Metal-ceramic Joining Research Articles

Metal ceramic joining with active filler metal in dental practice

This paper examines the phenomena that arise at the interface between ceramics and active filler metal during the metal-ceramics bonding process in dental practice. It focuses on three interrelated sub-processes: the wetting of the ceramic surface, the chemical interactions at the interface, and the diffusion across the moving interface. Additionally, the study explores the grain boundary grooves on the ceramic surface, highlighting their role as catalytic surface phenomena. Following a brief overview of dental metals and bioceramics, the composition and properties of the brazing alloys used in dental practice are presented and explained in detail.

Multilayer coatings on Ti substrate by SHS method

Explored was the deposition of multilayer TiCx–TixSiy-based coatings onto Ti substrate by SHS method. Sandwich-type green multilayer structures were assembled from Ti foils and Ti + 0.5C, Ti + Si, 5Ti + 3Si, and Ti + 0.65C pellets and ignited under 1 atm of Ar and a load (400 g). Burned sandwiches were characterized by SEM, EDS, and XRD. In all cases, we observed good metal–ceramic joining. Prerequisites for such a joining are (i) the presence of the liquid phase in combustion products, (ii) good metal–ceramic wettability, and (iii) closeness of reaction temperature to the melting point of substrate.

Functionalizing Ti-Surfaces through the EPD of Hydroxyapatite/NanoY2O3

Ceramic materials for skeletal repair and reconstruction are expanding to a number of different applications. Present research is addressing new compositions and performances to promote osseo-integration through metal coatings. Nanotechnology plays a key role in this research because nanostructures can be introduced into implants to functionalize them and/or to enhance their properties, such as the thermal or mechanical response. In this work, the insertion of Y(2)O(3) nanoparticles into a hydroxyapatite (HA) coating of Ti using colloidal processing technology was developed. The suspensions of HA and Y(2)O(3) nanoparticles were formulated with a focus on zeta potential, particle size distribution, and viscosity for the codeposition of both phases by electrophoresis. The microstructure of the nanocomposite coating was optimized by adjusting the main parameters of the electrophoretic deposition process. A threshold value of the applied electric field for the composite shaping was identified. The results demonstrate that the Y(2)O(3) nanoparticles are homogeneously distributed in the coating and decrease in concentration as the distance from the substrate increases. As a consequence of the presence of the Y(2)O(3), delays in the HA thermal decomposition and the improvement of metal-ceramic joining were observed.

Surface Modification of Al Components Using Spark Plasma Sintering

A strong push has been observed in the automotive industry to replace current components with high-performance and lightweight materials such as aluminum alloys. Novel monolithic materials such as bulk nanostructured materials, cannot always offer the best performance in hostile environments and often have high manufacturing costs. This has required the development and engineering of processes to allow nanostructured surface functionalization of conventional materials. This processing strategy, similar to the metal-ceramic joining approach, exploits the advantages of both materials while reducing overall manufacturing costs. Spark Plasma Sintering (SPS) will be evaluated as potential a method for manufacturing a nanostructured Al-Si cladding. This novel coating method has a significant advantage over traditional processes in that it forms metallurgical bonds at both the interface and throughout the deposited layer to produce a coating with isotropic properties. The objective of this work is to create a nanostructured eutectic Al-Si feedstock powder and simultaneously consolidate and clad the powder onto a forged aluminum substrate using Spark Plasma Sintering. Results show that after mechanical milling, the aluminum grain size was refined to 47nm. The results also show that SPS is capable of sintering the powder in extremely short sintering times while maintaining nanostructure, and that the heating rate has a large effect on increasing densification rates. Mechanical properties of the resultant coating were also investigated.

