Symposium CD
Joining Inorganic Materials at Different Length Scales

Session CD-1 - Basic Issues

CD-1:IL02  Towards Better Ceramic Joins via Control of Wetting & Adsorption
W.D. KAPLAN, Department of Materials Science and Engineering, Technion - Israel Institute of Technology, Haifa, Israel

It is well known that so called 'active elements' can be used to enhance joining of ceramics, or ceramics to metals, where an example is Ti added to braze alloys. Active elements are reported to improve wetting during the joining process, and in some cases improve the thermodynamic work of adhesion of the resulting solid-solid join. Recently it has been experimentally proven that interfaces can undergo first-order adsorption transitions with regards to their 2-D structure and chemical composition, and these transitions are correlated with a change in slope of the interface energy with thermodynamic parameters (e.g. active element composition). This presentation will demonstrate how such first order transitions can be utilized to improve wetting during joining processes and the subsequent adhesion of the final join, without formation of undesirable interface reaction products which often accompany the use of active elements.


CD-1:L03  Microstructural Evolution of Active Metal Brazed Ag-Cu-Ti/Alumina Interfaces
M. ALI, K.M. KNOWLES, Department of Materials Science and Metallurgy, University of Cambridge, Cambridge, UK; J.A. FERNIE, P.M. MALLINSON, T.R. BARNES, AWE, Aldermaston, Reading, UK

The evolution of the interfacial phases produced during the brazing of alumina to itself with Ag-Cu-Ti active metal brazes (AMBs) is still not fully understood. This is mainly because the few transmission electron microscopy (TEM) studies in this area have all been dedicated to the characterisation of single AMB interfaces, each of which has been prepared using disparate brazing conditions. Thus, only 'snapshots' of the interfacial phases have been reported. A typical snapshot shows a continuous interfacial bilayer consisting of a TixOy layer in contact with the alumina and a (Ti,Cu)6O layer in contact with the braze.
In this work, alumina/Ag-Cu-Ti/alumina joints have been prepared using 2 peak brazing temperatures and 4 brazing times and examined by TEM. It is evident that a continuous (TiCu)6O layer is produced at the ceramic-braze interface after holding for as little as 1.8 mins at the highest temperature of a brazing schedule. At the same time, nm-sized TiO particles are found at random points between the (TiCu)6O layer and the alumina. Over time at a particular peak brazing temperature, the TiO particles thicken and produce a continuous layer between the alumina and the (TiCu)6O layer. For extended brazing times, the interfacial morphology becomes more complicated.


CD-1:IL04  Modeling Surface Tension-driven Shape Changes in Micro- and Nano-scale Systems
R.V. ZUCKER, C.V. THOMPSON, W.C. CARTER, Department of Materials Science and Engineering, Massachusetts Institute of Technology, Cambridge, MA, USA

Owing to their extremely high aspect ratios, most single crystal thin films are unstable and when they are heated, they will dewet or agglomerate to form islands. This process can occur in the solid state through capillary-driven surface self-diffusion. Understanding this process is critical for the prevention of thermal degradation in micro- and nano-scale systems. It also offers a new avenue for the manufacture of stable, complex, small-scale geometries. Key features of the dewetting process include the retraction of the edges of the film, the development of rims at edges, and formation of wire-like structures via a pinch-off mechanism.
We present models of dewetting for highly anisotropic, faceted, single-crystal thin films. Edge retraction and the development of rims have been reproduced and studied using a two-dimensional model. The model agrees well with experiments, and provides insights into which physical parameters have the greatest influence on the edge retraction rate and how to better control thin film evolution. We also find that strong crystalline anisotropy can prevent pinch-off in some cases. To understand and control more complicated features, such as fingering instabilities and hole growth morphologies, we present a three-dimensional model.


CD-1:IL05  Residual Stress Tensor Distribution around Interface of Brazed Ceramics
SHUN-ICHIRO TANAKA, IMRAM, Tohoku University, Sendai, Japan

Micro-sin2psai method is based on the hypothesis of the plane stress state unmatched with the actual stressed positions. X-ray two-dimensional (2D) method developed in 2009 gives us one solution to measure stresses in three dimensional states and I have applied to various localized area using collimator from 2010. Fundamental principle to measure is detection of the diffracted Debye ring deformation using two-dimensional detector with various X-ray incident directions. Measured stresses are normal, shear and principal stress values as a tensor and their directions expressed by stress ellipsoid.
I have applied X-ray 2D method to measure actual residual stress tensor distribution around interface of brazed Si3N4/Cu/steel in the region of Si3N4, Cu and steel. Especially stresses at anomaly points in Si3N4 should be known in detail because of its brittleness and three dimensional stress states, and X-ray from Cr and Cu rotor target collimated to 0.1mm in diameter was irradiated and diffraction at (212) and (323) of Si3N4 was used, respectively. Maximum principal stress, sigma 1 exceeded 200 MPa in joined edge of Si3N4 which was lower than that by micro-sin2psai method, whereas sigma 1 along interface was similar in two methods.


