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Kabir A.S.H.,NRC Institute for Aerospace Research | Kabir A.S.H.,Concordia University at Montréal | Cao X.,NRC Institute for Aerospace Research | Medraj M.,Concordia University at Montréal | 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®.


Kabir A.S.H.,Concordia University at Montréal | Kabir A.S.H.,NRC Institute for Aerospace Research | Cao X.,NRC Institute for Aerospace Research | Baradari J.G.,NRC Institute for Aerospace Research | And 4 more authors.
Advanced Materials Research | Year: 2012

In this study, the global and local tensile behaviours of laser welded 5.1-mm thick Ti-6Al-4V alloy were obtained at various welding speeds and defocusing distances using a digital image correlation (DIC) technique with a full field three-dimensional deformation measurement system. The local tensile properties including elastic modulus, yield stress, and maximum plastic strain were determined at various locations by assuming an iso-stress condition. It was found that the elastic modulus and yield stress were maximum in the fusion zone (FZ) and minimum in the heat-affected zone (HAZ). Porosity and underfill defects were the main reasons for the failures in the FZ and/or the HAZ. Maximum plastic strain at fracture was observed at the failure location in most cases. © (2012) Trans Tech Publications, Switzerland.


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.


Cao X.,National Research Council Canada | Cao X.,Concordia University at Montréal | Kabir A.S.H.,National Research Council Canada | Kabir A.S.H.,Concordia University at Montréal | And 6 more authors.
Metallurgical and Materials Transactions A: Physical Metallurgy and Materials Science | Year: 2014

Ti-6Al-4V sheets, 3.2-mm in thickness, were butt welded using a continuous wave 4 kW Nd:YAG laser welding system. The effect of two main process parameters, laser power and welding speed, on the joint integrity was characterized in terms of the joint geometry, defects, microstructure, hardness, and tensile properties. In particular, a digital image correlation technique was used to determine the local tensile properties of the welds. It was determined that a wide range of heat inputs can be used to fully penetrate the Ti-6Al-4V butt joints during laser welding. At high laser power levels, however, significant defects such as underfill and porosity, can occur and cause marked degradation in the joint integrity and performance. At low welding speeds, however, significant porosity occurs due to its growth and the potential collapse of instable keyholes. Intermediate to relatively high levels of heat input allow maximization of the joint integrity and performance by limiting the underfill and porosity defects. In considering the effect of the two main defects on the joint integrity, the underfill defect was found to be more damaging to the mechanical performance of the weldment than the porosity. Specifically, it was determined that the maximum tolerable underfill depth for Ti-6Al-4V is approximately 6 pct of the workpiece thickness, which is slightly stricter than the value of 7 pct specified in AWS D17.1 for fusion welding in aerospace applications. Hence, employing optimized laser process parameters allows the underfill depth to be maintained within the tolerable limit (6 pct), which in turn prevents degradation in both the weld strength and ductility. To this end, the ability to maintain weld ductility in Ti-6Al-4V by means of applying a high energy density laser welding process presents a significant advantage over conventional arc welding for the assembly of aerospace components. © 2013 The Minerals, Metals & Materials Society and ASM International.


Cao X.,NRC Institute for Aerospace Research | Debaecker G.,École Centrale Nantes | Poirier E.,NRC Institute for Aerospace Research | Marya S.,École Centrale Nantes | And 3 more authors.
Journal of Laser Applications | Year: 2011

The effect of joint gap on the butt joint quality of Ti-6Al-4V alloy welded using a 4 kW Nd:yttrium aluminum garnet laser was evaluated in terms of the welding defects, microstructure, hardness, and tensile properties. The joint gap was proportionally filled using the filler wire with the compositions of the parent alloy. Fully penetrated welds without cracking were obtained up to a joint gap of 0.5 mm. The main defects observed in the welds were porosity and underfill. Specifically, the porosity area increased with increasing joint gap but remained less than 1% of the fusion zone area. Large underfill defects appeared in the weldments in the absence of a joint gap, but filler wire addition was observed to reduce this defect in the presence of a joint gap. The weld hardness decreased slightly with increasing joint gap, but the tensile properties were optimized at an intermediary gap size, probably due to the compromise between the low underfill (after the use of a filler wire) and a limited amount of porosity. © 2011 Laser Institute of America.


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.,École Centrale Nantes | Jahazi M.,15145 Decelles Ave | Marya S.,École 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.


Shariff T.,NRC Institute for Aerospace Research | Shariff T.,McGill University | Cao X.,NRC Institute for Aerospace Research | Chromik R.R.,McGill University | And 3 more authors.
Journal of Materials Science | Year: 2012

Ti-5Al-5V-5Mo-3Cr (Ti-5553) sheets were welded using a Nd: YAG laser system and Ti-6Al-4V filler wire. The effect of joint gap on weld geometry, defects, microstructure, and hardness was investigated. Fully penetrated welds up to a joint gap of 0.5 mm were produced. The two main defects observed were porosity and underfill. The addition of filler wire reduced underfill but increased porosity, especially at large joint gaps. The fusion zone (FZ) microstructure at low joint gaps consisted of retained β with a dendritic morphology. At a joint gap of 0.3 mm, regions of orthorhombic α″ martensite were observed in the weld zone which increased in proportion as the joint gap increased from a volume percentage of 4.9% at 0.3 mm to a volume percentage of 44% at 0.5 mm. Despite the differences in microstructure with increasing joint gap, the FZ hardness remained relatively constant for all joint gaps evaluated. © 2011 Springer Science+Business Media, LLC.


Kabir A.S.H.,NRC Institute for Aerospace Research | Kabir A.S.H.,Concordia University at Montréal | Cao X.,NRC Institute for Aerospace Research | Wanjara P.,NRC Institute for Aerospace Research | And 3 more authors.
Canadian Metallurgical Quarterly | Year: 2012

Owing to the high specific strength and excellent corrosion resistance, Ti-6Al-4V has been widely applied in aerospace industries. In this study, the welding performance of 3·2 and 5·1 mm thick Ti-6Al-4V sheets was studied using a 4 kW continuous wave Nd:YAG laser. It is found that the use of filler wire, matching the parent metal composition, can bridge the joint gap and produce full penetrated welds up to a width of 0·6 mm without cracking. The laser welds were characterised in terms of the bead geometry, defects, microstructures and hardness. With increasing joint gap, the percent porosity area increased, reaching just over 1% of the fusion zone area at a gap width of 0·6 mm for the 3·2 and 5·1 mm thick sheets. The maximum underfill depth in the Ti-6Al-4V laser welds was about 5%or 7%of the sheet thickness for the 3·2 and5·2 mmthick materials, respectively, meeting the AWS D17-1 specification. The microindentation hardness was maximum in the fusion zone and sharply decreased through the heat affected zone until reaching the base metal value. © 2012 Crown in Right of Canada.

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