Key Engineering Materials Vol. 659

Abstract: This research aims to produce TiO₂-based composite powder by growing of carbon nanotubes (CNTs) on the surface of micron-sized TiO₂ particles using a chemical vapor deposition (CVD) technique. This nanocomposite powder will be further used as feedstock powder to build up as a coating using a thermal spray technique. This coating is expected to have better photocatalytic efficiency over that of pure TiO₂ coating. For composite powder preparation, rutile-phase of TiO₂ powder with particle size in a range of 25 – 45 µm was used as a starting powder. The powder was placed in a CVD apparatus under ethanol atmosphere as a carbon source. The best CNTs growing condition was found to be 650°C for 60 min. The starting powder and as-synthesized composite powders were characterized by scanning electron microscopy, energy dispersive spectrum, Raman spectroscopy and UV-vis spectroscopy. The results showed that CNTs were successfully grown in-situ on the surface of TiO₂ particles. The photocatalytic activities under visible-light were examined based on a degradation of methylene blue. The degradation efficiency of the TiO₂/CNTs composite powder was found to be higher than that of pure TiO₂. It is expected that the TiO₂/CNTs nanocomposite powder could be further used to fabricate various of nanocomposite products.

Abstract: Organic based stabilizers have been considered as a new technology providing environmentally friendly heat stabilizer for PVC pipe production to substitute conventional lead stabilizer as well as calcium zinc stabilizer. In this research, PVC samples stabilized with 5 types of heat stabilizers i.e. 1) commercial lead stabilizer, 2) commercial calcium zinc stabilizer, 3) commercial organic based stabilizer (OBS), 4) 1,3-dimetyl-6-aminouracil (DAU) and 5) eugenol, were investigated. From dynamic mechanical analysis, storage modulus at room temperature of PVC stabilized with DAU was found to provide the highest value among those stabilizers. Glass transition temperature of the PVC stabilized with all types of heat stabilizers was determined to be approximately 99°C except the value of about 89°C in eugenol stabilized PVC. Furthermore, PVC stabilized with commercial lead, calcium zinc stabilizer and commercial OBS could be reprocessed up to at least 5 cycles. Whereas, PVC stabilized with DAU was found to be able to withstand the processing cycle up to 4 cycles. Additionally, PVC stabilized with DAU showed the most outstanding short term thermal stability and can maintain its original color for at least up to 4 processing cycles. Finally, repeated processing of PVC stabilized with each type of heat stabilizers showed negligible effect on mechanical properties for at least up to 3 processing cycles. From the above results, it is evident that DAU showed high potential use as a safe and effective organic based heat stabilizer for PVC to substitute traditional lead or calcium zinc compounds.

Abstract: Iron (Fe)-tin (Sn) intermetallics were synthesized by using two different routes. These two routes had a common synthesis step, in which Fe powder (19 wt. %) was mechanically alloyed with Sn powder (81 wt. %) for 25 h under argon atmosphere. The mechanically alloyed powders were then treated with different heating routes. In the first route, the compacts of the mechanically alloyed powders were sintered at different temperatures for different times. It was found that the FeSn₂ content increased with increasing temperature and time. There were small traces of Fe, Sn and FeSn found in the sintered materials. In the second route, the mechanically alloyed powders were plasma-sprayed using different currents of 300, 400 and 500 A. It was found that the porous coatings produced by plasma sprayng consisted of mixed Fe, Sn, FeSn₂, SnO, FeO and Fe₃O₄ for all employed currents.

