Characterization of silicon carbide joints fabricated using SiC particulate-reinforced Ag–Cu–Ti alloys

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, T_L: 900 °C) and Cusil-ABA (Ag–35.3Cu–1.75Ti, T_L: 815 °C) were pre-mixed with 5, 10 and 15 wt% SiC particulates (～20–30 μm) 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 45 vol% SiC.     

Brazing of silicon nitride ceramic composite to steel using SiC-particle-reinforced active brazing alloy

Silicon carbide particles have been introduced as reinforcements in a commercially available active metal braze filler alloy (Incusil ABA, Wesgo Metals) used for the joining of ceramic-to-metal. The effect of particle reinforcement of the braze filler on the flexural strength of ceramic to metal joints has been investigated at room temperature and at elevated temperatures. An average four point flexural strength of nearly 400 MPa is achieved at room temperature when using Incusil ABA + 30 vol.% SiC (sandwich foil system) compared to 330 MPa with Incusil ABA alone. At a test temperature of 250 °C relaxation of residual stresses in the joints results in an average flexural strength of approximately 520 MPa when using Incusil ABA + 10 vol.% SiC. These values compare with an average room temperature flexural strength of nearly 800 MPa for the ceramic composite. The reaction products of the braze alloy at the joint interface were identified by SEM.     

Brazing SiC ceramic using novel B4C reinforced Ag–Cu–Ti composite filler

The development of new composite fillers is crucial for joining ceramics or ceramics to metals because the composite fillers exhibit more advantages than traditional brazing filler metal. In this research, novel B₄C reinforced Ag–Cu–Ti composite filler was developed to braze SiC ceramics. The interfacial microstructure of the joints was characterized by scanning electron microscope (SEM), X-ray diffraction (XRD) and transmission electron microscopy (TEM). The effect of B₄C addition and brazing temperature on the microstructure evolution and mechanical properties of the joints was analyzed. The results revealed that TiB whisker and TiC particles were simultaneously synthesized in the Ag-based solid solution and Cu-based solid solution due to the addition of B₄C particles. As the brazing temperature increased, the thickness of Ti₃SiC₂+Ti₅Si₃ layers adjacent to SiC ceramic increased. Desirable microstructure similar to the metal matrix reinforced by TiB whisker and TiC particles could be obtained at brazing temperature of 950 °C. The maximum bending strength of 140 MPa was reached when the joints brazed at 950 °C for 10 min, which was 48 MPa (~52%) higher than that of the joints brazed using Ag–Cu–Ti filler.     

Microstructure and mechanical properties of the Si3N4/42CrMo steel joints brazed with Ag–Cu–Ti + Mo composite filler

The Si₃N₄ ceramic was joined to 42CrMo steel using Ag–Cu–Ti + Mo composite filler. Effect of Mo particles content on the microstructure and mechanical properties of the joints were investigated. Defect-free joints were received when the Si₃N₄/42CrMo steel joints were brazed with Ag–Cu–Ti + Mo composite filler. The results show that a continuous reaction layer which is composed of TiN and Ti₅Si₃ was formed near the Si₃N₄ ceramic. A double reaction layer which consists of Fe₂Ti and FeTi was also formed adjacent to 42CrMo steel, with Fe₂Ti being located near the steel. The central part of the joint is composed of Ag based solid solution, Cu based solid solution, Mo particles and some Cu–Ti intermetallic compounds. The maximal bending strength reached 587.3 MPa with 10 vol.% Mo particles in the joint, at which the joint strength was 414.3% higher than the average strength for the case without Mo particles addition.     

Revealing the strengthening mechanism in Si3N4 ceramic joint by atomic force microscopy coupled with nanoindentation techniques

The composite filler has been widely introduced for joining ceramic. However, the underlying formation and strengthening mechanisms in the joint remain uncertain. In this study, a commercial Ag–Cu–Ti brazing alloy with Mo particles reinforcement has been introduced for joining Si₃N₄ ceramic and the effect of Mo particles on the microstructure and flexural strength of the joint was investigated. Nanoindentation was employed to characterize the mechanical properties for reaction phases in the joints. The modulus and hardness values for Cu–Ti intermetallics and brazing alloy in the joint were first reported, providing a strong evidence to elucidate the strengthening mechanism. In addition, the strength was increased from 200 MPa, with Ag–Cu–Ti alone, to a maximum of 429 MPa while using Ag–Cu–Ti + 5 vol.% Mo composite filler. We are convinced that, for a well-bonded joint, the thermal expansion mismatch between the joined materials and the plastic deformation in the brazing alloy determined the joint strength.     

