In-situ nitriding on the textured titanium alloy using femtosecond laser

Abstract

Laser texturing has been proven to be an effective method to improve the tribological behavior of titanium and its alloys, while the hardness of the textured surface is still poor. To further strengthen the surface, a two-step laser processing experiment was conducted on Ti6Al4V alloy including femtosecond laser texturing and in-situ nitriding. Firstly, the sample was textured with femtosecond pulses at laser fluence of 6.37 J/cm2 and a repetition rate of 200 kHz. Then, the textured surface was micro-melted and nitrided by irradiation in a nitrogen atmosphere at a low laser fluence of 0.43 J/cm2 and a high repetition rate of 19 MHz. After nitriding, a uniform crack-free TiN coating was prepared on the top of the as-textured structures with thickness of 40–60 μm, and the surface hardness was significantly improved from 336 HV to 1277 HV. The reinforced phase TiN had microstructures of dendrites in the upper region and particles in the bottom region of the nitrided layer. The morphology analysis revealed that only a slight change in height was introduced to the textured structures by femtosecond laser nitriding and the designed functions could be maintained.

Keywords

• Titanium alloy
• Femtosecond laser processing
• In-situ nitriding
• Texturing
• Microstructure
• Microhardness