Tantalum Diboride Obtained by Reactive Sintering–Properties and Wear Resistance

Abstract

The paper present mechanical properties and wear behavior of tantalum diboride at temperatures in the range from room temperature up to 800°C. The materials for studies were obtained using Spark Plasma Reactive Sintering method from tantalum and boron powders. The mixture was prepared according to the reaction Ta+2B→TaB2. Reactive sintering processes were carried out at temperature of 2100°C during 30 minutes and pressure of 48MPa. During the heating, exothermic synthesis reaction, with visible change of sample height and temperature increase of about 160°C, takes place. The obtained materials have an apparent density of 11.22g/cm3, the Young's modulus of 500 GPa and Vickers hardness of 19.5 GPa. The tribological investigations were carried out using ball-on-disc method in dry friction conditions, at temperatures in the range from room temperature up to 800°C. The influence of temperature on the friction coefficient, specific wear rate and Vickers hardness of sintered materials was determined. In order to study the mechanisms of the surface oxide layer formation, the microstructural analyzes of cross-section were carried out. The values of friction coefficient up to 600°C were stable. The increase of temperature up to 700°C resulted in significant decrease of the friction coefficient to the value of 0.22. The microstructure analysis of the materials indicates that the oxidation of the surface takes place above the temperature of 500°C. The negative effect of the oxides surface layer formation is a gradual decrease of the material surface hardness.