Fatigue strength of Ti6Al4V titanium alloy machined under flood and cryogenic conditions

Andrea STRAMARE; R. BERTOLINI; S. Bruschi; A. Ghiotti; Alberto CAMPAGNOLO

doi:10.21741/9781644903131-214

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Fatigue strength of Ti6Al4V titanium alloy machined under flood and cryogenic conditions

STRAMARE Andrea, BERTOLINI Rachele, BRUSCHI Stefania, GHIOTTI Andrea, CAMPAGNOLO Alberto

Abstract. Ti6Al4V titanium alloy wrought round bars characterized by a fine equiaxed microstructure were machined using two different lubrication strategies, namely traditional water-based cutting fluid and liquid nitrogen. Surface integrity after machining was assessed in terms of (i) sub-surface severe plastic deformation layer, (ii) surface topography, and (iii) residual axial stresses as a function of the distance from the machined surface. Finally, the machined specimens were subjected to fatigue tests on a four-point rotating bending machine. For the two sets of specimens, the Wöhler curves were derived to determine their fatigue strength using the modified staircase method. No remarkable difference in terms of surface topography was found between the flood and cryogenic machined specimens, but the latter were characterized by higher and deeper compressive residual stresses and higher severe plastic deformation layer beneath the machined surface. Despite that, it is shown that the fatigue limit of the flood and cryogenic machined specimens is very similar, as well as crack initiation sites have the same location. An explanation of that can be found in the very fine microstructure of the as-received material, which prevails over the other characteristics induced by any machining strategy.

Keywords
Ti6Al4V, Cryogenic Machining, Surface Integrity, Fatigue Strength

Published online 4/24/2024, 10 pages
Copyright © 2024 by the author(s)
Published under license by Materials Research Forum LLC., Millersville PA, USA

Citation: STRAMARE Andrea, BERTOLINI Rachele, BRUSCHI Stefania, GHIOTTI Andrea, CAMPAGNOLO Alberto, Fatigue strength of Ti6Al4V titanium alloy machined under flood and cryogenic conditions, Materials Research Proceedings, Vol. 41, pp 1935-1944, 2024

DOI: https://doi.org/10.21741/9781644903131-214

The article was published as article 214 of the book Material Forming

Content from this work may be used under the terms of the Creative Commons Attribution 3.0 license. Any further distribution of this work must maintain attribution to the author(s) and the title of the work, journal citation and DOI.

References
[1] C. Leyens, & M. Peters (Eds.), Titanium and titanium alloys: fundamentals and applications, Wiley-vch (2006).
[2] M. O. Bodunrin, L. H. Chown, J. W. van der Merwe, K. K. Alaneme, Hot working of
Ti-6Al-4V with a complex initial microstructure, International Journal of Material Forming (2019), 12, pp. 857-874.
[3] Y. Yildiz, & M. Nalbant, A review of cryogenic cooling in machining processes, International Journal of Machine Tools and Manufacture (2008), 48(9), 947-964.
[4] D. Umbrello, & G. Rotella, Fatigue life of machined Ti6Al4V alloy under different cooling conditions, CIRP Annals (2018), 67(1), 99-102. https://doi.org/10.1016/j.cirp.2018.03.017
[5] R. Bertolini, A. Campagnolo, M. Sorgato, A. Ghiotti, S. Bruschi, & G. Meneghetti, Fatigue strength of LPBF Ti6Al4V machined under flood and cryogenic lubri-cooling conditions, International Journal of Fatigue (2022), 162, 106973.
https://doi.org/10.1016/j.ijfatigue.2022.106973
[6] A. Ghiotti, R. Bertolini, M. Sorgato, A. Campagnolo, E. Savio, & S. Bruschi, Ti6Al4V titanium alloy fatigue strength after AM-and machining-based process chains, CIRP Annals (2022), 71(1), 461-464. https://doi.org/10.1016/j.cirp.2022.04.021
[7] G. Lütjering, J.C. Williams, Titanium, Springer (2007).
[8] M. Dumas, F. Cabanettes, R. Kaminski, F. Valiorgue, E. Picot, F. Lefebvre, & J. Rech Influence of the finish cutting operations on the fatigue performance of Ti-6Al-4V parts produced by Selective Laser Melting, Procedia CIRP (2018), 71, 429-434.
https://doi.org/10.1016/j.procir.2018.05.054
[9] S. Sartori, A. Bordin, A. Ghiotti, S. Bruschi, Analysis of the surface integrity in cryogenic turning of Ti6Al4V produced by Direct Melting Laser Sintering, procedia CIRP (2016), 45 123-126. https://doi.org/10.1016/j.procir.2016.02.328
[10] S. Lee, B. Rasoolian, D. F. Silva, J. W. Pegues, N. Shamsaei, Surface roughness parameter and modeling for fatigue behavior of additive manufactured parts: a non-destructive data-driven approach, Addit Manuf (2021), 46, 10209. https://doi.org/10.1016/j.addma.2021.102094
[11] Y. Sun, B. Huang, D. A. Puleo, J. Schoop, & I. S. Jawahir, Improved surface integrity from cryogenic machining of Ti-6Al-7Nb alloy for biomedical applications, Procedia Cirp (2016), 45, 63-66. https://doi.org/10.1016/j.procir.2016.02.362
[12] G. Rotella, O. W. Dillon, D. Umbrello, L. Settineri, & I. S. Jawahir, The effects of cooling conditions on surface integrity in machining of Ti6Al4V alloy, The International Journal of Advanced Manufacturing Technology (2014), 71, 47-55.
https://doi.org/10.1007/s00170-013-5477-9
[13] R. Bertolini, S. Bruschi, A. Bordin, A. Ghiotti, L. Pezzato, M. Dabalà, Fretting Corrosion Behavior of Additive Manufactured and Cryogenic-Machined Ti6Al4V for Biomedical Applications, Advanced Engineering Materials (2016), 19(6), 1500629.
[14] R. W. Landgraf, & R. A. Chernenkoff, Residual stress effects on fatigue of surface processed steels. Analytical and experimental methods for residual stress effects in fatigue, ASTM STP (1988), 1004, 1-12.
[15] G. S. Schajer, (Ed.), Practical residual stress measurement methods. John Wiley & Sons (2013).
[16] Y. Murakami, Metal fatigue: effects of small defects and nonmetallic inclusions, Elsevier (2019).
[17] R. C. McClung, A literature survey on the stability and significance of residual stresses during fatigue, Fatigue & Fracture of Engineering Materials & Structures (2007), 30(3), 173-205.