Two-dimensional (2D) dynamic image analysis (DIA) is often used to measure particle size and shape distributions of metal powders in terms of various size and shape parameters. In this present work, ...five titanium alloy (Ti–6Al–4V or Ti64) powders that were previously characterized with DIA are now characterized in three dimensions (3D) using a combination of X-ray computed tomography (XCT) and mathematical analysis, with various size and shape parameters, including porosity, measured and calculated for each particle. Measured 3D XCT-measured parameters are compared to 2D DIA-measured parameters. The 3D characterization was also used to mathematically generate 2D projection data, with particle orientation averaged over many directions, so that comparisons could be directly made to the previous DIA measurements. The 3D characterization is used to clearly see differences between the powders, including internal porosity and the percentage of single near-spherical particles (SnS) and non-spherical (NS) particles (mostly multi-particles) in each powder. In addition, the 3D data was used to generate 2D projections that were oriented along different directions, which was employed to show that the DIA instrument generated particle projections that were partially oriented along different dimensions of the particles. This partial orientation was apparent in the 2D particle shape data, not the particle size data. All these results show that current powder standards, which all five powders met, are inadequate to completely characterize powder size and shape parameters that could be important in a metal additive manufacturing process.
Nanocomposite powder particles of aluminum with dispersed icosahedral quasicrystals were produced by gas atomization from an Al-Cr-Mn-Co-Zr alloy. Bulk dispersion-strengthened material was obtained ...from the powder by blind-die compaction and forging. The material exhibited an attractive combination of room temperature mechanical properties with a dynamic elastic modulus of 90.5GPa, a tensile yield strength of 690MPa with 6% elongation to failure, and a high cycle fatigue life of 109cycles at 207MPa applied stress. The material also exhibited significant potential for elevated temperature applications with a modulus of 75GPa and yield strength of 400MPa at 300°C.
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A series of novel, mesoporous transition metal doped titanium dioxide-reduced graphene oxide composites are synthesized where the dopants were Mn, Co, Ni, Mo, and W. An in-situ synthesis method was ...used which involves a green, economic, hydrothermal process which can be scaled up easily. The composites show high surface areas (165–245 m2/g) and monomodal pore size distributions with average pore diameters in the range of 3–5 nm. The homogeneous distributions of the dopants are seen in SEM-EDX mapping data. The indirect band gaps of the composite materials are in the range of 2.20–2.48 eV. The composites show excellent dye adsorption activities where 100% adsorption of Rhodamine B occurs within 5 min when Mo–TiO2/rGO composite is used. The adsorbed dye can either be desorbed or photocatalytically degraded and the composite is reusable up to 10 cycles without losing significant activity. Mo–TiO2/rGO composite showed excellent adsorption of both cationic and anionic dyes at neutral pH.
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•A series of transition metal doped TiO2- rGO composites are synthesized where the dopants are Mn, Co, Ni, Mo, and W.•The composites show high surface areas with monomodal pore size distribution curves.•The composites show excellent dye adsorption activities towards Rhodamine B.•Mo-TiO2/ rGO composite show 100% adsorption activities towards both anionic and cationic dyes at neutral pH.•The adsorbed dye can be either desorbed or degraded photocatalytically under visible light or by heating.
Metal-matrix composite powders of W with Al2O3 reinforcements were synthesized by a novel hydrothermal route, which includes calcination and hydrogen reduction steps. It was found that the pH value ...and reactant concentration in the hydrothermal reaction had a significant influence on the morphology and particle size of the powders produced. The precursor powder particle size was the smallest for pH values of <1.0 and a reactant concentration of 0.5g/ml. The addition of Al2O3 led to significant refinement of W particles produced via this route, and these particles gradually become more spherical with increasing Al2O3 content. Subsequently, bulk Al2O3-reinforced W composites were fabricated by spark plasma sintering. The Al2O3 content was varied from 0 to 15vol%, and sintering was performed under 30MPa pressure for 5min at temperatures of 1800–2100°C. The density of the sintered samples increased with sintering temperature, reaching a value of about 97% of the theoretical value for a sintering temperature of 1900°C. An increase in the Al2O3 content from 0 to 6vol% resulted in an increase in the micro-hardness of the sintered composite samples from 278 to 423HV and a decrease in the W grain size from 4.25 to 2.78μm.
•Metal-matrix composite powders of W with Al2O3 reinforcements were synthesized by a novel hydrothermal route.•Al2O3 addition refined effectively W particles.•An increase in the Al2O3 content resulted in an increase in the micro-hardness of the sintered composite samples.
