ارزيابي تاثير جوشكاري ليزر مشابه و غير مشابه آلياژ حافظه دار نيكل- تيتانيوم و عمليات حرارتي پس از آن بر ريز ساختار، خواص مكانيكي و رفتار خوردگي اتصال

چكيده انگليسي :

96Evaluating the effect of similar and dissimilar laser welding of nickel titanium shape memory alloy and post weld heat treatment on microstructure mechanical properties and corrosion behavior of the joint Gholamreza Mirshekari g mirshekari@ma iut ac ir Date of Submission January 27 2014 Department of Materials Engineering Isfahan University of Technology Isfahan 84156 83111 IranDegree M Sc Language FarsiSupervisors Advisor A Kermanpur Associate Professor S K Sadrnezhaad ProfessorA Saatchi ProfessorAbstractThe unique properties of nickel titanium NiTi alloy such as its shape memory effect super elasticity and biocompatibility make it ideal material in various fields such as aerospace andautomotive industries micro electronics and medical devices In this regard joining of thismaterial to itself and to other materials is of considerable importance and great attention has beengiven to it during past few years Stainless steels are one of the dominant materials which arewidely used in different applications especially in medical devices owing to their mechanicalproperties workability low cost and corrosion resistance Therefore joining of NiTi to stainlesssteel would be desirable for widening of its applications Due to the low and precise heat input lowenergy density small fusion and heat affected zones low residual stress low weld distortion andhigh welding speed laser welding is a suitable technique to join NiTi alloy Hence in this work acomparative study on Nd YAG laser welding of NiTi wire to itself and to AISI 304 stainless steelwire has been made Moreover to provide some foundation for improving the properties of thedissimilar laser welded NiTi stainless steel wires joint the effect of post weld heat treatments onthe joint properties of the dissimilar joint has been investigated Microstructures phasetransformation behavior and mechanical properties of the laser joints were investigated usingoptical microscopy scanning electron microscopy SEM energy dispersive spectroscopy EDS X ray diffraction analysis XRD differential scanning calorimetry DSC vickers microhardness HV0 2 and tensile testing techniques Corrosion behavior of weldments in the Ringer sphysiological solution at 37 C was also investigated using open circuit potential potentiodynamicpolarization and immersion tests Results indicated that the tensile strength of similar NiTi laserjoint was 835 MPa about 63 of the tensile strength of the as received NiTi wire with rupturestrain of about 16 This joint also possessed the superelastic property and enabled the possibilityto benefit from the pseudo elastic behavior of the NiTi component However tensile strength andstrain decreased significantly after dissimilar laser welding of NiTi to stainless steel due to theformation of brittle intermetallic compounds in the weld zone during laser welding In addition forthe similar laser joint corrosion resistance of the weld metal was better than that of the base metal On the other hand for the dissimilar laser joint the weld metal exhibited remarkable corrosionresistance which was close to the corrosion resistance of the stainless steel and better than that ofthe NiTi Also post weld heat treatments of laser welded NiTi shape memory alloy to stainlesssteel wire showed remarkable effects on mechanical properties and corrosion behavior of thewelded wires Post weld heat treatment at 200 C increased corrosion resistance and tensilestrength of the joint up to 1 8 times that of the as weld with no heat treatment joint Post weldheat treatment at 400 C on the contrary deteriorated the mechanical properties and corrosionbehavior mainly due to precipitation of newly made intermetallic compounds in the weld zone Theconclusion was that the post weld heat treatment temperature must critically be controlled in orderto improve the properties of the laser welded dissimilar NiTi stainless steel joint Keywords NiTi shape memory alloy Stainless steel Laser welding Post weld heat treatment

ميرشكاري، غلامرضا

ارزيابي تاثير جوشكاري ليزر مشابه و غير مشابه آلياژ حافظه دار نيكل- تيتانيوم و عمليات حرارتي پس از آن بر ريز ساختار، خواص مكانيكي و رفتار خوردگي اتصال

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