Influence of CeO2 addition on forming quality and microstructure of TiCx-reinforced CrTi4-based laser cladding composite coating

Abstract

TiCx-reinforced CrTi4-based composite coatings were successfully fabricated on a Ti6Al4V titanium alloy surface via laser cladding technology by using coaxial Ti6Al4V/NiCr-Cr3C2 mixed powders with different CeO2 contents (0, 1, 2, 3, and 4 wt%). The influence of CeO2 addition on the forming quality, phase composition, microstructure, and elemental distribution of the laser cladded coatings was investigated via penetrant flaw detection, optical microscopy, X-ray diffraction, scanning electron microscopy, energy spectrum analysis, electro-probe microanalysis, and transmission electron microscopy. The results showed that CeO2 addition can inhibit the formation of cracks and pores. The least number of cracks and pores were observed upon the addition of 2 wt% and 3 wt% of CeO2, respectively. The phases in the coatings consisted of vacant titanium carbide (TiCx) and β solid solution (CrTi4). The morphologies of TiCx in the transition, cladding, and bonding zones exhibited distinct granular, dendritic, and short needle-like differences, respectively. Notably, the addition of CeO2 did not affect the phase composition, but it significantly influenced the content of dendritic TiCx. The dendritic TiCx content was minimum (35%) for a CeO2 content of 3 wt%. The dendritic TiCx was mainly enriched by Ti and C, and the content of C in primary dendrites was higher than that in secondary dendrites. The Ce and O atoms from CeO2 decomposition were recrystallised as CeO2 and Ce2O3, and distributed in the interphase boundary between TiCx and CrTi4, within the TiCx and CrTi4 grains, and at their grain boundaries. The Al, V, and Cr elements were uniformly distributed in the matrix phase (CrTi4), while elements Ni and Cr appeared segregated.