Investigation and optimization of friction stir welding process parameters of stir cast AA6082/ZrO2/B4C composites

In the present investigation, aluminium-based alloy (AA6082) is stir-casted with 3 % ZrO2 and 5 % B4C reinforcement particulates to fabricate Aluminium Metal Matrix Hybrid Composites (AMMHCs) which are further friction-stir welded at different welding conditions to develop a welded joint with optimum ultimate tensile strength (UTS) and microhardness. This newly developed AMMHC will find its specific application as bulkhead partitions in the hull of a ship due to its excellent properties, such as lower weight, higher specific strength, superior resistance to wear, and lower thermal expansion coefficient than that of AA6061 and AA5083 composites. The friction-welded butt joints performance of AA6082/3%ZrO2/5%B4C is generally determined by varying the FSW process parameters such as tool rotational speed (TRS), welding speed (WS), axial load (AL), tool tilt angle (TTA), tool pin profile (TPP), shoulder diameter (SD), etc. In the present work, the empirical relationships are established between parameters highly influencing FSW process (TRS, WS, and AL) and their responses (UTS and weld nugget microhardness (WNH)). The desirability approach is employed for predicting the optimal UTS and WNH. The corresponding values of input process parameters are TRS of 1030.95 rpm, WS of 38.5 mm/min, and AL of 5.88 kN. The calculated UTS and WNH for the present investigation are 239.98 MPa and 94.2 HV, respectively, and these values are consistent with the results of validation experiments.

Raman Study of Barite and Celestine at Various Temperatures

The Raman spectra of barite and celestine were recorded from 25 to 600 °C at ambient pressure and both minerals were stable over the entire temperature range. Most of the Raman bands of barite decreased in wavenumber with increasing temperature with the exception of the ν2 modes and the ν4 band at 616 cm−1, which did not exhibit a significant temperature dependence. These vibrations may be constrained by the lower thermal expansion along the a-axis and b-axis of barite. Similar to barite, most of the Raman bands of celestine also decreased in wavenumber with increasing temperature, with the exception of the ν2 modes and the ν4 band at 622 cm−1, which showed very little variation with increasing temperature. Variations of Raman shift as a function of temperature and FWHM (full width at half maximum) as a function of Raman shift for the main, ν1 modes of barite and celestine show that both minerals have almost identical linear trends with a slope of −0.02 cm−1/°C and −0.5, respectively, which allows for the prediction of Raman shifts and FWHM up to much higher temperatures. The calculated isobaric and isothermal mode Grüneisen parameters and the anharmonicity parameters show that the M–O modes (M = Ba2+ and Sr2+) in barite and celestine exhibit much higher values of both mode Grüneisen parameters and anharmonicity than the SO4 tetrahedra. This indicates that the S–O distances and S–O–S angles are less sensitive to pressure and temperature increase than the M–O distances in the structure. Furthermore, the generally higher anharmonicity in celestine is due to the smaller size of the Sr2+ cation, which causes the celestine structure to be more distorted than the barite structure.

Advanced CFC Fixture Applications: Their Scientific Challenges and Economic Benefits

Following the work done at NASA to use carbon fiber reinforced carbon (CFC) materials as a replacement for mainly cast steel for Fixtures, Racks or parts of it in heat treatment industry, a successful development of a new generation of ingenious Fixtures was started in the mid 1990s by the author and his team. CFC have been shown to have lower density, lower thermal expansion and increased strength at high temperatures resulting in smaller, lighter Fixtures with shorter heating and cooling times, better process capability and, in some cases integrated material flow. The thermochemical and other details for still three main challenges like 1st oxidation of CFC, 2nd possible interaction between CFC and the steel parts and 3rd CFC Fixture interaction with liquid media like oil will be discussed. Furthermore, successful industry CFC Fixture applications which pay-off on several reasons are introduced.

Numerical Simulation of Failure of Composite Coatings due to Thermal and Hygroscopic Stresses

Due to the higher thermal and moisture expansions of epoxy coatings than the rigid substrate, these coatings suffer from high thermal and hygroscopic stresses, leading to coating/substrate interfacial crack growth. Herein, a parametric study was conducted systematically on epoxy coatings incorporated with fillers, in order to understand their effects on coating/substrate interface delamination caused by thermal and hygroscopic stresses. A finite element model (FEM) was developed to determine an indicator J-integral value (Ji), in comparison with a critical JC value to interpret the obtained interface delamination experimental results. FE simulations showed that interfacial pre-cracks located at coating edges were more serious than those at the centre. Once delamination was triggered by thermal shock or moisture absorption, it propagated rapidly along the coating/substrate interface. However, by adding suitable micro-/nano-fillers to the coating the thermal and hygroscopic stresses give lower Ji values, so that delamination crack growth can be effectively controlled. The simulation results demonstrate that the incorporation of fillers with lower Young’s modulus, lower thermal expansion and moisture absorption coefficients, smaller size for soft fillers, larger size for rigid fillers, and suitable aspect ratios for rod-shape fillers to the coatings, are more effective against interface delamination. Hence, useful guidelines for improving the design of epoxy composite coatings against delamination growth can be obtained for different engineering applications.

Preparation of Transparent Cellulose/PMMA Composite Sheet from Cellulose Aerogel

In this work, wet cellulose aerogel sheet was prepared via NaOH/urea dissolution system followed by multiple solvent exchanges. Firstly, hyacinth cellulose solution was prepared and then cast into plastic mold. The casting solution was left standing to become solid hydrogel. Then, multiple solvent exchanges by water was carried out in order to remove NaOH and urea completely to obtain wet hydrogel. Then, transparent cellulose sheet was successfully prepared by backfilling the nano/micro sized aerogel channel with a refractive index matching polymer which was PMMA emulsion in this study. The transparent cellulose sheet exhibited 80-90 percent transparency. In contrast, cellulose aerogel exhibited relatively low percent transmittance only 8.24%. In addition, the coefficient of thermal expansion (CTE) of transparent cellulose sheet with a thickness of 0.5 mm (10.45 ppmK-1) was significantly lower that pure PMMA sheet (79.70 ppmK-1), indicating that aerogel based transparent cellulose exhibited lower thermal expansion than neat plastic.