CD-1:IL06  Wetting and Adhesion of Copper in the Liquid and Solid States on Alumina
D. CHATAIN, Aix Marseille Université, CNRS, CINaM UMR 7325, Marseille, France

Liquid/solid and solid/solid wetting of a metal on a crystalline oxide is anisotropic. In the solid state, wetting and adhesion depend on the crystallographic planes of the metal and the oxide which abut at the interface. We have determined the preferred orientation relationship and the interface structure of submicron copper crystals equilibrated on sapphire substrates of different orientations (c(0001), a(11-20), r(1-102) and m(1-100)), by electron and near-field microscopies. It is observed that there are particular and recurrent crystallographic alignments of copper and sapphire crystals which favor certain crystallography at the interfaces and thus the adhesion, and which barely depend on the original orientation of the sapphire substrate. In addition, it is shown that the triple line fosters drastic shape changes of the interface and of the oxide surface.


CD-1:IL07  Active Metal Brazing of Alumina to Kovar using Copper ABA
J.A. FERNIE¹, P.M. MALLINSON¹, M. ALI², T.R. BARNES¹, K.M. KNOWLES²,  ¹AWE, Reading, UK; ²University of Cambridge, UK

Kovar alloy (Fe-29Ni-17Co) is known to have a significant effect on the active metal brazing of alumina. The titanium in the active metal braze is reported to migrate preferentially to the interface with the Kovar and react with elements in the Kovar to produce a number of complex intermetallic phases. Such chemical reactions can have a deleterious effect on the strength and hermeticity of the joint; with the titanium in the braze then being unavailable to induce sufficient wetting and chemical bonding with the alumina.
In this study, the ASTM F19-64 standard has been used as a basis to investigate Kovar brazing to alumina with Copper ABA (composition (wt%) - 92.75 Cu, 3 Si, 2.25 Ti, 2.0 Al). A range of times and temperatures were used, with the joint quality assessed in terms of hermeticity, tensile strength and microstructure. The microstructure of the braze joints showed considerable evolution over the range of conditions and significant changes to the interfaces between the alumina and braze, and the braze and Kovar were observed. It was found hermetic and high strength (> 50 MPa) joints could be produced over a wide range of conditions.


CD-1:IL08  Role of the Interfaces in Metal-ceramic Joints
A. PASSERONE, F. VALENZA, C. ARTINI, M.L. MUOLO, IENI-CNR, Genova, Italy

Manufacturing technologies based on joining remain a critical tool for reducing assembly time, cost and to obtain materials with improved performances. CMC's have to replace metals to optimize existing components, and their joining to themselves or to special alloys represents at the same time a special technological challenge.
Several joining techniques have been investigated for CMC's, in particular for SiC ceramics, by liquid joining media, also through a transient liquid phase. At the same time, studies on reactive and non-reactive wetting by metallic alloys, even if numerous for ceramic substrates, are quite scarce for CMC and in particular for the most interesting SiC-based composite materials.
We will present recent findings on the basic phenomena related to the joining and integration methods for CMC's. The basic role of solid-liquid interfacial interactions at high temperature will be addressed; in particular the main issues that will be taken into account are (i) wettability (ii) reactivity (iii) thermodynamic stability of the brazing alloy toward CMC's and (iv) the interplay of melting temperature, CTE mismatch between CMC and brazing alloys on the final joint performance. A particular attention will be given to SiC-based CMC's in relation to aerospace applications.


CD-1:IL09  Wetting and Interface Interactions in Ceramic/Metal Systems and their Effect on Ceramics Joining
M. AIZENSHTEIN¹, N. FROUMIN², N. FRAGE², ¹Department of Material Engineering, Ben-Gurion University, Beer-Sheva, Israel; ²NRC-Negev, Beer-Sheva, Israel

The need for joining of ceramics increases along with the increasing usage of ceramics in technological applications. The problems which make ceramic joining a difficult task are basically related to wetting issues and to thermal stress caused by differences of CTE between the ceramic and the joining metal.
Wetting problems of ceramics are traditionally overcome by using active elements, such as Ti, or by metallization of the ceramic surface. The use of active elements promotes wetting via reactive wetting mechanism, which leads to new phases formed at the metal/ceramic interface.The CTE of the new formed phase as well as its morphology and width determines the performance and mechanical stability of the joint, which is often compromised. In this study we will review our last ten years results related to the wetting mechanism and interface interactions between oxides, carbides, borides and liquid metals and will show in the case of B4C/Cu alloys the correlation between the reactions products formed at the interface and the mechanical properties of ceramic-to-ceramic joints.


