# Ultrasonic Surface Rolling Process: Properties, Characterization, and Applications
## 5 Applications and Recent Advances of USRP
The authors revealed that after USRP, the surface roughness of the uranium metal is reduced to 0.4 \(\upmu\)m, and gradient twin microstructure is developed on the surface due to the SPD. Furthermore, the authors observed enhancement in corrosion resistance after USRP, which  
Figure 16: Applications of USRP in various industries. is attributed to the formation of a stable passive film that prevents oxidation during the electrochemical corrosion test. [PERSON] et al. [26] conducted USRP experiments on the 17-4 PH SS, which is used for different applications, including chemical processing equipment, self-lubricating bearings, and pump shafts. The authors observed 20% improvement in surface microhardness. In addition, the wear rate and CoF were reduced by 25% and 14%. Furthermore, the authors revealed the formation of (100) and (211) strong textures after USRP, which significantly enhanced corrosion resistance. The authors accounted for the enhancement of abrasion resistance being due to the synergistic effect of improving the hardness and introducing high RCS on the specimen surface. [PERSON] et al. [40] performed USRP experiments on AZ31B Mg alloys used in aerospace and automotive industries. Their studies revealed that USRP reduced surface roughness and corrosion rate by 91.8% and 64.15% compared to the untreated base material. In addition, the authors reported enhancement in hardness, wear-resistance, and tensile properties due to SPD during USRP. In recent years, scholars adopted different variants of USRP. The most common amongst them is ultrasonic nanocrystal surface modification (UNSM). The SPD developed during this process is based on mechanical impacts. In this process, low amplitude, high-frequency ultrasonic vibrations are superimposed with static load [89]. Figure 17 represents the working of the UNSM process. The mechanical impacts were applied on the specimen surface using a spherical roller tip of tungsten carbide and alumina. The repeated high-frequency impacts of the hard spherical tip on the specimen surface develop SPD, leading to surface nanocrystallization, introducing the high amount of RCS, developing high-density dislocations, and GNS layer [44]. The high-frequency ultrasonic vibrations are produced using an ultrasonic generator, which is amplified using a booster with the help of a horn and probe. The SPD developed during the UNSM process depends on the input parameters, such as static load, number of strikes, and roller diameter. Proper selection of these input parameters can control the GNS layer thickness. In the UNSM process, the primary function of the spherical roller tip is to create a mechanical impact and produce the SPD. In the case of USRP, the primary function of the spherical roller tip is to perform DR. Scholars adopted UNSM techniques on different steel grades [90; 91; 92; 93; 94], titanium alloys [95; 96; 97; 98], aluminum alloys [99; 100; 101], and magnesium alloys [102; 103], nickel alloys [89; 104], copper alloys [105; 106], shape memory alloys [107; 108] high entropy alloys [109; 110; 111] and thus observed a significant enhancement in surface mechanical properties and surface integrity. In addition, there are advancements in USSM techniques, such as electropulsing-assisted UNSM and laser-assisted UNSM [112; 113]. Scholars used combination techniques along with UNSM for superior enhancement in the surface mechanical properties [114]. Figure 17: Schematics of the UNSM process. [PERSON] et al. [108] conducted UNSM on additive manufactured NiTi alloys to improve the surface roughness and wear resistance. NiTi shape memory alloys have potential application in biomedical implants because of their unique shape memory effect and superelasticity properties. In this experiment, the authors used a static load of 3 kg, a tungsten carbide tip with a diameter of 2.4 mm, and a frequency of 20 kHz.