Abstract: The benefit of pre-sintered machining is to avoid machining difficulty of sintered parts especially hardenable PM steels. Pre-sintering treatments of green PM part at temperatures lower than the normal sintering temperature of 1120 °C result in green strength improvement high enough for machining. In this study, the influences of various pre-sintering temperatures and several machining conditions on machined surface quality of pre-sintered PM samples were investigated. The pre-sintered samples were machined by a turning process using a carbide cutting insert with varied cutting speeds at a fixed feed rate and depth of cut without cutting lubricant. Chromium alloyed PM steel (Astaloy^® CrM) powder samples with (0.5 wt. %C) and without graphite (0 wt. % C) additions mixed with 1 wt. % of zinc stearate were prepared as green parts by cold compaction in a cylindrical die with diameter of 30 mm. Green density was about 7.00 g/cm³ and height of each sample was controlled by hydraulic pressure and powder weight of 80 g/sample. The green samples were treated by pre-sintering treatment before machining testing. Surface quality of each machined sample was evaluated by average surface roughness and surface texture by SEM analysis and the appearance of outlet edge breakout. The experimental results revealed that the pre-sintered samples with graphite addition showed better surface quality in terms of surface roughness and surface texture and small outlet edge breakout appearance. Moreover, at high pre-sintering temperatures of 900 and 1,000°C, the samples showed similar average surface roughness under the same turning conditions. The obtained surface textures were better than those of the samples pre-sintered at 700 and 800°C. The outlet edge breakout could not be found in the graphite-added samples pre-sintering at 1,000°C.

Abstract: Ni-Cr superalloy has been widely used in turbomachinery equipments. Gas turbine blade made from Ni-Cr superalloys experience the effect of high temperature and stress during service which certainly cause various microstructural changes. It is found that the formation of spheroidal gamma prime (γ') phase replacing the cuboidal γ' phase and also the formation of M₂₃C₆ carbides along the grain boundaries. Numerous previous study has been conducted and reported that the microstructure of the turbine blade are being modified by service. This study involved assessing changes in blade microstructure and microhardness as a function of service time.

Abstract: Lead-free frictional materials are important components in safety and power transmission parts of automobiles. In order to avoid using lead-containing friction modifiers, non-toxic ceramic particles are considered to be used as reinforcements. In this research work, copper-based friction materials have been developed by using press and sinter method. Pre-alloyed bronze (Cu-10Sn) powder was admixed with iron (Fe), graphite (C) and varied amounts of silicon carbide (SiC) powders. The admixed powders were compacted into disc-shape samples, which were then sintered at different temperatures in the range of 800-950 °C. It was found that sintered density and hardness of the sintered copper-based friction materials reduced with increasing SiC content. Microstructures of the sintered materials showed inhomogeneity due to uneven distribution of coarse Fe and SiC particles. The coarse SiC particles also prohibited bonding between metal powder particles. However, the sintered materials showed high room-temperature friction coefficients, which were in the range of 0.50-0.90, particularly the materials containing 4 wt. % of SiC particles.

Abstract: The aim of this work is to analyze the error of the calculated integrated intensity of the x-ray peaks of a-iron (BCC-Fe) powder from x-ray diffraction (XRD) pattern by using the numerical method and the statistical analysis. The a-Fe powder was characterized by the x-ray diffractometer using step scan mode, step sizes 0.03^o 2q and 0.05^o 2q, and preset times from 0.1 to 3.5 s. The integrated intensity () of an x-ray peak and its error () were calculated using numerical method. The correlation between the relative error () and the preset time or step size were analyzed by the statistical analysis methods which are linear regression and statistical hypothesis testing. The results from the statistical analysis at significance level of 0.05 show that the relative error () correlate with x = preset time or integrated intensity by when a₁ and a₂ are the positive constants. From the mathematical model, for this work, the step size does not affect the relative error. However, the increasing of preset time reduces relative error on integrated intensity calculation. To minimize the error on XRD analysis, the preset time should be greater than one second. Moreover, on a XRD pattern, the lower integrated intensity peak has the higher relative error.

