JOURNAL OF ADVANCED MATERIALS AND TECHNOLOGIES
Year:2017 | Volume:5 | Issue:4 |Papers Count:8

The severely deformed 1050-aluminum sheet was processed by friction stir processing (FSP) at different conditions of processing without nanoparticles in the ambient temperature and with SiC nanoparticles in the liquid Nitrogen medium. Microstructural assessments indicated that the appropriate distribution of SiC nanoparticles was obtained after 3-passes of FSP. In addition, electron backscattered diffraction (EBSD) analysis manifested that using nanoparticles along with the liquid Nitrogen medium during FSP was able to prevent the intense grain growth in the stir zone which occurred in the case of FSP without nanoparticles in the ambient temperature. Neither the orientation of grains nor the mechanism of grain formation in the stir zone was different comparing two mentioned FSP conditions. The mechanism of grain formation in the stir zone was determined to be dynamic recovery (DRV) and continuous dynamic recrystallization (CDRX) phenomena. However, discontinuous dynamic recrystallization (DDRX) mechanism was also evident in the limited extent in the case of FSP with SiC nanoparticles in the liquid Nitrogen medium. The microhardness results showed that the simultaneous use of SiC nanoparticles and liquid Nitrogen medium during FSP caused to the significant improvement in the mechanical properties of the stir zone.

Special mechanical properties of nano structure bainitic steel such as high tensile strength, hardness, toughness and low manufacturing cost have attracted considerable attention in the past few years. However, the main problem for this type of steels to be industrialized, long austempering process period which increases production costs. In this research, in order to accelerate the bainitic transformation, carbon concentration was decreased and two steps austempering process was employed to prevent the bainite laths thickening. Specimens were austenetized at 1000oC for 15 min and were kept in the salt bath between 1-12 hours at temperatures in the range of 250-300oC in one step or two step bainite transformation. Standard metallography, XRD and scanning electron microscopy techniques were utilized for the microstructural characterization and the tensile and hardness test were employed for mechanical properties evaluation. The obtained results show that two steps austempering process and lower carbon concentration lead to lower austempering period as well as formation of more stable retained austenite which results in higher mechanical properties.

Strain Induced Melt Activation (SIMA) process, is a semi-solid process to create globular grains in alloys. In this process, after applying a desired strain, the sample is heated up to semi-solid region and is hold for a desired time. In the present study, SIMA process was applied to form globular microstructure in 7075-Al alloy. The effects of strain value, strain temperature, semi-solid holding time and semi-solid holding temperature on the average grain size and shape factor were investigated. Optical and scanning electron microscopes were used to investigate the microstructure. The results revealed that, it is not possible to introduce a distinguished mechanism for generating the globular grains; while depending on the liquid fraction and strain value, there is a competition between recrystallization and internal melting of grains. Also, the results depicted that, in the SIMA process, the elongation would be increased with respect to T6 condition; while there is no considerable reducing in the strength.

In this research tungsten silicide powder was successfully produced from tungsten and silicon powders using mechanically activated self-propagating high temperature synthesis and then cladded on St37 substrate by gastungsten arc welding method. X-Ray diffraction analysis showed that the best milling time for activation of elemental powders was 10 h. Microstructure evaluation of coating by scanning electron microscope demonstrated that tungsten silicide mainly dispersed in dendrite phase and inter-dendritic phase rich from Iron. Hardness measurements revealed that the surface hardness of substrate increased from 200 to 850 HV. The wear resistance of substrate was improved by six fold via increasing surface hardness.

Quercetin is a safe herbal metabolism which has effective role on inhibition of tumor cells and growth of many types of cancers. In this study to improve the efficiency and bioavailability of Quercetin molecule, Chitosan-functionalized nanoporous mesoporous Silica was used as a pH-sensitive biopolymer. For this purpose, at first nanoporous Mesoporous silica was synthesized by sol-gel method; then Chitosan layer was coated on nanoporous of silica using GPTMS in an acidic medium. Different analysis methods such as FESEM, BET and FTIR were used to characterize the synthesized nanocarrier. FESEM and BET analysis results demonstrated nanometric sizes of particles and porosities. FTIR analysis picks showed successful drug loading on nanocarrier. On the other hand, calculation of drug loading content and encapsulation efficiency in acidic and physiologic pH, illustrated that nanocarrier has suitable performance and stability for drug loading and release. ytotoxicity of as-drug formulation in different concentrations was investigated by MTT assay on HeLa cells. The results showed that cytotoxicity of as-drug formulation increased in comparison to free drug and IC50 value of HeLa cells decreased from 58 mM for free Quercetin to 36 mM for loaded Quercetin. Eventually this study showed Chitosan-functionalized Mesoporous Silica nanocarrier could be considered as a smart and biocompatible drug delivery system to carry Quercetin drug for cancer cells treatment.

