Papers by Author: Mathieu Brochu

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Authors: Mathieu Brochu, C.A. León, Robin A.L. Drew
Authors: Priti Wanjara, Mathieu Brochu, Mohammad Jahazi
Abstract: The use of electron beam technology for freeforming 321 SS was investigated using 347 SS solid wire and BNi-2 brazing paste as filler materials. The electron beam freeforming (EBFF) studies involved examining the effect of processing parameters on the characteristics of the line build-ups. Specifically, the effective growth rate and the dimensional features (height-to-width ratio) of the build-ups were found to be dependent on the beam energy and the filler material conditions (e.g. wire feed rate and the number of re-melting passes). The EBFF work indicated that build-ups with either filler material could be deposited on 321 SS using an optimized processing window that resulted in properties comparable to technical data available for 347 SS and BNi-2.
Authors: Franck Armel Tchitembo Goma, Daniel Larouche, Carl Blais, Raynald Gauvin, Julien Boselli, Alexandre Bois-Brochu, Mathieu Brochu
Abstract: An integrally stiffened panel (ISP) made from extruded 2099-T83 Al-Li alloy was subjected to fatigue loadings to investigate the influence of both the local texture and grain structure on fatigue crack propagation (FCP) behavior. The microstructure was mainly unrecrystallized. Grains were mostly layered in the web and fibrous in the other locations. Fiber texture components were present in the stiffener locations, and a rolling-type texture in the web. Resistance to FCP decreases as the local aspect ratio increases. Changes in FCP rates in the web, stiffener base and stiffener web were consistent with the microstructural features and texture. The stiffener cap with a strong fiber texture similar to that of the stiffener base exhibited a lower resistance to FCP, suggesting that the influence of the texture is convoluted in the stiffener cap by the markedly different grain structure. Therefore, FCP behavior in this alloy appears to be governed by both texture and grain structure.
Authors: Rosen Ivanov, Julien Boselli, Diana Denzer, Daniel Larouche, Raynald Gauvin, Mathieu Brochu
Abstract: The aerospace industry strives to develop materials allowing an increase in payload and reducing fuel consumption. Al-Li alloys, with their low density and high strength are currently in use for such applications and have potential for additional applications. When compared to composites, utilizing Al-Li alloy products is cost effective for aerospace companies as they do not need to redesign pre-existing fabrication facilities. The joining of these alloys by conventional methods is limited by segregation of alloying elements and the formation of oxides during high temperature exposure. This study focuses on solid state joining method that has the potential to generate low heat and be defect free - Friction Stir Welding (FSW). AA2199 sheets were joined by FSW. Process variables included table force, tool rotation speed and weld travel speed. A post weld heat treatment (PWHT) was applied to improve the mechanical properties by precipitation of strengthening phases. An increase in hardness of the weld zone from 95HV to 125HV upon PWHT was recorded for selected welding conditions. The type and morphology of second phase precipitates is deemed responsible for this effect. It is suggested that the high temperature and high strain levels characteristic of welds with fast tool rotation allow for the dissolution of precipitates during welding. The re-precipitation of these second phases during PWHT allowed the welds to recover strength to the level of the base material.
Authors: David Levasseur, Mathieu Brochu
Abstract: The use of powder metallurgy for near net shape sintering of superalloy could lead to major savings in machining time and material. The main challenge in sintering Inconel 718 is to avoid the formation of a prior particle boundary (PPB) network that is deleterious to the mechanical properties. Using the Spark Plasma Sintering (SPS) technique, it is believed that Inconel 718 powders could be sintered without forming a PPB network due to the fast heating rate achieved and the reported cleaning effect of particle surfaces by the interparticle arc discharges. In this study, Inconel 718 was consolidated to near-full density at 1200°C under 50 MPa of pressure with heating rates ranging from 20°C/min to 800°C/min. The densification behavior of the powder was studied through the analysis of the densification curves and observation of the microstructure evolution from interrupted tests. The fast densification of Inconel 718 in SPS was linked to the formation of a supersolidus liquid phase due to the nature of the heating in this technique.
Authors: David W. Heard, Julien Boselli, Raynald Gauvin, Mathieu Brochu
Abstract: Aluminum-lithium (Al-Li) alloys are of interest to the aerospace and aeronautical industries as rising fuel costs and increasing environmental restrictions are promoting reductions in vehicle weight. However, Al-Li alloys suffer from several issues during fusion welding processes including solute segregation and depletion. Solid freeform fabrication (SFF) of materials is a repair or rapid prototyping process, in which the deposited feedstock is built-up via a layering process to the required geometry. Recent developments have led to the investigation of SFF processes via Gas Metal Arc Welding (GMAW) capable of producing functional metallic components. A SFF process via GMAW would be instrumental in reducing costs associated with the production and repair of Al-Li components. Furthermore the newly developed Controlled-Short-Circuit-MIG (CSC-MIG) process provides the ability to control the weld parameters with a high degree of accuracy, thus enabling the optimization of the solidification parameters required to avoid solute depletion and segregation within an Al-Li alloy. The objective of this study is to develop the welding parameters required to avoid lithium depletion and segregation. In the present study weldments were produced via CSC-MIG process, using Al-Li 2199 sheet samples as the filler material. The residual lithium concentration within the weldments was then determined via Atomic Absorption (AA) and X-ray Photoelectron Spectroscopy (XPS). The microstructure was analyzed using High Resolution Scanning Electron Microscopy (HR-SEM). Finally the mechanical properties of welded samples were determined through the application of hardness and tensile testing.
Authors: Jason Milligan, Mathieu Brochu
Abstract: A strong push has been observed in the automotive industry to replace current components with high-performance and lightweight materials such as aluminum alloys. Novel monolithic materials such as bulk nanostructured materials, cannot always offer the best performance in hostile environments and often have high manufacturing costs. This has required the development and engineering of processes to allow nanostructured surface functionalization of conventional materials. This processing strategy, similar to the metal-ceramic joining approach, exploits the advantages of both materials while reducing overall manufacturing costs. Spark Plasma Sintering (SPS) will be evaluated as potential a method for manufacturing a nanostructured Al-Si cladding. This novel coating method has a significant advantage over traditional processes in that it forms metallurgical bonds at both the interface and throughout the deposited layer to produce a coating with isotropic properties. The objective of this work is to create a nanostructured eutectic Al-Si feedstock powder and simultaneously consolidate and clad the powder onto a forged aluminum substrate using Spark Plasma Sintering. Results show that after mechanical milling, the aluminum grain size was refined to 47nm. The results also show that SPS is capable of sintering the powder in extremely short sintering times while maintaining nanostructure, and that the heating rate has a large effect on increasing densification rates. Mechanical properties of the resultant coating were also investigated.
Authors: Mathieu Brochu, Fabian Edelmann, Robin Valin, Robin A.L. Drew
Abstract: Transient Liquid Phase Bonding (TLPB) is a joining process that uses liquid as medium for the establishment of an interface between two faying surfaces. In TLPB, as opposed to brazing process, the careful selection of the interlayer materials and the use of a prolonged heat treatment, allows for isothermal solidification and results in interfaces possessing potential service temperature higher than the joining temperature itself. Such a process is attractive for joining ceramics to metals and composites. In this presentation, the applicability of TLPB for various systems: Si3N4/FA-129 iron aluminide alloy, Al2O3/Al2O3, Al-Al2O3/Al-Al2O3, Al-Al2O3/Al-SiC and Al-Al2O3/Al. Results on the interface formation, interfacial microstructure and mechanical properties will be presented. A comparison of the TLPB joint properties with traditional joining for similar systems will be illustrated.
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