The role of wettability in metal–ceramic joining

The effects of oxygen, applied DC voltage and surface orientation on the wettability of ceramics by liquid metals are clarified and new methods for metal–ceramic joining are proposed based on information from wetting experiments, using three examples. The strengths of Ni–Al 2O 3 joints obtained at very low oxygen potentials are higher than in high oxygen potential environments. Applying a DC voltage to the interface between metals and partially stabilized zirconia is shown to improve the strength of metal–zirconia joints. Cu and SiC can be strongly joined without using active elements such as Ti and Zr by controlling the joining conditions.

Dissolved oxygen control and monitoring implementation in the liquid lead–bismuth eutectic loop: HELIOS

A 12 m tall LBE coolant loop, named as HELIOS, has been developed by thermal-hydraulic scaling of the PEACER-300MWe. Thermo-hydraulic experiment and materials test are the principal purposes of HELIOS operation. In this study, an yttria stabilized zirconia (YSZ) based oxygen sensor that was hermetically sealed for long-term applications using the electromagnetically swaged metal–ceramic joining method, have been developed for high temperature oxygen control application over a long period of time. The rugged electrode design has been calibrated to absolute metal–oxide equilibrium by using a first principle of detecting pure metal–oxide transition using electrochemical impedance spectroscopy (EIS). During the materials tests in HELIOS, dissolved oxygen concentration was administered at the intended condition of 10 −6 wt% by direct gas bubbling with Ar + 4%H 2, Ar + 5%O 2 and/or pure Ar while corrosion tests were conducted for up to 1000 h with inspection after each 333 h. During the total 1000 h corrosion test, oxygen concentration was measured by oxygen sensor. The result confirmed that the direct gas bubbling method is a viable and practical option for controlling oxygen concentration in large loops including HELIOS.

Novel Metal-Ceramic Joining for Planar SOFCs

A novel method of ceramic-to-metal joining, referred to as reactive air brazing, was investigated as a potential method of sealing planar solid oxide fuel cells (SOFCs). In the present study, yttria stabilized zirconia (YSZ) and Fecralloy were selected as subject materials to simulate the cell-to-frame seal in planar SOFC. YSZ plates were joined with Fecralloy foils, using a range of CuO-Ag and braze compositions. Metallographic analysis revealed that a majority of the CuO in the braze preferentially migrates to the braze/Fecralloy interface, indicating a stronger affinity and interaction between the CuO and the alumina scale that had formed on the Fecralloy than with the YSZ substrate. The addition of to the braze had no significant effect on the microstructure or mechanical properties of the YSZ/Fecralloy joints, unlike what had been observed previously in YSZ/YSZ joining. Four-point bend tests indicated that joint strength improves with increasing CuO content up to 8 mol % CuO, the maximum concentration of copper oxide tested, likely due to the concomitant improvement in braze wettability. A maximum bend strength of 101 MPa was achieved using the 8 mol % CuO braze composition, demonstrating the feasibility of this joining technique for sealing planar SOFCs.

Review Article: recent advances in metal-ceramic brazing

Metal-ceramic joining has slowly but steadily become an important manufacturing step. The evolution of joining processes has allowed ceramics to be used in combination with metals in a number of hybrid devices from traditional light bulbs and seals to improved cutting tools and modern monitoring and measuring electronic devices. New joining methods and newer approaches to conventional methods have been developed aiming at joints characterized by improved reliability, and interfaces capable of withstanding high-temperature resistance with minimum residual stresses. A summary of recent improvements on alternative approaches to ceramic-metal joining as well as new developments on brazing are presented herein. The present review also focuses on recent advances towards brazing metallized ceramics and the selection of filler alloys, since in a scenario that includes joining by laser and direct bonding with liquid transient phases, brazing continues to be by far the most widely used approach to joining as a result of its low-cost and possibility to join intricate geometries for large-scale production. Finally, methods to evaluate the mechanical strength and residual thermal stresses are presented in addition to alternative approaches to minimize residual stresses and, consequently, improve joint reliability.

