GB2116212A

GB2116212A - Nickel-based soldering alloys

Info

Publication number: GB2116212A
Application number: GB08306462A
Authority: GB
Inventors: Kisuke Watanabe
Original assignee: Citizen Watch Co Ltd
Current assignee: Citizen Watch Co Ltd
Priority date: 1982-03-10
Filing date: 1983-03-09
Publication date: 1983-09-21
Also published as: HK43386A; DE3306330A1; GB2116212B; GB8306462D0

Abstract

A soldering alloy composition suitable for soldering ornamental metal articles made of a stainless steel, nickel-based heat-resistant or corrosion-resistant alloy and the like is disclosed. The soldering alloy is basically composed of at least 55% by weight of nickel, from 25 to 40% by weight of tin and from 0.5 to 10% by weight of chromium and is advantageous with the same color tone as stainless steels and high corrosion resistance and mechanical strength. The above mentioned advantages can be further increased by the addition of up to 6% by weight of one or more of auxiliary additive elements selected from the group consisting of beryllium, boron, silicon, phosphorus, titanium, vanadium, manganese, iron, germanium, niobium, molybdenum, palladium, indium, tantalum and tungsten.

Description

SPECIFICATION Nickel-based soldering alloys The present invention relates to a novel nickel-based soldering alloy usable for bonding ornamental or other articles such as watch cases and straps made of a corrosion-resistant metal or alloy including stainless steels and nickel-based alloys.

As is known, soldering of metal articles made of a corrosion-resistant alloy such as a stainless steel, nickel-based alloy and the like is performed usually by use of a soldering alloy of which the principal component is silver, gold or nickel.

The main components of the silver-based soldering alloys are silver and copper with addition of small amounts of zinc, cadmium and the like elements in order to improve the melt flowability of the solder along with decreasing of the melting point. By virtue of the decreased melting point of the silver based soldering alloys, the soldering works therewith can be performed at a relatively low temperature of 650 to 8000C either by torch soldering or in-furnace soldering so that silver-based soldering alloys are widely used in general purposes.

Silver-based soldering alloys are, however, not suitable for use in the soldering works of ornamental metal articles such as watch cases and straps because of the readiness to blackening of the surface due to the reaction of the silver as one of the main components thereof with the sulfide pollutants in the atmospheric air to form silver sulfide in addition to the discoloration by corrosion due to the relatively rapid oxidation of zinc and cadmium as the additive elements.

Gold-based soldering alloys are composed mainly of gold, silver, copper and nickel. Needless to say, the corrosion resistance of a gold-based alloy is higher as the content of gold therein is higher so that the gold content of the gold-based soldering alloys should desirably be 1 4-karat or higher.

Conventional gold-based soldering alloys have a content of gold of 14- to 1 8-karat. Such a high content of gold necessarily results in extreme expensiveness of the alloy so that the industrial applicability of gold-based soldering alloys is naturally limited to special cases.

Conventional nickel-based soldering alloys are prepared usually by adding several alloying elements such as boron, silicon, phosphorus and the like in an amount of a few percent to a few percent over 10% to the base component of nickel so as to decrease the melting point as is specified in JIS (Japanese Industrial Standard). Sometimes chromium is added in addition with an object to improve the corrosion resistance of the alloy. The soldering works with the nickel-based soldering alloys are performed usually at a temperature in the range from 1000 to 1 1 500C so that nickel-based soldering alloys are used for bonding stainless stell-made articles.A problem in the use of a nickel-based soldering alloy for soldering of stainless steel articles is that the boron as the additive element in the alloy diffuses to the grain boundaries of the stainless steel to cause remarkable decrease in the corrosion resistance of the soldered portion. The addition of chromium to the alloy cannot afford a remedy to the above problem.

Moreover, nickel-based soldering alloys are hard and brittle as a result of the admixture of the alloying elements of boron, silicon, phosphorus and the like so that cracks are frequently formed at the soldered portion due to the poor impact resistance of the soldering alloy.

