ICMCTF2015 Session E2-1: Mechanical Properties and Adhesion

This paper shows the results of wear, adhesion and hardness tests performed on Ni-based coatings deposited by flame spray technique at different flow conditions of oxygen in the mixture of combustion gas of the deposit system.

Ti-Al-N coatings have been widely studied especially those with high aluminum content for different industrial applications because they have a high wear resistance and a good thermal stability. In the present work TiAlN thin films were prepared by the simultaneous laser ablation of Ti and Al targets in a reactive atmosphere containing nitrogen. In this way we have compared films with low aluminum contents, up to 15 at. %, with titanium aluminum nitride coatings with an aluminum content of about 25 at.%. The structural characterization of the deposits was carried out using X-ray diffraction and it was found that the films were highly oriented in the (111) direction of TiN. Small shifts of the diffraction peaks towards higher values of 2θ were observed and were correlated to the distortion of the TiN lattice due to the incorporation of Al. The maximum coating hardness was 40 GPa for an aluminum concentration close to 11 at.%, whilst the coatings commonly used in industry with an aluminum content of about 25 at.% had a hardness of 25 GPa. The thermal stability of the films was studied by micro-Raman spectroscopy in the temperature range from 500 to 900 ºC. This technique was used to detect the formation of the TiO₂ phase. The results indicated that the inclusion of aluminum led to an improved thermal stability up to 850 ^oC.

In this study, plasma nitriding treatments were applied to the pure titanium at 500, 600, and 700°C. Tribological and electrochemical behaviors and structural properties of the nitrided pure titanium samples were comparatively investigated. Corrosion tests were conducted in a Ringer’s solution, which represents a human body environment, in order to determine electrochemical properties. Moreover, morphology and microstructure of the plasma nitrided surfaces were analyzed by scanning electron microscopy (SEM) and X-ray diffraction (XRD). Then, a micro-hardness tester was used to measure the hardness of the coatings and tribological and frictional properties were investigated using ball-on-disc tribometer. The results showed that the plasma nitrided samples exhibited higher surface hardness than the untreated samples. Also, the nitrided samples at 700°C presented significantly better performance than the other nitrided samples in dry wear conditions. Moreover, the corrosion test results showed that corrosion behaviors of untreated and nitrided samples had similar characteristic.

Surface coating is an effective way to improve the durability of substrate materials in aggressive environments or prolong the service life of mechanical tools. For protective coatings of mechanical tools, the most important properties are high hardness, wear resistance and the adhesion strength between the coating and substrate. In addition, the coatings on mechanical tools must be sufficiently thick to endure the long-term service in industry, at least a few micrometers. In our previous study, we have successfully deposited TiN thick coatings with excellent mechanical properties on AISI D2 tool steel substrates using an energy-efficient process. ZrN coatings are more attractive than TiN for industrial applications because of their higher mechanical properties, better wear resistance and warmer golden color than the corresponding properties of TiN coatings. The purpose of this study is to develop an energy-efficient process to deposit ZrN thick coatings (> 6 μm) on AISI D2 tool steel substrates and to investigate the properties of ZrN coatings with different thickness. ZrN coatings were prepared using dc unbalanced magnetron sputtering, where the opening of gate valve between turbomolecular pump (TP) and deposition chamber and the pumping speed of TP being the major controlling parameters. The hardness, adhesion strength and wear resistance were assessed by nanoindentation, scratch test and pin-on-disk test, respectively. The microstructure of the thick ZrN coatings was correlated to the deposition parameters, and the mechanical properties were also associated with the surface roughness and microstructure. The residual stress in the coating was determined by both cos²αsin²ψ X-ray diffraction (XRD) and laser curvature methods. In addition, the stress distribution in coatings was measured using cos²αsin²ψ XRD method at different incident angles, which may facilitate the understanding of the relation between mechanical properties and stress distribution in the coatings.