Effect of precipitated Co solid solution on moisture-induced embrittlement of L12-type Co3Ti ordered alloys Original Research Article

The moisture-induced embrittlement of the L12-type Co3Ti alloys (with nominal compositions of Co-19, 20 and 20.5 at.% Ti) was studied by tensile test, fractographic and microstructural observation. All the alloys exhibited age hardening at the examined temperatures due to precipitation of fcc Co solid solution in the L12 matrix. For the Co-19Ti alloy which contained primary Co solid solution particles, moisture-induced embrittlement did not occur in the solution treated condition but was caused by aging, and then reduced by prolonged aging. For the Co-20Ti and Co-20.5Ti alloys which contained no primary Co solid solution particles, moisture-induced embrittlement occurred in the solution treated condition and was increased by aging but significantly reduced by prolonged aging, similar to the Co-19Ti alloy. These results were discussed in association with the interaction of hydrogen with the Co solid solution particle because this interaction was greatly dependent on the morphology, size and interfacial structure of the second phase particles.