A Newly Generated Nearly Lamellar Microstructure in Cast Ti-48Al-2Nb-2Cr Alloy for High-Temperature Strengthening


Alloy 4822 (Ti-48Al-2Cr-2Nb at. pct) cast material was given a controlled heat treatment cycle to generate a casting nearly lamellar (CNL) microstructure that enhances the temperature capability over its current engineering casting duplex (CDP) microstructure form. The cycle consisted of three steps: a short α field annealing, an α + γ field annealing, and then aging at a low temperature, with each step being followed by controlled cooling. The resulted microstructure is shown to be a mixture of non-uniformly distributed ~ 250 μm size lamellar colonies containing ~ 0.15 µm spaced laths. Standard tensile testing at 700 °C shows a yield stress of 344 MPa that is ~ 55 MPa greater than that of the current engineering CDP form. The sequential microstructure evolution processes following the three-step thermal cycle are assessed and explained in terms of phase transformations taking place across and below the α transus upon isothermal treatment and subsequent cooling. The resulted increases in high-temperature strengthening are explained by the colony and γ grain size distributions. The strengthening mechanism along with the significance is discussed.

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The current study was financially supported by the National Natural Science Foundation of China (Nos. 51401168 and 51774238) and the 2018 Joint Foundation of Ministry of Education for Equipment Pre-research (No. 6141A020332).

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Correspondence to Jieren Yang or Sang-Lan Kim.

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Manuscript submitted April 19, 2019.

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Gao, Z., Yang, J., Wu, Y. et al. A Newly Generated Nearly Lamellar Microstructure in Cast Ti-48Al-2Nb-2Cr Alloy for High-Temperature Strengthening. Metall Mater Trans A 50, 5839–5852 (2019). https://doi.org/10.1007/s11661-019-05491-8

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