Diffusion bonding of two phase γ-TiAl alloys with duplex microstructure

Abstract

Solid state diffusion bonding of TiAl was carried out with different bonding parameters within the superplastic temperature range. The effect of post-bond heat treatment (PBHT) on the mechanical properties of the bonds was also studied. Defect free sound bonds were achieved within the temperature range 925–1150°C and the pressure range 20–40 MPa. Transverse microtensile specimens extracted from the bonds were tested to evaluate room temperature tensile properties of the bonds and to correlate them with bonding parameters. The bond strength increased with an increase in bonding temperature and pressure. All the specimens of the bond made at 925°C and 40 MPa, and most of the specimens of bonds made at 1000°C and 30 MPa and at 1100°C and 20 MPa, failed in the bond area; all the specimens of bonds made at 1100°C and 30 MPa and at 1150°C and 20 MPa failed in the base metal. Post-bond heat treatment at 1350°C for 1 h led to the transformation of the recrystallised γ grains at the bond inteface formed during bonding to a lamellar microstructure, resulting in an indiscernible bond line in all cases. This resulted in an improvement in the bond strength in most of cases. Moreover, the recrystallised γ grains were also formed away from the bond area in the bonds made at 1100°C and 30 MPa and at 1150°C and 20 MPa. After PBHT, these bonds exhibited slightly lower tensile strength values owing to the change in the base metal microstructure away from the bond area.     

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.     

Microstructure and Mechanical Properties of AlN/Cu Brazed Joints

In this study, the AlN/Cu bonding was explored using the brazing technique. During AlN/Cu brazing, the temperature was set at 800, 850, and 900 °C for 10, 20, 30, and 60 min, respectively. We studied the bonding mechanism, microstructure formation, and the mechanical characteristics of the bond. The reaction layer developed at the interface of AlN/Cu is observed to be TiN. The activation energy of TiN is about 149.91 kJ/mol. The reaction layer thickness is linearly dependent on the temperature and duration at 800 and 850 °C for 60 min and 900 °C for 30 min. However, the growth of the reactive layers decreases gradually at 900 °C when the duration changed from 30 to 60 min. The strength of the specimens with thickness ranging between 1 and 1.5 μm is 40-51 MPa.     

Thermal Stability Study of Ultrafine Grained 304L Stainless Steel Produced by Martensitic Process

An ultrafine grain 304L stainless steel with average grain size of about 650 nm was produced by martensitic process. 10 mm as-received sheets were 80% cold rolled in the temperature of ?15 °C and then annealed at 700 °C for 300 min to obtain ultrafine grained microstructure. The results showed that the ultrafine grained 304L steel has yield strength of 720 MPa, tensile strength of about 920 MPa, and total elongation of 47% which is about twice that of coarse grain structure. The effect of annealing temperature (750-900 °C) on the grain growth kinetics was modeled by isothermal kinetics equation which resulted in the grain growth exponent (n) and activation energy for grain growth of 4.8 and 455 KJ/mol, respectively. This activation energy was also compared with those for other austenitic steels to better understanding of the nature of grain growth and atoms mobility during annealing. It was found that activation energy for grain growth is about twice higher than self-diffusion activation energy of austenite that is related to the Zener pinning effects of the second phase particles.     

TLP bonding of Ti−6Al−4V to Al 2024 using thermal spray Babbitt alloy interlayer

Thermal spray assisted transient liquid phase (TLP) bonding of Ti−6Al−4V to Al2024 alloys was investigated, where the interlayer was 80 µm Babbitt thermal spray coat on Al substrate. Thermal spray creates a rough and clean surface which leads to establishing a joint with higher strength. The optimized parameters were bonding temperature of 580 °C and bonding time of 30 and 60 min. Microstructural observation together with XRD patterns confirmed the existence of Al₂Cu, Al₂CuMg, Cu₃Ti, TiAl₃, TiAl and Mg₂Sn intermetallic compounds formed in Al weld side. On the other hand, Ti₃Al, Sn₃Ti₅ and Ti₃Sn intermetallic compounds formed in Ti side. With increasing bonding time from 30 to 60 min, although the interlayer was not completely consumed, the thickness of remained Babbitt interlayer decreased to approximately 15 µm. The study showed that shear strength of the joint reaches the high value of 57 MPa obtained at larger bonding time of 60 min.     

