# Ultrasonic Surface Rolling Process: Properties, Characterization, and Applications
## 4 Effect of USRP on Mechanical and Tribological Properties of Engineering Materials
In addition, the authors observed pitting corrosion in the turned specimen with a size of more than 100 \(\upmu\)m. Figure 14, represents the polarization curve of the electrochemical test on turned and USRP treated specimens. In addition, the authors observed that the oxidation rate of uranium metal is lower after USRP. The improvement in corrosion resistance after USRP was attributed to the formation of a dense and continuous oxide layer that possesses excellent stability, which can prevent oxygen from further expanding. [PERSON] et al. [42] conducted USRP on Cu-10 wt.% Ni alloy, commonly employed for shipbuilding and marine applications. The authors  
Figure 14: Polarization curve of turned and USRP treated uranium metal bar. Reprinted with permission from ref. [41]. Copyright 2021 Elsevier. Figure 13: Variation of the residual stress of T4003 ferritic SS welded joint before and after USRP. Reprinted with permission from ref. [48]. Copyright 2020 MDPI. performed an electrochemical corrosion test in a 3.5 wt% NaCl solution showed enhanced corrosion resistance. The USRP treatment caused the development of the GNS layer on the surface with an average grain size of 70 nm. The authors attributed that nanostructured surface promotes passivation film, which ultimately prevents damage due to corrosion. The mechanism of enhanced corrosion resistance is the introduction of residual compressive stress and a higher number of grain boundaries on the surface. This research revealed that surface nano crystallization could improve the hardness and corrosion resistance of Cu-10 Ni alloys. [PERSON] et al. [78] conducted the USRP on 300M ultra high strength steel, which is predominantly used for manufacturing aircraft landing gears. The authors studied the corrosion fatigue (CF) properties before and after USRP in a 3.5 wt.% sodium chloride solution. The number of CF cycles (a representation of CF resistance) was recorded for untreated and USRP-treated samples, and experiments were performed with a maximum stress of 1100 MPa, and were repeated three times. The average number of CF cycles withstood by the untreated 300M steel specimen is \(29.9\times 10^{3}\). However, the mean number of CF cycles for USRP-treated samples is \(702.1\times 10^{3}\), which is 23 times higher than the untreated specimens. The authors summarized that improved surface finish, higher surface hardness, and introduction of RCS induced by USRP significantly enhanced corrosion fatigue and fretting properties. [PERSON] et al. [48] studied the influence of USRP on microstructure and corrosion property of T4003 ferrtic SS welds using electrochemical polarization curve measurement. The authors observed increased corrosion potential in the weld zone after USRP treatment compared to the untreated specimen. The reported value of corrosion potential for USRP treated weld joint is \(-0.41\) V, whereas the untreated specimen possesses \(-0.61\) V. The enhanced corrosion resistance after USRP is attributed to the reduction in surface roughness. The smooth surface formed after USRP reduces the exposed surface area to the corrosive medium, and the presence of RCS helps to prevent the generation and expansion of surface cracks. [PERSON] et al. [63] studied the corrosion behavior of alloy 690 before and after USRP in a secondary side environment containing chloride. Electrochemical corrosion experiments demonstrated the positive value of open circuit potential (OCP). In addition, the passive film generated on the USRP treated specimen was denser than that formed on the untreated specimen. A higher OCP value indicates better corrosion resistance. [PERSON] et al. [79] conducted USRP experiments on uranium metal that revealed excellent oxidation resistance. The authors concluded that the formation of nanograined microstructure and high RCS during USRP led to a stable and passive oxidation film, which enhanced the corrosion resistance. In addition to this, a strong texture in (002) direction was formed.