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Comparison of mechanisms of advanced mechanical surface treatments in nickel-based superalloy
Gill, A.,Telang, A.,Mannava, S.R.,Qian, D.,Pyoun, Y.S.,Soyama, H.,Vasudevan, V.K. Elsevier Sequoia 2013 Materials science & engineering. properties, micro Vol.576 No.-
Mechanical surface enhancement techniques are used to introduce compressive residual stresses to enhance the fatigue life and corrosion resistance of metallic components. In this study, we compare the effects of three advanced mechanical surface enhancements treatments: laser shock peening, cavitation shotless peening and ultrasonic nano structure modification on residual stress, hardness, plastic deformation and changes in near surface microstructure introduced in a Ni-Base superalloy, IN718 SPF(Super plastic forming). Coupons of the alloy were peened using two different conditions of each treatment and results compared to achieve a better understanding of underlying mechanisms of these techniques. Results indicate that there are significant differences in mechanisms of these surface treatments leading to differences in material response.
Surface grain boundary engineering of Alloy 600 for improved resistance to stress corrosion cracking
Telang, A.,Gill, A.S.,Tammana, D.,Wen, X.,Kumar, M.,Teysseyre, S.,Mannava, S.R.,Qian, D.,Vasudevan, V.K. Elsevier Sequoia 2015 Materials science & engineering. properties, micro Vol.648 No.-
In this paper, we demonstrate a novel method for grain boundary engineering in Alloy 600 using iterative cycles of ultrasonic nanocrystal surface modification (UNSM) and strain annealing to modify the near surface microstructure (~250@?m) for improved stress corrosion cracking (SCC) resistance. These iterative cycles resulted in increased fraction of special grain boundaries whilst decreasing the connectivity of random grain boundaries in the altered near surface region. A disrupted random grain boundary network and a large fraction of low CSL boundaries (Σ3-Σ27) reduced the propensity to sensitization. Slow strain rate tests in tetrathionate solutions at room temperature show that surface GBE lowered susceptibility to intergranular SCC. Detailed analysis of cracks using Electron Back-scattered Diffraction showed cracks arrested at J1(1-CSL) and J2 (2-CSL) type of triple junctions. The probability for crack arrest, calculated using percolative models, was increased after surface GBE and explains the increase in resistance to SCC.