Rotary bending as a mean for improving micro-cleanliness of stainless steels for high demanding applications

Stainless steels are used for automotive or medical applications which require a high fatigue resistance correlated to a high level of micro-cleanliness. A methodology based on rotary bending tests carried out on wires or bars has been defined to determine the material’s endurance limit (after 100 millions cycles) and identify the largest subcutaneous inclusions or precipitates where failures initiate. This methodology has been applied to EN 1.4568 spring wires. Failures were found to initiate both at oxide inclusions and AlN precipitates. For the same size, AlN precipitates were observed to be more critical towards crack initiation than oxide inclusions, due to their angular shape and lower thermal expansion at high temperatures. However, oxide inclusions larger than the AlN maximum size strongly impact the material’s fatigue limit, and their density and size should be reduced.

Research and development of new neodymium laser glasses

This work presents a brief introduction on three kinds of newly developed $\text{Nd}^{3+}$ -doped laser glasses in Shanghai Institute of Optics and Fine Mechanics (SIOM), China. Two $\text{Nd}^{3+}$ -doped phosphate glasses with lower thermal expansion coefficient and thermal shock resistance 4 times higher than that of N31 glass are developed for laser processing. Nd:Silicate and Nd:Aluminate glasses with peak emission wavelength at 1061 and 1065 nm, effective emission bandwidth of 34 and 50 nm, respectively, are developed for Exawatt-class laser system application. Fluorophosphate glasses with low nonlinear refractive index ( $n_{2}=0.6{-}0.86$ ) and long fluorescence lifetime ( $430{-}510~\unicode[STIX]{x03BC}\text{s}$ ) are investigated for the purpose of decreasing B integral in high-power laser system. The properties of all these glasses are presented and compared with those of commercial neodymium laser glasses.

Effect of the Cooling Ways on the Properties and Microstructure of ZrO2/ZrW2O8 Ceramic Composites

ZrO2 has been widely used due to its good physical and chemical properties and the ZrO2/ZrW2O8 ceramic composites with adjustable thermal expansion coefficient can be prepared by mixing and sintering the ZrO2 and ZrW2O8 powders. In this paper, the ZrO2/ZrW2O8 ceramic composites have been prepared by mixing, cold isostatic pressing and atmospheric sintering, and then being cooled in air or in water. We focus on the effect of the cooling ways on the properties and microstructure of the ZrO2/ZrW2O8 ceramic composites. The results show that the relative density of all samples is more than 98%. For the in-situ method, the density and flexural strength of the samples cooled in air and in water are 98.1% and 98.4%, 112.96MPa and 45.23MPa, respectively. The ZrW2O8 content and thermal expansion coefficient of the samples cooled in the air are less and higher than those in the water, respectively. For the direct mixture method, the density and flexural strength of the samples cooled in air and in water are 98.9% and 99.3%, 195.99MPa and 58.71MPa, respectively. For the four groups of the composite samples, they behave better mechanical properties after cooled in air, and lower thermal expansion coefficients after cooled in water.

Investigation of the Properties of Soda-Lime Silicate Glass Doped with TiO2

In this study, the properties of re-melted soda-lime silicate glass cullet doped with TiO2 were investigated in order to study the potentials to use as parent glass for glass-ceramics. TiO2 of 0.5, 1 and 3 mol% was doped into the 71SiO2-10Na2O-6K2O-5CaO-4MgO-2SrO-TiO2-Al2O3 glass cullet and melted at 1500°C for 3 hours, and then annealed at 550 °C. The optical and physical properties were examined. It was found that the refractive index and density of glasses were raised with increasing of TiO2 concentration. The optical properties measured by UV-Vis spectrophotometer showed that the UV edge in the absorption spectra was shifted to a higher wavelength, and the transmission at 583 nm was decreased. The CIE L*a*b* color measurement showed that the glasses were slightly colorless but the appearance of yellow increased with higher TiO2 concentration. Lower thermal expansion coefficient and higher glass transition temperature as well as the dilatometric softening point were observed as the concentration of TiO2 was increasing. Finally, the calculated activation energy was 476, 493, 506 and 637 kJ/mol with 0, 0.5, 1 and 3 mol% doped TiO2, respectively. At doped TiO2 of 3 mol%, the properties of glass were changed rapidly due to the substitution of [Ti4+] in local [Si4+] resulting in increasing the bond strength in glass structure.

Influence of Nano-Yb2O3, Nano-Nd2O3 and Nano-Dy2O3 on Sintering and Crystallization of Fused Quartz Ceramic Materials

Fused quartz powder (d50=19μm) was used as raw material, nano-Yb2O3, nano-Nd2O3 and nano-Dy2O3 were dividedly used as additive with dosages of 3% each. Fused quartz ceramic materials were sintered in reduction atmosphere at 1300°C, 1350°C and 1400°C for 1h. The influence of rare earth nanooxides on sintering and crystallization of the fused quartz ceramic were researched by measurements of apparent porosity, bending strength and thermal expansion ratios, and analyses of XRD and SEM. The results showed that samples added nano-Yb2O3 and nano-Nd2O3 have lower apparent porosity, higher bending strength and lower thermal expansion rate. It can be deduced that additives nano-Yb2O3 and nano-Nd2O3 have obvious effect on facilitating sintering and inhibiting crystallization of fused quartz materials at experimental temperatures.