Microstructural and mechanical characterization of the Si3N4/Si3N4 joint brazed using Au–Ni–V filler alloys

In this study, two Au–Ni–V filler metals were used to braze Si₃N₄ ceramic in the form of foils. The effects of brazing temperature and V content in the filler alloy on microstructure and bonding strength of the joint were studied. The results reveal that a VN reaction layer with a thickness about 4 μm was formed at the interface between Si₃N₄ substrate and filler alloy. With increasing brazing temperature or V content the thickness of VN reaction layer increased. A maximum joint bending strength of 242 MPa was achieved when the joint was brazed at the temperature of 1423 K for 30 min using Au58.7Ni36.5V4.8 filler alloy. The bonding mechanism was discussed with reference to the discovered phases and brazing parameters.     

Properties and rapid consolidation of nanostructured TiC-based hard materials with various binders by a high-frequency induction heated sintering

The densification of hard TiC–10 vol.% binder (Co, Ni, Fe) materials was accomplished within 2 min using a high-frequency induction heated sintering (HFIHS) method. The advantage of this process is not only rapid densification to almost the theoretical density but also the prevention of grain growth of the nano-structured materials. Highly dense TiC–binder (Co, Ni, Fe) composites with a relative density of up to 99.9% were obtained within 2 min by HFIHS under 80 MPa. The average grain size of TiC in the TiC–10 vol.% Ni composite was approximately 44 nm. The hardness and fracture toughness of the dense TiC–10 vol.% binder (Co, Ni, Fe) composite produced by HFIHS were also investigated.     

The protective properties of epoxy coating electrodeposited on Zn–Mn alloy substrate

The epoxy coating was cataphoretically deposited on steel and steel modified by electroplated Zn–Mn alloy of different chemical contents. The samples were immersed in 0.5 mol dm⁻³ NaCl solution for 60 days. The electrochemical impedance spectroscopy (EIS) analysis showed that the values of pore resistance for epoxy coating on steel and Zn–Mn alloy with 16 at.% Mn were two orders of magnitude higher, while the capacitance values were two orders of magnitude lower than those for the epoxy coating on Zn–Mn alloy substrates with 5 and 8 at.% Mn. It was assumed that the main reason for such a difference was metallic substrate dissolution during cataphoretic deposition, due to high pH (12.9). This assumption was supported by energy dispersive X-ray spectrometry (EDS) measurements showing that the amount of released Zn in epoxy coatings decreased as Mn percent in the Zn–Mn alloys increased. In addition, Zn–Mn alloy coatings on steel, as well as bare steel, were immersed in 0.1 mol dm⁻³ NaOH solution, pH 12.9, simulating conditions during cataphoretic deposition, and polarization resistance measurement in this solution indicated that Mn inclusions in Zn–Mn alloy substrate prevent Zn dissolution in alkaline medium.     

In-situ fabrication of TiC-Fe3Al cermet

Titanium carbide has high hardness, resistance to oxidation and abrasion while iron aluminide has proper ductility as well as good strength and excellent oxidation resistance up to high temperatures. Therefore, it can be expected TiC-iron aluminide cermet to have excellent mechanical properties as a cutting tool and a wear-resistance material. In this study, mechanical milling and hot press sintering processes were used to manufacture in-situ TiC-Fe₃Al cermet, whose microstructure and mechanical properties were examined according to the changes in volume fraction of TiC and milling time. After 48 h of milling each mechanically alloyed powder crystallized in a TiC and Fe₃Al biphasic material. The milled powder was hot-pressed at 1250 ℃ and 50 MPa for 30 min to obtain sintered bodies also consisting of only TiC and Fe₃Al phases. The hard phase, TiC, had a size of 100–300 nm with overall uniform distribution decreasing as the volume fraction of TiC increased. The hardness of each sintered body showed a linearly increasing tendency according to the increase in TiC content, the hardness for 90 vol% TiC cermet being as high as 1813Hv. On the other hand, the bending strength was 1800 MPa and 1780 MPa when TiC volume fraction was 50% and 70%, respectively, while it showed an abrupt decrease up to 580 MPa at 90% TiC volume fraction. Fe₃Al phase is effective to toughening of TiC-Fe₃Al cermet and the volume fraction of Fe₃Al phase significantly influences the bending strength of the cermet.     

