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Characterization And Hardness Modelling Of Alternate Tin/Ticn Multilayer Cathodic Arc Pdv Coating On Tool Steel
No full textCharacterisation and wear properties of industrially produced nanoscaled CrN/NbN multilayer coating
No full textPresent work deals with morphological, microstructural, compositional and tribological characterisation of nanoscaled multilayer CrN/ NbN coating produced by an industrial process presently in development phase. This coating has been applied on steel ring components used in textile plants subjected to contact erosion wear, at high frequency and low load, between the external surface of a ring and a bar where friction coefficient and corrosion resistance are critical. Nanoscaled multilayer structures usually show both high hardness and better wear resistance, correlated with grain refinement, coherency strain hardening, inhibition of dislocation motion, together with an excellent corrosion resistance due to the interruption of coating columnar pinholes and to the combined metal element effect. In order to obtain multilayer structure a non-conventional technique has been set up, consisting of triggering alternatively on Cr or Nb cathodes with appropriate time constant so as to obtain couple of layers of about 5 nm each. In order to satisfy industrial requirements, the process was optimised using a commercially available Cathodic Arc PVD equipment, routinely used to produce conventional CrN coatings. Microstructural and compositional properties were investigated and reported hereby. Low angle X-ray diffraction, Optical and Atomic Force Microscopy, Electron Probe Microscopy (SEM, TEM, SAD, EDS) and Focussed Ion Beam techniques has been used. Defects were also investigated, particularly microdroplets (shape, dimension, density, clustering and other process-sensitive features). Mechanical and tribological properties were characterized by micro and nano hardness measurements, scratch test, ball on ring, ball-cratering and residual stresses evaluation with X-ray diffraction (XRD) sin(2)psi method. Multilayer coating shows higher H/E ratio, a clear tendency to delaminate during fracture and a different size distribution of microdroplets. As a consequence, CrN/NbN coating results in a lower wear rate with respect to the CrN coating (up to 30%) but only if a normal force dominated stress is applied. Finally, performances results (e.g. wear rate and degradation behaviour) obtained by operating in line two different sets of components (respectively CrN and CrN/NbN coated) are presented; lifetime of industrially produced multilayer coated components has been elongated from 9 to 11 months. (C) 2004 Elsevier B.V. All rights reserved
Characterization And Hardness Modelling Of Alternate Tin/Ticn Multilayer Cathodic Arc Pdv Coating On Tool Steel
No full text
High thickness Ti/TiN multilayer thin coatings for wear resistant applications
No full textHard coatings like titanium nitride (TiN) normally contain a high degree of internal stress (usually compressive in-plane parallel with the surface) owing to growth defects developed during the deposition process and thermal mismatch effects after final cooling; it is, therefore, difficult to produce single-layer TiN coatings thicker than 6-7 mu m, without adhesion problems. In the present study, thick coatings (i.e. > 10 mu m) have been achieved by alternate multilayering of TiN with Ti interlayers, leading to a tougher and less-stressed film. However, having a constant distribution of titanium interlayer thickness is not necessarily the best solution to achieve maximum performance in terms of wear resistance and hardness. The residual stress distribution along the thickness is unlikely to be constant with the inner layers being more stressed due to a greater amount of thermal differential strain. Following this guideline, a series of numerical simulations was performed in order to calculate the residual stress through thickness distribution due to the deposition process. Three sets of multilayered Ti/TiN coatings having both constant and variable Ti interlayer thickness were modelled and deposited, using a reactive arc PVD process. Mechanical and turbological properties were characterized using static and depth sensing Vickers micro-hardness indentation tests, rotating wheel (dimpling grinder) abrasive wear tests and Rockwell C adhesion tests. Coating interface characterizations were made by SEM-EDS. Results showed that adhesion can be significantly improved by adopting a titanium through thickness quantity increasing towards the interface: an optimized distribution allows also higher hardness and wear resistance to be obtained, as it requires a lower total amount of titanium to obtain good adhesion properties. (c) 2006 Elsevier B.V. All rights reserved
Acoustic Emission Monitoring during Tensile Tests on CrN and CrN/NbN Coated Specimens, poster alla conferenza
No full textAcoustic Emission (AE) associated with uniaxial tensile tests was used to study failure mechanisms in CrN and CrN/NbN coated specimens.When a very fast release of elastic energy occurs during a loading cycle it generates waves in the range of ultrasound (usually between 20kHz and 1MHz). This short, transient acoustic emission event produced can be detected and measured so to investigate local damage within the material in a dynamic way during its load history. Tensile tests were performed by the use of an MTS (Alliance RT/10) Testing Machine on three micrometers thick CrN and CrN/NbN coated specimens deposited by reactive cathodic arc evaporation onto X5CrNiMo 17 12. Acoustic measurements were also made on one set of non-coated substrate specimens in order to discriminate events arisen in the substrate during the plastic deformation process.Signals were collected by four transducers: two “data” sensors, placed on the specimens surface enclosing the area of interest; two “guard” sensors to discriminate from sources originating outside. AE/strain curves obtained for all specimens showed a good repeatability and different types of acoustic events were evaluated in terms of amplitude and absolute energy. Moreover, acoustic emission results were correlated with microscopy evidences. Failure mechanisms and cracks propagation paths were characterized by SEM/EDS, both in plan view and cross section; the role of surface and bulk defects was evidenced and different behaviour was found in the case of multilayered structure
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