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

  • Zitong Gao
  • Jieren YangEmail author
  • Yulun Wu
  • Rui Hu
  • Sang-Lan KimEmail author
  • Young-Won Kim
Article
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Abstract

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.

Notes

Acknowledgments

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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Copyright information

© The Minerals, Metals & Materials Society and ASM International 2019

Authors and Affiliations

  1. 1.State Key Laboratory of Solidification ProcessingNorthwestern Polytechnical UniversityXi’anP.R. China
  2. 2.Gamteck LLCDaytonUSA

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