174 research outputs found

    MICRO FEATURE ENHANCED SINTER BONDING OF METAL INJECTION MOLDED (MIM) PARTS TO A SOLID SUBSTRATE

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    In metal injection molding (MIM), fine metal powders are mixed with a binder and injected into molds, similar to plastic injection molding. After molding, the binder is removed from the part, and the compact is sintered to almost full density. The obstacle to sinter bonding a MIM part to a conventional (solid) substrate lies in the sinter shrinkage of the MIM part, which can be up to 20%, meaning that the MIM part shrinks during sintering, while the conventional substrate maintains its dimensions. This behavior would typically inhibit bonding and/or cause cracking and deformation of the MIM part. It is also the reason, why sinter bonding MIM to solid substrates is not an industrially applied process and little to no prior research exists. By applying a structure of micro features to the surface of the MIM part, this allows for shrinkage while bonding to the substrate. The micro features tolerate certain plastic deformation to permit the shrinkage and thermal expansion/contraction without causing cracks after the initial bonds are established. The bonding and deformation behavior of the powder compacts is analyzed and modeled. A new approach to simulate the deformation is developed. Finally, the samples are evaluated and compared with other joining processes

    Applications of powder interlayers for large gap joining

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    Thesis (Ph.D.)--Massachusetts Institute of Technology, Dept. of Materials Science and Engineering, 1997.Includes bibliographical references.Large gap joints are frequently encountered in the manufacturing of massive components as well as in the repairing of damaged parts. Several methods using powder interlayers to produce large clearance transient liquid phase (TLP) joints have been developed and investigated in this work. One of the methods was using a mixture of powders of the melting point depressant (MPD) and the base material, from which a great amount of MPD (>30 vol.%) usually has to be used to eliminate residual porosity. To reduce the MPD in the joint, the liquid infiltrated powder interlayer bonding (LIPB) process was developed. For a material system that has a large mutual solubility between the liquid and the solid at the bonding temperature, a protective coating on the particles of the base material was applied to avoid excessive dissolution and inhibit early diffusional solidification, which can block the infiltration paths and prevent full infiltration. Direct coating of the MPD on the particles of the base material proved highly effective in producing tough and strong joints for certain material systems. The classic liquid phase sintering (LPS) theory was adopted to explain the physical process as occurring in the powder interlayer during joining. Despite the general applicability of the theory, there are several other important factors have to be considered as well. For example, the reaction rate between the MPD and the base material can markedly affect the densification of a mixed powder interlayer. Fast growth of the intermetallic compounds as a result of reaction can significantly retard the liquid flow. For the infiltration process, kinetics of dissolution and diffusional solidification largely depend on the mutual solubility between the liquid (infiltrant) and the solid (powder interlayer). Dissolution is needed to open up closed pores in the powder interlayer. However, excessive dissolution is undesirable due to fast liquid saturation and subsequent diffusional solidification, which may prevent complete infiltration of the interlayer. A protective coating on the particles of the base material provides a way of reducing the dissolution rate, which facilitates full infiltration of the interlayer. The solubility factor is also crucial for direct coating of the MPD on the particles of the base material. Higher solubility of the base material in the MPD is preferred to maintain enough liquid for complete densification. Experiments were performed on joining the materials including titanium alloy, Ti- 6A1-4V, nickel base superalloy, Inconel 625, stainless steel, SS304, and commercially pure copper. Application of the particular joining process depends on careful choice of the MPD, the base powders as well as the geometry of the interlayers.by Wei-Dong Zhuang.Ph.D

    Shock wave induced freeform technique (SWIFT) for manufacturing of diamond micro-tools

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    Diamond exhibits many attractive properties including extreme hardness, high thermal conductivity, high Young’s modulus, low coefficient of friction, low wear rate, biocompatibility and chemical inertness the Institutional Repository. Therefore, diamond tools have attracted number of applications in manufacturing of various microdevices and ductile machining of brittle materials. However, just because of these special features, manufacturing of diamond tools is very complex, time consuming and high cost. Laser shock wave induced freeform technique (SWIFT) can be considered as an innovative technique for manufacturing of diamond microtools that employing laser induced shock waves to mechanically sinter nanodiamond powders. Laser shocks can impart desirable dislocation structures and compressive residual stresses into material to improve the relative density and generate residual stress to enhance the fatigue strength. In this work, multiscale models based on laser-material interaction, high pressure sintering of nanodiamond powders and interface effects are utilized to explore the physics underlying this technique. Finite element simulation is applied to analyze the mechanical deformations induced by laser shock wave sintering. Scanning electron microscopy, optical profilometery, raman spectroscopy and micro-indentation are employed to characterize the microstructure evolution, phase transition, and hardness improvement. Tool wear test is carried out to investigate the product final performance

