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Item Effect of retrogression and re-ageing heat treatment on microstructure and microhardness of aluminium 7010 alloy(EDP Sciences edps@edpsciences.com, 2018) Nandana, M.S.; Udaya Bhat, K.; Manjunatha, C.M.Aluminium alloy 7010 is subjected to retrogression and re-ageing (RRA) heat treatment to study the influence of microstructural changes on hardness. Retrogression is performed at 190 °C for different time intervals ranging from 10 to 60 minutes. Optimum time for retrogression treatment is estimated based on the retrogression time that result with equivalent mechanical properties as that of peak aged (T6) condition. Retrogression performed for 30 minutes resulted with micro hardness of 203 HV, which is equivalent to that obtained by following T6 treatment. Microstructural characterization done with the help of transmission electron microscope (TEM) indicates RRA treatment results with the coarsened and discontinuous precipitates along the grain boundary which is similar to over aged (T7) condition, where as fine and densely populated precipitates in the matrix similar to T6 condition. Coarse and discontinuous grain boundary precipitates (GBP's) improves resistance to stress corrosion cracking. Fine and dense precipitates in the matrix ensures hardness equivalent to that of T6. © The Authors, published by EDP Sciences, 2018.Item Influence of heat treatment on near-threshold fatigue crack growth behavior of high strength aluminum alloy 7010(Springer Science and Business Media Deutschland GmbH, 2020) Nandana, M.S.; Udaya, B.K.; Manjunatha, C.M.In this study, aluminum alloy 7010 was subjected to three different ageing treatments i.e., peak ageing (T6), over ageing (T7451) and retrogression and re-ageing (RRA) to study the influence of precipitate microstructure on the fatigue crack growth rate (FCGR) behavior. The microstructural modifications were studied by using TEM to examine the change in size and morphology of the precipitates. The size of the precipitates in the matrix range from 16-20nm in T7451, 5-6nm in RRA and 2-3nm in T6 alloys, respectively. The FCGR tests were performed on standard compact tension (CT) specimens as per ASTM E647 standard in a computer controlled servo-hydraulic test machine with applied stress ratio, R = 0.1 and loading frequency of 10 Hz. The crack growth was measured by adopting compliance technique using a CMOD gauge attached to the CT specimen. The fatigue crack growth rate was higher in T7451 and lowest in RRA treated alloy. The RRA treated alloy showed higher (formula presented) compared to T7451 and T6 treated alloys. The measured (formula presented) was 11.1, 10.3 and (formula presented) in RRA, T6 and T7451 alloys, respectively. In the near-threshold regime, the RRA treated alloy exhibited nearly 2-3 times reduction in the crack growth rate compared to the T6 alloy. The growth rate in the RRA alloy was one order lower than that of the T7451 condition. The surface roughness of RRA treated alloy was more pronounced. The reduction in FCGR observed in RRA alloy was correlated to partial crack closure due to tortuous crack path and partially due to increased spacing between the matrix precipitates. The reduction in near-threshold FCGR and increase in (formula presented) is expected to benefit the damage tolerant capability of the aircraft structural components under service loads. © Springer Nature Switzerland AG 2020.Item Damage Tolerance Capability of Retrogression and Re-aged 7010 Aluminum Alloy Under FALSTAFF Loading(Springer, 2020) Nandana, M.S.; Bhat, K.U.; Manjunatha, C.M.The present work deals with the damage tolerance characteristics of high strength aluminum alloy tempered in T6 and reversion condition. The fatigue experiments were carried out by applying a service simulating load spectrum, i.e., standard mini FALSTAFF loading. The crack propagation speed was found to be lower and the total crack propagation life was longer by 22% for reversion-treated alloy. The crack growth was also predicted to be using two parameter crack driving force approach. The fatigue data of these treated alloys under constant amplitude loading at various stress ratios were analyzed to obtain crack growth law. The predicted crack growth behavior was conservative and followed similar trend in both the alloys as observed in experiments. Predicted results of reversion-treated alloy also showed longer crack growth life. The modified microstructure after reversion treatment was attributed for the observed improvement in damage tolerance capability. © 2020, The Indian Institute of Metals - IIM.