Abstract: The aim of this investigation is to study the fracture location as well as mechanical properties of weldments from elevated temperature tensile test in T22/T91 dissimilar joining by GTAW process. Two configurations of welding procedures are used: ER90S-B9 and ER90S-B3. Postweld heat treatment (PWHT) is carried out at 760°C for 30 minutes. The results demonstrate that the higher tested temperature, the lower the strength of welded sample; nevertheless, the greater the ductility of welded sample, except ER90S-B9 welded samples tested at 650°C. The fracture of both configurations tested at 550°C and 750°C occurs at T22 BM and T91 HAZ, respectively. At these temperatures, the fracture surfaces mainly reveal dimple ductile mode corresponding to mechanical properties’ results. On the contrary, the failure tested at 650°C occurs at T22 HAZ (Soft zone) and T91 HAZ of ER90S-B9 and ER90S-B3 welded samples, respectively. The mechanical properties’ results at this temperature are relatively different. The combination of brittle and dimple mode at the edge of samples is observed on the ER90S-B9 welded samples corresponding to low ductility at this temperature. Whereas samples welded by ER90S-B3 show only dimple ductile mode. The results exhibit that the fracture location could be affected by the configuration of T22/T91 dissimilar welding.

Abstract: Poly(lactic) acid (PLA) is bioplastic produced from corn starch; its brittleness limits the use of PLA in many applications. Biaxial stretching is one approach adopted by film manufacturers to enhance the properties of plastics such as polypropylene (PP). This study aims to produce biaxially-oriented PLA films which had been toughened with 1-10% core-shell rubber (CSR). Differential scanning caloriemetry (DSC) results indicated that all biaxially-stretched neat PLA and the PLA/CSR films possessed nearly 20% greater crystallinity than the as-cast film.The yield stress of the biaxially-stretched films were higher than that of the unstretched films in both machine (MD) and transverse (TD) directions. After biaxial stretching, the elongation at break of the stretched films was still much higher than that of the unstretched ones. The tear resistance was highest in the film with 5 wt% CSR, it became higher after biaxial stretching. The water vapor permeation (WVP) was also minimum in the film with 5 wt% CSR. The biaxially-stretched films had lower WVP than the unstretched ones due to the enhanced crystallization and chain orientation in the stretched films.

Abstract: A fluorine-containing benzoxazine monomer (BAF-4fa) from 4-(trifluoromethyl) aniline, 4,4′-(Hexafluoroisopropylidene) diphenol or bisphenol-AF and paraformaldehyde was synthesized using solventless method at temperature of 110°C without any catalyst. Chemical structure and thermal properties of as-synthesized benzoxazine resin were investigated and compared with fluorine-containing benzoxazine resin as well as with traditional bisphenol-A aniline based benzoxazine (BA-a) system. From Fourier transform infrared spectrum of BAF-4fa monomer, absorption band at 1243 cm^-1 which were assigned to C-O-C stretching mode of oxazine ring and band around 1505 cm^-1 and 951 cm^-1 which were attributed to tri-substitutued benzene ring from the oxazine ring moieties were observed. The result is in good agreement with the BA-a monomer, indicating successful preparation of BAF-4fa via solventless technology. The obtained BAF-4fa also exhibits thermal curing ability which is a signature of benzoxazine resin. The exothermic heat of reaction of BAF-4fa was found to be less than that of BA-a as observed by a differential scanning calorimeter. The BAF-4fa monomer was step-cured at 200°C for 2 hours, 250°C for 3 hours followed by 270°C for 2 hours to achieve its fully cured stage. Glass transition temperature of PBAF-4fa from tanδ of dynamic mechanical analysis was found to be much higher than that of PBA-a i.e. 288°C vs 189°C. From thermogravimetric analysis, thermal degradation at 10% weight loss of PBAF-4fa was found to be 453°C compared to the value of 341°C of PBA-a while the char yield was 53% vs 28% of the BA-a polymer. As a consequence, the incorporation of fluorine atoms into polybenzoxazine is able to improve various thermal stability of the polymer which allows such application as high temperature resistance materials including electronic packaging, thermal resistance coating.