Volume 110, Issue 2

Quantitative mechanical properties were obtained from simulated nanoindentation load–depth curves using three analysis methods. Unloading curve fits for stiffness, depth and contact area gave reliable and relatively accurate values of elastic modulus and hardness, though inaccuracies occurred in some cases. Work of indentation analysis was effective for finding the ratio of hardness to reduced elastic modulus, but a large discrepancy occurred in one case. Fitting the loading curves with parabolas gave good fits to the simulated curves. Accurate ratios of elastic modulus to hardness were obtained for some of the loading fits, though others were inaccurate. Each method has specific strengths and weaknesses, but crucially, they all consider different aspects of the load–depth data. This means the methods are potentially complementary and a single, combined analysis may be possible and beneficial in obtaining accurate values.

Experimental investigation of the gas/matte/spinel equilibria in the Cu–Fe–O–S system was undertaken at 1250°C, P (SO 2 ) = 0.25 atm, and a range of oxygen partial pressures. The experimental methodology involved high temperature equilibration using spinel substrates in controlled gas atmospheres (CO/CO 2 /SO 2 /Ar), rapid quenching of the equilibrated phases, followed by direct measurement of phase compositions using electron probe X-ray microanalysis technique. The influence of temperature on the gas/matte/spinel equilibria and comparison with previous studies are provided. The new data obtained in the present study can be used for revision of the existing thermodynamic database for the copper-containing systems.

Nanobainitic structures were produced in a low alloy carburised steel at temperatures of 200, 250 and 300°C. Scanning electron microscope micrographs indicated bainitic ferrites formed with a thickness range of 30–150 nm. Wear test results revealed that the coefficient of friction for nanobainitic samples was smaller and narrower compared to that of the martensitic sample which showed higher and larger variations indicative of better wear performance for nanobainite samples. The wear mechanism of nanobainitic samples due to their tough matrix was oxidative which resulted in small debris and smaller fluctuations in coefficient of friction. The large variation in the coefficient of friction in the martensitic sample was believed to be because of the detaching of larger fragments from the worn surface.

Aluminium alloy AA7075 matrix composites reinforced with different vol.% of niobium carbide were fabricated by friction stir processing. Microstructural investigations of the composites as well as the interface between AA7075 and NbC were conducted using optical microscopy and scanning electron microscopy. SEM micrographs revealed a homogeneous dispersion of NbC in the AA7075 matrix in all the composites. SEM studies also revealed very good bonding of the dispersoid particles with the matrix along with significant degree of grain refinement. Hardness and wear resistance of AA7075 matrix was enhanced both by the addition of NbC particles as well as grain refinement. Wear behaviour studies showed that predominant wear mechanisms were abrasive wear and adhesive wear.

The microstructure, mechanical, and high-stress abrasive wear of as-cast and heat-treated LM25-SiC composites were compared with those of a matrix alloy and a low-cost hypereutectic alloy (LM30). The microstructure of the composite exhibits uniformly dispersed SiC particles and good interfacial bonding between the SiC particles and the matrix. Heat treatment caused the needle-shaped silicon to become spherical and improved the homogeneity of its dispersion in the matrix. The hardness, ultimate tensile strength, yield strength, and wear resistance of the materials were improved, but the elongation was reduced as a result of the heat treatment. The wear rate and friction coefficient of the materials decreased as the sliding distance increased for both the as-cast and heat-treated samples. The wear surface morphology and wear debris analyses were performed by using high-resolution field emission scanning electron microscopy.

The aim of this study was to investigate the mechanical properties of bamboo mesoparticle/nylon 6 composites. The challenge in this paper is that there has been very limited research done on the effect of fibre loading on the mechanical properties of natural bamboo mesoparticles as reinforcement for nylon 6 in order to reduce the cost of production while maintaining the high composite mechanical properties. The average size of the bamboo mesoparticles used was 0.25 μm. The mesoparticle/nylon 6 composites were prepared by mixing bamboo mesoparticles and nylon 6 using a laboratory blender mixer machine, followed by preparation of samples using an injection moulding machine. The fibre loadings were 9 wt.%, 13 wt.%, and 18 wt.%. The mechanical properties of the composites examined were tensile, flexural, and impact properties, while tensile fracture surfaces of the mesocomposites were examined using scanning electron microscopy. The results showed that 13 wt.% fibre loading has the best tensile strength and modulus with improvements of 15% and 25%, respectively, compared to neat nylon 6. A slight increase in the flexural strength and modulus with increasing fibre loading from 9 to 13 wt.% was observed. However, a lack of performance was observed in the impact strength of the bamboo mesoparticle/nylon 6 composites. Electron microscopic examination revealed no filler clumping aggregation and less void formation when 13 wt.% fibre loading was used, which indicates that a relatively high amount of energy was consumed to break the 13 wt.% bamboo mesoparticle/nylon 6 composites. Overall, the results indicated that the tensile and mechanical properties of bamboo mesoparticle/nylon 6 composites increased with increased fibre loadings.

