3949

3727

كارشناسي ارشد

خوردگي و حفاظت از مواد

اصفهان: دانشگاه صنعتي اصفهان، دانشكده مواد

1386

ده، 85، [II]ص : مصور، جدول، نمودار

ص.ع. به: فارسي و انگليسي

محمود منير واقفي، احمد ساعتچي

كيوان رئيسي

22/03/87

ابراهيم حشمت دهكردي، فخرالدين اشرفي زاده

مهندسي مواد

ID3727

به فارسي و انگليسي: قابل رؤيت در نسخه ديجيتال

AbstractIn the present research electroless Ni P deposits were obtained on Al5083 substrate Theeffects of coating time substrate roughness heat treatment temperature and heat treatmenttime on morphology phosphorus content structure microhardness adhesion and corrosionbehavior of the deposits in 3 5 wt NaCl solution were investigated Deposits were heated attemperatures ranging from 200 to 400 C for 1 4 h Surface morphology of the coatingsexhibited a nodular feature with a typical cauliflower like structure By increasing thickness ofcoatings the phosphorus content of surfaces decreases but the number of porosities decreasesand the corrosion resistance increases Also the corrosion resistance of electroless deposits onsmooth substrate in comparison with rough substrate is better The structural characterizationwas done by means of X ray diffraction studies As deposited coating exhibit broadened X rayreflections indicative of a semi amorphous structure Heat treatment decreased the amorphousphase and the final equilibrium phases were Ni3P and Ni crystals within the nanocrystallinesize range The results of Vickers microhardness testing showed that the maximum hardnesswas achieved for the samples which have been heat treated at 400 C This is caused by theformation of intermetallic Ni3P stable phase at this temperature acting as a function ofprecipitation hardening Corrosion resistance of the coatings indicated that on heating to 240 C the corrosion resistance increased and then reduced at higher temperatures Heat treatmentat 400 C leads to crystallization of the amorphous phase making available more number ofgrain boundaries which are highly prone to corrosion attack Therefore the heat treatment ofelectroless specimens at 400 C significantly decreases their corrosion resistance Alsoevaluation of the corrosion behaviour coatings which heat treated at 240 C and 320 Ctemperatures and longer times indicated that by increasing heat treatment time noconsiderable decreasing in the corrosion behaviour observed until the formation of Ni3Pintermetallic phases For evaluation of susceptibility to localized corrosion cyclicpotentiodynamic polarization method is used All of the curves of the electroless coatingsexhibit positive hysteresis Positive hysteresis occurs when the passive film is unable to repairbreakdown at localized areas and pits initiate and continue For evaluation electroless coatingsadhesion to substrate bend test is used according to B 571 97 standard All of the electrolesscoatings aren t peeled in bended area and aren t separated from substrate even by insertion ofa sharp probe at the interface of the coating and substrate that exhibit good adhesion coatingsto substrate

محمود منير واقفي، احمد ساعتچي

كيوان رئيسي

ابراهيم حشمت دهكردي، فخرالدين اشرفي زاده