Interfacial microstructure evolution and mechanical properties of B4C-based composite joints bonded with Ti foil

The interfacial microstructure and mechanical properties of B₄C-SiC-TiB₂ composite joints diffusion bonded with Ti foil interlayer were investigated. The joints were diffusion bonded in the temperature range of 800–1200?°C with 50?MPa by spark plasma sintering. The results revealed that robust joint could be successfully obtained due to the interface reaction. B₄C reacted with Ti to form nanocrystalline TiB₂ and TiC at the interface at 800–1000?°C. Both the reactions between SiC and Ti and between TiB₂ and Ti were not observed during joining. A full ceramic joint consisted of micron- and submicron-sized TiB₂ and TiC, accompanied with the formation of micro-crack, was achieved for the joint bonded at 1200?°C. Joint strength was evaluated and the maximum shear strength (145?±?14.1?MPa) was obtained for the joint bonded at 900?°C. Vickers hardness of interlayer increased with increasing the joining temperature.     

Microstructure and mechanical strength of Ti3AlC2 joints bonded using oxides as interlayer

Ti₃AlC₂ ceramics were successfully joined with TiO₂ and Nb₂O₅ respectively as interlayers via solid-state diffusion bonding at 1300 °C. The joints bonded with TiO₂ and Nb₂O₅ exhibit distinct microstructures. Two continuous thin Al₂O₃ oxidation layers with a thickness around 1 μm were formed in the joints bonded with TiO₂. Between the oxidation layers there exists a dense oxycarbide (TiC_1-xO_x) layer. For the joint bonded with Nb₂O₅, a dense bonding layer with Nb₂AlC and Nb₄AlC₃ grains surrounded by thin Al₂O₃ oxidation layers at the grain boundaries were obtained. The shear strength of the final joints shows clear dependences on both the thickness and microstructure of the joints. Smaller joint thickness and the microstructure with complex phases favour for higher shear strength. Those result implies that bonding with oxides is a practical and efficient method for joining Ti₃AlC₂.     

Joining of SiC by Al infiltrated TiC tape: Effect of joining parameters on the microstructure and mechanical properties

SiC ceramics were successfully joined by Al infiltrated TiC tapes at 900-1100 °C for 0.5-2 h in vacuum. Phase constituents, microstructure and mechanical strength of the prepared SiC joints were characterized. The prepared SiC joints display dense interlayer and crack-free interface. The interlayer primarily consists of TiC and Al phases, together with small amount of TiAl₃ and trace of Al₄C₃. With increasing the joining temperature or time, the interface layer either thickens or grows to multiple layers. The bending strengths of the SiC joints are higher than 190 MPa as bonded at present conditions, and are closely related with the property of interface and interlayer.     

Microstructure and mechanical properties of Cf/SiC composite joints joined using AlCoCrFeNi2.1 eutectic high-entropy alloy filler via spark plasma sintering

C_f/SiC composites were joined by spark plasma sintering technology using AlCoCrFeNi_2.1 eutectic high-entropy alloy as the joining filler. The typical structure of the joint could be described as C_f/SiC/CrSi₂ + HEAF + Al₄C₃ + C-rich phase/HEAF/CrSi₂ + HEAF + Al₄C₃ + C-rich phase/C_f/SiC. Under the pressure of 30 MPa and at 1450 ℃ for 10 min, the shear strength of the joint was 9.85 MPa at room temperature. However, when a 50 µm thick Ti foil was added to obtain Ti foil/AlCoCrFeNi_2.1/Ti foil composite filler, the joint strength was remarkably increased to 21.15 MPa at room temperature. The formation of TiC phase relieved the thermal stress at the joining interface. Due to the high entropy effect of AlCoCrFeNi_2.1 filler, the central zone of the joint still contained the FCC structure of high-entropy alloy. The existence of the pulsed electric field was beneficial to element diffusion and microstructure homogenization, which improved the mechanical properties of the joint while shortening the joining cycle.     

