The high chemical activity, low thermal conductivity, and high strength of titanium alloys lead to severe tool wear during cutting. The coating applied to the tool surface insulates the effect of heat and chemical reactions. TiAlSiN coating and AlCrN coating are two representative coatings with excellent properties in TiN-based and CrN-based applications, respectively. Three types of nanocoatings—TiAlSiN monolayer, AlCrN monolayer, and TiAlSiN/AlCrN multilayer—were prepared, and the microstructure, mechanical properties, oxidation resistance, diffusion properties with titanium alloy, and cutting performance of the coatings were investigated utilizing SEM, TEM, XRD, TGA, GD-OES, nanoindentation, and scratching instruments. The hardness, elastic modulus, and adhesion strength of TiAlSiN/AlCrN multilayer coatings are between TiAlSiN monolayer and AlCrN monolayer coatings, which meet the “law of mixtures”. Adhesion strength is the primary condition for cutting applications and should have a minimum threshold value. Ti and N elements are the most significant in the diffusion between coatings and titanium alloys. The nitride coating containing Cr aggravates the loss of N in contact with the titanium alloy. In addition, multilayer structural coatings can lead to more severe diffusion than monolayer coatings due to their inherent interlayer defects. Although diffusion between titanium alloys and coated tools is more severe than with other workpiece materials, the main factor affecting tool cutting life is still the H³/E*² value determined by the hardness and modulus of elasticity together.

TiAlSiN and AlCrN coatings are two representative coatings with excellent properties in TiN-based and CrN-based coatings, respectively. Multilayering is one of the most important directions for coating performance optimization. In this paper, nanoscale monolayer TiAlSiN, AlCrN, and multilayer TiAlSiN/AlCrN coatings were prepared. The microstructure, mechanical properties, oxidation resistance, and wear resistance of the above three coatings were investigated. The following properties of the TiAlSiN/AlCrN coating, including phase, nanohardness, elastic modulus, adhesion strength, and oxidation resistance, fall between those of the TiAlSiN and AlCrN coatings and conform to the “law of mixtures”. Due to the interfacial effect of the multilayer coating, the residual stress of the TiAlSiN/AlCrN coating is less than that of the two monolayer coatings. At 500 °C, the order of wear resistance of the three coatings is consistent with the order of H³/E*² values, i.e., TiAlSiN > TiAlSiN/AlCrN > AlCrN; at 800 °C, the order of wear resistance becomes TiAlSiN/AlCrN > TiAlSiN > AlCrN because TiAlSiN coating has entered the rapid oxidization stage first, reducing its wear resistance.