Electrochemical boriding of titanium for improved mechanical properties

In this study, we introduce a rapid boriding technique that can produce very thick titanium diboride (TiB₂) layers on titanium substrates. We also discuss the effects of process duration on boride layer thickness, chemistry and, morphology. In our experiments, the boriding of commercial purity titanium (CP-Ti) substrates was carried out in an electrochemical cell in which we used a mixture of sodium tetraborate and sodium carbonate as the base ingredients of molten electrolyte at 950 °C and at current density of 300 mA/cm². The titanium test pieces were attached to the cathode holder of the electrochemical cell while a graphite crucible served as the anode. Both TiB and TiB₂ phases were detected by X-ray diffraction method even after 5 min of treatment. Scanning electron microscopy (SEM) images verified that the production of 4.5 µm thick TiB₂ layers was feasible after boriding for an hour. The boride layers consisted of a homogeneous TiB₂ phase on the top and TiB whiskers toward the substrate. The micro-indentation studies indicated that the layer on top has hardness values as high as 40 GPa. The main advantages of this technique are its ability to produce very thick and hard TiB₂ quickly and to create no gaseous emissions or solid wastes during or after the treatment.