# Ultrasonic Surface Rolling Process: Properties, Characterization, and Applications
## 5 Applications and Recent Advances of USRP
The commonly used combination techniques are shot peening [131], heat treatment [72; 132], laser cladding [133; 134], plasma nitriding [64], carburizing [135]. Table 3 summarizes the various combination techniques used with USRP to potentially improve surface integrity, and surface mechanical properties. [PERSON] et al. [131] used a combination of USRP and shot peening to alter the surface 17 Cr2 Ni2 MoVNb steel to improve wear resistance and fatigue resistance. After combined treatment, the authors observed superior grain refinement and the deepest grain refinement layer. The untreated specimen surface had a grain size of 9.91 \(\upmu\)m, which was reduced to 1.98 \(\upmu\)m, and the depth of the SPD layer was 133.5 \(\upmu\)m. In addition, grain refinement was correlated to intensive plastic strain and the ability of the material to absorb the deformation energy. The combination treatment specimen showed CRS of \(-\)1099 MPa and surface microhardness of 1109 HV, which was 229% and 39.5% higher than the untreated specimen. [PERSON] et al. [135] used a combination of carburizing and USRP on 20 CrMoH steel and studied the synergistic effect of these surface modification techniques on the rolling contact fatigue life. The authors reported a 100% increase in fatigue life during combined treatment compared to the carburized sample. The authors listed three methods of strengthening, such as strengthening due to carburization, \begin{table}
\begin{tabular}{c c c c} \hline \hline \multirow{2}{*}{**Materials**} & \multirow{2}{*}{**Process**} & **Roller material,** & \multirow{2}{*}{**Frequency and** **Amplitude**} & \multirow{2}{*}{**Observation**} \\  & & **Hardness and** & & \\  & **Diameter, Static Force** & & & \\  & **or Pressure** & & & \\ \hline \multirow{4}{*}{
\begin{tabular}{c} Commercial Pure Ti \\ [129] \\ \end{tabular} } & \multirow{4}{*}{EP-USRP} & Unspecified; & \multirow{4}{*}{27 Hz;} & Microhardness increased by 46.7\% in \\  & & & 14 mm; & EP-USRP and 26.7\% in USRP. \\  & & & 1030 N & \\ \cline{3-4}  & & & & Surface roughness decreased by 97\% in \\  & & & & EP-USRP and 95.6\% in USRP. \\ \cline{3-4}  & & & & Dislocation mobility was enhanced \\ \cline{3-4}  & & & Unspecified; & \\ \cline{3-4}  & & & & Increase in SFE due to thermal and athermal \\ \cline{3-4}  & & & 90 HRC;12 mm; & & effect \\ \cline{3-4}  & & & & Superior grain refinement \\ \cline{3-4}  & & & & Increase in impact depth \\ \cline{3-4}  & & & & Excellent thermal stability \\ \hline \hline \end{tabular}
\end{table} 
Table 2: _Cont._  
Figure 18: Schematic of the EP-USRP. strengthening due to dislocation, and stress. The combination method induced an RCS of \(-920\) MPa and surface hardness of \(900\) HV. USRP is a novel surface SPD technique capable of providing superior surface mechanical properties and surface integrity with an appreciable reduction in surface roughness [137]. It can induce in-depth CRS and GNS layers with higher intensity and deeper thickness than other SPD methods such as LSP, SP, SMAT, UIP, DR, and SMGT [86]. The primary  
\begin{table}
\begin{tabular}{p{56.9 pt} p{113.8 pt} p{113.8 pt} p{113.8 pt}} \hline \hline
**Material** & **Combination Method** & \begin{tabular}{c} **Static force, Roller Material,** \\ **Hardness, Diameter, Ultrasonic** \\ **Frequency, and Amplitude** \\ \end{tabular}  & **Results** \\ \hline
17 Cr2N2 MoVNb steel [131] & \begin{tabular}{c} USRP followed by shot \\ peening followed by \\ USRP \\ \end{tabular}  & \begin{tabular}{c} 600 N, 800 N, 1000 N; \\ Unspecified; Unspecified; \\ Unspecified; 25 kHz; 6 \(\upmu\)m \\ \end{tabular}  & \ \begin{tabular}{c} Significant ultra-fine grains \\ Improved surface microhardness \\ RCS of \(-1099\) MPa was observed on the surface. \\ Microhardness increased by 39.50\% \\ Lowest surface roughness \\ Surface roughness reduced from 0.284 \(\upmu\)m \\ Microhardness increased by 6.2\% HV \\ Improvement in wear resistance \\ Microhardness increased by 43.7\% HV \\ Fatigue strength increased by 40 MPa \\ \end{tabular}  &