An investigation of the effect of warm laser shock peening on the surface modifications of [001]-oriented DD6 superalloy

Davami

2022

Metals

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.

Section: Microstructure Modifications Resulting From Lpsupporting

confidence: 69%

Section: Microstructure Modifications Resulting From Lpmentioning

confidence: 99%

Section: Residual Stress Distribution and Measurement Following Lpmentioning

confidence: 99%

Section: Microhardness Distribution Following Lpmentioning

confidence: 99%

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

Davami

2022

Metals

“…The interaction of hot corrosion and fatigue is caused by elevated temperatures, mechanical loading, combustion gases and airborne contaminants [9,10]. Other studies investigated the surface and sub-surface properties post laser peening [11][12][13][14][15][16][17]. The results of the previous studies aforementioned were done with laser energies in the sub-joule range meaning that a small spot size has to be used to achieve the desired irradiance.…”

Section: Introductionmentioning

confidence: 99%

Effects of high energy laser peening followed by pre-hot corrosion on stress relaxation, microhardness and fatigue life and strength of single crystal nickel CMSX-4® superalloy

Morar

Hackel

et al. 2023

Preprint

This study investigated the stress relaxation and fatigue life and strength of laser peened single crystal nickel superalloy specimens compared to un-peened and shot peened specimens following hot corrosion exposure and then fatigue testing. The specimens were treated by conventional laser peening and a new cyclic laser peening plus thermal microstructure engineering process. The latter treatment supports the benefit of a unique process involving application of layers of laser peening using high energy with large footprint spots combined with interspersed cyclic annealing. Stress measurements by slitting showed the plastic penetration depth of laser peening exceeded shot peening by a factor of 24. Un-peened and peened specimens were exposed to sulphate corrosives at 700°C for 300 hours and then fatigue tested. Tests of five non-laser peened specimens all failed in low cycle fatigue regime whereas three identically tested laser peened specimens all achieved multi-million-cycle runout without failure, indicating fully consistent large benefit for life by laser peening. Additional tests also showed fatigue strength improvement of 2:1 by laser peening. Residual stress measurements post hot-corrosion exposure and fatigue testing showed notable 5 mm depth retention of residual eigenstress in a laser peened specimen.

Effects of high-energy laser peening followed by pre-hot corrosion on stress relaxation, microhardness, and fatigue life and strength of single-crystal nickel CMSX-4® superalloy

Morar

Int J Adv Manuf Technol

Hackel

et al. 2023

This study investigated the stress relaxation and fatigue life and strength of laser-peened single-crystal nickel superalloy specimens compared to unpeened and shot-peened specimens following hot corrosion exposure and then fatigue testing. The specimens were treated by conventional laser peening and a new cyclic laser peening plus thermal microstructure engineering process. The latter treatment supports the benefit of a unique process involving application of layers of laser peening using high energy with large footprint spots combined with interspersed cyclic annealing. Stress measurements by slitting showed the plastic penetration depth of laser peening exceeded shot peening by a factor of 24. Unpeened and peened specimens were exposed to sulphate corrosives at 700 °C for 300 h and then fatigue tested. Tests of five non-laser-peened specimens all failed in low-cycle fatigue regime, whereas three identically tested laser-peened specimens all achieved multi-million-cycle runout without failure, indicating fully consistent large benefit for life by laser peening. Additional tests also showed fatigue strength improvement of 2:1 by laser peening. Residual stress measurements post hot-corrosion exposure and fatigue testing showed notable 5 mm depth retention of residual eigenstress in a laser-peened specimen.