Investigation of hot corrosion behavior of plasma sprayed cermet composite coatings on titanium and special steel alloys

In the present study, titanium-15 alloy and a special steel alloy (MDN 420) were used as base materials. These components are employed in high-temperature applications. Three types of pure powders were deposited on titanium-15 and a special steel (MDN 420) alloys. The three coatings were 35 % (WC-Co) + 65 % (Cr₃C₂-NiCr), 70 % NiCrAlY + 30 % TiO₂, and 70 % NiCrAlY+25%Cr₂O₃ + 5%YSZ. The coatings and base alloys underwent various metallurgical, mechanical, and hot corrosion tests. The hot corrosion behavior of the coatings was investigated in a Na₂SO₄–60%V₂O₅ molten salt medium at 700 °C, with an accuracy of ±5 °C. Each test cycle consisting of 50 cycles, with heating followed by 1 h cooling for 20 min. When three coatings were compared, NiCrAlY+Cr₂O₃ + YSZ coating exhibited superior resistance to hot corrosion on both the alloys. The enhanced corrosion resistance of the NiCrAlY+Cr₂O₃ + YSZ coating was attributed to the formation of a protective oxide layer containing Cr₂O₃.The tests were conducted in a highly acidic molten salt environment, with Na₂SO₄ being less soluble (60 % V₂O₅). The results showed that the NiCrAlY+Cr₂O₃ + YSZ coating displayed better corrosion resistance for titanium-15 and MDN 420 alloys, when compared to the other two coatings. The formation of an oxide layer containing Cr₂O₃ was the main reason for the improved corrosion resistance.