Transient liquid phase bonding of 304 stainless steel using a Co-based interlayer

Transient liquid phase bonding of AISI 304 austenitic stainless steel was carried out using a Co-based interlayer with 40?μm thickness. The effect of bonding time and solid-state homogenisation time on the microstructure and mechanical properties of samples was investigated. The results showed that isothermal solidification was completed within 30?min at a constant temperature of 1180°C. With increasing homogenisation time, at 1000°C, a more uniform distribution of alloying elements and hardness profile across the joint region was achieved. The average shear strength of homogenised samples was about 72% that of the base metal at the same heat treatment cycle.     

Static tensile strength characteristics of fillet welding lap joints assisted with bonding

A series of tensile tests were carried out on fillet welded lap joints assisted with bonding for investigating the static tensile strength characteristics of the joints from the viewpoints of stress reduction effect around the welded part due to bonding. It was confirmed that the mechanical properties of epoxy resin bonding used in this study were not deteriorated by heating to less than 150°C. When the fillet welded lap joints with bonding were assembled, the bond layer 20 mm from the weld toe was subjected to heating to over 150°C. In other words, the mechanical properties in that region deteriorated. The strengths of the elastic limits of specimens with welding and bonding were higher than those of specimens with only welding by from 60 to 100 MPa. The ultimate tensile strengths of them were almost the same because they were broken at the base plate. The strains around the weld toe and the root of specimens with welding and bonding were smaller than those of specimens with welding by around 13% in the elastic region. The strengths of specimens with only bonding were 170 MPa, which could be explained by a theory of elastic stress distribution. Even if the bond layer 20 mm from weld toe of the specimens with welding and bonding was thermally damaged, the possibility was confirmed that the residual bond layer had around 100 MPa in strength. It could be concluded that the strength of the residual bonding assisted to decrease the stress around the welded part of the specimens with welding and bonding.     

Effect of bonding temperature and heat treatment on microstructure and mechanical property of Mg−6Gd−3Y alloy vacuum diffusion bonded joints

Diffusion bonding of as-cast Mg?6Gd?3Y magnesium alloy was carried out at temperatures of 400?480 °C with bonding pressure of 6 MPa for 90 min. Diffusion bonded joints were solution treated at 495 °C for 14 h and then aged at 200 °C for 30 h. Microstructures and mechanical properties of joints were analyzed. The results showed that rare earth elements and their compounds gathering at bonding interface hindered the grain boundary migration crossing bonding interface. Tensile strength of as-bonded and as-solution treated joints increased firstly and then decreased with the bonding temperature increasing due to the combined effects of grain coarsening and solid-solution strengthening. As-bonded and solution-treated joints fractured at matrix except the joint bonded at 400 °C, while aged joints fractured at bonding interface. The highest ultimate tensile strength of 279 MPa with elongation of 2.8% was found in joint bonded at 440 °C with solution treatment followed by aging treatment.     

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.     

Effect of Gas Pressure on Polarization of SOFC Cathode Prepared by Plasma Spray

A cermet-supported tubular SOFC was fabricated using thermal spray. The cell performance was investigated at temperatures from 750 to 900 °C and pressures from 0.1 to 0.5 MPa to examine the effect of operating gas pressure on the cell performance. The influence of gas pressure on the cathodic polarization was studied through the electrochemical impedance approach to examine the controlling electrochemical processes during cell operation. Results show that increasing the operating gas pressure improves the power output performance significantly. When the gas pressure is increased from 0.1 to 0.3 MPa, the maximum power density is increased by a factor of 32% at a temperature of 800 °C. The cathode polarization decreases significantly with the increase of the gas pressure. The electrochemical analysis shows that the main control processes of the cathode reaction are the oxygen species transfer at the three-phase boundary and oxygen diffusion on the surface or in the bulk of the cathode, which are enhanced with increasing gas pressure.     