    Sintering and joining of low temperature co-fired tungsten and aluminum oxide

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    Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Materials Science and Engineering, 2006.Includes bibliographical references (p. 181-189).Conventional methods used to fabricate co-fired tungsten/alumina composites usually rely on high temperature processing (>1500C). As it would be beneficial or even necessary for some applications to produce such composites at relatively low firing temperatures, low-temperature processing techniques and the attendant knowledge of processing-property relationships need to be developed. In this thesis, a set of experiments and simulations are performed to obtain a better understanding of sintering and joining of the tungsten/alumina system processed at temperatures near or below 12000C. The technique of activated sintering for tungsten is investigated, whereby a minimal content of additives enables low firing temperatures through a change in the sintering mechanism for tungsten. Tungsten compacts produced by this method are found to sinter only to the "initial stage" and are characterized by high residual porosity level. Hardness and fracture toughness of such partially-sintered materials are examined experimentally and analytically, and dependence of mechanical properties on the relative particle neck size is observed. Various studies are carried out to examine both fundamental and practical aspects of joining co-fired tungsten/alumina.(cont.) First, contributions to adhesion of co-sintered bilayers are studied where the properties of the tungsten layer are controlled using the process of activated sintering. Using a bending delamination test, improvements in sintered density of tungsten are found to increase the adhesive strength of the system only up to a point, beyond which shrinkage mismatch compromises the intrinsic toughness of the interface. A study of low-temperature co-fired tungsten/alumina is then focused on composite shells for an investment casting application. The influences of various processing parameters in a slurry-based route on the sintering and adhesion properties of tungsten/alumina are investigated. Binder content, stucco sand application, and powder characteristics are among the parameters found to critically control the quality of tungsten/alumina shells produced. Finally, the feasibility of several joining strategies, which involve the use of chemical additives, is examined on co-fired tungsten/alumina compacts processed at low temperatures. Some bonding techniques are verified to help improve the bonding of the co-sintered composites.by Yuttanant Boonyongmaneerat.Ph.D

    Nonterrestrial utilization of materials: Automated space manufacturing facility

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    Four areas related to the nonterrestrial use of materials are included: (1) material resources needed for feedstock in an orbital manufacturing facility, (2) required initial components of a nonterrestrial manufacturing facility, (3) growth and productive capability of such a facility, and (4) automation and robotics requirements of the facility

    Resistance bonding of dissimilar alloys using a powder interlayer: A feasibility study.

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    An experimental framework has been developed that allows investigation of a novel resistance bonding technique incorporating a metal powder interlayer as a means of forming sound joints between dissimilar alloys. Bonds have been produced between Ti- 6AI-4V, Inconel 718 and super CMV steel. Ti-6-4, BurTi and Inconel 718 powder interlayer layers have been trialed. The use of diffusion barrier coatings and transition layers have been explored with particular interest focussed on the effect of tantalum. These trials were then compared to analysis of corresponding bond chemistries produced by a conventional hot isostatic pressing technique. It was found that joints between Ti-6AI-4V and Inconel 718 and super CMV were prone to the formation of intermetallic films at the interface (NiTi, Ti2Ni, Fe2Ti), resulting in poor bond quality. Whilst the use of diffusion barrier layers reduced reaction zone size, tantalum layers in particular were found to severely degrade joint integrity. Bonds produced between Inconel 718 and super CMV performed more encouragingly; achieving around 70% of Inconel 718 parent metal properties in the optimum condition. Comparisons between conventional HIP procedures and resistance bonding elucidated far better powder consolidation in the former. This was shown to be due to a 'differential heating' effect under resistance heating. A quasi isostatic powder interlayer bonding technique (QUIP) has been developed that has shown to substantially improve joint integrity. This is under continuing development

    Advanced Sintering of Nano-Ceramic Materials

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    Thermal degradation of diamond compacts: a TEM investigation

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    Diamond compacts consist of fine diamond grains bonded together by using high pressure and high temperature. In this study transmission electron microscopy (TEM)was used to study thermal degradation of diamond compacts. Three different types of diamond compacts – namely cobalt polycrystalline diamond (PCD), calcium carbonate PCD, and diamond-SiC composites – were investigated with TEM to understand the processes that occur during synthesis. These compacts were then heated in inert atmospheres and the chemical changes studied with TEM. It was found that PCD, using cobalt as a bonding agent, will degrade after exposure to temperatures above 750ºC. The cobalt pools contain tungsten in solid solution. During heat treatment above 700ºC the solid solution tungsten combines with cobalt and dissolved carbon to form η-phase particles at the cobalt/diamond interface. At higher temperatures or insufficient tungsten levels the rate of dissolved carbon, into the cobalt pool, is too high and the excess carbon will form as graphite in the cobalt pool. Increased levels of solid solution tungsten, in the cobalt, is expected to delay the onset of graphitization in the diamond compact, thereby increasing the thermal stability of the diamond compact. Non-metallic PCD using calcium carbonate as a bonding agent was successfully sintered in this study. TEM revealed similar micro-structural features as in cobalt based PCD. No signs of thermal degradation were found after exposure to 1200ºC in vacuum for this PCD. Contaminants introduced during processing prevented a detailed study of the binder in this system. The effect of substitutional metal atoms and plastic deformation of diamond on the thermal stability of diamond-SiC composites were investigated. A piston cylinder press was developed and used to synthesize diamond-SiC composites with different levels of plastically deformed diamond. It was concluded that substitutional metal atoms and plastic deformation of diamond grains play no role in the thermal degradation of diamond compacts at 750ºC. The thermal degradation of cobalt PCD is therefore completely determined by the cobalt/diamond interaction at 750ºC
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