Study on functionally gradient coatings of Ti–Al–N

Functionally gradient coatings of Ti–Al–N were deposited on the 5CrNiMo steel substrate by multi arc ion deposition (MAID) technique by gradually increasing the nitrogen pressure during the deposition process. Scanning electron microscopy (SEM), and X-ray diffraction (XRD) were used to investigate the composition, microstructure and phases of coatings. Thermal shock resistance tests were carried out in a resistance furnace. The adhesion strengths of Ti–Al–N functionally gradient coatings were tested by an automatic scratch tester. It was shown that there are three phases, (Ti,Al)N, (Ti2,Al)N and Al, in the coatings. Along the thickness direction of Ti–Al–N functionally gradient coatings, the content of ceramic phase increases and the content of metal phase decreases gradually. The hardness distributed along the thickness direction increases with increasing the N2 pressure, namely increasing the content of ceramic. It is found that the adhesion strength and the thermal shock resistance property of Ti–Al–N functionally gradient coatings are better than that of homogeneous (Ti,Al)N coatings and increase with decreasing the composition gradient.