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Durocher J.,Standard Aerospace Ltd | Richards N.L.,University of Manitoba
Journal of Materials Engineering and Performance | Year: 2011

The repair of turbine blades and vanes commonly involves gas tungsten arc welding or an equivalent process, but unfortunately these components are often susceptible to heat-affected zone (HAZ) cracking during the weld repair process. This is a major problem especially in cast alloys due to their coarse-grain size and where the (Al + Ti) contents is in excess of 3-4%; vacuum brazing is also used but mainly on low stress non-rotating components such as vanes. Micro-welding has the potential to deposit small amounts of filler at low heat input levels with minimum HAZ and thus is an attractive process for depositing a quality weld. As with conventional fusion processes, the filler alloy is deposited by the generation of a low power arc between a consumable electrode and the substrate. The low heat input of this process offers unique advantages over more common welding processes such as gas tungsten arc, plasma arc, laser, and electron beam welding. In this study, the low heat input characteristic of micro-welding has been used to simulate weld repair using Inconel (IN) (Inconel and IN are trademarks of INCO Alloys International) 625, Rene (Rene is a trademark of General Electric Company) 41, Nimonic (Nimonic is a trademark of INCO Alloys International) 105 and Inconel 738LC filler alloys, to a cast Inconel 738LC substrate. The effect of micro-welding process parameters on the deposition rate, coating quality, and substrate has been investigated. © 2010 ASM International.

Durocher J.,Standard Aerospace Ltd | Cahoon J.R.,University of Manitoba | Richards N.L.,University of Manitoba
Materials Science and Technology (United Kingdom) | Year: 2013

The baseline metallography of single crystal alloy N5 was compared with laser welded material to evaluate the effect of the welding process on cracking behaviour. In addition, baseline thermomechanical fatigue data were compared with the fatigue properties of welded specimens. The solution treated and aged single crystal alloy was found to contain microporosity, Ta rich MC carbides, Cr-Mo rich grain boundary borides, gamma prime and fine secondary gamma prime. In addition, recrystallised grains were present in the weld heat affected zone and provided a path for crack propagation out of the fusion zone. The laser beam welds showed defects mainly associated with the fusion zone, while thermomechanical fatigue analysis of the laser weld data showed inferior values compared to the baseline solution treated and aged material. Metallographic analysis showed that this was due to increased defects in the fusion zone associated with surface oxidation and heat affected zone recrystallisation compared to the nonwelded alloy. © 2013 Institute of Materials, Minerals and Mining.

Balachander M.A.,Standard Aerospace Ltd | Vishwakarma K.,University of Manitoba | Tang B.,University of Manitoba | Richards N.L.,University of Manitoba
Materials Science and Technology | Year: 2011

A microstructural analysis has been carried out on the commercially solution treated and aged (STA) Incoloy 909 superalloy to evaluate the phases present using optical, SEM, TEM and differential scanning calorimetry. Comparison is made where possible with non-standard STA analyses reported in the literature. In the STA condition, the main phase present besides the γ matrix was a deliberately produced Laves phase to control grain growth. Increasing the solution temperature above that recommended for the alloy resulted in eventual solution of the Laves phase and concomitant grain growth. In the STA condition, in addition to the Laves phase, a copious precipitation of a γ' phase (Ni 3TiNb) was observed. In addition, a limited observation was made of the early stages of the transition of some of the γ' phase to the ε phase for the over aged condition. There was no e phase observed in the STA condition. A final observation was the presence of 'black grain' previously reported in the literature, in both the ST and STA conditions in the authors' research. The present view is that the phenomenon is an etching artefact and not a genuine microstructural feature. © 2011 Institute of Materials, Minerals and Mining.

Cao X.,15145 Decelles Ave | Debaecker G.,Ecole Centrale Nantes | Jahazi M.,15145 Decelles Ave | Marya S.,Ecole Centrale Nantes | And 2 more authors.
Materials Science Forum | Year: 2010

The effects of post-weld heat treatment on 3.05-mm thick Ti-6Al-4V alloy were investigated using a 4 kW Nd:YAG laser. Two main defects, underfill and porosity, were observed. The use of filler wire reduced underfill defects but slightly increased porosity. No cracks were detected. The as-welded and stress-relief annealed welds had very similar microstructures, hardness, and tensile properties. However, the post-weld solution heat treatment and aging transformed the martensite in the fusion zone into a coarse interlamellar α-β structure, causing a decrease in ductility but a more homogeneous distribution in the hardness of the welds. © (2010) Trans Tech Publications.

Kabir A.S.H.,NRC Institute for Aerospace Research | Kabir A.S.H.,Concordia University at Montreal | Cao X.,NRC Institute for Aerospace Research | Medraj M.,Concordia University at Montreal | And 3 more authors.
Materials Science and Technology Conference and Exhibition 2010, MS and T'10 | Year: 2010

In this study, the weldability of 5.1-mm thick Ti-6A1-4V sheets in the mill-annealed condition was investigated using a continuous wave 4 kW Nd:YAG laser at various welding speeds and defocusing distances. The joint quality was characterized in terms of weld geometry, microstructure, defects and hardness. Although some welding defects such as underfill and porosity were observed, sound welds without cracks can be obtained using a high power Nd:YAG laser. The hardness was found to be maximum in the fusion zone (FZ) and the heat-affected zone (HAZ) near the fusion boundary, beyond which a gradual decrease occurred to the base material. Copyright © 2010 MS&T'10®.

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