A simple method for measuring tensile and shear bond strength of ceramic-ceramic and metal-ceramic joining

A simple method for measuring the ceramic-ceramic and metal-ceramic bond strength was presented, by which uniaxial tensile stress normal to the interface or shear stress in the interface can be produced using uniaxial compression load on a cross-bonded sample. Both tensile and shear bond strength were obtained by this testing technique for Ti3SiC2-TiO2 and Ti3SiC2-Al2O3 composite as well as for glued steel samples, respectively. The novel method provided a solution for determining bond strength in solid (especially brittle) materials, and it is also demonstrated as a useful method for evaluating the tensile and shear strength of various glues.

High Temperature Interaction Behavior at Liquid Metal-Ceramic Interfaces

Liquid metal/ceramic interaction experiments were undertaken at elevated temperatures with the purpose of developing reusable crucibles for melting reactive metals. The metals used in this work included zirconium (Zr), Zr-8 wt.% stainless steel, and stainless steel containing 15 wt.% Zr. The ceramic substrates include yttria, Zr carbide, and hafnium (Hf) carbide. The metal-ceramic samples were placed on top of a tungsten (W) dish. These experiments were conducted with the temperature increasing at a controlled rate until reaching set points above 2000 °C; the systems were held at the peak temperature for about five min and then cooled. The atmosphere in the furnace was argon (Ar). An outside video recording system was used to monitor the changes on heating up and cooling down. All samples underwent a post-test metallurgical examination. Pure Zr was found to react with yttria, resulting in oxygen (O) evolution at the liquid metal-ceramic interface. In addition, dissolved O was observed in the as-cooled Zr metal. Yttrium (Y) was also present in the Zr metal, but it had segregated to the grain boundaries on cooling. Despite the normal expectations for reactive wetting, no transition interface was developed, but the Zr metal was tightly bound to yttria ceramic. Similar reactions occurred between the yttria and the Zr-stainless steel alloys. Two other ceramic samples were Zr carbide and Hf carbide; both carbide substrates were wetted readily by the molten Zr, which flowed easily to the sides of the substrates. The molten Zr caused a very limited dissolution of the Zr carbide, and it reacted more strongly with the Hf carbide. These reactive wetting results are relevant to the design of interfaces and the development of reactive filler metals for the fabrication of high temperature components through metal-ceramic joining. Parameters that have a marked impact on this interface reaction include the thermodynamic stability of the substrate, the properties of the modified interface, the temperature-dependent solubility limits of the liquids and solid phases, and the high-temperature stoichiometry of the ceramic.

The Reduction of Residual Stress Generated in Metal-Ceramic Joining

Finite element analysis was used to investigate the effect of altering the interface geometry on a axi-symmetrical metal-ceramic joint. The authors found that increasing the interface angle not only eliminated the singularity that existed at the intersection of the free edge and the interface boundary, but also saw a drastic reduction in the peak residual stresses contained in the joint. An experimental program was undertaken to validate the theoretical result. Electrical discharge machining was utilized to fabricate ‘novel’ convex ceramic interfaces with a variety of apex heights on a conductive, commercially available sialon ceramic. They were subsequently joined, using a Ag-Cu-Ti braze, to mating stainless steel members. Subsequent tensile tests showed a dramatic increase in tensile strength compared to planar interface joints, thus validating the theoretical model and expanding the potential for metal-ceramic joints to be used in engineering applications.

Predictive Analysis of Ti/AlN Interfacial Reaction Using Diffusion Simulation

Metal-ceramic joining or coating has increased its importance for high temperature applications. The interfacial reaction products give significant effects on the mechanical properties of the metal/ceramic joints. Therefore, a detailed understanding and prediction of interfacial reaction would be helpful to alloy or process design of the metal/ceramic joining. The purpose of the present work is to provide a more complete interpretation on the experimentally observed layer sequence between Ti and AlN, based on thermodynamic calculation and diffusion simulation. An attempt will be made to explain why a specific layer sequence, AlN/TiN/Ti{sub 3}AlN({tau}{sub 1})/Ti{sub 3}Al/Ti is formed at 1,200 C among various thermodynamically probable diffusion paths.

