Effect of Bonding Temperature on Crack Occurrences in Al2O3/SS 430 Joints Using Cu-Based Brazing Alloys

Abstract

The effect of bonding temperature on crack occurrences in α-Al2O3/SS 430 joints using Cu-based brazing alloys was investigated with emphasis on the microstructural characterization, hardness, and analytical residual stresses of the joints. The brazing was conducted using Cu-7Al-xTi and Cu-7Al-xZr (x = 2.5, 3.5, and 4.5) alloys at 1000 °C and 1080 °C leading to solid–liquid and liquid-state bonding, respectively. Cracks occurred in the joints brazed at 1080 °C irrespective of the alloys, while crack-free joints were obtained at 1000 °C for joints with only Cu-7Al-xZr alloys. Increases in the bonding temperature or utilization of Cu-7Al-xTi alloys led to a formation of brittle Fe-containing intermetallic or Fe-Cr phases in the brazed seams due to the dissolution of Fe from SS 430, which deteriorated the mechanical properties of the brazed seam. Maximum residual stresses of the real brazed joint were obtained by combining the calculated yield strength and measured hardness of the brazed seams. Eventually, when the hardness of the brazed seam was less than 107 Hv, the yield strength was 124 MPa or less and the maximum residual stress generated in the joint corresponded to 624 MPa or less, leading to a crack-free joint.

Formation of Interfacial Reaction Layers in Al2O3/SS 430 Brazed Joints Using Cu-7Al-3.5Zr Alloys

“…The majority of studies have been conducted above the liquidus temperature to improve the wettability of the brazing alloy and chemical reaction. However, in our previous experiment [17], it is interesting that although the brazing alloy was not fully liquefied, a tight bonding was obtained without cracking at the joint. In this study, to better understand the bonding mechanism of liquid-solid state bonding for the Cu-7Al-3.5Zr alloy, formation of the interfacial reaction layer was investigated in terms of microstructure analysis as the bonding temperature and dwell time increased.…”

“…°C , where the liquid and solid phases of brazing alloy coexisted, crack-free joints were observed for joints using only Cu-7Al-xZr alloys. In addition, it was proposed that the minimum residual stress causing cracking in the joint can be expected using the hardness of the brazed seam [17]. For the metal-ceramic joint using the brazing alloy such as Ag-Cu-Zr, AgZr, and CuZr systems, formation ZrO2 (zirconia) oxide is known to be the main factor in providing good adherence [17][18][19][20][21][22][23].…”

“…When the α-Al 2 O 3 /SS430 specimens were brazed using the alloys at 1000 • C, where the liquid and solid phases of brazing alloy coexisted, crack-free joints were observed for joints using only Cu-7Al-xZr alloys. In addition, it was proposed that the minimum residual stress causing cracking in the joint can be expected using the hardness of the brazed seam [17].…”

Recent Progress in the Joining of Titanium Alloys to Ceramics

“…The development of reliable joining of Al 2 O 3 to metals is crucially important to extend their use, particularly in aerospace and nuclear applications [63]. For instance, reliable bonding of titanium alloys, such as TiAl [22][23][24] or Ti6Al4V [25,26], or even steel [64] and Al 2 O 3 , can take advantage of the respective superiorities of ceramics and metals, and thereby extend their scopes of application.…”

“…The addition of W particles on the composite filler seems to act as a release of residual stresses formed during cooling. The increase of the brazing temperature led to an increase of the thickness of the reaction layers composed by Ti 3 (Cu,Al) 3 alloys, such as TiAl [22][23][24] or Ti6Al4V [25,26], or even steel [64] and Al2O3, can take advantage of the respective superiorities of ceramics and metals, and thereby extend their scopes of application. The fundamental problem of brazing an oxide ceramic is a resistance to wetting by the presence of the oxides on the surface.…”