Research On The Properties And Sintering Behavior Of Titanium Carbide Ceramics Consolidated By Spark Plasma Sintering

Titanium carbide with strong covalent bond is an attractive potential ceramic,which can be used widely in the field of mechanical processing, aerospace and nuclearreactor system because of its high melting temperature, high hardness, high strength,good corrosion resistance, excellent wear-resistance, low neutron absorptioncross-section and good thermal conductivity. However, high sintering temperature andintrinsic brittleness are the biggest limitations for its application. To reduce the sinteringtemperature and improve the fracture toughness, the sintering behavior and properties oftitanium carbide consolidated by spark plasma sintering (SPS) were studied in thispaper.The sintering kinetics of titanium carbide was firstly studied and the sinteringkinetic windows were proposed by analyzing the variation of density and the graingrowth of titanium carbide with sintering temperature. The effect of SPS-importantparameters (sintering temperature, pressure, rate and holding time) on the densificationprocess and mechanical properties of titanium carbide were systematically investigated.The results show that temperature and pressure are the two main factors affecting thedensification and mechanical properties of titanium carbide. The effect of holding timeon grain growth is more significant than on densification. Titanium carbides wereprepared under different sintering rate of20oC/min and175oC/min and no significantdifference of density and mechanical properties were observed.Sintering additives (Al2O3, WC) were used to reduce the sintering temperature ofTitanium carbide. A novel approach was adopted to fabricate the titanium carbide bydoping10wt%Al2O3from Al(NO3)3·9H2O via chemical precipitation method. Itrealized sintering aids coated in-situ onto the surface of the titanium carbide particles.Fully dense titanium carbide ceramic pellets were obtained under50MPa sinteringpressure at1500oC which is about100oC lower than pure titanium carbide with thesame density. Additionally, the sintering temperature of titanium carbide was loweredby150oC with3.5wt%WC sintering aid. The sintering mechanism improved by WCsintering aid was elaborated in detail according to the test results of SEM, XRD andTEM. The hardness, bending strength and fracture toughness of titanium carbide with3.5wt%WC were characterized. It is found that the fracture toughness of titanium carbide with3.5wt%WC is significantly improved. The highest toughness value of6.3MPa·m1/2was obtained at1600oC, which is improved by~47%compared to puretitanium carbide fabricated at the same condition.Silicon carbide (SiC) and carbon nanotubes (CNTs) as toughening agents weredispersed into titanium carbide matrix powders. The improvement in fracture toughnessof TiC-SiC composites can be attributed to the fracture mode transition fromintergranular type to transgranular type caused by the change of residual stressesoriginating from the addition of SiC particles. TiC-CNTs composites with high fracturetoughness were fabricated by combining the ultrasonic co-precipitation in-situ formingand SPS technique. The effect of sintering temperature on densification and graingrowth of was studied and the kinetic windows of TiC-1wt%CNTs composites wereobtained. In addition, the effect of CNTs on the thermal conductivity was studied and35W/m·K thermal conductivity of titanium carbide was obtained with2wt%CNTadditive, exhibiting enhancement by~84%over the CNT-free samples prepared underidentical conditions.