Center for Laser Shock Processing for Advanced Materials and Devices

Project Objective: The objective of this project, which includes close collaboration with scientists from INL and ANL, is to investigate and demonstrate the use of the laser shock peening (LSP) process and establish baseline parameters for enhancing the fatigue properties and SCC resistance of nuclear materials like nickel-based alloys 600 and 690. The primary focus of the project will be on alloy 600, whereas a few studies on alloy 690 will be conducted for comparison with previous work on non-surface treated materials and future potential application. The research program designed accordingly includes the following key elements/tasks:

1. Procurement of alloys 600 and 690, heat treatment studies, purchase and installation of devices for fatigue crack growth measurements
2. LSP processing of base metal and welds/HAZ of alloys 600 and 690
3. measurement and mapping of surface and sub-surface residual strains/stresses and microstructural changes as a function of process parameters using novel methods
4. determination of thermal relaxation of residual stresses (macro and micro) and microstructure evolution with time at high temperatures typical of service conditions and modeling of the kinetics of relaxation
5. evaluation of the effects of residual stress, near surface microstructure and temperature on fatigue properties, fatigue crack nucleation and growth and mechanisms, and SCC initiation and growth behavior and associated microstructural mechanisms
6. development of a robust modeling and simulation approach for determining the effects of LSP on residual stress, microstructure, thermal stability, fatigue life and SCC initiation mechanisms.

In this project the effects of Laser shock peening (LSP) on the aero engine Ni-Base alloys, IN718 and IN718 SPF were studied. The primary goal of the research was to secure the required fundamental knowledge of the impact of LSP process parameters on the microstructure, residual stress and local properties of alloys and thereby advance the science and application base of this process to other materials and parts. The research program designed accordingly includes the following key elements:

1. Developing LSP process parameters for typical Ni base aero engine alloys;
2. Characterization of surface and sub-surface macro and micro residual strains/stresses a function of LSP process parameters
3. Characterization of microstructural changes as a function of LSP process parameters and
4. Study of the thermal relaxation of residual stresses and understand the underlying kinetics.

Solid implant rods made of Ti-6Al-4V (ELI) are currently used in spinal implant devices. Due to the high stiffness of these solid rods, the implant devices are unable the meet the needs for increased flexibility over a wide range of human activities owing to changes in lifestyles and in human work environments, thereby, necessitating the need for more flexible rods. Hence, designing, developing, manufacturing and testing flexible spinal implant rods was the aim of this project. In this project, increased flexibility was achieved by reducing the cross-section of the solid rods. Since reduction in cross-section leads to reduced load bearing capacity, the fatigue endurance level of the flexible rods is lowered. In order to increase the endurance levels of these flexible rods, Laser Shock Peening (LSP) has been used. As a part of this project, the Ohio Center for Laser Shock Processing of Advanced Materials and Devices (LSP Center)was set-up at the University of Cincinnati through the Ohio State Third Frontier Wrights Projects funding. This project is a collaborative effort between the LSP Center and X-Spine Systems Inc., an implant devices manufacturer based in Miamisburg, Ohio.

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