CD-1:L10  Sealing of Glass-ceramics to Ti-6Al-4V
M.T. STAFF¹, P.M. MALLINSON², F.H. MCCARTHY², M.J. WHITING¹, J.A. YEOMANS¹, J.A. FERNIE², ¹University of Surrey, Guildford, UK; ²AWE, Reading, UK

Titanium and titanium alloys, such as Ti-6Al-4V, have an outstanding combination of strength-to-weight ratio and corrosion resistance. Thus, they are frequently the material of choice for the aerospace and biomedical industries where these properties are critical. Ti-6Al-4V is currently being investigated as a material for glass-ceramic-to-metal seals.
However there is difficulty in producing suitable seals due to the formation of deleterious titanium silicides when conventional silicate based glasses are used; these phases are incompatible with the production of a robust joint. Investigation into boroaluminate glasses has shown they are capable of overcoming these issues, whilst forming the desired hermetic seal.
In this work a range of borate based glasses have been examined as candidate compositions for a sealing system comprising a Ti-6Al-4V alloy housing and a single pin of an appropriate alloy (Alloy 52 or Kovar). A number of suitable glass compositions were identified and characterised using dilatometry, differential thermal analysis, X ray diffraction and electron microscopy. Optimised sealing procedures were then established and the seals evaluated as a function of hermeticity and microstructure.

 
Session CD-2 - Macro-joining

CD-2:IL01  A Critical Review on Modeling of Fracture Behavior of Ceramic Joints
H. SERIZAWA, H. MURAKAWA, Joining and Welding Research Institute, Osaka University, Osaka, Japan

Ceramic composites are candidate materials for high heat flux components because of their high-temperature properties. For fabricating large or complex shaped parts of these composites, the technique of joining between simple geometrical shapes is considered to be an economical and useful method. There, the shear strength of joints is one of the most important mechanical properties. Generally, the strength of the joint is largely influenced by the geometry of the joint and the test method for evaluating the strength. In order to study these influences, the level of stress and the order of the singularity in stress field computed using conventional FEM are commonly employed for the relative evaluation of strength. However, it is impossible to analyze the formation and propagation of crack with those FEM, since these FEM can model volumetric behavior although the crack involves the formation of a new surface. In this presentation, as one of the methods to overcome this problem, the applicability of the interface element, which models the formation of surfaces directly, is demonstrated through the analyses for determining the shear strength of ceramic joints. Also, the study on the microstructural fracture behavior of composite using the interface element is presented.


CD-2:IL02  Joining of Ceramic-metal Composite Materials
K. PIETRZAK, ITME and IPPT PAN, Warsaw, Poland

There is a wide agreement among scientists and engineers, who are involved in developing of ceramic-metal composite materials, that for the opportunity of using these materials in a wider range of modern industries, exists necessity of their joining. That's why, a sudden increase of new materials technology brings on parallel, increase of demand for new developed joining technologies. As composite materials are mainly used in extremely work conditions, their joints must be characterized by superior mechanical properties. The special challenge of joining of ceramic-metal composites to other materials arises largely from the variety of composites and, especially, their matrix and structure of ceramic-metal interface. That's why, the selection of the best joining technique depends both on the composition of CMC's and the future applications.
This paper comprises both, the review based on the selected specialist literature and the results of own investigations which were conducted as a part of European projects and cooperation with industrial partners. The results of brazing of Cu-C/SiC and brazing or friction welding of intermetallics are presented. The separate part of this paper shows the results of investigation of using the FGM's (alumina-chromium) in ceramics-steel joints.


