Non-ferrous metal | EPFL Graph Search

In metallurgy, non-ferrous metals are metals or alloys that do not contain iron (allotropes of iron, ferrite, and so on) in appreciable amounts. Generally more costly than ferrous metals, non-ferrous metals are used because of desirable properties such as low weight (e.g. aluminium), higher conductivity (e.g. copper), non-magnetic properties or resistance to corrosion (e.g. zinc). Some non-ferrous materials are also used in the iron and steel industries. For example, bauxite is used as flux for blast furnaces, while others such as wolframite, pyrolusite, and chromite are used in making ferrous alloys. Important non-ferrous metals include aluminium, copper, lead, tin, titanium, and zinc, and alloys such as brass. Precious metals such as gold, silver, and platinum and exotic or rare metals such as mercury, tungsten, beryllium, bismuth, cerium, cadmium, niobium, indium, gallium, germanium, lithium, selenium, tantalum, tellurium, vanadium, and zirconium are also non-ferrous. They are u

Interaction between liquid aluminium and solid iron Al-rich intermetallics formation

Guillaume Pasche

Intermetallic phases formation is one of the phenomena, which when coupled to thermal and mechanical strains leads to the premature wear of aluminium die casting tools made out of steel. This work focuses on two aspects of this wear problem. The first and major part investigates a simplified chemical system Fe(s)–Al(l) at 700 °C in order to study the formation of the intermetallic compounds. The second part focuses on the limitations of the tool wear by testing different coatings on the steel currently used for die casting. Experiments are performed on two sample types, differentiated by their interface orientation between the two initial phases (vertical and horizontal). Observation are also of two types. Post mortem observations are performed by light microscopy and both scanning and transmission electron microscopy. In situ observation are performed by X-ray tomography, that allows to follow the evolution of the intermetallic layer with time. In the Fe(s)–Al(l) system, one main phase, namely Fe2Al5 , forms with a particular morphology called tongue-like feature in the iron matrix. Tongue tips are generally single crystals. It is also observed that these exhibit a periodical contrast at the nanometre scale. This contrast is found to be due to a slight chemical variation within the existence domain of Fe2Al5. This splitting is linked to the spinodal decomposition of the phase observed at higher temperature. At the interface between tongues and the iron matrix, a layer of about hundred nanometres that surrounds the tongues is observed. It corresponds to the Æ2 FeAl phase. Iron matrix, due to the tongue growth, suffers a plastic deformation that is observed by recrystallisation of the direct tongue surrounding. The induced strain field also leads to porosity formation at the interface between the tongues and the matrix. Pores are then trapped in the Fe2Al5 phase and partially disappear near from the liquid interface. At this interface, a layer of the order of 10μm of Fe4Al13 is observed. The thickness of this layer is stable in the explored time range of 0-4 h. However, intermetallic blocks that detach from the layer are observed in the liquid. This is interpreted as mainly due to the dissolution of the formed layer in the bath to achieve its saturation in Fe. Intermetallic thicknesses and tongue density measurements as functions of time allow to highlight the presence of three main growth regimes. The first at the beginning of the contact corresponds to rapid emergence of the tongues in the matrix. The second is linked to their progressive slow down while they start to thicken. Both thickening and tip growth are in competition from the beginning of this regime. A third regime is however defined and corresponds to a more stable growth during which thickening and tip growth still act in parallel is but their effect is less visible as they vary with the square root of time. The tongue growth observed at the beginning of the reaction is explained by a growth front destabilisation, similarly to the destabilisation of a planar front that leads to dendritic solidification described by Mullins and Sekerka. A calculation based on their model is proposed and confirms the effect of the law aluminium diffusion in iron but is limited by assumptions made for its development. Technological investigation proceeds by modification of the studied system and comparison with the fundamental one. Two ferrous materials and one aluminium alloy are studied. In addition, different coatings deposited by electroless plating on one of the ferrous substrates are tested. A quality coefficient is proposed in order to compare the result of the contact between coating and liquid aluminium. One Co-based coating is revealed as the most promising material that allows to limit the wear of the ferrous part by liquid aluminium.

EPFL2013

Laser Welding of Nickel-Titanium and Stainless Steel Wires

Jonas Vannod

The biomedical industry has an increasing demand for dissimilar metal joining processes, which are used for complex configuration designs, such as guidewires and other intravascular interventional devices. Their production becomes more and more challenging as they decrease in size to reach components at the micron range. Nickel-titanium alloys are commonly used for their shape memory and biocompatibility properties, but are difficult to combine with other biocompatible metals, especially ferrous alloys such as stainless steels. Laser welding is a promising technique to achieve such small and complex shape joints. Indeed the laser high energy density reduces the size of the heat affected zone and the high cooling rate can avoid unwanted phase formation, especially in the particular case of dissimilar joining. Moreover, the high versatility of the technique allows to change the dilution factor in the weld pool in order to carefully select the joint microstructure. In this thesis, the laser welding process has been applied to superelastic nickel-titanium (NiTi) joining to stainless steel (SS) in the case of submillimetric diameter wires. The welded couple strength and microstructure have been optimized by investigating the influence of the laser parameters of both pulsed and continuous laser welding modes, to achieve sound welds. First, the NiTi-SS system has been studied using controlled speed solidification experiments that were performed to characterize the solidification path and its resulting microstructure according to the dilution factor of the base materials. Bridgman and infrared furnace experiments were correlated to the ternary Ni-Ti-Fe phase diagram to identify the possible phases that might form during laser dissimilar welding. Then, the laser welding process was optimized according to the previous results using several parameters to modify the solidification interval, dilution factor and cooling rate in particular. The weld quality was characterized by tensile testing and fracture surface analyses, in order to select the welding parameters leading to repeatable sound welded couples. Finally, the fracture behaviour of the welded couples was carefully investigated to understand the limitation of the tensile strength by the NiTi superelastic stress. In situ tensile experiments, mechanical property characterization and modelling were performed to determine the fracture mechanism occurring at the NiTi-weld interface during testing. Based on these observations, a simple composite model was designed to explain this precise fracture location and the upper limit, which is equal to the superelastic stress. Moreover, perspectives were detailed in order to possibly avoid this mechanical strength issue. This thesis has also emphasized the need to connect several complementary techniques, such as mechanical properties investigations, solidification path characterization and modelling to tackle complex materials science issues, such as dissimilar laser welding.

EPFL2011

Influence of a Nanometric Al2O3 Interlayer on the Thermal Conductance of an Al/(Si, Diamond) Interface

Christian Monachon, Ludger Weber

The effect of an Al2O3 interlayer on the thermal conductance of metal (Al)/non-metal (diamond and silicon) interfaces is investigated using Time Domain ThermoReflectance (TDTR). Interlayers between 1.7 and 20nm are deposited on oxygen-terminated diamond and hydrogen-terminated silicon substrates using atomic layer deposition (ALD). Their overall conductance is then measured at temperatures ranging from 78 to 290K. The contributions of the interlayer bulk and its interfaces with both substrate and metallic overlayer are then separated. Values thus obtained for the bulk interlayer conductivity are comparable with existing data, reaching 1.25Wm(-1)K(-1) at 290K. Interface contributions are shown to be very similar to the values obtained when a single Al/substrate interface is investigated, suggesting that interfacial oxides may govern TBC independently of the interlayer's thickness.