Anna Goral and colleagues investigated the influence of laser treatment on the corrosion resistance of the Cr3C2-25(Ni20Cr) cermet coating on the Al7075 substrate. They showed that laser treatment has a significant influence on the surface structure of the cermet coatings. For the lowest laser spot speed (i.e., 600 mm/min), they obtained the flattest and compact cermet surface on the Al7075 substrate. While, the corrosion rate was also reduced by more than two times compared to highest speed of laser spot. Their study recently appeared in the Journal Materials.
Cold sprayed is a coating deposition method. In this method, solid powders are accelerated in a supersonic gas jet to velocities up to 1200 m/s. During impact with the substrate, particles undergo plastic deformation and adhere to the surface, thereby forming a continuous coating.
The Al7075 alloy is a high-strength aluminum alloy that is comparable to many types of steel; it is applicable as aircraft fittings, shafts, gears valve components, and many other structural parts. However, this alloy has lower corrosion resistance than other aluminum alloys. This issue can be solved by the development of the ceramic coating with the improved corrosion resistance of the Al7075 alloy.
Now, Anna Goral and colleagues investigated the influence of laser treatment on the corrosion resistance of the Cr3C2-25(Ni20Cr) cermet coating on the Al7075 substrate (Cr3C2-25(Ni20Cr)/Al7075).
They first produced the Cr3C2-25(Ni20Cr)/Al7075 coatings by the cold sprayed (CS) method. Later, these coatings were irradiated with a laser spot speed of 600 mm/min, 800 mm/min, and 1000 mm/min. Finally, the Cr3C2-25(Ni20Cr)/Al7075 surface was subjected to the corrosion test in an acid chloride solution (1.2 M Cl¯). The exposure time of the specimen was five hours.
They showed that laser treatment has a significant influence on the surface structure of the cermet coatings. For the lowest speed (i.e., 600 mm/min), the flattest, regular, and compact cermet surface on the Al7075 substrate was obtained. However, the Vickers microhardness of the cermet coatings was decreased as the speed of laser irradiation was increased.
They also observed highest polarization resistance, thus, lowest corrosion damage (i.e. only 0.46 CR mm/year, as shown in Table 1 & 2 above) for the Cr3C2-25(Ni20Cr)/Al7075 surface, which was subjected to laser processing with a laser spot speed of 600 mm/min. In this case, the Cr3C2-25(Ni20Cr) coating was hardened and sealed as a result of the laser treatment, and the corrosion process of the investigated material was significantly slowed down. Thus, the Cr3C2-25(Ni20Cr) coating protects the Al7075 substrate well against contact with a corrosion environment, i.e., 1.2 M Cl¯.
On the other hand, for the higher laser spot speed, i.e., 800 mm/min or 1000 mm/min were much greater damage to the Cr3C2-25(Ni20Cr)/Al7075 surfaces due to corrosion in the aggressive environment of chloride. Meaning, for the higher speeds, laser treatment significantly reduces the mechanical and anti-corrosion properties of the cermet coatings.
Featured image: Structure of the Cr3C2-25(Ni20Cr) cermet coating on the Al7075 substrate after laser remelting for the spot speed of 600 mm/min: coating topography © Anna Goral et al.
Reference: Scendo, M.; Zorawski, W.; Staszewska-Samson, K.; Goral, A. Influence of Laser Treatment on the Corrosion Resistance of Cr3C2-25(Ni20Cr) Cermet Coating. Materials 2021, 14, 4078. https://doi.org/10.3390/ma14154078
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