用200nm铜颗粒在空气中快速压力辅助烧结及连续无压退火提高结合强度

为了设计一种有效且适用于功率器件的烧结结合工艺,提出一种两步工艺,使用约200 nm的铜颗粒基浆料形成具有高温可持续性和优越导热性的粘结层.该工艺涉及在空气中快速压力辅助烧结和在氮气气氛中连续无压退火.当使用20％(质量分数)的羟基丁二酸和80％(质量分数)的乙二醇混合物浆料时,在300℃、5 MPa烧结30 s后的剪...     

Transient liquid phase diffusion bonding of copper alloy to stainless steel using CuMn alloys as interlayer

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Improved mechanical properties of ZrB2-30 vol% SiC using zirconium carbide additive

Influence the different amount of ZrC as well as fabrication parameters on the mechanical properties such as flexural strength and densification behavior of spark plasma sintered ZrB₂-30 vol% SiC composites were investigated. The composites contained 4, 8 and 12 vol% ZrC were consolidated at 1650, 1725 and 1800 °C for 4, 9 and 14 min under 20, 30 and 40 MPa pressures. Relative density and the ratio of open porosities were measured and used to appraise the densification behavior. Three-point bending instrument applied for flexural strength measurement. Microstructural investigations were carried out using scanning electron microscopy. The results showed that the ZrC till to 4 vol%, have positive effect on grain growth and acts as grain growth inhibitor while more addition caused to grain growth happening. Also, ZrC ascent from 4 up to 12 vol%, accompanied by shrinkage temperature rising (from 1263 °C to 1389 °C and 1392 °C). Relative density reduction occurred from 94.4% to 92.2% by increasing ZrC amount from 4 up to 12 vol%. Flexural strength reached to its maximum value, 460 MPa, in the presence of 8 vol% ZrC for composite which was consolidated at temperature of 1800 °C, time of 9 min under 30 MPa pressure.     

Diffusion bonding of γ-TiAl sheets

Using advanced γ-TiAl based alloys and various ingot and powder metallurgical routes, several aerospace engine components are now being developed. Further application of this material in the aerospace industry can only be implemented provided that successful joining and cost effective fabrication methods for this material are developed. In this context, diffusion bonding and superplastic forming of this material is considered to be of particular interest. The possibility of producing sound bonds in γ-TiAl sheets by industrially available diffusion bonding equipment designed for conventional Ti-alloys was investigated. Defect-free bonds were achieved at 1000°C with pressure levels of 5, 10 and 20 MPa, the holding time varying between 5 and 8 h. The bond qualities were assessed by shear testing at room temperature. Reasonable shear strength levels were obtained by bonding at 1000°C. The bonds were also post bond heat treated at 1430°C for 30 min, which improved the bond quality in all cases.     

Effects of sintering pressure and temperature on microstructure and tribological characteristic of Cu-based aircraft brake material

A novel Cu-based P/M aircraft brake material was prepared and the effects of sintering pressure and temperature on microstructure and tribological characteristic were investigated. For the constant sintering temperature, when the sintering pressure increases from 0.5 MPa to 1.5 MPa, the porosity, wear loss and friction coefficient decrease remarkably. When the sintering pressure increases from 1.5 MPa to 2.5 MPa, the porosity further decreases but in a little degree and wear behaviors are improved slightly. However, once the sintering pressure is larger than 2.5 MPa, it has no obvious effect on microstructure and tribological characteristic. For the constant sintering pressure, when the sintering temperature increases from 900 ℃ to 930 ℃, the sintered density remarkably-increases, and wear behaviors are obviously improved. For further increasing sintering temperature to l 000 ℃, the density keeps on increasing, but wear behaviors change slightly.     

