بهبود ريزساختار و خواص مكانيكي سوپرآلياژ پايه نيكل PWA1483 تك كريستال از طريق اصلاح تركيب شيميايي

چكيده انگليسي :

Improvement of the microstructure and mechanical properties of the Ni base single crystal super alloy PWA1483 via chemical composition modification Ali Borouni ali borouni58@yahoo com Department of Mateials Engineering group Pardis College Isfahan University of Technology 84156 83111 Isfahan IranDegree PhD Language PersianDr Ahmad Kermanpur Prof Supervisor E mail ahmad k@cc iut ac irAbstract Nickel based single crystal SX superalloys have been using extensively in the aerospaceindustry foe the fabrication of high pressure turbine blades due to their exceptional properties at elevatedtemperatures According to the service condition of large centrifugal stresses and high temperatures improving mechanical properties especially creep resistance is pressingly desired In this study effectof Ta W ratio on microstructure and stress rupture properties of the single crystal SX PWA1483 Ni based superalloy was investigated For this purpouse the SX samples containing different amounts ofTa W ratio 0 75 1 0 1 32 and 1 5 in wt were fabricated The alloys were directionally solidified bythe Bridgman method with the same solidification condition withdrawal velocity of 3 mm min andthermal gradient about 7 K mm followed by age hardening heat treatment The microstructurescharacterization was performed by optical microscopy OM and scanning electron microscopy SEM and the stress rupture properties at 248 MPa 982 C was characterized by creep advice The experimentalobservations showed that the Ta W ratio influences microstructures and elemental microsegregationpatterns of the SX superalloys Based on the EDS results W Cr and Co segregate to dendrite coreregions while Al Ti Ta and Mo to interdendritic regions The microsegregation severity of Ta isincreased with increasing Ta W ratio In addition Ta and Ti tend to partition to phase while Mo W Co and Cr tend to partition to matrix phase The Al element has more tendency to partition to matrixphase Brody Felemings segregation model showed a better correlation to the present experimental dataof the SX PWA1483 superalloy The solidification path and sequence of experimental alloys werecalculated according to equilibrium condition and non equilibrium conditions such as Scheil and Brody Felemings models with Thermo calc software In order to describe the segregation behavior of alloyingelements in SX superalloys in relation with Ta W ratio and eutectic volume fraction a new segregationmodel was presented in this study according to Modified Brody Felemings segregation model Themicrostructural characterization of the as cast samples showed that by increasing the Ta W ratio microporosity is decreased while the volume fraction of TCP and eutectic phases increased Thesuperalloy with the Ta W of 1 showed the best homogeneous distribution of alloying elements in both and phases with no sign of stray grain defect Also the results showed that the size and valume fractionof micropores was decresed the size of precipitates was reduced and hence the stress rupture life wasincresed with increasing Ta W ratio The superalloy with the Ta W of 1 5 showed the minimummicroporosity 18 2 m and maximum stress rupture life 34 h The superalloy with the Ta W of 1showed the most uniform microstructure and stress rupture behavior It seems that presence of the phase topologically closed packed TCP is the main reason for decreasing the stress rupture of SXsuperalloys as micro pores is initiated within the TCP phases and also the interface of TCP and matrix Keywords Single crystal superalloy PWA1483 Solidification sequence Ta W ratio Segregationbehavior Creep behavior TCP phases Bridgman Thermo calc software

بروني، علي

بهبود ريزساختار و خواص مكانيكي سوپرآلياژ پايه نيكل PWA1483 تك كريستال از طريق اصلاح تركيب شيميايي

سوپر الياژ پايه نيكل تك كريستال , PWA1483 , مسير انجماد , رفتار جدايش , اصلاح تركيب شيميايي , نرم افزار ترموكلك , روش بريجمن , نسبت Ta/W , رفتار خزشي , فازهاي TCP