Preparation method of high-hardness and high-strength free-machining platinum-iridium alloy rod and platinum-iridium alloy rod

Abstract

This invention relates to a method for preparing high-hardness, high-strength, non-machining platinum-iridium alloy rods and the platinum-iridium alloy rods themselves. The raw material purity is higher than 99.95%, comprising 9.5-10.5 wt% iridium, with the balance being platinum and unavoidable impurities. The preparation method includes: Step 1, melting and casting; Step 2, diameter-reduction hot forging: the alloy casting rod is heated in sections to above 1100℃ and held for more than 100 minutes, and diameter-reduction hot forging is performed using at least three forging dies, with the diameter reduction ratio between each forging die being 8-25%; Step 3, cold working, to obtain non-machining platinum-iridium alloy rods with a diameter of 0.6-6.0 mm. The hardness of the platinum-iridium alloy rods is above 180 HV, and the tensile strength is above 550 MPa. This invention, through high-frequency melting, preheating casting, and diameter-reduction hot forging processes, takes into account the rod forming, internal structure, and surface quality control, directly obtaining high-hardness, high-strength, non-machining platinum-iridium alloy rod products.

Description

Technical Field

[0001] This invention relates to the field of platinum-iridium alloy rod manufacturing, specifically to a method for preparing high-hardness, high-strength, non-machining platinum-iridium alloy rods and the platinum-iridium alloy rods themselves. Background Technology

[0002] Platinum-iridium alloys are widely used in medical fields such as implantable medical devices, radiotherapy carriers, and physiotherapy electrode heads due to their stable chemical properties, high temperature resistance, corrosion resistance, and excellent biocompatibility. However, as a precious metal raw material, its cost is extremely high, which places strict requirements on the manufacturing process. Any waste of raw materials or inefficient processes will significantly increase production costs.

[0003] For high-melting-point materials like platinum-iridium alloys (melting point approximately 1770℃), the surface of the cast ingot is prone to defects and pits during casting, requiring descaling on a lathe. This leads to rapid wear of specialized tools, high costs, and low efficiency. Furthermore, the hardened layer produced during cold working causes uneven distribution of the mechanical properties of the ingot. Existing technical solutions typically include processes such as smelting and casting, homogenization heat treatment, descaling on a lathe, rolling, stress-relief annealing, cold drawing, and straightening. For example, invention patent CN111790866B discloses a forging method for large-sized TiAl alloy blanks without cladding, including smelting to obtain alloy ingots, machining off the oxide scale on the annealed blank surface to a surface roughness of Ra 6.3–1.6 μm, rounding the top and bottom end faces to R 10–20 mm, and finally sandblasting the overall surface; followed by forging and heat treatment processes. Furthermore, invention patent CN113351815B discloses a method for preparing corrosion-resistant Ti35 titanium alloy bars, including: S1, selecting Ti35 alloy round bar billets, heating and forging in multiple passes, and grinding the surface of the billet between forging passes; S2, heating the billet obtained in step S1 and performing multiple passes of forging; S3, performing atmospheric heat treatment on the hot-worked bar obtained in step S2 in a heat treatment furnace; S4, performing multiple passes of peeling on the annealed bar obtained in step S3 using a centerless lathe, controlling the amount of material removed per pass during peeling, and polishing the bar after peeling with a belt polisher to control the surface roughness of the bar. It is evident that peeling the ingot before forging, or peeling it after forging, is a crucial step in obtaining alloy intermediates with acceptable surface quality. However, peeling results in scrap loss and recycling problems, especially when using precious metal raw materials, where material loss and waste lead to high costs. Furthermore, turning processes consume a large amount of consumables such as cutting tools, and the production process is time-consuming and energy-intensive, resulting in low overall production efficiency and difficulty in reducing costs.

[0004] Existing technologies have explored solutions to address issues such as large machining operations and low yield. Invention patent CN112589022B discloses a method for manufacturing high-quality, difficult-to-deform high-temperature alloy low-segregation fine-grained bars. This method uses a combination of a high-speed forging mill and a radial forging mill to produce bars ranging from Φ85mm to Φ250mm, achieving a uniform and fine low-segregation grain structure from the center to the edge. It also avoids severe forging cracks during the forging process, reducing the machining operations and improving the yield. However, this invention primarily targets the production of large-size products. When product dimensions are reduced by several orders of magnitude and high precision requirements are needed, the aforementioned manufacturing method lacks universality. Furthermore, the high melting point of platinum-iridium alloys during smelting and casting easily leads to defects such as internal porosity and loose microstructure, affecting the material's mechanical properties and long-term reliability.

