On the fundamental mechanisms of active screen plasma nitriding

The nitriding mechanisms of conventional DC plasma treatments have been extensively studied and discussed, but no general agreement has been reached thus far. The sputtering and redeposition theory is among the most accepted ones but, even though this mechanism is feasible, its contribution to the nitriding effect is under question. Furthermore, the novel active screen plasma nitriding technique has been successful in treating samples left at floating potential, where sputtering can not be considered to play a major role. Therefore, it has been proposed that the material sputtered from the cathodic mesh of the active screen furnace (auxiliary cathode) and deposited onto the treated specimens is involved in the mass transfer of nitrogen. The contribution made by this transferred material is the focus of attention of the present study. The hardening effect on the treated specimens showed considerable correlation with the deposition layer, and the XRD analysis of this deposited material yielded possible FeN and FexN peaks. This finding supports the deposition of iron nitrides and their subsequent decomposition on the treated substrate as a mechanism of significance to the plasma nitriding treatments conducted in active screen experimental settings.

Study of active screen plasma processing conditions for carburising and nitriding austenitic stainless steel

Active screen (AS) is an advanced technology for plasma surface engineering, which offers some advantages over conventional direct current (DC) plasma treatments. Such surface defects and process instabilities as arcing, edge and hollow cathode effects can be minimised or completely eliminated by the AS technique, with consequent improvements in surface quality and material properties. However, the lack of information and thorough understanding of the process mechanisms generate scepticism in industrial practitioners. In this project, AISI 316 specimens were plasma carburised and plasma nitrided at low temperature in AS and DC furnaces, and the treated samples were comparatively analysed. Two diagnostic techniques were used to study the plasma: optical fibre assisted optical emission spectroscopy, and a planar electrostatic probe. Optimum windows of treatment conditions for AS plasma nitriding and AS plasma carburising of austenitic stainless steel were identified and some evidence was obtained on the working principles of AS furnaces. These include the sputtering of material from the cathodic mesh and its deposition on the worktable, the generation of additional active species, and the electrostatic confinement of the plasma within the operative volume of the furnace.

Three dimensional printing as a way to create an engaging and meaningful context for learning

Three-dimensional (3D) printers are now commonplace in both primary and secondary schools within Australia. As with most new technologies they present a range of challenges to users in terms of technical problems and support, and how to integrate their use into the curriculum in a meaningful way. This research reports on data from a small number of Victorian primary schools from urban and regional areas. A case study methodology has been used to examine how each setting has approached the use of these printers and includes a review of the literature concerning the uptake of new technologies by non-experts. Data include interview transcripts from teachers, principals and technicians and photographic artefacts of 3D printed objects. Teachers reflected on their reasoning behind lesson plans and their aspirations for future use of 3D printers in the classroom. Some of the issues identified were teacher confidence, time to ‘play’ with and become familiar with 3D printers; and technical challenges that arose such as the time taken to print an object and clogging of printer extruders (heads). Recommendations are made concerning possible ways forward.