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Microstructural response to thermomechanical processing of NbTiZr-containing refractory multi-principal element alloys
Balzac, Adira Tova Yermish
Balzac, Adira Tova Yermish
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2024
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Refractory multi-principal element alloys (RMPEAs) are of interest for high temperature applications due to their potential for high temperature strength and thermal stability. However, due to the conditions necessary, thermomechanical processing (TMP) of RMPEAs can be extremely difficult. Many bulk RMPEAs are produced via vacuum arc melting, which produces heterogeneous microstructures due to microsegregation during solidification and variations in grain size and morphology. This microstructural heterogeneity can lead to inhomogeneous properties and responses to TMP.
Homogenization of the solidification microstructure is difficult to predict due to model limitations. Interdiffusion data for multi-component systems is limited and difficult to determine experimentally or computationally. The Thermo-Calc® DICTRA diffusion model can predict compositional homogenization treatments, but becomes increasingly computationally intensive with increasing number of components. In this work, methods for predicting diffusion homogenization treatments are investigated. Predicted homogenization treatments from TC-DICTRA and characteristic diffusion distance (CDD) approximations are compared and validated with experimental homogenization treatments for three body-centered cubic (BCC) RMPEAs, namely NbTiZr, Nb30Ti26Zr14V30 (NTZV), and Nb26Ti23Zr8V20Mo23 (NTZVM). CDD approximations function as a rapid order-of-magnitude method for predicting homogenization treatments.
Grain size control is also not well-explored within the field of RMPEAs, and recrystallization behavior atypical for BCC alloys has been observed in BCC RMPEAs. This work investigates the viability of static recrystallization (SRX) treatments after room temperature deformation for grain refinement in BCC RMPEAs. SRX treatments of two BCC RMPEAs, namely NbTiZr and NTZV, are conducted; it is shown it is possible to achieve complete SRX with refined grains compared to the as-homogenized microstructure.
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