[Show abstract][Hide abstract] ABSTRACT: The mechanical properties of plasma-enhanced magnetron sputtering Si–C–N hard coatings with various compositions are characterized. The effect of chemical composition on the microstructure and properties of coating is investigated. The results show that the microstructure and mechanical properties of Si–C–N coatings are very sensitive to chemical composition. The nanocrystalline/amorphous composite structure is beneficial to the coating's mechanical properties. It also reveals that Si–C–N coating with low Si and high C concentrations has the highest hardness (≥40GPa) and the best wear property with dry friction coefficient about 0.2.
No preview · Article · Oct 2010 · Applied Surface Science
[Show abstract][Hide abstract] ABSTRACT: SiCW/SiC composites without an intergranular glassy phase are prepared by the CVI process. The microstructure and high temperature strength of SiCW/SiC composites are investigated. The high temperature strength of SiCW/SiC composites depends on the interfacial bonding strength between matrix and whiskers. The matrix is effectively strengthened and toughened by the whiskers, and SiCW/SiC composites show a constant strength of 475 ± 32 MPa below 1000 °C. The flexural strength gradually declines from 475 ± 32 MPa to 208 ± 15 MPa at the temperature from 1000 °C to 1500 °C due to the decreased whisker-matrix interfacial bonding strength. The interfacial bonding strength is too low to transfer stress from the matrix to the whiskers, and SiCW/SiC composites show a constant strength of 208 ± 15 MPa at temperatures from 1500 °C to 1800 °C. The fracture mode of SiCW/SiC composites changes from the toughened fracture below 1000 °C to the brittle fracture above 1000 °C.
No preview · Article · Aug 2010 · Materials Science and Engineering A
[Show abstract][Hide abstract] ABSTRACT: 37.2 vol.% SiCP/SiC and 25.0 vol.% SiCW/SiC composites were prepared by chemical vapor infiltration (CVI) process through depositing SiC matrix in the porous particulate
and whisker preforms, respectively. The particulate (or whisker) preforms has two types of pores; one is small pores of several
micrometers at inter-particulates (or whiskers) and the other one is large pores of hundreds micrometers at inter-agglomerates.
The microstructure and mechanical properties of 37.2 vol.% SiCP/SiC and 25.0 vol.% SiCW/SiC composites were studied. 37.2 vol.% SiCP/SiC (or 25.0 vol.% SiCW/SiC) consisted of the particulate (or whisker) reinforced SiC agglomerates, SiC matrix phase located inter-agglomerates and
two types of pores located inter-particulates (or whiskers) and inter-agglomerates. The density, fracture toughness evaluated
by SENB method, and flexural strength of 37.2 vol.% SiCP/SiC and 25.0 vol.% SiCW/SiC composites were 2.94 and 2.88 g/cm3, 6.18 and 8.34 MPa m1/2, and 373 and 425 MPa, respectively. The main toughening mechanism was crack deflection and bridging.
No preview · Article · Jan 2010 · Journal of Materials Science
[Show abstract][Hide abstract] ABSTRACT: A two-process model was developed according to the infiltration-induced structural evolvement in the porous fiber preforms and the physicochemical phenomena involved in the Isothermal Chemical Vapor Infiltration (ICVI) process. The structural evolvement was modeled by representing the void space by a small pore among filaments and a large pore among bundles. The mathematical model was implemented by finite-element method to investigate the effect of the preform structure on the deposition uniformity, processing time and final average density. Calculation results imply that the fiber preform structure plays a dramatic role in determining the deposition uniformity, processing time and final average density. The fiber preforms consisted of filaments and bundles of moderate diameters are preferable by combined consideration of the highest final average density, the relatively low density gradient and the relatively short infiltration time.