In this study, effects of alumina nanoparticles and stirring pass in mechanical behavior of friction stir welded AM60 magnesium alloy were studied. Microscopic analysis showed occurrence of dynamic recrystallization during plastic deformation in weld area and mechanical More
In this study, effects of alumina nanoparticles and stirring pass in mechanical behavior of friction stir welded AM60 magnesium alloy were studied. Microscopic analysis showed occurrence of dynamic recrystallization during plastic deformation in weld area and mechanical tests revealed optimum condition for hardness and tensile strength could be produced in 1200 rpm rotational speed not only in absence of reinforcing alumina nanoparticles but also in presence of them. Opposing effects of higher temperatures in grain growth and greater strains in lowering grain size should be considered. In lacking of alumina nanoparticles, grain size diminished with increasing stirring pass but in being nanoparticles, predominant mechanism in depressing grain size came from nanoparticles and negligible effect of stirring pass in grain size was found. XRD results showed increasing solubility of γ-Mg phase as a result of stirring operation. Better toughness performance of weldment was produced via decreasing size of agglomerated alumina particles. Higher hardness and greater ultimate tensile strength were achieved in specimens with alumina nanoparticle with increasing rotational speed. In a constant rotational speed, higher hardness and greater ultimate tensile strength achieved in samples having alumina nanoparticles in contrast with free alumina nanoparticle samples
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Mixtures of nickel oxide and activated carbon (99% carbon) with stiochiometric ratio were milled for different times in a planetary ball mill. The stiochiometric ratio of mixture was prepared in an un-milled condition. The unmilled mixture and milled samples were subjec More
Mixtures of nickel oxide and activated carbon (99% carbon) with stiochiometric ratio were milled for different times in a planetary ball mill. The stiochiometric ratio of mixture was prepared in an un-milled condition. The unmilled mixture and milled samples were subjected to thermogravimetric analysis (TGA) under an argon atmosphere and their solid products of the reduction reaction were studied using XRD experiments. TGA showed that the reduction of NiO started at ~800℃ and ~720℃ in un-milled and one-hour milled samples respectively whilst after 25 h milling it decreased to about 430℃. Increasing the amount of carbon more than stiochiometric ratio did not affect on the kinetics of carbothermic reduction. Thermodynamics assessments for NiO-C system were done using HSC software. Thermodynamics assessment and the experimental results indicated that Boudouard reaction plays a significant role in the carbothermic reduction reaction of nickel oxide. The results revealed that formation and increasing of monoxide carbon gas (COg) can change the kinetic reaction mechanism into solid-gas mechanism which has the major effect on increasing the rate of reaction. The decrease in the particle size/crystallite size of the nickel oxide in the milled samples not only resulted in decreasing in the reaction temperature, but also resulted in formation of fine particles of metallic nickel. Therefore, it is possible to achieve the metallic nickel particle in the range of submicron or nanometer via carbothermic reduction reaction of NiO using mechanical activation of NiO-C mixture.
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