Effect of B on improving wetting and imbibition of sintered porous Ta by Cu melt

Highlights: • Liquid Cu doesn't wet oxidized Ta. • Wetting and imbibition of Ta by liquid Cu can be critically improved by adding B to the melt. • Activation energy of spreading Cu(2 at.%B) on porous Ta is close to activation energy of TaB2 formation. • Wetting of Ta by Cu(2 at.%B) is reactive, with TaB2 formation and kinetic law changes with temperature. -- Abstract: The present study focuses on the interaction between copper melts and porous tantalum plates (purity, 99.99 wt% Ta). The samples were prepared by sintering tantalum powder with different grain size and were characterized by 65% porosity. A procedure to perform direct observations of the interaction between the melt and plates was developed. Equipment for high-speed recording of dipping of the samples into the melt was designed. The frame rate was up to 5000 fps. A high-vacuum furnace with a graphite heater was used. Wetting experiments were performed in the temperature range of 1100–1400 °C. As expected, at temperatures near 1150 °C the tantalum cake coated with an oxide layer is not wetted by pure copper and does not imbibe it. Rising temperature slightly improves wetting. Doping the copper melt with 2 at.% B at 1150 and 1275 °C reduced the contact angle to 60° it dropped below 25° at 1400 °C. The reason for the observed phenomenon was that doping with boron results in reactive wetting and formation of tantalum boride. Wetting of the porous samples was compared to wetting of cast tantalum plates. The kinetics of imbibition with Cu(B) melt were recorded. The imbibition dependence changed from power-law to linear one as temperature increased from 1275 to 1400 °C. This behavior is associated with degradation of the tantalum boride layer.