Growth kinetics and some mechanical properties of two-phase boride layers produced on commercially pure titanium during plasma paste boriding

Abstract

In this study, the plasma paste boriding (PPB) was applied in order to produce the boride layers on commercially pure titanium (Cp-Ti). PPB process was carried out in 50% H2–50% Ar atmosphere under a reduced pressure at various parameters (temperature and duration). The boride layers consisted of two zones: a continuous TiB2 zone close to the surface and a zone with TiB whiskers below the first one. The growth of both zones obeyed the parabolic growth law. The model of growth kinetics of such layers was analyzed. The parabolic growth constants were calculated and the boron diffusion coefficients were determined. Activation energy values of 123.33 and 178.71kJmol−1 were obtained for TiB2 and TiB phases, respectively. The calculated value for TiB2 phase was lower compared to the other boriding processes. Microhardness profile was determined for the layer of the highest depth. The maximal microhardness was characteristic of TiB2 zone (2452HV). Nanomechanical properties (nanohardness and Young's modulus) were studied using the nanoindenter. TiB2 zone was characterized by the nanohardness of 2867.6HV and indentation modulus EIT=383GPa. Wear resistance of plasma paste borided layers was up to 9 times higher when comparing to the untreated Cp-Ti.