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Silicon nitride/silicon nitride joints with refractory metal (W and Mo) interlayers were vacuum brazed using an active braze, Cu-ABA (Cu–3Si–2Al–2.25Ti, wt%), and two interlayer arrangements in a double-lap offset configuration: Si 3 N 4 /Cu-ABA/W/Cu-ABA/Mo/Cu-ABA/Si 3 N 4 and Si 3 N 4 /Cu-ABA /Si 3 N 4 . Titanium segregated at the Si 3 N 4 /Cu-ABA and Mo/Cu-ABA interfaces, but not at the W/Cu-ABA interface. The room-temperature compression-shear strength values of Si 3 N 4 /Cu-ABA/Si 3 N 4 and Si 3 N 4 /Cu-ABA/W/Cu-ABA/Mo/Cu-ABA/Si 3 N 4 joints were 118±24 MPa and 22±5 MPa, respectively. Elevated-temperature compression tests showed that Si 3 N 4 /Cu-ABA/Si 3 N 4 joints had strength of 31±6 MPa at 1023 K and 17±3 MPa at 1073 K. Likewise, Si 3 N 4 /Cu-ABA/W/Cu-ABA/Mo/Cu-ABA/Si 3 N 4 joints had strength of 19±4 MPa at 1023 K and 13±3 MPa at 1073 K. Knoop microhardness profiles revealed hardness gradients across the joints. The effect of joint microstructure and test configuration on the mechanical behavior is discussed. [ABSTRACT FROM AUTHOR]

Abstract: Si3N4 (SN-281)/Cu-clad-Mo joints, brazed using a soft (YS: 341MPa) and ductile (43% elongation) Pd–Co braze were sound and exhibited an interaction zone comprised of Pd66Mo14Cu10Co6Si3 and Pd74Mo11Co8Cu6Si. Similar joints made using a less ductile and stronger Pd–Ni braze led to cracking from large CTE mismatch-induced strain energy (∼64mJ to 348mJ). [Copyright &y& Elsevier]

Hot-pressed ZrB2–SiC and composites with carbon (ZSC) or SCS-9a SiC fibers (ZSS) were joined using Pd-base brazes, Palco (65% Pd–35% Co) and Palni (60% Pd–40% Ni). Joint integrity was exhibited by the defect-free ZS/Palco/ZS joints with large interaction zones. The ZSS/Palco and ZSC/Palco joints revealed substantial chemical interaction and interfacial cracking due to residual stresses. The joints with Palni exhibited either poor wetting/bonding or cracking. The ZS/Palco joints displayed high Knoop hardness within the ZS region and lower hardness within the Palco interlayer. [Copyright &y& Elsevier]

Abstract: Carbon–carbon composites with either CVI matrix or resin-derived matrix were joined to copper-clad-molybdenum using two active braze alloys, Cusil-ABA (1.75% Ti) and Ticusil (4.5% Ti). The brazed joints revealed good interfacial bonding, preferential precipitation of Ti at the composite/braze interface, and a tendency toward de-lamination in resin-derived Cte due to its low inter-laminar shear strength. Extensive braze penetration of the inter-fiber channels in the CVI Ctes was observed. The relatively low brazing temperatures (<950°C) precluded melting of the clad layer and restricted the redistribution of alloying elements but led to metallurgically sound composite joints. The Knoop microhardness (HK) distribution across the joint interfaces revealed sharp gradients at the Cu-clad-Mo/braze interface and higher hardness in Ticusil (∼85–250 HK) than in Cusil-ABA (∼50–150 HK). These C-Mo joints with relatively low thermal resistance may be promising for thermal management applications. [Copyright &y& Elsevier]

Abstract: The joining behavior of polycrystalline alumina sintered at different temperatures (1473–1773K) and times (0.5–4h) to itself and to Ti, Hastealloy and a CVI C–SiC composite using two Ag–Cu active metal brazes (Cusil–ABA and Ticusil) containing Ti has been evaluated. Partial densification and the resulting high porosity content of Al2O3 substrates sintered at low temperatures led to braze infiltration of Al2O3 pores in 20min contact but no penetration occurred in dense Al2O3 substrates sintered at high temperatures. The scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS) examination of the joints showed that chemical reactions between Al2O3 and braze constituents formed a Ti-rich reaction layer at braze/Al2O3 interface regardless of the sintering conditions and degree of densification of the Al2O3. Some redistribution of the substrate and braze constituents across the joint interfaces was observed due to dissolution and interdiffusion. The Knoop microhardness of sintered alumina was consistent with the degree of Al2O3 densification achieved, and microhardness profiles across the joint regions displayed a minimum (∼70–160KHN) in the braze region and a maximum (1900–2012KHN) in the alumina region. The polished CVI C–SiC composites led to better quality Al2O3/C–SiC composite joints and greater segregation of Ti at the composite/braze interface than unpolished composite specimens. [Copyright &y& Elsevier]

