Journal of Advanced Processes in Materials Engineering
Year:2009 | Volume:3 | Issue:3 (10)|Papers Count:8

At the present paper producing of Cu-3wt % Al2O3 and Cu-5wt % Al2O3 nanocomposite powder with thermochemical method was studied. The produced phases at different stages of heat treatments were characterized by differential thermal and thermogravimetric analysis (DTA-TGA), X-ray diffraction (XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). Nanocomposite powders were produced through the following stages: Preparing aquos solutions of copper nitrate and aluminum nitrate to achieving the final composition, heating water solution and making precursor powder, the salt-removing heat treatment, the heat treatments at different temperatures for the formation of alumina and the reduction of CuO into Cu at different temperatures in the H2 atmosphere. Optimum temperature for the formation of alumina and reduction of powders was obtained at 850oC and 820oC, respectively. The size of alumina particles produced by thermochemical method was about 20-50 nm.

Protective coating of components, especially by the application of a film containing ceramic particles is one of the most rapidly changing technologies involving a wide range of recently developed techniques. The present study focuses on the development of a novel ceramic coating technique. This novel method uses a mixture comprising fine grain alumina powder and reactive cyanoacrylate monomer (ethyl cyanoacrylate and alcoxy-ethyl cyanoacrylate) as a binder. This paper describes the outcome of an experimental investigation into controlling of polymerazation reaction rate of cyanoacrylate during mixing, application and curing of the coating mixture. Polymerisation of the cyanoacrylate is inhibited during the mixing stage by means of dissolving Para-tolune sulfonic acid and is initiated in a controlled manner using caffeine powder. Coatings have been successfully deposited onto aluminium substrates. SEM micrographs show good uniformity of the coating and that successful adhesion can be achieved, as also shown by joint shear strength test results. In addition, the coating mixture can be used on irregular as well as flat surfaces. It was found that with increasing the amount of polymerization initiator in the mixture, porosity was increased and hardness of the coating as well as adhesion strength at the interface was reduced. Moreover, when the volume percentage of powder in mixture increased, the hardness improved but the adhesion strength at the interface reduced. This paper also presents the results of debinding of the coating mixture. It is suggested that working temperature for the coating is up to 140oC.

This paper aims at investigating the microstructure and failure behavior of dissimilar resistance spot welds between low carbon steel (st14) and ferrite-martensite dual phase steel (DP600). The effects of welding current in the range of 7.5 to 9.5 kA on the metallurgical and mechanical behavior of the weld were investigated. Microstructural characterization, microhardness tests and the tensile shear tests were conducted. Mechanical properties of spot welds were described in terms of failure mode, peak load and energy absorption. The fusion zone microstructure exhibited martensite, bainite, allotriomorphic ferrite and Widmanstätten ferrite, resulting in high hardness of fusion zone compared to base metals. Results showed that the mode of failure changed from interfacial fracture to pullout as the welding current was increased. Fusion zone size proved to be the most important controlling factor for peak load and energy absorption of dissimilar DP600/St14 resistance spot welds.

The aim of this work was preparation, development and characterization of three kind bioactive glass coating by sol-gel technique for improvement of biocompatibility of 316L stainless steel implant used in dentistry and orthopaedic surgery. Three types of bioactive films, 45S, 49S and 58S, have been prepared by sol-gel method using different bioglass compositions on stainless steel 316L. The physicochemical properties, including surface morphology, crystallinity, crystal size and adhesion on steel substrate, of the three types of films were investigated by SEM, XRD, TEM and the crosshatch adhesion test. Crack-free and homogeneous bioglass coatings were obtained with no observable defects, amorphous, with particle size less than 100 nm and an excellent adhesion between the films and the stainless steel substrate (5B). The bioactivity of bioglass coatings was investigated by immersing the coatings in simulated body fluid (SBF) for 30 days. After 30 days immersion, there is a complete layer of carbonate-containing apatite formed on the 45S coating surface, but less formed on 49S and 58S coating.

Steels mechanical properties are related to chemical analysis and mainly to the heat treatment. Various thermal processes cause to wide range of properties in steels. Heat transfer and diffusion are two phenomena that determine the micro structure of heat treated steels. It is possible to predict the micro structure of continuous cooled steels with knowing cooling rate and CCT diagrams. Obtaining the cooling rate of internal point of part is difficult. In this research the cooling rate of internal point of cubic CK45 steel calculated in finite difference method. Then obtained diagrams plot on steel CCT diagram and the micro structure of each point and its hardness predicted. When steel heat treated, the part cut and the hardness of studied points measured. Results of hardness measurement validate the simulation calculation.

In this Investigation ST37-2 plates were used and coated by graphite and different amount of ferroniobium mixture, GTAW in bead on plate carried out in constant heat input and dilution, result of chemical analysis shown that can be produced hardface layers with different amounts Nb in chemical composition (0.16% to 1.34%). Result of hardness test shown that with increased Niobium in chemical composition of hardface layers, Hardness increased and maximum value was gained in sample No4 with 1.34% Niobium, the metallographic test result shown that with increased Niobium in chemical composition, volume fraction of martensite in microstructure decreased and amount of Austenite and NbC carbides increased, also carbides morphology were changed from rod shapes in sample No1 (0.16% Niobium ) to equiaxed in sample No4 (1.34% Niobium) and maximum wear resistance was gained in sample No4.

The material has been studied in this research is 1.5920 steel that was subjected in solid carburizing process. This process followed by quenching increases surface hardness of this steel according to formation of martensite structure in outer layer. The core region of steel has more flexibility and less hardness because its carbon content is lower than the surface. One of important parameters in this steel is using the energizer material for increasing the hardenability. In this research, steel specimens were subjected to graphite powder. Cementing boxes consisted of 0, 5, 10 and 15 wt% of an energizer material. Sodium carbonate was used as an energizer material. Then, they were heat treated at 925oC for about 3, 5, 8 and 12 hours respectively. Finally these parts were quenched in oil. For determining of case depth, microhardness test was done on cross section of specimens. Case depth was measured in different conditions by plotting the hardness-distance curves in different samples. Plotting the case depth versus energizer content and carburizing time determined necessary conditions for invention the specified case depth in this steel. Also, occurring boundary conditions for carburization and decarburization phenomena were studied in this steel.

When hardness of Iron Ore changes inside Autogenous (AG) mills it causes a significant effect on the throughput of Autogenous (AG) mills which in turn results in final production of the mineral processing plants. In this regard grindability or hardness of ore is the resistance of the ore in the comminution. The effect of increasing temperature on grinding of Iron Ore is considered with the hardness test as a standard available test. But in previous studies this effect has not been considered. Analyzing results show that. By increasing temperature up to 500°C hardness of Ore samples had a much decrease to 4.9 minute. Also It was observed that by applying heat to Iron Ore up to 500°C doesnot effect so much on chemical combination and Iron Ore alloy.