# Patent

## Title
Zr-Ti-Ni (Cu) based brazing filler alloy compositions with lower melting point for the brazing of titanium alloys

## Abstract

Disclosed is Zr—Ti—Ni(Cu)-based filler alloy composition having low melting point for brazing titanium and titanium alloys. The Zr—Ti—Ni(Cu)-based alloy composition is expressed as: ZraTibNic (Formula 1) where a, b and c denote atomic % of Zr, Ti and Ni, respectively; 47≦a≦52; 24≦b≦30; 22≦c≦26; and 0.3<c/(a+c)<0.35, or ZraTibNicCud (Formula 2) where a, b, c and d denote atomic % of Zr, Ti, Ni and Cu respectively; 48≦a≦60; 20≦b≦28; 19≦c+d≦30; 3≦d≦12; and 0.12<d/(c+d)≦0.5. Including Zr(Ti) solid solution phase as its major constituent phase, the alloy compositions of this invention have lower liquidus temperature than those of conventional alloys and they include a little amount of Cu or does not include it at all. When alloy of the present invention is used as filler alloy for brazing titanium and titanium alloys, brazing can be performed at remarkably low temperature. This prevents the microstructure of titanium base metal from changing and being damaged, keeping the titanium base metal preserving inherent properties after brazing.

## Background
TECHNICAL FIELD
The present invention relates to a filler alloy composition for brazing titanium which has a low melting point; and, more particularly, in case of brazing of Ti, Ti alloys or dissimilar materials including titanium or titanium alloy, brazing with this alloy can provide a robust joint body and preserve mechanical properties of titanium base metal after brazing process.
BACKGROUND ART
Many filler alloys have been developed and researched for brazing titanium and titanium alloy. The developed Filler alloys are largely divided into four groups: aluminum (Al)-based filler alloy, silver (Ag)-based filler alloy, titanium (Ti)-based filler alloy, and zirconium (Zr)-based filler alloy. In case of using the Al-based filler alloy and Ag-based filler alloy, a detrimental intermetallic compound phase is formed by reactions between the major elements comprising the filler metals and Ti base alloys in Ti brazed joint area. Thus, they are improper for the formation of a robust Ti joint body which requires heat-resistance, corrosion resistance, strength and reliability. On the contrary, active-element based filler alloys, containing large amount of active elements such as Ti and Zr element have been well known to provide a good Ti brazed joint body having excellent heat-resistance corrosion resistance and strength at room temperature and high temperature. However, since the active element-based filler alloys have relatively high melting points, their brazing temperature can be close to the recrystallization temperature and beta transus temperature of titanium base metals to be joined. So the microstructure of Ti base metal may be altered if the brazing temperature exceeds these restrictive temperatures. Eventually, the change of original microstructure of Ti-based alloy after brazing causes the mechanical properties of base metal to be impaired.
When brazing (α+β) type and β type Ti alloys, there has been actual restriction in selecting a brazing cycle and a filler alloy with a low melting point that can allow heat-treated (α+β) type and β type Ti alloys to braze without changing their heated structure. Theoretically, it is desirable that Ti-based alloy should be brazed at a temperature as lower as from 55 to 83° C. than its beta transus temperature. If Ti alloy is brazed at a temperature higher than the restrictive temperatures, the mechanical properties such as strength and ductility particular in the α+β type and β type Ti alloys heat-treated may be impaired. The damaged mechanical properties of Ti base metals are hard to be recovered without another heat treatment for the brazed assembly. After brazing, the re-heat treatment of brazed part such as quenching may deform the brazed assembly in large size with complicated shape due to the rapid change in the temperature. Therefore, post heat treatment of the brazed assembly after brazing is not preferable to solve this problem.
