Brazing of Al_2O_3 to Ti-6Al-4V alloy with in situ synthesized TiB-whisker-reinforced active brazing alloy

摘要

65.9Cu-24.4Ti-9.7TiB_2 (wt.%) composite filler was used to join Al_2O_3 and Ti-6Al-4V alloy. 30 vol.% TiB whiskers were in situ synthesized as reinforcements in joints. Brazing temperature was 890 °C, 910 °C, 930 °C, 950 °C and 970 °C, and the holding time was 0, 5, 10, 20, and 30 min. The microstructure and mechanical properties of brazed joints were analyzed by scanning electron microscope equipped with energy dispersive spectrometer, shear test and nano-indentation test. Results show that reaction layer Ti_4(Cu,Al)_2O forms at Al_2O_3/brazing alloy interface. The reaction between TiB_2 powders and Ti atoms in brazing alloy brings on in situ synthesizing TiB whiskers in (Ti,Al)_2Cu and AlCu_2Ti intermetallics. Formation of TiB whiskers minimizes the mismatch of thermal expansion coefficient between Al_2O_3 and brazing alloy, and makes the ductile-rigid-ductile multiple layer present in joints, which reduces residual stress of joints. The maximum shear strength of joints can reach 143.3 MPa when the brazing temperature is 930 °C, and holding time is 10 min.