Non-destructive measurement of residual stress distribution as a function of depth in sapphire/Ti6Al4V brazing joint via Raman spectra

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The residual stress distribution as a function of depth in a sapphire/Ti6Al4V brazing joint is non-destructively measured using Raman Spectra for the first time. A modified method that is suitable for brazing joints is developed to deconvolute the actual residual stress value in each depth from the measured averaged stress value. The measured in-plane residual stress is compressive and increases non-linearly from the surface to the interface. While the out-of-plane residual stress is compressive; it increases from the surface to the interface and peaks at a distance of 150 µm from the sample surface. Then the stress begins to decrease and becomes tensile stress, which increases to the interface. This method can also be applied to other brazing/ diffusion bonding joint with a transparent substrate.