Papers by Keyword: Diffusion Bonding

Abstract: Field-assisted sintering technology also known as spark plasma sintering is starting to be recognised as a potential route for metals processing and near net shaping for a range of sectors. FAST/SPS is an effective way of rapidly consolidating powder and particulate feedstocks, including waste streams such as machining swarf into shaped billets with as-forged properties. FAST/SPS can also be used as an intermediate step prior to conventional closed die forging or hot rolling (FAST-forge and FAST-roll, respectively). The solid-state technique has also been demonstrated to be an effective way to functionally grade and diffusion bond different alloys in the same FAST billet (FAST-DB). In this paper, we summarize some of the developments at The University of Sheffield around FAST/SPS over the last few years, with examples from different particulate types for a range of different sectors.

Abstract: Diffusion bonded joint of Commercially Pure Aluminum (CpAl) with Inconel 718 (IN718) superalloy was investigated for its mechanical and microstructural characteristics. Diffusion Bonding (DB) of CpAl/IN718 was performed at 500 °C for 60 minutes using vacuum tube furnace in the presence Argon (Ar) gas under pressure at a heating rate of 10 °C/minutes followed by furnace cooled. The resultant joint interface was investigated by using Optical and Scanning Electron Microscopy (OM and SEM), Energy Dispersive Spectroscopy (EDS), X-ray Diffraction (XRD), microhardness and shear strength. The microstructural analysis shows the formation of various Intermetallic Compounds (IMCs) at the bonding interface, such as NiAl_3, FeAl₂, FeAl₃, Fe₂Al₅ along with austenitic matrix, which was confirmed by XRD. Additionally, the hardness of the bonding interface was 15% and 255 higher as compared to BM of IN718 and CpAl respectively. Lastly, an average lap shear strength of 61 MPa was achieved with a joint efficiency of 84%.

Abstract: Solid-state diffusion bonding (DB) of Copper-Copper (Cu/Cu) was carried out under varying bonding parameters (time and temperature) in argon shielding gas environment. Initially, the bonding was performed at bonding temperatures of 800, 850, and 900 °C for 60 minutes. Secondly, the bonding was carried out at holding times of 90, 120, and 150 minutes at 900 °C. The microstructural and mechanical properties of the bonding interface were evaluated via lap shear and micro hardness tests, X-ray diffraction, and Optical microscopy. It was found that the optimal bonding parameters for the joint interface was 950 °C for 150 minutes, resulting in maximum shear strength of 133 MPa. The X-ray diffraction also shows the formation of solid solution of Cu without the formation of any intermetallic compounds (IMC). The micro hardness test revealed a maximum hardness of 89 HV at the joint interface. Optical microscopy shows the formation of voids at the joint interface take place due to the Kirkendall effect, which increased with higher temperatures for longer time, and cause a wide diffusion-affected zone (DAZ).

Abstract: Solid-state diffusion bonding effectively joins dissimilar materials, even with varying metallurgical properties and melting points. In this study, a Cu/Ni joint was produced at a bonding temperature of 950°C for 60 minutes under a vacuum. The microstructural and mechanical properties of the bonding interface were evaluated using scanning electron microscopy (SEM) equipped with energy-dispersive spectroscopy (EDS), microhardness tests, and X-ray diffraction (XRD). It was found that the EDS point scan analysis revealed the formation of a solid solution of Cu-Ni at the bonding interface. Since Cu-Ni exhibit complete solubility with each other, no intermetallic compounds (IMCs) were formed. The microhardness indicated that the bonding interface had a microhardness of 20% and 54% higher than the base metals (BM) of Ni and Cu, respectively.

Abstract: In previous research conducted by the authors, a new vibration-damping steel sheet was developed using a new method employing friction stir forming (FSF) to create a laminated composite sheet in which steel sheets and superplastic alloys are laminated in layers. However, the details of the bonding mechanism have not yet been clarified. The present study investigates the relationship between the pressure during the process and the weld interface in the creation of the mentioned superplastic composite sheet. More specifically, a 0.5mm thick perforated steel plate is inserted between two Zn-22Al superplastic alloys and the FSF is applied to the top layer of Zn-22Al. The probe of the FSF tool passes directly above the perforated steel plate, the material stirred by the probe plastically flows into the hole and is joined to the underlying Zn-22Al interface by superplastic diffusion bonding (SPF/DB). It was revealed that the process parameters (rotational speed and tool feed rate) must be perfectly adequate to produce adequate heat input and pressure leading to a proper plastic flow of the material and the occurrence of superplasticity in Zn-22Al. In this study, as a first step to clarify the detailed joining mechanism, the amount of pressure applied to the specimen during the process is measured. While changing the process parameters, the pressure was measured at three points, under the probe of the friction stir process tool and, on the advancing, and retreating sides, to investigate the relationship between the parameters and the pressure at the joint interface.

