Vacuum Fusion Research Articles

Study on the effect of vacuum fusion infiltration technology on the properties of tungsten/copper joining interface

In this paper, based on the need for high-strength connections between all-tungsten-oriented plasma materials and thermal sinking materials of copper and its alloys in nuclear fusion devices, a study on the effect of tungsten surface laser micro structuring on the interfacial bonding properties of W/Cu joints was carried out. In the experiment, the connectors were prepared by vacuum fusion infiltration technology, and the effects of microgroove structure on the mechanical and thermal conductivity of W/Cu connectors were investigated under different parameters (including microgroove pitch, microgroove depth, and microgroove taper). The maximum shear strength is 126.0 MPa when the pitch is 0.15 mm and the depth is 34 μm. In addition, the negative taper structure, i.e., the width of the entrance of the microstructure is smaller than the width of the interior of the microstructure, is also investigated. The shear tests show that there is an approximately linear relationship between the shear strength of W/Cu and taper. Compared with the positive taper, the shear strength of the samples with the same morphological density and depth of the tungsten surface is significantly higher.

The Influence of CEO2 Content on the Microstructure and Hardness of Ni-WC Coating Formed by Vacuum Fusion Sintering

Made Ni-WC-CEO2 composite coatings of different CEO2 content on 45 steel matrixes by vacuum fusion sintering. The coatings microstructure and the morphology of WC were observed by SEM, the elements diffusion between WC and Ni-base alloy by EDS；The Rockwell hardness of coatings’ surface and micro-hardness of coatings’ longitudinal section were measured by Rockwell hardometer and microhardness instrument. The results showed that: The defects in the coatings become less, WC in the coating is further refined, and its distribution changes uniform with adding content CEO2. When the content of CEO2 is 0.5%, the surface’s hardness and section’s microhardness are the highest, In this paper, the optimum content is 0.5%.

Effect of ZrB2 Addition on Sintering Temperature and Densification of Vacuum-Fused NiCr/WC Cermet Coating

NiCr/WC cermet coatings were fabricated by vacuum fusion sintering on the surface of nickel-base alloy at 1220 °C. The sintering temperature, densification mechanism and oxidation resistances of the cermet coating with ZrB2 additive were investigated using thermogravimetric and differential thermal analysis method, theoretical calculation of phase diagram with the FactSage software, X-ray diffraction, and scanning electron microscopy. The sintering temperature of NiCr/WC cermet coating with ZrB2 additive decreased 123 °C and obtained the dense cermet coatings. The densification mechanism of NiCr/WC cermet coating added ZrB2 is mainly attributed to the reaction occurred between Ni and ZrB2 and the ample liquid phases formed at 1220 °C. The surface of the WC particles is coated by CrxCy and surrounded by NiCr alloy result in the better oxidation resistance of the cermet coating added with ZrB2.

Simultaneous vacuum evaporation for CZT thin film fabrication

ABSTRACTTernary semiconductor Cd1-xZnxTe is a solid-state material for high energy radiation detection. This has wide and tunable bandgap (1.45–2.25 eV). It has high resistivity and low noise generation. This can be used for room temperature radiation detection. It has improved charge collection efficiency and very good radiation absorption power for high energy radiations. High energy imaging for diagnostic and surveillance science demands for large area detectors. Large area imaging can only be addressed in thin film form. Thin films of ternary semiconductor can be deposited by various methods like PVD, CVD, MOCVD, Liquid Phase Epitaxy (LPE), Closed Space Sublimation (CSS), Magnetron Sputtering, etc. In this paper, fabrication of thin film of Cd1-xZnxTe by simultaneous vacuum evaporation and fusion of CdTe and ZnTe powders from the same vacuum evaporation unit is presented. Fabricated film is then subjected to structural and optical characterisation studies. CZT thin films have immense applications in imaging areas and such thin films using PVD coating is fabricated in this work with simultaneous fusion of two constituent compounds.

Effects of CTCP Modification on Microstructure and Wear Behavior of CTCP-NiCrBSi/Heat Resistant Steel Composite Layer.

