Effect of CrB2 addition on densification, properties and oxidation resistance of TiB2

This paper presents the results of detailed studies carried out on the densification of TiB2 with CrB2 as sinter additive by hot pressing. The dense compacts were characterized by measurement of hardness, indentation fracture toughness, flexural strength, coefficient of thermal expansion and electrical resistivity. Oxidation characteristics were investigated between 600 degrees C and 1000 degrees C and isothermal oxidation kinetics at 850 degrees C. Phase identification and surface morphology analysis of hot pressed and oxidized samples were done using XRD and SEM. A high density of 96.61% T.D was obtained with the addition of 2.5% CrB2 by hot pressing at 1750 degrees C under 35 MPa. pressure. Hardness values of composites with 2.5-10% CrB2 were close to 24 GPa and fracture toughness in the range of 3-5 MPa m(1/2). Coefficient of thermal expansion of the composite with 10% CrB2 was measured in the range of 6.21-7.43 x 10(-6)/K from room temperature to 1000 degrees C. Electrical resistivity of TiB2 + 10% CrB2 Was measured as 32.83, 75.97 and 120 mu Omega cm at 25 degrees C, 500 degrees C and 900 degrees C, respectively. Observed nature of oxidation was parabolic for all composites. Formation of continuous and thick glassy film was observed with increased CrB2 content in the composite. TiO2 and CrBO3 phases were identified on the oxidized surface which are responsible for the improved oxidation resistance of this composite. (C) 2009 Published by Elsevier Ltd.