Journal of advanced materials and processing
Volume:1 Issue: 4, Autumn 2013

Thermally sprayed coatings are intrinsically associated with residual stresses in the deposits. These stresses are varied in nature and magnitude, and have a pronounced effect on the mechanical behavior of the system. In the current study, WC-12Co coatings were deposited using HVOF thermal spraying. The sin2ψ method was used to evaluate the through thickness residual stress by means of XRD after mechanical layer removal process. A nonlinear explicit-implicit finite element model was developed to study the peening and thermal stress during the high velocity impact of WC-12Co particle and cooling the splat and coating layers. The average of through thickness residual stress using X-Ray diffraction and numerical model was -157.1 MPa and -133.4 MPa respectively. The results showed that the residual stress was compressive and had a good agreement with the experimental results in literature.

This study focuses on the semiconductor properties of passive films formed on AISI 420 stainless steel immersed in four nitric acid solutions under open circuit potential (OCP) conditions. For this purpose, the passivation parameters and semiconductor properties of passive films were derived from potentiodynamic polarization and Mott–Schottky analysis, respectively. The OCP plots showed that the open circuit potential of AISI 420 stainless steel is directed towards positive amount, which are indicative of the formation of passive film and its role in increasing protectivity with time. The potentiodynamic polarization results showed that the corrosion current density of AISI 420 stainless steel increased with the increase in the concentration of solutions. Mott–Schottky analysis revealed that the existence of a duplex passive film structure composed of two oxide layers of distinct semiconductivities (n-type and p-type). Also, Mott–Schottky analysis indicated that the donor densities are in the range 1021 cm-3 and increased with solution concentration.

Parallel tubular channel angular pressing (PTCAP) process is a novel recently developed severe plastic deformation technique for fabrication of ultrafine grained (UFG) metallic tubes. This new process consists of two half cycles and is affected by several parameters such as channel angles, deformation ratio and curvature angles. In this paper, the effects of these parameters on the plastic deformation behavior, imposed strain, strain homogeneity and the process load were investigated using finite element method (FEM). The results indicated that an increase in the channel angle leads to a decrease in the imposed strain at the end of both half cycles of PTCAP process. Investigation on the effects of the curvature angles showed that better strain homogeneity is achieved in lower curvature angles. Also, minimum required process load and the best strain homogeneity could be obtained in the curvature angle equal to zero. Study on the deformation ratio (K) revealed that the best and worse strain homogeneity could be achieved in K values equal to 0.6 and 1 respectively. From the point of view of better strain homogeneity and needing lower process loads, it could be concluded that lower K value (0.6 t0) leads to best strain homogeneity and lowest process load.

In the present study, the Weldability and microstructure of dissimilar welds of AISI 347austenitic stainless steel to ASTM A335 low alloy steel was investigated. For this purpose, gas tungsten arc welding process and two filler metals including ERNICr-3 and ER309L were used. After welding, the microstructure of the different zones of each joint, including weld metals, heat affected zone (HAZ) 1, inter face and unmixed zones (UMZ) 2 were evaluated by using optical microscopy. The scanning electron microscopy (SEM) 3 equipped to energy disperse spectrometry (EDS) 4 was used to investigate the precipitates, in order to predict the micro structure of the weld metal and transmission zone in dissimilar joints. In ERNiCr-3 weld metal, the solidification was observed as the completely austenitic and equiaxed dendrite5 which contains the precipitates of carbide complex, and also Niobium segregation was happened in the inter dendrite zones. 309L weld metal was observed as the primary ferrite with austenitic matrix and also microstructure was seen as skeletal ferrite morphology. The epitaxial growth was observed in interface between 347austenitic stainless steel and two filler metals and a narrow zone was observed in interface between A335low alloy steel and filler metals, and also the coarse grains occurred in HAZ zone of both weld metals. Finally, it can be denoted that for the joints between the AISI 347 austenitic stainless steel and A335low alloy steel, by the ERNICr-3 filler material provides the optimum qualities.

Nanocrystalline strontium hexaferrite (SrFe12O19) powders have been successfully synthesized using the facile Co-precipitation method. The ferrite precursors were achieved from mixtures of strontium and ferric chloride in an aqueous medium without any surfactant and soft template. The as-received powders were calcined at 800 and 1000 ˚C for 2 hours in air. The final powders were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), BET surface area analysis and Vibrating Sample Magnetometer (VSM). The effects of the calcination temperature on the phase composition, particle size and shape as well as the magnetic properties of the products have been investigated. The results indicated that the higher calcination temperature (1000 oC) resulted in higher particle sizes (98.1 nm), maximum saturation magnetization (60.53 emu/g), remanence value (36.23 emu/g) and less surface area (12 m2g-1). The magnetocrystalline anisotropy constant, K, calculated from the Stoner–Wohlfarth theory are increased by increasing temperature up to 15.1 (HA2/kg).

In the present study, the microstructure of welded zone of Hastelloy X sheets with thickness of 1 mm via pulsed Nd-YAG laser welding were studied. This welding process was done by autogenus and conductive method. Microstructure were observed by metallurgical OM and SEM. Results shown Solidification of the weld metal is dendritic. The dendrites in the central zone of the welding are fine and equiaxed while they are larger and columnar in the fusion boundary. Epitaxial growth was observed in the interface of base metal and weld metal. Alloy elements Segregation did not occur during the solidification process and the fine cracks were not observed in the welding zone of the alloy. Micro hardness results indicated that the hardness of welded metal were more than base metal and cause to decrease grain size at welded metal more than base metal. This phenomenon was occurred due to more differences between heating and cooling rate in this welding process.

Microporous glass ceramic with skeleton of CaTi4(PO 4)6 with average pore size of 12.7 nm has been synthesized and used as a carrier of glucose oxidase. The glass ceramic was prepared by controlled heat treatment of glass samples, which causes the phase separation in their structure and creates CaTi4(PO 4)6 and β-Ca3(PO4)2 phases. The β-Ca3(PO4)2 phase was dissolved by soaking the glass ceramics in HCl and CaTi4(PO 4)6 built the skeleton of microporous glass ceramic. Analysis of the ability of the carrier for immobilization of glucose oxidase (GOx) was undertaken. Average amount of immobilized enzyme and percentage of enzyme activity on the carrier were 27 gr GOx/gr carrier and 60.15%, respectively. Effect of pH and temperature variations on the enzyme activity has been studied and results demonstrated that maximum activity for both free and immobilized enzyme was at T=40˚C and pH=7.0. Due to the same value of maximum activity, no serious conformational change of enzyme had taken place through immobilization. However, immobilization of GOx on CTP caused to considerable increase of enzyme stability under different environmental conditions.