Microstructure evolution and mechanical properties of a vacuum-brazed Al2O3/Ti joint with Mo-coating on Al2O3 and Ti surfaces

Au-foil was used to braze Al₂O₃ and Ti to obtain a joint with biocompatibility. Mo-coatings of thicknesses 2 or 4?μm were deposited on the surfaces of Al2O3 and Ti by magnetron sputtering before the brazing experiments. The microstructure evolution and mechanical property of the Al₂O₃/Ti joint were systematically investigated. Due to the (i) different wettabilities of Ti and Mo and (ii) thermal expansion mismatch between dissimilar components, defects were observed in the Al₂O₃Mo/Au/Ti joint when only Al₂O₃ was metallised by a Mo-coating. However, the Al₂O₃Mo/Au/MoTi joints were nearly defect free when both Al₂O₃ and Ti were coated with Mo films. The typical microstructure of an Al₂O₃Mo/Au/MoTi joint was characterised by Al₂O₃/Mo-rich phase + Au-rich phase/TiAl intermetallic compound/Au-rich phase + TiAu₂ intermetallic compound+(Ti, Mo) solid solution/Ti. The distribution of the (Ti, Mo) solid solution, width of the reaction layer, and quantity of the TiAl intermetallic compound varied with brazing temperature and holding time. The thickness of Mo-coating only affected the width of the reaction layer. Compared to those of the holding time and Mo-coating thickness, the influence of the brazing temperature on the microstructure and shear strength of joints was the most noticeable. The mechanical properties of the Al₂O₃/braze interface and seam were key factors for determining the shear strength of the Al₂O₃Mo/Au/MoTi specimens. The maximum shear strength was 208?MPa for the Al₂O₃Mo/Au/MoTi couple obtained at 1100?°C for 5?min with a Mo-coating thickness of 2?μm.     

Effect of carbon content on the microstructure and mechanical properties of Ti(C, N)-based cermets

Three series of Ti(C, N)-based cermets with various carbon content were studied using scanning electron microscopy (SEM), transmission electron microscopy (TEM), energy dispersive X-ray analysis (EDX) and X-ray diffractometry (XRD). Hardness (HV) and transverse rupture strength (TRS) were also measured. A lower carbon content resulted in the aggregation of ceramic grains because the absorbed oxygen of the powder mixture could not be outgassed completely, and then the ceramic grains could not be well-wetted by liquid metal during sintering. On the contrary, too high carbon content resulted in the formation of graphite phase. An increased carbon content decreased the dissolution of tungsten, titanium and molybdenum in the binder phase. The volume fraction of the binder is not much influenced by the carbon content. The highest hardness and TRS were found for the cermet with 1.5 wt.% carbon addition, which was characterized by fine grains and moderate thickness of rim phase.     

Effects of salt spray on the mechanical properties of aluminum-epoxy adhesive joints

The aluminum bonding joints were aged in salt spray fog for various aging time from 0 to 1200?h. Uniaxial tensile tests were conducted for the joints to obtain the residual strength of the joints. The test results showed that the residual strength of the joints increases firstly and then decreases with the aging time in salt spray environment. The mechanism of the spray fog environment effect on the joint residual strength is analyzed by infrared spectral analysis and energy dispersive spectroscopy experiments. It is suggested the effect of aging time in the salt spray fog on the joint residual strength is the competing result of two mechanisms. One positive mechanism is that the adhesive expands after absorbing water in the early aging and reaches its saturation after a certain time, which leads to releasing of the internal stress in joints and consequently increases the joint residual strength. Another negative mechanism is that the water molecules permeating into the adhesive when aged in salt spray fog leads to the plasticization of the adhesive, which results in decreasing the joint residual strength as the aging time increases.     

Effects of channel modification on microstructure and mechanical properties of C/SiC composites prepared by LA-CVI process

Carbon fiber reinforced SiC matrix composites (C/SiC) with four different deposition channel sizes were fabricated via a novel laser-assisted chemical vapor infiltration (LA-CVI) method. Effects of infiltration channel sizes on microstructure and mechanical properties of C/SiC composites were investigated. The results showed that increasing the size of channels could expand infiltration passages and densification bands, which was consistent with theoretical calculations. Due to the presence of channels, the flexural strength of C/SiC composite increased by 14.47% when the channel diameter was 0.3?mm, compared to C/SiC composites prepared via conventional CVI process. Characteristics of matrix cracking and crack propagation on fracture surface were analyzed by using scanning electron microscopy. LA-CVI C/SiC composites displayed significantly improved damage-tolerant fracture behavior. Thus, findings of this work demonstrate that LA-CVI fabricated C/SiC composites are promising for a wide range of applications, particularly for enclosed-structure and thick-section C/SiC composites.     

