Papers by Author: Patrick J. Masset

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Authors: Patrick J. Masset, Mathieu Laurent, Michael Schütze
Abstract: Surface modifications with well defined amounts of fluorine have proven to improve significantly the oxidation resistance of titanium aluminides and to offer the potential to decrease the sensibility of TiAl-based alloys against environmental embrittlement. By means of combined EPMA and SEM analyses the formation of an oxide layer on fluorine treated specimens was characterised. The thicknesses of the external oxide layer as well as the oxygen and nitrogen-rich subsurface layer were measured. Their growth kinetics was found to follow a cubic and a parabolic law, respectively. By subtracting the mass variation due to the ingress of oxygen and nitrogen into 2-Ti3Al, underneath the alumina layer, this allowed calculating the true value of the kinetic constant for the growth of a pure alumina layer on titanium aluminides.
Authors: Patrick J. Masset, Rossen Yankov, Andreas Kolitsch, Michael Schütze
Abstract: Surfaces of titanium aluminides were treated by fluorine either physically using Plasma Immersion Ion Implantation (PI³) or chemically with a F-based polymer. By controlling the fluorination parameters, both treatments improve the oxidation resistance even in the presence of sulfur dioxide (0.1 vol%). No sulfur was detected in the oxide scale although thermodynamic calculations predict the formation of sulfides. The inward diffusion of oxygen and nitrogen in the alloy was found to be reduced in the presence of SO2.
Authors: B. Pelic, D. Rafaja, Patrick J. Masset, H.J. Seifert, L. Bortolotto, Michael Schütze, G. Wolf, I. Loeh
Abstract: γ-TiAl intermetallics are attractive materials for high-temperature structural applications in the aerospace and automobile industries. However, they show environmental embrittlement at elevated temperatures that is mainly related to their low high-temperature corrosion resistance. One way how to improve the high-temperature corrosion resistance is the deposition of protective coatings on the surface of the base material. In this study, samples of a Ti-Al alloy with the chemical composition Ti-48Al-2Cr-2Nb (at.%) were covered by physically vapour deposited (PVD), by metalorganic chemically vapour deposited (MOCVD) and by high-velocity oxy-fuel (HVOF) sprayed coatings. All coatings were based on the Ti-Al alloys and contained different amounts of alloying elements. The corrosion experiments were performed in molten salts containing 75 wt.% Na2SO4 and 25 wt.% NaCl at 850°C up to 336 h. Both, PVD and CVD protected coatings reduced the changes in the mass of the samples over the corrosion time. Still, the formation of TiO2 could not be avoided, as it was confirmed by glancing-angle X-ray diffraction experiments.
Authors: Hans Eberhard Zschau, Daniel Renusch, Patrick J. Masset, Michael Schütze
Abstract: A new method is proposed to achieve a dense protective alumina scale for Ni-base superalloys with an Al-content lower than 10 wt.% at temperatures above 1000°C. The method is based on the halogen effect. Thermodynamical calculations show the existence of a region for a positive fluorine effect at temperatures between 900-1200°C for the alloys IN738 and IN939. By using fluorine ion implantation in combination with Monte Carlo simulation of the fluorine profiles these results were transformed into a region of F-concentrations at the metal surface. A dense protective alumina scale was formed for IN738 after oxidation at 1050°C. Due to the very low Al-content no alumina scale was found for IN939.
Authors: Agnieszka Bogusz, Patrick J. Masset
Abstract: The interface metal/molten oxide is of interest for several high temperature processes (metallurgy, gasification). The exchange reactions occurring at the interface between the metal and the molten slag are complex and up to date not well understood. More generally, this is of importance for the understanding of the exchange reaction kinetics between one metallic compound (solid or liquid) and an ionic one (slag). This work proposes a theoretical approach which takes into account the effect of speciation in the slag on the diffusion process of the species in the two phases and the redox reaction occurring within the vicinity of the interface. The systems investigated consist of Fe and CaO-SiO2 without convection. The concentration profiles of silicon and iron oxide in both parts were calculated. The effect of impurities present in metal phase such as sulphur in the molten slag was investigated. This provides a basis of comprehensive approach for the purification of metal and a better understanding of processes at metal/oxide interface.
