Processing of sintered and CVD coated SiC/CNFs thin composite tubes

Abstract

Silicon carbide (SiC) and its composite powders dispersed with 1–3 wt% carbon nano-fibres (CNFs) were spray freeze granulated to produce spherical granules with uniform composition. Powders were shaped to thin dense tubes for use in a harsh environment by cold isostatic pressing followed by pressureless sintering at 2150 °C for 1 h in argon and SiC coating by chemical vapour deposition (CVD) technique. The physical, microstructural and thermo - mechanical properties of the composite tubes were evaluated and compared with bare SiC tubes. Good dispersibility of CNFs and sintering additives in the matrix by spray freeze granulation processing technique resulted in more than 98.5% theoretical density of the composite tubes with superior mechanical properties. SEM & EBSD analysis show grains are platy and equiaxed in nature with many CNFs trapped at the triple points hindering the SiC grain growth which is also confirmed by TEM analysis. The thermal conductivity value of the composite was also found higher than bare SiC at all temperatures when measured up to 1000 °C due to uniform distribution of CNFs in the matrix.