Intermetallic composites of molybdenum disilicide reinforced with various amounts
of silicon carbide particulate were produced by combustion synthesis from their elemental
powders. Elemental powders were mixed stoichiometrically then ball-milled. The coldpressed mixture was then chemically ignited at one end under vacuum at approximately
700°C. The combustion temperature of the process was approximately 1600°C which was
lower than the melting point of molybdenum disilicide. This processing technique allowed
the fabrication of the composites at 700°C within a few seconds, instead of sintering at
temperatures greater than 1200°C for many hours. The end product was a porous composite,
which was densified to >97% ofthe theoretical density by hot pressing. The grains ofthe
matrix were 8-14 μm in size surrounded by SiC reinforcement of 1-5 μm.
The morphology and structure of the products were studied by x-ray diffraction and
scanning electron microscopy (SEM). Samples were prepared for hardness, fracture strength,
and toughness testing at room temperature. There were improvements in the mechanical
properties of the composites with increasing SiC reinforcement. The hardness of the materials
increased from 10.1 ± 0.1 GPa (959 ± 13 kg/mm2) to 11.7 ± 0.6 GPa (1102 ± 52 kg/mm2) to 12.7 ± 0.4 GPa (1199 ± 36 kg/mm2) with the 10 vol% and 20 vol% SiC reinforcement,
respectively. The strength increased from 195±39 MPa to 237±39 MPa with 10 vol% and to 299 ± 43.2 MPa with a 20 vol% SiC reinforcement. The fracture toughness increased from
2.79 ± 0.36 MPa.m1/2 to 3.31± 0.41 MPa.m1/2 with 10 vol% SiC and to 4.08± 0.30 MPa.m1/2
with 20 vol% SiC. The increase in hardness and flexural strength is due to the effective load
transfer across the strong interface in the composites. The main toughening mechanism is
crack deflection by the residual stress in the materials, induced by the differences in the
thermal expansion coefficients and the elastic moduli ofthe matrix and reinforcement. / Thesis / Master of Engineering (ME)
| Identifer | oai:union.ndltd.org:mcmaster.ca/oai:macsphere.mcmaster.ca:11375/29162 |
| Date | 11 1900 |
| Creators | MANOMAISUPAT, DAMRONGCHAI |
| Contributors | Wilkinson, D. S., Petric, A., Materials Science and Engineering |
| Source Sets | McMaster University |
| Language | English |
| Detected Language | English |
| Type | Thesis |
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