To enhance the service lifetime (R et al. , 2010) and the global behavior (R et al. , 2010) of material optimization of the surface properties and the micro structures SMAT is an effective approach to apply. With an extensive and intensive investigations and research on nanostructured materials in the past, more practical evidences via experiments have proofed this emerging class of materials possess a number of properties whose performances are basically from the old conventional course grained materials (Caballero et al. , 2014; X. C. Zhang, Lu, & Shi, 2011). This new set of materials are hard and strong(Sourmail et al. , 2013; Tong et al. , 2007; Tong, Tao, Wang, Lu, & Lu, 2003) with enhanced physical properties(Capdevila, 2013; Miller, Parish, & Li, 2013), extraordinary tribological properties(Capdevila, 2013; Ma, 2003) and super plastic at low temperature(Branagan et al. , 2013; Misra et al. , 2012). 1.1.
Surface mechanical attrition treatment process To realize a self-Nano-crystallization of a bulk material as the key point (Zing, Lu, & Lu, 2001) a large amount of interfaces and defects are introduced into the surface layers so that the surface micro-structure is changed into a Nano sized crystallites.
In another language used by Liu, (G Liu, Lu, & Lu, 2000; G. LIU, WANG, LOU, LU, & LU, 2001), a process of grain refinement into the Nano scale is required in the surface layer as the structure of the coarse grained matrix remains unaltered. It clearly comes out that surface mechanical attrition treatment is the most effective technique in relation to conventional ones to realize self-nano-crystalization on the surface of metallic materials (Lin et al. , 2006; Roland, Retraint, Lu, & Lu, 2007; Tong et al. , 2007; Tong et al. , 2003).
Figure 1 below illustrates an experiment of the SMAT process set up. Spherical steel balls possessing smooth surface properties are put in a reflecting chamber which is vibrated by a vibrational generator. The size of the balls is in between1-10 mm in diameter. Figure 1: (a and b) Schematic illustration of the surface mechanical attrition treatment set-up and the repeated multidirectional plastic deformation in the sample surface layer induced by impact of the flying balls(Lin et al. , 2006). The chamber has a vibrational frequency of the range 50 Hz TO 20 KHz.
Once the balls are resonated in the chamber, the surface to be treated is affected by the large number of balls within a short duration of time. The flying balls move at a velocity of between 1- 20m/s.