Time dependence of microstructure and hardness in plasma carbonized Ti–6Al–4V alloys

Ti–6Al–4V alloy was treated by plasma carburizing process at 950 °C for different durations of 1 h, 2 h, 3 h, and 4 h. Plasma carburizing was performed in pure Ar gas under 32 ± 2 Pa. Graphite rod was employed as carbon supplier. Optical microscope (OM) observations showed a carburizing layer formed after carburizing. Further FESEM examinations and XRD analysis confirmed that the carburizing layer consists of a TiC/α-Ti mixed layer and a thin compound (TiC) layer on the mixed layer. With increasing the carbonizing time, the thickness of the carburizing layer increased and the specimen treated at 950 °C for 3 h obtains maximum values of the hardness.

► A thin compound layer and a thick mixed layer with the microstructure of TiC and the α-Ti, formed.
► The carbonizing time takes significant effects on the formation of the carbonizing layer.
► The specimen treated at 950 °C for 3 h obtains maximum hardness.