KR0145741B1 - Tantalum or niobium base alloys - Google Patents

Abstract

A wrought metal alloy product having a tantalum or niobium base metal, 25 to 1000 ppm silicon, and 25 to 1000 ppm molybdenum. Fine uniform grain size contributes to improved tensile strength, processability, and high temperature stability.

Description

[Name of invention]

Tantalum or niobium-based alloys

Detailed description of the invention

[Background of invention]

The present invention relates to the field of smelting metal based alloy products with improved chemical and physical properties, and more particularly to tantalum or niobium metal based alloy products containing certain amounts of silicon and molybdenum.

Tantalum alloy powders have been recognized as desirable materials in furnace device applications such as trays and heating elements and radiation shielding applications because the thermal stability of the alloy is maintained and the life of the product is improved due to reduced brittleness. Tantalum alloys have also been used as lead for electrical components that require product properties such as wire fabrication, more particularly ductility, high dielectric constant and resistance to particle growth at elevated temperatures and improved processability. For example, in the production of capacitors, lead wires may be pressed together with tantalum powder anodes and then sintered at high temperatures, or spot welded to the sintered capacitor bodies (see US Pat. No. 3,986,869). In both electrical components and furnace equipment products, contamination by oxygen causes brittleness and destroys the components. For example, in a wire product, the region where the lead escapes from the anode body is very brittle because oxygen moves from the sintered body to the wire. Significant economic benefits can be obtained from tantalum or niobium based alloys that do not lose strength or ductility even after exposure to high temperatures. Tensile strength and ductility of the wire are important properties. Once produced by a series of extrusion, rolling and drawing steps, the annealed wire is moved through a series of transport pulleys and wheels to a spool for shipment. It is highly desirable to have the ability to withstand tension before and after the wire has been wound, i.e., unwrapped and cut by the consumer.

Tensile strength and ductility are also desirable properties for furnace products. For example, the furnace tray experiences handling and vibrational stresses over a sustained period of use. Improved strength and ductility extends product life.

For the sake of brevity, it should be understood that all the description below refers only to tantalum, but this also includes niobium.

The term ductility is a physical property of the same meaning as reduced bridging. This term typically refers to the rate of increase in the length of the metal just before breaking in the tensile test.

Oxygen bridging occurs by several mechanisms in tantalum based alloy products. Tantalum acts as a getter for oxygen in addition to other gaseous impurities such as carbon monoxide, carbon dioxide, nitrogen and water vapor present during the sintering operation. Attempts have been made to reduce the formation of tantalum oxide by doping carbon or carbonaceous materials to tantalum. Oxygen reacts with carbon at the metal surface rather than diffuse into tantalum, minimizing brittleness. While ductility is improved by the addition of carbon, the dopant can adversely affect the processability and electrical properties of the metal. Carbon particles on the tantalum surface increase electrical leakage due to non-uniform adhesion of the tantalum oxide film.

The term doping agent is known to those skilled in the art as a trace material which is typically added to a substrate. The term machinability is also known in the art, hereinafter defined as the ratio of tensile strength to yield strength. Workability is determined by mechanical evaluation of tantalum alloys by various methods, including the standardized ASTM test mentioned below.

U.S. Patent Nos. 4,128,421 and 4,128,629 describe the addition of silicon and / or carbon to tantalum to increase ductility. Silicon is partially volatilized during processing and must be added in excess to the first main blend. Therefore, an increase in cost occurred without improving product quality. Silicon is thought to act as an absorber similar to carbon, but the addition of excess silicon can affect the electrical properties of the wire product by the same mechanism as in the case of the carbon or carbonaceous materials described above.

Tantalum base alloys have also been produced using high concentrations of molybdenum. U.S. Patent No. 3,183,085 describes the production of smelting members from cast members consisting of tantalum alloys containing 1 to 8% molybdenum (10,000 to 80,000 ppm).

Doping of tantalum powder with phosphorus is outlined in US Pat. Nos. 3,825,802 and 4,009,007 as a means to improve the capacitance of the capacitor and the flowability of the tantalum powder. In US Pat. No. 4,009,007 some importance can be found in the amount of doping agent added (in the range of 5 to 40 ppm). The mechanism by which phosphorus acts as a dopant for tantalum metal is not fully known, but one theory is that phosphorus reduces the surface diffusion of tantalum, thereby reducing the sintering rate of tantalum.

Another mechanism for reducing the brittleness of tantalum based alloy products is to dop the tantalum powder using oxides of yttrium or thorium. Metal oxides act to reduce particle growth by fixing particle boundaries. Metal oxides typically have lower Gibbs free energy when compared to tantalum and have a higher boiling point and thus do not degrade product quality due to the mechanism described for the silicon doping agent.