Interfacial microstructure and performance of nano-diamond film/Ti-6Al-4V joint brazed with AgCuTi alloy

The CVD nano-diamond film and Ti-6Al-4V alloy were successfully brazed with AgCuTi active brazing filler. The interfacial microstructure was investigated by SEM, EDS, XRD and TEM. Typical interfacial microstructure of brazed joint was conformed as Ti-6Al-4V/diffusion layer/Ti₂Cu + TiCu + Ti₃Cu₄/Ag(s,s) + Cu(s,s) + Ti₂Cu₃/TiCu + TiC/nano-diamond film. The effects of brazing temperature on interfacial microstructure and mechanical properties of the brazed joints were analyzed. With the increasing brazing temperature, the thickness of reaction layers adjacent to Ti-6Al-4V substrate and nano-diamond film increased obviously. Moreover, the Ti₂Cu₃ phase coarsened and aggregated in brazing seam at higher temperature. The joint was formed by the diffusion and reactions between atoms, and the microstructure evolution of brazed joint was discussed. In addition, a slight graphitization of nano-diamond film occurred during brazing process, and the highest shear strength can reach 25 MPa when the joint was brazed at 880 °C for 10 min. Finally, the fracture positions and fractographs of brazed joints were also discussed.     

Hydrogen storage characteristics of melt spun Mg–23.5Ni–5Cu alloys mixed with LaNi5 and/or Nb2O5

Mg-based materials have a high potential for commercialization due to the large hydrogen storage capacity, low cost and abundance in the Earth's crust. Despite these advantages, reaction kinetics of Mg with hydrogen is slow. Various investigations to increase the hydriding kinetics of Mg were performed. Although LaNi₅ has a low hydrogen storage capacity, it can store hydrogen at a low temperature. In this study, a Mg–23.5Ni–5Cu alloy was prepared by gravity casting method in a large quantity (approximately 7.5 kg), and then melt-spun and heat-treated. LaNi₅, Nb₂O₅ or LaNi₅ + Nb₂O₅ were added to the Mg–23.5Ni–5Cu alloy by reactive mechanical grinding in a planetary mill. The hydrogen storage capacity and hydriding behavior of the Mg–23.5Ni–5Cu alloys with LaNi₅, Nb₂O₅ or LaNi₅ + Nb₂O₅ added were then investigated.     

Interfacial microstructure and mechanical property of ZrC-SiC ceramic and Ti6Al4V joint brazed with AgCuTi alloy

ZrC-SiC ceramic and TC4 alloy were brazed using AgCuTi alloy. The microstructure and mechanical property of the joints obtained at different brazing parameters were investigated and the reaction mechanism was analyzed. The results indicated that the Ti from the AgCuTi and TC4 reacted with the ZrC in the ceramic to form different shaped TiC crystals adjacent to the ZrC-SiC ceramic. With the increase of brazing temperature or extending of holding time, the dissolution of TC4 became vigorous and much Ti dissolved into the braze alloy. As a result, Ti reacted with the Cu from AgCuTi alloy to form a series of Cu-Ti compounds in the brazing seam due to the strong affinity between Cu and Ti. The Cu-Ti compounds made the hardness and brittleness of brazing seam increase, which deteriorated the property of the brazed joint. The maximum shear strength was 39 MPa obtained at 810 °C for 5 min.     

