Material surface and immediate subsurface layers can be called "skin". A novel Ultrasonic Nanocrystal Surface Modification (UNSM) technology produces uniformed micro dimples on the top surface and nanometer grain in the subsurface; increases surface hardness and induces compressive residual stress, therefore mechanical characteristics related to fatigue, wear, friction, etc. can be improved. The concepts and properties of nanoskin materials and components are proposed with their potential application.
Effect of Ultrasonic Nanocrystal Surface Modification on theshowed a higher fatigue life improvement. The fatigue life improvement was higher in crack initiation from the surface of specimens. The subsurface crack initiation depth in the alloy increased with increase in the fatigue failure cycles. It was concluded that UNSM treatment can increase the life of the alloy significantly up to very high cycle fatigue.
Rolling contact fatigue (RCF) is known as the dominant factor determining the service life of bearing materials. In this work, the fatigue life of the typical bearing alloy was significantly improved by introducing a nanoskin layer on the surfaces of the test specimens. The nanoskin layer structure was obtained by means of the ultrasonic nanocrystal surface modification (UNSM) technology. The microstructure of the nanoskin was analyzed via scanning electron microscope (SEM), electron back-scatter diffraction (EBSD), and transmission electron microscope (TEM). SUJ2 and SUJ3 bearings at different states of fatigue were subjected to UNSM treatment. For SUJ2 a rotary-bending fatigue (RBF) life average for three untreated specimens was chosen as 100% life, and then several untreated specimens were fatigued to 25%, 50% and 75% of life with subsequent UNSM treatment. This way used bearing conditions were simulated. The rotary-bending fatigue (RBF) tests of fatigue+UNSM SUJ2 specimens have shown 377-430% improvement of fatigue life, comparing to untreated specimens. For SUJ3 a RCF life untreated specimen was chosen as 100% life, and then several specimens were fatigued to approximately 100% of surface damage with subsequent UNSM treatment. Thus damaged surface conditions were simulated. The RCF tests of fatigue+UNSM SUJ3 specimens have shown 218% improvement of fatigue life, comparing to untreated specimens. This indicates the possibility of the restoration of the RCF life of bearing alloys by means of nanoskin treatment via UNSM technology.
This study investigates the influence of ultrasonic nanocrystal surface modification (UNSM), a novel surface treatment technology, on the mechanical characteristics and rotary bending fatigue performance of solution-treated and annealed (STA) Ti-6Al-4V and Ti-6AI-4V extra low interstitial (ELI) alloys. Various techniques have been developed to use surface modification in order to improve fatigue performance of machine parts. The UNSM treatment emerges due to its ability to induce a distinctive combination of modifications in the top surface and the subsurface of the material. The mechanical properties are acquired and compared for UNSM-treated and untreated specimens. Fatigue data is acquired and compared for UNSM-treated and untreated specimens of Ti-6Al-4V ELI alloy by subjecting specimens to rotary-bending fatigue tests. Fracture analysis of failed specimens is performed. The improvement in the fatigue performance is observed for UNSM treated specimens. This improvement is attributed mainly to the UNSM-induced combination of following modifications: compressive residual stress, micro-hardness, and nanograin in the subsurface of the material.
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