Journal of Advanced Processes in Materials Engineering
Year:2012 | Volume:6 | Issue:1 (20)|Papers Count:12

In this study, friction stir spot welding was used to make lap joints on strips of 2024 aluminum alloy. The effects of tool rotational direction (clockwise and counter clockwise) and holding time on bond formation and tensile shear strength of the resulting joints was determined. Macro structure of stir zone was monitored by optical microscopy and it was indicated that interface of sheet metals near the pin hole (Hook) was determined. Also with increasing of the holding time, width of the stir zone and tensile shear failure load increased. An optimum combination of parameters that maximizes joints tensile shear strength was identified.

In This study, hydroxyapatite nanoparticles (nHA) was synthesized via sol-gel method and then poly 3-hydroxybutyrate\Hydroxyapatite Nanocomposite scaffolds (PHB/nHA) prepared by solvent casting and particulate leaching Technique. The scaffolds were prepared from 0.4-0.8 gr PHB in 10mm choloroform. nHA weight percent was 0-10 and the ratio of PHB: NaCl was 30:70, 20:80, 10:90. synthesized nHA powder and nanocomposite scaffolds were characterized by XRD, FTIR, SEM, WDXA and TEM. nHA particle size was 30-40 nm and 35 nm according to TEM image and debbye sherrer equation rerpectively. XRD parren confimed HA formation. FTIR analysis shows that there is a chemical bond between polymer and nHA particles that causes strength of scaffold. SEM results shows that morphology, size and distribution of pores is uniform and pore size is 200-250mm. uniformity of pores is better in 4%wt of PHB \Choloroform solution and decreasing of salt amount, causes increasing of closed pores on the surface. Theoric porosity of prepared scaffolds was obtained 57-84 for 70-80 %w NaCl that is closed to measures obtained by diffusion method. uniform distribution of nHA in scaffolds were investigated by wavelength dispersive spectroscopy (WDXA). This study showed that (PHB/nHA) composite scaffold is a good candidate for bone tissue engineering.

Activated alumina and zinc oxide both have been used as a sulphur remover catalyst in different applications such as gas - oil - and petrochemical Indus tries. One of the main applications of activated alumina is removing of sulphur from sour natural gas in clause process and also ZnO can be used as a catalyst agent or support performing a Fischer Tropsch reaction to convert a mixture of carbon monoxide and hydrogen to hydrocarbons [1]. Apart from gas, oil and petrochemical processing, removing of the sulphur, to have clean environment also is very important. In this study we have tried to investigate synthesis of alumina and zinc oxide when they prepare in chemical root at the same time.  Precipitation of alumina and zinc oxide was performed by mixing of aluminum chloride and zinc acetate in different proportions. Calcined materials were characterized by DSC, XRD, BET, SEM and FTRI to see phase distribution and its effect on surface area activation. Also dispersion of different proportions of Al2O3-ZnO to have maximum surface area was evaluated.

Chromium containing alloys are among the best candidates for solid oxide fuel cell interconnects. However, the problem of reduction of electrical conductivity during high temperature oxidation should be solved. The aim of this research was to investigate the electrical behavior of AISI 430 ferritic stainless steel which was coated in a Mn-base pack mixture by pack cementation method. Electrical conductivity was tested as a function of oxidation time at 750oC and as a function of temperature by annealing the samples from 400 to 900oC. Results showed that the coating layer was converted to Mn3O4 and MnFe2O4 spinels during oxidation. These spinels caused to the improvement of the electrical conductivity of coated substrates compared to uncoated substrates.

In this paper, failure behavior of similar and dissimilar resistance spot welded joints of low carbon steel (CS) and austenitic stainless steel (SS) sheets was studied under tensile-shear test with attention focused on the failure mode transition form interfacial to pullout. Results showed that the microstructure of the fusion zone and the hardness distribution across the weld have a profound effect on the failure behavior. Similar SS/SS resistance spot welds exhibit the highest tendency to fail in interfacial failure mode, compared to CS/ CS similar and dissimilar SS/CS spot welds. This behavior is explained by the consideration of pullout failure location and hardness profile characteristics of each joint. It was shown that the failure mode transition is controlled by the hardness ratio of the fusion zone and the pullout failure location.

This study deals with the processing, microstructure, and sintering behavior of TiC-reinforced NiFe matrix composites, containing 5, 10, 20 and 30 wt.% TiC. Mechanical alloying and powder technology were used to successfully fabricate the composite. The characteristics of the milled powders and the consolidated specimens were examined using scanning electron microscopy and X-ray diffraction method. The microstructural study revealed that the TiC particles were distributed uniformly in the NiFe matrix phase. The composite hardness also increased with TiC content.

