Decorative PVD coatings as an enviromentally clean alternative to chrome plating

The objective of this work is to conduct applied research and development to demonstrate yhat metal or ceramic coatings deposited by Physical Vapor Deposition (PVD)are equivalent or superior in peformance and are a cost-effective alternative to chrome plating in decorative applications. Chromium plating is comercially used to produce wear-resistant and decorative coatings, but the plating bath contains hexavalent chromium, which has adverse health and environmental effects. The present study describes and compares the mechanical and tribological properties of TiN,AlTiN, ZrCN coatings deposited by CAPVD (cathodic arc plasma pgysical vapor deposition), on nickel plated aluminium substrates. The properties of the above mentioned PVD coatings have been compared with the properties of conventional chromium plating.Peer Reviewe

Cobalt free metallic binders for HVOF thermal sprayed wear resistant coatings

Thermal sprayed HVOF WC-based cermet coatings containing various metallic binders have been used in several different applications in industries that require abrasive sliding wear resistance, such as hydraulic pistons, shafts or bearings. The potential dangerousness and cost increase off cobalt-based metallic binders, underlining the challenge in reducing reliance on this metal as metallic binder in wear resistant coatings. The present work aims to study the feasibility of WC-NiMoCrFeCo, WC-CrC-Ni and WC-FeCrAl coatings, in contrast to conventional WCCoCr, by evaluating their microstructure, mechanical, tribological and corrosion resistance properties. Commercially feedstock powders were sprayed onto steel plates using a kerosene-fuelled HVOF WokaJet 400 gun. The WC-CoCr coating shows a slightly highest hardness than WC-NiMoCrFeCo and WC-FeCrAl coatings, showing a slight trend towards an increase in the wear rate as the coating hardness decreases. The WC-CrC-Ni coating is significantly the softest and least wear resistant coating, as a consequence of the presence of a high percentage of lower hardness CrC particles. Nevertheless, this coating shows similar corrosion resistance to of conventional WC-CoCr coating, while the WC-NiMoCrFeCo and WC-FeCrAl coatings show a slightly worse corrosion resistancPeer ReviewedPostprint (published version

Thixomixing as novel method for fabrication aluminum composite with carbon and alumina fibers

This study focuses on a novel method for dispersion and distribution of reinforcement under high intensive shear stress to produce metal composites. The polyacrylonitrile (PAN)-based short carbon fiber (Csf) and Nextel 610 alumina fiber were dispersed under high intensive shearing at mushy zone in semi-solid of A356 by a novel method. The bundles and clusters were embedded by infiltration of slurry into the clusters, thus leading to a uniform microstructure. The fibers were embedded homogenously into the aluminum around 576-580°C with around 46% of solid fraction. Other experiments at 615°C and 568°C which are contained 0% and 90% solid respectively were not successful for dispersion and infiltration of aluminum into bundles of Csf. The alumina fiber has been cracked by high shearing load. The morphologies and crystalline phase were evaluated by SEM and XRD. The adopted thixo-process effectively improved the adherence and distribution of Csf into Al that can be developed to produce various composites by thixomixing.This study focuses on a novel method for dispersion and distribution of reinforcement under high intensive shear stress to produce metal composites. The polyacrylonitrile (PAN)-based short carbon fiber (Csf) and Nextel 610 alumina fiber were dispersed under high intensive shearing at mushy zone in semi-solid of A356 by a novel method. The bundles and clusters were embedded by infiltration of slurry into the clusters, thus leading to a uniform microstructure. The fibers were embedded homogenously into the aluminum around 576-580°C with around 46% of solid fraction. Other experiments at 615°C and 568°C which are contained 0% and 90% solid respectively were not successful for dispersion and infiltration of aluminum into bundles of Csf. The alumina fiber has been cracked by high shearing load. The morphologies and crystalline phase were evaluated by SEM and XRD. The adopted thixo-process effectively improved the adherence and distribution of Csf into Al that can be developed to produce various composites by thixomixing.Peer ReviewedPostprint (author's final draft

Rheological Behavior of the A356 Alloy in the Semisolid State at Low Shear Rates

To control the semisolid processing of aluminum alloys produced by the additive manufacturing technique, an exhaustive knowledge of their rheological behavior is required. In the semisolid state, metallic materials can show rheological characteristics similar to those of polymers, so semisolid state shaping is one of the currently considered routes for additive manufacturing with metallic materials. In this work, an approximation of the rheological control of the A356 aluminum alloy for its subsequent 3D manufacturing was carried out at a very low shear rate. A continuous cooling rheometer was designed and used, evaluating the influence of different process parameters on the viscosity variation of the aluminum alloy in the semisolid state. The results show an anomalous flow variation, indicating dilatant, and not thixotropic behavior, for very low shear rates.Peer ReviewedPostprint (published version