Microstructural evolution and growth behavior of Bi5Ti3FeO15 whiskers in the lithium ferrite joints with different Ti substitution

The Bi₂O₃-B₂O₃-SiO₂-ZnO glass was used to join Li-Ti ferrites with three different Ti substitutions. The microstructural evolution and the resulting mechanical strength of the joints were systematically investigated. Needle-like, strip-like, rob-like and plate-like Bi₅Ti₃FeO₁₅ phases were observed within the joint domain. The Ti concentration gradient decreased as the Ti substitution increased. A sufficiently pronounced Ti concentration gradient promotes the Bi₅Ti₃FeO₁₅ nucleuses grow into whiskers along the c-axis orientation. The orientational distribution of Bi₅Ti₃FeO₁₅ whiskers is consistent with the Ti concentration gradient. When the Ti concentration gradient is small enough, the Bi₅Ti₃FeO₁₅ nucleuses evolve into plates due to a preferential growth of the ab crystalline plane of Aurivillius compounds. The resulting distribution of Bi₅Ti₃FeO₁₅ plates is random. The layered Bi₅Ti₃FeO₁₅ strip or rob phase represents a transition from a whisker to a plate. The Bi₅Ti₃FeO₁₅ whiskers offer a better joint strength enhancement effect when compared with the Bi₅Ti₃FeO₁₅ strips or robs.     

Microstructures and mechanical property of ZrCx joints diffusion bonded using Ti/Ta/Ti as the interlayer

In present study, homogeneous joint of ZrC_x ceramic was achieved by diffusion bonding using Ti/Ta/Ti as the interlayer. The effect of bonding temperature and time on the microstructure and mechanical property of the joints was uncovered. The homogeneous joints can be formed at 1400 °C for 2 h and at 1500 °C for 1 h, respectively. The Ti/Ta/Ti interlayer prefers to form Ti-Ta solid solutions rather than to form carbides with ZrC_x ceramic during the bonding process, which is more readily to be dissolved with the base ceramic, thus contributing to the formation of the homogeneous joints. The mechanical property of the homogeneous joints can be comparable to that of the base ceramics due to the similar composition of the joint with the base ceramics. The unique microstructure feature and mechanical property of the homogeneous joints illustrate the great potential of our method for joining transition metal carbides.     

铜离子浓度对电解铜箔组织性能的影响

针对国内超薄电解铜箔生产工艺不稳定问题,选择较易控制的参数──铜离子质量浓度为对象,在仅含硫酸、明胶和氯离子的镀液中研究其对电解铜箔表面形貌、毛面粗糙度、织构、抗拉强度和伸长率的影响。结果表明,电解液中铜离子质量浓度较低时,铜箔晶粒很不均匀,出现许多大尺寸晶粒。随铜离子质量浓度增大,铜箔晶粒的均匀性改善,毛面粗糙度减小,织构几乎不变,力学性能改善。适宜的铜离子质量浓度为80~90 g/L。     

Microstructural evolution and growth kinetics of interfacial reaction layers in SUS430/Ti3SiC2 diffusion bonded joints using a Ni interlayer

