Ti-Cu Compounds Research Articles

Microstructure and mechanical properties of Si3N4 ceramic and (TiB + Y2O3)/Ti matrix composite joints brazed with AgCu/Cu foam/AgCu multilayered filler

Abstract Silicon nitride ceramics (Si3N4) and (TiB + Y2O3)/titanium matrix composites (TMCs) were brazed using a multilayered filler consisting of AgCu foils and Cu foam. The microstructure and formation mechanism of the TMCs/Si3N4 joint were studied. The results showed that the TMCs/Si3N4 joint consisted of TMCs/TiCu + TiCu2/Ag(s, s) + Cu(s, s)/TiCu + Ti5Si3 + TiN/Si3N4 ceramic. The reaction layer consisting of TiN and Ti5Si3 formed first on the Si3N4 ceramic side is crucial for the joining the TMC and Si3N4. The influence of brazing temperature on the microstructure evolution and mechanical performance of the TMCs/Si3N4 joint was discussed. Element diffusion was intensified by increasing the brazing temperature, which reduced the Cu(s, s) and enlarged the Ti-Cu compounds. At 820 ℃, the Ag-Cu eutectic structure was uniformly distributed into the brazing seam, which improved the performance of the joint. The shear strength reached a maximum of approximately 165.0 MPa. At higher brazing temperatures, the Cu foam collapsed, the Ti-Cu intermetallics increased, the brittleness was aggravated, and the shear strength of the joint decreased.

Wetting behavior of AgCu-4.5Ti filler reinforced by carbon nanotubes on C/C composite

The effect of Carbon Nanotubes (CNTs) content on the wettability of AgCu-4.5Ti + x CNTs (wt%) composite filler alloys on C/C composite was investigated. The results show that the added CNTs reacted with element Ti in the filler and produced the dispersed fine in situ synthesized TiC particles, which increased the consumption of element Ti and provided the nucleus for the growth of Ti-Cu compounds simultaneously. The above effects of introducing CNTs, inhibited the formation of Ti-Cu compounds, also changed the distribution of compounds, which dramatically influenced the interfacial microstructure and characteristics of wetting behavior. The increase of CNTs content refined and dispersed coarse Ti-Cu compounds, decreased the initial spreading temperature, and improved the wettability, but high content of CNTs (more than 0.3wt%) decreased the wettability of the filler alloy. The wetting interfacial microstructure of corresponding composite filler alloys were analyzed by Scanning Electron Microscope (SEM), Energy Dispersive X-ray Spectrometer (EDS) and Transmission Electron Microscope (TEM), which consisted of TiC, TiCu, TiCu2 and TiCu4 compound. The typical wetting behavior of AgCu-4.5Ti + 0.3wt% CNTs composite filler on C/C composite was divided into four stages. The effect mechanism of CNTs content on the wetting behavior was proposed.

Interfacial structure and joint strength on Ti(C, N)–Al2O3 cermet/40Cr steel joints with diffusion bonding

The [Formula: see text]–[Formula: see text] cermet to 40Cr steel joint was conducted by liquid phase diffusion bonding under the auxiliary pulse current and using 73Cu–27Ti amorphous foil/Cu foil/72Ag–28Cu foil sandwich foils as the interlayer. The effect of holding time and duty ratio of the pulse current on interfacial structure at the [Formula: see text]–[Formula: see text] cermet side and joint strength were studied. The results showed that the longer bonding time can improve the melting of Cu–Ti foil and the dissolution of Cu interlayer to obtain a higher joint strength. The interfacial structure was composed of the TiCu compounds and Cu solid solution at the cermet side, and [Formula: see text] compounds and Cu solid solution at the Cu interlayer side. The auxiliary pulse current was beneficial to reach a higher joint strength in a shorter holding time. A higher duty ratio would accelerate the dissolution and reaction of cermet to the interlayer, but continuous increase on the duty ratio would result in the over dissolution of cermet into the interface to produce the Ti(C, N) and [Formula: see text] ceramic particles and the decrease on the joint strength.