In order to reduce the impairment of Ti base metal after brazing, using filler alloy with low melting point has been preferable as an effective method. With the active element based filler alloys developed, their brazing temperature has to be set at temperature more than 850° C. This is because a conventional filler alloy having the lowest melting point has a liquidus temperature of approximately 843° C. at Ti-37.5Zr-15Cu-10Ni in wt % (Ti48.5Zr25.7Cu14.8Ni10.6 in atomic %). In case of beryllium (Be) containing active brazing filler alloys such as Zr—Ti—Ni—Be have a liquidus temperature less than 800° C. because Be element is a strong melting point depressant of Ti and Zr. However, the use of Zr—Ti—Ni—Be has been restricted since Be is a hazardous element. Also, another Zr-based filler alloy in free of Be, which is Zr-11Ti-14Ni-13Cu (wt %) (Zr50.3Ti17.0Cu15.1Ni17.6 in atomic %), has a liquidus temperature about at 830° C. Even though its liquidus temperature is lower than that of other Ti-based filler alloys by approximately 20 ̃30° C., but it has a drawback that brazing should be performed at a high temperature more than 900° C.
Also, conventional filler alloys taking an active element, e.g., Ti or Zr, as a base includes copper (Cu) and/or nickel (Ni) more than 14% by atomic ratio as a melting point depressant. Herein, although Cu is effective in drastically dropping the melting point of an alloy in the presence of Ni, it has a shortcoming that it also deteriorates mechanical and chemical properties of the brazing joint body when it is included abundantly. In short, Cu causes a brittle intermetallic compound to be generated easily during a joining process and a process of cooling a joint body.
According to a study by Botztein et al published in Materials Science and Engineering A, Vol. 206, pp. 14-23, 1995, when a Ti alloy is brazed using a Cu—Ti—Zr filler alloy, a brittle λ-Cu2TiZr Lavas phase appears during slow cooling process. To prevent the formation of the brittle phase, it is recommended to limit the Cu concentration in the joint body to go not more than approximately 10 wt % to approximately 12 wt %.
Also, a study by Chang et al published in Journal of Materials Engineering and Performance, Vol. 6(6), pp. 797-803, 1997, reveals that when Ti-6Al-4V is joined at approximately 960° C. using Ti-21Ni-14Cu molten filler in a joint body reacts with an (α+β)-type Ti-based alloy to thereby form a lamellar-type Widmanstatten structure consisting of a Ti2Ni phase and a Ti2Cu phase. Herein, the Ti2Ni phase disappears as Ni component existing on a joint body in the initial state diffuses into the inside of a base metal during a 2-hour-long diffusion process. On the other hand, the Ti2Cu phase still remains on the joint body.
In consequences, the high melting temperature of conventional filler alloys and a high content of Cu have been pointed out as factors degrading durability of a Ti-brazed assembly. Therefore, when Ti alloy is brazed using typical filler alloy, a short brazing cycle is needed in order to protect base metal from being mechanically damaged. To be specific, the Ti alloy should be heated up to quickly reach as high brazing temperature as approximately 850° C. and up, maintained at the brazing temperature for a short time no longer than approximately 15 minutes, and quenched rapidly. The short brazing cycle may be disadvantageous when a metal like Ti having heat conductivity lower than other metals is used for a joint body.
To sum up, it is necessary to limit the amount of Cu added to a filler alloy to a minimum amount in developing new active element-based filler alloy having a low melting point.
DISCLOSURE
Technical Problem
An embodiment of the present invention devised to overcome the above problems is directed to providing a filler alloy composition having a low melting point that can be brazed at a temperature lower than conventional brazing temperature to preserve mechanical properties of a Ti-based metal during a heat cycle and form a robust joint body, when Ti, Ti alloy or dissimilar material joining including Ti or Ti alloy is brazed to be assembled.
Particularly, an embodiment of the present invention is directed to providing a filler alloy composition which does not include an element hazardous to a human body, such as Be, has a melting point much lower than typical active element-based filter alloy so that brazing can be performed at a temperature lower than approximately 800° C., and includes Cu element, which may degrade mechanical and chemical properties of a joint body, within a range of approximately 12 atomic % or does not include Cu at all.
Technical Solution
In accordance with an aspect of the present invention, there is provided a Zr—Ti—Ni ternary alloy composition, expressed as:

ZraTibNic  Formula 1

where a, b and c denote atomic % of Zr, Ti and Ni, respectively; 47≦a≦52; 24≦b≦30; 22≦c≦26; and 0.3<c/(a+c)<0.35.
In accordance with another aspect of the present invention, there is provided a Zr—Ti—Ni—Cu quaternary alloy composition, expressed as:

