Bilal Mansoor

A comparative study of image analysis and porometry techniques for characterization of porous membranes

AbstractFor porous membranes, characterization of a membrane’s key structural parameters, such as average and maximum pore size, pore size distribution, pore density, pore geometry, and surface roughness, is vital. The interplay between these parameters and membrane performance is detrimental for designing, evaluating, and developing the next generation of porous membranes. In this study, image analysis of scanning electron microscopy (SEM) micrographs is assessed as a technique to quantify such structural parameters. The focus of this work is on two open source software packages: ImageJ and Gwyddion. Comprehensive image analyses were carried out on three types of porous membranes: (i) phase inverted polyvinylidene fluoride, (ii) track-etched polycarbonate, and (iii) stretched polytetrafluoroethylene membranes. The information on key structural parameters acquired by image analysis was compared with data obtained from other established characterization methods. Based on current data, it was concluded that most membrane properties obtained by image analysis of micrographs were within acceptable accuracy, and consistent with other techniques except for surface roughness and pore size distribution. It was observed that optimum SEM micrograph’s magnification was essential to carry out an accurate image analysis. A major limitation of image analyses remains that they can only be carried out on surface pores. As such, they were found useful for characterizing membranes where surface pores define the overall pore size, geometry, and distribution.

Effect of oxygen vacancy on the improved photocatalytic activity of Cr-doped TiO2

We employed ab initio calculations to study the effect of various defects on the structural, electronic and optical properties of anatase TiO2. Single Cr doping at Ti sites introduced isolated Cr 3d states in the band gap of TiO2. Charge compensated Cr doped model was introduced by simultaneously doping two Cr atoms at Ti sites along with one oxygen vacancy (Ti14O31Cr2). It has been found that Ti14O31Cr2 can narrow the band gap significantly and passivate gap states. Removal of the isolated Cr 3d states from the band gap and improved visible light absorption would effectively enhance the photocatalytic activity of Cr doped TiO2. Our calculations provide reasonable explanation for the previously reported experimental findings.

Friction Stir Welding of AZ31B Magnesium Alloy with 6061-T6 Aluminum Alloy: Influence of Processing Parameters on Microstructure and Mechanical Properties

The success of Friction Stir Welding (FSW) in joining light metal alloys has inspired attempts to further exploit its potential for joining materials which differ in chemical composition, structure, and/or properties. The FSW of relatively soft (e.g., Al/Mg) and hard (e.g., Fe/Ni) combinations of alloys is of particular interest in automotive and aerospace applications. However, joining of dissimilar alloys presents several unique challenges that include the different deformation behaviors, formation of detrimental intermetallic compounds, and differences in physical properties such as thermal conductivity. These factors lead to amplified asymmetry in both heat generation and material flow and consequently lead to the formation of a heterogeneous weld. In this work, a dissimilar metal joint was created between twin roll cast AZ31B magnesium alloy and Al 6061-T6 aluminum alloy plates by FSW. The main aim here is to investigate the effect of key process parameters such as tool rotation speed and welding speed on microstructural evolution and mechanical properties of the resulting heterogeneous joint. A detailed microstructural analysis was carried out to understand the composition of the intermetallic phases generated in the stirred zone and their impact on microhardness and overall mechanical properties of the weld. Our key finding was that, weld configuration with placing the aluminum alloy plate on the advancing side resulted in a sound, defect free joint compared to the alternate configuration.

Structure and growth of core–shell nanoprecipitates in Al–Er–Sc–Zr–V–Si high-temperature alloys

Lightweight Sc-containing aluminum alloys exhibit superior mechanical performance at high temperatures due to core–shell, L12-ordered trialuminide nanoprecipitates. In this study, the structure of these nanoprecipitates was studied, using different transmission electron microscopy (TEM) techniques, for an Al–Er–Sc–Zr–V–Si alloy that was subjected to a two-stage overaging heat treatment. Energy-dispersive X-ray spectroscopy of the spherical Al3(Sc, Zr, Er ,V) nanoprecipitates revealed a core–shell structure with an Sc- and Er-enriched core and a Zr-enriched shell, without a clear V outer shell. This structure is stable up to 72% of the absolute melting temperature of Al for extended periods of time. High-angle annular dark-field scanning TEM was used to image the {100} planes of the nanoprecipitates, demonstrating a homogeneous L12-ordered superlattice structure for the entire nanoprecipitates, despite the variations in the concentrations of solute atoms within the unit cells. A possible growth path and compositional trajectory for these nanoprecipitates was proposed using high-resolution TEM observations, where different rod-like structural defects were detected, which are considered to be precursors to the spherical L12-ordered nanoprecipitates. It is also hypothesized that the structural defects could consist of segregated Si; however, this was not possible to verify with HAADF-STEM because of the small differences in Al and Si atomic numbers. The results herein allow a better understanding of how the Al–Sc alloys’ core–shell nanoprecipitates form and evolve temporally, thereby providing a better physical picture for future atomistic structural mappings and simulations.

