Active brazing of pure alumina to Kovar alloy based on the partial transient liquid phase (PTLP) technique with Ni–Ti interlayer

Pure alumina (99.9% grade compositions) was brazed to 4J33-Kovar alloy based on PTLP technique with nickel and titanium foils interlayer. The solder formed a sandwich microstructure: an α-Ti solid solution belt at mid part and Ti2Ni intermetallics belts at two sides. This structure accounts for the good property of the joint. Microanalysis identified a reaction product at the alumina-braze interface as Ni2Ti4O phase. The special properties and structural compatibility of Ni2Ti4O contributed to the firm joint. The effects of brazing conditions on the joint properties were investigated. The joint shear strength showed the highest value of about 65MPa and did not monotonously increase with the brazing temperature ascending. It was shown that extending of brazing time gave thicker reaction layer and higher joint strength.