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					                 Proceedings of the 12th Conference of the European Ceramic Society – ECerS XII
                                            Stockholm, Sweden - 2011

Evaluation of ceramic/ceramic joint interface prepared via brazing

                                    A. Ghazi Daryani (1) and A. Nemati (1) - ( 2 )
1: Ceramic Research Group, Dept. of Material Science &          2: Exelecence Center of Addvanced Materials, Dept. of
Eng., Sharif University of Technology, Tehran, Iran             Material Science & Eng., Sharif University of Technology
amirmetalsic@yahoo.com                                          Tehran, Iran



Abstract                                                        Some of the applications of these joints in industries
The purpose of this paper was to join two                       are: Air bone, automobile, medical, nuclear,
ceramics with metal fillers (SiC to SiC & Al2O3                 electricity and etc. These joints depend on base
to Al2O3) and to investigate the interface of                   metal and usage of joints. Ceramics and metals can
SiC/SiC and Al2O3/ Al2O3 with the same metal                    join together by direct or indirect mechanical
interlayer (Ag-Cu-Ti) and their effects on the                  methods. The methods with filler metal are indirect
properties. Both joints were performed by                       joints. Brazing lets joint two samples with low cost
brazing method and under constant conditions                    in large size with mixed geometry.
in a furnace with controlled atmosphere. The                    In this investigation, we used brazing method under
properties and characteristics of            the                certain conditions with filler metal (Ag-Cu with Ti-
connections were studied by using mechanical                    6Al-4V).at the end of this test, the properties of this
testing and microscopic evaluation (SEM) and                    connection was surveyed with mechanical test,
and formed phase with XRD along with                            SEM, XRD, line scan…
elemental distribution studies by EDAX. Heat
treatment was performed at different time and                   Experimental Procedure
temperature according to phase diagram to gain                  Sintered Alumina with 99.99% purity (Alumina
the desirable properties. The results showed                    substrate) in 10*10*2 mm dimension is supplied.
that the proper joining of Al2O3/ Al2O3 and                     Also all of samples are glazed for better mechanical
SiC/SiC was obtained applying a metal layer of                  joint and avoid of any oil and pollution. The
Ag-Cu as well as an active metal of Ti-6Al-4V.                  Pressure less sintered α-SiC was supplied by
The second one was used to increase the wet                     ceramic laboratory of Sharif University “used as
ability and proper strength.                                    heating elements- Kanthal furnace The disks shape
Microscopic         investigations      revealed                samples were prepared with 17 mm diameter and
penetration and activation of elements from                     10mm thickness. Ag- Cu (Alloy) foils composed of
interface to the bulk of ceramic body and this                  73.5%Ag-26.5% Cu, with 0.20 mm thickness and
“in turn” was the major reaction in the joints.                 Ti- 6AI-4V with 0.1 mm thickness were joined
Both joints showed the deepest penetration of                   together. The heat treatment curve of the specimens
Ti atoms from interface to ceramics. According                  is shown in figure (1).
to the XRD results, TiC and Ti5Si3 were the
most important phases in the SiC/SiC interface
and TiO2 and V2O5 in the Al2O3/Al2O3
interface. The strength of both joints was
increased till optimum time and temperature
condition and diminished after that by forming
of some phases as TiC in (SiC /SiC) and TiO2
in (Al2O3/Al2O3) which inhibit the formation of
more strong interface. The optimum time and
temperature were suggested to be 900 °C and
90 min for SiC/SiC and 900 °C and 60 min for
Al2O3/Al2O3.

Keywords: Ceramic/Ceramic Joints, Interface,
strength

Introduction
Ceramics joints are applied for producing the
products that should be made in general shape and
dimension for getting more advantages. Also these
joints should be having the good mechanical
properties and failure toughness in high temperature.           Fig. (1): Heat treatment for a) SiC/SiC, b)Al2O3/Al2O3




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                 Proceedings of the 12th Conference of the European Ceramic Society – ECerS XII
                                            Stockholm, Sweden - 2011

Then, they were fixed with a low carbon steel                      Alloys was major in the specimen (900 °C for 2h)
fixture. The environment of furnace protected with                 and it was emphasized that in near temperature
inert gas (Ar). Vanadium in filler metal with                      space, time was more effective.
Oxidation penetrate to Ceramic surface and it causes               The effect of time on these diagrams can be
a joint that resist till 1600 °C .After cooling of                 explained based on density decline of elements in
samples in furnace they are cut in certain shapes and              filler metal and the atomic percent of elements in
send to investigation with other tests. The samples                filler.
were polished with 600, 800, 1200 sizes with
Alumina powder and covered by Au for SEM test
and mechanical tests samples are cut in 1*1cm in 1
mm diameter.

Results and Discussion
The SEM (BE) from the joint zone and EDAX of
that zone are shown in figure (2). For the Alumina
samples, the results was similar.




                                                                              Cu                          Ti




Fig (2): SEM image of zone of filler metal and base metal
                  In SiC/SiC sample
The back scattered electron (BSE) image and
EPMA X-ray image analysis of joint SiC/SiC clearly
revealed the diffusion of Ti, Cu, Ag, and V and then
build up of ceramic-filler alloy and filler alloy-
metal interfaces Figure (3).




