γ’形成元素量を変動させたγ’析出強化型Co-W-Al合金の特性

概要

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Co-base superalloy has been generally strengthened through solid solution hardening and/or carbide precipitation hardening because dominant L12-γ’ phase has not been found as like L12-Ni3Al, which has been major strengthening phase for Ni-base superalloy. However, recently, γ’-Co3(W,Al) was found in Co-W-Al ternary alloy. Thereby new γ’ strengthening Co-base superalloy is expected. In this work, properties of four kinds of γ’ strengthening Co-W-Al alloys with the amount of γ’ phase from 20 % to 50 % on calculation were investigated and the following results were obtained. (1) High temperature ductility was decreased and flow stress was increased with increasing γ’ phase forming elements which were W, Al and Ta. Excessive additions of γ’ phase forming elements degraded the high temperature ductility drastically due to the precipitation of μ phase. (2) γ’ solvus temperature and nose temperature of peak aging hardness shifted to higher temperature by increasing γ’ phase forming elements. The alloy with 40 % γ’ phase showed adequate hot workability possessed 360 HV as peak aging hardness around 1073 K. (3) The oxidation resistance of alloys with 5 mol% Cr was improved by increasing Al content up to 9 mol%. However it is insufficient in order to form the homogeneous protective scale layer of Al2O3 and Cr2O3 at 1273 K.
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