Department of Metallurgical & Materials Engineering

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The results of constant load creep tests on AISI 304 stainless steel at 873 and 973 K for different test conditions were found to obey the first order kinetics for tertiary creep. Distinct master creep curves were obtained at 873 and 973K with a separate set of constant values of K′, εt, β′ and CMG. A relationship between steady-state creep rate ε̇s, time spent in tertiary creep tt and limiting tertiary creep strain εt is formulated as ε̇s·tt/εt = constant and is found to be valid for all test conditions. Further, this relation is identical to the modified Monkman-Grant relation (MMGR) for the conditions satisfying f = 1/λ; it is postulated that the validity of MMGR is a consequence of first order kinetics. Another important outcome of this study is a generalised relation of the form ε̇s·tr = (ε23·εf)1 2; and this relation is compared with the relation proposed by Radhakrishnan, i.e. ε̇s·tr = (ε223·εf)1 3. It is suggested that cavities act as vacancy sinks and accelerate dislocation climb controlled recovery process leading to tertiary creep. Copyright © 1996 Acta Metallurgica Inc.

World University root node

Acta Materialia

Analysis of first order kinetics for tertiary creep in AISI 304 stainless steel

Al-Cu alloys containing 6, 11, 17, 24 and 33 wt% Cu, annealed for 0.5-100 h, were deformed by the differential strain-rate test technique over a strain-rate range of ≈4×10-6 to 3×10-2s-1 at temperatures ranging from 460-540°C. Superplastic behaviour, with strain-rate sensitivity, m≈0.5, and activation energy, Q=171.5 kJ mol-1, is shown by the Al-24Cu and Al-33Cu alloys at lower strain rates and higher temperatures. All the alloys show m≲0.20 at higher strain rates, but the average activation energy for deformation of the Al-6Cu, Al-11Cu, and Al-17Cu alloys is evaluated to be 480.7 kJ mol-1, in contrast to a lower value of 211 kJ mol-1 for the Al-24Cu and Al-33Cu alloys. Instead of grain size, the mean free path between θ particles is suggested to be a more appropriate microstructural parameter for the constitutive relationship for deformation of the Al-Cu alloys. © 1995 Chapman &amp; Hall.

Journal of Materials Science

Stress-strain rate relations for high-temperature deformation of two-phase Al-Cu alloys

Scripta Metallurgica et Materiala

Serrated flow in a modified 9Cr-1Mo steel

Tensile specimens of Type 316L stainless steel having grain sizes in the range 3.1-86.7 μm were deformed to 34% strain at temperatures 24, 400 and 700°C and strain rate 1 × 10-4s-1 to investigate the Hall-Petch (H-P) relationship, the nature of stress-strain curves and the substructure development. Upto ∼5% strain the H-P relationship exhibits bi-linearity whereas the single Hall-Petch relation is exhibited at larger strains. The presence of bi-linearity is explained by the back stress associated with the difference in the dislocation densities in the vicinity of grain boundary and in the grain interior. The log stress (σ)-log strain (ε) plots depict three regimes and follow the relationship σ = Kεn in each regime, but with varying magnitudes of the strength coefficient (K) and strain-hardening exponent (n). © 1995 Acta Metallurgica Inc. All rights reserved.

Acta Metallurgica Et Materialia

On the Hall-Petch relationship and substructural evolution in type 316L stainless steel

Tensile specimens of an Al-24 wt% Cu alloy of grain sizes in the range 7.6-20.6 μm were deformed at 400-540 °C using constant initial strain rates ranging from 5×10-6 to 2×10-2 s-1. Initially the stress-strain (σ-e{open}) curves show work hardening which is followed by strain softening at higher strain rates and lower temperatures. At lower strain rates and higher temperatures, on the other hand, σ continues to increase with strain or tends to be independent of strain. Grain growth and cavitation occur to varying extents depending on strain rate and test temperature. While the grain growth can account for the work hardening at higher temperatures as well as at lower strain rates, it fails to do so at higher strain rates. The strain softening is associated with cavitation. The presence of non-steady-state flow influences the parameters of the constitutive relation to varying extents. © 1995 Chapman &amp; Hall.

High-temperature flow behaviour and concurrent microstructural evolution in an Al-24 wt% Cu alloy

Grain and phase growth in the two-phase Al-Cu alloys containing 6, 11, 1 7, 24 and 33 wt % Cu were investigated by annealing at 535 °C for 0.5-100 h. The grain and phase sizes of the κ phase are seen to be larger than that of the θ phase. The size of κ phase decreases whereas the size of θ phase increases with increasing copper content in the alloy. As such, the κ phase- and grain-size distributions are broader than the θ phase- and grain-size distributions, but the size range depends on annealing time and alloy composition. The grain sizes of the κ, dκ, and θ, dθ, phases can be related to the volume fraction of the θ phase, fθ, according to the equation dκ = 0.497 dθ/fθ. © 1994 Chapman &amp; Hall.

Grain growth in the two-phase Al-Cu alloys

Effect of k θ - phase proportion on the flow stress of AlCu alloys at 540° C

Superplastic behaviour of a Zr-2.5 Wt% Nb pressure tube alloy

Microstructural evolution and its effect on hardness were investigated during homogerization, hot rolling and static annealing of the Al-Cu alloys containing 6, 11, 17, 25 and 30 wt.% Cu. The hardness of the constituent Al and θ phases of the alloys decreases with increasing amount of hot working and static annealing in the beginning. The variation in hardness during rolling is explained by dynamic recrystallization while that during annealing is explained by grain growth. The grain growth obeys a kinetic law of the type d ∝ tn with n = 0.05 to 0.17, where d is the grain size at time t.