Comparing the surface characteristics of additively manufactured nitinol parts polished by femto-second and CO2 laser

Abstract

One potentially useful technique for producing NiTi intermetallic components is the laser powder bed fusion (LPBF). However, due to the deterioration of the mechanical qualities, other defects including the poor surface quality and the near surface porosity that are inherent to the process are restricting the technology's standardisation and broad use. This study employed a thorough investigation to use laser polishing of additively manufactured samples made from pre-alloyed NiTi powder by LPBF to enhance the surface quality and remove the near surface porosity. The use of laser polishing technique on the LPBF parts is preferred because it eliminates or reduces the amount of material removal through remelting and relocation of material from the high peaks to the lower valleys. Two types of laser systems carbon-dioxide (CO2) and femtosecond were used to process the surface and near-surface area. The optimum results for porosity healing have been found when using the CO2 laser power of 75 W, scanning speed of 11 mm/s and an input energy density of 34 J/mm2 and laser spot size of 200 μm. An improvement in the average surface roughness of 91 % was achieved when the CO2 laser beam was used. The X-ray test results showed slight intensity change for the samples polished by the CO2 laser. In contrast, a phase change was observed on the surface of the samples polished by the femtosecond laser due to the formation of oxide layer. Also, limited improvement in the surface quality was obtained when the femtosecond laser irradiation was used.

Keywords

• Nitinol
• Laser polishing
• Additive manufacturing
• Laser powder bed fusion
• X-ray