Effect Of The Scanning Speed On Microstructural Evolution And Wear Behaviors Of Laser Cladding NiCrBSi Composite Coatings

As one of the most important technologies in improving the surface characteristics of materials and rapid prototyping, laser cladding has lots of advantages such as high efficiency、low cost、low heat affected zone、pollution-free, which has proved the noticeable economical profit and was widely used in the fields of mechanical manufacturing. However, the quality of cladding layer is the development of the laser cladding technology barrier. Laser cladding process parameters is the most important factors determining the macro-mechanical properties of the composite coating. Therefore this article has emphatically studied on the scanning speed parameter on the influence of cladding layer.In this paper, laser cladding composite coatings were fabricated on the surface of the Ti6Al4 V substrate by fiber laser cladding the NiCrBSi alloy powder. The influences of scanning speed on the coating performance of many aspects, such as macro morphology, phase composition, microstructure, micro-hardness, friction performance. The coating composition, microstructure and phases were investigated in detail by optical microscopy(OM),scanning electron microscopy(SEM) coupled with energy dispersive spectroscopy(EDS) and X-ray diffraction(XRD). The comprehensive mechanical properties of the coatings under different scanning speed, such as micro-hardness, fracture toughness and wear resistance were analyzed. Fracture toughness of the coatings was tested to evaluate cracking susceptibility by the Vickers indentation method with the help of optical microscope. Dry sliding friction tests were carried out on a CFT-I ultra-functional friction and wear testing machine to evaluate the wear properties of the coatings under different scanning speed. The research was mainly focused on the phase composition of the coatings and its formation mechanism, and in the light of dilution rate the effect of the scanning speed on microstructural evolution was analyzed. The results indicated that NiCrBSi composite coatings with uniformly dense microstructure and possess excellent bonding with the substrate. Results indicated that the dilution rates of the coatings were similar(about 64.23%) with variations in scanning speed ranging from 5 mm/s to 15 mm/s. An abrupt decrease in dilution rate(37.06%) was observed at the scanning speed of 20 mm/s. Microstructural observation showed that the blocky TiB2 and the cellular dendrite TiC particles were uniformly dispersed in the TiNi-Ti2 Ni dual-phase intermetallic compound matrix at scanning speeds of 5 mm/s to 15 mm/s. When the scanning speed was further increased to 20 mm/s, the stripe-shaped CrB, gray irregular-shaped Cr3C2 and black blocky TiC particles uniformly dispersed in the ?(Ni) matrix were synthesized in situ. The particles became finer with the increase in scanning speed. The average microhardness of the coating(1026.5 HV0.2) at the scanning speed of 20 mm/s was enhanced significantly compared with that of the other three coatings(about 886.4 HV0.2). The lowest average friction coefficient(about 0.371) was obtained at the scanning speed of 20 mm/s and was relatively stable with the change in sliding time. The lowest wear loss of the coating was also obtained at the scanning speed of 20 mm/s. Analyses of the worn surfaces showed that the coating prepared at the scanning speed of 20 mm/s was in good condition because of its excellent combination of resistance to micro-cutting and brittle debonding. Comparatively speaking, the coating produced at the scanning speed of 20 mm/s possessed excellent comprehensive mechanical properties.