5 Dec 2017 @ 11am: PhD Colloquium by Mr. Hariprasad G

Name of student   :  Mr. Hariprasad G
Thesis Title      : “Synthesis, microstructural stability and high temperature  deformation of alumina carbon nanotubes composites”
Faculty advisor   :   Prof. Atul H Chokshi 
Date              :   Tuesday   5th December 2017
Time              :   11.00 A.M
Venue             :    Materials Engineering Lecture Theatre

Alumimium oxide is a structural ceramic material which finds numerous applications in diverse fields.  Poor fracture toughness and high temperature formability are difficulties that restrict its widespread use. Carbon nanotubes (CNT) are possibly ideal reinforcements to overcome some of these shortcomings.  However, a uniform dispersion of carbon nanotubes in alumina poses a significant challenge, which needs to be addressed to realize the potential benefits offered by CNT reinforcement.  This thesis deals with processing techniques to obtain a uniform, well dispersed CNT dispersed alumina composite.  The microstructural stability is assessed through high temperature grain growth experiments.  It is observed that with relatively small CNT additions,the matrix grain size is stabilized to a submicrocrystalline size regime.  A limiting grain size is observed in all composites  above  a nominal CNT volume fraction.  The influence of CNTs in the grain growth behaviour is analyzed through a grain boundary dragging model and the effect of the CNT volume fraction on the limiting grain size is understood using a geometrical model.  The high temperature deformation behaviour of the composites is studied using constant load compression creep experiments.  Steady state creep behaviour is observed for all composites.  At modest temperatures and applied stresses the composites deform with fairly high strain rates.  The influence of CNT reinforcement and the effect of volume fraction is analysed by comparing results with creep data for pure alumina.  In conjunction with microstructural characterization and experimental determination of creep parameters, the deformation mechanism of CNT reinforced alumina composites is deduced as Coble diffusion creep and interface reaction controlled Coble creep.  Based on the recent diffusivity measurements obtained from the literature, it was observed that the creep data agreed well with the theoretical predictions from a Coble creep deformation.

Tea and Coffee: 10.45 AM