In recent years, cement composites based on calcium silicate have been more generally considered for medical applications. Calcium silicate Cement are among the categories that are used in dental root canal treatment. The aim of this study is to make new calcium silicate cement to preserve and strengthen desirable properties of this type of cements. In this study, composite dental cement based on calcium silicate was prepared. Then effect of adding biodegradable and biocompatible polymer such as chitosan on setting properties and its structure were studied. In this study, a combination of calcium silicate, dicalcium phosphate (DCP) and bismuth oxide (Bi2O3) as powder phase and 2% solution of the chitosan dissolved in 1% acetic acid solution as liquid phase, was used. As well as control sample was obtained by mixing the powder with distilled water as the liquid phase. Based on the obtained results, setting time of composite cement was changed from 51 to 67 minutes by adding chitosan polymer. Presence of chitosan also reduced the compressive strength a little. the bioactivity of the cement were studied in a solution of simulated body (SBF) for 14 days. the samples were analyzed by SEM to identify the microstructure and by XRD to determine crystal structure. The composition of cement before incubation in SBF was included early phases (phase calcium silicate and calcium phosphate) that after 14 days of immersion in SBF, they were converted to layer-shaped hydroxy apatite and the presence of chitosan had not any influence on the final phase of hydroxy apatite.

MCrAlY coatings possess important role on the performance of turbine engines. Their main application is resistance to high temperature oxidation. Although the oxidation mechanism of these coatings were studied by other researchers, there is lack of published papers on the early stage of this phenomenon. In this project, the effect of surface splats produced during HVOF process on early stage oxidation mechanism of the CoNiCrAlY coating was studied in terms of both oxidation time and adhesion characteristics of splats to the coating surface. The experimental results showed that in the first oxidation moments, the oxide layer which forms on the splats is composed of significant amount of heavy metals (Ni, Co and Cr). By gradual aluminum diffusion to the coating surface, a rich aluminum oxide is replaced by the heavy element oxides. Diffusion of Al to the surface of coating over time in addition to increasing the thickness of oxide layer could also cause depletion of b phase from splats surface. These two resulted in the formation of crack in the coating and local oxide growth (spinel oxide in nodular shape), respectively. Consequently, the oxidation rate of areas covered by splats was much higher than the coating surface areas without splats due to high ratio of surface area to volume of splats and limited aluminum reservoir in the splats (specially for splats with poor bonding to the surface).

In this study, effect of aluminum alloying element on KIC and ac of Hadfield hypereutectoid steel was investigated by using the impact test results. For this purpose, initially 2 casting blocks were prepared from Hadfield steel (without addition of Al and with 1.68 wt% Al) by using coreless induction furnace. After casting, all blocks were austenitized in 1100oC for 2 hours and immediately quenched in pure water. In the next step, uniaxial tensile test, Vickers hardness test and Charpy impact test were applied on specimens at room temperature. Evaluation of microstructures were conducted by optical microscopy and the fractured surfaces were observed by scanning electron microscope. The results of impact tests and fracture toughness empirical relationships were used to evaluate the KIC and ac of the Hadfield steel. The optical microscopy images indicated that by increasing the amount of aluminum in the chemical composition of Hadfield manganese austenitic steel, austenite grains size increased from 111.9 to 142.5 micrometer. The results of tensile test, hardness test and impact test represents an increase in yield strength and hardness, and reduction of failure strain and impact energy of Hadfield steel because of adding aluminum to its composition. Calculations of fracture toughness and critical crack length for Hadfield steel showed that the addition of aluminum to steel leads to reduction of fracture toughness from 163.7 to 104.5 Mpa. (m)1.2 and reduced the critical crack length at surface from 0.014 to 0.007m.