[0005] In summary, how to provide a forming technology for platinum-iridium high-melting-point alloys that does not rely on surface treatment processes such as polishing and turning to ensure the surface quality of castings and reduce costs is a technical problem that urgently needs to be solved in this field. Summary of the Invention

[0006] To address the shortcomings of existing technologies that require surface treatment processes such as turning of castings to produce platinum-iridium alloy bars, resulting in wasted materials and increased costs, this invention provides a method for preparing high-hardness, high-strength, non-machining platinum-iridium alloy bars, as well as the resulting platinum-iridium alloy bars. Based on hot forging without machining, this method combines melting protection, mold selection, cold working, and parameter design, taking into account both surface forming and internal microstructure control. This ensures that the bars possess a smooth surface from the casting stage, which is maintained and optimized during subsequent plastic processing, ultimately yielding high-quality bar products with excellent internal and external properties.

[0007] In a first aspect of the present invention, a method for preparing a high-hardness, high-strength, non-machining platinum-iridium alloy rod is provided, wherein the raw material purity of the platinum-iridium alloy rod is higher than 99.95% by mass percentage, comprising: 9.5-10.5 wt% iridium, with the balance being platinum and unavoidable impurities;

[0008] The preparation method includes the following steps:

[0009] Step 1, Melting and Casting: The raw materials are melted at high frequency to obtain a casting molten liquid, which is then poured into a mold preheated to above 500°C and slowly solidified to obtain an alloy casting rod;

[0010] Step 2, diameter reduction hot forging: The alloy casting rod is heated to above 1100℃ in sections and held for more than 100 minutes. Diameter reduction hot forging is carried out using at least three-stage forging dies. The diameter reduction ratio between each stage of forging die is 8-25%, and the alloy rod material is obtained.

[0011] Step 3: Cold work the alloy bar to obtain a non-machining platinum-iridium alloy bar with a diameter of 0.6~6.0mm. The platinum-iridium alloy bar has a hardness of 180HV or higher and a tensile strength of 550MPa or higher.

[0012] This invention uses high-purity raw materials and combines them with specific process steps to obtain platinum-iridium alloy bars with smooth surfaces, high hardness, high strength, and good elongation. This avoids problems such as material waste, tool wear, and work hardening caused by the turning process of traditional castings, significantly improving material utilization and production efficiency. It is suitable for high-end fields such as high-precision electrical devices and medical implants.

[0013] Secondly, by preheating the mold to a high and uniform temperature through preheating casting, the molten alloy can slowly solidify after being injected into the mold, significantly improving the surface quality of the cast bar and reducing the number and depth of surface defects and pits, providing a basic guarantee for machining without cutting. Subsequently, multi-stage diameter reduction hot forging is used to effectively break up the as-cast structure and weld internal defects, greatly improving the density and uniformity of the material. The multi-stage hot forging of this invention can be carried out at a lower hot forging temperature, ensuring material performance while saving energy. Through the synergistic combination of cold rolling and cold drawing, while avoiding the risk of cracking due to excessive deformation in a single operation, grain refinement and dislocation strengthening are achieved, enabling the bar to directly obtain excellent comprehensive properties such as high surface finish, high hardness, high strength, and good elongation without any turning or polishing.

[0014] Preferably, the diameter of the platinum-iridium alloy rod is 0.6-6.0 mm, more preferably 0.8-5.5 mm. This invention offers strong process adaptability, allowing for efficient and high-quality adjustment of the rod diameter according to application requirements.

[0015] Preferably, in step two, the segmented heating of the alloy casting rod includes at least three stages of heating:

[0016] First stage of heating: Heat to 400-600℃ at a rate of 30-40℃ / min, and hold for 10-30 minutes;

[0017] Secondary heating: Heat to 800-1000℃ at a rate of 25-35℃ / min, and hold for 10-30 minutes;

[0018] Three-stage heating: Heat to above 1100℃ at a rate of 10-25℃ / min, and hold for more than 100 minutes.

[0019] Preferably, the segmented heating process is carried out entirely under vacuum or high-purity inert gas protection. This helps reduce oxidation on the surface of the cast rod and ensures the stability of its surface properties.

[0020] The first-stage heating can slowly and evenly eliminate residual casting stress in the cast rod, avoiding cracking caused by rapid heating; the second-stage heating can allow the cast rod to fully complete the preparatory stage of recovery and recrystallization, further homogenizing the internal structure; the third-stage heating can ensure that the core and surface of the cast rod are at a uniform temperature, and transform it into a single-phase austenitic structure with optimal plasticity, which is convenient for subsequent large-deformation hot forging of the cast rod, and avoids pre-forging cracking and post-forging uneven structure problems caused by excessive thermal stress or insufficient structural transformation.

[0021] Preferably, the specific holding time for the first-stage heating and the second-stage heating is determined according to the diameter D of the alloy casting rod. For example, the holding time T (unit: min) is numerically equal to K×D, where 0.4≤K≤0.7.

[0022] Establishing a correlation between the holding time and the size of the casting rod is beneficial for casting rods of different specifications to achieve a uniform temperature in both the core and the surface. This avoids the problem of grain coarsening caused by excessive holding time for small-diameter casting rods, or insufficient holding time for large-diameter casting rods leading to incomplete transformation of the core structure.

