Metallic wire rod comprising iridium-containing alloy

Abstract

The present invention is a metallic wire rod comprising iridium or an iridium-containing alloy and, the wire rod has in the cross section thereof biaxial crystal orientation of 50% or more of abundance proportion of textures in which crystallographic orientation has preferred orientation to <100> direction. In the present invention, crystal orientation in the outer periphery from semicircle of the cross section which is the periphery of the wire rod is important, and in this zone, abundance proportion of textures in which crystallographic orientation has preferred orientation to <100> direction is preferably not less than 50%.

Claims

1. A metallic wire rod comprising iridium or an iridium-containing alloy, wherein the wire rod has a diameter of less than 12 mm, which wire rod comprises a central area and an outer periphery, wherein the outer periphery has a biaxial crystal orientation and wherein the outer periphery has an abundance ratio of crystal textures of 50% or more across the diameter of the wire rod, and which outer periphery has a crystallographic orientation which is oriented in the <100> direction.

2. The metallic wire rod according to claim 1, wherein the iridium-containing alloy is an alloy containing rhodium, platinum, and nickel.

3. The metallic wire rod according to claim 1, wherein the metallic wire rod comprises an iridium-containing alloy, which iridium-containing alloy is present in the metallic wire rod in an amount up to 30 wt. % and the balance being platinum.

4. The metallic wire rod according to claim 1, wherein an entire diameter of the wire rod has a biaxial crystal orientation and an abundance ratio of textures of 50% or more.

5. The metallic wire rod according to claim 2, wherein the iridium-containing alloy comprises rhodium, platinum, and nickel in a total amount of up to 5% by weight, and the balance being iridium.

6. A method of manufacturing the metallic wire rod, the wire rod defined claim 1, comprising: a first step in which an ingot of iridium or an iridium-containing alloy is made into a rod-shape article by biaxial pressurization while intermediate heat treatment is performed, and a second step in which the rod-shape article undergoes wire drawing to be a wire rod, wherein hardness of the ingot in the first step is maintained in not more than 550 Hv, and temperatures of the intermediate heat treatment are set to be not more than the recrystallization temperature of the iridium or an iridium-containing alloy.

7. The method of manufacturing the metallic wire rod according to claim 6, wherein the ingot of iridium or the iridium-containing alloy is manufactured by a rotation upward drawing process.

8. A method of manufacturing the metallic wire rod, the wire rod defined in claim 2, comprising: a first step in which an ingot of iridium or an iridium-containing alloy is made into a rod-shape article by biaxial pressurization while intermediate heat treatment is performed, and a second step in which the rod-shape article undergoes wire drawing to be a wire rod, wherein hardness of the ingot in the first step is maintained in not more than 550 Hv, and temperatures of the intermediate heat treatment are set to be not more than the recrystallization temperature of the iridium or an iridium-containing alloy.

9. The method of manufacturing the metallic wire rod according to claim 8, wherein the ingot of iridium or the iridium-containing alloy is manufactured by a rotation upward drawing process.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 is an X-ray diffraction result of iridium ingot manufactured by rotation upward drawing process in a first embodiment.

(2) FIG. 2 is a view illustrating a processing step for iridium wire rod in the first embodiment.

(3) FIG. 3 is an X-ray pole figure of {111} plane in the cross section of an iridium processing material in the first embodiment.

(4) FIG. 4 is an X-ray pole figure of {111} plane in the cross section of iridium processing material in the second embodiment.

(5) FIG. 5 is an X-ray pole figure of {111} plane of iridium wire rod in Comparative Example.

(6) FIG. 6 is a schematic cross-sectional view of a wire rod of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

(7) Hereinafter, preferred embodiments of the present invention are described. In the present embodiments, ingots of iridium and various iridium-containing alloys were manufactured by rotation upward drawing process, and these were processed into wire rods.

First Embodiment

(8) (Manufacturing of an Iridium Ingot)

(9) From molten alloy of iridium by high frequency melting using a water-cooled copper mold, iridium ingot with 12 mm diameter was manufactured by pulling-up method (pulling-up speed 10 mm/min). The iridium ingot manufactured in the present embodiment were subjected to X-ray diffraction for its midsection. The results are shown in FIG. 1, and the ingot manufactured by the rotation upward drawing process has the appearance of extremely high peak intensity of {100} plane and high crystal orientation.

(10) (Wire Rod Processing)

(11) The above manufactured iridium ingot was processed into a wire rod through a step shown in FIG. 2. In this processing step, processing were repeatedly conducted at each step of hot forging, hot groove rolling for biaxial pressurization, until target dimensions was obtained. Moreover, at each processing step, hardness of the work piece was appropriately measured to confirm that the hardness is not over 550 Hv. Furthermore, when there was a possibility in that the hardness exceeded 550 Hv due to subsequent processing, intermediate heat treatment was conducted. In the present embodiment, if needed, hot swager processing was added after hot groove rolling.

