Tribological behaviors of LDED Inconel 718 samples polished with a hybrid laser polishing technique

Abstract

A hybrid laser polishing technique consisting of pulsed laser and continuous wave laser was utilized to polish the surface of laser directed energy deposition (LDED) Inconel 718 samples. The resulting surface morphology, microstructure and tribological performance of the polished samples were analyzed. The results showed that an increase in the average thickness of the remelted layer to 50 μm while preserving the columnar microstructure. However, the grain size was reduced. Additionally, the wear rate at 25 °C decreased remarkably by 70.9%, decreasing from 4.5 × 10−3 mm3/(Nm) for the as-fabricated sample to 2.2 × 10−3 mm3/(Nm) for the polished sample at 600 °C. Furthermore, there was a significant decrease in the average coefficient of friction from 0.42 for the as-fabricated sample to 0.29 for the laser-polished sample. To investigate the wear resistance enhancement mechanism of laser polishing, methods such as scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDS), X-ray diffraction (XRD) and electron backscatter diffraction (EBSD) were utilized. The results indicated an increase in the Nb and Mo element concentration in the surface layer of the LDED Inconel 718 sample after laser polishing, resulting in the formation of small-sized and homogeneously distributed fine grains with low angle boundaries in the precipitated phase. These features effectively prevented the growth of fatigue cracks and ultimately led to a significant enhancement in wear resistance.

Keywords

• Inconel 718
• Laser polishing
• Surface roughness
• Microstructure
• Tribological performance