PALLADIUM-COPPER-SILVER ALLOY

Abstract

A palladium-copper-silver alloy consisting of 40 to 58% by weight of palladium, 25 to 42% by weight of copper, 6 to 20% by weight of silver, optionally up to 6% by weight of at least one element from the group ruthenium, rhodium, and rhenium, and up to 1% by weight of impurities, wherein the palladium-copper-silver alloy contains a crystalline phase with a B2 crystal structure and has 0% by volume to 10% by volume of precipitates of silver, palladium, and binary silver-palladium compounds. The invention also relates to a molded body, a wire, a strip, or a probe needle made of such a palladium-copper-silver alloy and to the use of such a palladium-copper-silver alloy for testing electrical contacts or for electrical contacting or for the production of a sliding contact. The invention also relates to a method for producing a palladium-copper-silver alloy.

Claims

1. A palladium-copper-silver alloy consisting of (a) 40 to 58% by weight of palladium, (b) 25 to 42% by weight of copper, (c) 6 to 20% by weight of silver, (d) optionally up to 6% by weight of at least one element selected from the group consisting of ruthenium, rhodium, and rhenium, and (e) up to 1% by weight of impurities, wherein the palladium-copper-silver alloy contains a crystalline phase with a B2 crystal structure, and wherein the palladium-copper-silver alloy has 0% to 10% by volume of precipitates of silver, palladium, and binary silver-palladium compounds.

2. The palladium-copper-silver alloy according to claim 1, wherein the palladium-copper-silver alloy contains (a) 41 to 56% by weight of palladium, (b) 26 to 42% by weight of copper, and (c) 7 to 19% by weight of silver, preferably (a) 41 to 56% by weight of palladium, (b) 26 to 42% by weight of copper, and (c) 8 to 18% by weight of silver, more preferably (a) 41 to 56% by weight of palladium, (b) 26 to 42% by weight of copper, and (c) 9 to 18% by weight of silver, even more preferably (a) 41 to 56% by weight of palladium, (b) 26 to 42% by weight of copper, and (c) 10 to 18% by weight of silver.

3. The palladium-copper-silver alloy according to claim 1, wherein the palladium-copper-silver alloy has a weight ratio of palladium to copper of at least 1.05 and at most 1.6 and a weight ratio of palladium to silver of at least 3 and at most 6.

4. The palladium-copper-silver alloy according to claim 1, wherein the palladium-copper-silver alloy contains at least 0.1% by weight of at least one element selected from the group consisting of ruthenium, rhodium, and rhenium.

5. The palladium-copper-silver alloy according to claim 1, wherein the palladium-copper-silver alloy contains precipitates of ruthenium, rhodium, rhenium, or a mixture of two of the elements selected from ruthenium, rhodium, and rhenium, or a mixture of ruthenium, rhodium, and rhenium, wherein preferably at least 90% by volume of the precipitates are arranged at grain boundaries of the palladium-copper-silver alloy, particularly preferably at least 99% by volume of the precipitates are arranged at grain boundaries of the palladium-copper-silver alloy.

6. The palladium-copper-silver alloy according to claim 1, wherein the palladium-copper-silver alloy contains up to 6% by weight of at least one element selected from the group consisting of ruthenium and rhodium, preferably from 0.1% by weight to 6% by weight of at least one element selected from the group consisting of ruthenium and rhodium, particularly preferably from 1% by weight to 6% by weight of at least one element selected from the group consisting of ruthenium and rhodium.

7. The palladium-copper-silver alloy according to claim 1, wherein the crystalline phase with the B2 crystal structure has a silver content of at least 6% by weight.

8. The palladium-copper-silver alloy according to claim 1, wherein the crystalline phase with the B2 crystal structure is obtained by quenching the palladium-copper-silver alloy after a temperature treatment, in particular after tempering, or after annealing, and/or the palladium-copper-silver alloy is shaped and hardened by multiple heat treatments and multiple rollings, wherein the heat treatments preferably take place at a temperature between 700° C. and 950° C. and quenching takes place after the heat treatment, wherein no melting of the palladium-copper-silver alloy takes place during the heat treatment, and/or the palladium-copper-silver alloy is produced by melting metallurgy and is subsequently hardened by rolling and tempering, wherein the palladium-copper-silver alloy preferably has a hardness of at least 380 HV0.05.