CD-2:IL03  3D-visualization of Material Flow in Friction Stir Welding
Y. MORISADA, H. Fujii, Joining and Welding Research Institute, Osaka University, Ibaraki, Japan

Recently, much attention has been paid to Friction Stir Welding (FSW) which is a solid-state joining technique. A rotating tool is inserted into the interface at the butt line of metal plates and produces a highly plastically deformed zone. The metal plates are joined by the traveling of the rotating tool along the interface. It is well known that the FSW joint shows excellent mechanical properties because of recrystallized fine and equiaxed grains in the stir zone. Therefore, FSW has been widely developed as a spot joining and surface modification techniques. The material flow around the rotating tool in FSW is the key phenomenon for obtaining a sound joint. The material flow has been studied using various approaches because an accurate understanding of the material flow can lead to optimization of the process conditions. The material flow was investigated by the tracking of a tracer, observation of the flow pattern in the weld of dissimilar materials, and measuring the eutectic Si distribution. However, the material flow during the FSW is still unclear. It is difficult to understand the accurate material flow using these approaches because the obtained experimental results show only one part of the process. In this study, the material flow is three-dimensionally visualized using a tiny spherical tungsten tracer. The three-dimensional material flow is obtained using the locus of the tungsten tracer observed by two pairs of x-ray transmission real-time imaging systems.


CD-2:L04  Effect of TiC on Diffusion Bonding of Ti-6Al-4V to Carbon Steel
A. MIRIYEV, S. KALABUKHOV, E. TUVAL, A. STERN, N. FRAGE, Ben-Gurion University of the Negev, Beer-Sheva, Israel

The main problem of titanium to steel joining is the formation of brittle FeTi and Fe₂Ti phases. Moreover, it is very difficult to find any brazing alloys for this couple due to the formation of Ti-based intermetallic phases with almost all suitable metals.
The present work is focused on the investigation of diffusion bonding of Ti-6Al-4V alloy to carbon steel (0.28wt.%C) using Spark Plasma Sintering (SPS) technique. It was established that during bonding process in the 800-950°C temperature range, a very thin TiC layer (1-2 microns) is formed at the interface and prevents direct contact of Ti-alloy with steel and, consequently, the formation of the intermetallic phases. Tensile strength of the joints fabricated at 950° for 30 min. is about 250MPa. The formation of the titanium carbide layer and its thermal stability were analyzed based on the isothermal section of the ternary Fe-Ti-C phase diagram. The growth kinetics of this layer during prolonged heat treatment of the joints (up to 100 hours in the 800-950°C temperature range) was investigated experimentally. It was established that carbon transport from steel to Ti-alloy occurred during thermal treatment and the limiting stage of the process is carbon diffusion through grain boundaries of the TiC layer.

 
Session CD-3 - Micro-/Nano-joining

CD-3:IL01  New Micro-/Nanojoining Concepts using Ceramic Materials
J. JANCZAK-RUSCH, G. PIGOZZI, F. LA MATTINA, G. KAPTAY*, S. YOON, J. PATSCHEIDER, R. HAUERT, L.P.H. JEURGENS, Empa, Swiss Federal Laboratories for Materials Science and Technology, Dübendorf, Switzerland; *Bay Zoltan Applied Research Nonprofit Ltd, Department of Nanomaterials, Miskolc, Hungary

The use of nano-effects such as fast kinetics, grain boundary wetting or melting point depression in nano-sized materials offers new opportunities for joining technologies. Novel brazing and diffusion bonding concepts have been developed based on application of nano-structured metallic joining materials in a multilayer configuration, where ceramic thin films are used to confine the metallic interlayers. The ceramic nano-layers have been found to play a significant role when triggering the diffusion and melting behaviour of the nanosized joining material. Their composition and thickness has to be carefully chosen and the nanostructure properly designed to obtain the desired behaviour of the multilayer during the joining process and thereafter in the joint service conditions. The new concept will be shown on the example of Ag-Cu/AlN nano-multilayers which were deposited by magnetron sputtering and used for the joining of steel parts below the melting temperature of bulk eutectic Ag-Cu alloy. The requirements on the AlN barrier layers will be discussed based on the results of a combined theory-experiment approach involving thermodynamic calculations, He-ion microscopy, in-situ XRD, SEM, Auger electron spectroscopy and HR-TEM.


CD-3:IL03  Bonding Process by Sintering of Ag Nanoparticles Derived from Reduction of Ag2O
A. HIROSE, S. TAKATA, T. OGURA, Osaka University, Suita, Osaka, Japan

A novel bonding process using Ag2O paste consisting of Ag2O particles and a reduction agent has been proposed. During bonding process, Nano-size Ag particles were formed by the reduction of Ag2O particles. They were immediately sintered each other and also bonded to a substrate material because of high surface energy of the nanoparticles. Au-to-Au, Cu-to-Cu and Al-to-Al bondings have been achieved using this bonding process. In the Au-to-Au bonding, a hetero-epitaxial layer of Ag being oriented in the direction of the Au crystal was formed at the bonding interface. In the Cu-to-Cu bonding, a natural oxide layer on the Cu surface was reduced during the bonding process, and Ag nanoparticles were directly bonded to the Cu substrate. In the Al-to-Al bonding, however, interfacial bonding of Ag to the Al substrate was achieved through a natural aluminum oxide layer. Therefore, it was found that Ag nanoparticles derived from reduction of Ag2O can be directly bonded to the aluminum oxide in this bonding process.


