Reactive air brazing of 3YSZ ceramic to aluminized Crofer22H stainless steel using Ag–CuO fillers

Abstract

In this work, an effective protected Al2O3 layer was fabricated first on the surface of Crofer22H by reactive air aluminization to suppress cathodic poisoning in solid oxide fuel cells. Then, the reactive air brazing of aluminized Crofer22H to 3YSZ ceramics was carried out by using Ag–CuO fillers. The effects of CuO content and brazing temperature on the interfacial microstructure and mechanical properties of the joints were studied in detail. The results indicated that maintaining a continuous Al2O3 layer was the prerequisite for achieving a reliable joint. And the interfacial reaction gradually became intense with the increase of CuO content, and the continuity of the Al2O3 layer was disrupted as it was increased to 6 mol%. The well‐connected joints could be achieved when brazing at 970–1100°C with Ag–2CuO filler. The interfacial microstructure did not obviously change with increasing temperature, and the joint strength was stable at ∼35 MPa. While the interfacial reaction gradually weakened with increasing temperature as brazing with Ag–4CuO filler, the well‐connected joints were obtained when brazing above 1000°C, and the maximum shear strength of ∼44.3 MPa was obtained when brazing at 1050°C for 30 min.

Effect of TiO2 addition on microstructure and mechanical properties of Al2O3 ceramic joints brazed with Ag‐CuO fillers

“…When the CuO content was above 4 mol.%, the liquid filler consisted of Ag‐rich liquid phase L2 and CuO‐rich liquid phase L1. The studies in the literature have shown that the CuO‐rich L1 liquid phase showed a stronger affinity for ceramics and tended to enrich at the interface 27,37,38 …”

“…The studies in the literature have shown that the CuO-rich L1 liquid phase showed a stronger affinity for ceramics and tended to enrich at the interface. 27,37,38 In fact, the L1 liquid phase was not a eutectic liquid phase. The monotectic reaction occurred during natural cooling, as shown in Equation (1) to form the solid phase CuO and L2 liquid phase, which would not show eutectic structure at room temperature.…”

“…The common filler systems include Ag-CuO, [17][18][19] Ag-V 2 O 5 , [16][17][18][19][20] Ag-Nb 2 O 5 , 21 etc. Among these, Ag-CuO filler can be used to join a wide range of ceramic [22][23][24][25][26] and metallic materials, [27][28][29] with a wider range of applications, and the brazed joints have excellent properties, making it the most studied filler system.…”

Active Brazing for Energy Devices Sealing

“…As a result, efforts have been made to limit interdiffusion by using diffusion barriers. For instance, Zhou et al [60] applied an aluminum coating to Crofer22H, while Si et al [62] utilized Mn-Co spinel-coated Crofer22APU as their substrates.…”

“…This has minimized the deterioration of the brazed elements to a certain extent; at the same time, the gas tightness has been increased even under substantial pressure differentials. Enhancements have been implemented to address the unacceptable decline in strength and gas tightness during prolonged periods of stationary service as well as during start-stop cycles [8,60,107]. The RAB process has a significant drawback wherein it introduces an excessive amount of oxygen into the brazed joint.…”