The object of the present invention is therefore to provide a novel and improved soldering alloy suitable for soldering articles made of stainless steels, nickel-based alloys and other corrosion-resistant alloys without the above described problems in the conventional silver-, gold- and nickel-based soldering alloys and usable at a soldering temperature of 1050 to 1 200 C. That is, the soldering alloy of the invention should be excellent in the corrosion resistance to give and keep a pleasant appearance on the surface, should have a good strength without brittleness and a relatively low melting point, and should be inexpensive and suitable for wide industrial applications.

The investigations leading to the establishment of the present invention have been undertaken on the base of the facts in mind that nickel and tin form a eutectic alloy having a considerably decreased melting point and a good mechanical strength without brittleness while nickel and chromium also form a eutectic alloy having excellent corrosion resistance and mechanical strength and the experimental works have been carried out with these elements as the basic components of the soldering alloy.

Thus, the nickel-based soldering alloy of the present invention comprises 25 to 40% by weight of tin and 0.5 to 10% by weight of chromium, the balance except impurities and at least 55% by weight of the alloy being nickel. Further improvements can be obtained by the addition of 0.3 to 6% by weight of at least one auxiliary additive element selected from the group consisting of beryllium, boron, silicon, phosphorus, titanium, vanadium, manganese, iron, germanium, niobium, molybdenum, palladium, indium, tantalum and tungsten to the above mentioned three basic components of nickel, tin and chromium.

The upper limit of the-content of nickel in the inventive soldering alloy is preferably 70% by weight due to the increase in the melting point of the alloy when the content of nickel exceeds 70% by weight while the lower limit thereof should be 55% by weight because an alloy lean in the nickel content, for example, smaller than 55% by weight, is brittle by the formation of eutectic alloys of nickel and tin such as Ni3Sn and Ni3Sn2.

Addition of tin to the alloy has an effect of decreasing the melting point of the soldering alloy so that the content of tin in the inventive soldering alloy should be at least 25% by weight since an alloy containing less than 25% by weight of tin has a melting point higher than 1 2000C while an excess amount of tin larger than 40% by weight may result in the brittleness of the alloy as a result of the formation of eutectic alloys with nickel such as Ni3Sn and Ni3Sn2.

Chromium added to the inventive soldering alloy has an effect to improve the corrosion resistance of the alloy so that the content of chromium in the inventive soldering alloy should be at least 0.5% by weight. Although the corrosion resistance of the inventive alloy is improved more and more as the content of chromium is increased, the content thereof should be limited not to exceed 10% by weight since an excessive content of chromium in the alloy results in poor flowability or spreadability of the melt on the surface of the soldered article.

Among the above mentioned auxiliary additive elements, the addition of titanium, vanadium, iron, niobium, molybdenum, tantalum and tungsten has an effect to improve the mechanical strength of the soldering alloy and the addition of beryllium, silicon and manganese has an effect of improving the heat resistance of the alloy. Further, the addition of palladium has an effect of improving the heat resistance of the alloy as well as the flowability of the melt and the addition of beryllium, silicon, phosphorus, germanium and indium has effects to decrease the melting point of the alloy as well as to improve the flowability of the melt. The above mentioned effects are inherent to the respective elements and are not effected or reduced by the combined addition of two or more of the auxiliary additive elements.The amounts of addition of these auxiliary additive elements should desirably be at least 0.3% by weight in order to obtain substantial improvement over the properties of the alloys composed of the three basic components of nickel, tin and chromium while an excessively large amount of addition of them over 6% by weight is undesirable due to certain adverse effects such as the decrease in the flowability of the melt by the excessive amounts of titanium, vanadium, manganese, iron, niobium, molybdenum, palladium, indium, tantalum and tungsten and lowered corrosion resistance and appearance of brittleness of the alloy by the excessive amounts of beryllium, boron, silicon, phosphorus, germanium and indium.

The nickel-based soldering alloys of the present invention have melting points in the range from 1 130 to 12000C in coincidence with the solution temperature of stainless steels and the annealing temperature of nickel-based heat-resistant alloys and great industrial advantages are obtained by the use of the inventive soldering alloys because the soldering works therewith can be performed in an atmosphere of a reducing gas such as hydrogen and ammonia-decomposition gas as well as in an atmosphere of vacuum.

Following are examples to illustrate the nickel-based soldering alloys of the present invention in further detail.

