# Ultrasonic Surface Rolling Process: Properties, Characterization, and Applications
## 4 Effect of USRP on Mechanical and Tribological Properties of Engineering Materials
The reason for enhanced surface integrity can be attributed to the formation of strong texture, which weakened the adsorption and diffusion of the oxidative medium. This study concludes that USRP is an effective method to prevent oxidation failures in uranium. The inherent advantage of the USRP compared to other SPD techniques is the unique ability to enhance surface mechanical properties without deteriorating surface roughness. The rolling head impacts the surface of the metal parts at high speeds during the USRP process inducing intense plastic deformation on the surface and sub-surface layer of the specimen under consideration. Eventually, the valleys at the surface are filled with peaks, resulting in a reduction in surface roughness and the introduction of RCS. Finally, the formation of the GNS layer with severe plastic deformation enhances the surface mechanical properties. This attribute of USRP is extremely useful to improve the surface mechanical properties of the welded joint. The specimen is subjected to multiple weld thermal cycles during welding, resulting in the poor surface finish in the weld fusion zone and heat-affected zone. [PERSON] et al. [48] revealed that USRP on T4003 ferritic SS weld joints reduced the surface roughness significantly and changed the surface morphology. They used another nomenclature named surface ultrasonic rolling treatment (SURT), which is similar to USRP. The average surface roughness in the weld zone, HAZ, and base material of the untreated weld joints were \(1.06\) um, \(2.18\) um, and \(2.160\) um. However, after USRP, the average surface roughness reduced to \(0.320\) um, \(0.156\) um, and \(0.227\) um. Figure 15 illustrates the surface morphology of T4003 ferritic SS weld joints before and after USRP. The surface morphology was quite unsmooth before USRP with peaks and troughs at the welded zone, HAZ, and base metal as shown in Figure 15a-c. It is evident that after USRP, the surface morphology became noticeably smooth with no peaks or troughs at the welded junction shown in Figure 15d-f. The authors observed that USRP induced a plastically deformed layer of 100 \(\upmu\)m thickness and refined grains in the weldment. In addition, scholars performed USRP on various metals and alloys and observed a significant reduction in surface roughness. [PERSON] et al. [63] conducted USRP experiments on alloy 690, which is commonly used for heat transfer tubes and water reactor applications. The authors revealed that after USRP, surface roughness was significantly reduced. The alloy 690 has a surface roughness of 30 nm, and after USRP, the surface roughness was reduced to 1.4 nm. This reduction in surface roughness is attributed to the inflow of materials from the protrusion which is filled in the gullies on the base material. In addition, USRP produced nanograins with an average grain size of 55 nm and a GNS layer of thickness of approximately 1 \(\upmu\)m. [PERSON] et al. [80] performed USRP experiments on 300M steel and found that one pass of USRP can reduce the surface roughness by more than one order of magnitude (from 0.30 \(\upmu\)m to 0.025 \(\upmu\)m). [PERSON] et al. [40] conducted USRP experimental studies on AZ31B Mg alloy and found the surface roughness to be decreased by 91.8% compared with the untreated specimen. [PERSON] et al. [78] conducted USRP experiments on 300M ultra high strength steels and reported that surface roughness reduced from 0.32 \(\upmu\)m to 0.062 \(\upmu\)m. [PERSON] et al. [41] conducted USRP experiments on uranium metal and revealed that the surface roughness of uranium metal reduced to 0.38 \(\upmu\)m after three rolling passes. The base material possesses a surface roughness of 0.90 \(\upmu\)m, which is reduced to 0.35 \(\upmu\)m during the first stage of USRP and reduced to 0.31 \(\upmu\)m during the second stage of USRP.