Bonding of alumina to metals with Ag-Cu-Zr brazing alloy

In active metal brazing, the reactive element in the brazing alloy enhances the wettability of the brazing alloy on ceramics and causes strong bonding by the redox reaction [1, 2]. The joint quality is also a function of the interfacial microchemistry and microstructures, such as the species and the morphology of the reaction product formed at the ceramic=brazing alloy interface [3, 4]. Therefore, it is very important to characterize and understand the interfacial reaction and its product at the metal= ceramic interface. However, in active metal brazing, there are many possible reactions at the interface between the reactive element and the ceramic or brazing alloy together with the bonded metal. Because of these complex reactions, the interfacial reaction is difficult to control. There are many reports on metal-ceramic joining with Ti containing brazing alloy, but few attempts have been made in brazing of alumina to metal with Zr contained AgCu based filler metal nor investigations of the interfacial reaction. In this study, Zr was selected as an active element for the brazing alloy since it showed stronger work of adhesion (Wad) on Al2O3 ceramics and more negative G of oxide formation [5] than Ti. The interfacial reaction and the effect of the morphological change of the brazing on the joint strength are discussed here. Discs of 99.9% AE-Al2O3 (diameter 14.5 mm and thickness 5 mm) were brazed to Ni-Cr steel and copper (diameter 12 mm and thickness 8 mm) using three kinds of brazing alloys, Ag-28 wt % Cu ‡ 5 wt % Zr (BZR), BZR ‡ 5 wt % Sn (BZS) and BZR ‡ 5 wt % Al (BZA). The brazing alloys were made by vacuum induction melting. Prior to brazing, all materials used were prepared in the same way as described elsewhere [6]. An elliptical radiant furnace equipped with a quartz tube was employed in the brazing experiment and it was evacuated to less than 10y5 torr (1 torr ˆ 133.322 Pa). Brazing was carried out in the temperature range of 750– 950 8C and the holding time was 30 min. A shear test was performed to evaluate the joint strength, and the microstructure and the interfacial reaction product were analysed using electron probe X-ray micro-analysis, EPMA, (JEOL JXA 840A) equipped with an energy dispersive X-ray spectroscopy EDS, (Link analytical LZ5) and glancing X-ray diffraction, XRD (Regaku Rotaflex RTP 300RE) and X-ray photoelectron spectroscopy, XPS (SSI 2830-S). Fig. 1 shows the SEM microstructure of (a) the interfacial structure and the concentration profile and (b) the reaction layer for Al2O3=Ni-Cr steel joint brazed at 950 8C for 30 min with Ag 28 wt % ‡ 5 wt % Zr brazing alloy. As depicted in Fig. 1b, the reaction layer consisted of Zr and small amounts of Al and Ag. The low Al content in the reaction product might be a result of the higher diffusivity of Al compared to that of oxygen in the molten brazing alloy and an unfavourable reaction to produce Zr-Al compound as compared with Zr-oxide. XRD analysis indicated that the reaction product was monoclinic ZrO2 (a ˆ 5:1463, b ˆ 5:2135, c ˆ 53110 A) even though EDS results showed the existence of Ag in the reaction product. However, Al2O3 is a more stable oxide thermodynamically in comparison with ZrO2 hence it is not feasible to form ZrO2 from zirconium and Al2O3. Simple equilibrium thermodynamics can not sufficiently characterize the interfacial reaction phenomena in the present brazing system. The Ag

