Papers by Keyword: Oxidation Behaviour

Abstract: The effects of rare earth Y addition on microstructure and properties of pure copper were investigated. Mechanical test, electrical test, oxidation resistance test, metalloscope, scanning electronic microscope (SEM) and X-ray difffraction (XRD) were performed to study the properties, microstructure and constitution. The results showed that both the hardness and antioxidant properties obviously increased with the increase of Y, confirmed the successful refinement role of Y. A small amount of Y (less than 0.5 wt.%) could improve the electrical conductivity of pure copper. When the Y content reached 0.2 wt.%, pure coppers obtained optimum electrical conductivity which is 96.8% IACS. However, over-added Y (>0.5 wt.%) resulted in second phase of Cu₇Y coarsening and non-homogeneous microstructures forming, which reduces the conductivity of copper. In addition, Y can effectively purify the organization of molten copper.

Abstract: Light metals are contributing significantly to the weight saving of components and structures of transport means. Regarding airliners FAA recently published a report on the development of a flammability test for magnesium alloys to be used in aircraft seat construction which opens up the options to introduce specific parts in next seat models. In former projects, it was shown that magnesium alloys are offering interesting mass reduction and-by this-fuel & emissions saving potentials in air transport. The major concern is the behaviour of Mg alloys in case of an aircraft fire which was investigated by FAA for particular alloys of Magnesium-Neodymium-Gadolinium, Magnesium-Yttrium-Rare Earth as well as Magnesium-Aluminium-Zinc composition in course to the test methods development. While clearly the AZ31 alloy fails in such a laboratory test, the other two types pass flawlessly by exhibiting a self-extinguishing behaviour shortly after removing the fire source. None of them are specifically usable for high pressure die casting or thixomolding processes which both are common production methods. From the typically used thixomolding alloys like AZ91D, AM50A, AM60B or AJ62A, the Magnesium-Aluminium-Zinc again is likely to fail in flammability tests due to the low-temperature melting network of eutectic phase. Therefore, the development focussed on Magnesium-Aluminium-Manganese and Magnesium-Aluminium-Strontium type alloys. Calcium – well known for the ability to improve the flammability behaviour – was added in certain concentrations to those alloying systems and investigated regarding self-extinguishing performance, manufacturing issues as well as mechanical properties. The results of these examinations are presented in the following paper.

Abstract: Ni-base superalloys are approaching the melting point as their fundamental limitation. For high-temperature components one possibility aiming at a further increase of efficiency, e.g. of jet turbines, is the use of refractory metals. Mo as base material is suitable for operating temperatures far beyond 1200°C. As a consequence of the formation of volatile Mo-oxides, it exhibits no intrinsic oxidation resistance when exceeding 700°C. Mo-Si-B alloys have melting points around 2000°C and retain good mechanical properties and oxidation resistance at very high temperatures. In air, the three-phase Mo-Si-B alloy dealt with in this paper shows excellent oxidation behaviour between 900°C-1300°C as a consequence of the formation of a protective silica scale. Below 900°C, alloys of this class suffer from catastrophic oxidation, leading to an evaporation of Mo-oxide and giving rise to a linear rate law of the weight loss. A protective oxide layer is not formed as a consequence of simultaneous and competitive Mo- and Si-oxide formation. Several approaches are possible to improve the oxidation performance of Mo-Si-B alloys, especially in this moderate temperature range. These include classical alloying, e.g. with Cr aiming for protective Cr-oxide scales, addition of small amounts of reactive elements for microstructure-refinement as well as selective oxidation of silica in oxygen-deficient atmospheres prior to operation in air. The results presented show promising opportunities and indicate that an oxidation protection from room temperature up to 1300°C requires a combination of the suggested approaches.