Tribological behaviors of Ti–6Al–4V alloy with surface plasma molybdenized layer

Titanium alloys are important structure materials for the manufacturing of aircraft and aerospace craft due to its high specific strength. However, the poor tribological behavior is a major drawback which restricts their actual uses in many circumstances. As an attempt to resolve this problem, a plasma molybdenizing was carried out on titanium alloy Ti–6Al–4V to improve its wear resistance. The morphology, microstructures and composition distribution of the molybdenizing layer were analyzed by scanning electronic microscopy (SEM), X-ray diffraction (XRD) and energy dispersive spectroscopy (EDS). The molybdenizing layer was composed of a deposited sub-layer of 12 μm thick and a diffusing sub-layer of 15 μm thick. Micro-hardness distribution profile along the distance from surface to the center is measured.The tribological behaviors of the surface modified Ti–6Al–4V were investigated by ball-on-disc rubbing experiments under different sliding speeds. The results indicate that the wear resistance of the specimens with molybdenized layer was significantly improved due to the much higher surface hardness. A complete oxide film formed on the surface of wear trace which has an excellent mitigative effect. When the sliding speed changed from lower to higher, the specific wear ratio increased remarkably as a severe plowing took placed.

► Molybdenum as strengthening elements was introduced into Ti–6Al–4V by plasma surface alloying process.
► Molybdenized layer contributed to improved resistance in a wide arrangement of friction velocity.
► Wear mechanisms of molybdenized layer were dominated by oxidation and peeling off.
► Molybdenized layer had guaranteed a modest friction that has been sustained under a much higher speed.