15512

1560 دكتري

دكتري

مهندسي مواد

اصفهان : دانشگاه صنعتي اصفهان

1398

[پانزده]، 132ص.: مصور،جدول،نمودار

مرتضي شمعانيان

دكتر كيوان رييسي-دكتر مسعودعطاپور-دكتر اكبر اسحاقي

1398/12/14

كتابنامه

مهندسي مواد

مهندسي مواد

1398/12/14

2605635

Laser cladding of TiAl alloy for improvement of high temperature oxidation properties using Ni Cr C nanocomposite powders Sayyed Erfan Aghili e aghili@ma iut ac ir Date of Submission 2020 02 19 Department of Materials Engineering Isfahan University of Technology Isfahan 84156 83111 Iran Supervisor Morteza Shamanian Professor shamanian@iut ac ir Department Graduate Program Coordinator Dr Mahshid KharazihaAbstractIn the present study NiCr Cr3C2 powder mixture was prepared by mechanical alloying andcladded on titanium aluminide substrate by powder fed laser cladding process The effect ofprocessing parameters such as laser power P powder feeding rate F and scanning speed S were studied on the geometrical properties height width dilution and wetting angle ofsingle line claddings and their systematic correlation were predicted using the regressionanalysis method The high temperature oxidation behavior of the substrate and coating wasalso studied by isothermal annealing at 9000C for 5 h The results indicated that the cladheight shows a linear dependency on the P1 S 1 F0 85 parameters Similarly the width wettingangle and penetration depth depicted a linear dependency on the P1 S 1 F 0 7 P0 8 S 0 7 F1 andP0 75 S0 5 F 1 parameters respectively while the dependency on dilution was S0 8 F 0 8 Highvalues of the correlation coefficient were observed for all empirical dependencies Finally a processing window was developed for the laser cladding of the Cr3C2 NiCr powder mixtureon the TiAl substrate The microstructure of the coating with optimal geometry is composedof solid solution with different chromium carbide phases Cr3C2 Cr7C3 and Cr23C6 Thepresence of different chromium carbides in the microstructure of the coating can beattributed to the partial melting of primary Cr3C2 and subsequent formation of non equilibrium carbide phases during rapid cooling NiCr chromium carbide laser claddedcoating shows superior oxidation resistance compared to the TiAl substrate The oxidationmechanism of both coating and substrate follow the parabolic law where the parabolic rateconstant of the coating was 20 of that of the substrate at 900 C Keywords Laser Cladding Titanium Aluminides NiCr Cr3C2 Microstructure OxidationIntroductionTitanium aluminides are an excellent candidate for structural applications due to theirproperties such as low density high elastic modulus creep resistance and high specificstrength 1 On the other hand unsuitable ductility at room temperature and undesirablecorrosion and wear resistance at high temperatures are some of the main drawbacksrestricting the utilization of titanium aluminides in real industrial applications Titaniumaluminides lose their corrosion resistance at temperatures higher than 800 C due to the

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