Effect of introducing carbon fiber into AgCuTi filler on interfacial microstructure and mechanical property of C/C-TC4 brazed joints

In this work, carbon fiber was introduced into the Ag-26.7Cu-4.5Ti (wt%) filler to optimize brazed joints by participating in brazing reaction process. The interfacial microstructure was analyzed by SEM and TEM, the effects of carbon fiber content on the microstructure and mechanical property of brazed joints were studied, the formation of brazing interface was systematically discussed, and the action mechanism of carbon fiber was illustrated. Experimental results demonstrated that carbon fiber reacted with Ti to generate TiC during the brazing process, and formed a structure of carbon fiber wrapped by TiC and Ti-Cu compounds (TiCu+Ti3Cu4). Due to competitive reaction between carbon fiber and Cu to Ti, the formation of bulk Ti3Cu4 and TiCu4 was inhibited, while the formation of Cu-based solid solution was promoted. The microstructure of joints was dispersed as the increase of carbon fiber. The maximum shear strength of 27.8 MPa was achieved when 0.3 wt% carbon fiber was added into AgCuTi filler. The reinforcing effects of carbon fiber were mainly to relieve the residual stress generated by CTE mismatch and reduce the thickness of brittle TiC layer close to C/C composite. However, excessive carbon fiber would deteriorate the joints because of the insufficient reaction between filler and C/C composite.

Effect of heat input on microstructure and mechanical properties of Ti/Cu66V34/Cu joints by electron beam welding

The variations of microstructure and mechanical properties of the joints with different welding heat input were investigated. As the heat input increased, excessive melting of TA15 alloy facilitated the formation of Ti-Cu compounds at the TA15 interface, increasing the brittleness of the TA15 interface. Moreover, high heat input also caused the HAZ softening by grain coarsening and deteriorated the performance of the joint. However, low heat input was adverse to the complete melting of Cu66V34 alloy and induced the formation of welding pores. It also weakened the strength of the joint. Under optimum welding parameters, (Ti,V) solid solution formed at the titanium interface, replacing Ti-Cu intermetallic compounds (IMCs). Therefore, the joint of sample 2 presented the highest strength (378MPa) and fractured along the HAZ of QCr0.8 alloy due to the HAZ softening resulting from grain coarsening.

Effect of Cu66V34 filler thickness on the microstructure and properties of titanium/copper joint by electron beam welding

The joint with 1.0mm Cu66V34 filler metal produced a large amount of unmelted V alloy, weakening the joining quality of Ti/Cu joint. Due to the decreased thickness of filler metal, the melting quantity of Ti increased notably in the joint with 0.5mm Cu66V34 alloy, resulting in the formation of Ti-Cu compounds. The 0.7mm Cu66V34 filler metal could restrain the Ti-Cu compounds formed in the joint. The microstructure in zone A3 and FZ was mainly characterized by solid solution phases including (Ti,V) solid solution and Cu solid solution, improving the bonding strength at the interface of titanium side. The joint with 0.7mm Cu66V34 alloy presented the highest tensile strength of 384 MPa, approaching ∼80% of that of the copper base metal, and fractured in the HAZ of copper side, due to local softening by grains coarsening.

Effect of filler metal composition on microstructure and mechanical properties of electron beam welded titanium/copper joint

Electron beam welding of titanium to copper has been performed with different Cu-V filler metals. Microstructure, mechanical properties and fracture behavior were investigated. Compared with the welded joint without filler metal, the lower V content in Cu75V25 filler metal resulted in the formation of fine Ti-Cu compounds in the interface of TA15 side. Thus, the joint showed a lower tensile strength and fractured along the interfacial reactive layer. When V content is over 34 wt% in the filler metal, the interfacial microstructure near TA15 side formed cellular (Ti,V) solid solution to replace the Ti-Cu compounds, which improved the mechanical properties of the joint. As a result, the joint with Cu66V34 filler metal displayed the highest tensile strength (384 MPa), approaching 82% of that of the copper base metal (BM), and fractured in heat affected zone (HAZ) of copper side, due to the local softening by grains coarsening. In spite of the formed solid solution at the interface, the joint welded with Cu34V66 filler metal containing higher V content, produced amount of pores and unmelted V alloy, which resulted in the decrease of tensile strength down to 55% of that of the copper BM.

Microstructure, residual stress and mechanical properties of Al2O3/Nb joints vacuum-brazed with two Ag-based active fillers

Vacuum brazing was applied to join Al2O3 ceramic and pure Nb with two active Ag-based fillers, Ag-Cu-Ti and Ag-Cu-Ti + Mo. The influences of the brazing parameter and the content of Mo particles on the microstructure and mechanical properties of the brazed joint were studied. The typical interfacial structure of Al2O3/Nb joint brazed with Ag-Cu-Ti filler metal at 900 °C for 10 min was Al2O3/Ti3(Cu,Al)3O/TiCu+Ti2Cu3+TiCu4+Ag(s,s)+Cu(s,s)/Nb. In the joints brazed with Mo particle-modified composite filler, the large blocky Ti-Cu compounds disappeared, and a large number of fine phases formed in the brazing seam. The dissolved Mo played a better role in refining the microstructure compared with residual Mo particles. In addition, the finite element method (FEM) calculated results showed that the residual stress peak value of Al2O3/Nb brazed joint decreased from 296 MPa to 253 MPa when 8 wt. % Mo particles were added in the composite filler. The shear strength of Al2O3/Nb brazed joints could reach up to 203 MPa at 900 °C for 10 min. The joining properties of the Al2O3/Nb brazed joint were primarily dependent on the dispersion degree of fine Ti-Cu compounds and the thickness of Ti3(Cu,Al)3O reaction layer.

