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Este documento foi escrito baseando-se na experiência pessoal dos autores, os quais ensinaram e fizeram pesquisa por muitos anos na universidade, tendo ambos vivido pessoalmente as várias transformações que ocorreram na universidade italiana durante os últimos trinta anos. Muitos dos documentos citados foram retirados do volume do Ministério da Universidade e da Pesquisa Científica (MURST): “A reforma universitária”, Editora Salerno, 2001 Il presente documento è stato scritto sulla base dell’esperienza personale degli autori, che hanno per molti anni insegnato e fatto ricerca nell’università, avendo entrambi vissuto personalmente le molteplici trasformazioni che si sono succedute nell’università italiana durante l’ultimo trentennio. Molti dei documenti riportati sono stati ampiamente tratti dal volume del Ministero dell’Università e della Ricerca Scientifica (MURST): “La riforma universitaria”, Salerno Editore, anno 2001.

Present paper deals with modelling, production and characterization of HVOF PVD (WC-Co and TiN or CrN, respectively) duplex coatings deposited on Ti-6Al-4V substrate for application in automotive industry. As a preliminary analysis, an analytical study of the contact stress distribution under spherical indenter in both coated and uncoated systems, and a finite element evaluation of residual stresses were performed: results showed that the presence of an interlayer with intermediate hardness and stiffness (such as the WC-Co coating) plays a fundamental role in the improvement of the load carrying capacity. Starting from the results of simulations, morphological and compositional characterization of the coatings were performed using SEM and AFM techniques. Mechanical properties were investigated by micro indentation techniques and composite hardness modelling; toughness of the system was qualitatively analysed by Rockwell C indentation. Wear rate of the coatings was measured by an implemented rotating wheel method. Results show higher superficial composite hardness, toughness, adhesion and lower wear rate, in comparison with the simple monolayer system. (c) 2005 Elsevier B.V. All rights reserved.

Present 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.

Ball cratering and rotating wheel tests are useful techniques for abrasive wear resistance evaluation of thin coatings. Nevertheless, such techniques involve significant experimental errors, coming from equipment deficiencies and changes in wear response depending on test parameters. In case of rotating wheel test, common instrumental errors are: geometry-induced errors (curved or non-horizontal sample surface), alignment errors (misalignment between ball/wheel rotation axis and sample stage) and optical measurement errors. In the present paper, errors due to crater dimension detection system (penetration depth or crater diameter) and equipment deficiencies (rotating axes misalignment and sample slope) were numerically analysed. A general expression for volume calculation was obtained, considering axes misalignment and sample slope, and experimentally validated by wear tests on Ti/TiN CAE-PVD coatings and profilometer abraded volumes measurement. Results showed that axes misalignment and sample slope involve considerable errors in wear coefficient evaluation. However, errors can be corrected by the use of obtained expressions. Copyright © 2009 John Wiley & Sons, Ltd.

The aim of the present research activity was to verify the influence of the applied bias voltage on the microstructural and functional properties of magnetron sputtering physical vapour deposition (MS-PVD) niobium thin films for use in superconducting resonant cavities for particle accelerators. Four different sets of samples were produced, by varying both the applied bias voltage and the nature of the substrate (copper or quartz). The morphological, microstructural, and mechanical properties of the coatings were experimentally determined by focused ion beam scanning electron microscopy (FIB-SEM), atomic force microscopy (AFM), transmission electron microscopy (TEM), and nanoindentation techniques, and then correlated to the applied bias and nature of the substrate. The superconducting properties (critical temperature T(c) and residual resistivity) were determined by a calibrated four-contact probe and a cryogenic apparatus. The microstructures and surface properties of biased films grown on copper and quartz were compared. The observed differences are likely connected to the low conductivity of quartz that induces a re-sputtering effect and a consequent modification of the superconducting performances.

