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G. S. Murty

Bio: G. S. Murty is an academic researcher from Indian Institute of Technology Kanpur. The author has contributed to research in topics: Strain rate & Deformation (engineering). The author has an hindex of 7, co-authored 17 publications receiving 200 citations.

Papers
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TL;DR: In this article, high-temperature hardness data for thirty-seven metals have been collected from the published literature, and seven of these metals were further tested to confirm and improve the hardness data.
Abstract: The high-temperature hardness data for thirty-seven metals have been collected from the published literature. Seven of these metals were further tested to confirm and improve the hardness-temperature data. All data were analysed to calculate the softening parameter B and the apparent activation energy for indentation B′. The values of B′ are compared with the activation energies for lattice and dislocation pipe diffusion to obtain an estimate of the stress coefficient, α, for creep. The B′ and α values have been improved by considering the effect of elastic modulus.

72 citations

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TL;DR: In this paper, rate sensitive flow characteristics in the elevated temperature deformation of Al-Fe-V-Si alloys processed by rapid solidification/powder metallurgy route were assessed by the strain rate change tests in compression.
Abstract: The rate sensitive flow characteristics in the elevated temperature deformation of Al-Fe-V-Si alloys processed by rapid solidification/powder metallurgy route were assessed by the strain rate change tests in compression. With an ultrafine grain size, stabilized by fine dispersoids, a peak rate sensitivity index of ∼0.15 and normal ductility were observed in alloys containing dispersoids up to a volume fraction of 0.37. The lack of superplastic response is interpreted in terms of a high threshold stress for superplastic flow. The threshold stress assessed by an extrapolation procedure is observed to be grain size and temperature dependent. Its origin is suggested to be Zener drag limited boundary migration, which is an essential part of the superplastic flow mechanism.

22 citations

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TL;DR: In this article, the plastic behavior of CuAl2 was studied by compression testing of single crystals and polycrystals in the temperature range 300-575 °C. The results showed that the brittle-ductile transition (BDT) temperature was influenced by the initial dislocation density but not by the grain size.
Abstract: The plastic behaviour of CuAl2 was studied by compression testing of single crystals and polycrystals in the temperature range 300–575 °C. While single crystals were grown from the melt by the Bridgeman technique, ingot and powder metallurgy routes were adopted for polycrystalline specimens. In addition to exploring their flow behaviour, the deformation mechanism was assessed through thermal activation analysis. It was observed that CuAl2 failed in a brittle manner in compression below 375 °C and its ductility improved progressively with temperature. The brittle-ductile transition (BDT) temperature was influenced by the initial dislocation density but not by the grain size. The strong temperature dependence of flow stress and grain size strengthening effect as per the Hall-Petch relation, were dominant up to nearly the melting temperature of CuAl2. The measured activation parameters for deformation suggest that the Peierls mechanism is rate controlling over the investigated temperature range.

20 citations

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TL;DR: In this paper, banded and elongated grain microstructures of the Pb-Sn eutectic alloy were analyzed over 298 to 443 K to evaluate microstructural instability during differential strain rate tests in the superplastic region.
Abstract: Stress (σ)-strain rate (\(\dot \varepsilon \)) data of banded and elongated grain microstructures of the Pb-Sn eutectic alloy were analysed over 298 to 443 K to evaluate microstructural instability during differential strain rate tests in the superplastic region. With reference to a stable equiaxed microstructure exhibiting uniqueσ-\(\dot \varepsilon \) relation, banded structure is more susceptible to strain hardening while the elongated grain microstructure exhibits either strain softening or strain hardening depending on the test temperature. This flow behaviour is considered in terms of a change in grain size, represented by the cube root of the grain volume. Activation energy for grain growth calculated from the differential strain rate test data indicates that the activation energy depends on strain rate and type of microstructure.

13 citations


Cited by
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Journal ArticleDOI
TL;DR: In this paper, a method is developed for accurately determining strain rate sensitivities on a submicron scale using an indentation technique, which has been developed for use with the Nanoindenter.

385 citations

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TL;DR: In this article, a new indentation creep test is introduced in which the indenter is a circular cylinder with a flat end, and a steady state velocity is observed in this new test shortly after a transient period during which the indententer makes a shallow impression on the surface of the specimen; hence the name "impression creep".
Abstract: A new indentation creep test is introduced in which the indenter is a circular cylinder with a flat end Unlike conventional indentation tests, a steady-state velocity is observed in this new test shortly after a transient period during which the indenter makes a shallow impression on the surface of the specimen; hence the name “impression creep” This steady-state velocity is found to have the same stress and temperature dependences as the conventional undirectional creep tests using bulk specimens Three possible mechanisms are analysed in detail, bulk diffusion, surface diffusion, and dislocation creep They have different stress and indenter-size (radius) dependences Experimental results on succinonitrile crystals are reported

305 citations

Journal ArticleDOI
TL;DR: In this article, two eutectic lead-free solders (965Sn-35Ag and 91Sn-9Zn) are investigated for their creep and stress relaxation behavior.
Abstract: Because of the high homologous operation temperature of solders used in electronic devices, time and temperature dependent relaxation and creep processes affect their mechanical behavior In this paper, two eutectic lead-free solders (965Sn-35Ag and 91Sn-9Zn) are investigated for their creep and stress relaxation behavior The creep tests were done in load-control with initial stresses in the range of 10-22 MPa at two temperatures, 25 and 80°C The stress relaxation tests were performed under constant-strain conditions with strains in the range of 03-24% and at 25 and 80°C Since creep/relaxation processes are active even during monotonie tensile tests at ambient temperatures, stress-strain curves at different temperatures and strain rates provide insight into these processes Activation energies obtained from the monotonic tensile, stress relaxation, and creep tests are compared and discussed in light of the governing mechanisms These data along with creep exponents, strain rate sensitivities and damage mechanisms are useful for aiding the modeling of solder interconnects for reliability and lifetime prediction Constitutive modeling for creep and stress relaxation behavior was done using a formulation based on unified creep plasticity theory which has been previously employed in the modeling of high temperature superalloys with satisfactory results

232 citations

Journal ArticleDOI
TL;DR: In this paper, the Gibbs equation for stressed solids is extended to include constrained chemical equilibria among components whose chemical potentials may not be individually definable, and a programmed dif-fusion scheme is devised to minimize both the diffusion time and the stress developed dur-ing diffusion.
Abstract: Gibbs equation for stressed solids is extended to include constrained chemical equilibria among components whose chemical potentials may not be individually definable. Strain volume is introduced as a new tensorial extensive variable. Solubility enhancements in the presence of misfit inclusions of spherical as well as parallelepipedal shapes are cal-culated an compared with experiments involving excess nitrogen around TiN2 platelet inclusions in ferrite. Diffusion-induced stresses or the chemical stress effect is treated for some simple shapes such as thin slabs, cylinders, and spheres. A programmed dif-fusion scheme is devised to minimize both the diffusion time and the stress developed dur-ing diffusion. The effective diffusivity of an isotropic solute due to diffusion-induced stress gradients is given. Stress induced diffusion is exemplified by a new creep test in which diffusion is localized around an indenter. Finally, the chemical kinetics of the annealing of defects are discussed with new experiments reported on the recovery kinetics of shearbands produced in an amorphous polymer.

187 citations

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TL;DR: In this article, the processing regime relevant to superplasticity in the Ti-6Al-4V alloy was identified and the effect of grain size refinement involving recrystallisation and the formation of voids and cavities caused macroscopic softening; low ductility results.

170 citations