Surface hardening of titanium by laser nitriding

Nitriding and related hardening of titanium(Ti) and its alloys were investigated as anew method of laser surface treatment by using a pulsed Nd:YAG laser of 1.06 μm wavelength with 3.6 ms pulse width. When a laser beam was irradiated on Ti plate in nitrogen(N) atmosphere, it was found that a flat and smooth surface covered with TiN nitride layer could be produced by selecting a good combination of laser irradiation conditions such as beam energy, power density and the distance from the lens focal point to the material surface. Compared with Ti base metal having a Vickers hardness(Hv) of about 200, the hardness of the laser-nitriding surface could exceed about 700 Hv at a single pulse shot and increase up to 1700 Hv at overlap of twenty shots, and besides the fusion zone could be hardened up to about 400 to 700 Hv. These hardening mechanisms were interpreted in terms of the formation of TiN nitride layer on the surface and the enrichment of nitrogen in the fusion zone. Nitriding and hardening phenomena were observed as well in the case of titanium alloys such as Ti-6Al-4V and Ti-6Al-6V-2Sn. Moreover, it was confirmed that nitriding and hardening of Ti and its alloys were feasible by the use of a CW CO2 laser.Nitriding and related hardening of titanium(Ti) and its alloys were investigated as anew method of laser surface treatment by using a pulsed Nd:YAG laser of 1.06 μm wavelength with 3.6 ms pulse width. When a laser beam was irradiated on Ti plate in nitrogen(N) atmosphere, it was found that a flat and smooth surface covered with TiN nitride layer could be produced by selecting a good combination of laser irradiation conditions such as beam energy, power density and the distance from the lens focal point to the material surface. Compared with Ti base metal having a Vickers hardness(Hv) of about 200, the hardness of the laser-nitriding surface could exceed about 700 Hv at a single pulse shot and increase up to 1700 Hv at overlap of twenty shots, and besides the fusion zone could be hardened up to about 400 to 700 Hv. These hardening mechanisms were interpreted in terms of the formation of TiN nitride layer on the surface and the enrichment of nitrogen in the fusion zone. Nitriding and hardening phenomena wer...