Diode laser gas nitriding of Ti6Al4V alloy

Purpose: To produce erosion wear resistant and high hardness surface layers of turbofan engine blades and steam turbine blades made of titanium alloy Ti6Al4V laser gas nitrating (LGN) technology of laser alloying was selected to produce titanium nitrides participations in the titanium alloy matrix surface layers. Design/methodology/approach: Studies on influence of the parameters of laser gas nitriding of titanium alloy and partial pressure of nitrogen and argon in the gas mixture on the surface layers shape, penetration depth, microhardness, erosion wear resistance at different angles of erodent particles stream were conducted. The high power diode laser HPDL with a rectangular laser beam of even multimode intensity on the beam spot was applied in the laser gas nitriding process. Tests of erosion wear resistance were conducted according to the ASTM 76 standard at velocity of the erodent particles stream 70 [m/s], at angles 90 [°] and also 30 [°]. Findings: High quality surface layers of high hardness and erosion wear resistant were produced on the substrate of titanium alloy Ti6Al4V during Laser Gas Nitriding - LGN. Results of the study show that the erosion resistance of laser nitrided surface layers is significantly higher compared with the base material of titanium alloy Ti6Al4V, and depends strongly on the inclination angle of the erodent particles stream. Research limitations/implications: Further investigations of internal stresses in the nitrided surface layers and the fatigue strength of extremely hard surface layers are required, because the fatigue strength is decisive for the functional quality of the surface layers. Practical implications: The investigated technology of laser gas nitriding can be applied for increasing erosion wear resistance of surface layers of turbofan engine blades and steam turbine blades made of titanium alloy. Originality/value: Application of the rectangular diode laser beam spot of multimode and uniform intensity of laser radiation is very profitable in a case of laser surface remelting and alloying because it guarantees uniform heating of the treated surface, consequently uniform thermal cycle across the area of the beam interaction and also uniform penetration depth of the single bead of the surface layer.