Table 2. Top surface hardness Ti–6Al-4V Inconel738 Inconel690 Cu-Zn alloy Al6061-T6 Untreated/UNSM Hardness(HV) 380/424 405/448 164/280 130/210 100/141 Hardness at the top surface increased by 33% and 17% for SKD61 and SAE52110, respectively. Table 2 shows improvement of top surface hardness of some other materials nanoskin-treated by UNSM technology. 2.2.3. Increase of compressive residual stress A:SKD61 (H13) B: Ti-6Al-4V Figure 6. Compressive residual stress treated by UNSM technology Compressive residual stress within a nanoskin created by UNSM of SKD61 (equivalent of H13) is shown in Figure 6A, and of a Ti-6Al-4V for medical and aircraft application is shown in Figure 6B. Comparison between deep rolling (DR) and UNSM is also shown in Figure 6B [9, 12, 14]. 2.3. Mechanical performance of nanoskin: fatigue, wear, friction and rolling contact fatigue 2.3.1. Improvement of HCF and VHCF strength In order to evaluate the effects of UNSM generated nanoskin on fatigue performance of some automotive, aircraft and medical alloys, ultrasonic fatigue tests (UFT) were carried out on Al6061-T6, Ti-6Al-4V (TC4) and Ti-3Al-2Mo-2Zr (TAMZ) specimens. Using UFT device reduced test time and better simulated extremely high frequency loading and influence of strain rate on fatigue behavior of tested material. The test frequency was 20 kHz and stress ratio R=-1. The specimens were hourglass shape with neck diameter 6 mm and notch radius 60 mm for Al-alloy and 3 mm/31 mm for Ti-alloys. Figure 7 shows S-N curves acquired through UFT for UNSM treated and untreated specimens. a b Figure 7. S-N curves for UNSM treated and untreated Al6061-T6 specimens (a) and TC4 and TAMZ (b)
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