Fatigue Fracture Characteristics of Ti6Al4V Subjected to Ultrasonic Nanocrystal Surface Modification
Abstract
:1. Introduction
2. Experimental Procedures
3. Results and Discussion
3.1. Observation of the Severe Plastic Deformation Layer
3.2. Hardness and Residual Stress Distrubutions
3.3. Surface Topography
3.4. Fatigue Fracture Characteristics
4. Conclusions
- UNSM technique improves the microhardness and the surface compressive residual stress of TC4. The ultrasonic surface impact helps to achieve a regular surface, almost without changing the surface roughness.
- The fatigue strengths of TC4 subjected with two different heat treatments are improved by 7% (to stress-relief annealing) and 11.7% (to solid solution-aging), respectively.
- After UNSM, fatigue cracks mainly initiate from the surface of the specimen before the fatigue life of 106 cycles, while they appear at the internal compress deformed α-phase at the zone between the SPD layer and the core after the fatigue life of 106 cycles. The shapes of crack cores are long and narrow because of the ultrasonic impacts on the surface.
- The dimples change from equal-axis ductile voids to be parabolic fossae and oval toughening nests due to the dimensional change of the grains.
- The stress intensity factor calculated from the facet area ΔKfacet was in the range of 8.3–10.0 MPa·m1/2. The slip of the deformed α phase induces the propogation of microcracks.
- The energy field of crack evolution depends on both the deformed crystal slip and the surface remodeling.
Acknowledgments
Author Contributions
Conflicts of Interest
References
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Groups | SRA | SRA-UNSM | SSA | SSA-UNSM | |
---|---|---|---|---|---|
Treatments | |||||
Stress-relief annealing | 〇 | 〇 | |||
Solid solution and aging | 〇 | 〇 | |||
With UNSM | 〇 | 〇 |
Heat Treatment | σ0.2/MPa | σb/MPa | Elongation/% | Reduction of Area/% |
---|---|---|---|---|
Stress-relief annealing | 850 | 925 | 16 | 26 |
Solid solution & aging | 1180 | 1230 | 14 | 10 |
Group | SRA | SRA-NSM | SSA | SSA-UNSM |
---|---|---|---|---|
Roughness (Ra) | 0.35 μm | 0.5 μm | 0.39 μm | 0.58 μm |
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Cao, X.; Xu, L.; Xu, X.; Wang, Q. Fatigue Fracture Characteristics of Ti6Al4V Subjected to Ultrasonic Nanocrystal Surface Modification. Metals 2018, 8, 77. https://doi.org/10.3390/met8010077
Cao X, Xu L, Xu X, Wang Q. Fatigue Fracture Characteristics of Ti6Al4V Subjected to Ultrasonic Nanocrystal Surface Modification. Metals. 2018; 8(1):77. https://doi.org/10.3390/met8010077
Chicago/Turabian StyleCao, Xiaojian, Luopeng Xu, Xiaoli Xu, and Qingyuan Wang. 2018. "Fatigue Fracture Characteristics of Ti6Al4V Subjected to Ultrasonic Nanocrystal Surface Modification" Metals 8, no. 1: 77. https://doi.org/10.3390/met8010077