Journal of Advanced Processes in Materials Engineering
Year:2008 | Volume:2 | Issue:6|Papers Count:8

Thermal explosion mode of combustion synthesis was employed to produce a composite of titanium carbide in nickel aluminide matrix. Nickel titanium (NiTi2) powder was used as a source of both Ni and Ti, which is much cheaper than elemental powders. Phase analysis of the products was carried out using X-ray diffraction with Cu-Ka radiation. Microstructure of the product was also studied by SEM. The results show that a combustion reaction between Al, C, and NiTi2 powders could be maintained as long as the Ni + Al (the matrix) in the powder mixture is lower than 68 wt%. When the matrix content is higher, the reaction is not sustained due to the low combustion temperature. XRD results show that all reacted samples consist of TiC and NiAl intermetalic. Microscopic examination of the polished samples revealed a fine dispersion of particulate TiC in the NiAl matrix. The size of the TiC particles were a function of TiC:NiTi ratio in the composites. The lower the weight percent of the matrix phase the larger was the size of TiC particles. This was believed to be due to the higher combustion temperature in the samples with lower matrix weight percent.

Scherrer used the equation L=Kl/bCosq to measure the nano size of crystals L, by the width at half of the height b of the XRD peak diffracted at the angle 2q from diffracted ray of wavelength l and a constant of proportionality K according to the particle shape. This paper shows that diffracted peaks of the same crystal do not show identical results. Several peaks are often used to measure the average. This research by calculations based on natural nano size crystals of hydroxyl apatite from fined sheep bones provides a more accurate method. If Ln Kl/L is plotted against Ln(1/cosq) from different peaks using least squares method to reduce experimental errors, then Ln woud be an identical intercept with ordinate, from which a single L can be calculated. The nano size of 43 nanometer was obtained for natural hydroxyl apatite of sheep bone, which is in expected range. Similarly two spinel samples (MgAl2O3) fired at 1150 and 1400 degrees centigrade were evaluated which showed 21 and 68 nanometers respectively.

In the operation of conventional precipitation hardening, since we need a fine dispersion of precipitation there is an obligation to operate the ageing process at low temperatures in order to formation of GP zones and apply them as the nucleation sites for the more stable precipitates. Furthermore at the maximum hardness we encountered the SCC resistance dropped. In this research we have investigated the effect of cold rolling prior to ageing, on the mechanical properties and SCC resistance of Al-7075 alloy. This thermo mechanical operation maintained the uniform elongation constant and increased the strength relatively in addition to high reduction of the ageing time and considerable improvement of SCC resistance. The dislocations generated during rolling stage were an appropriate substitute for the GP zones as nucleation sites for secondary phase precipitations and made the possibility of operating ageing at temperatures higher than GP zones solves which leaded to formation of more stable precipitations and smaller precipitation free zones and so improved the SCC resistance and reduced the ageing time greatly.

In this research, cobalt ferrite nano-crystalline phase was formed after 30 hours mechanical milling of metallic cobalt and hematite powder with 1:6 and 1:2 molar ratios, according to -ray diffraction and Mossbauer spectroscopy results. To reduce stress, the milled samples then were heat-treated for 30 minutes at 500oC. Heat-treatment effect on phase formation and magnetic properties of synthesized nanopowder was investigated. X-ray diffraction results showed increase in crystallite size, crystallization and amount of cobalt ferrite phase. For heat-trated sample with molar ratio of 1:2, maximum magnetization (at 17 kOe) and Hc increased to 30 emu/g and 1.07 kOe and 3 emu/g and 1.5 kOe for the sample with molar ratio of 1:6. 

This paper focuses on the effects of annealing on the mechanical properties of polypropylene-hydroxyapatite composites with different amounts of hydroxyapatite. Ultimate tensile strength, Young’s modulus, bending strength and impact resistance were evaluated for composites. For all of produced composites by increasing of hydroxyapatite content ultimate tensile strength, bending strength and especially impact absorbed energy of composites decreases but their young modulus increase linearly. Annealing of composites at temperature of 130oC for 30 minutes caused enhancement of ultimate tensile strength, bending strength and Young’s modulus of annealed composites rather than un- annealed composites. On the other hand, by annealing of composites can be seen impact absorbed energy of composites decreases related to un-annealed composites. Generally, by annealing of composites polypropylene structure changes from amorphous to crystalline. Micrographs showed changes in fracture mode from ductile to brittle by annealing of composites.

Grain Refinement process is an important stage in production of aluminum castings. There is common question for all producer of aluminum castings that how they can be sure about the quality of nucleation. Thermal analysis is an important tool to answer this question. In this research, different types of inoculants were used Fesr investigation of nucleation in A356 aluminum alloy. The cooling curve of each sample was recorded and by using a special computer program, the first derivative was calculated. By calculating zero curves and analyzing the cooling curve, it is possible to predict the quality of nucleate and calculation fraction of solid, latent heat and other information. The result of this research have shown that if maximum undercooling of nucleation was approximately 4°C, the quality of nucleation process would be more reliable.

In the present paper, aging heat treatment is used for optimizing the best wear property of Al-4Si alloys, in order to achieve this purpose, we added some Mg to that alloy during casting process, after homogenization, cast alloys were done solutionized at 540oC for 2 h, followed by water quenching (30oC) and artificial aging at 180-240oC for 1-8hr, hardness and wear tests were conducted for as cast and heat treatment. A pin on disc type wear was used and load range of 5-30N was chosen. Scanning electron microscopy (SEM) of wear surface was carried to analyze the wear mechanism. Results show heat treating alloy have lower wear rate than the as-cast alloy and noticeable differences has taken in wear mechanisms which the main reason of this is due to broke down dendrite structure in heat treatment and leads to increase hardness and strength. The best wear property is achieved at 210oC for 8hr of aging treatment. After wear X-ray diffraction lines are broadened due to plastic deformation and increasing dislocation density in subsurface.

Heat treatment process can be very effective on final properties of steel and cast iron parts. The problem associated with heat treatment is inducing the residual stresses during cooling which can result in distortion or crack in the parts. Thermal and stress analysis in a cylindrical casting during heat treatment play a major role in controling the heat treatment’s defects. In this work a coupled thermal/stresses-strain model has been developed to predict the evolution of residual stresses during heat treatment of steel cylindrical parts, using ABAQUS commericial code.The residual stresses distribution predicted by the model was compared whit the experimentals reported in the literature. Overall, a good agreement between the model predictions and the measured stress distribution and distortion was obtained. The effects of various parameters such as quenching media and geometry on the induced residual stress and distortion for steel cylindrical were also studied.