بررسي تاثير فاز ثانويه بر سنتز و خواص مكانيكي تركيب بين فلزي نانو ساختار Ti5Si3

چكيده انگليسي :

107 Study on the Effect of Reinforcement Phases on the Synthesis and Mechanical Properties of Nanostructured Ti5Si3 S Sabooni Email address s sabooni@ma iut ac ir Department of materials engineering Isfahan University of Technology Isfahan 84156 83111 Iran Degree M Sc Language FarsiSupervisors name Fathallah Karimzadeh Associate Professor karimzadeh f@cc iut ac irMohammad Hassan Abbasi Professor abbasi32@cc iut ac irAbstractTi5Si3 intermetallic compound have several advantageous such as high melting point high hardness relativelylow density and high temperature oxidation resistance especially in temperatures lower than 1000 0C MonolithicTi5Si3 has been fabricated by various methods including arc melting of Ti and Si rhock assisted sintering reaction sintering and self propagating combustion synthesis The final product in all of these processes wasbrittle and had low fracture toughness It should be noted that low ductility and fracture toughness of thiscompound is related to low symmetry in crystal structure and highly covalent bonding that increase the peierlsstress Fracture toughness of Ti5Si3 can be overcome by decreasing of grain size to nanometric scale addition ofthird element and uniform distribution of fine stable reinforcements in the matrix It is reported that Al2O3 is agood reinforcement candidate in the intermetallic matrix composite In fact desirable properties of Al 2O3 such aslow density high specific strength and high modulus can provide stiff ceramic inclusions into and intermetallicmatrix such as Ti5Si3 In this study Nanostructured Ti5Si3 was synthesized by mechanical alloying of Ti 62 5Si37 5powder mixture and the effect of Nb was investigated on the formation mechanism and thermal stability of thiscompound Miedema model was used to predict first phase formed in the mechanical alloying of Ti 62 5Si37 5 Afterwards Ti5Si3 Al2O3 nanocomposites with different percentage of reinforcing phase were synthesized andthe effect of diluents was studied on the formation mechanism Nanostructured Ti 5Si3 and Ti5Si3 Al2O3nanocomposites were then cold pressed and sintered at 1400 0C to obtain suitable condensed pieces X RayDiffraction XRD Scanning Electron Microscopy SEM Transmission Electron Microscopy TEM ParticleSize Analyser PSA and Nanoindentation tester were used to characterize produced powders and sinteredsamples According to Miedema model intermetallic compound has the lowest Gibbs free energy compared withsolid solution and amorphous phases and so is the first phase formed in the mechanical alloying of Ti 62 5Si37 5powder mixture Mechanical alloying results showed that nanostructured Ti5Si3 and Ti5Si3 Al2O3 nanocompositewere formed gradually during milling with final crystallite size of 15 and 13nm after 45h TEM results alsoconfirmed nanometric crystallite size of produced powders In situ fabrication of Al2O3 reinforcements byreduction of TiO2 with Al caused fine distribution of nanometric Al 2O3 The macrohardness of bulkNanostructured Ti5Si3 and Ti5Si3 15Wt Al2O3 nanocomposite were evaluated as 950 and 1100 HV Fracturetoughness of these two compounds were calculated as 4 and 5 5 MPa m1 2 respectively Also elastic moduli ofthese two compounds were determined as 187 and 238 GPa respectively It is well known that fracturetoughness of a material is not dependent only to composition but also ability of its microstructure to dissipatedeformation energy without propagation of cracks In brittle materials such as ceramics and intermetallics toughening mechanisms are based on crack deflection and crack bridging These mechanisms were observed inthe Ti5Si3 Al2O3 nanocomposite The higher fracture toughness of Ti5Si3 Al2O3 nanocomposite among otherTi5Si3 based composite transform this material to a good candidate for industrial applications Keywords Intermetallic based nanocomposites Titanium silicides Miedema model Fracturetoughness Nanoindentation

صابوني، سهيل

بررسي تاثير فاز ثانويه بر سنتز و خواص مكانيكي تركيب بين فلزي نانو ساختار Ti5Si3

نانو كامپوزيت زمينه بين فلزي , سيليسايد تيتانيوم , مدل ترموديناميكي مديما , چقرمگي شكست , نانو سختي سنجي