Effect of surface condition and bonding pressure on quality of diffusion bonded high purity copper for linear collider accelerator structures

Abstract

Tests have been carried out to assess the feasibility of diffusion bonding as a fabrication technology for vacuum tight joints in linear accelerator cells for the Next Linear Collider. High purity copper specimens were diffusion bonded over a range of temperatures from 400 to 1000°C, under high (3.45 MPa) and low (3.45 kPa) bonding pressures, and at two different diamond machined surface finishes. Experiments showed that diffusion bonds with strengths equal to, or greater than, that of silver brazed joints could be made at temperatures ≥700°C at the 3.45 MPa bonding pressure, or ≥800°C at the 3.45 kPa bonding pressure. Partial strength diffusion bonds were made at temperatures as low as 400°C at the high bonding pressure, whereas no bonding (zero strength) was observed at temperatures below 700°C at the low bonding pressure. Observations of the fracture surfaces of the diffusion bonded specimens showed that bonding begins by point asperity contact. At low bonding pressures, surfaces created by diamond turning of annealed copper specimens produce higher strength bonds than those created by diamond flycutting of unannealed surfaces, whereas at higher bonding pressures the effect of surface finish was less important.     

Interfacial structure and mechanical properties of hot roll bonded joints between titanium alloy and stainless steel using copper interlayer

Abstract

The hot roll bonding was carried out in vacuum condition between titanium alloy and stainless steel using copper interlayer. The stainless steel/Cu can not be bonded if the bonding temperature is lower than or equal to 730°C, and the Cu–Ti alloy can not be bonded if the bonding temperature is higher than or equal to 880°C. The testing results show that the total thickness of intermetallic layers at the interface between copper and titanium alloy increases with the bonding temperature, and the tensile strength of bonded joints decreases with increasing bonding temperature. The maximum strength of 343 MPa was obtained at the bonding temperature of 780°C, the reduction of 20% and the rolling speed of 38 mm s^–1.     

Microstructural and Mechanical Properties of Hot Roll Bonded Titanium Alloy/Low Carbon Steel Plate

In this paper, a titanium alloy and low carbon steel were bonded via hot rolling in a vacuum, and the effect of roll bonding temperature and reduction ratio on the microstructural and mechanical properties of the plate was studied. When the bonding temperature was between 850 and 1050 °C, the shear strength of the interface increased with an increasing reduction ratio from 18 to 70%. At a bonding temperature of 950 °C and at a rolling reduction ratio of 70%, the best bonding strength was obtained, and a shear fracture occurred on the low carbon steel matrix. At 1050 °C, brittle compounds, i.e., TiC, FeTi, and Fe₂Ti, formed at the interface, which decreased the bonding strength. The large reduction ratio can break up compounds at the interface and extrude fresh metal for bonding, thereby increasing the bonding strength.     

Die sinter bonding in air using copper formate preform for formation of full-density bondline

Pressure-assisted sinter bonding was performed in air at 250?350 °C using a preform comprising copper formate particles to form a bondline that is sustainable at high temperatures. H₂ and CO generated concurrently by the pyrolysis of copper formate at 210 °C during the sinter bonding removed the native oxide and other oxides grown on bulk Cu finishes, enabling interface bonding. Moreover, Cu produced in situ by the reduction of Cu(II) accelerated the sinter bonding. Consequently, the bonding achieved at 300?350 °C under 5 MPa exhibited sufficient shear strength of 20.0?31.5 MPa after 180?300 min of sinter bonding. In addition, an increase in pressure to 10 MPa resulted in shear strength of 21.9 MPa after an extremely short time of 30 s at 250 °C, and a near-full-density bondline was achieved after 300 s. The obtained results indicate the promising potential of the preform comprising copper formate particles for high-speed sinter bonding.     

