Vacuum brazing ZSCf composite ceramics to TC4 alloy with Ag-Cu filler

Abstract In this study, the carbon fiber reinforced ZrB₂-SiC composite ceramic was joined to Ti6Al4V alloy with Ag-Cu eutectic alloy filler at varied holding time and a fixed temperature of 800℃. Interface microstructure and shear strength of brazing joints were studied. The brazed ZSCf ceramics/AgCu/TC4 alloy is endowed with good metallurgical bondings. A typical interfacial structure of joints brazed for 10 min was found as ZSCf/TiC/Ti₅Si₃/Ag(s,s)/Cu(s,s) + TiC/TiCu/Ti₂Cu/(TiC + TiCu)/TC4 alloy. Increase of holding time did not vary the precipitated phase of the joints but decreased thickness of the Ag(s, s) and Cu(s, s) reaction layer and gradually thickened the Ti-Cu reaction layer near the TC4 side. The formation process of reaction products was discussed in detail. The holding time substantially influenced shear strength of the joints. A maximum shear strength of 39 MPa was reached at a brazing time of 20 min

Microstructural and mechanical properties of inconel 600/ZrB₂-SiC joints brazed with AgCu/Cu-foam/AgCu/Ti multi-layered composite filler

Abstract A set of AgCu/Cu-foam/AgCu/Ti multi-layered composite fillers was designed and employed to braze the Inconel 600 alloy and ZrB₂-SiC ceramic. Microstructures, formation mechanism and shear strengths of the joints were investigated in detail with and without the addition of Ti foil. The shear strengths of the brazed joints were improved substantially with the presence of Ti foils. A maximum gain of 150 % was reached from 77 MPa to 198 MPa after introducing the Ti foil and brazing the joint at a 1173 K for 15 min. The mechanical property enhancement is attributed to a newly formed TiC phase, release of residual stress, and barrier effect of Cu foam to inhibit formation of Ti-Ni intermetallic compounds

A novel high entropy CoFeCrNiCu alloy filler to braze SiC ceramics

Abstract In order to reduce intermetallic compound formations in brazed joints, a CoFeCrNiCu high entropy alloy was invented and employed to braze SiC ceramics. Results show that SiC ceramics were tightly and strongly brazed with the CoFeCrNiCu filler. Microstructure, phase and shear strength were systematically studied for joints brazed at different temperature. Main compositions were identified as high-entropy FCC, Cu(s, s), Si(s, s), and Cr23C6 phases, regardless the brazing temperature differences. After being brazed at 1453 K, the joint reached a maximum shear strength of 60 MPa, much higher than those brazed with conventional AgCuTi filler. Thanks to high entropy effect of CoFeCrNiCu filler, random solid solution turned out in the seam and benefitted joint quality. The successful use of CoFeCrNiCu high entropy alloy as fillers can expand the application range of high entropy alloys and provide a new filler system to braze ceramics

Microstructure and mechanical properties of ZrB₂‐SiC/Nb joints brazed with CoFeNiCrCuTiₓ high‐entropy alloy filler

Abstract ZrB₂‐SiC ceramics and Nb alloy were brazed at 1160°C for 60 min with CoFeNiCrCuTix high‐entropy alloy filler. The influence of Ti content on the interface structure and mechanical properties of ZrB₂‐SiC/Nb joint was systematically studied. It is found that the rich‐Ti Laves phase was formed due to the addition of large atomic size Ti fill into the filler alloy or brazing joint, and its content increases with Ti content. The joint brazed by high‐entropy alloys filler without Ti can be divided into a tooth‐shaped Cr₂B reaction layer and a central area composed of a eutectic mixed structure of FCC phase and rich‐Nb lamellar Laves phase. Ti and Nb are mutual solid solution elements. The increase of Ti content in the joint makes the FCC phase and the rich‐Nb lamellar Laves phase to transform into a big bulk Ti‐rich Laves phase and the quadrilateral (Ti, Nb)B phase. The tooth‐shaped Cr₂B was disappeared. The residual stress generated in the joint during the brazing process tends to cause defects such as holes and microcracks in the bulk Ti‐rich brittle Laves phase. Therefore, with the addition of Ti, the normal temperature performance of the joint decreases from 216 MPa to 52 MPa. However, with the increase of Ti, the high‐temperature mechanical properties of the joint first decrease, and then increase. It was mainly due to the formation of rich‐Ti Laves phase and quadrilateral (Ti, Nb)B with excellent high‐temperature mechanical properties. When brazing with CoFeNiCrCuTi1.5 filler, the high‐temperature performance of the joint reached 92% of its room temperature performance

Microstructure and crystallization mechanism of Ti-based bulk metallic glass by electron beam welding

Abstract In this work, we report on the successful welding of the Ti-based bulk metallic glass (BMG) plates via electron beam welding route. Microstructure determination shows that crystalline phases exist both in weld zone (WZ) and heat affected zone (HAZ). The critical cooling rate for glass formation in WZ is depended on the solidification condition. The continuous heating transformation curve (CHT) of glass transition temperature (Tg) and crystallization temperature (Tx) during heating process, time-temperature-transformation diagram (C-curve) during cooling process, and the thermal cycle curves are obtained by Kissinger equation, nucleation theory, and temperature field simulation, respectively. The crystallization mechanism in HAZ was discussed in details during the heating and cooling processes. The intersection between cooling curve and C-curve denotes the crystallization of HAZ during the cooling process