Authors: Hadj Latreche, Guido Tegeder, Gerhard Wolf, Patrick J. Masset, Till Weber, Michael Schütze
Abstract: Chlorine gas is widely encountered in chemical industries, as well as in waste incinerators and plastic/polymer decomposition mills. The presence of chlorine may significantly reduce the life-time of the components. Under chlorine-based atmospheres, the process of scale formation may be considerably affected and the presence of chlorine usually impedes the formation of a long term protective dense oxide scale. Based on thermodynamic calculations and previous investigations, NiAl and NiAlMo APS-coatings were produced to be used as protection for conventional steels against chlorine corrosion. Indeed, thermodynamic diagrams showed that molybdenum should have a positive behaviour in “reducing”-chloridizing atmospheres, whereas aluminium has a positive behaviour in “oxidizing”-chloridizing atmospheres. Coatings of approximatively 300 μm thickness were thermally sprayed on Armco Iron and on a commercial ferritic 18 Cr steel. This work presents the corrosion behaviour of NiAl and NiAlMo APS-coatings under chlorine-based atmospheres at 800°C. In addition, metallographic characterisation as well as EPMA investigations of the coating cross sections were carried out before and after the corrosion tests.
Authors: Sven Neve, Kurt Stiebing, Lothar P.H. Schmidt, Hans Eberhard Zschau, Patrick J. Masset, Michael Schütze
Abstract: Using the halogen effect TiAl-alloys can be protected against high-temperature oxidation. Two different fluorination methods were applied to turbine blades. The mass increase due to oxidation can be drastically reduced compared to untreated specimen. A new vacuum chamber for ion beam analysis was developed to analyze the real parts. Using PIGE-technique the F-content as a function of depth before and after oxidation was detected. Thickness and composition of the oxide scale were measured by RBS. Both ion beam methods were non destructive and thus enabled for the first time quality assurance of the halogen treatment on real components.
Authors: Patrick J. Masset, Agnieszka Bogusz, Jan Sieniawski, Bartek Wierzba, Katarzyna Tkacz-Śmiech
Abstract: Results Concerning Nickel Aluminisation with Application of Chemical Vapour Deposition Method Are Presented. Two-Step Processing under Investigation Consists of Al Chloride Formation in the Primary Vessel and Al Deposition in the Secondary One. the Initial Gas Stream Is Composed of Hcl Dissolved in H2 at Various Ratios. it Was Shown that the Choice of the [HCl]/[H2] Ratio and the Determination of the Optimum Temperature to Produce Most Preferential β-Nial Phase May Be Done with the Use of Thermodynamic Calculations. the Results Obtained with Application of Factsage Program Confirm Essential Influence of both Initial [HCl]/[H2] Ratio (in the Range between 0,05 and 100) and the Temperature in the Second Vessel (1123 K – 1323 K) on Aluminium Chloride Partial Pressures and Hence Aluminium Content in its Gaseous Donors and at the Substrate Surface (boundary Condition for Interdiffusion in Ni-Al System). it Was Confirmed that β-Nial Growth Is Favoured at Low [HCl]/[H2] Ratios and High Temperatures for which Alcl and AlCl2 Partial Pressures Increase with Respect to that of AlCl3. the Thermodynamic Predictions Remain in Agreement with CVD Experiments. the Presented Thermodynamic Data May Be Used as a Source of Essential Information for Designing Further Experiments in this Field as Well as for Modelling of Solid-State Diffusion in Ni-Al System.
Authors: Hans Eberhard Zschau, Patrick J. Masset, Michael Schütze
Abstract: A new method for the oxidation protection of Ni-base superalloys with relatively low Al-content is proposed. By using the halogen effect the Al activity on the surface can be increased. Thus, the formation of a pure protective alumina scale becomes possible. The alloys IN738 and IN939 are considered in the present paper. Thermodynamic calculations for fluorine and chlorine predict the existence of the halogen effect for both alloys at temperatures between 900°C and 1200°C. The results also predict a change of the oxidation mechanism from internal alumina formation to external oxidation.
Authors: Ludovic Charpentier, Patrick J. Masset
Abstract: The thermal decomposition of pyrite was investigated under reducing atmosphere, e.g. p(O2)~10-6 bar. Thermogravimetric measurements were coupled with differential scanning calorimetry and mass spectrometry. Multi-scan method was used to calculate the values of the activation energy of the reaction of thermal decomposition of the pyrite. It was shown that the value of the activation energy of the decomposition of pyrite into pyrrhotite varies with the reaction progress. The values of activation energy vary from 250 to 350 kJ.mol-1.
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