Effect of oxygen/fuel ratio on the in-flight particle parameters and properties of HVOF WC–CoCr coatings

High Velocity Oxy-Fuel (HVOF) spray techniques can produce high performance alloy and cermet coatings for applications that require wear resistant surfaces. In HVOF spraying heat is produced by burning mixtures of oxygen and fuel, mainly hydrogen, kerosene, propane, propylene, natural gas or acetylene. In these processes, the particle velocity and temperature determine the resultant coating properties and in many cases enables a better understanding of the process. The aim of this study is to investigate influences of different oxygen/fuel ratios on velocity and temperature of flying particles as well as properties of the HVOF thermal sprayed WC-CoCr coatings. In this work the feedstock powders were thermally sprayed by two different variants of the high velocity oxy-fuel process, in which the fuels were hydrogen and kerosene. Particle parameters were recorded just prior to impact on the substrate using in-flight particle diagnostic tool Accuraspray-g3®. Detailed correlation of particle parameters and the coating properties is evaluated in order to deduce particle parameter ranges providing coatings with optimum properties.Postprint (published version

Decorartive PVD coatings as an environmentally clean alternative to chrome plating

Peer ReviewedPostprint (published version

The effect of heat treatment on hardness and drye wear properties of a semisolid processed aluminium alloy

Semisolid AlSiMg casting alloys are attractive alternatives for automotive and aeronautical applications. In this work the effects of heat treatments on hardness and tribological properties of A356 aluminium alloy obtained by Sub-Liquidus Casting (SLC) were studied. The optimum heat treatment conditions, in which the material presents the maximum hardening and wear resistance values, were determined. Heat treatment conditions investigated included: A356 SLC as cast, T5 and T6. Furthermore, AC-46500 and A6061/T6 were analyzed for comparison. The tribological properties of the samples were investigated by pin-on-disc tests at 5 N and 0.05 and 0.1 m·s-1 in dry conditions. The samples were studied by SEM-EDX techniques in order to determine the wear mechanisms and the determination of the products produced during the tests. The maximum hardness and the lowest dry wear rate were obtained through T6 thermal treatment condition.Peer ReviewedPostprint (published version

Study on the formability and texture evolution of AA6061 alloy processed by repetitive corrugation and straightening

The enhanced mechanical properties obtained by refining the grain size down to the ultrafine-grained (UFG) regime have attracted considerable attention in recent years. The severe plastic deformation (SPD) techniques allow obtaining ultrafine-grained materials. Different SPD techniques permit processing sheet shape materials such as repetitive corrugation and straightening (RCS) and accumulative roll bonding (ARB). In this study, the formability of an AA 6061-T6 processed by RCS was evaluated. The forming limit diagrams (FLD) were obtained by Nakazima tests of samples in initial condition (T6 state) and after one and two RCS cycles. The FLD curves showed that the forming capacity decreased from the first RCS cycle. Likewise, uniaxial tensile tests at different temperatures and strain rates were conducted to analyze the effect of the RCS process on the strain rate sensitivity. They showed a relatively high strain rate sensitivity coefficient in the samples after one and two RCS cycles, which indicates an improvement of i) the capacity of the material to delay the onset of the necking and ii) the formability at increasing temperatures. Finally, texture analysis was carried out employing X-ray diffraction, calculating the orientation distribution functions (ODFs). The initial texture showed a predominant cube texture component, whereas, for further RCS cycles, a weakening of the cube texture and an increment of the S texture component were observed.Peer ReviewedPostprint (published version

Surface finish effect on the anodizing behaviour of Al-Si components obtained by sub-liquidus casting process.

The aim of this study was to investigate the hard decorative anodizing components of A357 aluminium alloy, obtained in semisolid state by Sub Liquidus Casting® process, to improve its tribological properties and corrosion resistance. Components were heat treated in order to modify the shape and distribution of the eutectic silicon phase. The influence of shot peening pre-treatment on anodizing process was evaluated. Surface modifications were investigated as they might have beneficial effects on the wear and corrosion behaviour. Furthermore, the influence of surface condition on the anodization colouring behaviour of aluminium was studied. The microstructure and the surface finish influence on the anodic oxide film growth were studied by optical and scanning electron microscopy. Experiments using a tribometer (ball on disc configuration) were performed in order to evaluate the tribological properties of the material. Salt spray corrosion tests were used to study the corrosion properties before and after the anodizing process.Peer ReviewedPostprint (published version