# Ultrasonic Surface Rolling Process: Properties, Characterization, and Applications
## 5 Applications and Recent Advances of USRP  
USRP is an advanced surface modification technique that provides superior surface mechanical properties and surface integrity without increasing surface roughness. These inherent advantages of USRP compared to other SPD methods led the scholars to adopt USRP in diverse fields of applications, such as, aerospace industries [81; 82; 83], chemical industries [26], nuclear industries [41; 65], automotive industries [27; 30; 83], manufacturing industries [39], commercial industries [84], and biomedical industries [83; 85]. Within each industry, the needs are unique. Still, USRP displays finesse in the handling of different materials for prospects of improvement. Figure 15: Surface morphology of T4003 ferritic SS welded joint before USRP on (**a**) weld zone, (**b**) HAZ, (**c**) base metal and after USRP on (**d**) weld zone, (**e**) HAZ, and (**f**) base metal. Reprinted with permission from ref. [48]. Copyright 2020 MDPI. Scholars performed USRP on Ti6 Al4V, 300M steel, 7050-T7451 aluminum alloy, and GH4169 superalloy that is commonly used for various parts in aerospace applications. [PERSON] et al. [57] conducted USRP on Ti6 Al4V alloy and studied the fretting fatigue characteristics. The authors observed a GNS layer of 335 \(\upmu\)m and a grain size of 45.8 nm on the surface of the specimen. In addition, the observed surface microhardness was 45 times higher compared to the base material, and an RCS of \(-\)861 MPa was induced on the surface. The authors reported that USRP enhanced fretting fatigue life by approximately 113% compared to the base alloy. The increase in fretting fatigue life is attributed to the combined effect of RCS, GNS layer, and work hardening. The induced RCS played the domain role to enhance the fretting fatigue life. [PERSON] et al. [80] conducted USRP on 300M steel, commonly used as a load-bearing member for gears, shafts, and landing gears in aerospace industries, and studied the tensile and fatigue properties. The authors reported that single-pass USRP treatment improved the UTS by 3.8%. However, it reduced the YS by 5.9%. The authors observed that after USRP treatment, the LCF life was enhanced by 0.5 times, and HCF life was improved by 21 times. This is attributed to the introduction of high RCS on the top surface, which prevents the fatigue crack growth rate. Figure 16 represents the various applications of USRP in different industries. [PERSON] et al. [36] performed USRP on 7050-T7451 aluminum alloy, which is used as a monolithic component in aerospace applications. The authors summarized that USRP enhanced the surface microhardness by 41.3% and GNS layer of 140 \(\upmu\)m. After USRP treatment, the surface integrity of the metal was significantly improved. The authors summarized that the grain boundary fusion and impurity phase diffusion phenomenon played a significant role in providing the internal strengthening mechanism on the USRP treated surface. [PERSON] et al. [86] conducted USRP experiments three times on GH4169 superalloy and studied the fretting fatigue property. GH4169 superalloy is widely used for manufacturing aero-engine parts, such as turbine blades and compressors. The authors revealed that USRP increased surface microhardness, induced high RCS, and reduced surface roughness. The fretting fatigue life of the USRP'ed specimen increased from 3.6 during a single pass to 11 times after three passes of USRP. They attributed the presence of RCS to the enhancement in fretting fatigue life. [PERSON] et al. [41] performed USRP on uranium metal, which is widely used in nuclear industries, and studied the corrosion properties. The uranium metal demands superior surface mechanical properties; however, scholars reported that performance degradation due to friction, wear, and corrosion is a significant issue in these materials. Amongst these, degradations due to corrosion are the most common and severe problem [87; 88].