Ti₃SiC₂ ceramic and SUS430 stainless steel (SS) were successfully joined by a solid diffusion bonding technique using Ni interlayers. Diffusion bonding was performed in the temperature range of 850 °C–1100 °C under vacuum. The interfacial reaction phase, morphology evolution, growth kinetics and tensile strength were systematically investigated. In all cases, the inter-diffusion and reaction between Ti₃SiC₂ and SS can be effectively prevented by Ni foil, and the good transition in the joint benefit to the sound joining. The interface in the joints adjacent to SS matrix was composed of γ solid solution and a small amount of σ intermetallic compound. The compounds in the Ni/Ti₃SiC₂ interface was Ni/Ni(Si)/Ni₃₁Si₁₂ + Ni₁₆Ti₆Si₇ + Ti₃SiC₂ + TiC_x/Ti₂Ni + Ti₃SiC₂ + TiC_x/Ti₃SiC₂, which formed by the inter-diffusion and chemical reactions between Si and Ni atoms. The diffusion mechanism and reaction mechanism were interrelated, and decided the width of each reaction zones. Furthermore, the diffusion activation energy was 113 kJ/mol. The tensile strength increases with increasing the bonding temperature. The minimum and maximum strength of 32.3 MPa and 88.8 MPa were obtained from SUS430/Ni/Ti₃SiC₂ joints, which bonding experiments were carried out at 850 °C and 1100 °C, respectively.     

Effect of WC-Co granules on mechanical properties and microstructure of Ti(C,N)-based cermets

The effect of WC-Co granules addition on the microstructure and mechanical properties of TiC(nm)-TiN(nm)-Co-Mo-C cermets (shown as Ti(C,N)-based cermets in other part of the paper) was studied in this paper. The results show that the WC-Co granules distribute homogeneously in the matrix of Ti(C,N) based cermets. There was a transitional layer containing intermetallic compound between the WC-Co granules and the matrix of Ti(C,N) based cermets. Transverse rupture strength(TRS) and fracture toughness increase with the increase of WC-Co granules, reach a peak value at 15 vol% addition in comparing with that of without WC-Co granules addition. The toughening mechanisms were crack deflection, branching and trapping. However, when the content of WC-Co granules was higher than 15 vol%, the excessive content of WC-Co granules leaded to voids in the cermets, which decreased the mechanical properties of the cermets.     

Torsional behaviour of glass-joined,laser-processed Crofer 22 APU interconnect: Unravelling the effect of surface roughness on the shear strength

Glass-to-metal interfaces play a crucial role in the robustness and the mechanical integrity of solid oxide cells, and it is well known that a sound interface improves the mechanical reliability of the whole stack. The present work focuses on the torsional behaviour of hourglass-shaped Crofer 22 APU stainless steel joined by a glass sealant specifically designed for this application.Specific focus was given to the Crofer surface modification by laser processing, namely, the laser fluence was varied to find suitable roughness parameters; a laser fluence of 14.1 J cm^?2, leading to a Crofer surface roughness of about 4.6 μm, was selected as the optimal Crofer surface processing before the joining process.The torsional shear strength of glass-joined as-received Crofer was measured as 24 ± 7 MPa with mainly adhesive fracture mode, with failure jumping from one interface to the other, while the laser-processed Crofer gave 32 ± 5 MPa with cohesive failure. The approximate 30% increase of torsional shear strength is due to the mechanical interlocking effect given by glass infiltration inside the laser-induced protrusions on Crofer as evidenced by SEM/EDS on cross-sections and fracture surfaces after torsion tests.     

Effect of heat treatment on microstructure and mechanical properties of cold sprayed Ti coatings with relatively large powder particles

In this study, the effect of post-spray heat treatment on the microstructure, microhardness, and adhesive strength of the cold-sprayed Ti coating was investigated. It was found that a thick and relatively porous Ti coating was deposited by cold spraying. The coating surface layer presented a more porous structure. The microhardness of the as-sprayed Ti coating was slightly higher compared to pure Ti bulk, owing to the work hardening effect during deposition. After annealing at 850°C for 4 h under vacuum condition, the Ti coating also presented a porous structure with more uniformly distributed small pores. A metallurgical bonding between the deposited particles was formed through annealing treatment. The adhesive strength of coating was significantly improved after annealing. The microhardness of the annealed Ti coating was also increased.     

Effects of random chopped short carbon fibers on microstructure and mechanical properties of joints for Cf/SiC composites by reaction bonding process

Random chopped short carbon fibers (C_sf)/phenol-formaldehyde resin (PF)/SiC powder mixtures are used as filler for the joining of C_f/SiC composites to obtain SiC interlayer at the joining region. The influences of C_sf on the microstructure and mechanical properties have been investigated. Research shows that the introduction of C_sf can improve the microstructure uniformity of the joint and reduce residual silicon content in the interlayer. The joint achieve a high flexural strength of 232?±?33?MPa as the carbon fiber content is 30?wt.%, which is similar to that of the C_f/SiC composites (220?±?21?MPa). The decrease in residual silicon content and the formation of nano-sized SiC particles are the main reasons for high joining strength.     

