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Joining mechanism of ceramics to metals using an amorphous titaniu-based filler metal
Materials Science and Engineering, 98(1988) 407 410
407
Joining Mechanism of Ceramics to Metals Using an Amorphous Titanium-based Filler Metal* MASAAKI NAKA. IKUO OKAMOTO and YOSHIAKI ARATA
V~'elding Research Institute (~/Osaka University. I 1-1 Mihoga-Oka, Ibaraki, Osaka 567 (Japan)
Abstract
Because o f their flexibili O' and homogeneous structure, amorphous titanium-based fillers show ease and high reliabili O' in .joining ceramics to ceramics or ceramics to metals. The .joining o f alumina to alumina, silicon nitride to silicon nitride, silicon carbide to silicon carbide, and alumina to copper, silicon nitride or silicon carbide to metal or alloy (copper, iron, stainless steel, Invar, Super lnvar) were conducted using amorphous Culo, ,.Ti, (x = 34~57) and Ni24.sTi75 5 .fillers under cacuum conditions. At the interface between alumina and the filler, titanium oxide and an alumina solid solution containing titanium are ,formed. At Si3N 4 alloy .joint, TiN and Ti~Si 3 are Jormed at the interface between Sign o and C u - T i filler. 1. Introduction
The poor malleability of ceramics, resulting from their brittleness and hardness, necessitates the development of materials for joining ceramics to metals to produce large complex parts. Brunner et al. [ 1, 2] have reported the application of amorphous titaniumbased filler metals for joining ceramics to metals. Although this method utilizes the flexibility and compositional uniformity of amorphous fillers, the joining mechanism and actual application are still not clear in detail. The work reported in this paper also applies the amorphous titanium-based fillers to join ceramics to metals, and clarifies the joining mechanism. 2. Experimental details
Strips of Cu66Ti34, CusoTiso, Cu43Ti57 and Ni245TiT~5 (compositions given in atomic per cent) 1 cm wide and 45 Ftm thick, are produced by rapid quenching of the liquid. Ductile amorphous fillers with a high titanium content can be bent to the en-
*Paper presented at the Sixth International Conference on Rapidly Quenched Metals, Montr6al, August 3 7, 1987. 0025-5416/88/$3.50
counter side and cut to the desired size. This simplifies the joining process. The ceramics used are alumina, pressureless-sintered Si3N4 and SiC, and reactionsintered SiC containing 13 wt.% Si in free form. The metals and alloys used are copper, iron, Invar, Super Invar, Kovar and SUS304 stainless steel. Ceramics of diameter 15 mm and thickness 3 mm, and ceramics, metals or alloys of diameter 6 mm and 3 mm thick were used to make a lap joint using amorphous fillers of diameter 6 mm and thickness 45/~m which were inserted between the ceramic and the metal. Brazing of the ceramic was conducted in a vacuum of 1.33 mPa. The joining strength of the lap joint was determined by fracture shear loading using a cross-head speed of 1.67 x 10 2 mm s L The microstructures were examined using a scanning electron microscope and microanalyser, and an X-ray diffractometer with Cu Kzt X-rays. 3. Results and discussion
Figure l shows the joining temperature dependence of Si3N4-Si3N 4 joints brazed for 1.8 ks using Cu Ti amorphous fillers. The joining strength of joints brazed with copper-rich Cu66Ti34 is higher than that of joints brazed with CusoTis0 and Cu4~Ti~7 fillers at all brazing temperatures except 1237 K. Reactionsintered SiC pieces can also be jointed to each other using Ni24 sTi75 5 fillers at brazing temperatures above 1473 K for a brazing time of 1.8 ks. The maximum strength of the SiC-SiC joint is 50 MPa at a brazing temperature of 1523 K. The inherent brittleness of ceramics requires the joining of ceramics to metals in practical applications. Figure 2 shows that the brazing of AI203 to copper can be achieved using amorphous Cu Ti fillers. Si3N4 exhibits superior mechanical properties to those of A1203. Si3N4 possesses a low expansion coefficient of c~ = 3 . 7 x 10 S K ~, compared with :~=8.1 x 10 6K ~ for Al20~. This leads to difficulties in joining Si3N4 to metals. However, the use of Super lnvar alloy, which has a thermal expansion coefficient of 1.3 x 10 6 K ~, gives high strength ~' Elsevier Sequoia/Printed in The Netherlands
408
L
'
_300r ~--
/o~
/ /
'~q ~20o u~
o
~
'
' O SbN~-Cu66]q34-Si3N4 o Si3N~- Cu~Ti~o-S~:: ~' Si3N,- Cu,3Ti~-SigN, Brazing time: 18 k~
~ ~
/ ~
o
-- o
/
,
200
<>"
tO k,.
