US 3826886 A
A contact material having a high durability is prepared from an alloy consisting of 45 to 85 percent by atom of palladium and 55 to 15 percent by atom of aluminium.
Description (OCR text may contain errors)
United States Patent 1191 1111 3,826,886 Hara et al. July 30, 1974 CONTACT MATERIAL  References Cited  Inventors: Toshito Hara, Kawasaki; Hiroaki UNITED STATES PATENTS Tanaka, Yokohamarshmchl 2,418,710 4/1947 Hensel 75/172 R Shmwsato, Kawasakl, all of Japan 2,787,688 4/1957 Hall et al. 75/172 R x  Assigneei Fujitsu Limited, Kanagawa ken 3,428,490 2/1969 Bravo et al 75/172 R x Japan Primary Examiner-L. Dewayne Rutledge  Flled: 1972 Assistant Examiner-E. L. Weise [211 App]. No.: 241,326 Attorney, Agent, or Firm-Nelson E. Kimmelman;
Maleson Kimmelman Foreign Application Priority Data Apr. 15, 1971 Japan 46-23468  ABSTRACT Aug. 30, 197! Japan 46-66425 A contact material having a high durability is prepared from an alloy consisting of to 85 percent by atom Cl 5/l R of palladium and 55 to 15 percent by atom of alumin-  Int. Cl. HOlh l/02, C22c 5/00 i  Field of Search /172 R, 138; 200/166 C 3 Claims, 7 Drawing Figures PATENTEDJULBO m4 TEMPERATURE C CONSTITUTION OF Pd-AL ALLOY WEIGHT PERCENT PALADIUM I TOO l 500 I I o|o203o4o5oso7oso9o|oo AL ATOMIC PERCENT PALLADIUM Pd PATENTEDJULSO m4 3Q826L886 SHEET 2 OF 3 F/g. 2A
(6OPd-4OAg) Fig. 2C
(PdgAL) Fig. 20
(PdAL) The present invention relates to a novel contact material, more particularly, relates to a contact material consisting of a palladium-aluminium alloy and having a high durability.
Electromagnetic relays which include one or more contacts are generally utilized for electrical machinery and apparatus under low level to high level conditions. While electro-magnetic relays having a high durability have heretofore been proposed, such devices have not been found completely satisfactory because of undesirable properties of the conventional contact materials.
Broadly speaking, contact failures may be classified l broadly into two classes:
I. increase of contact resistance 2. failure to open. The contact failures as stated above mainly originate from the following sources, high power conditions not considered,
a. formation of corrosion products such as oxide or sulfide layers which have low conductivity on the contact surface,
b. formation of an organic polymer layer which has low-conductivity on the contact surface,
c. material transfer from one of the contact surfaces to the other, and
d. erosion of the contact material.
Therefore, in order to provide an excellent contact useful for electrical machinery and apparatus under low level to high level conditions, it is first necessary to provide a contact material having high resistance against corrosion, material transfer and erosion and low activity for formation of organic polymer. Further, it is desirable that the contact material has high hardness and melting point.
Generally, conventional contacts are made of gold, silver, platinum, palladium, rhodium, ruthenium, molybdenum, tungusten and alloys including one or more of the abovementioned metals. However, it is known that although contact material consisting of gold, silver or alloys thereof has a high resistance to corrosion and a low activity for formation of organic polymer, it has undesirably low resistance against material transfer and erosion. It is also known that contact material consisting of a platinum group metal, for example, platinum, palladium, rhodium, ruthenium and alloys thereof, has a high resistance against material transfer and erosion but it has an unfavourable high activity for formation of organic polymer. Further, it is known that a contact material consisting of a metal with a high melting point such as molybdenum, tungsten and alloys thereof has excellent resistance against material transfer and erosion and a low activity for formation of organic polymer while it has an undesirable low resistance against formation of corrosion products.
Generally, intermetallic compounds have a higher hardness and melting point than those of simple metals or nonintermetallic compound alloys because the metal atoms in the intermetallic compound are strongly and stably bonded to each other. Accordingly, contact materials consisting essentially of an intermetallic compound have a high resistance to material transfer and erosion. Also, since the intermetallic compounds have poor chemical activity, contact material consisting essentially of them have a poor activity for formation of organic polymer layer and a high resistance to corrosion.
