טכניון מכון טכנולוגי לישראל
הטכניון מכון טכנולוגי לישראל - בית הספר ללימודי מוסמכים  
M.Sc Thesis
M.Sc StudentGluzer Gali
SubjectInfluence of Processing on the Microstructure and Properties
of Ni-Al2O3 Nanocomposites
DepartmentDepartment of Materials Science and Engineering
Supervisor Professor Wayne D. Kaplan
Full Thesis textFull thesis text - English Version


Abstract

Alumina based nanocomposites have been widely investigated over the last two decades. These materials are based on two types of reinforcing phase; ceramic or metal particles. The goal of this work was to process alumina reinforced with Ni nanoparticles, and to evaluate the microstructural evolution during the different stages of the process in order to understand its influence on the mechanical properties.     Nanocomposites were prepared by infiltration of Ni nitrate, Ni(NO3)2, into fired alumina green bodies, followed by reduction and sintering. In order to understand the influence of multiple infiltration-reduction stages on the microstructure, samples were characterized both after reduction and after sintering. The second infiltration and reduction stage resulted in a narrower distribution in the size of the Ni particles. This was explained by the sessile drop experiment, which showed dissolution of the Ni particles into the Ni nitrate solution during the second infiltration, resulting in a higher effective Ni concentration in the solution and additional nucleation events during drying. In addition, heat treatment showed that nickel diffusion occurred before reaching the sintering temperature. Therefore the second infiltration does not prevent the growth of the Ni particles from nano -to submicron size. While doping alumina in MgO reduces the sintering temperature and enhances the densification, it promotes Ni particles occlusion. The influence of the occluded Ni particles on the strength of the nanocomposites was clearly shown form three point bending tests. The highest Weibull modulus (13.4) and highest strength (637±77[MPa]) were measured for a specimen which was sintered in He at 1400°C for 4 hours. This specimen had the lowest theoretical density of ~95%, but the lowest amount of Ni particles occluded within the alumina grains. Sintering in He at 1600°C for 4 hours resulted in 30% of the Ni particles occluded in the alumina, and a theoretical density of 99%. The Weibull modulus was reduced to 11.7 and the strength was reduced to 531±185 [MPa]. The occluded particles, in the case of Ni/alumina nanocomposites, have a negative effect on the strength of the material.