采用铌中间层的钛合金与不锈钢的真空热轧连接界面的显微组织及性能

进行了钛合金与不锈钢采用铌中间层的真空热轧连接实验,分析了连接界面的显微组织及性能。结果表明,采用铌中间层能够明显提高接头的塑性。当压缩率为25%,轧制速度为38 mm/s,热轧温度为800°C和900°C时,不锈钢与铌的连接界面没有明显的金属间化合物层;当热轧温度为1000°C和1050°C时,不锈钢与铌连接界面形成Fe-Nb金属间化合物层,并且当热轧温度为1050°C时在金属间化合物层与不锈钢之间出现开裂。铌与钛合金连接界面的扩散层厚度随着热轧温度的升高而增大。热轧温度为900°C的连接接头的拉伸强度可达-417.5MPa,拉伸试样断裂于铌中间层,断口呈塑性断裂特征。热轧温度为800°C的热轧过度接头分别与钛合金和不锈钢进行TIG焊接,TIG焊后热轧过度接头的拉伸强度可达-410.3 MPa,拉伸试样断裂于铌中间层,断口呈塑性断裂特征。     

Improvement of thermal and mechanical properties of graphite/copper composites through interfacial modification

Unidirectionally reinforced graphite/copper composites have been fabricated using a pressure infiltration casting procedure. T300 and T650 graphite fibers have been used to reinforce copper and copperchromium alloys. The effects of the chromium level in the copper matrix on the tensile strength, stiffness, and thermal expansion behavior of the composites have been evaluated through tensile and three-point bend testing, and thermal cycling. At the 0.5 wt% alloying level, chromium increases the stiffness and optimizes the thermal expansion behavior of graphite/copper composites. The longitudinal tensile strengths of these composites are above 1606 MPa, whereas the transverse tensile strengths are lower than 40 MPa due to incomplete infiltration during processing. Scanning electron microscopy analyses reveal that the unalloyed copper matrix composites experienced extensive fiber/matrix debonding under tensile loading. The addition of chromium to the copper increases the level of matrix bonding to the graphite fibers, as evidenced by observations of fractured tensile specimens. Auger electron spectroscopy analyses indicate that a chromium carbide phase present at the interface is responsible for the improved bonding.     

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

在低温下,利用Ag箔作中间层对Ti-6Al-4V钛合金（TC4）和无氧铜（OFC）进行了扩散焊接。结果表明Ag箔中间层阻止了Ti-Cu金属间化合物的生成,改善了TC4/OFC焊接接头的界面组织结构和焊接强度。同时,Ag箔中间层的添加也降低了TC4/OFC接头的焊接温度。焊接界面从TC4侧到OFC侧依次是TC4基体,AgTi金属间化合物,Ag中间层,Ag-Cu固溶体和OFC基体。在工艺条件：T=700 ℃,P=10 MPa,t=60 min下,TC4/Ag/OFC焊接接头的抗拉强度为150 MPa,其值高于直接焊接时的抗拉强度。焊接接头断裂发生在Ag/OFC界面,并且呈韧性断裂。我们可以推测AgTi化合物的韧性性能优于Ag-Cu固溶体。     

Microstructure and mechanical properties of C/C composite joint brazed with Ni-based filler

The novel Ni-based brazing filler was used to join C/C composites. When brazing temperature increased from 1080 to 1100 °C, the wetting angle decreased from 23° to 14°, and the brazing filler had good wettability on the surface of C/C composites. The brazing seam of the brazed joint consisted of Ni(s,s) and Cr₃C₂ phases. As brazing temperature increased, lots of Cr₃C₂ phases were generated at the bonding interface, and the thick reaction layer was formed. When brazing temperature was 1120 °C, the shear strength of C/C joint reached the maximum value of 31.5 MPa. The fracture path extended in the C/C matrix close to the bonding interface.     

