A brief discussion on the tensile creep deformation behaviour of wrought single-phase γ-TiAl

Abstract

Creep deformation behaviour in single phase c-TiAl alloy has been an extensively studied topic since the late 1970 s. A lot of literatures have reported creep behaviour of c-TiAl alloys, manufactured using different processing techniques [1][2][3][4][5][6][7]. The present discussion revisits the original work on understanding the tensile creep deformation behaviour of wrought single-phase c-TiAl alloy by Hayes et al. [8] and is aimed to develop an understanding of steady state creep, through strain vs strain rate and strain vs ln(strain rate) plots. Besides, it also attempts to study the variation of stress exponent with temperature between 760 and 900⁰C and also, to determine activation energies using the two most common approaches, namely: Zener-Hollomon (Z-H) [9] and Sherby-Dorn (S-D, temperature compensated time approach) [10] for stress levels of 69.4 and 103.4 MPa between 760 and 900⁰C.

ɤ-TiAl alloy: Tensile creep deformation behaviour and creep life at 832 °C

“…Moreover, a Ref. [28]), it may be inferred that a decrease in the creep activation energy (for both Coble and NH creep) significantly reduces the creep life of the material with increasing stress levels from 69.4-103.4 MPa.…”

“…2) with the aforementioned reports (Refs. [1], [28]), it may be inferred that M-G based approach to determine the creep life also predicts that tr decreases with increasing stress levels (from 69.4 to 103.4 MPa) at 832 Based on the Ashby's model [13], [14], [38], [39], the constitutive equation for NH (or lattice diffusion creep) is given as:…”

“…where, ε ' ̇is the steady state creep rate (~ ε ./0 ̇ based on the justification that many metallic materials may not exhibit steady-state creep (provided in Ref. [28])), tr is the rupture time (expressed in seconds) and 𝐶 ,-(~1.40 at 832 °C) is the M-G constant (obtained from Ref.…”

ɤ-TiAl Alloy: Tensile Creep Deformation Behaviour and Creep Life at 832^°C

“…[14], [16], [33]- [37]). Hayes and Martin [1] and Saha [28] have reported that ε̇ decreases with increasing stress levels (from 69.4-103.4 MPa) at 832 °C . Moreover, Saha [28] has reported that the creep mechanisms operating at different stress levels (69.4 and 103.4 MPa) at 832 °C are independent of each other and hence, are not sequential.…”

“…where, ε̇is the steady state creep rate (~ ε̇ based on the justification that many metallic materials may not exhibit steady-state creep (provided in Ref. [28])), tr is the rupture time (expressed in seconds) and (~1.40 at 832 °C ) is the M-G constant (obtained from Ref.…”