Equal Channel Angular Pressing of a Newly Developed Precipitation Hardenable Scandium Containing Aluminum Alloy

Precipitation hardenable aluminum alloys are well-known for their high strength-to-weight ratio, good thermal stability, electrical conductivity, and low cost. Equal channel angular pressing (ECAP) is proven to further improve the mechanical properties of metallic alloys through microstructure modification. In this work, ECAP of a recently developed, precipitation hardenable, cast Al–Er–Sc–Zr–V–Si alloy in peak-aged condition by route 4Bc was carried out to create an alloy with ultra-fine grain structure. The combined effect of grain refinement and precipitation on the tensile behavior and thermal stability of the ECAPed alloy is reported here. Improvement in yield strength and lack of strain hardening in ECAPed alloy were as expected. Microhardness contour plots with a narrower spread indicated enhancement in microstructural homogeneity after four ECAP passes as compared to the peak-aged condition. The variations in microhardness after annealing heat treatments at different temperatures highlighted the important role precipitates play in maintaining microstructure stability up to 250 °C in the ECAPed material.

Bifurcation in deformation mechanism to overcome strength-ductility paradox in metal-ceramic multilayer thin-films

Nanocrystalline multilayer thin-films are manufactured in configurations of alternating porous ceramic (TiN) layers of relatively high thickness (hceramic) with metal (Ti) layers of low thicknesses (0.8 nm < hmetal < 34 nm) and keeping a constant modulation ratio (η ∼ hceramic/hmetal ∼ 17.5). As hmetal decreases, the overall co-deformation mechanism in the multilayer films bifurcates into the dislocation dominant confined layer slip (CLS) mechanism in the metal and diffusional creep dominant processes in the porous ceramic layer at hmetal ∼ 6.7 nm. This bifurcation leads to simultaneously achieving the highest strain hardening rate due to the CLS mechanism in one layer and the highest strain rate sensitivity value due to the diffusional flow in the other and overcoming the strength-ductility paradox in multilayer thin-film materials at low temperatures.Nanocrystalline multilayer thin-films are manufactured in configurations of alternating porous ceramic (TiN) layers of relatively high thickness (hceramic) with metal (Ti) layers of low thicknesses (0.8 nm < hmetal < 34 nm) and keeping a constant modulation ratio (η ∼ hceramic/hmetal ∼ 17.5). As hmetal decreases, the overall co-deformation mechanism in the multilayer films bifurcates into the dislocation dominant confined layer slip (CLS) mechanism in the metal and diffusional creep dominant processes in the porous ceramic layer at hmetal ∼ 6.7 nm. This bifurcation leads to simultaneously achieving the highest strain hardening rate due to the CLS mechanism in one layer and the highest strain rate sensitivity value due to the diffusional flow in the other and overcoming the strength-ductility paradox in multilayer thin-film materials at low temperatures.

Friction Stir Welding on Light-Weight Metal - Aluminum Alloy Al6061

Friction stir welding (FSW) is a solid state joining process in which metals are joined together using frictional heat and severe plastic deformation. The heating and the mixing of the metals is performed using a hardened tool with a shoulder and pin. FSW of lightweight metal alloy Al6061 has been carried out in the present study. For welding aluminum the parameters used were a constant tool rotation speed of 1600 rpm and varying tool translation speeds of 250, 500, 750 and 1000 mm/min. The welded coupons were characterized for microstructural observations and mechanical properties such as tensile and Charpy impact properties. The tensile and impact properties were studied at two different temperature namely, room temperature (RT) and 300°C. The FS welded aluminum specimens showed 86% – 98% tensile yield strength, in comparison to the base material at RT. At 300°C, the yield strength was observed to be 85% to 93% of the base material value. For the impact properties, the Al specimens showed 60% – 140% specific impact energy, in comparison to their respective base materials. Based on the mechanical properties and microstructural examination, the optimal weld parameter was identified as 1600 rpm and 250 mm/min which is dependent on the tool pin and shoulder design utilized in the study.

Mechanical Response and Evolution of Damage of Al6061‐T6 Under Different Strain Rates and Temperatures

The mechanical response and damage mechanisms of rolled Al 6061-T6 alloy subjected to tensile testing at different temperatures and various strain rates have been investigated in this paper. The evolution of the microstructure has been examined for the different testing conditions showing strain rate and temperature effects. The fracture surfaces of samples damaged at different uniaxial testing conditions were observed through Scanning Electron Microscope (SEM). Annealing tests at different temperatures have been performed and microstructure analyses for each condition have been achieved showing grain size evolution. Investigation of the fracture initiation sites has been achieved by conducting interrupted tests and observing the microstructure through SEM. Observations has pointed out that precipitates and iron rich phases are privilege cites for crack initiation.

Cationic (V, Y)-codoped TiO2 with Enhanced Visible Light Induced Photocatalytic Activity for Photoelectrochemical Applications

To utilize the wide spectrum of solar irradiations, an effective co-doping approach is applied to modify the photoelectrochemical properties of TiO2 by doping vanadium (transition metal) and yttrium (rare earth element). V and/or Y codoped TiO2 was prepared using hydrothermal method without any post calcination for crystallization. V, Y codoped TiO2 exhibited high absorption coefficient with enhanced visible light absorption compared to monodoped samples. All the prepared samples showed pure anatase phase and spherical morphology with uniform particle distribution. It is found that both the doped V and Y exist in the form of substitutional point defects replacing Ti atom in the lattice. The photocatalytic activity, evaluated by the degradation of methyl orange, displays that the codoped TiO2 sample exhibits enhanced visible light photocatalytic activity. The synergistic effects of V and Y drastically improved the visible light absorption and electron-hole pair’s separation leading to the enhanced visible light catalytic activity.