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In this study, a novel Ag–Ti reactive composite brazing technology was employed to join carbon fiber reinforced carbon matrix composite (C/C) to Nickel-based superalloy GH3044. The microstructural evolution mechanism and the effects of process parameters on the microstructures and shear strength of the brazed joints were investigated systematically. The results showed that, during the brazing holding stage, Ti (α-Ti) in the liquid phase would convert to β-Ti (above 1020°C) or react with Ag formed AgTi (below 1020°C). Solid phase β-Ti or AgTi inhibited the loss of the molten filler material, thus forming a thicker interlayer, which was beneficial to relieve the residual stress of the joints. After brazing, an Ag matrix composite interlayer reinforced by in situ synthesized phases and a few residual Ti particles could be obtained. Notably, the reinforcing phases were various with different brazing parameters. Under weaker parameters (lower Ti content, lower temperature and shorter holding time), the reinforcing phases were mainly in situ synthesized AgTi phase and residual Ti particles, with which the Ag matrix composite interlayer had good plasticity and low coefficient of thermal expansion. As a result, the residual stress of the joints was further effectively relieved. Under stronger parameters, the reinforcing phases were mainly brittle phases Ti 2 Ni and Cr 1.93 Ti 1.07 , which increased the brittleness of the composite interlayer. The maximum shear strength of the joints reached 45.8 MPa brazed at 1020°C for 30 min using Ag–20Ti (Wt.%). [ABSTRACT FROM AUTHOR]

• (Cu) + Ti 5 Si 3 composite filler with foil form was developed by arc melting mixed-powders. • Large number of in-situ synthesized Ti 5 Si 3 reinforcements were distributed uniformly. • Ti 5 Si 3 reinforcements relieved the stress, and the shear strength of the joint reached 125.6 MPa. A novel foil (Cu) matrix filler reinforced by Ti 5 Si 3 particles was designed to join C f /SiC composite and 304 stainless steel. Results showed Ti and Si atoms in-situ reacted to form Ti 5 Si 3 reinforcement during arc melting of mixed-powders of Cu, Ti and Si. The foil composite filler with Cu:Ti:Si = 86.5:5:9.5 (at.%) as raw material can not only reduce the thermal stress in the joint, but also react appropriately with C f /SiC composite, and the corresponding joint shear strength was 126.5 MPa. [ABSTRACT FROM AUTHOR]

The application of C f /SiC-superalloy joints in aerospace typically demands high strength and good heat resistance. However, the simultaneous improvement of the two properties is a pressing problem that needs to be addressed. This paper proposes the addition of diamond (C) powder to the Cu-Ni-Ti brazing filler to regulate the interface reaction between the filler and C f /SiC composite and the initial liquefaction temperature of the interlayer, thereby achieving a balanced enhancement in both the mechanical performance and high-temperature resistance of the C f /SiC-GH3044 joints. The results indicate that during the joining process, a brittle compound layer composed of TiC, Ti 5 Si 3 , and Ni 16 Ti 6 Si 7 is formed at the C f /SiC/interlayer interface. The thickness of the compound layer increases with elevated joining temperatures or prolonged holding times, which is detrimental to the strength of the joint. The added C particles react with the active element Ti to synthesize in situ some TiC reinforcing particles with the low thermal expansion coefficient in the interlayer. This not only suppresses the excessive growth of the brittle compound layer but also alleviates the residual thermal stress in the joint. Additionally, since Ti is a lowering-melting element in the Cu-Ni-Ti filler, the consumption of Ti by the C/Ti reaction raises the initial liquefaction temperature of the interlayer, thus improving the heat resistance of the joint. When the joining temperature and holding time were kept constant, the shear strength of the joint reached a maximum value as the C particle content increased. If the joining temperature was elevated or the holding time was extended, the C content associated with the peak strength also increased. By optimizing the C particle content, both the shear strength and heat resistance of the joint were improved. The maximum shear strength of the joint at room temperature and 900 °C were measured to be 245 MPa and 138 MPa, respectively. Moreover, the joint exhibited a maximum temperature capability of 1064 °C. • Addition of carbon (C) powder to Cu-Ni-Ti filler improves mechanical performance and heat resistance of C f /SiC-GH3044 joints. • Brittle compound layer formation at bonding interface hampers joint strength, but C particles suppress its excessive growth. • In situ synthesis of TiC reinforcements with low thermal expansion coefficient reduces residual thermal stress in the joint. • Consumption of Ti by C/Ti reaction raises initial liquefaction temperature of the interlayer, improving heat resistance. [ABSTRACT FROM AUTHOR]