Si3N4/Metal
t
Super [nvar
~Fe
3 100
J:
u ql
¢~ 10C
0
,
1250
,
,
1300 1350 Brazing temperature
~-------~.
1400 ( K)
1450
~.
k.. "1 u
[nvar
Fig. I. Brazing temperature dependence of joining strength for Si3N4-Si3Na joints using amorphous Cu Ti fillers for a brazing time of 1.8 ks. Si3N4-metal and Si3N4-alloy joints as shown in Fig. 3. Another method of joining ceramics to metals is by metallizing ceramics using amorphous fillers. Pressureless-sintered Si3N 4 and SiC are first metallized at 1373 K for 1.8 ks and then brazed with silver filler to steel at 1053 K for 180 s after the metallized ceramics have been nickel plated; the strength of the resultant joints is 50 MPa. The surface of alumina revealed with concentrated hydrochloric acid was analysed by X-ray photoelectron spectrometry. The spectra of Ti 2p3/2 and Ti 2p]/2 correspond to that of TiO2, and the observed binding energy of O ls (531.20 eV) is slightly lower than that for A 1203 (531.55 eV). These results indicate that titanium in the Cu-Ti filler reacts with A120 3 to form the intermediate phases of TiO2 and an alumina solid solution containing titanium. The joining of the copper material and Cu-Ti filler takes place by the isothermal solidification process. Copper first dissolves into the filler, and then the copper-rich solid solution contain-
Kovar
0
I
'
'
10 o(
9n
(xi0-6 K-)
Fig. 3. Fracture shear stress of Si3N4-metal or Si3N4-alloyand Si3Ni-oxide ceramic plotted against the thermal expansion coefficient of the material. ing titanium precipitates from the filler, as shown in Fig. 4. Titanium in Cu-Ti filler reacts with Si3N4 and forms TiN and TisSi3 by the following reactions: Si3N4(s ) + 4Ti(1) = 4TiN(s) + 3Si(s) AG=-639
(1)
+ 0.652T kJ mol ~
Si3N4(s ) -I- 9Ti(1) = 4TiN(s) + TisSi3(s )
(2)
AG = - 130.9 + 0.152T kJ mol 1 The microstructure and line analysis of copper in Fig. 5, and the line analyses of nitrogen, titanium and silicon in Fig. 6 for the joining layer brazed at 1373 K for 1.8 ks demonstrate that TiN is formed at the interface
i
150
Q.
f / ~
zx
~100
CulC.uTi/AI203 Brazing time 1~ KS
5O u LL N
2so
'
'
i i 13b0 i Brazing temperature
n : Cuz.3Ti57 o : CusoTiso Cu66Tix i L i
1350
K
Fig. 2. Brazing temperature dependence of joining strength for AI203~Cu joints using amorphous Cu-Ti fillers for a brazing time of 1.8 ks.
Fig. 4. Line analyses of titanium and copper across the joint interface for a Cu A1203 joint brazed with C%oTiso filler at 1323 K for 1.8 ks.
409 I
I
3.0 E :a. ;4 2.0 x V
o\
E
Fig. 5. Micrograph and line analyses of copper across an Si3N 4 Si)N 4 .joint brazed with CusoTis. filler at 1373 K for 1.8 ks.
between Sign 4 and Cu Ti filler. The growth of TiN at the joint interface is governed by Fick's law as shown in Fig. 7, where X and T are the thickness of TiN and the brazing temperature respectively. The activation energy Q of 206.3 kJ mol ~ obtained from the slope in the plot is comparable with that for diffusion of nitrogen in TiN ( Q = 2 1 7 . 6 k J m o l ~); in other words, the growth of TiN formed during brazing Si3N 4 is governed by the diffusion of nitrogen into TiN. The joining strength of ceramic-ceramic or ceramic metal joints at elevated temperatures is shown in Fig. 8. The Al203-Kovar joint [3] exhibits a higher strength than the AI203-Cu joint since Kovar alloy has almost the same thermal expansion coefficient ( ~ = 6 x 10 ~ K ]) as A]203 ( ~ = 8 . 1 x 10 6 K l).
