ساخت قطعات نانو كامپوزيت Al-B4C به روش آسياب كاري و پرس گرم و ارزيابي رفتار سايشي آنها

چكيده انگليسي :

128 Fabrication of Bulk Al B4C Nanocomposites by Ball Milling and Hot Pressing and Evaluation of their Wear Behavior Ehsan Mohammad Sharifi Email address e mohamadsharifi@ma iut ac ir Date of Submission Department of Materials Engineering Isfahan University of Technology Isfahan 84156 83111 Iran Degree M Sc Language Farsi Supervisor s Name Fathollah Karimzadeh Associate Professor karimzadeh f@cc iut ac ir Mohammad Hossein Enayati Associate Professor ena78@cc iut ac irAbstractAluminum matrix composites are important applicable materials for automotive and aerospace industries Lightweight environmental resistance high specific strength and stiffness good wear resistance and highthermal and electrical conductivity are characteristics that promote research and development to extend theirapplications by further improvement in the properties Ceramic particles are the most widely used materialsfor reinforcement of aluminum alloys Boron carbide B4C is one of the most promising ceramic materials due to its attractive properties includinghigh strength high melting point 2450 C low density 2 52 gr cm3 extremely high hardness the thirdhardest material after diamond and boron nitride good chemical stability and neutron absorption capability The combination of these properties makes it an interesting candidate for neutron absorption materials wearresistant materials electrode materials and cutting tools In addition to many uses of sintered shapes particulate B4C has been used as reinforcement for metal and ceramic matrix composites for increasing wearresistance More recently Considerable attention has been paid to Al B4C composites In this study aluminum matrix nanocomposite reinforced by boron carbide nanoparticles was producedusing mechanical milling and hot pressing methods For fabrication of this nanocomposite two general pathswere considered First path involved insitu formation of B4C nanoparticles in Al matrix by ball milling of Al B C powder mixtures The second path included two steps preparation of B4C nanoparticles bymechanochemical route and then ball milling of B4C with pure Al powder to obtain Al B4C nanocomposite In order to produce of B4C nanoparticles various routs such as milling of elemental B C mixture carbothermic reduction of boron oxide B2O3 aluminuthermic and magnesiothermic reduction of B2O3 inthe presence of carbon were investigated Morphological and structural changes of powders duringmechanical milling were examined using scanning electron microscopy SEM observations and X raydiffraction XRD analysis Results showed that ball milling of Al B C powder mixture did not yield B4C in Al matrix even after longmilling time Subsequent heat treatment of this mixture led to the formation of undesirable phases Inmechanochemical route only magnesiothermic reduction of B2O3 in the presence of carbon led to theformation of B4C phase XRD analysis and transmission electron microscopy TEM observations confirmedthat magnesiothermally synthesized B4C had nanometer size ranging from 10 to 80 nm The prepared B4C nanoparticles were mixed with pure Al powder by ball milling for 5 h to produce Al B4Cpowder Al B4C powder containing different amount of B4C was subsequently hot pressed at 500 C and 300MPa for 30 min to produce bulk nanocomposite sample Consolidated samples were characterized by hardness compression and wear tests Results showed thatsample with 15 wt B4C had the optimum properties This sample had a value of 164 HV which issignificantly higher than 33 HV for pure Al Also ultimate compressive strength of sample was measured tobe 485 MPa which is much higher than that for pure Al 130 MPa The wear resistance of thenanocomposites increased significantly with increasing the B4C content Dominating wear mechanisms forAl B4C nanocomposites were determined to be formation of mechanical mixed layer on the surface ofsamples KeywordsAluminum matrix nanocomposite Boron carbide Mechanical milling Hot pressing Wear

محمد شريفي، احسان

ساخت قطعات نانو كامپوزيت Al-B4C به روش آسياب كاري و پرس گرم و ارزيابي رفتار سايشي آنها

كامپوزيت زمينه آلومينيومي , كاربيد بور