Micropillar compression experiments on 001-oriented CaFe2As2 single crystals have recently revealed the existence of superelasticity with a remarkably high elastic limit of over 10%. The collapsed ...tetragonal phase transition, which is a uni-axial contraction process in which As-As bonds are formed across an intervening Ca-plane, is the main mechanism of superelasticity. Usually, superelasticity and the related structural transitions are affected strongly by both the microstructure and the temperature. In this study, therefore, we investigated how the microstructure and temperature affect the superelasticity of 001-oriented CaFe2As2 micropillars cut from solution-grown single crystals, by performing a combination of in-situ cryogenic micromechanical testing and transmission electron microscopy studies. Our results show that the microstructure of CaFe2As2 is influenced strongly by the crystal growth conditions and by subsequent heat treatment. The presence of Ca and As vacancies and FeAs nanoprecipitates affect the mechanical behavior significantly. In addition, the onset stress for the collapsed tetragonal transition decreases gradually as the temperature decreases. These experimental results are discussed primarily in terms of the formation of As-As bonds, which is the essential feature of this mechanism for superelasticity. Our research outcomes provide a more fundamental understanding of the superelasticity exhibited by CaFe2As2 under uni-axial compression.
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Highly uniform single‐crystal Na‐OMS‐2 (OMS: octahedral molecular sieve), pyrolusite, and γ‐MnO2 nanostructures with an interesting 3D urchinlike morphology have been successfully prepared using a ...hydrothermal method based on a mild and direct reaction between sodium dichromate and manganese sulfate. The crystal phases, shapes, and tunnel sizes of the manganese dioxide nanostructures can be tailored. Reaction temperature, concentrations of the reactants, and acidity of the solution play important roles in controlling the synthesis of these manganese dioxides. Field‐emission scanning electron microscopy and transmission electron microscopy (TEM) studies show that the nanomaterials obtained are constructed of self‐assembled nanorods. X‐ray diffraction and TEM results indicate that the constituent manganese dioxide particles are single‐crystalline materials. Energy dispersive X‐ray analysis and magnetic studies imply that chromium cations may be incorporated into the framework and/or tunnels of the manganese dioxides. A mechanism for the growth of manganese dioxides with urchinlike architectures is proposed.
Manganese oxide octahedral molecular sieve (OMS) nanoarchitectures (see figure) with controlled crystal phases, shapes, and tunnel sizes have been prepared. The effects of reaction parameters on the growth of OMS nano‐urchins and chromium‐ion incorporation have been investigated. A mechanism of formation is proposed.
High manganese steels offer exceptional combinations of high strength and ductility, resulting in weight reduction when utilized in structural applications. Nevertheless, the conventional ...manufacturing routes of these steels is hindered by many production problems. Additive Manufacturing (AM) has emerged as a reliable solution to fabricate thin or complex shape compounds using these steel grades. Indeed, several studies have demonstrated the success to fabricate high manganese twinning-induced plasticity (TWIP) and transformation-induced plasticity (TRIP) steels by laser-powder bed fusion (L-PBF). However, a recent study on a high manganese triplex steel composition has revealed the occurrence of both hot cracking and micro segregation during rapid solidification in L-PBF, highlighting potential processability issues of this family of high alloy steels. In this study, the hot cracking susceptibility of different triplex steels is evaluated, focusing on the impact of the composition on the solidification paths and final microstructures. A Computer Coupling of Phase Diagrams and Thermochemistry (CALPHAD) approach is employed to predict alloy-dependent hot cracking susceptibility so as to establish guidelines for preventing hot cracking and provide insights into alloy design for AM. Microstructural observations are used to determine the accuracy of CALPHAD predictions in terms of elemental segregation, phase formation and hot cracking susceptibility. To this end, scanning transmission electron microscopy is used to evaluate elemental segregation at grain boundaries, while the local distribution of phases and their relative amount is measured by electron backscattered and X-ray diffraction, respectively. Hot cracking susceptibility is experimentally evaluated by measuring the length of cracks (when present) in the cross section of printed specimens.
•Fabrication of crack-free high-Mn triplex steels in laser-powder bed fusion.•Evaluation of fast solidification segregation and microstructures in gas-atomized triplex steel powders.•CALPHAD-based criteria proposed to prevent hot cracking.•Evaluation of hot cracking susceptibility criteria with respect to experimental observations.
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