Accession Number:

ADA330577

Title:

Creep Resistance of Gamma TiAl Microstructures.

Descriptive Note:

Final rept. 1 Jul 96-30 Jun 97,

Corporate Author:

CARNEGIE-MELLON UNIV PITTSBURGH PA DEPT OF METALLURGICAL ENGINEERING AND MATE RIALS SCIENCE

Personal Author(s):

Report Date:

1997-09-01

Pagination or Media Count:

3.0

Abstract:

The developtment of microstructure and its influence on creep properties has been studied in two Ti-48Al-2Cr-2Nb alloys. The addition of 0.9 atomic Mo to the Ti-48Al-2Cr-2Nb composition results in the formation of the ordered B2 phase. The presence of this phase along with a small amount of alpha2 at grain boundaries was found to effectively limit grain growth at 1125 deg C during heat treatments that produce equiaxed gamma microstructures. The gamma - alpha transformation produces a2 plates with several orientation variants within gamma grains during subsequent anneallng of the equiaxed gamma microstructures below the a-transus. Formation of this a2 morphology results from rapid up-quenching and this structure persists through annealing, cooling, and creep testing. Differences in minimum creep rates for several microstructures containing varying amounts multi or single variant gammaa2 grains are shown to be minimal. The presence of Mo has also resulted in improved creep resistance in equiaxed gamma, and gamma a2 B2 structures as compared to similar microstructures in the Ti-48Al-2Cr-2Nb alloy. Deformation during creep at 760 deg C at stresses between 200 and 400 MPa occurs by a combination of twinning and dislocation glide without recrystallization, resulting in power-law stress exponents in the range of 6 to 9. Ony minimal strain path dependence of the minimum creep rate was detected in a comparison of creep rates in stress jump, stress drop and single stress tests.

Subject Categories:

  • Inorganic Chemistry
  • Properties of Metals and Alloys
  • Crystallography

Distribution Statement:

APPROVED FOR PUBLIC RELEASE