EXAMPLE 1 A soldering alloy was prepared by melting nickel, tin and chromium together in a weight proportion of 60%, 38% and 2%, respectively, in a vacuum furnace and the solidified alloy was pulverized into a powder passing through a screen of 200 mesh opening by the Tyler standard.

A small amount of the above prepared powdered soldering alloy was placed on a 0.2 mm thick plate of Hastelloy C (a tradename of a nickel-based heat-resistant alloy by Union Carbide Corp.) alloy and solderability test was performed by heating the plate at 1 2000C for 5 minutes in an atmosphere of vacuum of 10-2 Torr to find that the spreadibility of the soldering alloy on the Hastelloy C alloy was satisfactory.

Measurement of the hardness of the solidified soldering alloy prepared above gave a value of Hv 350 to be much lower than the hardness of conventional nickel-based soldering alloys with the Hv values of 650 to 750 indicating the superiority of the inventive soldering alloy in respect of the mechanical strength.

The corrosion resistance of the above prepared soldering alloy was examined by the dipping test in a simulated perspiration prepared by dissolving 9.9 g of sodium chloride NaCI, 1.7 g of urea, 1.7 g of lactic acid, 0.8 g of sodium sulfide Na2S and 0.2 g of ammonia water as ammonium hydroxide NH4OH per liter of water to find that no discoloration by corrosion was detected even after 1 50 hours of dipping at 400C not only on the soldering alloy per se but also on the boundary line between the soldering alloy and the Hastelloy C alloy.

EXAMPLE 2 Another soldering alloy was prepared by melting nickel, tin and chromium together in a weight proportion of 65%, 30% and 5%, respectively, in a vacuum furnace and the solidified alloy was pulverized into a powder passing through a screen of 200 mesh opening.

The above prepared powdered soldering alloy was used for bonding a watch case and a wiremesh strap for watch each made of 304-grade stainless steel. Thus, a small amount of the powdered soldering alloy was put to the end portion of the wire-mesh strap followed by heating at 1 1 500C for 5 minutes in an atmosphere of an ammonia-decomposition gas so as to solidify the wire-mesh at the end portion of the strap in a mass with the molten and then solidified alloy. Then the thus solidified end portion of the strap was mechanically ground to be shaped in conformity with the shape of the lateral surface of the watch case. The result of this grinding was satisfactory without loosening of the wire mesh of the strap.Thereafter, the thus shaped end of the wire-mesh strap was put to the lateral surface of the watch case with gentle pressure and bonded thereto by heating at 1 500C for 5 minutes in an atmosphere of an ammonia-decomposition gas to effect soldering with the soldering alloy. The bonding strength in the soldered portion was examined by use of a tensile tester to find that the bonding could withstand a tensile force of 100 kg or larger without being destroyed at the soldered portion and without separation into the watch case and the strap.

The here prepared soldering alloy had the same color tone as the stainless steel so that the soldered portion had a very pleasant and beautiful appearance. The corrosion resistance of the soldering alloy was examined by the dipping test in the simulated perspiration under the same conditions as in Example 1 to find that no discoloration by corrosion took place even after 1 50 hours of dipping not only on the surface of the soldering alloy per se but also on the boundary line between the soldering alloy and the stainless steel.

EXAMPLE 3 Six kinds of soldering alloys each composed of nickel, tin and chromium were prepared and pulverized in the same manner as in Example 1 with the formulation shown in Table 1 below and solderability tests therewith were undertaken on plates of Hastelloy C alloy.

Thus, 0.2 g of the powdered soldering alloy was put on a plate of Hastelloy C having a thickness of 0.5 mm and heated in an atmosphere of vacuum of 10-2 Torr at 1 2000C for 5 minutes to effect soldering, where the performance of each soldering alloy was examined in respect of the spreadability of the molten soldering alloy on the Hastelloy C plate. The bonding strength by soldering was determined by the test as follows.

Thus, two rectangular plates of Hastelloy C alloy, each having dimensions of 1 mm thickness, 10 mm width and 25 mm length, were placed one on the other with an overlapping of 5 mm width at the lengthwise ends and bonded together with the soldering alloy by heating at 1 2000C for 5 minutes in an atmosphere of vacuum of 10-2 Torr followed by the determination of the tensile force required for pulling apart the plates in the direction within the plane of the soldered surfaces.

