Mechanical response of silicon oxycarbide materials processed by spark plasma sintering

Nano- and micro-indentation experiments have been used to evaluate the mechanical properties of dense silicon oxycarbide (SiOC) derived materials obtained by spark plasma sintering (SPS). The sintering temperature varied from 1300 to 1700 degrees C, with a pressure of 40 MPa. The relationship between the mechanical properties and densification, porosity, evolution of the composition, structure and crystallization depending on the SPS sintering temperature has been determined. The SiOC sample obtained at 1400 degrees C shows the highest values of hardness (12 GPa) and elastic modulus (95 MPa) in both nano- and micro-indentation tests. The SPS treatment produces a neat densification of the material without promoting the phase separation of the Si-O-C matrix. In terms of the elasto-plastic behaviour, hf/hmax >0.5 and Wel/Wtot <0.7, in conjunction with AFM images, highlight the negligible formation of pile-ups. The elastic recovery is quite high, and is probably due to the flexible segregated carbon phase. The Vickers indentation patterns show the Hertzian cones typical of anomalous glasses. Some minor radial cracks can also be seen, and can be attributed to the presence of both stiffer Si-C bonds which reduce the propagation of cracks, and to carbon, which reduces the brittleness of the SiOC derived materials.

Automated summary

Nano- and micro-indentation experiments were conducted to evaluate the mechanical properties of dense SiOC materials obtained by SPS. The sintering temperature and pressure were varied, and the relationship between mechanical properties and several factors such as densification, porosity, composition evolution, and crystallization was determined. The SiOC sample sintered at 1400 degrees C showed the highest values of hardness and elastic modulus in both indentation tests. The SPS treatment resulted in neat densification without phase separation of the Si-O-C matrix, and the presence of carbon reduced brittleness.