•Nanosized TiB2 particle reinforced Al matrix composites are cold rolled at different strain levels.•Microstructure evolution associated with the two different distributions of TiB2 nanoparticles has been characterized.•TiB2 nanoparticle-clusters along Al grain boundaries result in local grain refinement and dynamic recrystallization.•Alternatively, TiB2 nanoparticles dispersed in Al matrix delay the generation of new high angle grain boundaries.Nanosized TiB2 particle reinforced Al matrix composites, cold-rolled at the true strain levels in the range from 0.9 to 3.0, were characterized by scanning electron microscopy (SEM) and electron backscatter diffraction (SEM/EBSD) and transmission electron microscopy (TEM) in order to examine microstructure evolution associated with the different deformed states. Two types of TiB2 particle-distributions were observed, the majority of TiB2 reinforcement particles were agglomerated along the grain boundaries forming particle-clusters and the rest was dispersed inside the grains. The TiB2 particle-clusters were found to improve local grain refinement by locally increasing the density of high angle grain boundaries (HAGBs). The small submicrometer sized Al grains were observed next to the TiB2 particle-clusters in which dynamic recrystallization mechanism was partially promoted. On the contrary, the presence of the fine TiB2 particles within the primary coarse Al grains generally led to the reduction of HAGBs by hindering the generation of dislocation cell structures and microshear bands during deformation.Download high-res image (433KB)Download full-size image

The phase stability, elastic and electronic properties of binary Hf–Rh compounds have been studied using first-principles calculations based on density functional theory. The equilibrium lattice constants, formation enthalpies, elastic constants, and elastic moduli are presented. Among the binary Hf–Rh compounds, Hf3Rh5 is the most stable with the lowest formation enthalpy. For the equiatomic HfRh phase, it tends to crystallize in the ZrIr-type structure, followed by L10, and then B2 at the ground state based on the analysis of formation enthalpies. Therefore, the crystal structure of the lower temperature HfRh phase is suggested to be the ZrIr-type. This conclusion is in agreement with the experimental reports in the literature. Besides, Hf3Rh4 are proposed to be the Pu3Pd4-type for the first time. Furthermore, our calculated elastic constants for Hf2Rh, ZrIr-HfRh, L10-HfRh, B2-HfRh, Hf3Rh4, Hf3Rh5 and HfRh3 can all satisfy the Born criteria, indicating their mechanical stabilities. When ZrIr-HfRh is adopted, the bulk modulus (B) increases linearly with the growing Rh atomic concentration. Meanwhile, Young's modulus linearly increases with growing shear modulus, and the compound with a higher Poisson's ratio owns a higher B/G ratio simultaneously. Overall, the results also indicate that all the considered Hf–Rh compounds should be ductile. Finally, the electronic structure is analyzed to understand the essence of structural stability of the binary compound.

An in-situ nano-TiB2 decorated AlSi10Mg composite (NTD-Al) powder was fabricated by gas-atomisation for selective laser melting (SLM). Fully dense and crack-free NTD-Al samples were produced using SLM. In contrast to the NTD-Al powder without cell-like microstructure, the SLMed NTD-Al had a textureless microstructure, consisting of fine grains and cells, with well dispersed nano-TiB2 particles inside the grains and rod-like nano-Si precipitates inside the cells. Both nano-TiB2 particles and nano-Si precipitates exhibited a highly coherent interface with the Al matrix, indicative of a strong interfacial bonding. The formation of this microstructure was attributed to the sequential solidification of non-equilibrium and eutectic Al-Si upon rapid cooling during SLM. As a result, the SLMed NTD-Al showed a very high ultimate tensile strength ∼530 MPa, excellent ductility ∼15.5% and high microhardness ∼191 HV0.3, which were higher than most conventionally fabricated wrought and tempered Al alloys, previously SLMed Al-Si alloys and nano-grained 7075 Al. The underlying mechanisms for this strength and ductility enhancement were discussed and a correlation between this novel microstructure and the superior mechanical properties was established. This study provides new and deep insights into the fabrication of metal matrix nanocomposites by SLM from in-situ pre-decorated composite powder.Download high-res image (305KB)Download full-size image

•In-situ TiB2/Al-Mg-Si composites were processed by friction stir processing.•FSP can enhance both the ultimate strength and the elongation of the composite samples.•High strength was achieved without sacrificing the ductility in TiB2/Al-Mg-Si composites.In this paper, we reported microstructure and mechanical properties of the in-situ TiB2/Al–Mg–Si composites processed by friction stir processing (FSP). Compared with the initial state, the proper FSP conditions can enhance both the ultimate strength and the elongation of the composite samples obtained from the nugget zone. Detailed microstructure investigation has been performed by synchrotron X-ray diffraction, scanning and transmission electron microscopy and associated electron backscattered diffraction in order to reveal the mechanisms being responsible for the unusual mechanical behaviors. The results show that the initial composite has a grain size of 50–100 μm and the synthesized nanosized TiB2 particles are almost agglomerated to form micrometer sized clusters at grain boundaries. Comparatively, after FSP, the nugget zone is characterized by fine and equiaxed recrystallized grains (1–5 μm in average grain size). The initial clusters are also broken up, while the nanosized TiB2 particles are distributed much more uniformly in the matrix and act as effective pins to interact with dislocations. Hence, the significantly refined grains and the uniform distribution of the nanosized TiB2 particles mainly contribute to the increase of both strength and ductility of the FSPed composites. The strengthening mechanisms are also discussed.

Zirconia (ZrO2) thin films were deposited by LI MOCVD technique using the precursor Zr(thd)4 over large ranges of deposition parameters. These films were studied by field emission gun scanning electron microscopy (FEG-SEM) for surface and cross-section morphologies. The crystalline structure and crystallographic texture evolution of obtained films were analyzed by X-ray diffraction. Based on those experimental results, two typical deposition mechanisms were discussed from the view of film morphologies and crystallographic texture evolutions. Besides, the influence of deposition conditions on the crystalline structures of ZrO2 films is studied, to bring information about the deposition of tetragonal phase ZrO2 films.Highlights► Microstructures and texture evolution in ZrO2 thin films deposited by MOCVD ► The deposition mechanisms of ZrO2 film deposited by MOCVD ► The growth of tetragonal ZrO2 without doping for microelectronic applications