Effect of Preoxidation and Grain Size on Ductility of a Boron-Doped Ni3Al at Elevated Temperatures

Abstract

The ductility of preoxidized Ni3Al (Ni-23Al-0.5Hf-0.2B, at.%) specimens with various grain sizes (17∼193 μm) was evaluated by means of tensile tests at 600 and 760°C in vacuum. It was found that the preoxidation does not affect the ductility of the finest-grained material at either temperature, whereas it causes severe embrittlement in the largest-grained material, especially at 760°C. A continuous, thin Al-rich oxide layer, which forms on the fine-grained samples, protects the underlying alloy from oxygen penetration, preventing any loss of ductility, whereas the nickel-rich oxide which forms on the large-grained samples allows oxygen to penetrate along grain boundaries, causing severe embrittlement. The grain boundaries act as short-circuit paths for rapid diffusion of aluminum atoms from the bulk to the surfaces, and this is responsible for the difference in oxidation behavior between fine- and large-grained materials. The embrittlement of large-grained samples can be eliminated through control of oxide formation on Ni3Al surfaces.

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Correspondence to M. Takeyama.

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Takeyama, M., Liu, C.T. Effect of Preoxidation and Grain Size on Ductility of a Boron-Doped Ni3Al at Elevated Temperatures. MRS Online Proceedings Library 133, 293 (1988). https://doi.org/10.1557/PROC-133-293

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