open access

https://hdl.handle.net/2115/49357

Phase Transformation Behavior of Al2O3 Scale Formed on Pt-Modified γ'-Ni3Al-Based Alloys With and Without Hf Addition

英語

Short-term kinetics

2012-06

Springer Netherlands

Oxidation of Metals

77(5-6)

237-251

The allotropic phase transformation behavior of Al2O3 scale formed on Ni-22Al-30Pt (in at.%) with and without 0.5Hf was investigated during short-term (i.e., 3 min dwell) cyclic oxidation at 1150℃ in air. Hafnium addition did not appear to affect the oxidation rate in the early oxidation cycles, but it did delay the phase transformation from the metastable θ-Al2O3 structure to the stable α-Al2O3. Small dimples, which corresponded to α-Al2O3 grains, started to form on the Hf-free alloy after only 3 oxidation cycles; whereas, no apparent morphological change of the oxide scale surface was observed on the Hf-modified alloy. The transformation to α-Al2O3 was found to initiate at scale/alloy interface on the Hf-free alloy, but it initiated at gas/scale interface on the Hf-modified alloy. Depth profiling using glow discharge optical emission spectroscopy revealed that Hf enriched at the scale/alloy interface due to Hf rejection associated with the formation of an Al-depleted γ-layer, which has a low Hf solubility. Higher positive strain energy due to Hf solution in the metastable Al2O3 was inferred to be the main contributor to the delayed the transformation.

学術雑誌論文

Accepted Manuscript

The final publication is available at www.springerlink.com

0030-770X