Improvement in tribological behavior of commercial pure titanium (CP-Ti) by surface mechanical attrition treatment (SMAT)

In the present work, commercial pure titanium (CP-Ti) samples were subjected to surface mechanical attrition treatment (SMAT) under different durations in order to improve surface properties and produce an ultrafine grain layer. Cross section and surface of SMATed samples were analyzed through optical microscopy (OM) and scanning electron microscopy (SEM) methods. The finest grain size on surface, measured with X-ray diffraction (XRD) test, was 12.2 nm. While the initial grain size was measured to be averagely 70 μm. Hardness of SMATed samples increased by 2.8 times. Increase in hardness was due to plastic deformation and work-hardening. SMAT led to improvement of wear properties in CP-Ti so that its friction coefficient decreased by 66%. On the other hand, wear rate of CP-Ti samples decreased by about 60%. According to the established relationships between hardness and wear rate, increase in surface hardness and creation of a deformed layer led to reduction of wear rate. Surface roughness continuously increased with SMAT. Surface roughness after SMAT was increased by almost 6 times. Increase in surface roughness was due to impact of balls on samples surfaces leading to formation of valleys and peaks.