AMP_06_September_2021

A D V A N C E D M A T E R I A L S & P R O C E S S E S | S E P T E M B E R 2 0 2 1 1 7 CONCLUSIONS MTRs represent apotential life-lim- iting microstructural feature of titanium alloys, especially for the important ro- tating components of a jet engine. Our understanding of the processing con- ditions that create and mitigate MTRs has advanced substantially. Howev- er, the elimination of these life-limit- ing microstructures is impractical at the component scale and their impact on deformation must be understood and accounted for. Many excellent studies have identified and characterized MTRs to accurately predict crack growth and material mean behavior [2,11-14] . More recent investigations on the effect of MTRs on slip length indicate that different metrics must be used to define and characterize MTRs for this application [25] . These results reveal the importance of an MTR’s ability to trans- mit long-range basal slip, creating large dislocation pileups and stress intensi- ties for crack initiation. To fully under- stand the influence of MTRs on titanium components used in service and cor- rectly estimate their life span, some key questions remain: 1. What should the target MTR size be in rotor-grade titanium alloys? In billets? In forgings? 2. Which characteristics of an MTR need to be quantified to deter- mine the quality of the component relative to slip length and crack nucleation? What are the allowable values of these quantified param- eters? While the community has a better understanding of the relevant mechanisms involved, it is still a long way from developing a stan- dard for determining if a component should go into service—especially from the perspective of volumetric inspection. 3. What are the best tools and meth- ods to determine the MTR charac- teristics that contribute to long- range slip? Once identified—and because the weakest link in a large component needs to be found—can the same characteristic features be identified with ultrasound or some other volumetric scanning method? By focusing attention on these questions, MTRs can be better charac- terized and defined relative to the in- tended use of the component and to prevent the catastrophic failures associ- ated with this weak link feature. ~AM&P Acknowledgments The authors wish to extend their gratitude to the following collabora- tors for many useful discussions related to microtexture: T.R. Bieler, T.F. Brod- erick, S. Daly, M.G. Glavicic, P.D. Nico- laou, V. Venkatesh, J.C. Williams, and A. Woodfield. Michelle Harr wishes to acknowledge the support of the Na- tional Science Foundation Graduate Research Fellowship under Grant No. 1256260 DGE and the Air Force Research Labs under Contract #FA8650-16-C-5235 during completion of this work. For more information: Adam Pilchak, senior materials scientist, fatigue & frac- ture group lead, Materials Resources LLC (MRL), Dayton, Ohio 45440, adam. pilchak@icmrl.net . References 1. G. Lütjering and J.C. Williams, Titanium, 2nd ed., Springer, 2007. 2. V. Sinha, et al., Observations on the Faceted Initiation Site in the Dwell-Fatigue Tested Ti-6242 Alloy: Crystallographic Orientation and Size Effects, Metall. Mater. Trans. A, Vol 37, p 1507-1518, 2006. 3. G. Venkatramani, S. Ghosh, and M. Mills, A Size-Dependent Crystal Plasticity Finite-Element Model for Creep and Load Shedding in Poly- crystalline Titanium Alloys, Acta Mater., Vol 55, p 3971-3986, 2007. 4. D. Rugg, M. Dixon, and F.P.E. Dunne, Effective Structural Unit Size inTitanium Alloys, J. Strain Anal. Eng. Des., Vol 42, p 269-279, 2007. 5. K. le Biavant, S. Pommier, and C. Prioul, Local Texture and Fatigue Crack Initiation in a Ti-6Al-4V Titanium Alloy, Fatigue Fract. Eng. Mater. Struct., Vol 25, p 527-545, 2002. 6. M.G. Glavicic, et al., The Origins of Microtexture in Duplex Ti Alloys, Mater. Sci. Eng. A, Vol 513-514, p 325-328, 2009. 7. L. Germain, et al., Analysis of Sharp Microtexture Heterogeneities in a Bimodal IMI 834 Billet, Acta Mater., Vol 53, p 3535-3543, 2005. 8. M.P. Echlin, et al., Incipient Slip and Long Range Plastic Strain Localization in Microtextured Ti-6Al-4V Titanium, Acta Mater., Vol 114, p 164-175, 2016. 9. D. Lunt, et al., Microscopic Strain Localisation in Ti-6Al-4V during Uniaxial Tensile Loading, Mater. Sci. Eng. A, Vol 680, p 444-453, 2017. 10. A.P. Woodfield, et al., Effect of Microstructure on Dwell Fatigue Be- havior of Ti-6242, in TMS Fall Meeting ‘98, p 111-118, 1998. 11. A.P. Woodfield, et al., Effect of Microstructure on Dwell Fatigue Be- havior of Ti-6242, Titanium ’95: Science and Technology, p 1116-1123, 1995. 12. A.L. Pilchak and J.C. Williams, Observations of Facet Formation in Near-α Titanium and Comments on the Role of Hydrogen, Metall. Mater. Trans. A, Vol 42, p 1000-1027, 2011. 13. V. Venkatesh, et al., ICME of Microtexture Evolution in Dual Phase Titanium Alloys, Proceedings of the 13th World Conference on Titanium, Vol VI, No. 1, p 1907-1912, John Wiley & Sons Inc., 2016. 14. V. Venkatesh, et al., Data Driven Tools and Methods for Microtexture Classification and Dwell Fatigue Life Prediction in Dual Phase Titanium Alloys, MATEC Web of Conferences, Vol 321, p 11091, 2020. 15. A.L. Pilchak, Fatigue Crack Growth Rates in Alpha Titanium: Faceted vs. Striation Growth, Scripta Mater., Vol 68, p 277-280, 2013. 16. A.L. Pilchak, et al., On the Cyclic Fatigue and Dwell Fatigue Crack Growth Response of Ti-6Al-4V, Proceedings of the 13th World Conference on Titanium, No. 1, p 993-998, 2016. 17. C. Szczepanski, et al., Combined Experimental and Computational Mod- eling to Understand the Role of Microstructure on Fatigue Behavior of Ti-6Al-2Sn-4Zr-2Mo-0.08Si, conference presentation, 2014. 18. W.J. Evans and M.R. Bache, Dwell- Sensitive Fatigue under Biaxial Loads in