A CTCP-NiCrBSi/heat resistant steel composite layer was designed and fabricated by vacuum fusion sintering. The structure of the composite layer was similar to reinforced concrete. Numerous reinforced regions with a cylindrical shape were evenly distributed in the heat resistant steel. Modified cast tungsten carbide particles (CTCP) reinforced NiCrBSi matrix composite constituted the reinforced region (CTCP-NiCrBSi). The microstructure of the composite layers was investigated by scanning electron microscope (SEM), energy dispersive x-ray spectrometer (EDS), and image analysis. The wear behavior of the composite layer was estimated on the ring-on-disc rig at a temperature range of room temperature (RT) to 800 °C in air. The microstructure and wear behavior of the composite layer with modified CTCP were compared with those with primary CTCP. The results showed that the poor chemical resistance of W2C and the interdiffusion of elements were responsible for the dissolution of unmodified CTCP in the molten NiCrBSi alloy. A WC outer shell formed on the surface of the CTCP after surface carburizing modification. The WC outer shell could effectively resist the dissolution of CTCP in NiCrBSi during the sintering process. The content of WC/W2C in modified CTCP-NiCrBSi increased by about 12.0 vol. % when compared with that in the primary CTCP-NiCrBSi. The wear rate of the composite layer with modified CTCP was lower than that with primary CTCP between RT and 700 °C. The wear rates of the composite layer decreased with increasing temperature from RT to 700 °C and increased above 700 °C.

Surface Metallization of SiC Ceramic by Mo-Ni-Si Coatings for Improving Its Wettability by Molten Ag

Abstract Three kinds of Mo-Ni-Si metallized coatings with various chemical compositions were deposited on SiC ceramic substrates by vacuum fusion sintering process, and the phase compositions of the coatings and their interface microstructures were analyzed. The wetting and spreading properties of molten Ag on the coated SiC ceramic substrates were investigated by the sessile drop technique, and the interfacial behavior of the Ag/coated SiC systems was analyzed. The results show that the coatings are mainly composed of Mo5Si3, MoSi2, Ni2Si, NiSi2 and MoNiSi. The tetragonal MoSi2 grains on the coating surface disappear gradually with the concentration of Mo increasing from 20 at% to 40 at%. The final contact angles of Ag/coated SiC systems at 1000 °C for holding 30 min are 45°, 79° and 85° for the coating compositions of Mo20-Ni32-Si48, Mo30-Ni28-Si42 and Mo40-Ni24-Si36, respectively. This result could be closely related to the interactions between the Ag drop and the microstructures of the three Mo-Ni-Si coatings. No obvious reaction layers are found at all the coating/substrate interfaces before and after the wetting tests.

The Effect of Different CeO<sub>2</sub> Addition on Performance of Ni-WC Composite Coating by Vacuum Fusion Sintering

By vacuum fusion sintering technique made different CeO2 addition Ni-WC composite coatings on 45 steel. Hardness, wear resistance property and corrosion resistance property of the Rare-earth Ni-WC composite coatings were measured and analyzed by Rockwell hardness tester,micro-hardness tester, friction wear testing machine and Salt spray corrosion box. The results showed that:The CeO2 content comes up to 0.75% of the coatings` hardness, wear resistance and corrosion resistance property better than those of other coatings.