Abstract: CVD silicon carbide was brazed to itself using two Ag–Cu–Ti braze alloys reinforced with SiC particulates to control braze thermal expansion and enhance joint strength. Powders of the braze alloys, Ticusil (composition in wt%: Ag–26.7Cu–4.5Ti, TL: 900°C) and Cusil-ABA (Ag–35.3Cu–1.75Ti, TL: 815°C) were pre-mixed with 5, 10 and 15wt% SiC particulates (∼20–30μm) using glycerin to create braze pastes that were applied to the surfaces to be joined. Joints were vacuum brazed and examined using optical microscopy (OM), field emission scanning electron microscopy (FESEM), energy dispersive spectroscopy (EDS) and the Knoop hardness test. The SiC particles were randomly distributed in the braze matrix and bonded to it via reaction with the titanium from the braze alloy. Titanium together with Si and C segregated at the particle/braze interface, and promoted nucleation and precipitation of the Cu-rich secondary phase on particle surfaces. The Si–Ti–C-rich reaction layers also formed at the interface between CVD SiC substrate and the braze alloy. The loss of Ti in the reaction with SiC particulates did not impair either the bond quality or the thickness of the reaction layer on the CVD SiC substrate. Microhardness measurements showed that the dispersed SiC particulates lowered the braze hardness by depleting the braze matrix of Ti. Theoretical calculations indicated the CTE of the braze to decrease by nearly 45–60% with the incorporation of about 45vol% SiC. [Copyright &y& Elsevier]

Abstract: Silicon nitride/silicon nitride joints were vacuum brazed at 1317K for 5min and 30min using ductile Cu-base active metal interlayers. The joints were characterized using scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), electron back scattered diffraction (EBSD), and transmission electron microscopy (TEM). An inhomogeneous Ti-rich reaction layer (∼2–3μm thick) formed in 5min at the Si3N4/braze interface. The inhomogeneity disappeared after brazing for 30min and was replaced with a compact and featureless reaction zone. TEM studies revealed fine grains in the reaction layer, and larger grains in the inner part of the joint interfaces. The joints were crack-free and presented features associated with plastic deformation, which indicated accommodation of strain associated with CTE mismatch. Electron Backscatter diffraction (EBSD) revealed a highly textured braze alloy interlayer and its crystallographic orientation was determined. The formation of additional phases at the joint interface during brazing is discussed. [Copyright &y& Elsevier]

Abstract: The wetting behavior of liquid Ni and NiW10 on MgO(100) single crystals was examined by the sessile drop method at 1773K in flowing Ar. A special procedure was used for in situ opening of the Ni/MgO and NiW10/MgO interfaces directly during wettability test at high temperature. Scanning probe microscopy revealed evidence of strong surface modification of MgO(100) during wettability tests that was found to be affected by metal evaporation, the chemistry of the liquid metal and the primary oxide film. [Copyright &y& Elsevier]

Abstract: The Ti-metal/C–C composite joints were formed by reactive brazing with three commercial brazes, namely, Cu-ABA, TiCuNi, and TiCuSil. The joint microstructures were examined using optical microscopy and scanning electron microscopy coupled with energy dispersive X-ray spectrometry. The results of the microstructure analysis indicate solute redistribution across the joint and possible metallurgical bond formation via interdiffusion, which led to good wetting and spreading. A tube-on-plate tensile test was used to evaluate joint strength of Ti-tube/C–C composite joints. The load-carrying ability was greatest for the Cu-ABA braze joint structures. This system appeared to have the best braze spreading which resulted in a larger braze/C–C composite bonded area compared to the other two braze materials. Also, joint load-carrying ability was found to be higher for joint structures where the fiber tows in the outer ply of the C–C composite were aligned perpendicular to the tube axis when compared to the case where fiber tows were aligned parallel to the tube axis. [Copyright &y& Elsevier]