ZraTibNicCud  Formula 2

where a, b, c and d denote atomic % of Zr, Ti, Ni and Cu respectively; 48≦a≦60; 20≦b≦28; 19≦c+d≦30; 3≦d≦12; and 0.12<d/(c+d) 0.5.
Advantageous Effects
The Zr—Ti—Ni ternary filer alloy compositions have a constituent phase of Zr(Ti) solid solution phase, (Zr,Ti)2Ni phase, and Zr2Ni phase at room temperature after slow solidification, and the filler alloys can have low melting temperature ranging approximately 797° C. to approximately 825° C. upon heating through eutectic reaction between the phases. Also, the Zr—Ti—Ni—Cu quaternary filer alloy compositions have a constituent phase of Zr(Ti) solid solution phase with Cu dissolved therein, (Zr,Ti)2Ni phase with Cu dissolved therein, and Zr2Ni phase with Cu dissolved therein at room temperature, or it may have a constituent phase of Zr(Ti) solid solution phase with Cu dissolved therein, (Zr,Ti)2Ni phase with Cu dissolved therein, and Zr2Cu phase with Ni dissolved therein to thereby have a low melting point not higher than approximately 772° C. to approximately 809° C. Furthermore, the total Cu content in the Zr—Ti—Ni—Cu quaternary filer alloy composition ranges from approximately 3 atomic % to approximately 12 atomic %, and the amount of Cu in the Ni+Cu obtained by aggregating the Ni content and the Cu content does not exceed approximately 50 atomic %. In short, the Ni content is equal to or greater than the Cu content.
Therefore, the filler alloy compositions of the present invention have a lower brazing temperature than those of conventional filler alloys, it can be brazed at a temperature not higher than approximately 800° C. and thus it can minimize the damage on the mechanical properties of Ti-based alloy caused by phase change or grain growth of the Ti-based metal. In short, the use of the filler alloy composition of the present invention having a low melting point can minimize the extent of degradation in the strength of Ti base metal caused by a brazing heat cycle and maximize joining strength.



BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 shows a composition range of a Zr—Ti—Ni ternary alloy composition in accordance with an embodiment of the present invention.
FIG. 2 shows a composition range of a Zr—Ti—Ni—Cu quaternary alloy composition in accordance with an embodiment of the present invention.
FIG. 3 is a ternary phase diagram of Zr—Ti—Ni system at 700° C.
FIG. 4 is a pseudo binary Zr2Ni—Ti2Ni phase diagram.
FIG. 5 is a DTA curve of Zr50Ti26Ni24 alloy composition of Example 6 according to a first Experimental Example during heating and cooling processes.
FIG. 6 is a DTA curve of Zr54Ti22Ni16Cu8 alloy composition of Example 39 according to a third Experimental Example during heating and cooling processes.
FIG. 7 shows scanning electron microscopic (SEM) images showing Zr50Ti26Ni24 alloy composition prepared according to Example 6 and Zr43.9Ti22.8Ni33.3 alloy composition prepared according to Comparative Example 8, respectively, according to Experimental Example 2.
FIG. 8 is a SEM image of Zr54Ti22Ni16Cu8 alloy composition of Example 39 according to Experimental Example 4.
FIG. 9 is a graph showing an X-ray Diffraction (XRD) analysis result of Zr50Ti26Ni24 alloy composition of Example 6 prepared through melt-spinning according to Experimental Example 5.
FIG. 10 is an XRD analysis result of Zr54Ti22Ni16Cu8 alloy composition of Example 39 prepared through melt-spinning according to Experimental Example 5.
FIG. 11 is a graph showing tensile strengths of a base metal and a joint body using an alloy composition according to Experimental Example 6 at room temperature.



BEST MODE FOR THE INVENTION
Zr—Ti—Ni ternary alloy composition of the present invention is expressed as the following Formula 1:

ZraTibNic  Formula 1

where a, b and c denote atomic % of Zr, Ti and Ni respectively; and 47≦a≦52, 24≦b≦30, 22≦c≦26, and 0.3<c/(a+c)<0.35.
FIG. 1 shows a composition range of a Zr—Ti—Ni ternary alloy composition in accordance with an embodiment of the present invention.
Also, Zr—Ti—Ni—Cu quaternary alloy composition of the present invention is expressed as the following Formula 2:

ZraTibNicCud  Formula 2

where a, b, c and d denote atomic % of Zr, Ti, Ni and Cu, respectively; and 48≦a≦60, 20≦b≦28, and 19≦c+d≦30, 3≦d≦12, and 0.12<d/(c+d)≦0.5.
FIG. 2 shows a composition range of a Zr—Ti—Ni—Cu quaternary alloy composition in accordance with an embodiment of the present invention.
As shown in FIGS. 5 and 6, Zr—Ti—Ni ternary composition or Zr—Ti—Ni—Cu quaternary alloy composition of the present invention goes through melting and solidification in a narrow temperature range during heating and cooling. To be specific, the Zr—Ti—Ni ternary alloy composition of the present invention has a solidus temperature lower than approximately 800° C. Specifically, the solidus temperature ranges from approximately 797° C. to approximately 798° C. The liquidus temperature is not higher than approximately 825° C. At the liquidus approximately, melting is completed. Specifically, the liquidus temperature ranges from approximately 809° C. to approximately 825° C. Also, the Zr—Ti—Ni—Cu quaternary alloy of the present invention has a solidus temperature lower than approximately 800° C. Specifically, the solidus temperature ranges from approximately 772° C. to approximately 792° C. The liquidus temperature is not higher than 809° C. Specifically, the liquidus temperature ranges from approximately 783° C. to approximately 809° C. As described above, the ternary and quaternary alloy compositions of the present invention have a narrow melting temperature range and a low melting point.
The low melting point is a characteristic of the Zr—Ti—Ni ternary alloy or Zr—Ti—Ni—Cu quaternary alloy suggested in the present invention and originates from a eutectic reaction among constituent phases constituting the composition.
As shown in FIGS. 3 and 4, when a Zr—Ti—Ni ternary alloy contains Ni in a uniform content of approximately 33.3 at %, the constituent phase in the Zr-rich region includes Zr2Ni phase and (Zr,Ti)2Ni phase, and it is known that there is a pseudo binary eutectic point of Zr2Ni—(Zr,Ti)2Ni of approximately 850° C. based on a eutectic reaction between the two phases.
The present invention in a Zr-based Zr—Ti—Ni alloy limits the Ni content to less than approximately 30 at %, specifically, to approximately 22 at % to approximately 26 at % to thereby form Zr solid solution phase as a new constituent phase other than the two phases. In short, as shown in FIG. 3, the ternary alloy composition range of the present invention is formed in an inverse triangle region including three types of phases: Zr2Ni phase (body-centered tetragonal, bct), (Zr,Ti)2Ni phase (hexagonal close-packed, hcp), and Zr(Ti) solid solution phase (hcp). A eutectic system including the three types of constituent phases comes to have a eutectic temperature lower than the eutectic temperature of the pseudo binary eutectic system and thus it is understood that the ternary alloy composition of the present invention comes to have the lower melting temperature. To be specific, the ternary alloy composition of the present invention can have a low melting temperature ranging from approximately 797° C. to approximately 825° C. through a eutectic reaction of Zr2Ni+(Zr,Ti)2Ni+Zr(Ti)→L during heating. Thus, it is understood that the ternary eutectic system of the present invention appears by reducing the content of Ni by less than approximately 30 at % from the composition of the pseudo binary eutectic system.
The present invention also provides a quaternary alloy composition obtained by adding Cu to the Zr—Ti—Ni ternary alloy as a melting point depressant and limiting the Cu content to approximately 3 at % to 12 at %. The quaternary alloy of the present invention can have solidus and liquidus temperature lower than the ternary alloy composition by substituting part of Ni of the ternary alloy composition with Cu, that is, by adding Cu in an amount less than or equal to the amount of the remaining Ni (Ni content≧Cu content). To be specific, the quaternary alloy composition of the present invention has a melting point as low as approximately 772° C. to approximately 809° C. through a eutectic reaction. The quaternary alloy composition can have a wider composition range including the ternary eutectic points although the liquidus temperature of the quaternary composition is lower than that of the ternary alloy composition.
Furthermore, the alloy composition of the present invention has a characteristic that it tends to easily form glassy phase (amorphous structure) without crystallization. The characteristic is so-called glass forming ability (GFA). Thus, it can be prepared as amorphous foil having a thin film shape through a rapid solidification method, e.g., melt-spinning. The amorphous foil is not fragile, differently from a crystallized structure. Moreover, it is mechanically flexible and its thickness can be controlled as thin as approximately 20 μm to approximately 80 μm. In Ti brazing, the thickness of filler foil controls the supply amount of filler metal, which decides the size of joint clearance. If the joint clearance is greater than a certain size, fragile inter-metal chemical compound is formed at the center of a brazing zone, which may lead to adverse influence on joint integrity. Therefore, it is advantageous to have the alloy composition a glass forming ability and form it in a thin film-shaped amorphous foil.
Hereafter, specific embodiments of the present invention will be described in detail. The following Examples are not restrictive but illustrative only.
EMBODIMENTS
Examples 1 to 12
Zr—Ti—Ni Ternary Alloy
The following Table 1 shows Zr—Ti—Ni ternary alloy compositions prepared according to Examples 1 to 12 and Comparative Examples 1 to 8, constituent phases identified through X-ray diffraction analysis, and solidus temperature and liquidus temperature obtained through differential thermal analysis.











TABLE 1








Composition

Solidus
Liquidus



(at. %)
Constituent Phase
Temperature
Temperature















Examples
Zr
Ti
Ni
Zr2Ni
(Zr,Ti)2Ni
Zr(Ti)
(Ts, ° C.)
(Tl, ° C.)


















