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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.

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.

Advanced titanium alloy metal matrix composites offer significant mechanical improvements over many conventional materials. In order to minimize fiber-matrix chemical reactions due to high temperatures involved in the fabrication methods, the final component can be obtained using two different steps: (1) fabrication of preforms (monotapes) by inert plasma spraying and (2) hot pressing of the fabricated preforms. Continuous SiC fiber-reinforced Ti-6Al-4V preforms were hot pressed to fabricate a composite multilayer. Different values of hot pressing processing parameters (temperature, applied load, bonding time) were investigated on the basis of a two-level factorial design. Metallographic and scanning electron microscopy (SEM) analyses were carried out to evaluate the bonding degree of the fabricated preforms. Preliminary three-point bending tests were also performed to understand the mechanical behavior and to show the more suitable values of the processing parameters for a hot pressing procedure. These values should be in the range of 830 to 950°C (temperature), 80 MPa (applied stress), 20 to 30 min bonding time to avoid undesired phase transformation, large plastic flow of the metal matrix, and detrimental chemical reaction at fiber-matrix interface.