Compression Behavior of Entrapped Gas in High Pressure Diecasting

Die castings generally contain a large quantity of porosities due to the entrapment of air or gas in molten metal during mold filling. Although the entrapped air or gas is compressed by high casting pressure during pressurization, it will eventually remain in the castings as defects after solidification. Therefore, it is important to clarify the relation between the volume of gas defects and the pressure applied to the molten metal so as to optimize the casting design.In this study, we investigated the compression behavior of entrapped gas during casting. We determined the volume of gas defects and gas content in die castings by density measurement and vacuum fusion extraction method respectively. Then we calculated the gas pressure in the defects from the above volume of defects and gas content, and compared with the die casting pressure. The calculated gas pressure in the defects was found to be not equal to the die casting pressure, but equal to the pressure of the molten metal just before it dropped abruptly due to the complete blocking of the liquid metal channel by solidification. From the experimental results, the behavior of the entrapped gas can be inferred as follows. Immediately after the mold was filled with molten metal, the entrapped gas was instantly compressed. After that, the pressure of molten metal decreased gradually with the progress of solidification of the molten metal channel, and the volume of entrapped gas increased correspondingly until the pressure of the molten metal dropped abruptly. Then the volume of the entrapped gas showed a slight expansion equal to the solidification shrinkage of the enclosed molten metal.The above inference was verified by measuring the volume of the entrapped gas defects in castings made with intentional depressurization carried out at the time when mold filling just finished or halfway through the solidification of the molten metal channel.

Gas content in high pressure die castings

This paper presents the results of a quantitative study of the gas level in various types of castings from the high pressure die casting (HPDC) process using a vacuum fusion method. It was found that the major part of the gas was from the air entrapment during cavity filling. Other sources such as air entrapment during ladling, residual die lubricant and quenching water were also noticeable. Measurements of a large casting and castings from a multi-cavity die showed that the gas content was unevenly distributed. The modified vacuum fusion method has been proved to be a valuable tool for evaluating and quantifying the level of gas in castings as well as for an assessment of the influence of different process parameters on gas evolution in castings.

Thermal Expansion Coefficient of Ni Base Alloy Composite Coating Containing Spheroidal Ceramic Grains

Ni base alloy composite coating containing spheroidal ceramic grains can be fabricated by a vacuum fusion sintering method. Composite coating was mainly composed of Ni base alloy and spheroidal ceramic grains with random orientation. The three-phase model is used to determine the thermal expansion coefficient of the composite coating. First, Eshebly-Mori-Tanaka method was used to determine thermal disturbance strain in two-phase cell aroused thermal inconsistency. Then, average thermal strain in the two-phase cell aroused by thermal inconsistency is gained by the means of volume equilibration. The two-phase cell is transverse isotropy and has two independent thermal expansion coefficients. Finely, based on mean strain of Ni base alloy ceramic composite coating containing spheroidal ceramic grains, the effective thermal expansion coefficient of the composite coating is obtained by considering random orientation of two-phase cells. Ni base alloy composite coating containing spheroidal ceramic grains is isotropy and has one independent thermal expansion coefficient.

Effects of MgO Addition Level on Microstructure and Wear Resistance of Ni-WC Vacuum Fusion Sintering Coating

Ni-WC-MgO compound coatings were made by way of Vacuum Fusion Sintering (VFS). Effects of MgO addition level on the microstructures of coating surface and longitudinal section, element diffusion in fusion sintering area and wear resistance were analyzed through scanning electron microscope (SEM) and energy dispersive spectrometer (EDS). The results showed as the following: MgO addition made coating and matrix combined closely; there existed obvious transition region. When the addition level of MgO was 0.5%, the coating had the fewest defects and best combination. Ni, Cr, W, C and other elements in the coating diffused to the direction of the base metal while Fe in the base metal diffused to the coating, during which the diffusion of Fe and Ni was most obvious at the junction. Therefore, when the addition level of MgO was 0.5%, the surface microstructure of the coating was the densest and finest, and the wear resistance of the coating was the best.

