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Comparison of TiAlN coatings grown by unbalanced magnetron and arc bond sputtering techniques
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1993
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EngineeringMechanical EngineeringTi-ion PretreatmentSurface TechnologyCorrosionPenetration DepthEtching StageProtective CoatingMaterials ScienceMaterials EngineeringThermal Spray CoatingHard CoatingMulti-functional CoatingPlasma EtchingTialn CoatingsDepth-graded Multilayer CoatingMicrostructureCorrosion ProtectionSurface ScienceApplied PhysicsSurface EngineeringThin FilmsUnbalanced MagnetronSurface Processing
During cathodic‑arc etching, Ti ions embed into the substrate surface, and an unbalanced magnetron can produce dense, droplet‑free TiN layers; combining these in arc‑bond sputtering (ABSTM) is expected to yield coatings with excellent properties. The study investigates how metal‑ion pretreatment improves the adhesive strength of Ti₀.₅Al₀.₅N coatings on high‑speed steel and cemented‑carbide substrates. Adhesive strength was evaluated using LC and Rockwell indentation tests on TiAl‑nitride layers produced by the combined arc‑bond sputtering process. Ti‑ion pretreatment made adhesive strength less sensitive to process variations, and using shutters reduced TiAl droplet formation during arc‑based etching.
Basic research has shown that, during the etching stage of the cathodic-arc process, metal atoms of the coating material become embedded in the surface of the substrate to be coated. If 1200-eV Ti ions are used for etching, the penetration depth may be as great as 1500 Å. Paralleling this, more recent results reveal that an unbalanced magnetron can be used to produce dense, droplet-free TiN layers in an exactly reproducible form. Hence, when the arc-mode etching process is combined with unbalanced magnetron-mode coating, the resulting coating can be expected to have excellent properties. The technical implementation of this combined technique is known as ‘‘arc bond sputtering,’’ and is known commercially as ABSTM. This article describes how the process of producing TiAl-nitride layers is used to demonstrate the advantages of metal-ion pretreatment on the adhesive strength of Ti0.5Al0.5N layers applied to high-speed steel and cemented-carbide substrates. The adhesive-strength criteria are the LC and the Rockwell indentation test. The result of this study indicates that the Ti-ion pretreatment renders the measured adhesive-strength values for the subsequent films much less sensitive to uncontrolled variations of the coating-process parameters. It is also shown how the formation of TiAl droplets during the arc-based etching process can be reduced through the use of shutters.