Sauerstoffaufnahme von Vanadium,Niob und Tantal bei hohen Temperaturen und niedrigen Drücken

Oxygen absorption by vanadium, niobium and tantalum at high temperatures and low pressures A general view is presented of the oxygen absorption by vanadium, niobium and tantalum at temperatures above 1000°C and at oxygen partial pressures below 10^?2 torr. In this context the kinetics of oxygen dissolution is given a detailed treatment while oxidation is dealt with but shortly. The review includes a theoretical treatment of oxygen dissolution. In addition quantitative relations are given which enable the oxygen dissolution in vanadium, niobium and tantalum to be estimated at given conditions of temperature and oxygen pressure.     

Effect of Vacuum Annealing on the Characteristics of Plasma Sprayed Al2O3-13wt.%TiO2 Coatings

Adhesion strength is one of the critical properties for plasma-sprayed coating. In this study, the plasma-sprayed Al₂O₃-13wt.%TiO₂/NiCrAl coatings were annealed at 300-900?°C for 6?h in vacuum. The tensile bond strength and porosity of the coatings were investigated. The microstructure and the fracture were studied using optical microscopy, scanning electron spectroscopy, and x-ray diffraction. It was found that the tensile bond strength of coatings increased with the increase of annealing temperature until 500?°C, reaching the maximum value of 41.2?MPa, and then decreased as the annealing temperature continues to increase. All coatings presented a brittle fracture and the fracture occurred inside the ceramic coatings except for the coating annealed at 500?°C, which had a brittle-ductile mixed fracture and the fracture occurred at the interface of bond coating and the substrate.     

Formation of high-density TiN/Ti<Subscript>5</Subscript>Si<Subscript>3</Subscript> ceramic composites using preceramic polymer

The formation, microstructure and properties of high-density TiN/Ti₅Si₃ ceramic composites created by the pyrolysis of preceramic polymer with filler were investigated. Methylpolysiloxane was mixed with TiH₂ as filler and ceramic composites prepared by pyrolysis at 1200°C to 1600°C under N₂, Ar and vacuum were studied. When a specimen with 70 vol.% TiH₂ was pyrolyzed up to 1600°C in a vacuum after a preheat treatment at 850°C in a N₂ atmosphere and subsequently heat-treated at 1600°C for 1 h under Ar at a pressure of 2 MPa, a ceramic composite with full density was obtained. The microstructure of the ceramic composite was composed of TiN and Ti₅Si₃ phases. Under specific pyrolysis conditions, a ceramic composite with a density of 99.2 TD%, a Vickers hardness of 18 GPa, a fracture toughness of 3.5 MPam^1/2, a flexural strength of 270 MPa and a electrical conductivity of 6200 ohm⁻¹·cm⁻¹ was obtained.     

Oxygen induced interfacial phenomena during wetting of alumina by liquid aluminium

Sessile drop experiments of liquid Al on sapphire (α-Al₂O₃) were conducted under a low pressure (10⁻³ Torr) controlled Ar atmosphere as a function of oxygen partial pressure, temperature and/or time. Microstructural investigations of the samples from the experiments indicated that two different dominant processes occur at the liquid Al-sapphire interface: epitaxial growth of new α-Al₂O₃ layers on the sapphire substrate at temperatures below ≈1100°C and dissolution of the sapphire substrate at temperatures above ≈1100°C. Possible mechanisms by which oxygen affects wetting and adhesion of liquid Al on sapphire are examined. The non-wetting to wetting transition in this system may be explained by formation of an oxygen-rich interphase at the liquid Al-sapphire interface. It is concluded that dissolution of sapphire under Al oxidation conditions is capillary driven.     

The kinetics of the corrosion of copper containing different amounts of oxygen in 1.7 M H2SO4

The rate of corrosion of rotating copper discs was measured as a function of the concentration of oxygen in metal. It was found that the catastrophic acceleration of the corrosion of the sample occurs at 3 × 10³ ppm of oxygen in metal. In the temperature range 5–75°C, the corrosion resulting from the presence of the oxygen in the metal occurs in the regime of activational control, and it is not influenced by the oxygen dissolved in the acid. The corrosion resulting from the oxygen depolarization occurs in the activational control regime in the temperature range 5–35°C, in the mixed kinetics regime in the range 45–55°C, and in the range 65–75°C in the diffusional regime with respect to the oxygen dissolved in the acid. The overall rate of corrosion of copper containing 8 × 10³ ppm of oxygen is about 20 times greater than the rate of corrosion of copper with oxygen depolarization.     

