**4. Conclusion**

The work presented in this chapter has hopefully contributed to a better understanding of the mechanical behaviour and tribological characteristics of both as-austempered ductile iron (ADI) and shot-peened (SP) ADI. A case study was presented in which bending fatigue tests and three different tribological tests were carried out on Cu-Ni-alloyed ADI. The major conclusions of can be summarised as follows:


**5.** Lubricated rolling contact fatigue tests revealed that SP resulted in a 72% decrease in the average contact fatigue life when compared to the resulting fatigue life obtained by the asaustempered specimens. This was attributed to the rough surfaces of SP specimens, which in turn caused a low specific film thickness, leading to rolling in the boundary lubrication regime. In contrast, rolling of the polished as-austempered specimens was conducted in the presence of a full lubricant film, which is the ideal lubrication regime of components under rolling contact.

The SP process is constantly maturing, and many questions still remain open as the industry is continuously on the search for process improvements that improve and extent the service lifetime of components. For example, the improvement in surface roughness has improved the tribological characteristics, the ability to create textured nanostructured surface layers and also new equipment and techniques to characterise the treated surfaces [11].
