Influence of laser scanning speed on nitrided Ti6Al4V surface

Abstract

The influence of laser scan speed during nitriding in the range 30–150 cm min⁻¹ on the physical properties, microstructure and corrosion behaviour of Ti6Al4V was studied. The surface energy of nitrided Ti6Al4V remained almost constant up to the scan speed of 60 cm min⁻¹ followed by an increase in the maximum value at 80 cm min⁻¹. A gradual drop in the microhardness of the coating from the outermost surface was noticed for specimens nitrided up to 80 cm min⁻¹; an abrupt decrease, however, was found at a scan speed ≥100 cm min⁻¹. The laser nitriding produced dendritic microstructure; an exponential decay in the secondary dendrite arm spacing (SDAS) with the increase in laser scan speed was revealed. The SDAS produced was smaller at the interphase and centre of the coating, compared to that at outermost surface. The passivation behaviour of Ti6Al4V at lower potentials shifted to the smaller current side after laser nitriding.