Josep A. Picas

Oxidation behavior of HVOF sprayed nanocrystalline NiCrAlY powder

Abstract This paper describes recent progress on the research into improving the oxidation behavior of the bond coat using a HVOF nanostructured NiCrAlY coating. Commercially available NiCrAlY powder was mechanically cryomilled and HVOF sprayed onto Ni-based alloy to form a nanocrystalline bond coat. The powder and coating structure were characterized by XRD, SEM, and TEM. Oxidation experiments were performed on the coating to form the thermally grown oxide layer (TGO). After heat treatment at 1000 °C for 24 and 95 h, a homogeneous α-Al2O3 layer was formed on top of the bond coat. The oxide layer was analyzed and compared to the coating sprayed using the as-received powder. As shown in the results, the nanostructured characteristic of the coating and the presence of Al2O3 within the cryomilled powders (oxidation occurred during cryomilling process) seem to affect the nucleation of the alumina layer on the top of the coating. The formation of a continuous TGO layer protects the coating from further oxidation and avoids the formation of mixed oxide protrusions, such as those presented in the coating sprayed using the as-received powder.

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.

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.

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.

Effect of Ultrasounds during the Solidification Process of the A357 Aluminium Alloy

It is known that ultrasonic waves promote nucleation and globulization of solid particles in aluminium alloys. However, the studies performed up to date have been conducted, in the laboratory, using small volumes of aluminium. This article aims to establish the application of ultrasound effect in the A357 aluminium-silicon alloy in amounts of about 2 kg of material. The experiments have been conducted with different parameters of ultrasonic treatment, evaluating the microstructure of the slurry quenched from the semi-solid state. The globulization effect of aluminium α phase by ultrasounds is very effective in the area close to the ultrasonic horn tip and the transmission system, but its effect highly reduces in the regions far away from the source of ultrasonic waves.

Characterisation of Laser Modified WC‐CoCr Coatings

In this work the affects of laser characteristics on surface morphology, microstructure, microhardness and wear rates of high velocity oxygen fuel (HVOF) WC–CoCr coatings were investigated. Continuous and pulsed laser treatments were applied on the HVOF coatings using a CO2 laser of 10.6 μm wavelength. Continuous laser treatment significantly improved homogeneity of the coatings. Pulsed laser treatment produced significantly higher discontinuities compared to continuous mode. Microhardness increased by 45% for continuous mode laser modified WC-CoCr coatings. However, wear resistance deteriorated, with a notable 40% increase in wear rate. The variations in coating properties were attributed to the re-melting and rapid quenching of the CoCr bonding matrix allowing for WC redistribution.