Design and synthesis of a novel d10–d10 mixed metal-based polymer with superior luminescent properties to select Ca2 + and Zn2 +

A novel luminescent probe based on Ag–Cu mixed metal coordination polymer has been designed and synthesized. Luminescent experiment indicates two peaks with maxima near 425 (Ag) and 660 nm (Cu), which shows high selectivity to Ca^2 + and Zn^2 +.     

Vacuum brazing of cubic boron nitride to medium carbon steel with Zr added passive and Ti activated eutectic Ag-Cu alloys

Active element like Ti is usually added to Ag-Cu passive alloy to braze cubic boron nitride (cBN) ceramic particles with steel substrate under high vacuum. Current work focusses on another group-IV element Zr, having more negative Gibbs free energy than Ti, concerning its reaction capability with cBN. In the present study, its effectiveness as an additive to the 72Ag28Cu alloy in brazing of cBN has been investigated. Zr is added to both passive and Ti-activated Ag-Cu alloys. Interestingly, the addition of 2 wt% Zr to the composition of eutectic alloy fails to braze cBN, unlike the addition of 2 wt% Ti. The underlying science is critically investigated. A new formulation of the alloy with the composition of (72Ag28Cu)-4Zr-4Ti alloy is found to be a beneficial alternative. Wetting of this new alloy on cBN is appreciable and simultaneously an additional benefit of 50% increase in wear resistance is achieved, compared to the (72Ag28Cu)-2Ti alloy. A significantly hard new intermetallic phase, AgCu₄Zr is detected in the microstructure which contributes to the enhancement of wear resistance of the new alloy. The joint strength thus achieved in brazing cBN with medium carbon steel using (72Ag28Cu)-2Ti and (72Ag28Cu)-4Zr-4Ti alloys is also compared but found to be compromised in case of the later. The results are analyzed in the light of microstructure, alloy-cBN interfacial chemistry and interfacial fracture under load.     

Characterization of carbon/carbon composite/Ti6Al4V joints brazed with graphene nanosheets strengthened AgCuTi filler

Carbon/carbon (C/C) composite and Ti6Al4V alloy (wt%) were successfully brazed with graphene nanosheets strengthened AgCuTi filler (AgCuTiG). Graphene nanosheets (GNSs) with low CTE and high strength were dispersed into AgCuTi filler by ball milling. The interfacial microstructure was systematically characterized by varieties of analytical means including transmission electron microscopy (TEM). Results show that typical interfacial microstructure of the joint brazed at 880 °C for 10 min is a layer structure consisting of (Ti6Al4V/diffusion layer/Ti2Cu + TiCu + Ti3Cu4 + TiCu4/GNSs + TiCu + TiC + Ag(s,s) + Cu(s,s)/TiC/C/C composite). The interfacial microstructure and mechanical properties of brazed joints changed significantly as temperature increased. High temperature promoted the growth of TiCu and TiC phases, which were attached to GNSs. Meanwhile, the diffusion layer and primary reaction layers thickened as temperature increased, while the thickness of brazing seam decreased. The maximum shear strength of 30.2 MPa was obtained for the joint brazed at 900 °C for 10 min. GNSs decreased the thickness of brittle reaction layers and promoted the formation of TiCu and TiC phases in brazing seam, which caused the strengthening effect and decreased the CTE mismatch of brazed joints. The fracture modes are also discussed in this paper.     

Microstructure and mechanical properties of Al2O3 ceramic and TiAl alloy joints brazed with Ag–Cu–Ti filler metal

Al₂O₃ ceramic was reliably joined to TiAl alloy by active brazing using Ag–Cu–Ti filler metal, and the effects of brazing temperature, holding time, and Ti content on the microstructure and mechanical properties of Al₂O₃/TiAl joints were investigated. The typical interfacial microstructure of joints brazed at 880 °C for 10 min was Al₂O₃/Ti₃(Cu,Al)₃O/Ag(s.s)+AlCu₂Ti+Ti(Cu,Al)+Cu(s.s)/AlCu₂Ti+AlCuTi/TiAl alloy. With increasing brazing temperature and time, the thickness of the Ti₃(Cu,Al)₃O reaction layer increased, and the blocky AlCu₂Ti compounds aggregated and grew gradually. The Ti dissolved from the TiAl substrate was sufficient to react with Al₂O₃ ceramic to form a thin Ti₃(Cu,Al)₃O layer when Ag–Cu eutectic alloy was used, but the dissolution of TiAl alloy was inhibited with an increase in Ti content in the brazing filler. Ti and Al dissolved from the TiAl alloy had a strong influence on the microstructural evolution of the Al₂O₃/TiAl joints, and the mechanism is discussed. The maximum shear strength was 94 MPa when the joints were brazed with commercial Ag–Cu–Ti filler metal, while it reached 102 MPa for the joint brazed with Ag–Cu+2 wt% TiH₂ at 880 °C for 10 min. Fractures propagated primarily in the Al₂O₃ substrate and partially along the reaction layer.     

