Microstructure evolution and cooperative reinforcement mechanisms of Al2O3/Al2O3 joints brazed by low-melting borosilicate glass

Abstract

The Al2O3/SiO2–B2O3–Al2O3–Na2O glass/Al2O3 joints reinforced cooperatively by glass matrix and in-situ Al4B2O9 whiskers were obtained via a low-melting borosilicate glass braze. The composition of glass seam transformed from SiO2–B2O3–Na2O to SiO2–B2O3–Al2O3–Na2O due to continuous diffusion and dissolution of Al2O3. An appropriate amount of [AlO4] units introduced into the glass braze played a vital role in strengthening the glass network structure resulting to considerably improved mechanical strength of the glass seam. Meanwhile, plenty of in-situ Al4B2O9 whiskers growing from the Al2O3/glass braze interface to the center of glass seam in various directions generated. Three-dimensional crisscross structures were fabricated at the Al2O3/glass braze interface domains, where were enhanced by crack-bridging and pull-out effect of the whiskers. Generally, ascribed to the cooperative reinforcement of the glass matrix in the seam and in-situ Al4B2O9 whiskers at Al2O3/glass braze interface domains through reactions of Al2O3 and borosilicate glass braze, strength of the as-brazed joints was promoted prominently. The shear strength of the joints reached a maximum of 61 MPa brazed at 1050 °C for 60 min.