Corrosion and Wear Properties of Composite Coatings Reinforced with Particles Produced by PTA on Steel Substrate in Different Atmospheres

Abstract

Titanium diboride (TiB2) and titanium carbonitride (Ti(C,N)) coatings are widely used as reinforcing materials in applications demanding high corrosion and wear resistance. In this paper, plain carbon steel has been surface alloyed with TiB2 by plasma transferred arc (PTA) technique using two different gas atmospheres. The first metal matrix composite (MMC) is produced with TiB2 particles and argon as shielding and plasma gas. In addition, a mixture of Ar and 5% N2 was used as shielding and plasma gas for producing of second MMC coating. The microstructure of both alloyed layers consists of primary titanium boride particles surrounded by a eutectic matrix, containing ferrite, eutectic boride, and titanium carbonitrides. The presence of these carbonitrides is more intense in the case of the N-enriched alloyed layer, as it was also proved via X-ray Diffraction. The alloyed layers are susceptible to pitting corrosion in 3.5% NaCl or 1 N H2SO4. The alloyed layer produced with nitrogen mixture gas is slightly more noble than the one produced with pure Ar. The metallic-ferritic matrix corrodes in 6% FeCl3∗6H2O leaving TiB2 particles protruding from the matrix. The wear performance of both TiB2 MMC depends on the counterbody (tool steel or alumina ball).