Microstructure performance and formation mechanism of laser alloying rare earth oxides modified nanocrystalline layer on TA7

• LA of Ni60A–Si3N4–Ag–Y2O3 mixed powders on TA7 can form an nanocrystalline layer.
• High scanning speed made existing time of laser molten pool become shorter than before.
• The high scanning speed favored the formation of a fine microstructure.
• Wear resistance of a LA layer with 3 mm/s was good and stable.
• Y2O3 addition favored the formation of the fine microstructure and NP.

Nanoscale particles (NP) were observed in a Ni60–Ag–Si3N4–Y2O3 laser alloying (LA) layer on a TA7 titanium alloy, NP usually locate on the grain boundaries, which are able to block the motion of dislocation in a certain extent. Such layer mainly consisted of γ-Ni, TiN, γ-(Fe, Ni), TiAg and lots of amorphous phases. The wear resistance of such layer with laser scanning speed 3 mm/s was better than that of a LA layer with 6 mm/s, which was mainly ascribed to an uniform microstructure and less defect of layer. The high laser scanning speed made the existing time of laser molten pool be shorter than before, favoring the formation of a fine microstructure. However, the defects, such as pores were produced in LA layer (higher scanning speed), decreasing the wear resistance.