Influence of Fe on the room and high-temperature sliding wear of NiAl coatings

High temperature mechanical properties of Ni-Al intermetallic alloys make them potential candidates as wear-resistance materials or coatings to protect components operating in harsh environments. In-situ processing of Ni-Al intermetallic coatings has been successfully carried out previously. The role of interaction with the substrate, measured by the Fe content in NiAl coatings, on the wear performance is addressed in this study. Mixtures of Ni and Al powders were prepared (65at.%Ni-35at.%Al) and deposited onto 1020 steel disks. Three deposition current were used (100, 120 and 150A) resulting in coatings with Fe content ranging from 36 to 50at.%, as a consequence of the metallurgical bond with the substrate steel. The development of the NiAl was confirmed by X-ray diffraction together with austenite. Dry sliding tests were carried out at room temperature and 710°C, using a ball-on-disk tribometer with a 3.0mm Al₂O₃ ball under different normal loads (1, 3 and 5N). Temperature played an important role on the wear behavior and the wear coefficient was reduced by one order of magnitude at 710°C. At room temperature, wear coefficients increased with the applied load, and abrasion was the main observed mechanism regardless of the iron content in coatings. However, at 710°C the variations on the wear coefficient cannot be associated with the coating hardness and wear was dominated by oxidation. Hematite was identified on all the oxidized surfaces. Notwithstanding, for the coatings with higher Fe content the continuous and thicker scale accounts for the measured stable wear coefficient regardless of the applied load.