High thermal conductive diamond/Ag–Ti composites fabricated by low-cost cold pressing and vacuum liquid sintering techniques

Diamond/Ag–Ti composites were fabricated by a low-cost liquid sintering technique. The Ti addition can effectively improve wetting and promote penetration in composite pores during liquid sintering. The interface structure of the diamond/Ag–Ti composite was identified as Ag/TiC/Ag–Ti/diamond. A high thermal conductivity of 719 W/mK was obtained for the 50 vol.% diamond/Ag-1 at.% Ti composite. Using a bimodal mixture (60 vol.% 150 μm + 10 vol.% 50 μm diamond/Ag-2 at.% Ti composite), a low coefficient of thermal expansion of 6.3 × 10^− 6/K still with high thermal conductivity of 687 W/mK was achieved. These composites have potential applications for thermal management of high integration electronic devices.     

Interfacial microstructure and strengthening mechanism of BN-doped metal brazed Ti/SiO2-BN joints

Ag–Cu–Ti + BN composite filler was developed to braze SiO₂-BN ceramic and titanium. The effects of BN particles content on the microstructure and mechanical properties of the joints were investigated. The fine TiB whiskers and TiN particles were synthesized in the brazing seam by introducing BN particles. TiN–TiB₂ reaction layer formed adjacent to SiO₂-BN ceramic while Ti–Cu compound layer formed at Ti substrate. With the increase of BN content, more fine-grains formed in the joint and the reaction layer nearby the base materials became thinner. The hardness and modulus of the reaction phases were characterized by nanoindentations to reveal the plastic deformability of the brazing seam. The improvement of the joint strength was 340% with 3 wt.% BN addition. The joint strength was determined by the thermal expansion mismatch between the joined materials, plastic deformation in the brazing seam, and interfacial structure of the joint.     

Sinterability,microstructures and electrical properties of Ni/Sm-doped ceria cermet processed with nanometer-sized particles

Ni/Sm-doped ceria (SDC) cermet was prepared from two types of NiO/SDC mixed powders: Type A—Mechanical mixing of NiO and SDC powders of micrometer-sized porous secondary particles containing loosely packed nanometer-sized primary particles. The starting powders were synthesized by calcining the oxalate precursor formed by adding the mixed nitrate solution of Ce and Sm or Ni nitrate solution into oxalic acid solution. Type B—Infiltration of Ni(NO₃)₂ solution into the SDC porous secondary particles subsequently freeze-dried. Type B powder gave denser NiO/SDC secondary particles with higher specific surface area than Type A powder. The above two types powders were sintered in air at 1100–1300 °C and annealed in the H₂/Ar or H₂/H₂O atmosphere at 400–700 °C. Increased NiO content reduced the sinterability of Type A powder but the bulk density of Type B powder compact showed a maximum at 34 vol.% NiO (25 vol.% Ni). Type B cermet was superior to Type A cermet in achieving fine-grained microstructure and a homogeneous distribution of Ni and SDC grains. The electrical resistance of the produced cermet decreased drastically at 15 vol.% Ni for Type B and at 20 vol.% Ni for Type A.     

Interfacial characterization of silicon nitride/silicon nitride joints brazed using Cu-base active metal interlayers

Silicon nitride/silicon nitride joints were vacuum brazed at 1317 K for 5 min and 30 min 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 (～2–3 μm thick) formed in 5 min at the Si₃N₄/braze interface. The inhomogeneity disappeared after brazing for 30 min 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.