TiAl–Nb melt interaction with AlN refractory crucibles

The paper considers contamination of cast TiAl-based alloy, related microstructure evolution and chemical contact interaction when using refractory aluminium nitride crucibles/moulds as an alternative to the traditional Al 2O 3-, ZrO 2- and Y 2O 3-based oxide ceramics. A series of melting tests has been performed in resistive SiC electro-furnace with Ti–46Al–8Nb (at%) alloy in 99.99% purity AlN boat crucibles with fixed melt superheating times 5, 12 and 25 min at 1670 °C and consequent quenching with high-purity Ar gas flow. As-cast samples were examined by X-ray diffractometry, SEM, SIMS, EDX, EBSD and vacuum fusion analysis of O, N, C and S interstitials content with respect to the initial material. The key features of TiAl–Nb melt interaction with AlN ceramics are revealed. As a result of slow thermal dissociation AlN → Al + N, and the reaction of nascent nitrogen with the melt, a solid continuous TiN-based reaction layer is formed up to 6.4 μm in thickness, together with an enriched Al liquid film between it and the crucible wall. It causes perfect wetting of crucible with the melt and easy removal of the solidified sample. The partial suitability of AlN crucible is restricted by 12 min of the melt superheating from the point of view of invariable (α 2 + γ)-microstructure and reasonable contamination of the as-cast samples.

Residual Stress Field of Ellipsoidal Ceramic Particles Ni-Base Alloy Composite Coating

Ni base alloy ceramic composite coating fabricated through vacuum fusion sintering process can acquire high strength and good thermal fatigue resistance. Composite coating was mainly composed of Ni base alloy and ellipsoidal ceramic particles with random orientation. The three-phases model is used to study the thermal expansion strains in composite coating. First, Eshebly-Mori-Tanaka method was used to determine effective eigen strain of two-phases model formed by the ellipsoidal matrix shell being around a ellipsoidal ceramic particle, then disturbance strain in two-phases model aroused thermal inconsistency is obtained. Finally thinking average stress in effective matrix vanish, the residual stress field in Ni base alloy and particles can be gotten by considering random orientation of two-phases models. It will exert influence on strength and fatigue life of the composite coating.

DC and high-frequency conductivity of CuInSe 2 bulk crystals

Bulk crystals of CuInSe 2 (CIS) were grown by vacuum fusion technique with specific proportions of Cu, In and Se. The studied samples, cut from the central part of the ingots, were first characterised by scanning electron microscopy, X-ray diffraction and energy dispersive spectroscopy. The conductivity of the crystals was investigated by using a contactless technique based on hyper-frequency microwave. The method consisted in measurements made in a rectangular resonance cavity at 9192 MHz. Conductivity has been also measured by conventional Van der Paw method and the values obtained, varied in the range [3.10 − 3 –7.10 − 3 ]Ω − 1 cm − 1 , didn't show significant discrepancies between the two techniques.

Fabrication and characterization of semicircular detection electrodes for contactless conductivity detector – CE microchips

This study uses simple and reliable microfabrication techniques to fabricate CE biochips, integrating a novel contactless conductivity detector in a miniaturized detection system in a microfluidic biochip. The off-channel electrodes are deposited around side channels by Au sputtering and patterned using a standard "lift-off" process. A vacuum fusion bonding process is employed to seal the lower substrate containing the microchannels and the electrodes to an upper glass cover plate. The variations in the capacitance between the semicircular detection electrodes in the side channels are measured as different samples and ions pass through the detection region of the CE separation channel. Samples of Rhodamine B, commercial sports drinks, mineral waters, and a red wine, respectively, are mixed in different buffer solutions, separated, and successfully detected using the developed device. The semicircular detection electrodes for the contactless conductivity detector have microscale dimensions and provide a valuable contribution to the realization of the lab-on-a-chip concept.

Design and Fabrication of 3D-Structured Contactless Capacitive-Type Detector for Capillary Electrophoresis Microchip

Using simple and reliable microfabrication techniques, this study develops a capillary electrophoresis (CE) microchip with 3-dimensional-structured (3D-structured) contactless capacitive detector electrodes mounted parallel to the separation channel. The offchannel electrodes are deposited by Au sputtering and patterned using a standard 'lift-off’’ process. A vacuum fusion bonding process is employed to seal the lower substrate containing the microchannels and electrodes to an upper glass cover plate. The variation in the capacitance between the electrodes in the side channels is measured as different samples and ions pass through the detection region of the CE separation channel. Samples of Rhodamine B and a commercial sports drink are mixed in different buffer solutions and successfully separated and detected using the developed device. The 3D-structured contactless capacitive-type detection device has microscale dimensions and provides a valuable contribution to the realization of the lab-on-a-chip concept.