Example 1
48
30
22
√
√
√
798
813


Example 2
52
25
23
√
√
√
798
815


Example 3
51
26
23
√
√
√
798
809


Example 4
48
29
23
√
√
√
798
812


Example 5
52
24
24
√
√
√
798
811


Example 6
50
26
24
√
√
√
798
809


Example 7
48
28
24
√
√
√
798
815


Example 8
47
29
24
√
√
√
798
818


Example 9
50
25
25
√
√
√
798
820


Example 10
49
26
25
√
√
√
797
817


Example 11
47
27
26
√
√
√
798
825


Example 12
49
25
26
√
√
√
797
825


Comparative
50
31
19
√
√
√
796
850


Example 1










Comparative
46
33
21
√
√
√
799
845


Example 2










Comparative
55
23
22
√
√
√
798
842


Example 3










Comparative
53
22
25
√
√
√
798
846


Example 4










Comparative
44
29
27
√
√
√
798
847


Example 5










Comparative
45
22
28
√
√
√
798
849


Example 6










Comparative
46
24
30
√
√
√
798
858


Example 7










Comparative 
43.9
22.8
33.3
√
√
—
850
869


Example 8









The ternary alloy compositions of the Examples 1 to 12 showed liquidus temperature not higher than approximately 825° C., specifically, ranging from approximately 809° C. to approximately 825° C. These temperatures are remarkably lower than those of Comparative Examples 1 to 8. The composition having the lowest liquidus temperature among the Examples was Zr50Ti26Ni24 of Example 6.
It should be noted that the Examples 1 to 12 and Comparative Examples 1 to 7 have a solidus temperature ranging from approximately 796° C. to approximately 799° C., except for Comparative Example 8. This implies that their solidus temperature is closely related to the Ni content. In other words, when the Ni content was not more than approximately 30 at %, the solidus temperature of approximately 850° C. dropped drastically to a temperature lower than 800° C. This result proves that the alloy composition of the Comparative Example 8 and the alloy compositions of the Examples 1 to 12 and the Comparative Examples 1 to 7 belong to different eutectic systems.
Since the alloy composition of the Comparative Example 8, whose Ni content is approximately 33.3%, belongs to a pseudo binary Zr2Ni—(Zr,Ti)2Ni eutectic system, which is already known, it has a high solidus temperature of approximately 850° C. Since the alloy compositions of the Examples 1 to 12 and the Comparative Examples 1 to 7 whose Ni content is not more than approximately 30 at % belongs to a pseudo ternary eutectic system of Zr(Ti) solid solution phase, Zr2Ni phase, and (Zr,Ti)2Ni phase, they have a low solidus temperature lower than approximately 800° C.
Experimental Example 1
DTA of Ternary Alloy Composition According to the Present Invention
Differential thermal analysis (DTA) was performed on the Zr50Ti26Ni24 alloy composition of the Example 6 based on heating and cooling cycle and the result was presented in FIG. 5.
FIG. 5 shows that only a single endothermic and exothermic peak appeared in the heating and cooling cycle, respectively, and the temperature difference (ΔT) between the peaks was as narrow as 11° C.
This result showed that the alloy composition of the Example 6 is the deepest eutectic point among the Zr—Ti—Ni ternary alloy compositions of the present invention.
Experimental Example 2
Observation of Microstructures of Ternary Alloy Compositions of the Present Invention and Alloy Compositions of the Comparative Examples and Comparison of their Constituent Phases
Samples were prepared by re-melting the Zr50Ti26Ni24 alloy composition of the Example 6 and Zr43.9Ti22.8Ni33.3 alloy composition, which is an alloy composition at a pseudo eutectic point between a Zr2Ni phase and (Zr,Ti)2Ni phase of Comparative Example 8 illustrated in FIG. 4 re-melted and slowly solidified at a rate of 1° C./min in a vacuum furnace. FIGS. 7 (a) and 7(b) show Scanning Electron Microscope (SEM) images of the microstructure of the acquired samples.
As shown in FIG. 7(a), the alloy composition of the Example 6 has a typical eutectic structure formed of three constituent phases. Also, composition and crystal structure analysis using an X-ray diffraction (XRD) and a Transmission Electron Microscope (TEM) confirmed that the three phases were an α-Zr(Ti) solid solution phase (hcp), Zr2Ni phase (bct), and (Zr,Ti)2Ni phase (hcp) at room temperature.
Meanwhile, as shown in FIG. 7(b), the microstructure of the alloy composition of the Example 8 exhibited a typical eutectic structure formed of two constituent phases. The composition and crystal structure analysis using the XRD analysis of FIG. 4 and a TEM analysis revealed that the two constituent phases were Zr2(Ni) phase (bct) and (Zr,Ti)2Ni phase (hcp).
Examples 13 to 56
Zr—Ti—Ni—Cu Quaternary Alloy
The following Table 2 shows compositions of Zr—Ti—Ni—Cu quaternary alloys prepared according to Examples 13 to 56 of the present invention and Comparative Examples 9 to 24, their constituent phases analyzed through X-ray diffraction, and their solidus temperature and liquidus temperature obtained through differential thermal analysis.