CD-3:IL04  In Situ Transmission Electron Microscopy Characterization of Thin Film/Substrate Interfaces under Externally Applied Stress Fields
K. VAN BENTHEM, Department of Chemical Engineering and Materials Science, University of California, Davis, CA, USA

The investigation of structure-property relationships for functional nanomaterials and the determination of mechanisms for defect evolution under extreme conditions is an important task for the development of novel materials systems. In situ transmission electron microscopy (TEM) provides access to the atomic structure and composition of defect structures and enables their characterization as a function of externally applied stresses, such as elevated temperatures, electrical fields and currents, etc. For kinetically constrained thin films, changes in temperature alter the wetting behavior of thin films on substrates. Unbalancing the current equilibrium state of surface and interface energies can lead to interface reactions and/or rupturing and subsequent agglomeration of the film. Cross-sectional characterization of as-deposited metal films on silicon and SrTiO3 substrate surfaces and subsequent in situ annealing has revealed the formation of complex interface structures. We will discuss how in situ TEM can elucidate the evolution of interface structures on the atomic length and/or nanosecond time scales.
This research was supported by a Faculty Early CAREER Award from the U.S. National Science Foundation (DMR-0955638) and the UC Laboratory Fee Program (12-LR-238313).


CD-3:IL05  Modeling Micro-laser Solidification for Microstructure Tailoring during Additive Manufacturing
M. BROCHU, D.W. HEARD, R. GAUVIN, McGill University. Montreal, Canada

Among the numerous challenges surrounding additive manufacturing of Al alloys, the understanding of the solidification cracking and ways to prevent it are of paramount importance to aim at obtaining defect-free materials. The successful stories around AM of Al are limited to pure and to foundry alloys (AlSi10Mg and AlSi12). The solidification cracking sensitivity of the majority of the wrought alloys is one of the hurdles to overcome to fabricate crack-free materials. This talk will present an approach aimed at changing the solidification front composition and solidification behavior to eliminate solidification cracking. Modeling using the Aziz and the KGT models were used to understand the relation between the fabrication parameters and the solidification front characteristics, and experimental validations were done on some aerospace Al alloys.


CD-3:IL06  Transmission Electron Microscopy of Interfaces in Diffusion Bonded Silicon Carbide Ceramics
H. TSUDA, S. MORI, Osaka Prefecture University, Osaka, Japan; M.C. Halbig, NASA Glenn Research Center, Cleveland, OH, USA; M. SINGH, Ohio Aerospace Institute, Cleveland, OH, USA; R. ASTHANA, University of Wisconsin-Stout, Menomonie, WI, USA

Silicon carbide (SiC) is enabling material for a number of high-temperature structural and extreme environment applications due to its excellent high temperature mechanical properties, oxidation resistance, and thermal stability. However, in order to fabricate large and complex shaped components, innovative joining and integration approaches have to be developed and optimized. A number of joining approaches for SiC-based materials have been developed and reported in the literature. However, in most cases, detailed microstructural observation of the bonded area by Transmission Electron Microscopy (TEM) has not been carried out due to difficulty in preparing TEM samples. Recently, we have successfully prepared clean and less damaged TEM samples from diffusion bonded regions in CVD-SiC and fiber bonded ceramic (SA-Tyrannohex) by Focused Ion Beam (FIB) system. In these systems, PVD-Ti, metallic Ti foil, and Mo-B foil were used as joint interlayers. Detailed analysis of interfaces using SEM, elemental analysis, and TEM were conducted. In this presentation, microstructural details from different interlayer materials, effects of interlayer thickness and fiber orientation in fiber bonded ceramic, and the mechanism of interfacial phase formation in the bonded regions will be discussed.


CD-3:L07  A Study on the Interfacial Reactions of Ti-6Al-4V and Boroaluminate Glasses / Glass-ceramics used in Glass to Metal Seals
P.M. YATES¹, M. STAFF^{1, 2}, M.J. WHITING¹, J.A. FERNIE², J.A. YEOMANS¹, ¹University of Surrey, Guildford, UK; ²AWE, Reading, UK

Currently components requiring an electrical feed-through, or other glass to metal seal, can be manufactured successfully and reliably using stainless steel housings and silicate glasses. In order to reduce component weight there is a need to replace steels with metals such as titanium and its alloys. The use of titanium alloys with conventional silicate glasses, however, is problematic because interfacial reactions tend to result in poor quality seals which are not reproducibly hermitic.
As part of a drive to use titanium alloys, new aluminoborate glass compositions have been proposed. However the interfacial reactions are not extensively studied or well understood, nor are their crystallisation characteristics. X-Ray Photoelectron Spectroscopy and Scanning Transmission Electron Microscopy have been used to characterise the small-scale reaction products and interfacial chemistry. Once the reactions are fully understood they can be controlled to allow continuous bonding across interfaces and provide reproducible and reliable hermetic seals.


