The laser clad TiB-TiC/TiNi-Ti2Ni intermetallic matrix composite coating has a uniform microstructure and is metallurgically bonded to the TA15 titanium alloy substrate, as indicated in Fig.1. Only a few pores and incompletely dissolved B4C particulates are observable in the coating. As indicated in Fig.2, the phase constituents mainly consist of TiNi(M), Ti2Ni, TiB and TiC.
Fig. 1 OM micrograph showing overview longitudinal cross-section (a) and SEM micrograph showing microstructure in coating/substrate transition zone (b) of laser clad coating on substrate of TA15 titanium alloy
Fig. 2 X-ray diffraction pattern of laser clad coating
SEM micrographs of a gently etched compositecoating, as shown in Fig.3, clearly reveal the morphology of each phase. The flower-like TiB-TiC eutectic ceramics are dispersed in the dual-phase intermetallic matrix which is mainly composed of the TiNi dendrite (49.43Ti-48.80Ni-1.18Al-0.59V according to the EDS analysis in mole fraction,%) andinterdendritic TiaNi (62.75Ti-31.39Ni-5.26A1-0.60V). The dark regions in Fig.3(c) by the electron back scattering TiB-TiC eutectic ceramics are due to low atomic mass of light elements B and C.A more detailed SEM image of the dual-phase TiB-TiC ceramic microstructure is shown in Figs.3(b) and(d). It is clear that the eutectic consists of coarse needle TiB with hexagon cross section and near-equiaxed TiC particulates. Quantitative image analysis shows that the volume fraction of TiB-TiC eutectic is approximately 8%.
Fig. 3 SEM images showing typical microstructures of laser clad coating (a, b), electron back-scattering micrograph (c) and detailed SEM image of TiB-TiC eutectic (d)
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