TABLE 2








Composition





Solidus
Liquidus













(at %)
Cu/
Constituent Phase
Temperature
Temperature


















Examples
Zr
Ti
Ni
Cu
(Ni + Cu)
Zr2Ni
(Zr,Ti)2Ni
Zr(Ti)
Zr2Cu
(Ts, ° C.)
(Tl, ° C. )





















Example 13
60
21
13
6
0.31
√
√
√
—
775
800


Example 14
57
24
13
6
0.31
√
√
√
—
774
791


Example 15
56
25
13
6
0.31
√
√
√
—
775
789


Example 16
53
28
13
6
0.31
√
√
√
—
775
800


Example 17
60
20
13
7
0.35
√
√
√
—
773
803


Example 18
59
21
13
7
0.35
√
√
√
—
775
792


Example 19
55
25
13
7
0.35
√
√
√
—
773
785


Example 20
58
21
14
7
0.33
√
√
√
—
775
786


Example 21
54
25
14
7
0.33
√
√
√
—
773
795


Example 22
57
21
14
8
0.36
√
√
√
—
774
785


Example 23
55
23
14
8
0.36
√
√
√
—
772
793


Example 24
53
25
14
8
0.36
√
√
√
—
774
796


Example 25
55
22
20
3
0.13
√
√
√
—
789
798


Example 26
55
22
17
6
0.26
√
√
√
—
776
785


Example 27
55
22
13
10
0.43
√
√
√
—
775
788


Example 28
55
22
15
8
0.34
√
√
√
—
773
785


Example 29
54
23
15
8
0.34
√
√
√
—
774
786


Example 30
55
21
15
9
0.37
√
√
√
—
774
785


Example 31
54
22
15
9
0.37
√
√
√
—
772
787


Example 32
54
22
18
6
0.25
√
√
√
—
778
790


Example 33
54
22
16
8
0.33
√
√
√
—
773
784


Example 34
53
23
15
9
0.37
√
√
√
—
774
787


Example 35
52
24
21
3
0.12
√
√
√
—
788
800


Example 36
50
26
21
3
0.12
√
√
√
—
788
806


Example 37
56
20
16
8
0.33
√
√
√
—
773
805


Example 38
55
21
16
8
0.33
√
√
√
—
774
784


Example 39
54
22
16
8
0.33
√
√
√
—
774
783


Example 40
52
24
16
8
0.33
√
√
√
—
773
793


Example 41
51
25
16 
8
0.33
√
√
√
—
774
797


Example 42
50 
26
16 
8
0.33
√
√
√
—
773
807


Example 43
48 
28
16 
8
0.33
√
√
√
—
773
809


Example 44
54 
22
12 
12
0.50
√
√
√
—
775
802


Example 45
52 
24
12 
12
0.50
√
√
√
—
780
809


Example 46
50 
26
12 
12
0.50
—
√
√
√
792
809


Example 47
48 
28
12 
12
0.50
—
√
√
√
790
808


Example 48
55 
20
16 
9
0.36
√
√
√
—
773
799


Example 49
54 
21
16 
9
0.36
√
√
√
—
774
784


Example 50
54 
21
17
8
0.32
√
√
√
—
774
784


Example 51
53 
22
15 
10
0.40
√
√
√
—
773
796


Example 52
51 
24
15 
10
0.40
√
√
√
—
773
791


Example 53
50 
25
17 
8
0.32
√
√
√
—
774
800


Example 54
52 
20
18 
10
0.35
√
√
√
—
772
794


Example 55
48
22
18 
12
0.26
√
√
√
—
773
808


Example 56
50
20
18
12
0.33
√
√
√
—
773
807


Comparative 
56
27
9
8
0.47
√
√
√
—
775
825


Example 9













Comparative 
63
20
9
8
0.47
√
√
√
—
775
823


Example 10













Comparative 
48
32
12
8
0.40
√
√
√
—
774
830


Example 11













Comparative 
65
15
10
10
0.50
√
√
√
—
790
856


Example 12













Comparative 
58
18
21
3
0.12
√
√
√
—
788
846


Example 13













Comparative 
46
30
21
3
0.12
√
√
√
—
787
828


Example 14













Comparative 
46
30
16
8
0.33
√
√
√
—
774
819


Example 15













Comparative 
58
18
12 
12
0.50
√
√
√
—
775
837


Example 16













Comparative 
58
18
8
16
0.66
√
√
√
—
782
872


Example 17













Comparative 
52
24
8
16
0.66
—
√
√
√
797
849


Example 18













Comparative 
48
28
8
16
0.66
—
√
√
√
803
830


Example 19













Comparative 
60
15
15
10
0.40
√
√
√
—
771
828


Example 20













Comparative
46
25
21
8
0.27
√
√
√
—
773
825


Example 21













Comparative
55
15
20
10
0.33
√
√
√
—
772
853


Example 22













Comparative
45
22
18
15
0.44
√
√
—
√
800
840


Example 23













Comparative
50
16.5
18.5
15
0.46
√
√
—
√
799
819


Example 24









The Zr—Ti—Ni—Cu quaternary alloy compositions of the present invention prepared according to the Examples 13 to 56 had a liquidus temperature under approximately 809° C. ranging from approximately 783° C. to approximately 809° C., which is considerably lower than those of the alloy compositions prepared according to the Comparative Examples 9 to 24. Among the alloy compositions of the Examples, Zr54Ti22Ni16Cu8 alloy of the Example 39 showed the lowest liquidus temperature, which was 783° C.