Interfacial Microstructure and Formation Mechanism of Zirconia Ceramic and Nb Brazed with Ag-Cu-Ti Powder without and with Mo-Particle-Reinforced

Zirconia (ZrO2) ceramic and Nb were brazed using Ag-Cu-Ti powder without and with Mo-particle-reinforced. The effects of the brazing temperature, holding time and Mo content of the composite filler on the interfacial microstructures and joining mechanism of ZrO2/Nb brazed joints were investigated. By increasing the brazing temperature and holding time, the thickness of Ti3Cu3O layer increased and the thickness of TiO layer decreased, while the total thickness of the reaction layers increased slightly with the sufficient interfacial reaction. Meanwhile, the blocky Ti-Cu compounds gradually accumulate and grow up in the brazing seam. The calculated Ti activity increased first and then decreased as the Mo content was increased from 5 to 40 wt%. When the Mo content was 5wt%, only single Ti3Cu3O reaction layers formed adjacent to the ceramic substrate. By increasing of Mo particles, TiO layer became thicker. When 40 wt% Mo particles were added to the composite filler, Mo particles aggregated into larger clumps damaged the shear strength of brazing joint.

Joining of Cf/SiC composite to Ti-6Al-4V with (Ti-Zr-Cu-Ni)+Ti filler based on in-situ alloying concept

In this paper, a novel brazing process based on in-situ alloying concept was carried out to join Cf/SiC composite to TC4 alloy at 940°C for 20min. Mixed powders of Ti-Zr-Cu-Ni alloy and pure Ti metal were used as interlayer. In the process, Ti-Zr-Cu-Ni alloy melted and then dissolved pure Ti metal via liquid-solid reactions, achieving in-situ alloying of the interlayer. The interfacial microstructure and formation mechanism of the brazed joints were investigated. The effect of Ti powder content on the microstructure and the mechanical properties of joints were analyzed. The results showed that: the maximum lap-shear strength of the in-situ alloying brazed joints was 283±11MPa when using (Ti-Zr-Cu-Ni)+40vol% Ti composite filler, and this value was 79% higher than the mechanical strength when using Ti-Zr-Cu-Ni alone. A reaction layer of (Ti,Zr)C+Ti5Si3 formed near Cf/SiC composite side, while a diffusion layer of Ti2Cu+Ti(s,s) formed near Ti-6Al-4V side. In the interlayer, lots of Ti(s,s) were distributed uniformly and few of Ti-Cu compounds were found, contributing to the plasticity of joints. Adding moderate Ti powder was beneficial for improving the interfacial reaction between Cf/SiC composite and filler material, which affected the lap-shear strength of joints.

Control interfacial microstructure and improve mechanical properties of TC4-SiO2f/SiO2 joint by AgCuTi with Cu foam as interlayer

Brazing SiO2f/SiO2 ceramics to TC4 is often associated with the problems of excessive Ti from the dissolution of TC4 and high residual stress, which results in low-strength joints. To overcome these problems, here we put forward an effective method by introducing Cu foam as interlayer to obtain high-strength joints of SiO2f/SiO2-TC4. The effect of Cu foam on the microstructure and mechanical properties of brazed joints was investigated. Cu foam can consume Ti from TC4 and inhibit forming too many brittle compounds at the SiO2f/SiO2 side. Furthermore, Cu foam can react with Ti, forming the dispersed homogeneous distribution of fine-grained Ti-Cu compounds in the brazing seam, due to its unique 3D porous structure. The formation and distribution of fine-grained Ti-Cu compounds at the brazing seam could significantly help to reduce the residual stress and reinforce the mechanical properties of the joint. Maximum shear strength of 59.6MPa is approached.

