Influence of Laser Treatment on the Corrosion Resistance of Cr3C2-25(Ni20Cr) Cermet Coating

The influence of the laser treatment on the corrosion resistance of the Cr3C2-25(Ni20Cr) cermet coating on the Al7075 (EN, AW-7075) substrate (Cr3C2-25(Ni20Cr)/Al7075) was investigated. The coating was produced by the cold sprayed (CS) method. The tested coatings were irradiated with a laser spot speed of 600 mm/min, 800 mm/min, and 1000 mm/min. The mechanical properties of the Cr3C2-25(Ni20Cr)/Al7075 were characterized by microhardness (HV) measurements. The surface and microstructure of the specimens were observed by ascanning electron microscope (SEM) and other assistive techniques. The corrosion test of materials wascarried out by using the electrochemical method in the acidic chloride solution. Cermet coatings perfectly protect the Al7075 substrate against contact with an aggressive corrosion environment. The laser remelting process of the Cr3C2-25(Ni20Cr) layer caused the homogenization of the structure cermet coatings. The irradiation with the laser beam eliminates microcracks and pores on the Cr3C2-25(Ni20Cr) surface. However, the best effect of improving the anti-corrosion properties of cermet coating was obtained for the lowest laser spot speed (i.e., 600 mm/min). It was found that the corrosion rate of the Cr3C2-25(Ni20Cr) cermet coating was reduced by more than two times compared to the highest speed of the laser spot.

Corrosion Behavior of FeB-30 wt.% Al0.25FeNiCoCr Cermet Coating in Liquid Zinc

The corrosion of galvanizing equipment parts by liquid zinc is an urgent problem that needs solving. In this work, FeB-30 wt.% Al0.25FeNiCoCr cermet coating was deposited on the surface of 316L stainless steel by AC-HVAF to protect galvanizing equipment parts from corrosion by liquid zinc. The microstructures and phase compositions of powders and the coating were determined by SEM, EDS, and XRD in detail. Additionally, the microhardness, fracture toughness, abrasion wear resistance, and corrosion resistance of the coating to liquid zinc were also studied. The results indicate that the abrasion wear resistance and corrosion resistance of the coating are much better than that of the 316L stainless steel substrate. The failure of the coating in liquid zinc is mainly due to the penetration of liquid zinc into macro-cracks, which causes the coating to peel off.

The Cavitation Resistance of WC-CoCr Cermet Coating Deposited by HVOF for Hydraulic Application

Thermal spray is a versatile technique for enhancing the cavitation resistance of hydraulic water passage components, especially in on-site repair situation. Based on the application in hydraulic components, a WCCoCr cermet coating was deposited by high velocity oxygen fuel spraying. The microstructure and hardness were characterized, and the cavitation was studied by ultrasonic vibratory system according to ASTM G32 standard. The coating shows superior anti-cavitation behavior in term of mass weight loss compared with the martensite stainless steel. The cavitation erosion mechanism is elaborated with wrinkles and craters observed on the worn surfaces, and correlated with the incubation and accelerating stages.

Erosion-Corrosion Protection Due to Cr3C2-NiCr Cermet Coating on Stainless Steel

Cr3C2–NiCr coatings have been used extensively to combat the erosion corrosion of hydro power turbine blades made of stainless steel. Cr3C2–NiCr coatings are also used in aqueous corrosive environments due to the high corrosion resistance rendered by the NiCr binder. In this investigation, both erosion and corrosion environments are introduced to cermet coating to study corrosion behavior using potentiodynamic polarization and electrochemical impedance spectroscopy (EIS) techniques. The cermet coatings are useful for reducing the risk of deterioration of mechanical properties of hydro power turbines due to the continuous exposure to the erosive and corrosive action of the corrosive environment containing silt. It was observed that Cr3C2–NiCr coating offered a reasonable improvement in corrosion resistance when compared to bare substrate. The corrosion behavior of the coating was studied in a 150 mL solution of 0.1 M NaCl with 2 gms of quartz particles (0.2–0.8 mm) at various rotation speeds (3000, 4500, 6000 rpm) of the solution over a 1 h immersion using potentiodynamic polarization and EIS studies in a specifically designed experimental set-up for erosion corrosion. When compared to the bare stainless steel samples at 3000 rpm and 6000 rpm, the coating showed the highest improvement at 6.57 times and the least improvement at 3.79 times, respectively.