                                                                              V                          Ag
         Figure (3)-SEM image of alumina joint
                   (at 900 °C for 1.5 hr)
This indicates the efficacy of indigenously
developed brazing alloy (Ag-Cu-Ti). To survey the
effect of time & temperature on three specimens,
SEM images and line scan images from interface
which indicted the diffusion of Ti is shown in
figures (4 and 5). These figure show that increasing
of time causes to increases of penetration and
distance of penetration of elements in to the
ceramics.
It is clear that after a duration this density decrease
                                                                                           Si
in filler and never and less density of elements
                                                                   Fig.(4). BSE and X-ray maps of SiC/Ag-Cu-Ti/SiC
increase in ceramics. This matter results a better and
stronger joint between filler metal and ceramics. The
results of this comparison is shown that quantity and
diffusion of Ti and other elements in interface



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                 Proceedings of the 12th Conference of the European Ceramic Society – ECerS XII
                                            Stockholm, Sweden - 2011




             Fig.(5).Ti distribution graph
The addition of titanium and formation TiC
considerably improves the wetability of molten
copper on SiC. That is why, copper alloys with high
Ti content could be applicable as a filler metals for
joining SiC. In other words, the Ti diffusion and
buildup at ceramic – filler alloy interfaces, indicates            Fig (6) the effect of time on element dispense of
the efficacy of indigenously developed brazing                                  a)Ag, b)Cu, c)Ti , d) V
alloy (Ag-Cu-Ti) [5].




                      950 C -1 h




                      900 C-2 h


                                                                 Fig. (7): XRD analyses of joint in the Al2O3
                                                                 sample




                     900 C-1.30 h




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                Proceedings of the 12th Conference of the European Ceramic Society – ECerS XII
                                           Stockholm, Sweden - 2011

                                                                the reason for the failure of welding, as it has been
                                                                reported earlier [5].




                                                                Fig. (9): effect of time on shear strength of joint


                                                                Conclusions
                                                                1.        The SiC to SiC joint was conducted using
                                                                Ti-6AI-4V and (Ag 37.5%-Cu 26.5%).
                                                                The results obtained are summarized as follows:
                                                                2. The reaction of filler with ceramic at higher
                                                                temperature and longer time resulted in a joint with
                                                                different strength.
    Fig. (8): XRD pattern of SiC/Ag-Cu-Ti/SiC                   3. The result showed that incearsinge of
                                                                temperatures and time had positive effects on the
preliminary investigation by the X-ray maps analysis            diffusion of Ti from interface towrds the base
(ontained from XRD) revealed thecharacteriztics of              materials.
the interfacial layer elements (figure 6). The diagram          4 . The data indicated that the strength of joints was
(7) shows the phase analysis of joint with XRD .                improved with increasing temperature.
The main peak of XRD was α- Al2O3 . Other phases
were: Mg Al2O4,.Cu Al2O4، Cu2Ti2O5، VO،
Cu3TiO4 and CuAlO2.                                             References
In the SiC sample, preliminary investigation showed             [1]       Kornmann, X.; PhD thesis, “Synthesis and
that the interfacial layer can be expected to comprise          Charactrisation of thermoset – clay Nanocomposites”.
of TiC, Ti Si3, Ti Cu3,Ti SiC2, clearly indicated the           [2]       Basara, C.; Bayram, Goknur.; Yilmazer, U.
presence of these phases. The XRD pattern of this               Synthesis and Characterization Of Epoxy Based
joint is shown in Figure (8).                                   Nanocomposites, Middle East Technical University,
                                                                Chemical Engineering Department, 06531, Ankara,
                                                                Turkey, J. Appl. Polym. Sci., 2005, 98, 1081-1086.
The effect of time on strength:
                                                                [3]       Hoa, Suong.; Liu, W.; Pugh, Martin.
The result of shear strength test of Alumina joint is           Morphology and Performance of Epoxy Nanocomposites
shown in figure (9). The result indicated that                  Modified With Organoclay and Rubber, Concordia Center
increase of time caused more and stronger joints.               For Composites, Department of Mechanical and Industrial
The figure (9) shows the optimum time for                       Engineering, Concordia University, Montreal, Quebec
penetrating and increasing of interface. This is very           H3G1M8, Canada., Macromol. Mater. Eng., 2004, 291,
important to have a strength joint. Finally,                    1358-1366.
penetration rate decreases when t was less than 90              [4]     Shen, L.; Wang, L.; Liu, T.; He, C.
min. But, after that (from 90 min to 120 min) the               Nanoindentation and Morphological Studies of Epoxy
                                                                Nanocomposites, Macromol. Mater. Eng., 2006, 291,
strength was not significently increased.
                                                                1358-1366.
Since the addition of titanium considerably improves            [5]       Deng, Y.; Gu, A.; Fang, Z. The Effect Of
the wetability of molten Cu on SiC, the strength of             Morphology On the Optical Properties of Transparent
joint decrease with increasing temperature and time.            Epoxy/Montmorillonite composites, Institute of Polymer
Beside the presence of TiC may decrease the                     Composites, Zhejiang University, Hangzhou, Zhejiang
mobility of the remaining active components                     310027, china., 2003, 0959-8103.
leading to reduce the opportunity of contact
between SiC ceramic and the active components to
form hard phases as Ti Si53. This, in turn, may be



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