The particles and microstructures in the coarse-grained heat-affected zones of Al–Ti–Ca complex deoxidized steels with different Al content were investigated by in-situ observation, various analytical techniques and calculations. The results show that the inclusions in high Al steel consist of Al–Ca oxides containing small amounts of TiO x surrounded by an outer layer of MnS. In low Al steel, the inclusions consist of Al–Ca–Ti oxides with high TiO x content covered by an outer layer of MnS, and the high TiO x content in the inclusions can remarkably enhance the ability of the inclusions to promote acicular ferrite nucleation. The fine-grained microstructure obtained in the coarse-grained heat-affected zones of low Al steel is attributed to the pinning effect of the finer particles and the formation of a high density of acicular ferrite.

The present study evaluates the corrosion behavior of Al–TiB 2 metal matrix composites in 3.5% NaCl solution. Composites are fabricated using stir-casting with varying wt.% of TiB 2 . Composite surfaces are characterized using scanning electron microscopy (SEM) images. Micro-hardness values of composites are obtained using a Vicker's micro-hardness tester. The hardness of the base matrix is enhanced due to the incorporation of hard TiB 2 phase. Corrosion characteristics of composites are investigated using potentiodynamic polarization and electrochemical impedance spectroscopy measurements. Corrosion resistance of composites is estimated from the parameters such as corrosion potential, corrosion current, linear polarization resistance etc. Corrosion resistance of the base alloy improves due to incorporation of TiB 2 but only up to a certain amount of TiB 2 phase in the matrix. The composite with 1 wt.% TiB 2 shows the highest corrosion resistance. Corroded surfaces are studied using SEM images that reveal localized pitting corrosion on composite surfaces.

The effect of anodization variables on the morphology and surface properties of oriented titania nanotube arrays (TNAs) was investigated. The arrays were synthesized using hydrofluoric acid based ethylene glycolelectrolyte. The results show that the anodization time plays a significant role in the surface properties as well as length of the nanotubes. However, the contribution of anodization potential to debris formation was found to be negligible within the investigated range of the potential. The F − ion concentration and aging of electrolyte were found to play crucial roles in the formation of ordered clean nanotubes. The studies conducted by employing these TNAs as photo-anodes for dye-sensitized solar cells (DSCs) show that the morphology variations alone alter the photovoltaic properties of DSCs to a great extent.

In order to realize reliable sealing and combining of constructional glass and copper, the effects of temperature, holding time, and roughness on their wetting properties were studied. The contact angle and drop diameter were measured by microscopy. The microstructure, element distribution and chemical composition of the reaction interface were analyzed by scanning electron microscopy and energy dispersive X-ray spectroscopy to reveal the relationship between the contact angle and the reaction interface. The results show that the glass/copper contact angle of the sample tested constantly decreases with increasing temperature. If the holding temperature is increased from 980°C to 990°C, and the wetting angle is reduced from 83.22° to 55.28°. When the holding time is prolonged from 5 min to 40 min at 1000°C, the wetting angle decreases and the size of the black halo around the glass reduces. The copper surface roughness has little effect on the wetting angle. Therefore, during the actual sealing process, increasing the temperature and holding time, could effectively improve the wetting behavior of the glass and copper. The black halo formation and interfacial reaction mechanism are also discussed.

Cordierite-based glass/ceramic composites reinforced with different volume fractions of carbon nano-tubes were successfully prepared by isostatic pressing. Results showed the increase of flexural strength and fracture toughness of cordierite-based glass/carbon nano-tube composites with carbon nano-tube content. By incorporation of 5 vol.% carbon nano-tubes, the flexural strength and fracture toughness of the composites were increased by up to 50% and 72% compared to the unreinforced cordierite-based glass matrix, respectively. Scanning electron microscopy images indicated that the main strengthening and toughening mechanisms are load transfer, fiber pull out and crack bridging.