Daniel Fabijanic

Influence of Surface Mechanical Attrition Treatment Attrition Media on the Surface Contamination and Corrosion of Magnesium

Surface mechanical attrition treatment (SMAT) is a mechanical peening process used to generate ultrafine grain surfaces on a metal. SMAT was carried out on pure magnesium using different attrition media (zirconia [ZiO2], alumina [Al2O3], and steel balls) to observe the effect on microstructure, surface residual stress, surface composition, and corrosion. Surface contamination from SMAT was characterized using glow discharge optical emission spectroscopy (GDOES). The SMAT process produced a refined grain structure on the surface of Mg but resulted in a region of elemental contamination extending ~10 μm into the substrate, regardless of the media used. Consequently, SMAT-treated surfaces showed an increased corrosion rate compared to untreated Mg, primarily through increased cathodic kinetics. This study highlights the issue of contamination resulting from the SMAT process, which is a penalty that accompanies the significant grain refinement of the surface produced by SMAT. This must be considered if attemp...

Advances in tailored hot stamping – innovations in material and local patchwork topology

Hot stamping is now commonplace in the automotive industry. The continuing need by automotive manufacturers to reduce weight while increasing crashworthiness has driven the industry to seek new hot stamping solutions. Tailored hot stamping can be thought to produce a part that has patchwork of hard and soft regions. In this context, patchwork means that there is a relational organization (topology) to the network of hard and soft regions. The next generation of tailored hot stamping will therefore combine new steel grades together into a single part, and secondly will be able to locally tailor material properties to meet detailed engineering targets. The key to meeting engineering demands will be how the patchwork material properties are organized on the part. This paper will briefly outline our latest research in tailoring parts.

Cold spray of Al-MMC coatings on magnesium alloys for improved corrosion and wear resistance

Cold spray coatings are considered promising for surface protection of Mg alloys from wear and corrosion since the process temperature is low enough to avoid oxidation of the Mg or any adverse affects on artificial ageing heat treatments. A special version of cold spray known as Kinetic Metallization has been used to produce pure Al and Al alloy metal matrix composite (MMC) coatings on AZ91 Mg alloy substrates in the present work. This surface treatment produces dense coatings with high adhesive and cohesive strength, which have substantially higher hardness and wear resistance than the AZ91 substrate material. The influence of coating composition and subsequent heat treatment on wear and corrosion performance have been investigated, using pin-on-disc wear tests, salt spray testing and electrochemical polarisation techniques. The heat treatment of the cold spray coatings is compatible with the solutionising and T6 ageing heat treatment of AZ91Mg. The results show that cold spray deposition of MMC coatings is a simple and effective technique for improving the surface properties of Mg alloys, both in the as-cast and in the heat treated condition

Enhancing the localised corrosion resistance of 316L stainless steel via FBR-CVD chromising treatment

ABSTRACT The resistance of stainless steels to localised corrosion can be adversely affected by environmental and metallurgical heterogeneities existed in complex industrial infrastructures such as seawater desalination plants exposed to aggressive evnironments. It is therefore critical to enhance the localised corrosion resistance and understand the corrosion behaviour of stainless steels in complex and aggressive industrial environmental conditions. In this work, the localised corrosion resistance of chromised stainless steel 316L (SS316L) in simulated seawater desalination systems has been investigated by electrochemical and surface analytical techniques. It has been found that chromising processes have improved the localised corrosion resistance of SS316L by reducing its susceptibility to pitting, crevice, and welding zone corrosion in simulated seawater desalination environments. This increased corrosion resistance has been explained by electrochemical polarisation studies and surface analysis showing that the chromising treatment at 1050°C resulted in a continuous and stable chromium-enriched layer on the SS316L surface.

Characterization and Tribological Performance of Cu-Based Intermetallic Layers

Fluidized bed reactor chemical vapor deposition (FBR-CVD) has been used to enrich the surface of oxygen free high conductivity (OFHC) copper with titanium, silicon and aluminum. This technique enables the production of coherent and adherent intermetallic surface layers of uniform thickness and high hardness. The characterization of the coatings was performed using backscatter scanning electron microscopy (BS-SEM), X-ray diffraction (XRD), glow discharge optical emission spectroscopy (GDOES) and micro-hardness. The tribological properties of the coatings in dry sliding contact with steel were evaluated by pin-on-disc wear testing.

Microstructure and mechanical properties of nitrided and chromized short steel fiber reinforced aluminum based P/M composites

The present investigation is on the microstructure evolution and hardness of powder metallurgically processed Al- 0.5 wt.%Mg base 10 wt.% short steel fiber reinforced composites. The 0.38 wt.% C short steel fibers of average diameter 50μm and 500-800μm length were nitrided and chromized in a fluid bed furnace. Nitriding was carried out at 525°C for 90, 30 and 5 min durations. Chromizing was performed at 950°C for 53 and 7 min durations, using thermal reactive deposition (TRD) and diffusion technique. The treated fibers and resulting reaction interfaces were characterized using metallographic, microhardness and XRD techniques.

Surface Modification for Enhanced Corrosion Resistance Using Fluid Bed Reactor Chemical Vapour Deposition (FBR-CVD)

The use of materials with otherwise desirable mechanical properties is often problematic in practice as a result of corrosion. Susceptibility may arise for a number of reasons, including an electrochemically heterogeneous surface or destabilisation of a passive film. These shortcomings have historically been overcome through the use of various coatings or claddings. However, a more robust surface layer with enhanced corrosion resistance could possibly be produced via local surface alloying using a fluidised bed. A fluidised bed treatment allows a surface to be alloyed, producing a distinct surface layer up to tens of microns thick. Surface alloying additions can be selected on the basis of whether they are known or suspected to enhance the corrosion resistance of a particular material, whilst at a minimum, surface alloying likely provides a more electrochemically homogeneous surface. Electrochemical evaluations using potentiodynamic polarisations in NaCl electrolytes have shown chromised plain carbon and stainless steel surfaces have decreased rates of corrosion, decreased passive current densities, and ennobled pitting potentials relative to untreated specimens.

Surface alloying of metals using fluid bed reactor

The use of fluidised bed reactors for surface alloying is reviewed. Research at Deakin has includes the use of chemical vapour deposition to form chromium rich layers on ferrous substrates, including stainless and tool steel grades. These layers can be modified to carbide or nitride if required by the end application. The deposition of aluminium and silicon has also been successfully achieved.