Session CD-4 - Application Engineering

CD-4:IL01  Interfacial Reactivity in Diamond Cutting Tools
C. ARTINI, Department of Chemistry and Industrial Chemistry, University of Genova, and CNR-IENI, Genova, Italy; F. VALENZA, A. PASSERONE, M.L. MUOLO, CNR-IENI, Genova, Italy

Cutting tools generally consist of a metal matrix segment containing an abrasive material (e.g. diamond or c-BN), fixed to the steel core of the tool. Diamond grits can be embedded in a metal (often Co-based) powder by hot-press sintering (impregnated tools), or they form a thin layer brazed to the steel core by a filler phase, generally consisting of a Cu-, Ni- or Ag-based alloy (brazed tools), or are mechanically entrapped in a Ni layer forming the matrix (electroplated tools).
In all cases the diamond/matrix interfacial reactivity is a relevant technological issue, as a strong adhesion is essential to avoid early detachment of diamonds; thus, small amounts of active elements (e.g. Cr, Ti or V), are sometimes added to the matrix to promote the formation of a chemical bond. Moreover, to prevent oxidation and graphitization phenomena occurring during the sintering process of the segment, coated diamonds (by Ti, Co, etc.) can be used too, as a carbide film forms on the diamond surface avoiding graphitization.
We will present a review on the most significant basic issues in the production of diamond cutting tools, such as the diamond/matrix interfacial behavior, the choice of the metal matrix, the search for Co-free matrixes, and the effect of minor additions on the metallic bond.


CD-4:IL02  Compact, Ceramic Heat Exchangers and Microchannel Devices: Joining and Integration
C. LEWINSOHN, J. FELLOWS, M. WILSON, Ceramatec, Inc., Salt Lake City, UT, USA

Many energy conversion systems use thermal processes to convert chemical energy to mechanical or electrical energy. In these situations, microchannel components can be used to make heat exchangers and microreactors to make processes more energy efficient. Ceramic heat exchangers permit operation at higher temperatures than with other materials. Additionally, compact heat exchangers are highly efficient and cost-effective. This talk will describe principles of design, methods of fabrication, and joining methods for ceramic, compact heat exchangers for integration of such heat exchangers into practical applications. Particular emphasis will be placed on methods for joining silicon carbide to itself and the results of a novel bonding method that can be performed art relatively low temperatures in air. The mechanical behavior, at room temperature and elevated temperature, of this bonding method will be compared to that of diffusion bonded joints.


CD-4:IL03  Microscale Evaluation of Fracture Toughness and R-curves in Bond Coats and the Role of Platinum
B.N. JAYA, V. JAYARAM, Indian Institute of Science, Bangalore, India

The diffusion aluminised bond coat that provides oxidation resistance to superalloy components in aero-engine gas turbines is a graded structure whose response to thermomechanical stresses critically determine the life of the component. Platinum additions allow the retention of a less brittle, low aluminium beta-Pt-Ni-Al phase while maintaining sufficient oxidation resistance. We describe fracture toughness tests on a new micromachined clamped beam geometry, both ex-situ as well as inside the SEM. The geometry is validated through compliance measurements and FEM as well through measurements on model materials including glass and silicon. The micromachined beams display stability of crack extension which allow R-curves to be determined in selected regions of the bond coat with sub-micron spatial resolution.
The presentation of the above results will be followed by a description of preliminary fatigue tests and of alternate fracture geometries that allow meaningful measurements when the plastic zone size becomes large.


