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In order to improve the ZrC-SiC ceramic and TC4 brazed joint property, graded double-layered SiC particles (SiCp)-reinforced TC4-based composite structure (named as GLS for convenience) was designed to relieve the residual stress in the joint. The GLS was successfully fabricated on TC4 substrate by double-layered laser deposition technology before the brazing process. The investigation of the GLS shows that the volume fraction of SiCp in the two composite layers was graded (20 and 39 vol pct, respectively). Ti5Si3 and TiC phases formed in the GLS due to the reaction of SiCp and TC4. The laser power-II (the laser power for the second deposition layer) affected the microstructure of the GLS significantly. Increasing the laser power-II would promote the reaction between the SiCp and TC4. But the high laser power-II made the layer I remelt completely and the two layers became homogeneous rather than graded structure. In the ZrC-SiC and TC4 brazed joint, the CTE (coefficient of thermal expansion) was graded from the TC4 to the ZrC-SiC due to the GLS, and the strength of the joint with the GLS (91 MPa) was higher than that without the GLS (43 MPa). [ABSTRACT FROM AUTHOR]

An AgCu-4.5 wt.%Ti/W/AgCu-1 wt.%Ti composite interlayer was designed to braze the Invar-SiO 2f /SiO 2 joints. Ti contents in the interlayer between the tungsten foil and the Invar alloy was optimized. The effects of the tungsten-foil thickness on the microstructure, elemental distribution and mechanical properties of the brazed joints were investigated. Compared with a single AgCu-4.5 wt.%Ti interlayer, a sufficient metallurgical reaction happened on the SiO 2f /SiO 2 composite side and the formation of Fe 2 Ti, Ni 3 Ti compounds which are detrimental to the joint properties, was greatly inhibited by using a low-expansion composite interlayer (LECI). The tungsten interlayer can reduce the CTE (coefficient of thermal expansion) mismatch in the Invar-SiO 2f /SiO 2 joint. The highest shear strength of joints brazed with an LECI was 33 MPa, which was 1.75 times higher than the joints brazed with a single AgCu-4.5 wt.%Ti interlayer. [ABSTRACT FROM AUTHOR]

Due to the poor wettability of the AgCuTi alloy on the SiO2f/SiO2 composite, direct brazing of the composite with an Invar alloy could hardly achieve a reliable joint. To overcome that, the SiO2f/SiO2 composite was decorated with few-layer graphene (FLG) by a plasma enhanced chemical vapor deposition (PECVD) method. Sessile drop experiments indicate that the contact angle dropped from 123.8° to 50.7° after FLG was grown on the surface of the SiO2f/SiO2 composite. Afterwards, the effects of brazing temperature and Ti contents on the microstructure evolution and mechanical properties of joints (Invar/SiO2f-SiO2 modified with FLG) were investigated. The typical interface structure of the joint is SiO2f- SiO2/Ti5Si3 + TiO2 + CuxTi6 - xO(x = 2,3)/Ag(s,s) + Cu(s,s) + Cu-Ti blocks/wave-like Fe2Ti + Ni3Ti/Ag(s,s) + Cu(s,s) + Fe2Ti + Ni3Ti blocks/Invar. As the brazing temperature and Ti contents increase, the reaction layer on the SiO2f/SiO2 side becomes thicker and cracks gradually propagate. Meanwhile, a few dispersive Fe2Ti + Ni3Ti phases change into large-area wave-like compounds and more Cu-Ti compounds form with the increase of the Ti content. The microstructure evolution significantly affects the shear strength of the brazed joints. The highest shear strength is 26 MPa brazed at 860 °C for 10 min with 4.5 wt.% Ti content. [ABSTRACT FROM AUTHOR]

A novel composite interlayer with a reinforced network was designed using a SiC ceramic with a network structure and Ti-Ni-Nb composite filler foils, to which the Nb and BN-SiO 2 ceramic were successfully brazed under vacuum. For a brazing temperature of 1160 °C and holding time of 10 min, the interfacial microstructure of the Nb/BN-SiO 2 ceramic joint was Nb/(βTi,Nb)-TiNi eutectic structure+(βTi,Nb) 2 Ni+SiC+TiC/TiN+Ti 2 N+TiB+Ti 5 Si 3 +TiO/BN-SiO 2 ceramic. In addition, the shear strength and nano-hardness were analyzed to evaluate the effect of the composite interlayer with a network reinforcement architecture on the mechanical properties of the joint. During brazing, the Ti-Ni-Nb filler metal infiltrated and reacted with the SiC to form the network reinforcement architecture, resulting in the residual stress being relieved and the mechanical performance of the joint being significantly improved. A maximum shear strength of 102 MPa was achieved, which was 60 MPa (142%) higher than that of the joint brazed without the network reinforcement architecture. A reduction in the residual stress on the BN-SiO 2 ceramic side from 328 MPa to 210 MPa was observed with the network reinforcement architecture, and the fracture path of the joint changed from the surface of the BN-SiO 2 ceramic to the interfacial reaction zone. [ABSTRACT FROM AUTHOR]

Abstract A graphene nanosheets reinforced Ag-Cu composite filler (Ag-Cu + GNSs) was developed by introducing GNSs into Ag-Cu powder filler. Unidirectional carbon fiber reinforced lithium aluminosilicate matrix composites (UD-C f /LAS composites) and Ti–6Al–4V alloy were brazed with Ag-Cu + GNSs composite filler. The typical interfacial microstructure of joint was Ti–6Al–4V/Ti(s,s)/Ti 2 Cu/TiCu/Ag(s,s)/Ti 3 Cu 4 /Cu(s,s)+TiCu + TiC/Ti 3 Cu 4 /TiC + TiSi 2 /UD-C f /LAS composites. The in situ synthesized TiCu + TiC composite from the reaction between Ti and GNSs had the following benefits: 1) refined the microstructure of the joint; 2) reinforced the joint; 3) alleviated the thermal stress of the joint by constraining the growth of continuous Ti 3 Cu 4 intermetallic layers. Moreover, with the increase of GNSs content, the amount of TiCu + TiC phases increased. Ag(s,s) and Ti 3 Cu 4 became uniform and fine in the interlayer. Both the thickness of reaction layers and the size of granular Ti 3 Cu 4 and TiCu + TiC phases firstly increased and then decreased with the rise of the brazing temperature. On the contrary, the content of Ag based composite decreased at first and then increased. The highest shear strength of joints reached 45.5 MPa with 0.5% GNSs addition when brazed at 900 °C for 10 min. Based on the experimental results, the interface evolution mechanism of the Ti–6Al–4V/Ag-Cu + GNSs/UD-C f /LAS composites joint was investigated. Highlights • TC4/C f /LAS composites joints were brazed by GNSs reinforced composite filler. • The determination of interface reaction phases was realized by TEM. • Brazing temperature and addition of GNSs had influence on the joints microstructure. • The highest shear strength of joints reached 45.5 MPa. • Microstructural evolution mechanism and reactions of brazed joints were expounded. [ABSTRACT FROM AUTHOR]