Microstructural evolution during reactive brazing of alumina to Inconel 600 using Ag-based alloy

A metal–ceramic bonding process was developed to produce vacuum tight alumina–Inconel 600 joints using an Ag-based active metal brazing alloy that can withstand continuous operating temperature up to 560 °C. The microstructure and microchemistry of the braze zone was examined using extensive microanalysis of the constituent phases and a mechanism for the interfacial reactions responsible for the bonding is proposed. Prolonged heat treatment at 400 and 560 °C under simulated in-service conditions revealed that the microstructure of braze zone of the joints was stable and maintained leak-tightness and strength. The bond strength of the interface was high enough to cause failure in the alumina side of the joints. Failure of the joints was caused by initiation of crack on the surface of alumina as a result of high tensile residual stress adjacent to the metal–ceramic interface.     

Effect of brazing temperature and brazing time on the microstructure and tensile strength of TiAl-based alloy joints with Ti-Zr-Cu-Ni amorphous alloy as filler metal

An amorphous Ti-37.5Zr-15Cu-15Ni (wt.%) ribbon fabricated by vacuum arc remelting and rapid solidification was used as filler metal to vacuum braze TiAl alloy (Ti-45Al-2Mn-2Nb-1B (at.%)). The effects of brazing temperature and time on the microstructure and strength of the joints were investigated in details. The typical brazed joint major consisted of three zones and the brazed joints mainly consisted of α_2-Ti₃Al phase, α-Ti phase and (Ti, Zr)₂(Cu, Ni) phase. When the brazing temperature varied from 910 °C to 1010 °C for 30 min, the tensile strength of the joint first increased and then decreased. With increasing the brazing time, the tensile strength of the joint increased. The maximum room temperature tensile strength was 468 MPa when the specimen was brazed at 930 °C for 60 min. All the fracture surfaces assumed typical brittle cleavage fracture characteristic. The fracture path varied with the brazing parameter and cracks preferred to initiate at (Ti, Zr)₂(Cu, Ni) phase and propagation path were mainly determined by the content and distribution of α-Ti phase and (Ti, Zr)₂(Cu, Ni) phase.     

Effect of Substrate Preheating on Bonding Strength of Cold-Sprayed Mg Coatings

A poor bonding strength between the magnesium coating and substrate limits magnesium coating’s application. This paper aims at improving the bonding strength between the coating and substrate using substrate preheating. Aluminum substrates were heated to 100, 200 and 300 °C by a flame nozzle prior to cold spraying. The effects of substrate preheating on the microstructure and bonding strength were studied. The deformation behavior of single particles was simulated by a commercial software ABAQUS, and observed using SEM. The results show that substrate preheating can increase the bonding strength significantly. The bonding strength increased from 3.3 ± 0.8 to 11.6 ± 0.5 MPa when the substrate temperature increased from room-temperature to 200 °C. The fracture analyses show that the coating fracture occurred within the coating when the substrate was preheated at 200 °C.     