Titanium and its alloys are extensively used in aerospace and mechanical application because of their high specific strength and high fracture toughness. On the other hand, titanium alloys often show low hardness, very low load bearing capacity and poor resistance to sliding wear, so that surface properties improvement is in many cases recommended, often by PVD processes. Present work deals with design, production and experimental characterisation of a duplex coating for Ti-6A1-4V components, consisting of a thick WC-Co interlayer deposited by High Velocity Oxygen Fuel (HVOF), followed by a Ti/TiN multilayer (two layer pairs, including the Ti bond layer) deposited by Cathodic Arc Evaporation (CAE) PVD. Before deposition, a preliminary coating design was carried out, based on finite element simulation of residual stress fields on the PVD coating for a range of configurations of its multilayered structure (Ti buffer layer position and thickness). Morphological properties of the produced coatings (thickness, grain size, surface defect size distribution, roughness) were measured by means of Digital Optical (DOM), Scanning Electron (SEM), Atomic Force (AFM) and Focused Ion Beam (FIB) microscopy techniques. Coatings mechanical properties were investigated by micro-scratch testing, Rockwell C adhesion test, nano-indentation techniques, Vickers/ Knoop micro-hardness testing and composite hardness modelling. Results showed that the use of a CAE-PVD multilayer Ti/TiN top layer, whose thicknesses and Ti distribution were suggested by finite element modelling optimisation, leads to a significant increase (45%) in adhesion of PVD coating to the HVOF layer and load bearing capacity of the coated system, compared to monolayered TiN, without reduction in superficial hardness and load bearing capacity. (C) 2007 Elsevier B.V. All rights reserved.

Composite ZrB2-SiC materials offer well known resistance to ablation at high temperature. An inert plasma spraying technique was used to manufacture composite ZrB2-SiC as potential thermal protection systems for composite based substrates. Due to the rapid solidification experienced by sprayed droplets, amorphous and/or nanostructured phases can be formed; advanced characterization techniques are therefore required in order to collect all the necessary data for process/product optimisation. In addition, silicon carbide, selected for its contribution to the oxidation resistance of the ceramic coating, is well known to be considered as a non sprayable material, due to the lack of a stable liquid phase. In this paper, two issues are investigated: the first is the use of advanced characterization techniques, such as high resolution scanning and transmission electron microscopy, for microstructural analysis of plasma sprayed coatings. The second is the evaluation of possible implications of rapid solidification processes in composite systems for which at least one liquid phase is not stable, but, at the same time, the development of eutectic-like structures results in the formation of nanostructured stable solid phases.