Brazing ZrB₂-SiC ceramics to Ti6Al4V alloy with TiCu-based amorphous filler

Abstract In this work, the Ti-6Al-4V alloy and ZrB₂-SiC ultra-high temperature ceramic joint was brazed by TiCuZrNi amorphous filler at 910 °C with varied holding time. The element diffusion, microstructure and precipitation phase of the joints were analyzed in details. Reaction products in the joints were identified as β-Ti, (Ti,Zr)₂(Cu,Ni), TiCu, Ti₂Cu, TiC, Ti₅Si₃, TiB and TiB₂. The formation schemes of reaction products were investigated. The holding time has substantial impacts on interfacial microstructure and shear strength of joints. A maximum shear strength of 345 MPa of the joint was reached under a brazing temperature of 910 °C and holding time of 1200 s. It is also found that the shear strength depends on the amount of eutectic structure and brittle compounds in the joints

Microstructure and shear strength of ZrB₂-SiC/Ti6Al-4V joint by TiCuZrNi with Cu foam

Abstract In this paper, brazing behaviors between ZrB₂-SiC and Ti-6Al-4V by Cu foam interlayer were studied. The microstructure, formation mechanism, mechanical property and fracture surface of the joints were systematically studied. The results showed that the phases in the joints were α+β-Ti, TiCu, Ti₂Cu, Cu(s, s), TiC, TiB₂ and Ti₃SiC₂. An optimum shear strength reached up to 435  MPa at a brazing temperature of 910 °C and holding time of 20 min. Such a shear strength was 90 MPa higher than the one without the Cu foam. The obtained high shear strength of joint was discussed from microstructure and residual stress. With the increase of brazing time, Cu(s,s) gradually disappeared and the content of Ti₂Cu intermetallic compound increased, which was harmful for the joint. Furthermore, the residual stress of joint with Cu foam was calculated to be 324 MPa, lower than the one without Cu foam interlayer

Effect of brazing temperature on microstructure and mechanical properties of TiAl/ZrB₂ joint brazed with CuTiZrNi filler

Abstract The TiAl alloy and ZrB₂-SiC ceramic are promising materials used at high temperature. One route to extend their unique applications under extreme conditions relies on successful brazing them together with proper fillers. In this work, brazing temperature influences on microstructural, mechanical, and fractural properties were systemically studied for brazed joints after brazing the TiAl to the ZrB₂-SiC with amorphous CuTiZrNi fillers. An optimized brazing condition was found as 1183 K for 1200s, yielding a high shear strength of 187 MPa. The joints were mainly consisted of AlCuTi, Ti₂Al, (Ti,Zr)₂(Cu,Ni), TiB, TiB₂, TiCu Ti₅Si₃, and TiC phases. Brazing temperature substantially changed joint composites. It is found that lower temperatures lead to insufficient reaction and remained filler and higher ones to large stress-induced microcracks. Based on element diffusions, a formation mechanism of brazed joint was also proposed

Brazing Ti-48Al-2Nb-2Cr alloys with Cu-based amorphous alloy filler

Abstract In this work, the Ti-48Al-2Nb-2Cr (at. %) alloy was successfully brazed using a Cu-based amorphous filler in 600 s under varied brazing temperatures. The element diffusion, microstructure, and precipitation phase of the joints are analyzed in detail, and the formation schemes are discussed. Reaction products in the joints are found as AlCuTi, Ti2Al, α-Ti, and (Ti,Zr)2(Cu,Ni). The interfacial microstructures varied subjected to the brazing temperature, while the shear strength of the joint firstly increased, and then accordingly decreased. The maximum shear strength of 266 MPa was reached under a brazing temperature of 1213 K and a holding time of 600 s. A formation mechanism was proposed to explain the shear strength variation following the width and amount of brittle compounds in the interfacial reaction layer

AgCuTi/graphene-reinforced Cu foam:a novel filler to braze ZrB2-SiC ceramic to Inconel 600 alloy

Abstract In order to relieve high residual stresses between ceramics and metals during brazing processes, an AgCuTi/graphene-reinforced Cu foam composite filler was developed and used to braze the ZrB₂-SiC ceramic and Inconel 600 alloy. Microstructures and shear strengths of the joints were systematically studied. The joints are composed of TiFe₂, TiCu, TiC, Cu(s, s), Ag(s, s), and Ti₅Si₃ phases. It is found the addition of graphene on the Cu foam surface can effectively retard diffusions of metal atoms and avoid the collapse of the foam matrix. After being brazed at 900 °C, the joint can get a maximum shear strength of 157 MPa, much higher than those brazed without graphene addition. The high shear strength was investigated in detail and attributed to the integrity of the Cu foam, formation of the TiC and thickness of the reaction layer at the ceramic side