Interfacial microstructure and mechanical properties of zirconia ceramic and niobium joints vacuum brazed with two Ag-based active filler metals

Reliable brazing of a zirconia ceramic and pure niobium was achieved by using two Ag-based active filler metals, Ag-Cu-Ti and Ag-Cu-Ti+Mo. The effects of brazing temperature, holding time, and Mo content on the interfacial microstructure and mechanical properties of ZrO2/Nb joints were investigated. Double reaction layers of TiO and Ti3Cu3O formed adjacent to the ZrO2 ceramic, whereas TiCu4+Ti2Cu3+TiCu compounds appeared in the brazing interlayer. With increasing brazing temperature and time, the thickness of the Ti3Cu3O layer increased with consumption of the TiO layer, and the total thickness of the reaction layers increased slightly. Meanwhile, the blocky Ti-Cu compounds in the brazing interlayer tended to accumulate and grow. This microstructural evolution and its formation mechanism are discussed. The maximum shear strength was 157MPa when the joints were brazed with Ag-Cu-Ti at 900°C for 10min. The microstructure and bonding properties of the brazed joints were significantly improved when Mo particles were added into the Ag-Cu-Ti. The shear strength reached 310MPa for joints brazed with 8.0wt% Mo additive, which was 97% higher than that of joints brazed with single Ag-Cu-Ti filler metal.

Low Temperature Diffusion Bonding of Ti-6Al-4V to Oxygen Free Copper with High Bonding Strength Using Pure Ag Interlayer

Abstract Diffusion bonding of Ti-6Al-4V (TC4) to oxygen free copper (OFC) at low temperature was carried out using silver foil as interlayer. Results show that the interlay can prevent the formation of brittle Ti-Cu compounds and improve the interfacial microstructure and bonding strength of the TC4/OFC joint. Moreover, adding the silver interlayer greatly lowers the bonding temperature. The composition of the joint from the TC4 side to the OFC side is TC4 substrate, AgTi compound, Ag interlayer, Ag-Cu solid solution and OFC substrate. The tensile strength of the joint bonded at 700 °C for 1 h under 10 MPa bonding pressure has an excellent value of 150 MPa, higher than those previously reported in literatures. Fracture failure takes place in the Ag/OFC interface and ductile fracture can be observed on the fracture surface. It is suggested that the ductile properties of the AgTi compounds are superior to that of Ag-Cu solid solution in this joint.

Combinatorial Influence of Bimodal Size of B2 TiCu Compounds on Plasticity of Ti-Cu-Ni-Zr-Sn-Si Bulk Metallic Glass Composites

We report on the formation of Ti-Cu-Ni-Zr-Sn-Si bulk metallic glass composites containing bimodal size of B2 TiCu compounds. The small B2 TiCu compound with a size of 1 to 10 μm has a strong influence on the oscillation of the shear stress, thus causing wavy propagation of the shear bands. In contrast, the large B2 TiCu compound with a size of 70 to 150 μm dissipates the shear stress by branching and multiplication of the shear bands. By forming the bimodal size of B2 TiCu compound, it is possible to determine the harmonic influence to further enhance the plasticity of the Ti-Cu-Ni-Zr-Sn-Si bulk metallic glass composites.

Rapid Consolidation of Nanostuctured TiCu Compounds

TiCu nanopowder was produced using an electrical wire explosion method and subsequently consolidated into dense nanostuctured TiCu by a high frequency induction heated sintering method. The consolidation was accomplished by the combination of an induced current and a high mechanical pressure within two minutes. This process results in very quick densification to near the theoretical density and prohibits grain growth in nano-structured materials. The grain sizes and mechanical properties of the sintered TiCu were investigated.

Details on the Formation of Ti2Cu3 in the Ag-Cu-Ti System in the Temperature Range 790 to 860 °C

Silver-copper-titanium (Ag-Cu-Ti) ternary alloys are often used as active braze alloys for joining ceramics to metals at temperatures ranging from 780 °C (the melting point of the Ag-Cu eutectic) up to 900 °C. When Ti/Ag-Cu joints are brazed at low temperature (near 800 °C), the intermetallic compound Ti2Cu3 (tetragonal, P4/nmm, a = 0.313 nm, c = 1.395 nm) is systematically missing from the interface reaction layer sequence. An experimental investigation based on isothermal diffusion experiments in the Ag-Cu-Ti ternary system has then been undertaken to clarify the issues of thermal stability and formation kinetics of this compound. Evidence has been found for the stability of Ti2Cu3 at temperatures ranging from 790 to at least 860 °C. By heat treating Ag-Cu-Ti powder mixtures at 790 °C for increasing times, it has moreover been shown that Ti2Cu3 forms at a much slower rate than the two adjacent Ti-Cu compounds: TiCu4, the first phase to form, and Ti3Cu4. This explains why although thermodynamically stable, Ti2Cu3 is not obtained when temperature is too low or reaction time too short.