Adhesion measurements and chemical and microstructural characterization at interfaces of titanium nitride and titanium aluminum nitride coatings on stainless steel, inconel and titanium alloys

To assess the adhesion of nitride coatings on metal alloys, Ti 6Al-4V, 17-4 PH stainless steel and Inconel 718 alloy substrates were coated with titanium nitride (TiN) using both cathodic arc and electron beam evaporation. Titanium aluminum nitride ((Ti,Al)N) was also deposited using cathodic arc evaporation.; X-ray photoelectron, Auger electron, and energy dispersive x-ray spectroscopies were used in tandem with cross-sectional transmission electron microscopy to analyze the coatings and the coating-substrate interfaces. The interfaces were found to be abrupt with a thin layer of W contamination located between the substrate and the Ti interlayer, deposited to improve adhesion, on electron beam evaporated samples. Metallic macroparticles up to two microns in diameter were observed in cathodic arc evaporated coatings.; Residual stress analysis of the coatings revealed the presence of biaxial compressive residual stresses in all coatings. Residual stresses increased for coating-substrate systems with a larger mismatch between the coefficients of thermal expansion for the coating and the substrate. Scratch tests of the coatings revealed lower critical load values for coatings on Ti 6Al-4V due to the lower hardness of the substrate alloy relative to the stainless steel and Inconel alloys. The scratch test is a common method for evaluating adhesion of a coating to its substrate; however, this technique is not well understood due to complex loading of specimen as coating is removed.; Plate impact spallation, is a more uncommon method for evaluating adhesion, but the advantage of this technique is that the interface is subjected to purely tensile loading. During plate impact spallation, the interfaces of the coated samples were loaded in tension using a high speed shock wave which caused spallation either at the interface, in the coating or in the metal. Failure in cathodic arc deposited coatings occurred in the form of isolated spallation craters located within the stressed areas. This is attributed to a lower adhesive strength at sites in which a macroparticle was in contact with the interface relative to areas in which the interface was free of macroparticles.; DYNA2D modeling of plate impact spallation experiments revealed the tensile adhesion strengths for cathodic arc evaporated TiN were approximately 2.0, 1.5 and 1.25 GPa for Ti 6Al-4V, 17-4 PH stainless steel and Inconel 718 alloy substrates, respectively. The electron beam evaporated TiN coatings were found to be thinner than the cathodic arc evaporated coatings, resulting in a decreased interfacial tensile stress in the former during plate impact spallation experiments. The only noteworthy failure observed in an electron beam evaporated coating was at an interfacial tensile stress of 2.0 GPa for TiN coated Ti 6Al-4V. A minimum coating thickness of 5 {dollar}mu{dollar}m is therefore recommended for application of this technique to similar ceramic coating-metallic substrate systems.; Work of adhesion values determined from existing models based on scratch test analysis showed little agreement with those determined from existing models based on shock wave spallation analysis. However, work of adhesion values determined from each method were consistent with those found in the literature, indicating an inconsistency between the two existing types of models for work of adhesion.