Microstructural and mechanical properties assessment of transient liquid phase bonding of CoCuFeMnNi high entropy alloy

The transient liquid phase (TLP) bonding of CoCuFeMnNi high entropy alloy (HEA) was studied. The TLP bonding was performed using AWS BNi-2 interlayer at 1050 °C with the TLP bonding time of 20, 60, 180 and 240 min. The effect of bonding time on the joint microstructure was characterized by SEM and EDS. Microstructural results confirmed that complete isothermal solidification occurred approximately at 240 min of bonding time. For samples bonded at 20, 60 and 180 min, athermal solidification zone was formed in the bonding area which included Cr-rich boride and Mn₃Si intermetallic compound. For all samples, the γ solid solution was formed in the isothermal solidification zone of the bonding zone. To evaluate the effect of TLP bonding time on mechanical properties of joints, the shear strength and micro-hardness of joints were measured. The results indicated a decrement of micro-hardness in the bonding zone and an increment of micro-hardness in the adjacent zone of joints. The minimum and maximum values of shear strength were 100 and 180 MPa for joints with the bonding time of 20 and 240 min, respectively.     

GH4141镍基合金的扩散连接工艺

对GH4141高温镍基合金的扩散连接进行了工艺研究，确定了扩散连接工艺参数对室温抗剪强度的影响，确定了获得优质接头的最佳工艺参数区间，即扩散连接温度r=990～1080℃，连接时间t=15～60min，连接比压力P=5～20MPa，选用Ni箔作为中间层，厚度为25um。通过SEM、EPMA和金相技术对接头微观组织进行了观察和分析。     

Study on Ag/Sn multilayer thin film bonding for 3D stacked semiconductor

Through-silicon via (TSV) technology for 3D stacking is attracting much attention as a means of alleviating the miniaturization limits on advanced semiconductor devices. Despite a great deal of research, low load (<1 MPa), low temperature (<473 K) and short time (<300 s) solid phase bonding with high heat resistance (>623 K) to prevent the damage of weak low-k dielectric material, etc. has not been realized. In this work, we examine a new Ag–Sn thin film bonding system to replace Cu–Cu direct bonding. It is found that Ag/Sn/nano Ag-nano Ag/Sn/Ag thin film bonding systems (especially when the film thickness of the surface Ag is controlled to around 10 nm) is a promising approach because (1) it enables low load (<0.4 MPa), low temperature (<453 K) and short time (<300 s) bonding, and (2) the bonded interface has a high heat resistance (>673 K) and joint strength (>29 MPa). It is found that it may be possible to realize an optimal solid-phase bonding system for wafer-level 3D-stacking for 3D-IC which can satisfy a hierarchical temperature-based bonding method that includes TSV formation.     

Influences of diffusion bonding process parameters on bond characteristics of Mg-Cu dissimilar joints

In many circumstances,dissimilar metals have to be bonded together and the resulting joint interfaces must typically sustain mechanical and/or electrical forces without failure,which is not possible by fusion welding processes.The melting points of magnesium(Mg)and copper(Cu)have a significant difference(nearly 400℃)and this may lead to a large difference in the microstructure and joint performance of Mg-Cu joints.However,diffusion bonding can be used to join these alloys without much difficulty.This work analyses the effect of parameters on diffusion layer thickness,hardness and strength of magnesium-copper dissimilar joints.The experiments were conducted using three-factor,five-level,central composite rotatable design matrix.Empirical relationships were developed to predict diffusion layer thickness,hardness and strength using response surface methodology.It is found that bonding temperature has predominant effect on bond characteristics.Joints fabricated at a bonding temperature of 450℃, bonding pressure of 12 MPa and bonding time of 30 min exhibited maximum shear strength and bonding strength of 66 and 81 MPa, respectively.     

扩散连接温度对304不锈钢接头性能与组织的影响

以304不锈钢为研究对象,探究了扩散连接温度(925～1000℃)对接头厚度变形量及力学性能的影响,并分析了其对界面组织的影响作用.扩散连接接头剪切强度随扩散温度升高呈现抛物线式变化.在950℃,30 MPa和60 min条件下扩散连接,接头抗剪切强度为580 MPa,达到母材剪切强度的98.47％,厚度变形量为1.2...