9. The palladium-copper-silver alloy according to claim 1, wherein the palladium-copper-silver alloy has a mean grain size of at most 2 μm.

10. The palladium-copper-silver alloy according to claim 1, wherein the palladium-copper-silver alloy has from 0% to 5% by volume of precipitates of silver, palladium, and/or binary silver-palladium compounds, preferably from 0% to 2% by volume of precipitates of silver, palladium, and/or binary silver-palladium compounds, particularly preferably from 0% to 1% by volume of precipitates of silver, palladium, and/or binary silver-palladium compounds, more particularly preferably no precipitates of silver, palladium, and/or binary silver-palladium compounds.

11. A molded body consisting of a palladium-copper-silver alloy according to claim 1, wherein the molded body preferably has the shape of a general cylinder with any base or of a coil-like general cylinder with any base, wherein particularly preferably, the height of the general cylinder is greater than all dimensions of the base of the general cylinder, wherein more particularly preferably, a minimum cross section of the base is at most 500 μm and a maximum cross section of the base is at most 10 mm.

12. A probe needle or a sliding contact wire consisting of a palladium-copper-silver alloy according to claim 1, wherein the probe needle or the sliding contact wire preferably has, at least in sections, the shape of a general cylinder with any base or of a curved general cylinder with any base, wherein particularly preferably, a minimum cross section of the base is at most 500 μm and a maximum cross section of the base is at most 10 mm, and/or the probe needle is attached to a card and electrically contacted at one end and the other end is mounted in a freely floating manner, or the sliding contact wire is attached to an electrical contact and electrically contacted at one end and the other end is mounted in a freely floating manner.

13. A use of a palladium-copper-silver alloy according to claim 1 for testing electrical contacts or for electrical contacting or for producing a sliding contact.

14. A method for producing a palladium-copper-silver alloy, wherein the chronological steps of: A) optionally prealloying palladium with at least one of the elements selected from the list of ruthenium, rhodium, and rhenium, with a molar ratio of palladium to the at least one element selected from the list of ruthenium, rhodium, and rhenium of at least 3:1, by melting to produce a palladium prealloy; B) alloying palladium or the palladium prealloy with copper and silver by melting and solidification in vacuo and/or under a protective gas, wherein at least 40% by weight and at most 58% by weight of palladium or at least 40% by weight and at most 64% by weight of palladium prealloy, at least 25% by weight and at most 42% by weight of copper and at least 6% by weight and at most 20% by weight of silver are weighed out; C) repeated processing by annealing at a temperature of more than 750° C. for at least 10 minutes and subsequent quenching and subsequent rolling; D) rolling to achieve a final thickness of at most 100 μm; E) final annealing at a temperature between 250° C. and 600° C. for a period of at least 1 minute.

15. The method according to claim 14, wherein in step B), a weight ratio of palladium to copper of at least 1.05 and at most 1.6 and a weight ratio of palladium to silver of at least 3 and at most 6 are weighed out, and/or in step B), the melting takes place by induction melting or by vacuum induction melting, and/or in step B), a noble gas, in particular argon, is used as protective gas, preferably at a partial pressure between 10 mbar and 100 mbar, and/or in step B), the solidification is carried out by casting in a copper permanent mold, in particular in an uncooled copper permanent mold, wherein the temperature of the melt before casting is preferably less than 100° C. above the melting temperature of the palladium-copper-silver alloy.

