Effects of La 2O 3 on microstructure and wear properties of laser clad γ/Cr 7C 3/TiC composite coatings on TiAl intermatallic alloy

Abstract

The effects of La 2O 3 addition on the microstructure and wear properties of laser clad γ/Cr 7C 3/TiC composite coatings on γ-TiAl intermetallic alloy substrates with NiCr–Cr 3C 2 precursor mixed powders have been investigated by optical microscopy (OM), scanning electron microscopy (SEM), X-ray diffraction (XRD) and energy-dispersive spectrometer (EDS) and block-on-ring wear tests. The responding wear mechanisms are discussed in detail. The results are compared with that for composite coating without La 2O 3. The comparison indicates that no evident new crystallographic phases are formed except a rapidly solidified microstructure consisting of the primary hard Cr 7C 3 and TiC carbides and the γ/Cr 7C 3 eutectics distributed in the tough γ nickel solid solution matrix. Good finishing coatings can be achieved under a proper amount of La 2O 3-addition and a suitable laser processing parameters. The additions of rare-earth oxide La 2O 3 can refine and purify the microstructure of coatings, relatively decrease the volume fraction of primary blocky Cr 7C 3 to Cr 7C 3/γ eutectics, reduce the dilution of clad material from base alloy and increase the microhardness of the coatings. When the addition of La 2O 3 is approximately 4 wt.%, the laser clad composite coating possesses the highest hardness and toughness. The composite coating with 4 wt.%La 2O 3 addition can result the best enhancement of wear resistance of about 30%. However, too less or excessive addition amount of La 2O 3 have no better influence on wear resistance of the composite coating.