Iranian Journal of Materials science and Engineering
Volume:10 Issue: 2, Jun 2013

The objectives of this research were to find an economical way of reducing porosities in the microstructure of coatings deposited by flame spraying technique on CK45 steel and also trying to increase their cohesive strength to the substrate, so that the overall wear properties of this type of coating can be improved. So several specimens from this steel coated with NiCrBSi powder under specific conditions were subjected to various furnace heat treatment at 1000, 1025, 1050, 1075 and 1100 °C, each for periods of 5, 10 and 15 minute before cooling them in air. Tribological properties of treated coatings were evaluated by pin on disc method. The results show the highest wear resistance and microhardness values observed in one of the sample was due to lower amount of porosity and higher amount of very fine Cr2Ni3B6 particles precipitated homogeneously throughout its microstructure during specific heat treatment.

The probable reasons for evolution of weld porosity and solidification cracking and the structure- property relationship in aluminium welds were investigated. Aluminium plates (1xxx series) were welded by Tungsten Inert Gas (TIG) welding process, 5356 filler metal was used and heat input was controlled by varying welding current (145A, 175A and 195A). The welded samples were examined under optical and scanning electron microscopes and mechanical tests were performed to determine tensile and impact strengths. Secondary phase, identified as globules of Mg2Al3 precipitates, was found to be formed. Solidification cracking appeared in the heat affected zone (HAZ) and porosities were found at the weld portion. The tendency for the formation of solidification cracking and weld porosities decreased with increased welding current.

In this research, variant selection of martensite transformed from ultrafine-grained (UFG) austenite fabricated by accumulative roll bonding (ARB) process and subsequent annealing was investigated with respect tomorphology of parentaustenitic phase. The results show that the original shape of austenite grain is very effective factor in determiningthe preferred variants of martensite transformed from the elongated ultrafine-grained austenite fabricated by 6-cycles via the ARB process. Annealing treatment of the austenitic samples subjected to the 6-cycle ARB processed at 873 K for 1.8 ks suppressed the variant selection by changing the morphology of austenite grains from elongated ultrafine-grains to fully-recrystallized and equiaxed fine-grains

Nitriding is a surface treatment technique used to introduce nitrogen into metallic materials to improve their surface hardness, mechanical properties, wear resistance and corrosion resistance. In this research, the effects of plasma nitriding parameters including frequency and duty cycle were investigated on samples with different grooves dimensions. Steel blocks prepared from DIN1.2344 hot working steel were plasma nitride at 500 °C under the atmosphere contents of %75H2-%25N2, the duty cycles of 40%, 60%, 80%, and the frequencies of 8, 10 kHz for 5 hours. Then characteristics and micro hardness''s of the nitrided samples were investigated using SEM, XRD, and Vickers Micro Hardness method. The results of the experiments indicated that with increasing frequency, the duty cycle, and the thickness of the grooves, the roughness of the surfaces increased. With an increase in duty cycle from 40% to 80%, the hardness of the surface rose and the thickness of the compound layer built up. Hollow cathode effect occurred in the samples with small grooves and high duty cycle in plasma nitriding. This will result in over heating of the sample which leads to a decrease in the slope of hardness values from the surface to the core of the sample and also a decrease in the diffused depth of nitrogen. The compound layer of the treated samples consisted of @: Fe4N and: Fe2-3N phases and the proportion of the A to @ increased with the decrease in the duty cycle. Increasing the frequency did not affect the proportion of phases and micro hardness of the samples.

In this study, the effect of different parameters such as time and temperature of calcination and milling on the formation of calcium aluminosilicates was investigated. Raw materials used in this study were calcium carbonate and kaolin in high purity. Powder X-ray diffraction patterns were obtained from all samples after heat treatment at various temperatures and times. To study the microstructure scanning electron microscope was used. Milling the samples contributed to the amorphous structure due to inducing defects in the structure. Moreover, increasing the milling time reduced crystallization temperature of anorthite. Uptake experiments were performed using solutions containing different concentrations of nickel. Samples were exposed to the solution for 24 h with stirring then the samples were filtered and the concentrations of the cations in the separated solutions were analyzed. FTIR analysis was conducted on the adsorbents before and after nickel uptake. Nevertheless, they hardly helped understand sorption mechanisms. Therefore, adsorption isotherms were studied instead. Three adsorption isotherms of Langmuir, Freundlich and DKR were used to model sorption data. Results suggested monolayer sorption occurs on the surface of the adsorbent and sorption energy calculated by DKR model was 22.36 kJ/mol which can be described as a strong chemical adsorption mechanism

In recent years, there have been many attempts to improve the properties of dental amalgam. The aim of the present investigation was fabrication and characterization of dental amalgams containing TiO2 nanoparticles and evaluation of their compressive strength, antibacterial and corrosion behavior. In this experimental research, TiO2 nanoparticles (TiO2 NPs) were added to reference amalgam alloy powder and then, dental amalgam was prepared. In order to investigate the effect of TiO2 NPs on properties of dental amalgam, 0, 0.5, 1, 2 and 3 wt. % of TiO2 NPs were added to amalgam alloy powder and the prepared composite powder was triturated by a given percent of mercury. Xray diffraction (XRD), Scanning Electron Microscopy (SEM) and Energy-Dispersive Spectroscopy (EDS) techniques were used to characterize the prepared specimens. Potentiodynamic polarization corrosion tests were performed in the Normal Saline (0.9 wt. % NaCl) Solutions as electrolytes at 37°C. The results showed that the corrosion behavior of the dental amalgam with 0.5 or 1 wt. % TiO2 NPs is similar to the corrosion behavior of the reference amalgam, while with increasing the weight percent of TiO2 NPs, the corrosion rate increases. Also, the results of this investigation indicated that adding TiO2 NPs in amounts of up to 1 wt. % to amalgam alloy powder improve compressive strength of dental amalgam and has no destructive influence on its corrosion behavior. As well as, according to antibacterial results, TiO2 NPs can increase the biocompatibility and antibacterial activity of dental amalgam. The results of present study suggest that amalgam/ TiO2 NPs nanocomposite with 1% of TiO2 NPs could be regarded as a biocompatible and bioactive dental material that provide better characters for dental applications.

In the present study, bioceramic composites based hydroxyapatite (HAp) reinforced with carbon nanotubes (CNTs) was synthesized via sol-gel technique. The dried gels were individually heated at a rate of 5°C/min up to 600°C for 2 h in a muffle furnace in order to obtain HAp-MWCNTs mixed powder. Composites were characterized by XRD, FT-IR, SEM, TEM/SAED/EDX and Raman spectroscopy techniques. Results showed the synthesis of HAp particles in the MWCNTs sol which was prepared in advance, leads to an excellent dispersion of MWCNTs in HAp matrix. Apparent average size of crystallites increased by increasing the percentage of MWCNTs. The average crystallite size of samples (at 600°C), estimated by Scherrer’s equation was found to be ~50-60 nm and was confirmed by TEM. MWCNTs kept their cylindrical graphitic structure in composites and pinned and fastened HAp by the formation of hooks and bridges.