Surface, Subsurface and Tribological Properties of Ti6Al4V Alloy Shot Peened under Different Parameters

Abstract

Ti6Al4V alloy was shot peened by using stainless-steel shots with different sizes (0.09–0.14 mm (S10) and 0.7–1.0 mm (S60)) for two durations (5 and 15 min) using a custom-designed peening system. The shot size was the main parameter modifying the roughness (0.74 µm for S10 vs. 2.27 µm for S60), whereas a higher peening time slightly increased roughness. Hardness improved up to approximately 35% by peening with large shots, while peening time was insignificant in hardness improvement. However, longer peening duration with large shots led to an unwanted formation of micro-cracks and delamination on the peened surfaces. After dry sliding wear tests, the mass loss of peened samples (S60 for 15 min) was 25% higher than that of un-peened samples, while the coefficient of friction decreased by 12%. Plastically deformed regions and micro-scratches were observed on the worn surfaces, which corresponds to mostly adhesive and abrasive wear mechanisms. The present study sheds light on how surface, subsurface and tribological properties of Ti6Al4V vary with shot peening and peening parameters, which paves the way for the understanding of the mechanical, surface, and tribological behavior of shot peened Ti6Al4V used in both aerospace and biomedical applications.

Modification of Surface and Subsurface Properties of AA1050 Alloy by Shot Peening

“…The surface roughness significantly increased at the higher pressure since the crater formation resulted in an uneven surface (Figure 7b) [40]. Crater formation was the active deformation mechanism that modified the surface and changed the roughness via the formation of irregular valleys and peaks in the surface profile, similar to the results reported in the literature [4,25,55,56,63]. The influence of cover rate on the surface roughness was insignificant at the low pressure, whereas the [20], ECAP2 [77], HPT [31], ARB [17], CGP [71], HE [77], SP, homogenisation annealing.…”

“…Besides, the increase in surface roughness (Figure 7b) and changes in the surface morphology (Figures 3 and 4) at the elevated peening pressure are indicative of the larger plastic deformation of the alloy at the higher peening pressure, leading to improved hardness. The improvement in hardness gradually decreases with increasing depth (Figure 2), in parallel to the literature on SP of 2024 Al alloy [74], 6061 Al alloy [42], Ti6Al4V alloy [56], ferrite-pearlite steels [63], pure copper [6], and AZ31 magnesium alloy [4]. The influence of the cover rate on hardness is not notable at the lower peening pressure, where it slightly enhances the hardness at high peening pressure (Figure 2b).…”

“…SP was performed on the metallographically prepared AA1050 Al alloy samples with stainless-steel shots (diameter: 0.7-1.0 mm (type: Chronital S60), shot hardness: 450 HV) as detailed elsewhere [55,56]. Figure 1 shows the SP of AA1050 by highlighting some of the important parameters and dimensions.…”

“…Furthermore, forming a nanocrystalline layer with high dislocation density beneath the shot-peened surface improves microhardness [58]. This improvement is more pronounced at higher peening pressures (Figure 2b) since the deformation energy of the shots that can be transferred to the material is directly related to their kinetic energy (i.e., SP pressure) [24,42,52,53,56,58,64,72]. The increasing coverage rate of the embedded shots and the size of the shots supports that the impact energy of the shots is higher at the elevated pressure (Figures 5 and 6).…”

Effects of Shot Peening and Cavitation Peening on Properties of Surface Layer of Metallic Materials—A Short Review

“…Avcu et al also conducted research on Ti-6Al-4V [ 116 ]. Two different peening times and two stainless steel sheet sizes were used.…”