1.0
O
I
I
7.0
I
7.5 IO'IT ( K-' )
8.0
Fig. 7. Relationship between the thickness X of a TiN layer and the brazing temperature T for an Si3N 4 Si:~N4 joint brazed for 1.8 ks.
I
~
!
I
200
I
.
I
!
s~J%%
A[203/AI203
Si3N4-CusoTiso- SIGN4 1273K, 18ks
J.I
,I LI
m
E
Ti J¢ t
S~
iI
@
E
0;00
1 6gm L _ _ J
;'
I
--
Si-~N~
"I
Fill ....
~ ,~,~' ,,
2'
>
~ ~k~,
' 5(k) ' 760 ' 9~ Testing temperature (K)
Fig. 8. Joining strength of ceramic-ceramic or ceramic-metal joints brazed with amorphous Cu Ti filler at elevated temperatures.
I ta(
l~
S i t N , , - - - -
Fig. 6. Line analyses of nitrogen, titanium and silicon across an Si3N 4 SigN 4 joint brazed with CusoTiso filler at 1373 K for 1.8 ks.
The distribution of TiN and TisSi~ in the filler is attributable to the maintenance of the strength up to 973 K.
410 4. Conclusion The joining of ceramics to metals using amorphous Cu Ti and Ni-Ti filler metals was carried out under vacuum conditions. The ductility and compositional uniformity of the amorphous filler led to an easy joining process and to reliability of the joints. Titanium in the fillers reacts with the ceramics and forms the intermediate phases TiO2 and A1203 containing titanium during the brazing of A1203 with Cu-Ti filler, and the phases TiN and TisSi3 during the brazing of Si3N4 with Cu-Ti filler. The use of Super Invar or Kovar alloy, which possess the low thermal expan-
sion coefficients, leads to high strength ceramicsmetal joints.
References 1 K. Brunner, M. Fischer and R. S. Perkins, Proc. Int. Conf. on Joining of Ceramics, Glass and Metals, Deutscher Verband fiir Schweiss., 1980, p. 37. 2 M. Fisher, R. S. Perkins and K. Brunner, 84th Ann. Meet. American Chemical Society, 1982.
3 M. Naka, K. Sampath, I. Okamoto and Y. Arata, in M. M. Schwartz (ed.), Engineering Applications of Ceramic of Materials, American Society for Metals, Metals Park, OH, 1985, p. 205.
407
Joining Mechanism of Ceramics to Metals Using an Amorphous Titanium-based Filler Metal* MASAAKI NAKA. IKUO OKAMOTO and YOSHIAKI ARATA
V~'elding Research Institute (~/Osaka University. I 1-1 Mihoga-Oka, Ibaraki, Osaka 567 (Japan)
Abstract
Because o f their flexibili O' and homogeneous structure, amorphous titanium-based fillers show ease and high reliabili O' in .joining ceramics to ceramics or ceramics to metals. The .joining o f alumina to alumina, silicon nitride to silicon nitride, silicon carbide to silicon carbide, and alumina to copper, silicon nitride or silicon carbide to metal or alloy (copper, iron, stainless steel, Invar, Super lnvar) were conducted using amorphous Culo, ,.Ti, (x = 34~57) and Ni24.sTi75 5 .fillers under cacuum conditions. At the interface between alumina and the filler, titanium oxide and an alumina solid solution containing titanium are ,formed. At Si3N 4 alloy .joint, TiN and Ti~Si 3 are Jormed at the interface between Sign o and C u - T i filler. 1. Introduction
The poor malleability of ceramics, resulting from their brittleness and hardness, necessitates the development of materials for joining ceramics to metals to produce large complex parts. Brunner et al. [ 1, 2] have reported the application of amorphous titaniumbased filler metals for joining ceramics to metals. Although this method utilizes the flexibility and compositional uniformity of amorphous fillers, the joining mechanism and actual application are still not clear in detail. The work reported in this paper also applies the amorphous titanium-based fillers to join ceramics to metals, and clarifies the joining mechanism. 2. Experimental details
Strips of Cu66Ti34, CusoTiso, Cu43Ti57 and Ni245TiT~5 (compositions given in atomic per cent) 1 cm wide and 45 Ftm thick, are produced by rapid quenching of the liquid. Ductile amorphous fillers with a high titanium content can be bent to the en-
*Paper presented at the Sixth International Conference on Rapidly Quenched Metals, Montr6al, August 3 7, 1987. 0025-5416/88/$3.50
