A Review of Laser Peening Methods for Single Crystal Ni-Based Superalloys

Abstract

Single crystal Ni-based superalloys are often used to create gas turbine engine blades for their high strength under intense thermo-mechanical loading. Though they are remarkably capable under these conditions, a particular class of premature failure mechanisms known as surface-initiated damage mechanisms can lead to the early fracture of an otherwise healthy blade. This review paper discusses the current progress of post-processing techniques that can greatly mitigate the potency of surface-initiated damage mechanisms. In particular, laser peening (LP) is of significant interest due to the relatively low amount of cold work it induces, greater depth of compressive residual stresses than other cold working methods, ability to accommodate complex part geometries, and the minuscule effect it has on surface roughness. The residual stresses imparted by LP can greatly hinder crack growth and consequently allow for enhanced fatigue life. Given that turbine blades (constructed with single crystal Ni-based superalloys) are prone to fail by these mechanisms, LP could be a worthy choice for increasing their service lives. For this reason, initiative has been taken to better understand the mechanical and microstructural modifications imparted by LP on single crystal Ni-based superalloys and a summary of these investigations are presented in this review. Results from several works show that this class of alloy responds well to LP treatment with improvements such as ~30–50% increase in microhardness, 72% increase in low cycle fatigue life, and elevated resistance to hot corrosion. The primary objective of this review is to provide insight into current state-of-the-art LP techniques and summarize the findings of numerous works which have utilized LP for increasing the service lives of single crystal Ni-based superalloy components.

Failure analysis of gas turbine in first stage turbine blades in an urban power plant

“…An otherwise healthy blade may shatter too soon due to a form of premature failure mechanism known as surface-initiated damage processes, notwithstanding its remarkable ability under certain circumstances. The simultaneous development of post-processing techniques that can greatly lessen the effectiveness of surface-initiated degradation processes was detailed in a review paper [21]. Laser peening (LP) is particularly important because it creates comparatively less cold work than other cold working methods, causes a greater depth of compressive residual stresses than other methods, is flexible enough to match complicated component geometries, and has minimal influence on surface roughness.…”