CD-4:IL04  Joining of UHTC Diborides using Metallic Interlayers
N. SAITO, K. NAKASHIMA, Kyushu University, Fukuoka, Japan; L. ESPOSITO, L. SILVESTRONI, D. SCITI, CNR-ISTEC, Faenza, RA, Italy; S. GUICCIARDI, CNR-ISMAR, Ancona, Italy; A.M. GLAESER, UC Berkeley, Berkeley, CA, USA

Ultra-high temperatures ceramics (UHTCs) are the subject of intense worldwide research effort, and their stability in severe environments makes them candidates for aerospace, nuclear and solar energy applications. Widespread usage UHTCs requires the development of effective and reliable joining methods that facilitate the fabrication of large, complex-shaped, and potentially multimaterial components and devices.
Joining of HfB2 and ZrB2, UHTC diborides, which exhibit outstanding thermo-mechanical and thermochemical properties and good erosion and corrosion resistance, was the focus of the present study. MoSi2 is an effective sintering aid for both HfB2 and ZrB2, resulting in dense bulk materials with excellent mechanical properties. HfB2-X vol% MoSi2 (X = 5 or 10) composites were joined at 1500°C with a Ni/Nb/Ni interlayer that forms a thin liquid film. Joint-region characterization revealed well-bonded interfaces with microstructures strongly dependent on the MoSi2 content. Well-bonded interfaces were also obtained for a ZrB2-10 vol% MoSi2 composite bonded at 1500°C with both Ti and Zr interlayers. Interfacial microstructures, their evolution during heating to the joining temperature, and mechanical test results will be presented.


CD-4:L05  Brazing of Metals, Alloys and Ceramics using Rapidly Quenched Ribbon-type Filler Metal STEMET
A.N. SUCHKOV, V.T. FEDOTOV, O.N. SEVRYUKOV, B.A. KALIN, A.A. IVANNIKOV, I.V. FEDOTOV, National Research Nuclear University «MEPhI», Moscow, Russia

Recently, in high-tech industries brazing is widespread. In view of this an interest has appeared in new solders which can ensure reliability and durability of brazed structures and devices. MEPhI for 20 years has been working on the development and manufacture of rapidly quenched ribbon-type filler metals (solder) «STEMET®» with amorphous and nanocrystalline structure based on Al, Cu, Ni, Fe, Ti, Zr, intended for a wide range of brazing materials: from refractory metals and alloys up to various ceramics. These solders have been satisfactorily used for brazing elements in nuclear, thermonuclear, aerospace, automotive, aerospace and other industries.
This report systematizes and summarizes the main results obtained during the development of rapidly quenched ribbon-type solders «STEMET^®» and in brazing copper-based alloys, titanium-based alloys, zirconium-based alloys, steels, refractory metals, ceramics, etc.


CD-4:IL07  Glass and Glass-ceramic Based Sealants for Solid Oxide Cells
F. SMEACETTO, Politecnico di Torino, Torino, Italy

A critical issue in the fabrication of solid oxide fuel cells (SOFC) and solid oxide electrolysis cells (SOEC) is the joining of the electrolyte with the metallic interconnect. There are a number of possible joining (or sealant) materials including glasses, glass-ceramics as well as brazing alloys. The development of sealants is a significant challenge as they must meet very restrictive requirements, i.e. withstand the severe environment of the solid oxide cells (high O2 partial pressures and reducing environments) and be thermo-mechanically compatible with the materials to which are in contact (at 800°C). Glasses and glass-ceramics are likely to be the materials of choice as they exhibit better resistance to the severe service environment than brazing alloys. This work focuses on the design, characterization and testing in stack relevant conditions of silica-based glass compositions. The glasses were characterized by heating stage microscopy, differential thermal analysis, X-ray diffraction in order to study the optimal joining process. The compatibility with the interconnect (Crofer22APU, spinel coated and preoxidised) and anode-supported-electrolyte (YSZ) and the mechanical properties (torsional shear strength) of the joined samples are reviewed and discussed.


CD-4:IL08  Biocompatibility of Titanium Dioxide Film Irradiated with Femtosecond Laser
M. TSUKAMOTO, T. SHINONAGA, Joining and Welding Research Institute, Osaka University, Osaka, Japan; P. CHEN, A. NAGAI, T. HANAWA, Institute of Biomaterials and Bioengineering, Tokyo Medical and Dental University, Tokyo, Japan

Titanium (Ti) is widely used in biomaterials because of its excellent anti-corrosion properties and high strength. Coating of the titanium dioxide (TiO2) film on Ti plate surface is useful methods to improve biocompatibility of Ti plate. It is suggested that direction of cell spreading can be controlled due to grooves direction on the TiO2 film. In the experiments, the film was formed on Ti plate with an aerosol beam. The wavelength, pulse duration and repetition rate of our femtosecond laser were 775 nm, 150 fs and 1 kHz, respectively. Periodic nanostructures, lying perpendicular to the laser electric field polarization vector, were formed on the film by scanning of the femtosecond laser focusing spot. The period was shorter than wavelength of femtosecond laser. In the cell test, The percentage of cells with good attachments on the film with the periodic nanostructures was not decreased. Then, cell spreading along the grooves of the periodic nanostructures was observed although it was not done for the film without the periodic nanostructures. These results indicate that the direction of cell spreading on the film could be controlled by periodic nanostructure formation generated using a femtosecond laser.


