@article{joshi_kombaiah_cinbiz_murty_2020, title={Characterization of stress-rupture behavior of nuclear-grade C26M2 FeCrAl alloy for accident-tolerant fuel cladding via burst testing}, volume={791}, ISSN={["1873-4936"]}, DOI={10.1016/j.msea.2020.139753}, abstractNote={Abstract FeCrAl alloys demonstrate excellent high-temperature oxidation resistance compared to zirconium alloys used in LWRs. FeCrAl C26M2 has been down-selected as one of the candidate ATF cladding materials for Gen II LWRs. This study investigates the stress-rupture behavior of the nuclear-grade FeCrAl C26M2 tubing in the temperature range of 753-923 K. Rupture time and uniform strain at rupture were determined as a function of the temperature and applied stress using burst tests. The rupture data was found to obey the Larson-Miller Parameter and the Monkman-Grant relationship. Furthermore, the stress exponent (n) and the activation energy (QC) at lower stresses were determined as 4.4 ± 0.3 and 289 ± 25 kJ/mol, respectively, confirming power-law behavior. Above the normalized stress (σ/E) of 2 × 10−3, the power-law creep transited into the power-law breakdown regime. The steady-state deformation microstructure was examined using transmission electron microscopy (TEM) to detect the rate-controlling creep mechanism(s). Observation of sub-grains with dislocations at the boundaries in the power-law regime along with a stress exponent of 4.4 suggests dislocation climb as the rate-controlling mechanism. Two different fracture modes were observed: the tubing failed either by direct open-up or small crack and pinhole formation. The outcome of this study would provide essential data for the development of informative mesoscale deformation models paving way for discovery of new creep resistant alloys.}, journal={MATERIALS SCIENCE AND ENGINEERING A-STRUCTURAL MATERIALS PROPERTIES MICROSTRUCTURE AND PROCESSING}, author={Joshi, P. and Kombaiah, B. and Cinbiz, M. N. and Murty, K. L.}, year={2020}, month={Jul} }
 @article{wang_zheng_kombaiah_tan_sprouster_snead_zinkle_yang_2020, title={Contrasting roles of Laves_Cr2Nb precipitates on the creep properties of novel CuCrNbZr alloys}, volume={779}, ISSN={["1873-4936"]}, DOI={10.1016/j.msea.2020.139110}, abstractNote={To enhance the creep resistance at elevated temperatures, a new precipitation-strengthened CuCrNbZr alloy has been designed and fabricated to achieve a target microstructure with coarse Laves_Cr2Nb precipitates at grain boundaries and fine Cr-rich precipitates in the matrix. This work systematically studied the creep property of the CuCrNbZr alloy at 500 °C under 90–140 MPa applied stress and compared to that of a reference commercial CuCrZr alloy without Laves_Cr2Nb precipitates. Microstructures before and after creep testing were investigated by optical and transmission electron microscopy. Based on the creep testing and microstructural characterization results, the dominant creep mechanism in both alloys was grain boundary sliding with a threshold stress of ~80 MPa. The CuCrNbZr alloy has higher creep strength and higher creep fracture ductility, and longer creep life than the CuCrZr alloy. The improved creep property in the CuCrNbZr alloy was due to the presence of Laves_Cr2Nb precipitates that efficiently impede the crack propagation.}, journal={MATERIALS SCIENCE AND ENGINEERING A-STRUCTURAL MATERIALS PROPERTIES MICROSTRUCTURE AND PROCESSING}, author={Wang, Ling and Zheng, Ce and Kombaiah, Boopathy and Tan, Lizhen and Sprouster, David J. and Snead, Lance L. and Zinkle, Steven J. and Yang, Ying}, year={2020}, month={Mar} }
