Investigation on the Microstructure Evolution and Properties of a Novel In-Situ Fiber Phase-Reinforced Nickel Composite Coating Deposited by Wide-Band Laser

In this paper, a novel hard nickel composite coatings were fabricated by wide-band laser cladding technique. The effects of Si alloying on the composite coatings were investigated by microstructure characterization, phase identification, microhardness and wear resistance. Results showed that the in-situ precipitated phases in the laser molten pool were composed of the gamma-Ni solid solution and hard phases such as Cr23C6, CrSi, Cr5B3. With the increase of Si element, the morphology of the precipitated phases changed significantly. When the added content of Si was 1.0 wt.%, the precipitated phase was a mainly block morphology. As the added content of Si was increased to more than 2.0 wt.%, the main precipitated phase was transformed into a long stripe morphology. With the increase of Si content, the stripe-like precipitated phase was gradually refined and finally becomes density needle-like precipitates. Element distribution analysis showed that the block precipitated phase was enriched in Cr, W and Si elements. Additionally, the enriched elements in the long strip precipitation phase were essentially the same as those in the block precipitation phase. The added Si element was highly involved in the in-situ reactions of precipitated phase. The TEM results showed that the precipitated phases contained the crystal structures of Cr5B3 and Cr7C3. The pin-on-disc wear tests revealed that the composite coating with the addition of 6 wt.% Si exhibited the best wear resistance in the experimental group. The average friction coefficient was about 0.6 and the wear mass loss rate was about 2.38 x 10-5 g/m under counter-abrasive conditions. The worn surface analysis indicated that the wear mechanism of composite coatings was mainly abrasive wear. The refined needle-like precipitated phase was closely bound to the matrix and thus not easy to peel off, providing a significant improvement in the wear resistance of the laser cladding coatings.