Self healing by Cu precipitation in deformed Fe-Cu-B-N-C

Self healing by Cu precipitation in deformed Fe-Cu-B-N-C

Zhang, S.
Langelaan, G.
Schut, H.
Brück, E.
Van der Zwaag, S.
Van Dijk, N.H.

2013-06-16

Steels are among the most widely used construction materials as their mechanical properties can be tuned over a very wide range of desired combinations of strength formability and other properties. However, when exposed for long times to high temperatures steel components can exhibit premature and low-ductility creep fracture, which arises from the formation, growth and coalescence of (initially) nanoscale pores. Self-healing of such defects is regarded as a promising new approach to enhance the component lifetime. In principle, it could be achieved by nanoscale precipitation on the creep cavity surface preventing further growth. Earlier work has shown that Cu may be a suitable alloying element to induce such a healing behaviour in stainless steels. In the present work the high temperature precipitation behaviour of Cu on deformation inducted defects is studied for a number of high-purity Fe-Cu-B-N-C alloys using positron annihilation spectroscopy (PAS) and hardness tests. Samples with 0% and 8% cold pre-strain are utilized to study the influence of prior tensile deformation on the precipitation kinetics of copper. The time evolution of the S-W points derived from Coincidence Doppler Broadening spectra indicates that deformation-induced defects enhance the Cu precipitation kinetics. A clear reduction in open volume defects is accompanied by a strong increase of Cu signature during the initial stage of aging, demonstrating the self-healing potential in the Fe-Cu-B-N-C alloy. A comparison between the hardness behaviour of Fe-Cu, Fe-Cu-B-N, and Fe- Cu-B-N-C indicates the added carbon counteracts the acceleration of Cu precipitation caused by the addition of B and N.

self-healing
Cu precipitation
deformation-induced defects
carbon addition
positron annihilation spectroscopy

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Conference proceedings

conference paper

(c) 2013 Zhang, S.; Langelaan, G.; Schut, H.; Brück, E.; Van der Zwaag, S.; Van Dijk, N.H.