Electroplating of TiB2 in NaF-NaBF4 Eutectic Melt with Titanium Fluoride

TiB 2 -Coated metal should be a very promising material for many purposes. One of the hardest problems on TiB 2 coating is to prevent cracking or stripping by thermal expansion gap between TiB 2 deposit and substrate. In this study, we have investigated the electroplating of TiB 2 in NaF-NaBF 4 eutectic melt(m.p.657K) with Na 2 TiF 6 or TiF 3 . The constant-potential electrolysis was carried out at various potentials. The electrodeposit was obtained at more negative potential than that of reduction of Ti(III) to Ti(II). The result of EPMA and XRD showed that the main ingredient of electrodeposit was TiB 2 . The morphology of electrodeposit changed remarkably at the potential where the cathodic current began to increase sharply in a voltammogram. The flat and adhesive deposit was obtained at more positive potential, while the electrodeposit became powdery at more negative potential. The morphology also changed with time, that is, the protuberant deposit grew with the current increase after a certain time even at the potential where the flat deposit was expected. The monitoring of current was important for depositing the thick and flat layer in this process, and the layer up to 50 μm was obtained under suitable conditions. The dependence ofthe morphology on Ti ion concentration or substrate was not critical in this process.