M. Grech

Post-deposition heat treatment of co-deposited Cr3C2 and AISI 410 stainless steel using the coaxial laser deposition technique

Cr3C2 ceramic powder is added in varying amounts to AISI 410 stainless steel powder to develop AISI 400 based alloys with varying chromium and carbon content using the coaxial laser deposition technique operating at parameter sets which guarantee full melting of the constituent powder particles. Theoretical isothermal curves for the in situ generated alloys are correlated with the as-deposited and heat-treated microstructures using electron microscopy, X-ray and electron backscatter diffraction techniques. It is concluded that with an increased carbon loading in the mixture, post-deposition heat treatment involving full re-austenitising and tempering is necessary in order to reduce the effect of solute trapping which negatively affects the material mechanical properties.

Determination of the fatigue limit of an austempered ductile iron using thermal infrared imagry

Previous work by the authors showed that the endurance limit of specimens, or mechanical components, can be predicted using thermal infrared imagery. The new technique enables the determination of the fatigue strength limit in a comparatively short period of time (few thousands cycles), and using very few specimens (theoretically only 1). The present work applies this technique to rotating-bending test specimens of austempered ductile iron, an alloy whose fatigue limit is, due to the high scatter dispersion of the data points and the long testing period required, generally difficult to determine by the traditional technique. This material exhibited higher fatigue strength than the familiar nodular cast iron. This was confirmed by the results derived from the traditional Wohler test and the new technique, and supported by the data gathered from literature.

Characterisation, wear and corrosion testing of laser-deposited AISI 316 reinforced with ceramic particles

Abstract Direct laser deposition was used to create tracks and surfaces using AISI 316 stainless steel powder blended with alumina, tungsten carbide or chromium carbide, with the aim to apply localised reinforcement to stainless steel components. Co-deposition of the powders was carried onto an AISI 316 stainless steel surface to evaluate parameters, and to produce specimens for metallography, EDX and XRD analysis and microhardness tests. Testing of the specimens produced using selected parameters included pin-on-disc wear tests, slurry pot erosion and corrosion testing. The alumina failed to produce a useful improvement to material properties. Tungsten carbide improved wear resistance by 260 times while erosion resistance was doubled; chromium carbide gave a maximum improvement of 88 time to sliding wear resistance, and a 2·3 times maximum improvement of erosion resistance. Chromium carbide-reinforced material furthermore performed well in corrosion tests. The deposition and testing of these materials is described and the outcome of the tests carried out is reported.

Direct laser deposition and sliding wear of AISI316/WC10Ni and AISI316/Cr3C2 surfaces

Abstract The deposition of AISI316 stainless steel with tungsten carbide agglomerates and chromium carbide powder was carried out as part of an investigation aimed at determining the feasibility of applying localised reinforcement to stainless steel components. The codeposition of tungsten carbide agglomerates or sintered chromium carbide powder with AISI316 stainless steel powder was carried out to evaluate parameters and produce surfaces for pin on disc wear tests. The wear resistance of the surfaces was improved by the addition of both materials, with the tungsten carbide reinforcement resulting in a higher wear performance while the chromium carbide produced better surface consistency. The deposition and structure of these test pieces are described and the outcome of the tests carried out reported.

RIBAD Deposition of TiN on Magnesium Alloy

TiN coatings were produced by depositing a series of Ti layers and subsequently ion implanting 80 keV nitrogen ions. TRIDYN FZR software simulation was used to estimate the maximum Ti layer thickness which could be successfully transformed to TiN by ion implantation. The chemical profile of these coatings was achieved by conducting a series of EDS measurements across coatings, sectioned at shallow angles. It was found that the structure of the RIBAD TiN films produced changes significantly with the implanted nitrogen ion dose. Their hardness and wear resistance were found to increase rapidly as the post implantation time was increased up to 230 minutes, reaching a maximum of 27GPa and 2.5x10-12 mm3m-1N-1 respectively. On the other hand, the electrochemical corrosion resistance of TiN coated magnesium substrate was inferior to that of the untreated substrate material. The results suggest that the coating developed is attractive as a topcoat of a duplex coating; having as underlay a corrosion protective film. In a separate study, it has been shown that such coatings could be ion beam sputtered titania or alumina.