Wetting and spreading of NiTi melt on graphite and carbon felt

Abstract

Experiments were carried out on the wetting and spreading of the nitinol melt over the polished surface of high-density pure graphite. The furnace heater and the dispenser from which the melt was extruded were also made of graphite of the same quality. The measurements were carried out in vacuum of 10−3 Pa at a temperature close to the melting point and higher, up to 1430 °C. High-speed filming of the transferred drop was used simultaneously with high-speed thermal imaging. As a result, the kinetics of the spreading of the nitinol melt over the graphite surface was obtained, and the surface tension was also measured by the pendant drop method. The dissolution of carbon in the melt prevents the formation of a barrier layer of titanium carbide. Electron microscopic studies confirmed the formation of a dense layer of titanium carbide on the contact surface. An experiment was carried out on the melting of nitinol on carbon felt at a temperature of 1350 °C. It is shown that nitinol's drop on felt with a density of about 100 kg/m3 (porosity 93%) does not impregnate into the felt, retains volume and shape for more than 15 min. This indicates that carbon felt or cloth may be good candidates for lining materials.