Surface modification of g-TiAl alloys by acetylene plasma deposition

Surfaces of two g-TiAl alloys, Ti–47 at% Al–2at% Nb–2 at% Cr (MJ12) and Ti–47 at% Al–2 at% Nb–2 at% Mn + 0.8 at% TiB2 (MJ47), have been modified by acetylene plasma deposition at bias voltages of 4, 5 and 6 kV for 3.6 103 s (1 h) and 1.44 104 s (4 h). Knoop hardness (HK) of the alloys is increased with the increase of bias voltage and prolonged time for the deposition. HK of MJ12 and MJ47 deposited at 6 kV for 1.44 104 s is, respectively, 3.36 and 3.32 times as hard as the untreated alloys. SEM and AFM analyses show that the deposited alloys compose of a number of nano-dots which reflect their surface properties. The phases analyzed by XRD are in accord with the elements analyzed by EDX.