T. Mahata

Carbothermal route for preparation of boron carbide powder from boric acid–citric acid gel precursor

Abstract Boron carbide (B4C) powder has been prepared by carbothermal process using boric acid and citric acid as raw materials. Aqueous solution of boric acid in presence of citric acid forms a stable gel under controlled pH condition. The gel on subsequent pyrolysis under vacuum yields a precursor powder consisting of boron oxide and carbon. The precursor is heated under vacuum at 50 °C/h up to 1450 °C and the product obtained has been characterized by X-ray diffraction (XRD), chemical analysis, particle size analysis and scanning electron microscopy. XRD pattern shows that the product consists of B4C and carbon (graphite). Presence of free carbon (11.1 wt%) indicates boron loss in the carbothermal reaction. Boron loss has been calculated to be 11.3 wt%. Boron carbide powder obtained is composed of near equiaxial particles of narrow size distribution having a median size of 2.25 μm.

Impression creep behaviour of TiB2 particles reinforced steel matrix composites

ABSTRACT Impression creep behaviour of the powder metallurgy processed steel matrix composites was investigated under constant stress at different temperatures in the range of 873–973 K. By using the power-law relationship, the estimated activation energy for unreinforced steel was found to be 149 kJ mol−1 and steel reinforced with 2 and 4 vol.-% TiB2 was found to be 298 and 338 kJ mol−1, respectively indicating better creep resistance of the reinforced steel matrix composites. Dislocation creep is the dominant creep mechanism based on the calculated values of stress exponent and activation energy. Hence, this method can be used to assess the potential of steel matrix composites for use as structural materials for high-temperature application.