Formation Process of Ti3Al in Ti/Al2O3 System

ABSTRACTIt has been reported that Ti reduces Al2O3 forming Ti3Al at the interface. From the viewpoint that the structural change of the Ti3Al phase influences the metal-ceramic joining strength, the Ti3Al formation process was analyzed by XPS, XRD, TEM and RBS. Titanium films were deposited on the (1102) surface of Al2O3 substrates and annealed. XRD analysis shows that Ti3Al formation starts at 1073 K. Initially, the (1120) and (2020) Ti3Al planes are oriented parallel to the surface. After 1173 K-300 s heat treatment, XRD shows only the (2020) Ti3Al peak; After 1173 K-600 s heat treatment, HREM observation shows that the lattices of the Ti3Al (0220) plane match those of the A12O3 (1210) plane at the interface. It is suggested that the (2020) oriented grains grow preferentially on the (1102) Al2O3 plane.The quantity of formed Al increases with heating time. After 420 s, the rate of Al formation falls off. The rate of the Al2O3 reduction is in good agreement with the slightly modified Johnson-Mehl equation. The Ti2O/Ti3Al(O)/Al2O3 layer sequence and morphology can be explained by the pure Ti decrease.

Chemical thermodynamics as a predictive tool in the reactive metal brazing of ceramics

Thermodynamics have long been applied to our understanding of the reactive wetting phenomena in metal-ceramic joining. We postulate the existence of a “solvent effect” due to the interaction between the reactive element addition and the brazing alloy. This effect plays a significant role in reactive wetting. By taking this effect into account, more realistic reactivities of different reactive element additions into a given brazing base alloy are predicted. Irreversible thermodynamics are also used to characterize the driving forces for reactive metal-ceramic joining.

A review of: “Metal-Ceramic Joining”Edited by P. Kumar and V. A. Greenhut

(1995). A review of: “Metal-Ceramic Joining”Edited by P. Kumar and V. A. Greenhut. Materials and Manufacturing Processes: Vol. 10, No. 1, pp. 115-117.

Active Brazing Alloy Containing Carbon Fibers for Metal–Ceramic Joining

The addition of 8.4 vol% short metal‐coated carbon fibers to an active brazing alloy increased the debonding strength of metal/ceramic joints by 18% to 28%. The carbon fibers helped to strengthen the brazing alloy and to decrease slightly the thermal stress at the brazing interface. The carbon fibers were either uniformly distributed in the brazing layer or concentrated near the ceramic side of the metal/ ceramic brazing interface. The latter resulted in a lower thermal expansion in the part of the brazing filler near the ceramic arid gave superior joints such that the debonding occurred in the part of the brazing filler without carbon fibers. The titanium in the active brazing alloy was segregated at the interfaces between the brazing filler and the ceramic, between the brazing filler and the metal (steel), and between the carbon fibers and the matrix of the brazing filler. The amount of titanium at the interface between the brazing filler and the ceramic was smaller when carbon fibers were present in the brazing filler. Titanium segregation at the fiber–matrix interface was also observed when bare carbon fibers instead of metal‐coated fibers were used. The bare carbon fibers gave joints comparable in quality to the metal‐coated carbon fibers. The carbon fibers also served to lower the cost of the brazing material.

Metal-ceramic joining by laser

Within the scope of increase in cutting tools efficiency, a CW CO 2 laser beam has been used for butt welding sintered tips containing cobalt and tungsten carbide to a medium carbon steel core. After optimization of the laser processing conditions, full penetrating, sound and homogeneous welds are observed. Hardness is found to be nearly constant across the entire weld bead cross-section. Micrographic observations in the same area show a fine dendritic microstructure; microanalysis (EDS) as well as X-ray diffraction experiments reveal that dendrites contain mainly iron and cobalt, while tungsten has segregated in the interdendritic zone where complex (Fe-Co-W) rich carbides are likely to form

特集『金属・セラミック接合の基礎』 金属・セラミック接合の化学的問題

特集『金属・セラミック接合の基礎』 金属・セラミック接合の化学的問題

特集『金属・セラミック接合の基礎』 金属・セラミック接合の今後の課題

特集『金属・セラミック接合の基礎』 金属・セラミック接合の今後の課題