Intellectual Merit

1. Mechanisms Governing the Thermal Stability of Microstructure and Residual Stress in Surface-Treated Aero Engine AlloysVijay K. Vasudevan, University of Cincinnati Main Campus, DMR 0706161 The LSP process leads to deep compressive residual stresses with minimal cold work and better thermal relaxation and fatigue resistance • Research Elements • LSP processing of typical aero engine alloys (IN718, IN718 SPF, IN718+, Ti-6Al-4V). • Characterization of near/sub-surface residual stresses & microstructural changes as a function of process parameters using novel methods. • Determination of thermal stability of residual stresses and microstructure with time at high temperatures and modeling of the kinetics of relaxation. • Modeling and simulation of LSP-induced residual stresses. • Integration of research with undergraduate and graduate education. Intellectual Merit Study aimed at securing the required fundamental knowledge of the impact of high temperatures and thermal cycling on materials behavior and properties generated by processes like laser shock peening (LSP) and thereby advancing the science and application base of advanced surface treatments to high temperature materials Residual Stress Vs Depth Thermal Relaxation - Near-Surface Diffraction Strain Vs Azimuth - IN718 Plus High Energy Synchrotron X-ray Diffraction (SXRD) LSP-treated IN718 SPF LSP-treated+750°C, 70 mins As-LSP-treated Top Surface Bottom Surface

2. OIM for near-surface microstructure, texture & strains TEM for Near-Surface Microstructure (IN718) g = -111 Mechanisms Governing the Thermal Stability of Microstructure and Residual Stress in Surface-Treated Aero Engine AlloysVijay K. Vasudevan, University of Cincinnati Main Campus, DMR 0706161 Aging Effects in IN718 Plus 750°C, 250 h Broad Impact SXRD experiments have been performed at the APS/ ANL and changes in near-surface microstructure and mechanical properties were also studied. Valuable new results were obtained that help advance the state-of-the-art understanding of the effects of advanced surface treatments and thermal influences thereupon. Resulting publications will have co-authors from APS. A nonlinear FEM simulation approach has been developed that employs a physics-based rate-dependent material model for the accurate prediction of LSP responses and various parametric studies have also been performed. Results were presented at MS&T 2008 and TMS 2009 conferences; several journal articles are under preparation. Project involves in-kind support from and extensive collaborations with industry (GE, LSPT Inc.) and government labs (AFRL). Results will aid them in their development of advanced surface treatments for high temperature structural applications. FEM for Residual Stress Prediction • Education • Three PhD students and 1 postdoctoral fellow are involved in the project. • The PhD students conducted synchrotron x-ray diffraction experiments at the APS/ANL and also attended the National School in X-ray and Neutron Scattering there, as well as the EBSD workshop at Buehler. • One undergraduate is involved in the project. • Research results are being incorporated into current courses in Materials Science and Mechanical Engineering. Micropillar Compression Tests for Local Strength (LSP-Treated IN718 SPF)