The corrosion resistance of the soldering alloy as well as the soldered portion therewith was examined by the dipping test in the simulated perspiration in the same manner as in Example 1 to detect the appearance of discoloration on the surface.

The results of the above tests are summarized in Table 1 below together with the melting points of the soldering alloys. In the table, each of the marks A, B, C and D in the column of spreadability corresponds to excellent, good, fair or poor spreadability of the molten alloy, respectively, and the meanings of the marks A, B, C and D in the column of corrosion resistance are that A and B indicate appearance of no discolouration even after 1 50 and 100 hours, respectively, of dipping and C and D indicate first appearance of discoloration after 50 and 25 hours, respectively, of dipping in the simulated perspiration.

TABLE 1

Components, % by weight Soldering Alloy Spread- Corrosion Strength, Melting No. Ni Sn Cr ability resistance kg/ mm2 point, oc 1 61 38 1 B B 62 1167 2 57 35 8 C A 43 1170 3 69 29 2 B B 63 1190 4 56 39 5 B A 48 1164 5 66 26 8 C A 55 1188 6 65 32 3 B B 65 1138 The bonding test of the watch case and wire-mesh strap made of 304-grade stainless steel undertaken in the same manner as in Example 2 excepting the modification of the soldering temperature was successful and satisfactory results as in Example 2 were obtained with each of the above prepared 6 kinds of the soldering alloys.

EXAMPLE 4 Ten kinds of soldering alloys were prepared in the same manner as in Example 1 except that one or more of the auxiliary additive elements were added to the basic formulation of nickel, tin and chromium in the amounts shown in Table 2 below. The thus prepared and pulverized soldering alloys were tested in the same manner as in Example 3 and the results of the spreadability, corrosion resistance and soldering strength are summarized in Table 2 together with the melting point of each of the soldering alloys. The marks A, B, C and D in the columns of spreadability and corrosion resistance in Table 2 each have the same meaning as explained in Example 3. The names of the component elements are given in Table 2 by the respective symbols of elements.

TABLE 2

Base component, Auxiliary % by weight additives, Soldering Melting Alloy % by Spread- Corrosion strength, point, No. Ni Sn Cr weight ability resistance kg/ mm2 C 1 59 38 1 Si : 2 A B 47 1134 2 64 26 8 B : 2 B A 57 1168 3 70 26 1 P :2 B B 45 1182 4 64 30 3 Mo: 3 B B 68 1147 Si : 0.5 5 65 30 3 Pud : 1.5 A B 65 1136 B : 2.5 6 62 27 5.5 Ta: 1 2 B A 55 1135 Pd : 2 Si : 2.5 7 56 35 4 Mo : 2.5 B A 49 1143 Mn: 2.5 8 65 31 1 Nub:0.5 B B 70 1132 Ge: 3 9 65 28 2 Ti : 1 A B 52 1123 V :1 Be: 0.5 10 65 30 2 Fe : 2 B B 72 1130 W :1.5

Claims

1. A nickel-based soldering alloy which comprises from 25 to 40% by weight of tin and from 0.5 to 10% by weight of chromium, the balance except impurities and incidental ingredients and at least 55% by weight of the alloy being nickel.

2. A nickel-based soldering alloy which comprises from 25 to 40% by weight of tin, from 0.5 to 1 0% by weight of chromium and up to 6% by weight of at least one auxiliary additive element selected from the group consisting of beryllium, boron, silicon, phosphorus, titaniu, vanadium, manganese, iron, germanium, niobium, molybdenum, palladium, indium, tantalum and tungsten, the balance except impurities and incidental ingredients and at least 55% by weight of the alloy being nickel.

3. The nickel-based soldering alloy as claimed in claim 1 or claim 2 wherein the amount of nickel in the alloy does not exceed 70% by weight.

4. The nickel-based soldering alloy as claimed in claim 2 wherein the amount of the auxiliary additive element or elements is at least 0.3% by weight.

5. The nickel-based soldering alloy as claimed in claim 1 or 2 substantially as hereinbefore described in any of the Examples.