•The micro-arc oxidation behaviors of in-situ TiB2/A201 composite are studied.•The characteristic U-t curves are studied based on morphological and phase evolutions.•TiB2 particles have the played dual role in the micro-arc oxidation.•β-Al2O3 is initially found in the MAO film, and converted to α-Al2O3 finally.•TiB2 particles should be oxidized and then melted during the MAO process.The Micro-arc oxidation (MAO) treatment on the in-situ TiB2/A201 composites was performed using the aluminate-based electrolyte, and the corresponding MAO behavior was discussed in this work. In connection with the film thickness-time curve, the voltage-time for the MAO process on the TiB2/A201 composite can be divided into two periods, namely the initial period (Stage I and II) and linear growth period (Stage III and IV). The phase and morphologies evolutions of the composite experienced these stages have been characterized by X-Ray diffraction, scanning electron microscopy and Micro-Raman spectroscopy. It is found the TiB2 particles have played a dual role in the MAO process. Firstly, the external current can leak through conductive TiB2 particles in the initial period. However, this leaking way has been quickly cut off by the oxidation of TiB2 to TiO2. Secondly, the TiB2 particles beneath the metal-oxide interface can impede MAO film from growing inward. Nevertheless, these TiB2 particles should be oxidized and then melted gradually, and finally dissolved into the oxide film.

•The microstructural correlated damage mechanisms were studied in in-situ TiB2/Al composite.•A microstructural-based multistage damage in HCF was identified.•Effects of GBs, grains orientations and TiB2 particles on damage mechanisms were discussed.•An energy model for dislocation slip in nano or sub-micron particles reinforced metal composites was proposed.The damage mechanisms during high-cycle fatigue (HCF) process were systematically investigated in the in-situ TiB2/2024 Al-composite. It is found the HCF endurance limit of in-situ TiB2/2024 Al-composite is ~ 360 MPa, which is much higher than the reported ex-situ particle-reinforced composites (~ 180–300 MPa). A microstructural-based multistage damage in HCF is identified from fracture surface: Stage I (crack initiation), Stage II (stable crack propagation), and Stage III (ultimate fracture). In Stage I, the (S/θ + TiB2) particles generally act as initiation sites in most cases. The nano or sub-micron TiB2 particles can homogenize stress and reduce dislocations piling-up at grain boundaries (GBs), impeding the crack nucleation from GBs. In Stage II, the GBs, grain orientations and TiB2 particles are the major factors for the damage behaviors. The GB effects depend on their misorientations, geometries and nearby particles. The crack propagation shows crystallographic characteristics of {100}〈001〉, {111}〈110〉 and {111}〈112〉, which have different propagation rates. For TiB2 particles, the complex effects on the HCF damage behavior depend on their size and distribution. Considering the microstructural factors, the HCF damage mechanisms was discussed in detail and an energy model of dislocation slipping for nano or sub-micron particle-reinforced metal composites was proposed.Download high-res image (355KB)Download full-size image

•The microstructures and textures of in-situ TiB2/Al composites are characterized quantitatively.•The effects of TiB2 particles on the (sub-)grain boundaries and dislocations are characterized and discussed.•The dynamic recovery and recrystallization mechanisms of in-situ TiB2/Al composites are studied.The microstructural evolution of in-situ TiB2 nano-particle reinforced AlZnMgCu composites during hot extrusion was investigated from micro to macro scales by a combination of various techniques, including neutron and synchrotron X-ray diffraction, optical microscopy, scanning and transmission electron microscopy and electron backscatter diffraction (EBSD). The development of microstructure has shown a bimodal grain structure with distinctive spatial distributions of TiB2 particles: the elongated coarse grain structure with smaller dispersed particles and the fine grains mixed with clusters of relatively larger particles. The particle stimulated nucleation occurs at large particle clusters, resulting in recystallized (sub)micron sized fine grains. The dispersed smaller particles are observed to promote dislocation generation and to prohibit recovery. They are shown to reduce the misorientation of low angle grain boundaries due to the pinning effects on independent dislocations, which also lead to the suppression of dynamic recovery and increase of driving force for dynamic recrystallization. Quantitative texture analysis combined with neutron diffraction and EBSD has exhibited the development of a strong 〈111〉 and 〈001〉 dual fiber texture, and both texture volume fractions are changing with the particle content. In addition, the synchrotron diffraction experiments have shown that dislocation density increases with the particle content in both texture components. The microstructure evolution is the result from a complex process of particles/matrix interaction during the deformation and dynamic recrystallization. In comparison with its particle-free alloy counterpart, the thermomechanical response of the composites at high temperature is discussed in terms of aluminum deformation and recrystallization mechanisms combined with nanosized particle effects.Download high-res image (307KB)Download full-size image

•The elastic and electronic properties of Al5Mo and Al5W under pressure are studied.•The elastic constants and elastic moduli are enhanced with the rising pressures.•The brittleness should be kept up to 40 GPa on the analyses of B/G ratios and Poisson’s ratios.•Al5Mo and Al5W have stable structure without phase transition under pressures.This work investigated the elastic and electronic properties of hexagonal Al5Mo and Al5W intermetallics using the first-principle method. In both phases, the structural, elastic and electronic properties showed the substantial pressure dependent behaviors. For formation enthalpies, they were both negative to indicate their stability at the ground state thermodynamically. In comparison, Al5Mo has the superior stability over Al5W owing to its more negative Hf. Elastically, the calculated elastic constants can satisfy Born’s criteria from 0 to 40 GPa, suggesting their mechanical stability. With the increasing pressures, the elastic constants exhibited linearly rising tendencies. Using elastic constants, the bulk modulus (B), shear modulus (G) and Young’s modulus (E) were derived using the Voigt-Reuss-Hill method. All these moduli displayed the increasing behaviors with the growing pressures. The analysis of B/G ratio and Poisson’s ratio indicated that the Al5Mo and Al5W should be brittle at 0–40 GPa. Electronically, both compounds were suggested to possess metallic behavior through the DOS (density of states) analysis. Under pressures, the shapes of peaks and pseudogaps showed few changes, suggesting Al5Mo and Al5W has kept structurally stable up to 40 GPa.Al5Mo has the stable structure without phase transition under pressures on the analyses of the DOS spectra. The similar situation can also be identified in Al5W.Download high-res image (59KB)Download full-size image

The influence of crystallographic texture, grain shape and TiB2 particle distribution on the mechanical anisotropy with respect to three-dimensional directions of in-situ TiB2/2024 composite plate has been investigated. The grains of the composite are strongly elongated along extrusion direction (ED). Most of TiB2 particles are aligned along the long grain axis in both ED-TD (TD: transverse direction) and ED-ND (ND: normal direction) planes to form the particle bands. In the concerned three directions, the yield/ultimate tensile strength and elongation are all increasing in the directional sequence of ND