Microstructure and wear of in-situ Ti/(TiN + TiB) hybrid composite layers produced using liquid phase process

• In-situ Ti/(TiN + TiB) hybrid composite layers were synthesized by TIG processing on commercially pure titanium.
• The microstructure features were characterized by several methods.
• Microhardness enhanced three to five times higher than that of the CP-Ti substrate after surface modification.
• The fabricated composite layers improved wear resistance of CP-titanium.
• Severe adhesive wear mechanism of CP-titanium surface changed to mild abrasive one as a result of the surface modification.

Tungsten inert gas (TIG) technique was conducted on commercially pure (CP)-Ti substrate, which was coated with h-BN-based powder mixture prior to the treatment. The treated surfaces were evaluated and characterized by means of scanning electron microscope (SEM), X-ray diffraction analysis, and electron dispersive spectrometry (EDS). The microhardness and wear experiment were also performed by using a microhardness machine and pin-on-disk tribometer. As h-BN reacted with titanium, an in-situ hybrid composite layer was formed showing near stoichiometric dendrites of TiN, platelets of TiB and interdendritic regions of α′-Ti martensite crystal structures. The population level of TiN and TiB regions were found to increase using a pre-placed powder mixture with greater h-BN content. However, the fabricated layers exhibited cracking and porosity; these were minimized by adjusting arc energy density and h-BN content of powder mixture. The microhardness value of the fabricated hybrid composite layers was found to be in the range of ∼650 HV0.2–1000 HV0.2; this is three to five times higher than that of the untreated CP-Ti substrate. In addition, the in-situ hybrid composite layers exhibited superior wear behavior over CP-Ti substrate; this is attributed to the formation of newly formed ceramic phases in the solidified surface layers and good coherent interface between the composite layer and CP-substrate. Meanwhile, severe adhesive wear mechanism of CP-titanium surface changed to mild abrasive one as a result of surface treatment.