counter side and cut to the desired size. This simplifies the joining process. The ceramics used are alumina, pressureless-sintered Si3N4 and SiC, and reactionsintered SiC containing 13 wt.% Si in free form. The metals and alloys used are copper, iron, Invar, Super Invar, Kovar and SUS304 stainless steel. Ceramics of diameter 15 mm and thickness 3 mm, and ceramics, metals or alloys of diameter 6 mm and 3 mm thick were used to make a lap joint using amorphous fillers of diameter 6 mm and thickness 45/~m which were inserted between the ceramic and the metal. Brazing of the ceramic was conducted in a vacuum of 1.33 mPa. The joining strength of the lap joint was determined by fracture shear loading using a cross-head speed of 1.67 x 10 2 mm s L The microstructures were examined using a scanning electron microscope and microanalyser, and an X-ray diffractometer with Cu Kzt X-rays. 3. Results and discussion
Figure l shows the joining temperature dependence of Si3N4-Si3N 4 joints brazed for 1.8 ks using Cu Ti amorphous fillers. The joining strength of joints brazed with copper-rich Cu66Ti34 is higher than that of joints brazed with CusoTis0 and Cu4~Ti~7 fillers at all brazing temperatures except 1237 K. Reactionsintered SiC pieces can also be jointed to each other using Ni24 sTi75 5 fillers at brazing temperatures above 1473 K for a brazing time of 1.8 ks. The maximum strength of the SiC-SiC joint is 50 MPa at a brazing temperature of 1523 K. The inherent brittleness of ceramics requires the joining of ceramics to metals in practical applications. Figure 2 shows that the brazing of AI203 to copper can be achieved using amorphous Cu Ti fillers. Si3N4 exhibits superior mechanical properties to those of A1203. Si3N4 possesses a low expansion coefficient of c~ = 3 . 7 x 10 S K ~, compared with :~=8.1 x 10 6K ~ for Al20~. This leads to difficulties in joining Si3N4 to metals. However, the use of Super lnvar alloy, which has a thermal expansion coefficient of 1.3 x 10 6 K ~, gives high strength ~' Elsevier Sequoia/Printed in The Netherlands
408
L
'
_300r ~--
/o~
/ /
'~q ~20o u~
o
~
'
' O SbN~-Cu66]q34-Si3N4 o Si3N~- Cu~Ti~o-S~:: ~' Si3N,- Cu,3Ti~-SigN, Brazing time: 18 k~
~ ~
/ ~
o
-- o
/
,
200
<>"
tO k,.
Si3N4/Metal
t
Super [nvar
~Fe
3 100
J:
u ql
¢~ 10C
0
,
1250
,
,
1300 1350 Brazing temperature
~-------~.
1400 ( K)
1450
~.
k.. "1 u
[nvar
Fig. I. Brazing temperature dependence of joining strength for Si3N4-Si3Na joints using amorphous Cu Ti fillers for a brazing time of 1.8 ks. Si3N4-metal and Si3N4-alloy joints as shown in Fig. 3. Another method of joining ceramics to metals is by metallizing ceramics using amorphous fillers. Pressureless-sintered Si3N 4 and SiC are first metallized at 1373 K for 1.8 ks and then brazed with silver filler to steel at 1053 K for 180 s after the metallized ceramics have been nickel plated; the strength of the resultant joints is 50 MPa. The surface of alumina revealed with concentrated hydrochloric acid was analysed by X-ray photoelectron spectrometry. The spectra of Ti 2p3/2 and Ti 2p]/2 correspond to that of TiO2, and the observed binding energy of O ls (531.20 eV) is slightly lower than that for A 1203 (531.55 eV). These results indicate that titanium in the Cu-Ti filler reacts with A120 3 to form the intermediate phases of TiO2 and an alumina solid solution containing titanium. The joining of the copper material and Cu-Ti filler takes place by the isothermal solidification process. Copper first dissolves into the filler, and then the copper-rich solid solution contain-
Kovar
0
I
'
'
10 o(
9n
(xi0-6 K-)
Fig. 3. Fracture shear stress of Si3N4-metal or Si3N4-alloyand Si3Ni-oxide ceramic plotted against the thermal expansion coefficient of the material. ing titanium precipitates from the filler, as shown in Fig. 4. Titanium in Cu-Ti filler reacts with Si3N4 and forms TiN and TisSi3 by the following reactions: Si3N4(s ) + 4Ti(1) = 4TiN(s) + 3Si(s) AG=-639
(1)
+ 0.652T kJ mol ~
Si3N4(s ) -I- 9Ti(1) = 4TiN(s) + TisSi3(s )
(2)
AG = - 130.9 + 0.152T kJ mol 1 The microstructure and line analysis of copper in Fig. 5, and the line analyses of nitrogen, titanium and silicon in Fig. 6 for the joining layer brazed at 1373 K for 1.8 ks demonstrate that TiN is formed at the interface
i
150
Q.
