Modelling the growth and filling of creep-induced grain-boundary cavities in self-healing alloys

A set of numerical and analytical models is presented to predict the growth and contraction of grain-boundary creep cavities in binary self-healing alloys. In such alloys, the healing is realised by preferential precipitation of supersaturated solutes at the free surface of the cavity. The cavity grows due to the diffusional flux of vacancies...

Self healing of creep-induced damage in Fe-3Au-4W by multiple healing agents studied by synchrotron X-ray nano-tomography

Constant stress creep experiments at 550 °C were performed on a high-purity Fe-3Au-4W (wt.%) ternary alloy with about 1 at.% supersaturation for Au and W in order to study self healing of grain-boundary cavities by both Au-rich and W-rich precipitates. Using synchrotron X-ray nano-tomography, the development of the creep cavities and the...

A novel 3D mixed-mode multigrain model with efficient implementation of solute drag applied to austenite-ferrite phase transformations in Fe-C-Mn alloys

A computational 3D model that accounts for both nucleation and interface migration is a very useful tool to monitor and grasp the complexity of microstructure formation in low-alloyed steels. In the present study we have developed a 3D mixed-mode multigrain model for the austenite-ferrite and the austenite-ferrite-austenite formation capable...

Precipitation of supersaturated solute in H ion irradiated Fe-Au and Fe-Au-W alloys studied by positron annihilation spectroscopy

The effect of thermal aging of homogenized Fe-Au and Fe-Au-W alloys, irradiated at room temperature with hydrogen ions, was studied for an aging treatment at 300 °C for aging times up to 100 h. The aging behavior of the Fe-based alloys is compared to the results for pure Fe. The precipitation behavior of Au-rich and W-rich precipitates and...

Competitive Healing of Creep-Induced Damage in a Ternary Fe-3Au-4W Alloy

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...

Surface precipitation of supersaturated solutes in a ternary Fe–Au–W alloy and its binary counterparts

Abstract: The precipitation of supersaturated solutes at free surfaces in ternary Fe–3Au–4W and binary Fe–3Au and Fe–4W alloys (composition in weight percentage) for different ageing times was investigated at a temperature of 700 °C. The time evolution of the surface precipitation is compared among the three alloys to investigate the...

A Review of Self-healing Metals: Fundamentals, Design Principles and Performance

Self-healing metals possess the capability to autonomously repair structural damage during service. While self-healing concepts remain challenging to be realized in metals and metallic systems due to the small atomic volume of the mobile atoms, the slow diffusion unless at high temperatures and the strong isotropic metallic bonds, the...

Self healing of radiation-induced damage in Fe–Au and Fe–Cu alloys: Combining positron annihilation spectroscopy with TEM and ab initio calculations

Self healing of early stage radiation damage by site selective solute segregation is a promising approach to extend the lifetime of nuclear reactor components. In the present study, the creation and autonomous healing of irradiation-induced damage is investigated in pure Fe and high purity Fe–Au and Fe–Cu model alloys. To create radiation...

Mediation of high temperature radiation damage in bcc iron by Au or Cu precipitation

High temperature radiation damage in binary bcc Fe alloys containing 1 atomic % Au or Cu due to Fe ion irradiation at 550 °C to a peak dose of 2.8 and 8.3 dpa is studied. The precipitation behavior of gold and copper and its correlation to the irradiation-induced defects is studied by transmission electron microscopy and variable energy...

Self healing of creep damage in iron-based alloys by supersaturated tungsten

When metals are mechanically loaded at elevated temperatures for extended periods of time, creep damage will occur in the form of cavities at grain boundaries. In the present experiments it is demonstrated that in binary iron-tungsten alloys creep damage can be self healed by selective precipitation of a W-rich phase inside these cavities. Using...

A Computational Design Study of Self-healing Creep Resistant Steels

Modelling study on the three-dimensional neutron depolarisation response of the evolving ferrite particle size distribution during the austenite–ferrite phase transformation in steels

The magnetic configuration of a ferromagnetic system with mono-disperse and poly-disperse distribution of magnetic particles with inter-particle interactions has been computed. The analysis is general in nature and applies to all systems containing magnetically interacting particles in a non-magnetic matrix, but has been applied to steel...

Analysis of the grain size evolution for ferrite formation in Fe-C-Mn steels using a 3D model under a mixed-mode interface condition

A 3D model has been developed to predict the average ferrite grain size and grain size distribution for an austenite-to-ferrite phase transformation during continuous cooling of an Fe-C-Mn steel. Using a Voronoi construction to represent the austenite grains, the ferrite is assumed to nucleate at the grain corners and to grow as spheres....

Self-Healing Phenomena in Metals

In comparison to other materials, in metals and metallic systems self-healing of cracks and crack-initiating defects is difficult to achieve due to the fact the solute atoms that act as healing agents are relatively small and generally have a relatively low mobility at the prevailing operating temperatures. In this review, the scientifically...

In Situ 3D Neutron Depolarization Study of the Transformation Kinetics and Grain Size Evolution During Cyclic Partial Austenite-Ferrite Phase Transformations in Fe-C-Mn Steels

We have analyzed the evolution of the ferrite fraction and average ferrite grain size during partial cyclic austenite-to-ferrite and ferrite-to-austenite phase transformations in an Fe-0.25C-2.1Mn (wt pct) steel using three-dimensional neutron depolarization (3DND). In the 3DND experiments, the ferrite fraction is derived from the rotation...

Linking Surface Precipitation in Fe-Au Alloys to Its Self-healing Potential During Creep Loading

The precipitation of Au-rich precipitates on the external surfaces of Fe-Au alloys has been studied by scanning and transmission electron microscopy. The surface precipitates formed at elevated temperatures are found to self-organize in regular patterns and their growth rate is determined quantitatively. The observed surface precipitation at...

Autonomous filling of grain-boundary cavities during creep loading in Fe-Mo alloys

We have investigated the autonomous repair of creep damage by site-selective precipitation in a binary Fe-Mo alloy (6.2 wt pct Mo) during constant-stress creep tests at temperatures of 813 K, 823 K, and 838 K (540 °C, 550 °C, and 565 °C). Scanning electron microscopy studies on the morphology of the creep-failed samples reveal irregularly...