16. The method according to claim 14, wherein in step C), the quenching is carried out in water, and/or in step C), the annealing is carried out at a temperature between 850° C. and 950° C., preferably at a temperature of 900° C., and/or in step E), the final annealing takes place at a temperature between 300° C. and 450° C., preferably at a temperature between 360° C. and 400° C.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0197] Measurement results obtained on Pd-Cu-Ag alloys are explained below with reference to twelve figures. The figures show:

[0198] FIG. 1: an electron diffraction image with 265 mm camera length of a Pd51.5Cu36.5Ag10.5Ru1.5 SHT alloy, which was finally stored for 4 minutes at 380° C., wherein the diffraction reflections of the B2 crystal structure (CuPd) and of an fcc structure (Cu) to be expected at the corresponding angles are drawn as rings;

[0199] FIG. 2: an electron diffraction image with 265 mm of a Pd51.5Cu36.5Ag10.5Ru1.5 LHT alloy, which was finally stored for 3 hours at 380° C., wherein the diffraction reflections of the B2 crystal structure (CuPd) and of the fcc structure (Cu) to be expected at the corresponding angles are drawn as rings;

[0200] FIG. 3: an electron diffraction image with 1680 mm camera length of a Pd51.5Cu36.5Ag10.5Ru1.5 SA alloy, which was finally not annealed, is thus finally solution-annealed and has no B2 crystal structure, wherein the diffraction reflections of the fcc structure (Cu) to be expected at the corresponding angles are drawn in;

[0201] FIG. 4: an XRD analysis of the LHT and SA alloys according to FIGS. 2 and 3;

[0202] FIG. 5: a nanodiffraction image with convergent electron beam of a grain of the Pd51.5Cu36.5Ag10.5Ru1.5 LHT alloy according to FIG. 3 in the direction of the 203 zone axis, with lattice parameters determined therefrom;

[0203] FIG. 6: a nanodiffraction image with convergent electron beam of a grain of the Pd51.5Cu36.5Ag10.5Ru1.5 LHT alloy according to FIG. 3 in the direction of the 102 zone axis, with lattice parameters determined therefrom;

[0204] FIG. 7: an element distribution map, obtained by EDX mapping, of silver (Ag) of the Pd51.5Cu36.5Ag10.5Ru1.5 LHT alloy according to FIG. 3;

[0205] FIG. 8: an element distribution map, obtained by EDX mapping, of ruthenium (Ru) of the Pd51.5Cu36.5Ag10.5Ru1.5 LHT alloy in the same image section as FIG. 7;

[0206] FIG. 9: an element distribution map, obtained by EDX mapping, of palladium (Pd) of the Pd51.5Cu36.5Ag10.5Ru1.5 LHT alloy in the same image section as FIG. 7;

[0207] FIG. 10: an element distribution map, obtained by EDX mapping, of copper (Cu) of the Pd51.5Cu36.5Ag10.5Ru1.5 LHT alloy in the same image section as FIG. 7;

[0208] FIG. 11: an electron-microscopic STEM image over the region of the Pd51.5Cu36.5Ag10.5Ru1.5 LHT alloy that was scanned in FIGS. 7 to 10; and

[0209] FIG. 12: an XRD analysis of the LHT alloy according to FIG. 2 with the reflections characteristic of the B2 structure.

DETAILED DESCRIPTION OF THE INVENTION

[0210] The reflections or rings of the electron diffraction images of the STEM examinations show that the B2 crystal structure forms in the two Pd51.5Cu36.5Ag10.5Ru1.5 SHT and LHT alloys (see FIGS. 1 and 2). The rings of the B2 crystal structure modeled with a B2 crystal structure (CuPd) are marked with white arrows pointing left. The rings of another structure assumed as fcc structure (Cu) and modeled are marked with white arrows pointing right. The B2 structure corresponds to the CsCl structure and, only for this reason, this generic designation (CsCl ) was used in FIGS. 1 and 2 in addition to CuPd. Of course, no CsCl is to be expected in the LHT and SHT alloys. In addition, only the designation CuPd was used for the modeling, even though it is a B2 crystal structure additionally containing silver and also a small amount of ruthenium besides copper and palladium, as could be subsequently confirmed by EDXS mapping (see FIGS. 7 to 10). The fcc structure was also modeled only with the structure of copper, and it is not pure copper. In the Pd51.5Cu36.5Ag10.5Ru1.5 SA alloy, on the other hand, no B2 crystal structure can be seen (see FIG. 3). Only the other structure assumed as the fcc structure (Cu) and modeled accordingly was found there. The rings of the fcc structure are marked in FIG. 3 with white arrows pointing right. The found rings of the SHT and LHT samples can be identified primarily by the rings calculated by the B2 crystal structure (see the white arrows pointing left), which can be seen most clearly in the Pd51.5Cu36.5Ag10.5Ru1.5 alloy (LHT), which was tempered for a long time (see FIG. 2).

