Abstracts:A new analytical model was developed to quantify the role of dislocation climb assisted by vacancy pipe and bulk diffusion in controlling the damage resistance and self-healing of perturbed low angle grain boundaries. Dislocation climb assisted by vacancy pipe diffusion predominantly controls the self-healing process at lower temperatures, while that assisted by bulk diffusion becomes important only at higher temperatures. A relaxation time for the perturbed grain boundary structure was also derived to quantify the time associated with the self-healing process. The extent of this self-healing increases with decreasing grain size, which explains the enhanced damage resistance of nanocrystalline materials.

Abstracts:The structural and chemical changes at ω/β interfaces and the evolution of the morphology of ω in a near-β alloy during isothermal ageing at 573 K were investigated by atom probe tomography and aberration-corrected high-resolution transmission electron microscopy. Ledges and local O enrichment at semi-coherent isothermal ω interfaces are proposed to provide the key driving force for nucleation of ω-assisted α. Following nucleation of α, the morphology of ω evolves from ellipsoidal to rod-like, induced by rapid consumption of ω by α.

Abstracts:Electron microscopy and atom probe tomography were combined to investigate the crystallography and chemistry of a single twin boundary (TB) in a rare-earth-free ferromagnetic MnAl Heusler alloy. The results establish a significant segregation of Mn along the twin boundaries. An enrichment of approx. ~8 at.% Mn was measured along the twin boundary with a confined depletion outside the twin boundary, suggesting short range solute diffusion occurring during massive transformation.

Abstracts:This work investigates the separate influence of porosity and γ/γ′-eutectics on the low-cycle fatigue life of a single-crystal Ni-base superalloy at high temperatures. A conventional vacuum furnace heat-treatment but also integrated heat-treatments in a hot isostatic press are applied to produce different material variants of the same alloy. High-resolution electron microscopy revealed that both pores and γ/γ′-eutectics act as crack starters, thus initiating early failure. Moreover, the results indicate that remaining γ/γ′-eutectics can weaken the fatigue resistance even more than pores. Furthermore, the results confirm the beneficial effect of proper integrated hot isostatic pressing heat-treatments on the fatigue performance.

Abstracts:Extreme-low (even negative) and strong temperature-dependent stacking fault energy (SFE) is one of the most unique properties in face centered cubic (FCC) high entropy alloys (HEAs). Here, by making full use of this unique property, we present a proof-of-principle investigation of tuning defects in FCC HEAs through changing SFE during deformation. A qualitative model is proposed to predict the possibilities of different types of defects in FCC HEAs. Following this model, different defects combinations, instead of individual defects, are well controlled by rolling. FCC HEAs with balanced dislocation, stacking faults and twins show good balance between strength and ductility.

Abstracts:A new candidate fusion engineering material, WC-FeCr, has been irradiated with He ions at 25 and 500 °C. Ions were injected at 6 keV to a dose of ~15 dpa and 50 at. % He, simulating direct helium injection from the plasma. The microstructural evolution was continuously characterised in situ using transmission electron microscopy. In the FeCr phase, a coarse array of 3–6 nm bubbles formed. In the WC, bubbles were less prominent and smaller (~2 nm). Spherical-cap bubbles formed at hetero-phase interfaces of tertiary precipitates, indicating that enhanced processing routes to minimise precipitation could further improve irradiation tolerance.

Abstracts:The present work revealed that equal-channel angular pressing (ECAP) deformation combined with appropriate annealing could represent as an efficient route to modify immiscible as-cast microstructure of a monotectic Al–8Bi alloy by a complete redistribution of immiscible Bi particles and grain refinement of alloy matrix. Especially, we found that the mean size of Bi particles in the 4-pass ECAPed Al–8Bi sample decreases after annealing at 200 °C for 8 h, due to inverse coarsening driven by the reduction of elastic energy and interfacial energy induced by morphology change and spatial distribution of Bi particles.

Abstracts:Uniform macroscopic samples of nanoporous metal with high deformability have so far been limited to precious metals such as Au, Pd and Pt. Here we propose nanoporous Copper-Nickel (npCN) as a nanoporous base metal that can be made with mm dimensions and exhibits significant deformability. NpCN forms a uniform bicontinous network structure with feature sizes that can be controlled from 13 to 40 nm by thermal annealing. Continuous compression tests confirm ductile deformation behavior accompanied with a high strength compared to macroporous Cu- and Ni-foams with similar solid fraction.

Abstracts:Transitions of pyramidal ⟨ c  +  a ⟩ dislocations to sessile structures contribute to poor ductility in pure Mg. Mg-3 wt% Rare Earth (RE) alloys have good ductility, possibly due to ⟨ c  +  a ⟩ dislocation stabilization upon addition of RE solutes. Here, ⟨ c  +  a ⟩ stability is investigated in a model Mg-3 at.%Y random solid solution alloy using molecular dynamics simulations. Favorable fluctuations of Y solutes lower all dislocation energies and have no appreciable effects on the transition mechanism, energy barrier, or time. Enhanced ⟨ c  +  a ⟩ activity and improved ductility in Mg-3 wt%RE alloys are thus not likely associated with solute-stabilization of pyramidal ⟨ c  +  a ⟩ dislocations.

Abstracts:Traditional preparation technology is difficult to achieve near full densified indium tin oxide targets with thickness more than 10 mm. By introducing an anti-densification sintering model into studying the densification behavior of In2O3-SnO2 mixed powders, we proposed secondary cold isostatic pressing and oxygen exchange treatments to improve the densification of the targets by experiment. It is found that the application of secondary cold isostatic pressing and oxygen exchange treatments can increase the densification of targets and reduce the number and size of pores in sintered bodies effectively. Besides, two mechanism models were introduced to reveal the underlying causes.