Thermal Conductivity Changes in Titanium-Graphene Composite upon Annealing
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zirconium alloys are very similar in nature.[1] These alloys are used in many high-strength light-weight applications such as aerospace, biomedical, sporting, and nuclear fuel rod cladding.[2] Although the alloys exhibit higher specific strength, corrosion resistance, and fracture toughness,[3] lower thermal conductivity [K~21 W/mK at 300 K (27 C)] limits their applications. In addition, susceptibility to interstitial elements such as H, O, and N is also important for high-temperature applications.[4] We have recently[5] prepared samples of composite of graphene with Ti matrix and determined that the thermal conductivity improved to a value of K = 40 W/mK at 300 K (27 C) when the graphene filler volume fraction is 0.35. The interface thermal conductance between graphene and Ti in the C-direction or normal to the graphene planes is found to be low at 22 MW/m2K; however, its value in the ab plane (normal to the C-axis) was found to be ~440 MW/m2K.[5] Thus, the limitation to the improvement in thermal conductivity of the Ti-graphene composites is associated with the anisotropic thermal
KASICHAINULA JAGANNADHAM, Associate Professor, is with the Department of Materials Science and Engineering, North Carolina State University, Raleigh, NC 27695. Contact e-mail: [email protected] Manuscript submitted August 27, 2015. Article published online December 1, 2015 METALLURGICAL AND MATERIALS TRANSACTIONS A
properties and more so with the smaller size of graphene platelets dispersed in Ti matrix. The inherent higher thermal conductivity of graphene platelets (K~6000 W/ mK)[6,7] is reduced with smaller size, higher thickness, and phonon energy leakage into the matrix.[8,9] Ti-graphene and Zr-graphene composites offer an opportunity to improve the thermal conductivity and widen the scope for favorable applications. In the present work, the effect of thermal treatment of Ti-graphene composite films on thermal properties is investigated. Higher temperature applications require the stability of the microstructure and thus retention of properties. In particular, Zr-graphene composites suitable for nuclear fuel rod cladding are subjected to higher temperature but submerged in water. Our recent work on W-graphene composites[10] deposited on Cu substrate showed stability until the temperature at which W reacted with graphene to form WC. While the formation of WC was not detrimental, the volume change accompanying formation of WC was responsible for nucleation of voids along the interface between the film and Cu substrate. As a result, the increase in interface roughness and loss of good thermal contact were responsible for higher interface thermal resistance between the film and Cu when the films were annealed at 1173 K (900 C) and WC formed. The effective thermal conductance of the W-graphene film is reduced as a result of interfacial interactions. We have prepared Ti-graphene (Ti-gr) composite film on Ti substrate and annealed at different temperatures. The effect of annealing on the thermal properties of the Ti-gr composite film is dete
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