U.S. Patent No. 3,268,328 describes doping of tantalum with small amounts of rare earth metals and oxides. Average particle sizes of 4 to 6 (by ASTM) were optically measured from tantalum doped with yttrium oxide at a temperature of 1,815 to 2,204 ° C.

The term particle size can be defined as the number of grains or grains of tantalum as compared to a standard ASTM particle size chart with a magnification of 100 times. The term particulate size may be defined to mean an ASTM value that is greater than 5 microns or less than about 55 microns. The term uniform particle size means a particle size that does not change by more than one ASTM number based on the test method as described above.

Metal oxides, including oxides of rare earth metals, are not stable after applying elevated temperature conditions as seen in the furnace environment. Although the mechanism is not fully understood, one theory describing dopant particle growth or dispersant coarsening is that disassembly occurs due to the high rate of dispersion of the metal atoms and oxides of the oxides in the refractory metal and the interface of the dispersoid It is driven by energy. The expanded dispersed particles have lower surface energy and therefore cannot act to prevent particle boundary movement. Particle growth also causes loss of ductility.

Combinations of doping agents in tantalum base alloys for use in smelting wires are described in US Pat. No. 4,859,257. This patent describes an alloy made by adding 125 ppm silicon and 400 ppm thorium to tantalum powder. ASTM particle size numbers 20 and 5 were obtained for the doped tantalum powder and the undoped control pure tantalum powder, respectively. This can be interpreted as a particle size of the doped tantalum base alloy, in contrast to a 55 micron control, of 10 microns. Here too, the mechanism by which silicon acts as the oxygen absorber and the metal oxide as the grain boundary limiter explains the basis of the reported particle size and ductility. However, this mechanism has the aforementioned problems of product quality due to particle evaporation and silicon evaporation after exposure to high temperatures due to dispersant particle growth. Tantalum based alloys that provide consistently high ductility and processability even after exposure to high temperatures will be a significant advance in the field of tantalum metals.

Another object of the present invention is to provide a tantalum alloy that maintains processability and ductility even when the doping agent concentration is low.

It is yet another object of the present invention to provide a doped tantalum alloy that maintains a high level of processability and ductility and wherein the dopant inhibits granulation after high temperature exposure.

It is yet another object of the present invention to provide a smelting wire product that minimizes DC electrical leakage from tantalum base alloys that maintain processability and ductility.

Accordingly, the present invention solves the above problems by providing a smelting metal alloy product using an alloy prepared by adding about 25 to about 1000 ppm silicon and about 25 to 1000 ppm molybdenum to a metal based on tantalum or niobium. Achieved. The doped tantalum alloys exhibit a uniform particulate size of about 20 to about 55 microns. The inventors have discovered that the unexpected physical and chemical properties of the present invention are largely due to the synergistic effects of silicon and molybdenum dopants.

The formation of this molybdenum silicide is unexpected because of the addition of small amounts of silicon and molybdenum. Those skilled in the art will expect a mechanism by which silicon competes with tantalum as an absorber for available oxygen and trace gases. Similarly, those skilled in the art will expect that smelting wire products made from the doped alloys will have non-uniform ductility due to the low boiling point of silicon oxide.

The production of molybdenum disulfide is an alloy which is characterized by improved ductility and high processability and which inhibits grain growth after exposure to elevated temperatures below about 1600 ° C.

Another advantage is that molybdenum disilicate has a higher boiling point than silicon and is more resistant to dispersant particle growth than metal oxides such as yttrium oxide or thorium oxide.

Another advantage is that there is no need for the excess dopant that was conventionally needed to replace evaporated silicon. The problem of excess doping agent gathering on the surface of the smelting alloy product and the related discontinuous tantalum oxide insulation has also been solved.

[Brief Description of Drawings]

The above objects, features and advantages will be described in detail by the following drawings, detailed description and claims.

1 is an optical micrograph after annealing at 1300 ° C. for 2 hours of two tantalum wires doped with one silicon and molybdenum, and another with silicon and yttrium oxide,

FIG. 2 is the same two light micrographs as in FIG. 1 annealing at 1600 ° C.,

3 is a ductility graph of the period of time when tantaro doped with silicon and molybdenum was exposed to the temperature of tantalum doped with silicon and yttrium oxide,

4 is an electron diffraction pattern of tantalum doped with silicon and molybdenum as described in Example 7 showing the presence of molybdenum silicide;

FIG. 5 is a dark field transmission electron micrograph showing the shape of molybdenum disulfide precipitate.

