ABSTRACT
Laser gas nitriding process is a widely accepted technique for modifying the surface
structure and composition of titanium and titanium alloys without altering the bulk
properties. In the present work, laser gas nitriding of commercial purity titanium with
continuous wave 3 kW Co2 laser has been investigated experimentally. The aim is to
increase the surface hardness and hence improve related properties such as wear and
erosion. The processing parameters were as follow: 2.5 kW laser power, 15 mm/s
specimen scanning rate, and 17 L/min nitrogen gas flow rate. Single and overlapping
layers were produced and pure and diluted nitrogen gas was used. The results indicated
that laser surface melting of pure titanium in nitrogen atmosphere produced unevenly
distributed TiN of dendritic morphology extended to a depth of ~ 0.5mm. The volume
fraction of the TiN dendrites decreased gradually with increasing depth from the
surface. As a result of TiN formation, the hardness increased substantially. Diluting the
nitrogen gas with argon gas was found to have a beneficial effect in decreasing cracking
but decreased the resulting hardness level and the nitrided depth.
KEYWORDS: Laser hardening; CP Titanium, XRD; Microstructure.