Fatigue behaviour of notched PVD-coated titanium components

In this paper the fatigue behaviour of Ti-6A1-4V alloy coated with a TiN arc-deposited PVD film was studied. Rotating bending tests (R = -1) were carried out on standard "hourglass" specimens to evaluate the fatigue limit at 200000 load cycles. Conventional and notched (120° V-notch transversal to the rotating axis at the minimum cross section area) specimens were tested, both coated and uncoated, to investigate the effect of the coating on the fatigue limit of the titanium alloy, with and without the surface notch. Fracture surfaces were observed by SEM. The coating did not improve the titanium alloy fatigue life

Surface appearance and mechanical strength of multi-layer polymeric films

This paper deals with the analysis of a multi-layer polymeric film made from a hybrid organic-inorganic bond-layer, a decorative epoxy-based basecoat and, finally, a protective polyurethane-based topcoat. The establishment of visual appearance and mechanical strength of the multi-layer polymeric films has been investigated by varying both baking time and temperature on a very wide range. Furthermore, two different two-step baking procedures (i.e., with and without full post-curing of the topcoat) were also proposed and comparatively evaluated. Improved trends of average roughness and mechanical strength of the multi-layer films were found at any time progressively higher baking time and/or temperature was set. Accordingly, the overall adhesion between multi-layer films and underlying metal surfaces was found to increase, as well. Nonetheless, experimental results show that even though satisfactory surface roughness and mechanical properties of the multi-layer films can be established over wide enough ranges of baking time and temperature with both baking procedures, an acceptable visual appearance is only achievable if the topcoat is superimposed at least on an almost fully cured basecoat. (C) 2007 Elsevier B.V. All rights reserved

Surface appearance and mechanical strength of multi-layer polymeric films

This paper deals with the analysis of a multi-layer polymeric film made from a hybrid organic–inorganic bond-layer, a decorative epoxy-basedbasecoat and, finally, a protective polyurethane-based topcoat.The establishment of visual appearance and mechanical strength of the multi-layer polymeric films has been investigated by varying both bakingtime and temperature on a very wide range. Furthermore, two different two-step baking procedures (i.e., with and without full post-curing of thetopcoat) were also proposed and comparatively evaluated.Improved trends of average roughness and mechanical strength of the multi-layer films were found at any time progressively higher baking timeand/or temperature was set. Accordingly, the overall adhesion between multi-layer films and underlying metal surfaces was found to increase, aswell. Nonetheless, experimental results show that even though satisfactory surface roughness and mechanical properties of the multi-layer filmscan be established over wide enough ranges of baking time and temperature with both baking procedures, an acceptable visual appearance is onlyachievable if the topcoat is superimposed at least on an almost fully cured basecoat

Epoxy-based thermosetting powder coatings: surface appearance, scratch adhesion and wear resistance

The deposition of protective coatings from thermosetting polymer powders is undergoing rapid growth as an ecological, economic and energyefficienttechnology. Nevertheless, a combination of conflicting needs is characterizing new formulations: (i) minimization of premature crosslinkingduring material production and storage; (ii) film levelling and cross-linking at the lowest possible temperature in the least possible time.We address the problem by developing an experimental study in which the evolution of film morphology and its thermal, rheological, mechanicaland tribological properties are analyzed in the light of film baking time and temperature.Experimental results show that smooth films can be achieved at relatively low baking time and temperature, while film mechanicalperformances are not yet fully developed. In contrast, good film strength, adhesion and wear endurance can be attained, only if longer baking timeor higher temperature is set. However, a generalized scratch map, which correlates the adhesion strength of the polymeric films with the thermorheologicalbehaviour of the base material, has been also built.Our results open up the possibility of predicting best baking programs and how full film performances are progressively established with timeand temperature by better understanding of the mechanisms involved in polymeric films formation from loose powders

Microstructural and tribological characterisation of as sprayed and heat treated HVOF deposited Ni alloys