Fracture properties of interfacially doped Nb-A12O3 bicrystals: I,fracture characteristics

The influence of orientation and impurities on the fracture behavior of Nb–sapphire interfaces was studied using notched bending tests. Single crystals were diffusion bonded in UHV for different interface orientations. The bicrystals were doped to produce prescribed fractional interfacial coverages of Ag. The interfacial impurity content was measured after fracture with Auger spectroscopy.The tougher bicrystals exhibit significant nonlinearity in loading. A J-integral analysis was used to account for the large plastic zones. For undoped bicrystals bonded at 1400°C, the interfacial fracture energy ranged from J_c of 77 to 2100 J/m² depending on the interface planes of the Nb and sapphire. Greater toughnesses were derived from bonding at 1300°C, owing to less oxygen contamination of the Nb. Interfacial doping by Ag atoms leads to a strong reduction of J_c at coverages of only 0.2 to 0.5 of a monolayer. Higher fracture energy is caused by greater plastic deformation in the Nb as observed by slip lines on the metal fracture surface. Evaluation of the loading and fracture characteristics revealed that sharp precursor cracks developed initially in the ceramic. Extensive crack blunting also occurs, especially for the tougher bicrystals, but is often followed by erratic or unstable extension during which far less plasticity occurs, apparently owing to the rate sensitivity for Nb deformation.     

Effect of temperature on leaching behavior of copper minerals with different occurrence states in complex copper oxide ores

The effect of temperature on leaching behavior of copper minerals with different occurrence states in complex copper oxide ores was carried out by phase analysis means of XRD, optical microscopy and SEM−EDS. The results indicated that at ambient temperature, the easily leached copper oxide minerals were completely dissolved, while the bonded copper minerals were insoluble. At lukewarm temperature of 40 °C, it was mainly the dissolution of copper in isomorphism state. With increasing temperature to 60 °C, the copper leaching rate in the adsorbed state was significantly accelerated. In addition, when the temperature increased to 80 °C, the isomorphic copper was completely leached, leaving 11.2% adsorbed copper un-leached. However, the copper in feldspar−quartz−copper−iron colloid state was not dissolved throughout the leaching process. Overall, the leaching rates of copper in different copper minerals decreased in the order: malachite, pseudo-malachite > chrysocolla > copper-bearing chlorite > copper-bearing muscovite > copper-bearing biotite > copper-bearing limonite > feldspar−quartz−copper−iron colloid.     

The Joint Strength and Fracture Mechanisms of TC4/TC4 and TA0/TA0 Brazed with Ti-25Cu-15Ni Braze Alloy

In this paper, Ti-25Cu-15Ni (mass ratio) braze alloys were prepared by vacuum arc melting. Additionally, the TA0 pure titanium and TC4 titanium alloy were brazed with the Ti-25Cu-15Ni braze alloy at 960, 980, 1000, 1020, and 1040 °C. The effects of the braze temperature on the tensile strength of the TA0 and TC4 joints and their fracture mechanisms were studied. The maximum tensile strength of the TA0 joints of 219.9 ± 0.1 MPa was achieved at a brazing temperature of 980 °C, and the maximum tensile strength of the TC4 joints of 832.9 ± 0.1 MPa was achieved at the same brazing temperature. These results indicate that their ideal joint strength is comparable. According to the fractography results of the TA0 joints, a mixed fracture morphology is indicated. The TA0 fracture surface is dominated by cleavage fracture with a small contribution from ductile fracture. The TC4 joint fracture arises from cleavage.     

Degradation of strength properties and its fracture behaviour of TiB2-TiC-based composite ceramic cutting tool materials at the high temperature

Strength retention is important for tool materials at high temperature because cutting temperature in machining is ranged from room temperature to 1000 °C. A study examining the strength properties and fracture behaviour of TiB₂-TiC-based composite ceramic cutting tool materials is presented at different temperatures. MoSi₂ and SiC additives are considered to investigate their effects on the density, microstructure, strength and failure mechanism of composites. It is found that the addition of SiC contributed more to the high-temperature strength of composites than MoSi₂, but it did not improve the room-temperature strength, despite grain refinement. The TBAVS8 composite has a flexural strength of 800 MPa at room temperature and can retain 75% at 900 °C. At room temperature, the fracture behaviour of composites was dominated by the strong bonding of the Ni binder phase. At high temperatures, the softer Ni binder phase was pinned, and its sliding was inhibited by SiC particles, which decelerated the strength degradation.