Growth kinetics of titanium borides produced by CRTD-Bor method

Abstract

Abstract In this study, a new boriding method called CRTD-Bor (Cathodic Reduction and Thermal Diffusion based boriding) was applied to titanium in a systematic manner and the effects of boriding process parameters on the morphological and chemical state of boride layers were explored. The presence of both TiB and TiB2 phases was confirmed by the X-ray diffraction technique. The cross-sectional examination of borided titanium verified the boride layers consisted of a homogeneous TiB2 phase on the top and TiB whiskers toward the substrate. Moreover, the growth kinetics of the TiB2 layers forming on titanium substrates was investigated during CRTD-bor which was performed at a constant current density of 200 mA/cm2 in a borax based electrolyte at temperatures ranging from 900 to 1100 °C for periods of 15 to 120 min. The rate of the TiB2 layer formation was found to have a parabolic character at all applied process temperatures. The activation energy (Q) and the pre-exponential factor (Ko) of the TiB2 layer were determined as 189.9 kJ/mol and 4.66 × 10− 7 m2 s− 1, respectively. The specific empirical equation that can be used to estimate the thickness of the TiB2 layers (dTiB2) for the conditions explored in the study is d TiB 2 = 682.67 exp − 22833 / T t 1173 K ≤ T ≤ 1373 K ; 200 mA / cm 2 .