 @article{kombaiah_sarkar_murty_2019, title={Effect of hydriding on the creep behavior of HANA-4 zirconium alloy}, volume={767}, ISSN={["1873-4936"]}, DOI={10.1016/j.msea.2019.138435}, abstractNote={HANA-4 (High Temperature Alloys for Nuclear Applications) is Zr-1.5 Nb alloy developed by the Korea Atomic Energy Research Institute for advanced nuclear fuel cladding applications. In this work, the effect of hydriding on the biaxial creep behavior of HANA-4 alloy was studied through internal pressurization of closed end tubes by applying a range of hoop stresses (27 MPa–156 MPa) at two temperatures: 400 °C and 500 °C. Test specimens included two HANA-4 tubes hydrided using an electrolytic method with 387 ppm and 715 ppm of hydrogen, respectively, and non-hydrided HANA-4 tubes as the control sample. To understand the effect of hydriding on creep, steady state creep rates and stress exponents of the specimens were determined from the creep data. Furthermore, in situ X-ray diffraction (XRD) experiments were conducted on the hydrided HANA-4 specimens during heating to detect the dissolution limit of the hydride phase. On examining the results of the creep tests and the XRD experiments collectively, it is concluded that hydrogen while being fully dissolved into the solid solution enhances the creep rate of HANA-4 tubes. On the other hand, hydrogen present, even partially, as hydride phase at the creep test temperature lowers the creep rate. The rate controlling mechanisms of creep in HANA-4, however, remained unchanged as noted from similar stress exponents of the hydrided and non-hydrided specimens. The rationale behind these observations is explained based up on models predicting the interaction of dislocations with hydrogen and hydride phase.}, journal={MATERIALS SCIENCE AND ENGINEERING A-STRUCTURAL MATERIALS PROPERTIES MICROSTRUCTURE AND PROCESSING}, author={Kombaiah, Boopathy and Sarkar, Apu and Murty, Korukonda Linga}, year={2019}, month={Nov} }
 @article{kombaiah_murty_2015, title={Coble, Orowan Strengthening, and Dislocation Climb Mechanisms in a Nb-Modified Zircaloy Cladding}, volume={46A}, ISSN={["1543-1940"]}, DOI={10.1007/s11661-015-3060-8}, abstractNote={Biaxial creep tests on HANA-4 tubes, Nb-added Zircaloy-4 were conducted using internal pressurization of closed-end tubes to investigate the rate-controlling mechanisms over a range of hoop stresses, $$ 8.38 \times 10^{ - 5} E - 2.87 \times 10^{ - 3} E $$ , at three different temperatures 673 K, 723 K, and 773 K (400 °C, 450 °C, and 500 °C). The mechanistic creep parameters such as stress exponent (n) and activation energy (Q C) were then determined from steady-state creep rates. Based on the variance in stress exponent with respect to the applied stress, three regimes have been identified: a stress exponent close to 1 at low stresses that increased to 3 at the intermediate stresses, which became 4.5 at high stresses. An activation energy value of 226 kJ/mol was evaluated for the n = 3 and n = 4.5 regimes, which lies close to the activation energy for self-diffusion (Q L) in α-Zr alloys. Further, TEM analyses of crept microstructures and comparison of experimental results with standard models were undertaken to find out the rate-controlling mechanisms. Coble creep, climbing of dislocations to bypass β-Nb precipitates, and dynamic recovery by edge dislocation climb are proposed as the rate-controlling mechanisms in the n = 1, n = 3, and n = 4.5 regimes of HANA-4, respectively.}, number={10}, journal={METALLURGICAL AND MATERIALS TRANSACTIONS A-PHYSICAL METALLURGY AND MATERIALS SCIENCE}, author={Kombaiah, Boopathy and Murty, Korukonda Linga}, year={2015}, month={Oct}, pages={4646–4660} }
 @article{kombaiah_murty_2015, title={High temperature creep and deformation microstructures in recrystallized Zircaloy-4}, volume={95}, ISSN={["1478-6443"]}, DOI={10.1080/14786435.2015.1042939}, abstractNote={Uniaxial creep tests were performed on recrystallized Zircaloy-4 tensile specimens with an average grain size of 8.5 μm at the stress range of , where E is the elastic modulus, at three temperatures: 500, 550 and 600 °C with an objective to uncover the rate-controlling mechanism(s). A transition in creep mechanism was observed as the stress exponent increased from a value close to 1 at the low stress range to 4.1 at high stresses