate significant ly, however, gave no effect in 150 MPa. It was also observed that the N add ition significantly enhanced the creep resistance in primary regime. Precip itate hardening of p-phase (TI,AIN) and solute hardening of nitrogen atoms may be responsible for this beneficial effect. While creep fracture of moth er 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.