(12) In this processing step, X-ray pole figure analysis (XPFA) was conducted for cross section of the work piece in the middle of the processing. FIG. 3 shows X-ray pole figure of {111} plane in the cross section of the work piece. As can be seen in the Fig., the cross section of the work piece at each processing stage has clear appearance of poles, and it can be confirmed to have texture with good <100> preferred orientation and to maintain its preferred orientation. Furthermore, even in the state of a wire rod, it has <100> preferred orientation.

Second Embodiment

(13) In the above first embodiment, an ingot initially having high crystal orientation at the manufacturing was manufactured by drawing process, and this was the wire rod. In the present embodiment, an iridium ingot was manufactured by a typical melting method and processed with increasing crystal orientation to produce the wire rod. For manufacture of the iridium ingot, the ingot with a diameter of 12 mm was obtained by argon arc melting method. Subsequent processing steps were conducted in a similar manner to the first embodiment.

(14) FIG. 4 shows X-ray pole figure of {111} plane in the cross section of the work piece. As can be seen in the figure, it is recognized that the processing material manufactured from the ingot by argon arc melting method also has good crystal orientation.

Third and Fourth Embodiments

(15) Here, wire rods from Pt alloy with 5% Ir by weight and Ir alloy with 10% Pt by weight were processed by steps similar to the first embodiment. To produce these wire rods, ingots manufactured by drawing process were processed, and processed in the conditions similar to the first embodiment.

Comparative Example 1-3

(16) Here, although processing steps themself are similar to the present embodiment in order to confirm the meaning of setting intermediate heat treatment temperatures in the present embodiment, wire rods of iridium-containing alloy were manufactured with setting temperatures of the intermediate heat treatment to temperatures over 1200 C. which is the recrystallization temperature. Note that the ingots were manufactured by arc melting method.

(17) X-ray pole figure of {111} in work piece at processing process for these Comparative Examples are shown in FIG. 5. As can be seen in the Fig., wire rods of Comparative Examples are possibly said to be random crystals with small crystal orientation.

(18) Next, for wire rods manufactured in each embodiment and Comparative Example, abundance ratio of crystals having <100> orientation in their cross section were investigated. In this investigation, crystallographic orientation analysis by electron backscatter diffraction pattern analysis (EBSP) was employed. EBSP allows for measuring crystallographic orientation and crystal system in each of crystal grains in inspection zone. Here, with respect to the cross sections of the wire rods, proportion of crystals with <100> orientation was measured in the entire cross section and its periphery. The results are shown in Table 1.

(19) TABLE-US-00001 TABLE 1 Abundance rate of <100> orientation crystals Composition Central area Periphery Entire First embodiment Ir 85.3% 57.2% 60.0% Second 60.1% 50.2% 38.8% embodiment Comparative 38.2% 14.2% 19.8% example 1 Third embodiment Ir5% Pt 79.9% 53.0% 61.0% Comparative 40.3% 12.4% 17.8% example 2 Fourth embodiment Pt30% Ir 90.1% 62.1% 70.3% Comparative 45.0% 18.2% 22.6% example 3

(20) The results of these EBSP coincide with the results of the above X-ray pole figure measurements, and it can be seen that good textures in which crystals with <100> orientation obtain majority are generally indicated. Furthermore, even in the periphery of the wire rods of each embodiment, crystals with <100> orientation are not less than 50%.

(21) After the above physical property identification, wire rods manufactured in each embodiment and Comparative Example were subjected to high-temperature oxidation test. In this test, chip with 1.0 mm length was cut out from each wire rod and this was heated at 1100 C. for 20 hours in the atmosphere, and mass decrease rate was calculated by weight measurements before and after the test. The results are shown in Table 2.

(22) TABLE-US-00002 TABLE 2 Composition Mass decrease rate First embodiment Ir 55% Second embodiment 57% Comparative example 1 60% Third embodiment Ir5% Pt 45% Comparative example 2 51% Fourth embodiment Pt30% Ir 15% Comparative example 3 20%

(23) It can be seen from Table 2 that, in relation to wire rods with random orientation, mass decrease due to high-temperature oxidation is improved in the wire rods of each embodiment having textures with <100> preferred orientation.

INDUSTRIAL APPLICABILITY

(24) The present invention is a material which has good high-temperature oxidation resistance and can be used for a long term in high-temperature oxidative atmosphere. The present invention is suitable for a material which is used in such as spark plug electrode, various sensor electrode, and lead wire in high-temperature oxidative atmosphere.