According to the aforementioned results of wear mass loss and worn morphologies shown from Fig.5 toFig.8, it can be concluded that although the average hardness value(HV580) is not very high, the laser clad coating exhibits an excellent wear resistance compared with the reference material TA15 under dry sliding wear test conditions. This outstanding tribological property is the outcome of combined action of hard TiB-TiC eutectic ceramic reinforcements and ductile TiNi-Ti2Ni dual-phase intermetallic matrix.
On one hand, the TiB-TiC ceramic reinforcements make an important contribution to resisting the abrasive and adhesive wear in the process of the dry sliding owning to the high hardness and strong covalent atomic bonds. When the asperities on the coupling counterpart surface encounter the mixture of TiB-TiC illustrated in Fig.1(a), the hard TiB-TiC ceramics could smash them to weak the degree of abrasive wear effectively. Meantime, the unique binary-phase ceramic eutectic microstructure improves itself efficiently the toughness of monolithic ceramic, and hence avoids brittle fracture of ceramic particles to some extent.
Fig. 1 Schematics of main wear process observed on worn surface of laser clad coating: (a) Initial stage of wear process; (b) Wear process after forming transferred layers
On the other hand, the existence of TiNi-Ti2Ni dual-phase intermetallic matrix having excellent properties of ductility and toughness plays a dominate role in preventing TiB-TiC ceramic particles from removal by toughening them and relieving the stress concentration. The excellent interfacial bonding betweenthe in-situ formed TiB-TiC and TiNi-TizNi intermetallic matrix ensures the smoothness of the worn surface as shown in Fig.8 and enhances the wear resistance of the laser clad coating.
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