Fe-based bulk glassy alloy properties indicates that coatings can represent good applications opportunities for metallic glasses. The Fe72Nb4Si10B14 (at%) bulk metallic glassy (BMG) alloy in order to produce coatings over AISI 1020 mild steel substrate using spray forming and laser cladding processing routes. For the spray forming process an additional Ni brazing alloy was applied on the substrate before the deposition to improve adhesion. For the laser cladding process, different laser parameters, power (W) and scanning speed (mm/s), were tested, using a Yb fiber laser (up to 2kW), to verified the best condition for to obtained the coatings [1]. The coatings was characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM) and differential scanning calorimetry (DCS). The Fe72Nb4Si10B14 and Ni59Nb35Sn6 (at%) coatings obtained by spray forming presented high fraction of amorphous phase when produced with thickness up to 1 mm), some porosity and low oxidation level. XRD analysis showed Fe-α, Fe23B6 and halo of amorphous phase, depending on thickness. In addition, these coatings presenting partial or complete glassy structure with high hardness around 1150 HV. The amorphous overspray powder of the BMG alloy obtained by spray forming, grain size < 45 µm, was used in order to produce coatings on AISI 1020 mild steel substrate by laser cladding of the pre-placed powder. SEM micrographs of the clad tracks showed that at 200 W and 100 mm/s, no crystalline phases were observed, indicating maintenance of glassy phase due to high glass forming ability (GFA) of this alloy. XRD analysis showed only halo of amorphous phases in this condition. Moreover, for higher powers and same scanning speed, the diffractograms showed halo of amorphous phases and the Fe-α and FeNbB crystalline phases. The coatings showed hardness ranging from 340-1180HV, depending on laser parameters. These results suggesting that processing routes are promising to fabricate coatings for industrial applications.

Figures:

SEM micrographs of cross-section of the single clad track obtained from Fe72Nb4Si9B15 (at%) alloy in the pre-placed powder at (a) 200 W with 100 mm/s and microstructure of the clad track center, (b) coating/substrate interface at 400 W with 10 mm/s.

SEM image (a) in BSE signal of Ni59Nb35Sn6 (at%) laser cladding track showing nanocrystalline phase (dark) embedded in an amorphous matrix (bright), and X-ray mapping through EDS showing distribution of elements: (b) Fe-K, (c) Nb-L e (d) Ni-K.

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EMC Abstracts - https://emc-proceedings.com/abstract/ferromagnetic-nanocrystalline-coatings-over-steel-trough-laser-cladding-of-fe-and-ni-based-glass-former-alloys/