AbstractResidual stresses in vacuum-arc coatings of the TiAlSiYN system deposited on a PcBN base were studied by X-ray diffractometry. The substructure characteristics of the TiN phase suggest that all the studied coatings have compressive stress from –1.51 to –5.85 GPa and significant (up to ε = 1.13 × 10–2) microstrain at the microlevel. The equivalent stress Seqv in the near-contact layer of the tool material is determined in samples with residual compressive stress in the coating. We evaluated the effect of residual stress in protective coatings on the equivalent stress in the tool under the action of contact loads typical for the machining process. Compressive stress in the coatings of –1.0 GPa helps to decrease the equivalent stress at critical points at the front surface of the tool in the initial period of cutting. To lower the equivalent stress from the back surface of the tool with significant (~0.3 mm) wear, coatings with a residual compressive stress of –3 GPa are optimal. The most significant decrease (from 1.9 to 0.5 GPa) in equivalent stress at critical points at the front surface of the tool was observed upon impact loads.