Stephen Abela

Autogenous Laser Keyhole Welding of AISI 316LTi

Effective autogenous full-penetration welding of 4 mm thick AISI 316LTi austenitic stainless steel bars was achieved using a CO2 laser. The welding process parameters required to obtain an optimal and repeatable procedure giving the best quality welds were identified. The use of side jet of gas suppressing plasma formation was investigated, and it was discovered that there are optimal conditions that result in increased power transmission and improved repeatability. Tests were carried out on the final welds in the as-welded state and in the annealed state. These included microstructural and X-ray diffraction (XRD) analysis as well as potentiodynamic and salt spray corrosion tests. Microstructural analysis showed that solidification occurred in primary ferrite solidification (FA) mode. Application of a heat treatment to the welded samples dissolved the ferrite, but resulted in carbide precipitation diminishing resistance to pitting, and the corrosion tests carried out demonstrated that the corrosion-resistant properties of the material were not compromised by the welding process, and that a post-process heat treatment was unnecessary.

Coating of diamond particles for production of metal matrix composites

Abstract In an effort to produce more cost effective diamond to metal interfaces, mono- and polycrystalline diamond powders were coated with nickel alloys using electroless chemical deposition techniques. Ni–P and Ni–B coatings were deposited using an acidic and an alkaline solution respectively. These deposition procedures were preceded by a thermal surface functionalisation step and a sensitisation step using a Pd–Sn colloidal solution. Imaging by SEM and chemical analyses show uniform coverage of the coating, independent of diamond’s crystalline planes, and having thicknesses consistently <200 nm.

The Effect of Climatic Parameters on the Heat Transfer Mechanisms in a Solar Distillation Still

This paper deals with a simple and inexpensive solar desalination configuration. The performance of a simple solar still operating under Maltese climatic conditions is analyzed both theoretically and experimentally. The internal and external heat transfer modes of the distillation unit are examined. This paper concludes that the distillation rate in a simple solar distiller increases with ambient temperature and solar radiation, even though the condensation capacity of the glass is reduced. A higher wind speed decreases the evaporation and condensation processes. The energy fractions within the solar still have also been analyzed. The simulations and the experiments conclude that the glass components handle the bulk of the heat transferred in a solar still, namely, radiation, evaporation, and condensation, and thus the distillation efficiency is enhanced by improving the thermal and optical properties of the glass.

Protective Coatings for Magnesium Alloys

In the past two decades considerable effort was dedicated to the development of a series of low temperature Physical Vapour Deposition (PVD) techniques suitable for the protection of magnesium alloys. Only a handful of the developed technologies have produced promising results. Some variants of the Ion beam sputter deposition (IBSD), ion beam assisted deposition (IBAD), and reactive ion beam assisted deposition (RIBAD) are among the most promising, as these allow the deposition of hard and dense protective coatings even at room temperature. In the first part of this chapter, the wear and corrosion properties of the selected coating systems will be presented together with a critical analysis of the work published by the author and selected researchers. This will be followed by a more in depth description of the IBAD and RIBAD process. The effect of the various processing parameters on the coating endurance as well as the surface integrity of the substrate materials will be discussed. The relative wear resistance to the pin on disc wear test will be presented and discussed in the light of various experimental evidence collected by the author over the years. This will be followed by a description of a series of test conducted to establish the effectiveness of various coatings in protecting the substrate from electrochemical corrosion in acidified NaCl solutions. The chapter will be concluded with an overview of the current state of PVD technologies with particular emphasis on the strengths and limitations of the existent technology as far as the treatment of light alloys is concerned. Based on the acquired knowledge, the author will endeavour in a discussion of the future trends in PVD and plasma surface modification technologies. A handful of innovative processes and some preliminary results will be included.

Physical vapour deposition of magnesium alloys

Abstract: Ion beam assisted deposited (IBAD) coatings offer corrosion protection comparable to that offered by many conversion coatings in mild corrosive environments. The wear resistance of these coatings is, however, far superior and is comparable to that of the hard coatings deposited on steel substrates. Furthermore, thick alumina coatings can electrically isolate magnesium components and thus minimize the risk of galvanic corrosion in complex assemblies. These coatings are still at the research and development stage. Duplex IBAD coatings can offer both wear and corrosion protection. Complex components can be treated in a relatively short time using an innovative Plasma Immersion Ion Implantation and Deposition (PIIID) technology.

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.