Competitive Healing of Creep-Induced Damage in a Ternary Fe-3Au-4W Alloy
Y. Fu (TU Delft - Novel Aerospace Materials)
Cees Kwakernaak (TU Delft - (OLD) MSE-1)
W.G. Sloof (TU Delft - (OLD) MSE-1)
F.D. Tichelaar (TU Delft - QN/Afdelingsbureau, Kavli institute of nanoscience Delft)
E. H. Brück (TU Delft - RST/Fundamental Aspects of Materials and Energy)
S van der Zwaag (School of Materials Science and Engineering, Tsinghua University, TU Delft - Novel Aerospace Materials)
Niels Harmen H. Dijk (TU Delft - RST/Fundamental Aspects of Materials and Energy)
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Abstract
Autonomous healing of creep-induced grain boundary cavities by Au-rich and W-rich precipitates was studied in a Fe-3Au-4W (wt pct) alloy at a fixed temperature of 823 K (550 °C) with different applied stresses. The ternary alloy, with two supersaturated healing solutes, serves as a model system to study the interplay between two separate healing agents. The creep properties are evaluated and compared with those of the previously studied Fe-Au and Fe-W binary systems. The microstructures of the creep-failed samples are studied by electron microscopy to investigate the cavity filling behavior and the mass transfer of supersaturated solute to the defect sites. Compared to the Fe-Au and Fe-W alloys, the new Fe-Au-W alloy has the lowest steady-state strain rate and the longest lifetime. The site-selective filling of the creep-induced cavities is attributed to two different categories of precipitates: micron-sized Au-rich precipitates and nano-sized W-rich precipitates. The Au-rich precipitates are found capable to fully heal the cavities, while the W-rich precipitates show only a limited degree of healing. The two types of precipitates show a reluctance to coexistence, and the formation of W-rich precipitates is suppressed strongly. A model is proposed to describe the competitive healing behavior of the Au-rich and W-rich precipitates.
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