No abstract

Double shot peening is the development of shot peening by shooting large media as a first shot and re-shooting again with smaller media as a second shot in order to achieve high residual compressive stress and hardness at the surface, while the in-depth effect can still be maintained. This research aims to examine the effect of media type and media size when used in the second shot of double shot peening on hardness, roughness, and residual stress to identify the suitable conditions and compare them with single shot peening, such as conventional shot peening and fine shot peening, which was used as the first shot and second shot. Ti–6Al–4V was used as the substrate material, while various diameter sizes of silica and SUS304 media were selected as the media for the second shot in the process. The results showed that in the case of the larger size of silica media in the second shot of double shot peening, the hardness and residual compressive stress on the surface clearly increased more than with the smaller media due to the higher Almen intensity, which affected impact energy. On the other hand, when shooting with SUS304 media as a second shot, the increment of residual compressive stress and hardness, including roughness reduction on the surface, showed less effect than was the case for silica media, due to the lower Almen intensity, which affected the impact energy transfer. This research found that the condition of shooting with 80 μm of silica media as the second shot could generate the highest hardness and residual compressive stress on the surface, which increased by 14% and 53%, respectively, while roughness was decreased by 20% when compared with single shot peening.

As the bone fracture is now considered the second most serious disease in the world, a huge number of orthopedic devices for bone healing is being developed. However, there happened to be a number of incidents in which the orthopedic plates were broken inside the body due to inadequate strength. The present study aims to investigate the effects of Fine Shot Peening (FSP) conditions on performances of orthopedic plates and screws. In this research, there are 3 types of medical alloys to be studied namely SUS316 alloy, Ti6Al4V alloy and Ti6Al7Nb. In FSP process, 40 and 80 μm diameter of silica media was selected and utilized. FSP was carried out under the pressure of 0.5 MPa in Nitrogen atmosphere. The study shown that Ti6Al4V alloy with FSP media diameter of 80 μm resulted in 11% increment of bending strength and 40% increment of surface hardness. Regarding the orthopedic screw, the result shown that after applying FSP, the pull out strength from bone could be increased above 76%.

The residual stress and hardness generated by the nitriding process are important parameters for increasing the bending fatigue strength to Ti-6Al-4V. Therefore, this research is focused on the analysis of residual stress and hardness, including surface morphology and microstructure generated by the nitriding process at different times and temperatures. The plasma nitriding at temperatures of 750 °C and 800 °C with times of 5 h and 10 h were selected in this research. After plasma nitriding, the material would have residual compressive stress and higher hardness, including changes in the surface morphology and microstructure. The results also indicated that higher temperature and processing times generated more surface roughness and thickness in the compound layer, resulting in higher surface hardness. Moreover, higher time and temperature could generate deeper residual compressive stress and case depth hardness. This research revealed maximum hardness in the cross-sectional analysis of 643 HV and residual compressive stress of −65.3 MPa. In conclusion, the depth of the residual stress and case depth hardness were well compatible with the depth of the diffusion layer of plasma-nitrided Ti-6Al-4V, which confirmed the effect of plasma nitriding.