Design of a functional Al2O3/Al2O3 joint for sensing the brazing seam temperature with high sensitivity

Highlights: • ²H_11/2 and ⁴S_3/2 levels of Er³⁺ in Al₂O₃ joint show excellent temperature sensing properties. • The maximum temperature sensing sensitivity in brazing seam is 0.0182 K^-1. • Shear strength of joint brazed with Yb³⁺/Er³⁺:Y₂O₃ composited glass is up to 83.5 MPa. • Results will promote joint reliability research and temperature sensing in micro-region. Temperature monitoring of braze seam with high sensitivity and fast response is essential for safe working of a joint. Herein, a non-contact optical thermometry for joint is designed. The Yb³⁺/Er³⁺:Y₂O₃ micro-crystals were prepared and mixed into bismuth borate glass to bond Al₂O₃ ceramics. After brazing, Y₂O₃ particles still preserve perfect crystal structure, and its addition widens the thickness of braze seam. The obtained shear strength of joint is up to 83.5 MPa. Under 980 nm excitation, ²H_11/2 and ⁴S_3/2 levels of Er³⁺ ion in braze seam are thermally coupled levels and show excellent temperature dependent characteristic. The temperature sensing sensitivity is superior and the maximum values of absolute sensitivity and relative sensitivity are 0.0182 K^-1 and 0.51 %K⁻¹, respectively. This optical thermometry for brazing seam will further promote the joint reliability research and provide new strategies to measure the temperature in micro-region of component.