Referring to the Table 2 and the following Experimental Example 4, the quaternary alloys of the present invention were acquired by solidly dissolving Cu in the ternary alloy compositions of the present invention. Thus, it can be seen that the quaternary alloys includes a constituent phase of Zr(Ti) solid solution phase (hcp) with Cu dissolved therein, Zr2Ni phase (bct) with Cu dissolved therein, and (Zr,Ti)2Ni phase (hcp) with Cu dissolved therein, or a constituent phase of Zr(Ti) solid solution phase (hcp) with Cu dissolved therein, Zr2Cu phase (bct) with Ni dissolved therein, and (Zr,Ti)2Ni phase (hcp) with Cu dissolved therein.
A study, entitled “Non-Crystalline Solids,” Vol. 250-252, 1999, pp. 560-565, reports that Zr50Ti16.5Ni18.5Cu15 alloy composition of Comparative Example 24 has three constituent phases: Zr2Ni (bct), (Zr,Ti)2Ni (hcp), and Zr2Cu (bct). The alloy composition of the Comparative Example 24 has a significant difference from the alloy compositions of the present invention in that it does not include Zr(Ti) solid solution phase. When the total amount of Ni and Cu (Ni+Cu) is not more than approximately 30 at %, the quaternary alloy compositions of the present invention and the alloy compositions of the Comparative Examples included Zr(Ti) solid solution phase as their constituent phase. Therefore, when the value obtained by summing the Ni content and the Cu content exceeds 30 at % as shown in the Comparative Examples 23 and 24, the constituent phase did not include Zr(Ti) solid solution phase. Thus their solidus temperature and liquidus temperature were decided to be high. When the ternary alloy compositions of the present invention including Ni not more than approximately 30 at %, a new type of eutectic alloy including the Zr(Ti) solid solution phase is formed, which leads to descending solidus temperature and liquidus temperature.
To be specific, referring to the Table 2, the constituent phases of the quaternary alloy compositions prepared according to the present invention included
Zr(Ti) solid solution phase (hcp) with Cu dissolved therein, Zr2Ni phase (bct) with Cu dissolved therein, and (Zr,Ti)2Ni phase (hcp) with Cu dissolved therein, or they included Zr(Ti) solid solution phase (hcp) with Cu dissolved therein, Zr2Ni phase (bct) with Ni dissolved therein, and (Zr,Ti)2Ni phase (hcp) with Cu dissolved therein. In short, the quaternary alloy compositions of the present invention are considered to have low solidus temperature not higher than approximately 792° C. due to the presence of Zr(Ti) solid solution and dissolution of Cu in each constituent phase. This solidus temperature is more than 8° C. lower than those of the Comparative Examples 23 and 24, which are as high as approximately 800° C.
Meanwhile, as the content of Cu in the Examples 46 and 47 is higher than those of the other examples, this results in the formation of the Zr2Cu (bct), raising the solidus temperature somewhat higher than the compositions of the other Examples. Since the alloy compositions of the Examples 46 and 47 also included the Zr(Ti) solid solution phase, just as the other Examples do, it can be seen that they have relatively lower solidus and liquidus temperatures than those of the Comparative Examples. When the content of Cu exceeded approximately 12 at %, the liquidus was increased drastically, which is shown in the Comparative Examples 17 to 19, 23 and 24.
Experimental Example 3
DTA of Quaternary Alloy Compositions According to the Present Invention
Differential thermal analysis was carried out to the Zr54Ti22Ni16Cu8 of the Example 39 according to heating and cooling. The result was as shown in FIG. 6.
FIG. 6 shows that only a single endothermic and exothermic peak appeared in the heating curve and the cooling curve, respectively, and the temperature difference (ΔT) between the peaks was as narrow as 9° C. This result shows that the alloy composition of the Example 39 had the deepest eutectic point among the Zr—Ti—Ni—Cu quaternary alloy compositions prepared according to the present invention.
Experimental Example 4
Observation of Microstructure of Quaternary Alloy Compositions of the Present Invention and Comparison of Constituent Phases
The Zr54Ti22Ni16Cu8 alloy composition of the Example 39 was re-melted at a temperature over its melting point in vacuum and slowly solidified at a rate of 1° C./min to thereby produce a sample. FIG. 8 shows Scanning Electron Microscophic (SEM) images of the sample.
