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The Effects of Strain Rate and Minor Baron Addition on Brittle-to-Ductile Transition Temperature in Gamma TiAl Alloy

Published online by Cambridge University Press:  10 February 2011

Dongliang Lin(T. L. Lin) ,
Yu Wang ,
Junliang Liu  and
Chi C. Law
Dongliang Lin(T. L. Lin)
Affiliation:
School of Materials Science and Engineering, Shanghai Jiao Tong University, Shanghai, 200030 P R. China
Yu Wang
Affiliation:
School of Materials Science and Engineering, Shanghai Jiao Tong University, Shanghai, 200030 P R. China
Junliang Liu
Affiliation:
School of Materials Science and Engineering, Shanghai Jiao Tong University, Shanghai, 200030 P R. China
Chi C. Law
Affiliation:
Materials & Mechanics Engineering, United Technologies - Pratt & Whitney, East Hartford, Connecticut, 06108, U. S. A.
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Abstract

Brittle-to-ductile transition (BDT) temperature (TBD) was evaluated according to temperature dependence of tensile properties under different strain rates from 10−5to 10−1s−1in two-phase Ti-47Al-2Mn-2Nb and Ti-47A1–2Mn-2Nb-0.8 TiB2alloys with nearly lamellar microstructure. Based on the strain rate dependence of the determined TBD values, apparent BDT activation energies were determined using Zener-Hollomon factor. Tensile fracture surfaces were observed using a scanning electron microscope while deformation substructures were investigated by transmission electron microscopy. It was found that the BDTT of both alloys increased sharply with the strain rate and that the minor addition of 0.8 vol% TiB2reduced TBD by about 100K at the same strain rate. The TiB2addition also decreases the apparent BDT activation energy from 324 to 256 kJ/mol. Both of these values approximate to self- or inter-diffusion of Ti and Al atoms in TiAl phase. Transgranular fracture and dimple fracture were found dominant in fracture surfaces below and above TBD, respectively. The most common 1/2<110] ordinary dislocations were found to begin climb at mound TBD. All this evidence, as well as a theoretical calculation using the Nabarro Model, add up to a conclusion that the BDT is controlled by dislocation climb in both alloys.

Type
Research Article
Information
MRS Online Proceedings Library (OPL) , Volume 552: Symposium KK – High-Temperature Ordered Intermetallic Alloys VIII , 1998 , KK2.7.1
Copyright
Copyright © Materials Research Society 1999

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