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.

Comparison of mechanisms of advanced mechanical surface treatments in nickel-based superalloy

https://www.umbc.edu/lamp/pubwork/Arola_et_al_Wear_2002.pdf

Waterjet and abrasive waterjet surface treatment of titanium: a comparison of surface texture and residual stress

Impact force of low velocity liquid droplets measured using piezoelectric PVDF film

Effective parameters for erosion caused by water droplet impingement and applications to surface treatment technology

Cavitation impact from a cavitation jet, which is formed from bubbles induced by a high-speed water jet in water, can be used for surface modification in a similar manner to shot peening. A cavitating jet is normally produced by injecting a high-speed water jet into a water-filled chamber. It is possible to make a cavitating jet in air by injecting a high-speed water jet into a concentric low-speed water jet that surrounds the high-speed jet. In order to demonstrate this, a high-speed water jet with a concentric low-speed water jet was impacted onto an aluminum specimen to observe the pattern of erosion. The mass loss of the specimen was weighed to measure the capability of the jet, since a more powerful jet produces a larger mass loss. It was shown that the combination of high- and concentric low-speed water jets produced a typical erosion pattern such as that obtained using a cavitating jet in a water-filled chamber. When the injection pressure of the concentric low-speed water jet was optimised, the capability of the cavitating jet in air was much greater than that of a cavitating jet in a water-filled chamber. It was demonstrated that an optimized cavitating jet in air introduced more compressive residual stress in the surface of tool steel alloy than that from a cavitating jet in a water-filled chamber. In addition, this stress was larger than that induced by shot peening. The peened surface was also less rough compared with shot peening.

Introduction of Compressive Residual Stress Using a Cavitating Jet in Air

An experimental study was conducted to determine the influence of high-pressure waterjet (WJ) peening and abrasive waterjet (AWJ) machining on the surface integrity and texture of metals. A combination of microstructure analysis, microhardness measurements, and profilometry were used in determining the depth of plastic deformation and surface texture that result from the material removal process. The measurement and evaluation of residual stress was conducted with X-ray diffraction. The residual stress fields resulting from treatment were analyzed to further distinguish the influence of material properties on the surface integrity. It was found that waterjet peening induces plastic deformation at the surface layer of metals as good as shot peening. The degree of plastic deformation and the state of material surface were found to be strongly dependent on the peening conditions applied.

Waterjet Machining and Peening of Metals

An experimental study of high-pressure waterjet peening on 7075-T6 aluminum alloy was conducted to investigate the effects of waterjet on high-cycle fatigue life and fatigue crack growth. Unnotched hourglass-shaped circular cross section test specimens were fatigue tested in completely reversed rotating bending (R =S min /S max = -1) to determine fatigue life behavior (S-N curves). Single-edge-notched flat tensile test specimens were tested in the tension-tension fatigue crack growth tests (R=S min /S max =0.1) to determine fatigue crack propagation behavior (da/dN versus AK). Surface characteristics and fracture surfaces were evaluated by scanning electron microscopy (SEM). Results show that waterjet peening can increase high-cycle fatigue life, delay fatigue crack initiation, and decrease the rate of fatigue crack propagation.

Fatigue performance of high-pressure waterjet-peened aluminum alloy

Waterjet peening has recently emerged as one of the alternative surface treatment processes to improve the fatigue life of the components. Part I of this experimental study has been concentrated on surface characteristics of waterjet peened material. In this part of the study, unnotched hourglass shaped circular cross section test specimens were fabricated and surface treated for selected waterjet peening conditions. Completely reversed rotating bending fatigue tests were conducted on peened aluminum specimens to evaluate fatigue performance (S-N curves). Fracture surfaces were evaluated by scanning electron microscopy (SEM) to identify the fatigue mechanisms. Results show that waterjet peening can enhance the fatigue strength by 2030% to that of unpeened Al7075-T6 material.

https://www.shotpeener.com/library/pdf/2001148.pdf

J. Hopkins

Papers

Waterjet Machining and Peening of Metals

Fatigue performance of high-pressure waterjet-peened aluminum alloy

Ultra high pressure waterjet peening part ii: high cycle fatigue performance

Peening with High Pressure Waterjets