Detailed Description of the Preferred Embodiments

Referring to Figures 1 and 2, two sets of light micrographs were taken after annealing wires of approximately 0.024 cm (0.0094 in) in diameter in a vacuum furnace at temperatures of 1300 ° C and 1600 ° C. FIG. 2 at ° C exposes each for 2 hours at 1600 ° C. As shown, tantalum wire doped with 100 ppm yttrium oxide and 400 ppm silicon exhibits incomplete recrystallization and non-uniform particle structure. As described above, the nonuniform particle structure is due to the granulation of yttrium particles. In contrast, the photomicrographs of FIGS. 1 and 2 prepared according to the method of Example 1 below show complete recrystallization and uniform particle structure.

3 shows the improved ductility of 12.6 to 17.5 of the present invention prepared by Example 1, in contrast to the 3.7 to 5.9 ductility found for the tantalum based wire doped with silicon and yttrium oxide of Example 3. FIG.

4 shows electron diffraction patterns of selected regions of the tantalum sheet prepared in Example 7. FIG. The relative position and intensity of the diffraction points means molybdenum silicide as known to those skilled in the art.

FIG. 5 shows the shape of the precipitate as measured by dark field transmission electron micrographs of the areas associated with the diffraction points indicated in FIG. 4.

The tantalum base wires of FIGS. 1 to 3 are generally manufactured by a method of blending tantalum powder with silicon and molybdenum powder by mechanical means, such as conical paired blenders. The blended powder is made into rods by cold isostatic compression molding at 60,000 PSI. The rods are then placed in a vacuum chamber and sintered by direct resistive sintering at 2350 to 2400 ° C. for about 4 hours.

Doped tantalum rod material can be used to produce a variety of smelting products, including furnace trays and leads for electronic components. For simplicity, the following description and examples refer to smelting wire products.

Smelting wire is produced by rolling a sintered rod into a cross section of 20 mm x 20 mm and then annealing. This process is carried out at 1300 ° C. for 2 hours, usually in a standard vacuum furnace. The annealed rods are then rolled into a cross section of 9 mm × 9 mm and then reannealed at 1300 ° C. for 2 hours. Additional processes are performed by drawing through various dies and annealing at 1300 ° C.

Tantalum powder can be prepared by several methods, including those described in US Pat. No. 4,684,399, assigned to Cabot Corporation. The methods described in columns 4, 5 and Examples 2-9 are incorporated herein by reference.

Example 1

Tantalum powder was blended with silicon and molybdenum powder (nominal particle size 200 mesh) to obtain a standard composition of tantalum powder with 400 ppm silicon and 200 ppm molybdenum (by weight). Blending was performed for about 2 minutes in the cone pair blender. The total weight of the blend was about 22,680 g (about 50 lb). The physical and chemical properties of the starting tantalum powder are shown in Table 1 below. The blended powder was made into two rods by cold isostatic compression molding at 60,000 PSI. Each bar weighed about 9980 g (about 22 lb). The cross section of the rod was about 41 mm x 41 mm. The rod was sintered by direct resistance sintering in a vacuum furnace. The temperature during sintering was 2350 to 2400 ° C. The rod was left in this temperature range for about 4 hours.

The sintered rod was rolled to a cross section of 20 mm x 20 mm and annealed at 1300 ° C. for about 2 hours. The rod was then rolled to 9 mm × 9 mm and then reannealed at 1300 ° C. for a further 2 hours. As noted above, the rods were drawn continuously through various dies and annealed at a temperature of about 1300 ° C. The final wire diameter produced according to the purpose of embodiments of the present invention is 0.249 mm.

The analytical ASTM test method was used to determine the particle size (B-214), grain size (B-112) and tensile strength and elongation (E-8) of the doped tantalum based powders and articles of the present invention.

Example 2

This example describes a method of making a commercially available formulation. Microalloys using thorium oxide are carried out through the decomposition of thorium nitrate to thorium oxide during sintering. The thorium nitrate solution is mixed with tantalum powder such that thorium is about 100 ppm by weight. The total weight of the blend was about 22,680 g (about 50 lb). Physical and chemical properties of the starting tantalum powder are shown in Table 1 above.

The blended powder was made into two rods by cold isostatic compression molding at 60,000 PSI; Each bar weighed about 9980 g (about 22 lb). The cross section of the rod was about 41 mm x 41 mm. The rod was vacuum sintered by direct resistance sintering. Sintering temperature was about 2350 to 2400 ℃. The rod was left at this temperature for about 4 hours.

The sintered rod was processed according to the method described in Example 1 to make a wire.

Example 3

Tantalum powder is silicon and yttrium powder (nominal particle size 200 mesh) to obtain a standard composition to which 400 ppm of silicon and 100 ppm of yttrium oxide were added, with a predominantly high number of tantalum powders. Blending was performed for about 2 minutes in the cone pair blender. The total weight of the blend was about 22,680 g (about 50 lb). The physical and chemical properties of the starting tantalum powder are shown in Table 1.