CD-4:L09  Mechanical Characterization of Sintered and Laser Solded Monolithic Ceramics and Ceramic Matrix Composites (CMC)
J. SCHMIDT, C. GADELMEIER, M. GÖTHE, Fraunhofer Institute of Silicate Research ISC, Center for High Temperature Materials and Design, Composite Technology Group, Bayreuth, Germany

Within the scope of the project Energy Efficiency of Sustainable Thermal Processes (EnerTherm) high temperature ceramic components and systems are developed. High temperature Ceramic heat exchangers (HX), which are key components for the heat recovery in furnaces are in the focus of the sub-project. Joining is needed to obtain high geometrical complexity and appropriate gas-tightness. Possible candidates for HX applications are mullite, SiSiC and CMC due to their high shock resistance and fracture toughness. CMC can withstand high heating and cooling rates, and steep temperature gradients during the joining process. The joining of these ceramics was performed by using a CO2-laser with the wave length of 10.6 µm and the continuous beam power of 1.6 kW. For the purpose of comparison joining in a high temperature resistance sintering furnace under argon atmosphere was accomplished. As high temperature joining material the eutectic braze Ti-Si and the glass braze from the type SiO2-Al2O3-MgO were selected. The microstructure and phase composition of the joining area was investigated by SEM and XRD. The mechanical properties of the brazed ceramics were determined according to the standards DIN EN 843, DIN EN 658 and DIN EN 1894, and up to 1000 °C with DIN EN 820-1.
 
 
Poster Presentations

CD:P02  Advanced Manufacturing Routes for Metal/Composite Components for Aerospace
M. FERRARIS, M. SALVO, and ADMACOM Team, Dept. of Applied Science and Technology, Politecnico di Torino, Torino, Italy

ADMACOM (Advanced manufacturing routes for metal/Composite components for aerospace) is a EU project started on October 2013, gathering seven EU partners: Politecnico di Torino (coordinator) and CRN (Italy), EMPA (CH), Fraunhofer Institute, MTA and EADS (Germany), NanoForce (UK).
The aim of ADMACOM is to develop innovative manufacturing technologies based on advanced design of interfaces and of joining materials for aerospace components.
The combination of advanced design of interfaces and joining materials/technologies, selective matrix removal from the composite surface, laser structuring and mechanical machining of the composite/metal surface will be exploited, together with a suitable joint design ("brush-like" joining).
The experimental approach of ADMACOM will be focussed on innovative joining of CMC (i.e C/SiC) to Ti- and Nb-based alloys for aerospace applications; the novel manufacturing technologies will be based on a selection among: innovative high temperature metal brazing alloys (i.e. graded high T brazing alloys), Transient Liquid Phase Bonding, Spark Plasma Sintering, two-component powder injection moulding for simultaneous shape forming joining.
This paper will report on the project teams' results at the end of the first year of activity.


CD:P03  Effects of He Irradiation on Glass Ceramics for Nuclear Applications
M. FERRARIS, V. CASALEGNO, S. RIZZO; L. GOZZELINO, R. GERBALDO, G. GHIGO, F. LAVIANO, Dept. of Applied Science and Technology, Politecnico di Torino, Torino, Italy and INFN Sez. Torino, Torino, Italy

Due to their low induced activity from exposure to particle irradiation in harsh environments, SiC/SiC composites are very promising materials for use in fusion reactors. However, a still open problem consists in SiC/SiC joining in order to obtain complex components. Therefore the use of joining materials having radiation hardness comparable to SiC is needed. Glass ceramics such as CaO-Al2O3 (CA), SiO2-Al2O3-Y2O3 (SAY) and SiO2-Al2O3-MgO (SAMg) showed big potentialities as joining materials and their preliminary radiation tests under neutron beam are encouraging. In this framework we checked the radiation hardness of CA, SAY and SAMg ceramics by means of 5.5 MeV He-ions up to fluences able to induce in localized regions of the samples tenths of displacements per atom (dpa), i.e. a damage comparable with that expected for locations in nuclear fusion apparatus where particle/neutron flux of 1E16 - 1E17 n/(m² s) is reached. Advanced morphological investigation through TEM analysis has been performed to correlate the micro/nanostructural changes with the dpa distribution and to detect changes in crystalline and amorphous phases as well as voids or defects induced in the glass-ceramic systems.