Characteristics and growth kinetics of plasma paste borided Cp–Ti and Ti6Al4V alloy

Abstract

In the present study, CpTi and Ti6Al4V alloy were successfully plasma paste borided using borax paste. The process was carried out in a dc plasma system at temperatures of 973, 1023 and 1073K for 3, 5 and 7h in a gas mixture of 70% H2–30% Ar under working pressure of 5mbar. The properties of the boride layers were evaluated by scanning electron microscopy, X-ray diffraction and the micro-Knoop hardness tester. Growth kinetics of the titanium boride layers on the Cp–Ti and Ti6Al4V alloy were obtained by analyzing the experimental results and parameters including the thickness of boride layer, correspondent diffusion temperature and holding time. The presence of both TiB2 top-layer and TiB whisker sub-layer was confirmed by the X-ray diffraction and scanning electron microscopy techniques. The formation rate of the dual titanium boride layers was found to have a parabolic character at all applied process temperatures. The surface hardness of TiB2 layer ranged between 2077 and 2373 HK0.025. The activation energies of boron in Cp–Ti and Ti6Al4V alloys were calculated as 93.61 and 99.79kJ·mol−1, respectively depending on the temperature and layer thickness.