The blended powder was processed into a rod according to the method of Example 2 and then made into a wire.

Example 4

The wires obtained in Examples 1 and 3 were evaluated after annealing in a vacuum furnace at 1300 ° C. and 1600 ° C. for 2 hours. 1 through 3 and Table 2 show the microstructure, physical and mechanical properties of the wire. Wires containing silicon and yttrium oxide were notable for lack of recrystallization, abnormal grain growth, and associated inferior ductility.

Example 5

Table 3 shows the microstructure, mechanical and chemical properties of annealed wires of diameter 0.249 mm prepared in Examples 1,2 and 3. The microstructure of the wire produced by Example 3 was significantly different from those of Examples 1 and 2. This accounts for higher tensile strength and lower ductility, both of which can adversely affect the machinability of the wire.

Example 6

The compositions of Examples 1 and 2 were evaluated for tensile strength and ductility at room temperature in various intermediate steps. Table 4 shows the results of these tests. Similarity in the properties listed means that the processability of the composition of Example 1 will be similar to the wire produced by the method of Example 2.

Example 7

The composition of Example 1 was rolled into a 0.33 mm thick sheet. 9 mm x 9 mm annealed rods were rolled into 2.3 mm thick sheets, annealed at 1300 ° C. for 2 hours in a vacuum furnace, rolled to 0.76 mm thick sheets, and annealed at 1300 ° C. for 2 hours in a vacuum furnace. I was. It was further rolled into a 0.33 mm thick sheet and annealed under vacuum at 1300 ° C. for 2 hours.

A low speed diamond saw was used to cut a discroll of about 250 μm in thickness. The disks were then ion milled to a thickness of 50-100 μm and then electropolished in 90% HSO + 10% HF solution until microporation occurred. Transmission electron microscopy techniques were performed near the perforations.

6 is a bright field electron micrograph of a sample. The diffraction pattern of the selected area is shown in FIG. Diffraction patterns were analyzed for relative intensities (I / Io) and plane spacing (d: unit = d) for several points using standard methods in crystallography. Comparing d and I / Io at points in FIG. 7 with those reported for MoSi in Table 5, it can be seen that MoSi is present.

The shape of the precipitate was determined by dark field transmission micrograph, which is shown in FIG. The size of the precipitate was about 150 mm 3.

Those skilled in the art will appreciate that many changes and modifications within the above description may be made without departing from the spirit of the invention. It should be understood that the present invention is not limited by the theory or the details except as described in the claims below.

Claims (11)

A smelting metal alloy product comprising a tantalum or niobium based metal doped with silicon in an amount of 25 ppm to 1000 ppm and molybdenum in an amount of 25 to 1000 ppm and having a carbon content of not more than 40 ppm. The smelting metal alloy article of claim 1, wherein the alloy maintains a uniform particulate size after being exposed to elevated temperatures of 1200 ° C. or higher. The smelting metal alloy article of claim 2, wherein the uniform particulate size is 10 to 55 microns. The smelting metal alloy article according to claim 1, 2 or 3, having a ductility of 20% after exposure to elevated temperatures of at least 1200 ° C. 5. 4. The smelting metal alloy article of claim 1, 2 or 3, having molybdenum silicide intermetallic precipitates detected by transmission electron microscopy and electron diffraction pattern. The smelting metal alloy product according to claim 1, 2 or 3, wherein the amount of silicon is 100 to 1000 ppm and the yield of molybdenum is 100 to 1000 ppm. The smelting metal alloy product according to claim 6, wherein the tantalum metal has an impurity content of 10 ppm or less of carbon, 540 ppm or less of O ₂ , 5 ppm or less of H ₂ , and 10 ppm or less of N ₂ . The smelting metal alloy product according to claim 1, 2 or 3, wherein the amount of silicon is 100 to 400 ppm and the amount of molybdenum is 100 to 400 ppm. The smelting metal alloy product according to claim 8, wherein the impurity content of the tantalum metal is 10 ppm or less of carbon, 540 ppm or less of O ₂ , 5 ppm or less of H ₂ , and 10 ppm or less of N ₂ . A tantalum base metal containing 100 to 400 ppm of silicon and 100 to 400 ppm of molybdenum, wherein the impurity content of the tantalum base metal is 10 ppm or less of carbon, 540 ppm or less of O ₂ , 5 ppm or less of H ₂ , and 10 ppm or less of N ₂ , and a metal alloy A metal alloy wire having a uniform particulate size of 9 to 25 microns after it has been exposed to 1600 ° C. The metal alloy wire of claim 10 having a ductility of 12% after exposure to elevated temperatures of 1200 ° C. or higher.