f / ~
zx
~100
CulC.uTi/AI203 Brazing time 1~ KS
5O u LL N
2so
'
'
i i 13b0 i Brazing temperature
n : Cuz.3Ti57 o : CusoTiso Cu66Tix i L i
1350
K
Fig. 2. Brazing temperature dependence of joining strength for AI203~Cu joints using amorphous Cu-Ti fillers for a brazing time of 1.8 ks.
Fig. 4. Line analyses of titanium and copper across the joint interface for a Cu A1203 joint brazed with C%oTiso filler at 1323 K for 1.8 ks.
409 I
I
3.0 E :a. ;4 2.0 x V
o\
E
Fig. 5. Micrograph and line analyses of copper across an Si3N 4 Si)N 4 .joint brazed with CusoTis. filler at 1373 K for 1.8 ks.
between Sign 4 and Cu Ti filler. The growth of TiN at the joint interface is governed by Fick's law as shown in Fig. 7, where X and T are the thickness of TiN and the brazing temperature respectively. The activation energy Q of 206.3 kJ mol ~ obtained from the slope in the plot is comparable with that for diffusion of nitrogen in TiN ( Q = 2 1 7 . 6 k J m o l ~); in other words, the growth of TiN formed during brazing Si3N 4 is governed by the diffusion of nitrogen into TiN. The joining strength of ceramic-ceramic or ceramic metal joints at elevated temperatures is shown in Fig. 8. The Al203-Kovar joint [3] exhibits a higher strength than the AI203-Cu joint since Kovar alloy has almost the same thermal expansion coefficient ( ~ = 6 x 10 ~ K ]) as A]203 ( ~ = 8 . 1 x 10 6 K l).
1.0
O
I
I
7.0
I
7.5 IO'IT ( K-' )
8.0
Fig. 7. Relationship between the thickness X of a TiN layer and the brazing temperature T for an Si3N 4 Si:~N4 joint brazed for 1.8 ks.
I
~
!
I
200
I
.
I
!
s~J%%
A[203/AI203
Si3N4-CusoTiso- SIGN4 1273K, 18ks
J.I
,I LI
m
E
Ti J¢ t
S~
iI
@
E
0;00
1 6gm L _ _ J
;'
I
--
Si-~N~
"I
Fill ....
~ ,~,~' ,,
2'
>
~ ~k~,
' 5(k) ' 760 ' 9~ Testing temperature (K)
Fig. 8. Joining strength of ceramic-ceramic or ceramic-metal joints brazed with amorphous Cu Ti filler at elevated temperatures.
I ta(
l~
S i t N , , - - - -
Fig. 6. Line analyses of nitrogen, titanium and silicon across an Si3N 4 SigN 4 joint brazed with CusoTiso filler at 1373 K for 1.8 ks.
The distribution of TiN and TisSi~ in the filler is attributable to the maintenance of the strength up to 973 K.
410 4. Conclusion The joining of ceramics to metals using amorphous Cu Ti and Ni-Ti filler metals was carried out under vacuum conditions. The ductility and compositional uniformity of the amorphous filler led to an easy joining process and to reliability of the joints. Titanium in the fillers reacts with the ceramics and forms the intermediate phases TiO2 and A1203 containing titanium during the brazing of A1203 with Cu-Ti filler, and the phases TiN and TisSi3 during the brazing of Si3N4 with Cu-Ti filler. The use of Super Invar or Kovar alloy, which possess the low thermal expan-
sion coefficients, leads to high strength ceramicsmetal joints.
References 1 K. Brunner, M. Fischer and R. S. Perkins, Proc. Int. Conf. on Joining of Ceramics, Glass and Metals, Deutscher Verband fiir Schweiss., 1980, p. 37. 2 M. Fisher, R. S. Perkins and K. Brunner, 84th Ann. Meet. American Chemical Society, 1982.
3 M. Naka, K. Sampath, I. Okamoto and Y. Arata, in M. M. Schwartz (ed.), Engineering Applications of Ceramic of Materials, American Society for Metals, Metals Park, OH, 1985, p. 205.