Titanium and its alloys are extensively used in aerospace and mechanical applications because of their high specific strength and fracture toughness. On the other hand, titanium alloys often show poor resistance to sliding wear, low hardness and load bearing capacity, so that surface performance improvement is often recommended. Present work deals with design, production and characterization of a duplex coating system for Ti6Al4V components (i.e. crankshafts, piston rings, connecting rods) consisting of an high velocity Oxygen fuel (HVOF) WC-Co interlayer and a Ti/TiN multilayer (two layer pairs) deposited by cathodic arc evaporation physical vapour deposition (CAE-PVD). A preliminary coating design was carried out, based on Finite Element simulation of residual stress fields on the PVD coating for a range of configurations of its multilayered structure (Ti buffer layer position and thickness). After the choice of the optimal PVD coating configuration, the influence of HVOF WC-Co substrate roughness on PVD adhesion on cylindrical components was analysed, with the aim of optimising the cost to performance ratio of the coating system. Morphological properties of the produced coatings (thickness, roughness, grain size, interfaces) were measured by means of Scanning Electron (SEM) and Focused Ion Beam (FIB) microscopy techniques, while mechanical properties were investigated using Rockwell C adhesion test, micro-scratch, microand nano-indentation techniques. The use of a multilayer Ti/TiN PVD coating, which thicknesses and Ti distribution were suggested by Finite Element Modelling, lead to a significant increase (about 60%) in adhesion to the HVOF coating, compared to monolayer TiN, without reduction in superficial hardness. Furthermore, the maximum allowed HVOF coating surface roughness (Ra) for an optimal adhesion of the PVD coating has been evaluated. INTRODUCTION An excellent combination of high specific strength, fracture toughness, corrosion resistance and thermal stability makes Titanium and its alloys particularly suitable candidates for biomedical, aerospace and extreme mechanical applications. Titanium alloys do however exhibit some disadvantages: low resistance to sliding wear; low hardness; low load bearing capacity; and poor adhesion with respect to coatings. * Corresponding author: marco.sebastiani@stm.uniroma3.it Plasma nitriding and PVD coating are commercial methods for improving properties in those applications which involve high contact stresses and severe sliding wear. However, a very thin, hard layer on a Titanium alloy substrate (even if hardened by plasma nitriding) cannot lead to a mechanically improved structure in terms of load bearing capacity: differences in both coating and substrate hardness and stiffness do not provide a good distribution of contact stresses, while the presence of localised cracks under contact or tribological loads can generate galvanic corrosion between substrate and the PVD coating. An optimised duplex coating may contain a harder and also stiffer (compared to the nitrided layer) interlayer, which provides a better distribution of contact stresses, avoiding plastic deformation of the substrate and brittle failure of the coating. Bemporad et. Al. showed in a recent work that an effective configuration in terms of enhanced load bearing capacity on Ti6Al4V substrates can be achieved by a duplex coating system, consisting of an HVOF thermally sprayed WC-Co thick interlayer and a cathodic arc evaporation (CAE) PVD (TiN or CrN) thin coating. Adhesion can be enhanced by deposition of multilayered PVD metal/ceramic systems: as an example, several studies showed that the interposition of a Ti interlayer with a thickness of 0.5–1.5 μm accommodates the PVD TiN internal stresses and allows thicker composite coatings to be produced, with significant improvements in toughness, adhesion, impact resistance and corrosion resistance; however, the presence of a relatively thick Ti buffer layer usually involves a significant reduction in hardness and wear resistance of the PVD coating, especially in the case of a hard PVD coating on a soft Ti-alloy substrate. It is therefore clear that a deeper optimisation of coating procedures for Ti alloy based components is required, with respect to their surface mechanical performances and corrosion resistance. The idea for the present research activity was therefore to develop and optimise a coating system for Ti6Al4V components, consisting of a Ti/TiN (two layer pairs) CAE-PVD coating on a HVOF WC-Co thick interlayer, with the aim of increasing adhesion and load bearing capacity of the PVD coating. All experimental work consisted of three different steps: (1) design optimisation procedure of the PVD coating (parametric study of the influence of the Ti buffer layer position and thickness on interfacial stress peak, based on finite element simulation of residual stress); (2) produced coatings morphological, microstructural and mechanical characterisation, (3) study of the influence of the HVOF surface roughness on PVD coating adhesion and final coating procedure application on crankshafts for high performance engines. COATING DESIGN AND OPTIMISATION Starting from results of a previous experimental work by the same authors, coating optimisation consisted of a Finite Element based design of the Ti/TiN (two layer pairs) PVD coating, based on residual stress evaluation for several configurations of its multilayered structure. The objective of this numerical study was to determine the influence of the Ti buffer layer position and thickness on the interfacial residual stress field due to deposition processes. Delamination failure of PVD coatings is generally caused by high interfacial residual stress fields resulting from the deposition process parameters and from poor adhesion. Residual stresses in PVD coatings arise from the contribution and interaction of two main factors: (A) thermal stress (σth), arising from differences in thermal expansion coefficient between coating and substrate during final cooling from deposition to room temperature, and (B) intrinsic stress (σi), which occur as a consequence of deposition parameters induced crystallographic growth orientation; according to models available in literature, they can be expressed as a function of the ionic and atomic flux arriving at the substrate during deposition, and of the energy distribution of the bombarding ionic species. Usually the resulting residual stress field is approximately calculated as follows: th i tot σ σ σ + = (1) CAE-PVD coatings always show high in-plane compressive intrinsic stress, which necessarily involves high normal to surface tensile stress. The use of ductile Titanium interlayers in multilayer Ti/TiN coatings can be effective for the residual stresses relaxation, in order to improve coating-substrate interfacial adhesion and impact wear resistance, but the presence of a Ti interlayer involves also a reduction in mechanical properties of the coating, such as hardness and sliding and abrasive wear resistance. In the case of HVOF coatings, residual stresses also arise from two sources: the quenching stress (σq), due to the instantaneous cooling of impacting droplets, and thermal stress, due to differential thermal contraction. Quenching stresses can be evaluated by the following equation