UC Riverside

The growing interest in non-equilibrium processing over the past few decades has led to numerous published works. A few examples of these techniques include rapid solidification, age hardening, mechanical alloying, and severe plastic deformation. This has also led to the creation of new types of materials such as bulk metallic glasses and nanomaterials. This work presents a novel approach for producing non-equilibrium materials in bulk form through a combination of Non-Thermal Plasma (NTP) synthesis and Spark Plasma Sintering (SPS). First, amorphous silicon carbonitride nanoparticles are produced non-thermal plasma synthesis from a combination for gaseous precursors including silane (SiH4), methane (CH4), and ammonia (NH3). A combination of high temperature baking experiments followed by X-Ray Diffraction (XRD), show that the plasma synthesized SiCN can maintain an amorphous phase up to 2000 °C, whereas literature reports a typical crystallization temperature ranging from 1400 °C-1600 °C. However, porosity of these samples remained high, severely impacting mechanical properties, due to N2 outgassing occurring at 1450 °C. A follow up experiment was conducted to consolidate SiCN nanoparticles into a dense, bulk material via SPS with varying degrees of devitrification and segregation of the SiCN into a composite of crystalline SiC/Si3N4. With a custom high temperature, high pressure tooling consisting of SiC punches graphite dies, achieving a density of 3.21 g/cm3. Mechanical testing of the sintered SiCN shows a maximum Vickers hardness of 16.1 GPa, fracture toughness of 2.6 MPa⋅m1/2, and Young’s Modulus of 247 GPa, placing these samples well within the margin of those reported on in literature. Post-sintering analysis shows that the presence of β-SiC nanocrystals after sintering of both samples, with the one sintered at 1600 °C also containing ɑ-Si3N4 and β-Si3N4.