As shown in FIG. 8, the alloy composition of the Example 39 had a typical eutectic structure including three constituent phases. Composition and crystalline structure analysis through XRD and TEM revealed that the three constituent phases were Zr(Ti) solid solution phase (hcp) including Cu dissolved therein, Zr2Ni phase (bct) with Cu dissolved therein, and (Zr,Ti)2Ni phase (hcp) with Cu dissolved therein at room temperature. The three constituent phases included Cu up to its solubility limit, and there was no change in the type of constituent phases in comparison with ternary alloy composition of the present invention.
Experimental Example 5
XRD Analysis of Ternary and Quaternary Alloy Compositions Prepared Through Melt-Spinning According to the Present Invention
XRD analysis was performed onto samples prepared by melt-spinning ternary and quaternary alloy compositions of the present invention in the form of foil. The results were presented in FIGS. 9 and 10, respectively. FIGS. 9 and 10 showed that the ternary and quaternary alloy compositions of the present invention had a glass forming ability that was proved by diffuse hallow pattern from XRD analysis due to their amorphous structure, and they were easily formed into amorphous foil through the melt-spinning.
Experimental Example 6
Tensile Strength Test at Room Temperature Based on Brazing Heat Cycle of Joint Body Using Alloy Composition of the Present Invention as Filler Alloy
A joint body was manufactured using Ti-6Al-4V having strength of approximately 1040 MPa as base metal and the Zr54Ti22Ni16Cu8 alloy composition of the Example 39 as filler alloy and brazing them at a joining temperature of approximately 800° C. to approximately 950° C. for 60 minutes. Also, tensile strengths of the base metal (Ti-6Al-4V) without joint were tested at room temperature after exposing only the base metal to the same brazing heat cycle.
The tensile strengths of the joint body and the base metal at room temperature obtained from the test are presented in FIG. 11. In FIG. 11, the tensile strength of the base metal is the maximum tensile strength and the tensile strength of the joint body is rupture strength. FIG. 11 shows that the higher the heat cycle temperature becomes, the lower the maximum tensile strength of the base metal grows. Thus, the tensile strength of the joint body is decreased, too. The tensile rupture of the joint body occurred at a joint under all joining conditions. According to the test result, when the brazing temperature was high, the strength of the base metal was decreased and the joining strength became low, too. The joint strength of the joint body brazed at approximately 800° C., which is the lowest temperature, is 965 MPa, which is the closest to the strength (1040 MPa) of the base metal before the thermal exposure.
Consequently, the present invention lowers the brazing temperature to approximately 800° C. by using a filler alloy having a low melting point, minimizes a decrease in the mechanical properties of Ti base metal and maximizes the mechanical characteristic of the joint body from the brazing heat cycle.

## Claims

1. A Zr—Ti—Ni—Cu quaternary alloy composition, expressed as:


ZraTibNicCud  Formula 2

where a, b, c and d denote atomic % of Zr, Ti, Ni and Cu respectively; 48≦a≦60; 20≦b≦28; 19≦c+d≦30; 3≦d≦12; and 0.12≦d/(c+d)≦0.5,
wherein constituent phase of the alloy composition at room temperature includes three phases, which are Zr2Ni phase with Cu dissolved therein, (Zr,Ti)2Ni phase with Cu dissolved therein, and Zr(Ti) solid solution phase with Cu dissolved therein, or which are Zr2Cu phase with Ni dissolved therein, (Zr,Ti)2Ni phase with Cu dissolved therein, and Zr(Ti) solid solution phase with Cu dissolved therein.

2. The Zr—Ti—Ni—Cu quaternary alloy composition of claim 1, wherein liquidus temperature of the alloy composition ranges from approximately 783° C. to approximately 809° C.

3. The Zr—Ti—Ni—Cu quaternary alloy composition of claim 1, wherein solidus temperature of the alloy composition ranges from approximately 772° C. to approximately 792° C.