Effects of Ni coating thickness on the microstructure and mechanical properties of resistance-welded WC-Co/B318 steel joints

WC-Co pellets electroplated with different Ni coating thicknesses and B318 steel were resistance welded for carbide-tipped saw blade applications. The effects of the Ni coating thickness on the welding process, interfacial microstructures, and mechanical properties of the joints were investigated. The results showed that the shear force increased before decreasing as the Ni coating thickness increased. When the coating thickness was 40 μm, expulsions began to appear during welding, while a thicker coating resulted in longer expulsion times. Voids and macro cracks were generated at the joints because of the expulsions, which reduced the shear force of the joint. The XRD results of the welding slag and the EDS results of the interface indicate that the microstructures can be divided into five phase categories: light gray (Fe₃W₃C), gray (Co₃W₃C), white (WC), fishbone eutectic structure (Fe₆W₆C), and dark [(γ Fe, Ni) solid solutions]. As a thicker Ni coating hinders reactions between molten Fe and dissolved WC, the joint interface contained more Fe₆W₆C at 20 μm and 30 μm but had more bulk Fe₃W₃C at 40 μm and 50 μm. The upper part of the joint showed brittle fractures on the WC-Co side, while most of the lower part fractured at the interface. Only the joints at 20 μm and 30 μm had a small fracture area on the steel side. Moreover, the fracture on the steel side at 30 μm showed elongated shear dimples, which explains the maximum shear force of the joint at 30 μm.     

Microstructure and shear strength of ZrB2SiC/Ti6Al4V joint by TiCuZrNi with Cu foam

In this paper, brazing behaviors between ZrB₂SiC and Ti6Al4V 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 sintering on the microstructure and mechanical properties of alloy titanium-wollastonite composite fabricated by powder injection moulding process

Composite biomaterials are in high demand in the medical field of today. The combination of bioactive wollastonite (WA) glass ceramic with the biocompatibility of alloy titanium (Ti6Al4V) could be a good candidate for implant applications. The rheological properties of Ti6Al4V/WA feedstock show a pseudoplastic behaviour with low activation energy. The feedstock was successfully injected as a green part with no defects. The green part was solvent debound for 6?h in heptane and thermal debound in an argon environment for 1?h. The brown part was successfully sintered at 1300?°C for 3?h with 5?°C/min heating and cooling rates. The average sintered density was 4.12?g/cm³; which is 97.5% from the theoretical density. The highest Young's modulus obtained was 18.10?GPa; which is in the range of human bone strength. EDX analysis shows that by increasing sintering temperature, the level of oxygen decreased. Cell viability test shown an absorbance increased with days increasing indicated that the cellular were proliferated on the composite Ti6Al4V/WA composite which also proved that the composite was non-toxic. This indicates that the Ti6Al4V/WA composite is suitable for bone implant applications.     

Reactive sintering process and thermoelectric properties of boron rich boron carbides

Dense boron rich boron carbides were reactive sintered by hot pressing at 2050 °C using elementary boroncarbon compositions with carbon contents of 9.1, 11.1, 13.3 and 18.8 at.%. The following material characteristics are presented: relative density, SEM images, EDX, X-ray diffraction and corresponding lattice parameters, Seebeck coefficient, electrical conductivity and thermoelectric power factor. Significant grain growth has been obtained with increasing boron content. A deeper understanding of the boron and carbon reaction and the overall sintering process is gained by thermal and chemical analysis in combination with X-ray diffraction. Additionally a thermal experiment with boron and carbon layers illustrates the solid state diffusion behaviour. The found results of boron carbide properties of this paper correspond with results by other authors. The aim is to correlate technological aspects of sintering procedure with material properties. This should help to improve the thermoelectric efficiency of boron carbide based materials.