Abstract: Ultra-pure copper sputtering target is a key material widely used in large-scale integrated circuits with 90-28 nm feature size. The copper target for 300 mm integrated circuit requires a reliable diffusion bonding between the ultra-pure copper target and the copper alloy backplate. The bonding ratio and bonding strength of diffusion bonding should reach over 99% and 80 MPa respectively. In this paper, the ascendant structure of electron beam welding united diffusion bonding with high quality was designed. The ultra-pure copper target and the C18000 copper alloy backplate were machined to coordinating size, meanwhile the backplate underwent surface treatment of toothed/smooth, ion cleaning, magnetron sputtering coating, then the combination of target and the backplate was proceeded electron beam welding and diffusion bonding. Metallographic microscope, scanning electron microscope (SEM), mechanical tensile machine, C-scan flaw detector were used to analyze the bonding properties including interface microstructure, bonding strength and bonding ratio. The results show that the bonding ratio of copper target was above 99%, and the bonding strength was up to 80-160 MPa.

Abstract: The FEM (finite element method) simulation was used to study the diffusion bonding deformation of high purity tungsten target. The influence of different welding structure, bonding temperature on the deformation of the final high-purity tungsten target was systematically studied. Meanwhile, some microscopic properties of tungsten target were developed, such as internal stress size and distributions, strain size and distributions. Finally, physical experiments are used to verify numerical simulation results. The results show that the method of adding an intermediate layer can release the residual stress between the high-purity target and back plate. The bonding stress of high-purity tungsten target is mainly concentrated with the tungsten target and the intermediate layer in between, which is easy to fail during the later leveling process. Small deformation of bonding tungsten target can be obtained by low diffusion bonding temperature.

Abstract: The main point of successful manufacture of metallic composites by direct bonding of dissimilar materials is achieving a homogeneous interface bonding. Two different types of deformation techniques for fabrication of metal composites were investigated. The first one was developed on the basis of high pressure torsion associated with a high energy impact on the material where part of energy involved can be dissipated via non equilibrium phase transition realization. This deformation due to high shear deformations allows not only to form a nanostructure, but also to bond dissimilar metals. Moreover, this method allows for a relatively short time and in a number of compounds to receive in one step at room temperature monolithic composites of sufficient size to certify the structure and properties. The second technique is diffusion bonding which integrate one material with the other by pressure under high temperature. In order to clarify the bonding mechanism by plastic deformation of dissimilar materials, the microstructural and some mechanical properties were studied in the processed samples.

Abstract: During the last decade, silicon carbide (SiC) and its heterostructures with other semiconductors have gained a significant importance for wide range of electronics applications. These structures are highly suitable for high frequency and high power applications in extremely high temperature environments. SiC exists in more than 200 different polycrystalline forms, called polytypes. Among these 200 types, the most prominent polytypes with exceptional physical and electrical attributes are 3C-SiC, 4H-SiC and 6H-SiC. Heterostructures of these SiC polytypes with other conventional semiconductors (like Si, Ge) can give rise to interesting electronic characteristics. In this article, Germanium (Ge) has been used to make heterostructures with 3C-SiC and 4H-SiC using a novel technique called diffusion welding. Microscale and nanoscale simulations of nn-heterojunction of Ge/3C-SiC and Ge/4H-SiC have been done. Microscale devices have been simulated with a commercially available semiconductor device simulator tool called Silvaco TCAD. Whereas nanoscale devices have been simulated with QuantumWise Atomistix Toolkit (ATK) software package. Current-voltage (IV) curves of all simulated devices have been calculated and compared. In nanoscale device, the effects of defects on IV-characteristics due to non-ideal bonding (lattice misplacement) at heterojunction interface have been analyzed. Our simulation results reveal that the proposed heterostructure devices with diffusion welding of wafers are theoretically possible. These simulations are the preparations of our near future physical experiments targeted to fabricate SiC based heterostructure devices using diffusion bonding technique.

Abstract: The manuscript considers microstructure, mechanical and processing properties (formability and solid state weldability) of sheet titanium alloy VT6(Ti-6Al-4V) with improved superplastic properties production of JSC «VSMPO-AVISMA Corporation" for the process of superplastic forming at low temperatures and new experimental cheaper sheet titanium alloy VST2k. Complex studies of microstructure, mechanical properties, formability and weldability in the solid state of these titanium alloys were carried out. Studies have shown that both alloys in the temperature range 750-850oC have good weldability in the solid state and exhibit good superplastic properties. Technological properties of the alloy VST2k almost as good as the properties of the alloy VT6. This makes it possible to recommend the sheet alloy VST2k along with the alloy VT6 for the manufacture of hollow structures by SPF/DB in low-temperature superplasticity.