Therefore, the intermetallic compounds have an adoptability for the contact material higher than that of the conventional simple metals or alloys. However, in the case where the intermetallic compound contains no noble metal such as gold, silver and platinum group metals for example, in the case of tungsten carbide (WC) or nickel tin intermetallic compound (NiSn), such intermetallic compounds have an undesirable high tendency to form a stable oxide film on the surface thereof in atmosphere. Accordingly, contacts made up of the intermetallic compounds containing no noble metal frequently suffer from contact failures and thus can not be used under medium or low level conditions.
As is clear from the above description, an ideal contact material which completely satisfies all the above stated requirements has not yet been realized.
An object of the present invention is to provide a contact material satisfying the above-stated requirements that is, having high resistance to corrosion, material transfer, and low erosion and low activity for formation of an organic polymer layer and thus excellent durability.
The object of the present invention can be accomplished by a contact material composed of an alloy consisting of 45 to percent by mol of palladium and 55 to 15 percent by atom of aluminium.
' The features and, advantages of the present invention will be apparent upon reading the following description and inspecting the accompanying drawings, in which;
FIG. I is a phase diagram of palladium-aluminium system,
FIGS. 2A, 2B, 2C and 2D are photographs showing the resistance of Pd metal, Pd-Ag alloy and PdgAl and PdAl compounds to material transfer and erosion,
FIG. 3 is a graph showing'the relationship between cumulative failure rate and number of operations for Pd metal and Pd Al and PdAl compounds, and
F IG. 4 shows a circuit for testing the properties of the contact material.
The palladium-aluminium alloys are prepared by an arc-melting method in which a predetermined quantity of palladium (purity: 99.98 percent or higher) is meltmixed with a balanced quantity of aluminium (purity: 99.999 percent or higher) in an electric furnace using a non-consumption type tungsten anode in an argon atmosphere.
Referring to FIG. 1, the palladium-aluminium alloy includes three intermetallic compounds, Pd Al PdAl and Pd Al which have properties as shown in Table l.
Item 3 4 w Table 1 Material ltcm Pd Pd Al PdAl Pd Al Al Annealing temperature (C) 1200 1300 800 Hardness before annealing 549 Hv 560 Hv 672 Hv Hardness after annealing 40 594 Hv 495 Hv 668 Hv l7 23 X-ray micro No No No No No analysis segresegresegresegresegregating gating gating gating gating Note: Hv Vickcrs hardness number As Table 1 clearly shows, the compounds Pd Al and PdAl have an extremely high hardness of about 500 to 600 Hv. The compound Pd Al has a very porous structure which is unsuitable for use as a contact material.
The inventors have discovered that an alloy consisting of 45 to 85 percent by atom of palladium and 55 to l5 percent by atom of aluminium and containing at least one of PdgAl and PdAl, has excellent resistance to corrosion, high hardness and melting point and low chemical activity for formation of organic polymer, and therefore is useful as a contact material having high resistance to material transfer and erosion.
For example, a contact made of the material of the present invention can stably retain a low contact resistance even after the contacts are operated times at a contact force of about 4 g at a drive frequency of 1.5 Hz under a contact load of mV 6 mA in air of a relative humidity of 80 to 90 percent.
lf palladium in the alloy is in an amount more than 85 percent by atom, the resultant alloy has a undesirable high activity for the formation of organic polymer on the surface thereof. Also, if the amount of palladium in the alloy is less than 45 percent by atom, the resultant alloy has a low resistance to corrosion, material transfer and erosion.
FlGS. 2A to 20 show the resistance to material transfer and erosion of button-shaped contact made up of a simple Pd metal alloy consisting of 60 parts by atom of Pd and 40 parts by atom of Ag, and intermetallic compounds consisting of Pd Al and PdAl, respectively.
The button-shaped material was made the cathode and the Pd wire was made the anode.
After the button-shaped cathodes were brought into contact with the anodes about 10 times under a contact load of V 3 A at a contact force of 4 g at a drive frequency of 10 Hz hair the appearance of the cathodes and anodes was observed in order to estimate the resistance of the materials to material transfer and erosion.
Referring to FlGS. 2A and 28, it will be observed that the lower Pd metal and Pd-Ag alloy cathodes were remarkably eroded and transferred to the upper Pd metal mode so as to form a projection on the anode.