The microstructural, micromechanical (Vickers microindentation, scratch testing) and tribological (pin on disk tests against steel and alumina spherical pins) properties of three High velocity oxyfuel (HVOF) sprayed Ni based alloy coatings, namely Diamalloy 4006 (Ni-20Cr-10W-9Mo-4Cu-1B-1C-1Fe), Tribaloy-700 (Ni-32Mo-16Cr-4Si-2Co) and lnconel-625 (Ni-22Cr-9Mo-4Nb), were characterised, both in the as sprayed condition and after thermal treatments at 600°C and 800°C. As deposited Tribaloy-700 possesses a low degree of crystallinity and lower hardness; crystalline intermetallics are formed after heat treatments, definitely improving mechanical strength and tribological resistance against 100Cr6 steel counterpart, but not against alumina counterpart. The lnconel-625 and Diamalloy 4006 as sprayed coatings consist of supersaturated crystalline solid solutions. The former is not much affected by heat treatments and has low hardness and poor tribological properties. The latter, instead, displays precipitation of secondary phases after heat treatment. Particularly, the 600°C treatment improves coating strength and wear resistance against steel, whereas the 800°C one is less effective, probably because it causes excessive crystal grain size increase. © 2007 Institute of Materials, Minerals and Mining

Epoxy-based thermosetting powder coatings: Surface appearance, scratch adhesion and wear resistance

The deposition of protective coatings from thermosetting polymer powders is undergoing rapid growth as an ecological, economic and energy-efficient technology. Nevertheless, a combination of conflicting needs is characterizing new formulations: (i) minimization of premature cross-linking during material production and storage; (ii) film levelling and cross-linking at the lowest possible temperature in the least possible time. We address the problem by developing an experimental study in which the evolution of film morphology and its thermal, rheological, mechanical and tribological properties are analyzed in the light of film baking time and temperature. Experimental results show that smooth films can be achieved at relatively low baking time and temperature, while film mechanical performances are not yet fully developed. In contrast, good film strength, adhesion and wear endurance can be attained, only if longer baking time or higher temperature is set. However, a generalized scratch map, which correlates the adhesion strength of the polymeric films with the thermo-rheological behaviour of the base material, has been also built. Our results open up the possibility of predicting best baking programs and how full film performances are progressively established with time and temperature by better understanding of the mechanisms involved in polymeric films formation from loose powders. © 2007 Elsevier B.V. All rights reserved

Enhanced tribological properties of PECVD DLC coated thermally sprayed coatings

This research investigates the enhancement of the tribological properties of various thermally-sprayed coatings (APS Ni–50Cr, APS Al2O3–13%TiO2 and HVOF WC–17Co) on steel substrate, achieved through the deposition of a thin DLC-based film. Higher adhesive strength betweenthin films and thermally-sprayed coatings compared to the simple thin film/carbon steel system was found by scratch testing. Dry sliding ball-ondisktests performed under lower contact pressure conditions (5 N normal load, 6 mm diameter alumina ball) indicated a significant decrease inwear rates and friction coefficients of thermally-sprayed coatings when the thin DLC-based film is employed; little differences exist between thetribological behaviour of the various thin film/thermal spray coating systems and that of DLC-based film on carbon steel. Under higher contactpressure conditions (10 N normal load, 3 mm diameter alumina ball), the thin film/WC–Co system exhibited the best wear performance. Theseresults indicate the superior tribological performance of DLC/thermal spray coating systems, especially under severe contact conditions

Microstructural and Tribological Characterization of As-Sprayed and Heat-Treated HVOF Deposited Ni Alloys

The microstructural, micromechanical (Vickers microindentation, scratch testing) and tribological(pin on disk tests against steel and alumina spherical pins) properties of three High velocity oxy\u2013fuel (HVOF) sprayed Ni based alloy coatings, namely Diamalloy 4006 (Ni\u201320Cr\u201310W\u20139Mo\u20134Cu\u20131B\u20131C\u20131Fe), Tribaloy-700 (Ni\u201332Mo\u201316Cr\u20134Si\u20132Co) and Inconel-625 (Ni\u201322Cr\u20139Mo\u20134Nb), werecharacterised, both in the as sprayed condition and after thermal treatments at 600uC and 800uC.As deposited Tribaloy-700 possesses a low degree of crystallinity and lower hardness; crystallineintermetallics are formed after heat treatments, definitely improving mechanical strength andtribological resistance against 100Cr6 steel counterpart, but not against alumina counterpart. TheInconel-625 and Diamalloy 4006 as sprayed coatings consist of supersaturated crystalline solidsolutions. The former is not much affected by heat treatments and has low hardness and poortribological properties. The latter, instead, displays precipitation of secondary phases after heattreatment. Particularly, the 600\ub0C treatment improves coating strength and wear resistanceagainst steel, whereas the 800u\ub0C one is less effective, probably because it causes excessivecrystal grain size increase