Effect of Strain Ratio on Fatigue Model of Ultra-fine Grained Pure Titanium

Abstract

The ultra-fine grained (UFG) pure titanium was prepared by equal channel angular pressing (ECAP) and rotary swaging (RS). The strain controlled low cycle fatigue (LCF) test was carried out at room temperature. The fatigue life prediction model and mean stress relaxation model under asymmetrical stress load were discussed. The results show that the strain ratio has a significant effect on the low cycle fatigue performance of the UFG pure titanium, and the traditional Manson-coffin model can not accurately predict the fatigue life under asymmetric stress load. Therefore, the SWT mean stress correction model and three-parameter power curve model are proposed, and the test results are verified. The final research shows that the three-parameter power surface model has better representation. By studying the mean stress relaxation phenomenon under the condition of R≠−1 it is revealed that the stress ratio and the strain amplitude are the factors that significantly affect the mean stress relaxation rate, and the mean stress relaxation model with the two variables is calculated to describe the mean stress relaxation phenomenon of the UFG pure titanium under different strain ratios. The fracture morphology of the samples was observed by SEM, and it was concluded that the final fracture zone of the fatigue fracture of the UFG pure titanium was a mixture of ductile fracture and quasi cleavage fracture. The toughness of the material increases with the increase of strain ratio at the same strain amplitude.

Keywords

ultra-fine grained pure titanium / low cycle fatigue / life model / mean stress relaxation mode / strain ratio / fracture morphology

References

[1] Din S H. Biomedical Applications of Titanium and Its Alloys[J]. Proceedings on Engineering Sciences, 2021, 3(1): 41-52.

[2] Rack H J, Petruzelka J, Dluhos L, et al. Nanostructured Titanium for Biomedical Applications[J]. Advanced Engineering Materials, 2010, 10(8): B15-B17.

[3] Zhernakov V S, Latysh V V, Stolyarov V V, et al. The Developing of Nanostructured SPD Ti for Structural Use[J]. ScriptaMaterialia, 2001, 44(8–9): 1771-1774.

[4] Geetha M, Singh A K, Asokamani R, et al. Ti based Biomaterials, the Ultimate Choice for Orthopaedic Implants - A Review[J]. Progress in Materials Science, 2009, 54(3): 397-425.

[5] Naseri R, Kadkhodayan M, Shariati M. Static Mechanical Properties and Ductility of Biomedical Ultrafine-grained Commercially Pure Titanium Produced by ECAP Process[J]. Transactions of Nonferrous Metals Society of China, 2017, 27(9): 1964-1975.

[6] Liu X, Zhao X, Yang X, et al. Progress in Research on Deformation Behavior of Ultrafine-grained Metallic Materials Processed by ECAP[J]. Materials Reports, 2011, 25(09): 11-15.

[7] Segal V M. Equal Channel Angular Extrusion: from Micromechanics to Structure Formation[J]. Materials Science & Engineering A, 1999, 271(1–2): 322-333.

[8] Li J, Yang G. Effect of Extrusion Pass on Microstructure and Properties of ECAP Pure Aluminum for Aviation[J]. Hot Working Technology, 2019, 48(03): 176-178.

[9] Suresh M, Sharma A, More A M, et al. Effect of Equal Channel Angular Pressing (ECAP) on the Evolution of Texture, Microstructure and Mechanical Properties in the Al-Cu-Li Alloy AA2195[J]. Journal of Alloys and Compounds, 2019, 785: 972-983.

[10] Tan Y, Li W, Hu W, et al. The Effect of ECAP Temperature on the Microstructure and Properties of a Rolled Rare Earth Magnesium Alloy[J]. Materials, 2019, 12(9): 1 554

[11] Jahadi R, Sedighi M, Jahed H. ECAP effect on the micro-structure and mechanical properties of AM30 magnesium alloy[J]. Materials Science & Engineering A, 2014, 593: 178-184.

[12] A Y J C, B Y J L, B J C W Microstructure Evolution of Commercial Pure Titanium during Equal Channel Angular Pressing[J]. Materials Science and Engineering: A, 2010, 527(3): 789-796.

[13] Koujalagi M B, Siddesha H S. ECAP of Titanium Alloy by Sever Plastic Deformation: A Review[J]. Materials Today: Proceedings, 2020, 45: 71-77.

[14] Agarwal K M, Tyagi R K, Singhal A, et al. Effect of ECAP on the Mechanical Properties of Titanium and Its Alloys for Biomedical Applications[J]. Materials Science for Energy Technologies, 2020, 3: 921-927.

[15] Kim H K, Lee Y I, Chung C S. Fatigue Properties of a Fine-grained Magnesium Alloy Produced by Equal Channel Angular Pressing[J]. Scripta Materialia, 2005, 52(6): 473-477.

[16] Chen W, Wang H, Yi X, et al. Evaluation of Strain Fatigue Life in ZTC4 Alloy Under Different Strain Ratio[J]. Hot Working Technology, 2012, 41(12): 56-57. 90

[17] Su Y L, Lu S. A New Strain-Life Model Accounting for Effects of Various Strain Ratios[J]. Tuijin Jishu/Journal of Propulsion Technology, 2018, 39(1): 169-175.

[18] Pz A, Bcb C, Jk D, et al. High-cycle-fatigue Induced Continuous Grain Growth in Ultrafine-grained Titanium[J]. Acta Materialia, 2019, 174: 29-42.

[19] Arcari A, Vita R D, Dowling N E. Mean Stress Relaxation during Cyclic Straining of High Strength Aluminum Alloys[J]. International Journal of Fatigue, 2009, 31(11–12): 1742-1750.

[20] Yu Q, Shan Z W, Ju L, et al. Strong Crystal Size Effect on Deformation Twinning[J]. Nature, 2010, 463(7279): 335-338.

[21] Zhang G D, Bin S U, Wang H, et al. Effect of Elastic Modulus on Parameter of Low Cycle Fatigue Performance[J]. Journal of Aerospace Power, 2005, 20(5): 768-771.

[22] Li C, Ying S H, Shen B L, et al. A Study of Masing Behavior in Zircaloy-4[J]. Hedongli Gongcheng/Nuclear Power Engineering, 2003, 24(3): 219-222.

[23] Smith K N, Watson P, Topper T H. Stress- strain Function for the Fatigue of Metals[J]. J. Mater., 1970, 5: 767-778.

[24] Zhang G D, Su B. A Method Based on Energy and Three-parameter Power Function for Low Cycle Fatigue[J]. Acta Aeronautica Et Astronautica Sinica, 2007, 28(2): 314-318.

[25] Ye D, Xu Y, Lei X, et al. Effects of Low-cycle Fatigue on Static Mechanical Properties, Microstructures and Fracture Behavior of 304 Stainless Steel[J]. Materials Science & Engineering A, 2010, 527(16–17): 4092-4102.

[26] Lin Y C, Chen X M, Liu Z H, et al. Investigation of Uniaxial Low-cycle Fatigue Failure Behavior of Hot-rolled AZ91 Magnesium Alloy[J]. International Journal of Fatigue, 2013, 48: 122-132. Mar.

[27] Landgraf R W, Chernenkoff R. Residual Stress Effects on Fatigue of Surface Processed Steels[J]. Analytical and Experimental Methods for Residual Stress in Fatigue, ASTMSTP, 1988(1004): 1–12

[28] Laird C. Cyclic Deformation and Fatigue Mechanisms[J]. Fracture, 1984: 261–271