"a comparison in FIGS? zeaiazniareraaaa and maraerarbaeaaon's saturated x' ienavaaora e051 parison with Pd metal. The term cumulative failure rate (C.F.R.) used herein refers to the ratio in percent of the cumulative failure number in excess of the failare level 2 w to the cumulative measurement number. The measurement was carried out at a contact force of 4 g, at a drive frequency of 1.5 Hz under a contact load of 20 mV 6 mA. For every material, 5 to 8 samples were measured.
Referring to FIG. 3, in the measurement of the simple Pd metal contact, the number of contact failures increases after the contact number exceeds 3 X 10 whereas in the measurements of the Pd Al and PdAl compound contacts, no contact failures are observed even after the contact number exceeds 10 From FIG. 3, it is obvious that PdgAl and PdAl compounds have no activity for the formation of organic polymers derived from xylene vapor.
The following examples are intended to illustrate the application of the present invention but are not intended to limit the scope thereof.
EXAMPLE I An intermetallic compound PdAl was prepared from 50 parts by atom of palladium (purity: higher than 99.98 percent) and 50 parts by atom of aluminium (purity: higher than 99.999 percent) by arc-melting them in a water-cooled copper hearth using a non consumption type tungsten anode in an argon atmosphere for 30 to seconds. The resultant compound was repeatedly arc-treated in the water-cooled copper hearth on the alternate surfaces thereof in order to homogenize the internal structure thereof. The homogenized compound was annealed at l300C for 5 to 6 hours.
The annealed compound was formed into a buttonshaped contact strip at 500 to 700C.
The resultant contact strip had a hardness of 495 Hv.
The two PdAl contact strips were made the anode and cathode, facing each other, of an electromagnetic relay in the circuit as shown in FIG. 4. The contacting operation was carried out in air of a relative humidity of to percent.
Even after 1.5 X 10 contactings the PdAl contact showed no contact failure.
In comparison, a simple silver metal contact showed a cumulative failure rate of about 25 percent at 6 X 10 contactings.
An intermetallic compound PdgA] was prepared from 66.7 parts by atom of pure palladium and 33.7 parts by atom of pure aluminium by the same procedure as Example But the annealing temperature was at 1200C.
The same testing as in Example 1 was applied to the compound Pd Al in air containing 100 ppm. of H S gas and having a relative humidity of 80 to 90 percent.
At 1.3 X contactings, the Pd Al contact showed, acumulative failure rate of about 54 percent whereas a simple Pd metal contact showed a cumulative failure;
rate of about 64%.
EXAMPLE 3 EXAMPLE 4 An alloy was prepared from 60 parts by atom of pure palladium and 40 parts by atom of pure aluminium by the same method as in Example 1.
The resultant 60 Pd 40 Al alloywas given the same tests as in Example 1 in air of a relative humidity of 80 to 9 0 percent ii'v'efirtr 1.4 X l0 ope rations, no
contact failures were recorded.
EXAMPLE 5 The same procedure as in Example 1 was repeated using parts by atom of pure palladium and 15 parts ,by atom of pure aluminium. But the annealing temperature was llO0C.
The same testing procedure as in Example 1 was carried out for the above 85 Pd 15 Al alloy in air containing saturated xylene vapor. Even after 1.0 X 10 operations, the 85 Pd 15 Al alloy contact showed no contact failures.
In comparison, a Pd 10 Al alloy contact showed a cumulative failure rate of 25 percent at 1.0 X 10 operations.
What we claim is:
1. In an electrical switch having at least one contact, the improvement wherein said contact is composed of an alloy consisting of l from 45 percent to 85 percent by atom of palladium and (2) from 55 percent to 15 percent by atom of aluminium.
2. An electrical switch as claimed in claim 1, wherein said alloy consists substantially of an intermetallic compound of the formula: Pd Al.
3. An electrical switch as claimed in claim 1, wherein said alloy consists substantially of an intermetallic compound of the formula: PdAl.
PC1-1050 UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent 3,826,886 Dated July 30, 1974 Q Toshito Hara et al Inventor-(s) It is certified that error appears in the aboveidentified patent and that said Letters Patent are hereby corrected as shown below: C
Page 1 left column fourth line from the bottom, H n1 delete "Aug. 30, 1971 Japan .46-66425 I Signed and Sealed this 0 thirteenth Day of April 1976 [SEAL] Arrest:
RUTH C. MASON C. MARSHALL DANN Altcsn'ng Officer (mmnissium-r uflateirls and .Tradwnurks