טכניון מכון טכנולוגי לישראל
הטכניון מכון טכנולוגי לישראל - בית הספר ללימודי מוסמכים  
M.Sc Thesis
M.Sc StudentBenes Dahan Dana
SubjectMicrostructure and Mechanical Properties of Silicon Carbide
Based Nanocomposites
DepartmentDepartment of Materials Science and Engineering
Supervisor Professor Wayne D. Kaplan
Full Thesis textFull thesis text - English Version


Abstract

SiC nanocomposites were prepared by infiltration of an ethanol-based solution of nickel nitrate (Ni(NO3)*6H2O) into fired SiC preforms, followed by reduction and sintering by pressureless sintering (PLS) and spark plasma sintering (SPS). During sintering, the Ni reacted with SiC to form Ni2Si. The results show that the sintering technique has an influence on the final density of the nanocomposite and on the mechanical properties. The Ni-SiC nanocomposites that were sintered by SPS reached nearly full density with an average relative density of 100.0%±3.1%TD. The Ni-SiC nanocomposites that were sintered by PLS reached a lower density compared to those sintered by SPS, and compared to monolithic SiC sintered by PLS. The average relative density of the Ni-SiC nanocomposites sintered by PLS is 81.3%±5.0 %TD. The average relative density of the monolithic SiC sintered by PLS and SPS is 94.8%±1.7%TD and 98%±2.8%TD, respectively. The Ni-SiC nanocomposites sintered by SPS exhibited high hardness values of 2594.2±102.0 [Kg/mm2]. Due to the existence of porosity in the Ni-SiC nanocomposite sintered by PLS (~10%), the hardness is lower compared to the samples sintered by SPS and compared to the monolithic SiC sintered by SPS and PLS with an average hardness of 1839.9±48.1 [Kg/mm2]. The monolithic SiC sintered by SPS and the monolithic SiC sintered by PLS have similar flexural strengths of 347.2±33.5 MPa (m=4.8) and 369.9±87.3 MPa (m=3.5), respectively. The low Weibull modulus of both monolithic SiC samples suggests that the ceramics have highly variable fracture strengths. The flexural strength of the Ni-SiC nanocomposite sintered by PLS is lower than the flexural strength of monolithic SiC samples with an average flexural strength of 267.7±44.0 MPa (m=4.1). The low flexural strength is expected due to the low relative density of those samples (80-90%TD). The Ni-SiC nanocomposite sintered by SPS had an average flexural strength of 343.4±117.6 (m=5), which is higher by ~22% compared to the SiC nanocomposite sintered by PLS. Contrary to the hardness results, the flexural strength of the nanocomposite Ni-SiC sintered by SPS is similar to the flexural strength results of the monolithic samples.

The sintering technique has also an influence on the microstructure of the Ni-SiC nanocomposite. The SiC nanocomposite and the monolithic SiC sintered by PLS and the SiC nanocomposites sintered by SPS have uniform equiaxed grains. In the monolithic SiC sample sintered by SPS the grains are much less uniform. The second phase particles prevent AGG in the nanocomposite samples sintered by SPS.