Authors: Ivo Dlouhý, Zdeněk Chlup, Aldo Roberto Boccaccini
Abstract: A number of examples exist that indicate the potential for increasing the toughness of brittle matrices by dispersing different reinforcements. For further development of these advanced materials the actual material response during mechanical loading under presence of flaws appears to be important. Theoretical and experimental knowledge acquired on different kinds of brittle matrix composites is summarised in the paper. These include glass matrix composites with metallic particles, alumina platelets, continuous SiC (Nicalon®) fibres, and both chopped fibres and ZrO2particles (hybrid composites). The composites were tested in as-received state but also after different forms of thermomechanical loading, e.g. thermal shock, thermal cycling in air, which were investigated according to the envisaged composites application. Chevron notch technique was mainly used for fracture toughness evaluation. Microstructural damage is explained based on identified fracture micromechanisms.
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Authors: Sedigheh Salehi, Omer Vander Biest, Jef Vleugels
Abstract: 1.75 mol % Y2O3-stabilized ZrO2-based composites with 35-95 vol % TiN were fully
densified by hot pressing for 1 hour at 1550°C under a load of 28 MPa. The TiN grain size was
found to increase with increasing TiN content, resulting in a decreasing hardness and strength. The
best mechanical properties, i.e., an indentation toughness of 5.9 MPa.m1/2 in combination with a
Vickers hardness of 14.7 GPa and an excellent bending strength of 1674 MPa were obtained for the
composites with 40 vol % TiN. The active toughening mechanisms were identified and their
contribution to the overall composite toughness is discussed. Transformation toughening was found
to be the primary toughening mechanism in all investigated composites.
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Authors: Tao Jiang, Hai Yun Jin, Zhi Hao Jin, Jian Feng Yang, Guan Jun Qiao
Abstract: The machinable B4C/BN ceramics composites were fabricated by hot-pressing sintering
process at 1850oC for 1h under the pressure of 30MPa. The mechanical property, thermal shock
behavior and machinability of the B4C/BN ceramics composites were investigated in this article. The
experimental results showed that the fracture strength and fracture toughness of the B4C/BN
nanocomposites were significantly improved in comparison with the B4C/BN microcomposites. The
Vickers hardness of the B4C/BN nanocomposites and B4C/BN microcomposites decreased gradually
with the increasing content of h-BN, while the machinability of the B4C/BN nanocomposites and
B4C/BN microcomposites were significantly improved. The B4C/BN ceramics composites with the
h-BN content more than 20wt% exhibited excellent machinability. The thermal shock resistances of
the B4C/BN ceramics composites were better than that of the B4C monolith, and the thermal shock
resistance of the B4C/BN nanocomposites was much better than that of the B4C/BN microcomposites.
The thermal shock temperature difference (-Tc) of B4C monolith was about 300oC, while the -Tc of
the B4C/BN microcomposites was about 500oC, the -Tc of the B4C/BN nanocomposites was about
600oC.
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Authors: Yan Jun Wang, Bin Wang, Li Ying Yang, Shou Ren Wang
Abstract: High speed steel based ceramic preforms with three-dimensionally interpenetrated micropores were fabricated using the mixture of TiH2, CaCO3 and stearic acid as pore-forming agent. A self-made vacuum high pressure infiltration furnace was used to infiltrate the preforms with Pb-Sn based solid lubricants to create almost fully dense self-lubrication composites. The microstructure and properties of HSS-based self-lubrication composites were investigated as a function of sintered porosity. A quantitative analysis of microstructure was correlated with crushing strength，microhardness and wear rate to understand the influence of pore size, shape and distribution on mechanical and tribological behavior. Crushing strength and microhardness decreased with an increase in porosity. Meanwhile the decrease in microhardness with increasing porosity was slightly. The friction coefficient of HSS-based self-lubrication composites decreased with increasing the volume fraction of lubricant due to the self-lubrication and unique micropore structure. Within the range of lubricant volume fraction from 0% to 14%, the wear rate of the composites decreased steadily with the increase of lubricant content in the composites. Micropore structure and lubricant volume fraction play an important role in determining wear resistance of the composites whereas the measured bulk properties seem to be of minor importance.
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Authors: Wan Chang Sun, He Jun Li, Qian Gang Fu, Shou Yang Zhang
Abstract: PAN-carbon fibers were pretreated using three methods. 2D-C/C composites were fabricated by a rapid chemical liquid-vaporized infiltration (CLVI) processing. Surface morphologies of carbon fiber pretreated and fracture micrographs of 2D-C/C composites were observed by scanning electron microscopy (SEM) and high resolution transmission electron microscope (HRTEM). The interlaminar shear strength(ILSS) of C/C composites was tested. The influences of carbon fiber surface pretreatments on ILSS and fracture behaviors of C/C composites were analyzed. The experimental results indicated that the C/C composite with carbon fiber coated CVI pyrocarbon possesses both higher flexural strength and interlaminar shear strength than composites with other fiber pretreatments. The fractographes revealed the differences in the mechanical behavior depending on the interface strength of fiber/matrix.
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