Study on vacuum brazing of high purity alumina for application in proton synchrotron

• Study compares Mo–Mn metallization & active brazing routes for joining alumina.
• Targeted application: UHV chamber of proton synchrotron.
• Both kinds of joints were UHV compatible with helium leak rate <1.1 × 10−10 mbar l/s.
• Active brazed joints met tensile & flexural strength design requirement (>50 MPa).
• Active brazing is a simpler & economical route for joining high purity alumina.

The paper describes an experimental study to evaluate two different vacuum brazing processes to obtain high purity alumina (99.7%) joints suitable for application in rapid cycle proton synchrotron. Two different brazing routes, adopted for making alumina–alumina brazed joints, included (i) multi-step Mo–Mn metallization, followed by brazing with BVAg-8 alloy and (ii) advanced single-step active brazing with CuSil-ABA® alloy. Both the brazing routes yielded helium leak tight and ultra-high vacuum (pressure < 10−9 mbar) compatible joints. Active-brazed specimens exhibited tensile and mean flexural strengths of 62 and 110 MPa, respectively. Metallized-brazed specimens, although associated with relatively lower tensile strength (35 MPa) than the targeted value (>50 MPa), displayed higher mean flexural strength of 149 MPa. The results of the study demonstrated that active brazing is a simple and cost effective alternative to conventional multi-step metallization route for producing quality joints of high purity alumina for application in rapid cycle proton synchrotron machine.