Carboborosilicide and oxide composite coatings on carbon materials

Complex carboborosilicide and oxide coatings on carbon materials prepared by vacuum activated diffusion impregnation predominantly through a liquid phase, vacuum fusion, and enamelling are studied. It is established that coating formation from the vapor phase hardly reduces the original porosity of carbon materials. The complex protective coatings developed that are formed by vacuum activated diffusion impregnation through a liquid phase lead to a reduction in the original porosity and gas permeability of carbon materials thereby increasing their high-temperature strength and heat resistance at elevated temperatures. It is shown that higher heat resistance in the temperature range 1800–2000 °C is provided by multilayer coatings based on carbides and borides of silicon, titanium and zirconium, borosilicides of tungsten, hafnium, molybdenum, and also oxides of silicon, aluminum, zirconium, and hafnium. It is established that the protective properties of coatings depend markedly both on their composition, structure, preparation method and on the form of the original carbon materials.

Influence of Interfacial Diffusion on Mechanical Property of Vacuum Fusion Sinter (VFS) WC-Co Composite Coating

The WC-Co composite coatings bonded tightly to steel substrate have been made by vacuum fusion sinter (VFS). The concentration distribution of some components were measured by the electron probe, and the microstructure and morphology of VFS coatings were observed and analyzed by SEM, X-ray diffractometer and microhardness tester. Diffusion coefficient of every element was calculated by using the experimental results. The influence of the interfacial diffusion on the microstructure, Vickers hardness and interfacial bond strength of the VFS coatings was studied in detail. The experimental results show that there is a metallurgical bond area between the VFS WC-Co coatings and the steel substrate. The VFS coatings are characterized by the gradient hardness of the interface and the high bond strength to the steel substate, both of which are beneficial to the improvement of the wear resistance and corrosion resistance.

Structural and optical characterization of polycrystalline CdSe x Te 1-x thin films

Solid solutions of CdSexTe1-x (0.7≤x≤1) were synthesized by vacuum fusion of stoichiometric amounts of CdSe and CdTe constituents in a silica tube. X-ray and electron microscope diffractometry techniques revealed that the CdSexTe1-x thin films were polycrystalline with a hexagonal structure. The variation of lattice constants with composition was found to obey Vegard’s law. The compositional dependence of the optical constants, the refractive index n and the absorption index k, of the films was determined in the spectral range of 400–2000 nm. The dispersion of the refractive index of the films could be described using the Wemple–DiDomenico single oscillator model. Changes of the dispersion parameters were also studied as a function of the mole fraction x. A plot representing α2=f(hν) showed that the CdSexTe1-x thin films of different compositions have two direct transitions corresponding to the energy gaps Eg and Eg+Δ. The variation in either Eg or Eg+Δ with x indicates that this system belongs to the amalgamation type. The variation follows a quadratic dependence and the bowing parameters were found to be 0.4 and 0.5 eV, respectively.

The Effect of Post-Treatment of a High-Velocity Oxy-Fuel Ni-Cr-Mo-Si-B Coating Part I: Microstructure/Corrosion Behavior Relationships

The microstructure and aqueous corrosion characteristics of a Ni-Cr-Mo-Si-B high-velocity oxy-fuel (HVOF) coating have been assessed. It has been shown that postprocessing by vacuum fusion has a significant effect on the coating microstructure by increasing the type and concentration of hard phase particles. The principal hard phases in the as-sprayed condition and vacuum-sealed condition are chromium carbides, whereas molybdenum-containing boride phases are also present after vacuum fusion. Vacuumfusion post-treatment eliminates splat boundaries, which can act as sites, where preferential corrosion can occur and, hence, the dominant corrosion mechanisms change. In as-sprayed and vacuum-sealed coatings, localized attack at splat particle boundaries and crevice corrosion dominate, whereas in vacuum-fused coating, the principal mechanism of corrosion is “micropitting” as a result of the hard phase loss.