[0211] Besides the B2 crystal structure, one or more other phases, in particular the phase assumed as the fcc structure, can also be seen in the Pd51.5Cu36.5Ag10.5Ru1.5 LHT alloy since some of the experimentally observed rings are not covered by the B2 crystal structure. The extrinsic phase could have a face-centered cubic structure (fcc). The rings that cannot be ascribed to the B2 crystal structure are all very weak so that only a small proportion of the other phase (possibly fcc) is present in the measured section.

[0212] The B2 crystal structure in the Pd51.5Cu36.5Ag10.5Ru1.5 LHT alloy can also be seen in the XRD examinations according to FIG. 4 and FIG. 12 (the corresponding reflections are marked with arrows), while the Pd51.5Cu36.5Ag10.5Ru1.5 SA alloy does not show a B2 crystal structure (the reflections are missing completely there, see FIG. 4). FIG. 4 shows x-ray diffractograms of the Pd51.5Cu36.5Ag10.5Ru1.5 SA alloys (in FIG. 4, displaced to the right at slightly higher angles 2Θ) and LHT alloys (in FIG. 4, displaced to the right at slightly lower angles 2Θ). In the LHT alloy, proportions of an extrinsic phase with a face-centered cubic crystal structure can be seen as the main component. The SA alloy shows exclusively this face-centered cubic crystal structure. FIG. 12 shows the XRD image of the Pd51.5Cu36.5Ag10.5Ru1.5 LHT alloy isolated and shown with the reflections typical of the B2 crystal structure, wherein the reflections typical of the B2 crystal structure are marked by the arrows in FIG. 12. The reflections of the B2 crystal structure to be seen in FIG. 12 allow the conclusion that the proportion of the B2 crystal structure in the Pd51.5Cu36.5Ag10.5Ru1.5 LHT alloy is significantly greater than 1% by volume and is also greater than 5% by volume.

[0213] By means of TEM, grains of the B2 crystal structure in the Pd51.5Cu36.5Ag10.5Ru1.5 LHT alloys were measured with a convergent electron beam (see FIGS. 5 and 6, which show different zone axes of the crystal lattice of the B2 crystal structure). The diffraction patterns were recorded in different zone axes (ZA) in the bright regions of the STEM images, where the B2 crystal structure was expected. All electron diffraction images and the calculated lattice distances, which are drawn in in FIGS. 5 and 6, are consistent with the B2 crystal structure. This can be seen by comparing the experimental pattern to the relevant simulation based on the quotient method. Methods of this kind are known to the person skilled in the art from the literature (see, for example, “Werkstoffkunde Grundlagen Forschung Entwicklung” [“Materials Science, Basics, Research, Development” by Prof. Dr. Eckard Macherauch and Prof. Dr. Volkmar Gerold (Vieweg Verlag)-Vol. 1: “Einführung in die Elektronenmikroskopie Verfahren zur Untersuchung von Werkstoffen and anderen Festkörpern” [“Introduction to electron microscopy methods for examining materials and other solids”] by Manfred von Hemendahl (1970), Chapter 3.5. “Methode der Quotienten von R.sub.n” [“Method of quotients of R.sub.n”] (page 91 et seqq.) and “Cu—Pd (Copper-Palladium) P. R. Subramanian, D. E. Laughlin, Phase Diagram Evaluations: Section II, page 236, Table 7 “Lattice Parameters of Ordered CsCl-Type CuPd” by [39Jon] -->50.0% =0.2977, Journal of Phase Equilibria Vol. 12, No. 2, 1991). An exact calibration of the cathodoluminescence (CL) is not important here since only the ratio of two measured reciprocal distances is of interest here. The angle between all measured distance pairs is 90°. The absolute values of the lattice parameters are not relevant here, but only the ratio between the two lattice parameters of an image, since the camera length of the simulation (i.e., the “magnification”) was not calibrated 1:1. In addition, some rings appear slightly widened so that not all reflections lie exactly on the associated ring. This could potentially be caused by local internal stresses or variations in the composition.

