AMP_06_September_2021

FEATURE 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 4 8 indeed due to departure from the dimensional change due to thermal contraction because the 3% strain test is more closely aligned with the unconstrained rate of thermal contraction on the sample. Instead, the higher strain tests show two lower inflection points at 740°C and 645°C, and these correspond well with the phase transformation from β to α, and formation of TiAl 3 , respectively [4] . The 740°C inflection point is more pronounced showing a sharp in- crease in strength beyond this temperature. Further, the relative final strengths indicates that 6% test results in higher total strain compared to the 3% test. This is reason- able considering the higher strain rate and total strain for the 6% test. CONCLUSIONS The preliminary results from flow stress testing of Ti-6Al-4V alloy specimens highlight particular tempera- ture ranges where transitions in the flow stress behavior of the alloy are seen. By testing the specimens at different cooling rates and strain rates, shifts to these inflection points are observed. When combined with other charac- terization methods (for example traditional dilatometry measurements of CTE) as well as Calphad-type modeling of the alloy, one can link the strength changes to phase transformations. One benefit of developing nontradition- al test methods, such as that reported here, is that they can accelerate the materials characterization process. Iso- thermal testing can miss these critical transitions. Further, using this continuous cooling while straining test as a starting point helps to identify a temperature region (e.g., 750-800 o C and 640-660 o C) for closer inspection of the be- havior of the alloy. ~HTPro For more information: Lesley Frame, assistant professor, Center for Materials Processing Data, University of Con- necticut, 97 North Eagleville Rd., Storrs, CT 06269, lesley. frame@uconn.edu , frame.mse.uconn.edu. Acknowledgments The authors would like to thank the Center for Mate- rials Processing Data, industry members Dave Furrer and Jean-Philippe Thomas at Pratt & Whitney, Mark Timko at Weber Metals, and Mike Shepherd, formerly at MTS Sys- tems, ASM International, and partner universities includ- ing Danielle Cote at Worcester Polytechnic Institute and Krishna Rajan at University at Buffalo. We also thank Rain- er Hebert, UCONN CMPD member, for his support with the Gleeble 3500, and Matt Beebe for machining shop support. References 1. P.K. Chaudhury and D. Zhao, Atlas of Formability, National Center for Excellence in Metalworking Technology, Naval Industrial Resource Support Activity, 1992. 2. S. Bruschi, et al., Workability of Ti–6Al–4V Alloy at High Temperatures and Strain Rates, Materials Letters, 58 (27–28), p 3622–3629, 2004, https://doi.org/10.1016/ j.matlet.2004.06.058. 3. T. Seshacharyulu, et al., Hot Working of Commercial Ti–6Al–4V with an Equiaxed α –β Microstructure: Mater- ials Modeling Considerations, Materials Science and Engi- neering: A, 284 (1–2), p 184–194, 2000, https://doi.org/ 10.1016/s0921-5093(00)00741-3. 4. A. Majorell, S. Srivatsa, and R. Picu, Mechanical Behavior of Ti–6Al–4V at High and Moderate Tem- peratures—Part I: Experimental Results, Materials Science and Engineering: A, 326 (2), p 297–305, 2002, https://doi. org/10.1016/s0921-5093(01)01507-6. 5. J.S. Jha, et al., Flow Stress Constitutive Relationship Between Lamellar and Equiaxed Microstructure during Hot Deformation of Ti-6Al-4V, Journal of Materials Processing Technology, 270 , p 216–227, 2019, https://doi. org/10.1016/j.jmatprotec.2019.02.030. 9 10