Taking the advantages of reaction-composite brazing and transient liquid phase bonding (TLP), a novel process with the features of low-temperature bonding & high-temperature resisting was implemented to join C-SiC composite and GH4169 superalloy. In the new process, mixed powder of low-melting-point Cu85Ti15 alloy and carbon (C) was used as an interlayer. At a relatively low bonding temperature (990 °C), in-situ reaction of (Cu-Ti) l +C s →(Cu) s +TiC s and interdiffusion between the (Cu-Ti) l liquid and the GH4169 substrate concurrently occurred to transform the interlayer into a TiC-reinforced (Cu) s matrix composite joining layer. The low-CTE reinforcement TiC helped to alleviate the high residual stress in the joint, and the (Cu) s matrix provided the high-temperature resistance for the joint. In the current work, microstructural behavior, formation mechanism, heat resistance and shear strengths of the bonded joints were investigated. Results indicated that the (Cu-Ti) l /C s in-situ reaction had an effect of shortening the solidification time of the joining layer, thus decreasing the formation of Ti-C and Ti-Si brittle compounds at the C-SiC side interface. The bonded joints exhibited excellent comprehensive properties: melting temperature of the joining layer reached 1052 °C, which was much higher than that of Cu85Ti15 alloy (898 °C) and the bonding temperature (990 °C); the maximum shear strength at room temperature and 900 °C reached 234 MPa and 101 MPa, respectively. [ABSTRACT FROM AUTHOR]

With the aim of alleviating the residual thermal stress in the C/C-GH3044 joints, a novel composite brazing, which combines Ag-Ti reactive composite brazing and TiC particle-reinforced composite brazing, was adopted for joining C/C composite to Ni-based superalloy GH3044 using (Ag-10Ti)+TiC composite filler material. The results showed that the composite interlayer was strengthened by four kinds of reinforcements, containing the introduced TiC, the in situ synthesized AgTi and Ti 2 Ni phases, and the residual Ti particles. With increasing TiC content from 0 to 32 %, the thermal expansion coefficient of the composite interlayer declined by 18.2 %, which is helpful in alleviating the residual thermal stress in the joints. In addition, the introduced TiC particles decreased the fluidity of the filler material and inhibited the inter-diffusion of atoms between GH3044 and filler material. As a result, the continuous brittle compound Ti 2 Ni in the composite interlayer was effectively reduced, so the composite interlayer had good plasticity. Meanwhile, the thickness of the composite interlayer gradually increased from 260 μm to 520 μm, and the finite element analysis showed that the corresponding peak value of von Mises stress decreasedby 20.1 %. The highest shear strength of the joints was 67.2 MPa obtained with (Ag-10Ti)+24 %TiC at 1020°C for 30 min,which is almost the same strength as the C/C composite matrix used in this study. [ABSTRACT FROM AUTHOR]

The microstructure and formation mechanism of the C f /SiC composite and stainless steel joints brazed with Ag+Ti filler were investigated. The effects of Ti content (10%˜40%, at %), bonding temperature (990˜1080 °C) and holding time (15˜60 min) on microstructure and mechanical properties of the joints were discussed. The results indicated that a large-thickness interlayer was formed after bonding, in which in-situ formed TiAg particulates and residual Ti particles were dispersed in Ag matrix. Compared with the common composite interlayers, the interlayer formed via Ag+Ti in-situ alloying had more and finer reinforcing phases without reducing the activity of the filler material. The ductile Ag matrix contributed to accommodate the large strain mismatch by elastic deformation. The interfaces between the adjoining materials and the interlayer were well-bonded without any cracks. At C f /SiC side interface, TiC, Ti 5 Si 3 and Ti 3 SiC 2 grains were generated from SiC matrix and carbon fibers were exposed. A meshing interface was formed, which was beneficial to arrest and deflect cracks and improve the shear strength of the joints. Kirkendall voids were observed at 304 side interface. Especially they were formed in the joints prepared using high Ti content filler materials (Ag+30%˜40%Ti, at %) or bonded at relatively low joining temperature (990 °C). When the content of Ti was fixed, the joint shear strength increased firstly and then decreased with the bonding temperature. Different Ti contents corresponded to different peak bonding temperatures. The holding time had a similar effect on the joint strength as bonding temperature. The maximum joint shear strength at room temperature was 141 MPa obtained at 1020 °C for 30 min with Ag+30 at %Ti composite filler. [ABSTRACT FROM AUTHOR]