3470

3276

كارشناسي ارشد

شناسايي و انتخاب مواد

اصفهان: دانشگاه صنعتي اصفهان، دانشكده مواد

1385

نه، 105، [II] ص.: مصور، جدول، نمودار

ص. ع. به فارسي و انگليسي

محمدرضا طرفي نژاد

فخرالدين اشرفي زاده

15/2/86

عباس نجفي زاده، محمد محسن مشكسار

مهندسي مواد

ID3276

به فارسي و انگليسي: قابل رويت در نسخه ديجيتال

106AbstractAccumulative roll bonding ARB is a severe plastic deformation process for achievingultra fine grains in metallic sheets without changing the sample dimensions In this study ARB process was carried out on pure copper 99 9 sheets up to 10 cycles In thisprocess the surfaces of the strips to be joined are roughened and cleaned and then stacked After stacking the specimen is roll bonded by rolling using a 50 reduction The rolledspecimen is cut into two halves and the above mentioned procedure is repeated for severaltimes Microstructural characterizations were analyzed by transmition electron microscopy TEM and electron backscattered diffraction EBSD Tension and Vickers hardness testswere performed on produced sheets for evaluating their mechanical properties In order toclarify the failure mode fracture surfaces after tensile tests were observed by scanningelectron microscopy SEM Moreover X ray diffraction system equipped by goniometerwas utilized to investigate the textural changes on the surface of samples The results indicated that at the early stages of ARB process grains were subdivided bydeformation induced boundaries After several ARB cycles lamellar structure elongated inthe rolling direction contains lamellar boundaries was formed With increasing the strain mean spacing of lamellar boundaries decreased Finally continuous recrystallizationresulted in a microstructure covered with small recrystallized grains with an averagediameter below 100 nm at the end of eighth cycle The tensile strength and hardness of the10 cycle ARB processed copper increased about two and three times of the initial values respectively Results indicated conformity between mechanical evolutions andmicrostructural changes during ARB process Fracture surfaces observations showed thatfailure mode in ARB processed copper is shear ductile rupture with elongated smalldimples Texture analysis revealed shear component in the subsurface regions This sheartexture has been developed at the sheet surface due to shear deformation induced by a largefriction between the rolls and the sheet

محمدرضا طرفي نژاد

فخرالدين اشرفي زاده

عباس نجفي زاده، محمد محسن مشكسار