with the calculated activation energies (Qc) of 196 kJ/mol and 241 kJ/mol, respectively. Possible creep mechanisms have been shortlisted based upon the values of n and Qc. Transmission electron microscopy analyses of the dislocation structures in the crept specimens as well as validation of the experimental results with the predictions by standard creep models were undertaken to ascertain the underlying rate-controlling mechanisms. While Coble creep was noted to be the dominant mechanism in the n ~ 1 regime at low stresses, dislocation climb was identified to control the creep rate in the n ~ 4.1 regime at high stresses.}, number={15}, journal={PHILOSOPHICAL MAGAZINE}, author={Kombaiah, B. and Murty, K. Linga}, year={2015}, month={May}, pages={1656–1679} }
 @article{sarkar_boopathy_eapen_murty_2014, title={Creep Behavior of Hydrogenated Zirconium Alloys}, volume={23}, ISSN={["1544-1024"]}, DOI={10.1007/s11665-014-1129-y}, number={10}, journal={JOURNAL OF MATERIALS ENGINEERING AND PERFORMANCE}, author={Sarkar, A. and Boopathy, K. and Eapen, J. and Murty, K. L.}, year={2014}, month={Oct}, pages={3649–3656} }
 @article{kombaiah_murty_2015, title={Dislocation cross-slip controlled creep in Zircaloy-4 at high stresses}, volume={623}, ISSN={["1873-4936"]}, DOI={10.1016/j.msea.2014.11.040}, abstractNote={Uniaxial creep tests were performed on Zircaloy-4 sheet in the temperature range of 500–600 °C at high stresses (>10−3E), to uncover the rate-controlling mechanism. A stress exponent of 9.3–11 and a stress-dependent activation energy in the range of 220–242 kJ/mol were obtained from the steady state creep data. TEM analyses revealed an extensive presence of hexagonal screw dislocation network on the basal planes indicating recovery of screw dislocations by cross-slip to be the dominant mechanism. The creep data was therefore analyzed in the light of Friedel׳s cross slip model for HCP metals according to which the stress-dependency of the activation energy determined from the creep data was written in the form,U=(150±4)+(2236±124τ)kJ/mol The constriction energy of screw dislocations of 150 kJ/mol is in agreement with the values reported in the literature for zirconium and other HCP metals. Further analysis of the yield strength and the activation volume data obtained from stress relaxation tests in the temperature range 500–600 °C favors cross-slip of screw dislocations as the rate controlling mechanism over the test conditions.}, journal={MATERIALS SCIENCE AND ENGINEERING A-STRUCTURAL MATERIALS PROPERTIES MICROSTRUCTURE AND PROCESSING}, author={Kombaiah, B. and Murty, K. Linga}, year={2015}, month={Jan}, pages={114–123} }
 @article{murty_seok_kombaiah_2013, title={Burst and Biaxial Creep of Thin-Walled Tubing of Low c/a-Ratio HCP Metals}, volume={55}, ISSN={["1877-7058"]}, DOI={10.1016/j.proeng.2013.03.278}, abstractNote={Thin-walled tubing used in various structures are made of low c/a-ratio hcp metals such as Zr and Ti based alloys, and their integrity to internal pressures is of prime importance in the life of these engineering structures. We summarize here ome of the work performed on Zircaloy cladding commonly used in LWRs as thin walled tubing as well as Cp-Ti and Ti3Al2.5 V that find applications in aerospace industry. Considered here are three different types of tests: (i) burst tests using closed- end internal pressurization, (ii) uniaxial ring tests for characterization of hoop creep properties and (iii) hoop creep under biaxial internal pressurization. Burst and ring tests yielded identical hoop creep and rupture characteristics indicating the utility of ring tests to replace burst tests. Importance of transitions in creep mechanisms with decreased stress levels in predicting in-service dimensional changes is emphasized.}, journal={6TH INTERNATIONAL CONFERENCE ON CREEP, FATIGUE AND CREEP-FATIGUE INTERACTION}, author={Murty, K. Linga and Seok, C. S. and Kombaiah, B.}, year={2013}, pages={443–450} }