[0214] By detecting multiple different zone axes of the B2 crystal structure, the presence of this B2 crystal structure in the sample could be detected and thus proven. In addition, a match with the XRD measurements is apparent. In order to clarify the origin of the different diffraction rings in the recorded ring pattern, the “Draw ring diffraction pattern” function in JEMS under “Crystal >Structure Factor” was used, and the radii of the individual rings to be expected are thus schematically placed over the ring pattern recorded in the TEM (see FIG. 2). In addition to the expected rings of the B2 crystal structure (a=0.2977 nm), the rings of a possible fcc matrix (a=0.365 nm for Cu) were taken into account here.

[0215] Furthermore, by means of EDXS mapping, the distribution of silver (FIG. 7), ruthenium (FIG. 8), palladium (FIG. 9), and copper (FIG. 10) in a cut surface through the Pd51.5Cu36.5Ag10.5Ru1.5 LHT alloy was determined. The relevant image section is shown in FIG. 11. It can be seen from the images that small amounts of ruthenium precipitates are present and the elements are otherwise largely identically distributed. In particular, the silver in the Pd51.5Cu36.5Ag10.5Ru1.5 alloy is uniformly distributed, which is surprising when starting from the examinations known from the prior art regarding the ternary phase diagram. As a result, a high electrical conductivity and a high breaking strength of the Pd51.5Cu36.5Ag10.5Ru1.5 alloy can be achieved.

[0216] In the measurements of the EDXS mapping, no precipitates of silver, palladium, or of binary silver-palladium compounds could be detected since the copper in the Pd51.5Cu36.5Ag10.5Ru1.5 LHT alloy can be detected over a wide area except in the ruthenium inclusions (see FIG. 10) and since the distribution of palladium and silver in the Pd51.5Cu36.5Ag10.5Ru1.5 LHT alloy outside of the ruthenium precipitates appears largely homogeneous (see FIGS. 7 and 9). This is surprising when starting from the examinations regarding the phase diagram in the prior art, which would suggest to expect a significant proportion of silver, palladium, or binary silver-palladium compounds of more than 10% by volume.

[0217] For the measurements of FIGS. 7 to 10, a SuperXG2 X-ray detector was used, wherein all 4 segments were used in an energy range of 20 kV with a dispersion 5 eV. The recording duration is about 125 minutes (145 frames, 780×642 pixels, dwell time 100 μs, recording duration per frame 51.4 s). The data set was recorded under nanodiffraction conditions in order to enable a correlation with regions with a superstructure (bright in DF2). The detector DF2 has a minimum diameter of 2.3 mm and a maximum diameter of 24 mm

[0218] Quantification settings: default settings (lines/families) for each element; empirical background correction; quantification in at %; pre-filtering with 4-pixel average filter; post-filtering with 4-pixel average filters; all other settings were left at their default values.

[0219] Since the (maximum measured) Ag concentration is lower in the Ag map (FIG. 7) than in the other elements, the gray scale ends at 17 atom %. The background noise is therefore better seen in FIG. 7 than in the other maps according to FIGS. 8, 9, and 10.

[0220] The examinations show that the B2 crystal structure in the Pd51.5Cu36.5Ag10.5Ru1.5 LHT alloy is contained in the examined LHT composition and no or only very small amounts (<1% by volume) of silver precipitates, palladium precipitates, or binary silver-palladium precipitates form in the Pd51.5Cu36.5Ag10.5Ru1.5 alloy. The proportion of the B2 crystal structure can be estimated by the intensity of the reflections caused by the B2 crystal structure in XRD, to at least 5% by volume of the total Pd51.5Cu36.5Ag10.5Ru1.5 LHT alloy. At least no silver precipitates, palladium precipitates, or binary palladium-silver precipitates in the Pd51.5Cu36.5Ag10.5Ru1.5 LHT alloy can be seen.

[0221] The features of the invention disclosed in the above description and in the claims, figures and exemplary embodiments, both individually and in any desired combination, can be essential for implementing the invention in its various embodiments.