Combination of Electron Beam Remelting and Subsequent Nitriding or PA-CVD Hard Coating to Improve Surface Properties of Cast Irons

摘要

The typically high contents of carbon and silicon in cast irons as well as their soft graphite limit their treatability and load-bearing capacity for nitriding and hard coating. If an electron beam remelting process is carried out before these surface treatments, a hard ledeburitic surface layer free of graphite is produced, and serves as a supporting layer for the hard and typically thin compound layer or PA-CVD coating after combined treatments. Comparative wear tests (ball-on-disc) have shown that, especially for low loads, the wear rates of all single and duplex treatments are comparable, though considerably better than for the untreated base material. For higher loads, the superiority of the combined treatments is clearly apparent when compared to the single treatment. The formation of thin, defect-free surface layers after combined treatments also results in a notable improvement of corrosion resistance in chloridic solution. In comparison to the single surface treatments, the pitting-corrosion potential is adjusted to more positive values.