In this study, ZrO2 particle reinforced SiO2-CaO-MgO-Al2O3 glass-ceramic with amounts of 5, 10 and 20 wt% as reinforcement in presence CaF2 additive as sintering aid was investigated. The composites prepared by sinter- crystallization. The sinterability of samples was evaluated via relative density. The crystallin phases are characterized by X- Ray Diffraction. The samples examined by Scaning electron microscopy. The fracture toughness of composites was determined by the microindentation method. The reinforced glass ceramic with 10wt% ZrO2 was shown the higher fracture toughness than glass- ceramic. The residual stress amount due to volum expansion arien of Zirconia transformation caused to increase the fracture toughness. The addition 20 wt% ZrO2 rather than 10 wt% ZrO2 wasn't created significant changes in fracture toughness because absence compelet sintering due to increasing viscosity.

In this research, continius cooling behavior of 1.2304 cold work tool steel was investigated by dilatometry tests. All samples heat treated in vacuum furnace, then quenched with nitrogen gas in different cooling rates. The results showed that ferrite - perlite, bainite and martensite phase transformatios occurred in 596-713oC, 360-468oC, 253-268oC, respectively. CCT diagram of steel has been drawn after analysis of dilatometric curves. Morever by cryogenic treatment, martensitic finish temperature was determined at -87 °C.

In this paper, the reaction beetwen Cr2O3, MgO, Al2O3 was investigated for spinel formation in the ternary system. different amount of (1, 2 and 3%) Cr2O3 was studied on the properties and microstructure of spinel ULCC refractory castables. In this study spinel formation and effect of amount of additive Cr2O3 is under review by X-ray diffraction analysis (XRD) and scanning Electron microscope analysis (SEM) in the temperature 110oC and 1400 and 1600oC on The microstructure and properties of spinel refractory casables. results of phase analysis show that small amounts of Cr2O3 lead to complete dissolution of chromia in the alumina (encapsulation), which define absorbed completely and no existed freely. Phase of the Cr+3 enter to spinel network and replaced Al+3 ions and Al2O3 and Cr2O3 solid solution will form. Consequently chromia presence, accelerate the process of spinel formation and increased mass transfer and density will be.

In this investigation, metal cored wire contains Ferro boron used and hardfaced by FCAW process on mild steel. Chemical analysis test result shows that hardface layer contained of boron element. XRD, OM, SEM, EDX examination test result shows that microstructure of hardface layer consisted of Fe2B+FeB in A+M+Fe2B matrix, macrohardness (RC) test result shows, high value hardness of the deposit layer was gained. In addition wear test result of hardface layer in dry and wet conditions shows that hardface deposited had higher wear resistance in different conditions (dry and wet) than that base metal. moreover study of worn surface with SEM shows that wear mechanism of hardface layer in dry abrasive wear condition was microploughing with less cutting and in wet abrasive wear condition was less microploughing with oxides cutting.

In this research, Electrochemical deposition of Ni-SiC-Gr nano composites was studied. The watts bath was used for electrodeposition. The SiC and graphiteparticles were suspended in the electrolyte and stirred. The effects of SiC nanoparticles Content in bath on the composite coating were investigated. The X-Ray diffraction (XRD) an scanning electron microscopy (SEM) and field emission scanning electron microscopy (FESEM) metods were used to characterize the micro structure of deposited layer. The results showed that the microhardness the increases with increases in pif value. The coating that pericipitated at 25 gr/lit were maximum hardness. The results demonstrate the morphological properties and hadness of Ni-SiC-Gr nano composite coatings fabricated via electrodeposition were improved with increase SiC nanoparticles in the bath. also demonstrated the hardness of coatings were not related to the graphitparticles content in the composite coating.

In this research, a modified, cost efficient and quick sol-gel procedure was used for preparation Of Tehran, Iran BaTiO3 nanoparticles. By a modified selection of precursors and utilization of optimized precursors ratio and controlling the hydrolysis conditions, finer BaTiO3 nanoparticles were synthesized in shorter period of time and lower temperature contrary to results obtained in previous researches. In this research the sol is prepared only in 90 minutes but other researchers prepared their sols in more than 8 h. Moreover barium titanate nanoparticles have been prepared after calcination in 800oC for 1h but similar results show the presence of carbonate phases in composition of prepared nanopaticles. The proposed procedure seems to be more preferable for mass production.