Antonio Forn

Mechanical and tribological properties of high velocity oxy-fuel thermal sprayed nanocrystalline CrCNiCr coatings

Abstract One of the most important use of high velocity oxy-fuel (HVOF) thermal spray coatings is for wear resistance. In this work, the characteristics of nanocrystalline CrCNiCr coating and their effect on the mechanical and tribological properties of the material have been investigated. The objective of this study is the replacement of hazardous hard chromium plating technology used today in industry for an efficient and clean HVOF technology, using micro- and nanocrystalline CrCNiCr coatings. Commercially available, CrCNiCr powder was mechanically treated, in order to obtain nanopowders. Later, the HVOF thermal spray process was used to produce conventional and nanocrystalline CrCNiCr coatings. The coating microstructures were characterised by SEM and optical microscopy. Differences in roughness have been determined by profilometry. The ultra-microindentation technique was applied to measure the hardness and the elasto-plastic properties of the coating. In order to evaluate the friction and wear properties of different substrate materials, a pin-on-disc method has been used.

Mechanical and tribological properties of TiCxN1−x wear resistant coatings

The aim of this work is to investigate the mechanical and tribological properties of Tic x N 1-x wear resistant coatings grown on a Ti-0.2 Pd alloy substrate. Films were deposited by dual ion beam sputtering (DIBS) system with different proportions of N 2 and Ar in the assisting beam. The friction tests have been carried out with a pin-on-disc tribometer with different applied loads. The films present high hardness and elastic properties whose values depend upon preparation conditions. The mechanical properties and the tribological behaviour of the coatings seem to depend on their stoichiometry and microstructure. The coating TiC 0.5 N 0.5 shows less hardness and better wear resistance than the coating with stoichiometry Tic 0.15 N 0.85 . The influence of the stoichiometry and the local structure of the films on its mechanical properties have been ruled out.

Spinel effect on the mechanical properties of metal matrix composite AA6061/(Al2O3)p

Abstract The effect of 22% Al2O3 particles addition on the 6061 aluminium cast alloy, has been evaluated. With the aim of achieving a suitable understanding about this effect, a comparative study of mechanical behaviour, at room temperature, of the reinforced and unreinforced AA6061 alloy was carried out. The results suggest a decohesion between matrix and reinforcement, that involves a loss of mechanical properties. A fractographic study carried out by scanning electron microscopy (SEM), reveals that the fracture of the reinforced material takes place in the matrix–Al2O3 particles interface. The fracture mechanism seems to be influenced by spinel presence surrounding the aluminium oxide particle surface. The spinel creation comes about during the cast process promoting the loss of adherence between the aluminium matrix phase and the reinforced particles. In spite of the spinel attendance, one can notice that the aluminium matrix composite AA6061/(Al2O3)p in the T6 condition, that is, submitted to age hardening treatment, suffers a remarkable mechanical behaviour improvement. Transmission electron microscopy and X-ray diffraction techniques have allowed the microstructural change study and the spinel role in the Al–Al2O3 interface.

Effect of Heat Treatments in the Silicon Eutectic Crystal Evolution in Al-Si Alloys

This paper describes the heat treatment effect on the eutectic silicon evolution in the A357 alloy, obtained by semisolid forming process (SSM). The coarsening rate of the silicon was determined by Image Analysis Technique in specimens from rheocasting ingots and thixocasting components. The study was realized in the temperature range from 450 to 550°C by applying heating times between 1 and 24 hours. The results show that during the heat treatment the coarsening and sphereodization of the silicon particles is produced and the fragmentation stages, which are observed in conventional alloys, do not appear. Kinetic silicon growth has been adjusted to the Oswald’s ripening equation.

Mechanical and tribological properties of Al–Si–Mo plasma-sprayed coatings

Abstract One of the most important uses of plasma spray coatings is for wear resistance. In this work, the coating characteristics of plasma spray Mo, Al–Si and Al–Si–Mo coatings and their effect on the mechanical and tribological properties of the material have been investigated. The coating microstructures were characterised by SEM and optical microscopy and the porosity percentage was determined by image analysis technique. The mechanical properties of the coatings have been determined by means of an ultra-microindenter and the wear tests have been carried out with a pin on disc tribometer under several load conditions. The mechanical properties of Al–Si–Mo coatings increases with the Mo percentage and Al–Si with 30% Mo shows the optimum tribological characteristics.

Thixoextrusion of A357 aluminium alloy

The aim of this work is to attempt the application of A357 Al-Si-Mg cast alloy in the thixoextrusion process, evaluating the different forming parameters effect. Thixoextrusion offers several advantages compared with traditional hot-extrusion such as lower pressure, minor friction forces, higher material fluidity and longer tool life. This type of semi-solid process requires high solid fraction (0.7 0.85) is less sensitive to temperature drops and allows more stable material flow at higher speeds. To know the forming parameters that improve the mechanical properties of thixoextruded parts, some extrusion tests were carried out. The results were used as the main criteria for assessing the thixoforming viability of the A357 alloy.

Sub Liquidus Casting Technology for the Production of High Integrity Component

This work is a contribution to improve the knowledge of components behavior produced by semi-solid processes particularly the Sub-Liquidus-Casting process. Die design was supported by using the Procast simulation program. The effect of the different variables of the process in structural integrity of the product has been described and analyzed. The components were produced using A356 alloy formed on a pilot plant with a 400 Ton THT press. The components study was made by RX, metallographic analysis and mechanical tests. The effects of T5 and T6 heat treatments were also studied.

Anodic Oxide Layer Formation on A357 Aluminium Alloy Produced by Thixocasting

Anodizing is widely used in the surface treatment of aluminium alloys in order to preserve the integrity of the alloy surface, to minimize the need for maintenance and repair, and to maximize the component life. The aim of this work is to study the influence heat treatments (T5 and T6) have on the anodization of A357 aluminium alloy produced by a Thixocasting process. In particular the effect of shape, size and distribution of silicon and intermetallic phases on the anodic oxide film formation. SEM and EDS analyses were used to examine the microstructural features found on, within and under the anodic oxide layer. Experiments using a tribometer (pin-on-disc tests) were performed in order to evaluate the friction and wear properties of the different layers.

Anodizing of A356 T6 Alloys Obtained by Sub-Liquidus Casting

Semi solid processing reduces porosity and amount of trapped gas and it allows heat treatment T6 that improves a hard anodized oxide layer. The aim of this work is to show the anodizing possibility of A356 T6 components conformed by Sub-liquidus Casting (SLC) to improve wear and corrosion resistance. This work compares the anodizing effect on tribological properties and corrosion resistance between components obtained by A6061 T6 extruded alloys and from A356 T6 produced by SLC. The effect of rounded silicon crystals on the coating formation and the fracture produced during the coating growth are described.

EN AC-46500 Injected by Semi-Solid Rheocasting

EN AC-46500 aluminium components are formed by Semi-Solid Rheocasting (SSR) in an industrial plant using a 700 tons high pressure machine. The dies wear was designed by the PLCO model of the ProCast simulation software. The components have had a good structural integrity and the mechanical properties after T6 treatment have been equivalent to that obtained by the same alloy by die cast. The present work describes the SSR forming process, the resulting microstructure as well as the optimization of the ageing heat treatment by hardness evolution. The results of the tensile tests make these clear.