Thesis Defence: Effect of Gas Metal Arc Welding Process Parameters on Distortion and Residual Stress of Weld Overlays of Inconel 686

Zahra Khodamoradi, supervised by Dr. Dimitry Sediako and Dr. Michael Benoit, will defend their thesis titled “Effect of Gas Metal Arc Welding Process Parameters on Distortion and Residual Stress of Weld Overlays of Inconel 686″ in partial fulfillment of the requirements for the degree of Master of Applied Science in Mechanical Engineering.

An abstract for Zahra Khodamoradi’s thesis is included below.

Defences are open to all members of the campus community as well as the general public. Registration is not required for in-person defences.

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ABSTRACT

This thesis investigates the influence of Gas Metal Arc Welding (GMAW) process parameters on residual stress and distortion in Inconel 686 weld overlays. Weld overlays are crucial in industrial applications, particularly for improving the durability of components exposed to high temperatures and corrosive environments. Inconel 686, known for its excellent corrosion resistance and crack mitigation, has been identified as a promising material for such applications.

However, significant deformation and residual stress arising from welding processes remain a challenge, often leading to material failure or increased post-weld processing. Motivated by the need to optimize welding parameters to minimize residual stress and distortion, this research systematically explores the effects of key GMAW parameters, including arc voltage, travel speed, wire feed speed, bead overlap, and heat input. Six welded plates were analyzed using Electronic Speckle Pattern Interferometry (ESPI) to measure residual stress and a Coordinate Measuring Machine (CMM) to evaluate distortion.

Results indicate that increasing heat input from 426.37 J/mm to 533.07 J/mm leads to a 22% increase in transverse residual stress, with stress values reaching as high as 184 MPa (tensile). This is attributed to slower cooling rates, causing non-uniform thermal contraction. Similarly, lowering the travel speed intensifies distortion, increasing perpendicular distortion by up to 12%. Higher arc voltage results in a more uniform stress distribution but raises the overall tensile stress,
particularly at the surface. Additionally, increasing wire feed speed from 99.9 mm/sec to 166.3 mm/sec amplifies thermal gradients, leading to a 56% increase in distortion (parallel direction). This could be due to the fact that higher wire feed speeds introduce more heat into the weld zone, accelerating the melting of the base and filler material. The higher heat input results in faster material expansion and contraction during the cooling process, which creates greater thermal
gradients. These thermal gradients can induce more significant residual stresses and, consequently, increased distortion, particularly in the parallel direction where heat distribution is less uniform. Also, optimizing bead overlap ratios (from 1/2 to 1/3 overlap) reduces both stress and distortion,
with an 11% reduction in transverse residual stress and a corresponding 16% decrease in parallel distortion.

These results underscore the critical balance between heat input and other process parameters to minimize residual stress and distortion, leading to more durable and reliable weld overlays. These findings offer practical insights for industries seeking to enhance equipment performance while minimizing post-weld treatments and operational downtime.