توليد و مشخصه يابي نانو كامپوزيت هاي ريختگي AZ91-CNT با وارد كردن پودرهاي Mg-Ni-P-CNT به مذاب

چكيده انگليسي :

109 Abstract Due to need for fuel savings nowadays light metal alloys are worth considering for transportation structures In this regard magnesium and its alloys with the least density among industrial metals have increasing scientific and industrial applications However magnesium has limited formability and low strength so development of magnesium composites are desired to reduce the mechanical property related shortcomings of this light metal and its alloys Carbon nano tube CNT with a unique atomic structure is known as a modern material with new applications CNT has a combination of perfect mechanical physical and electrical properties and with its extraordinary strength and high toughness is an ideal candidate for reinforcement of composite materials Although CNT will be useful for improving magnesium properties there are some disadvantages for production of composites reinforced by CNT High agglomeration tendency and poor wetability of CNTs with metal melts due to their surface energy differences are the main challenges for using this modern material as the reinforcement in composites Considering the desire to overcome these challenges coating CNTs or putting them in a metallic coating are two practical solutions In this study nickel phosphorous electroless coating process was employed for the first time for uniform co deposition of CNTs into a Ni P matrix coated on magnesium powder In the first steps important parameters of electroless bath like pH and temperature were optimized for the best condition of entangling CNTs Then different amount of CNTs are introduced to the electroless bath for the best situation of dispersion and reinforcing Due to very large surface area of the particles to be coated intense coating reactions which would prevent CNT agglomeration in the coatings were expected Also moving powder as coating surface caused a homogenous suspension of reinforcement in the electroless bath so uniform composite coating could be produced The magnesium powder with the optimum composite coating was used as the reinforcement for uniform addition of CNTs to AZ91 alloy through mechanical mixing in the molten alloy Similar composites were also produced with untreated as purchased CNTs for comparison It was observed that addition of dispersed CNTs in the coating resulted in notable grain refinement of the matrix whereas addition of untreated CNTs were not very effective Also the composites produced with addition of untreated CNTs had more porosity due to the greater CNT agglomeration resulting in poor mechanical properties On the other hand one percent dispersed CNTs in the coating caused 32 percent enhancement in UTS 16 percent enhancement in Young modulus 23 percent enhancement in yield stress 36 percent enhancement in hardness and 30 percent enhancement in flexural strength in comparison with the monolithic samples Moreover while the type of fracture did not change by reinforcement addition and was still brittle the toughness was not impaired in the composites with well dispersed CNTs In contrast samples with untreated CNTs didn t show such improvements in the mechanical properties due to the poor reinforcement dispersion and expected weak reinforcement matrix bonding Key words Metal matrix composite Carbon nanotube AZ91 Nickel phosphorus electroless coating Composite coating on powder Stir casting

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توليد و مشخصه يابي نانو كامپوزيت هاي ريختگي AZ91-CNT با وارد كردن پودرهاي Mg-Ni-P-CNT به مذاب

مواد كامپوزيتي , نانو لوله كربني , پوشش الكترولس نيكل-فسفر , پوشش كامپوزيتي بر پودر , ريخته گري هم زدني