[0023] Optionally, in the three-stage heating process, once the temperature reaches 1000℃, the heating rate is further reduced to 10-15℃ / min until it reaches above 1100℃. Using a relatively slower heating rate near the final temperature allows more time for the alloying elements to diffuse sufficiently and for the austenite structure to homogenize. This helps eliminate compositional segregation, obtain a more uniform single-phase structure, and provides a good plasticity foundation for subsequent hot forging.

[0024] Preferably, in the diameter reduction hot forging of step two, each forging die has an elliptical hot forging cavity, and the diameter reduction ratio is the same or gradually decreases based on the minor axis of the elliptical hot forging cavity of each forging die.

[0025] Preferably, when using five-stage diameter reduction hot forging, the diameter reduction ratio of the first and second hot forgings is 15% or more. For example, when using a five-stage forging die for diameter reduction hot forging, the diameter reduction ratios of the five stages are 18-25%, 15-18%, 12-16%, 10-13%, and 8-10% respectively.

[0026] Large deformation is used in the early stage when the material has good high-temperature plasticity to efficiently improve the internal structure. As the material's work hardening trend increases, the deformation is gradually reduced to smoothly transition to the predetermined size. This avoids defects such as internal cracks and surface wrinkles that may be caused by excessive deformation in a single pass or uneven distribution, and helps to improve the surface and internal quality of the forging billet.

[0027] Preferably, the ratio of the major axis to the minor axis of the elliptical hot forging cavity is between 12:10 and 18:10. The specific dimensions of the elliptical hot forging cavity are configured according to the original and target dimensions of the cast bar, but the ratio of the major axis to the minor axis has a certain impact on the hot forging product. If the ellipticity is too small, it will affect the effect of multi-directional forging and dendrite breaking; if the ellipticity is too large, it may cause the bar stock to become unstable or not fully filled in the cavity.

[0028] Preferably, each stage of diameter reduction hot forging includes heavy hammer forging, light hammer finishing, and stress-relieving annealing in sequence;

[0029] The force ratio of heavy hammer forging to light hammer finishing is (20-40):(5-15);

[0030] The stress-relief annealing temperature is 800-1000℃, and the annealing time is 45-90min.

[0031] Preferably, after the stress-relief annealing of the final stage of hot forging, the temperature is cooled to below 600°C by furnace cooling or by controlling the cooling rate to no more than 100°C / h, and then air-cooled to room temperature.

[0032] By slowly cooling through the recrystallization temperature range, thermal stress caused by excessively rapid cooling can be avoided, resulting in a more stable internal structure of the bar, maximizing the annealing effect, and providing a billet with good plasticity and stable structure for subsequent cold rolling.

[0033] Heavy forging using an air hammer can effectively break up the as-cast structure and densify internal defects, while light hammer finishing can eliminate surface wrinkles or microcracks that may be caused by heavy forging, improving surface finish. Stress-relief annealing between each stage of hot forging can promptly eliminate the processing stress accumulated during that hot forging, restore the material's plasticity, and facilitate the next hot forging.

[0034] Through multi-stage diameter reduction hot forging and the synergistic effect of heavy hammer forging, light hammer finishing, and stress-relief annealing in each stage of hot forging, forging cracks caused by stress concentration can be avoided. Stress relief and microstructure optimization are achieved alternately, gradually obtaining a uniform and refined recrystallized structure, thereby further optimizing the surface and internal quality of the alloy bar. After the multi-stage hot forging process, the few defects and pits on the surface of the cast bar can be completely eliminated, resulting in a smooth and clean bar appearance, which is beneficial for the efficient execution of subsequent forming processes.

[0035] Preferably, the force of the heavy hammer forging gradually decreases as the number of forging die stages increases, while the force of the light hammer trimming can remain essentially constant or gradually decrease. The ratio of the forces of heavy hammer forging to light hammer trimming gradually decreases or remains essentially constant as the number of forging die stages increases.

[0036] Preferably, at least four stages of forging dies are used for diameter reduction hot forging. By using forging dies with elliptical hot forging cavities for multi-stage diameter reduction hot forging, the bar stock undergoes greater elliptic deformation during the forging process without damaging the bar surface. This effectively breaks up coarse cast grains and heals loose defects in the microstructure.

[0037] Preferably, when using five-stage reduction hot forging, the force ratio of heavy hammer forging to light hammer finishing in each stage of reduction hot forging is as follows: (35-40): (10-15), (30-35): (8-12), (28-32): (8-12), (22-28): (6-10) and (20-25): (5-10).

[0038] The use of high-intensity hammer forging in the first stage of hot forging can deeply deform the alloy bar, fully break up the as-cast structure and densify internal defects, focusing on improving the internal structure of the bar to enhance its internal quality. In subsequent stages, the hammer force gradually decreases as the diameter of the alloy bar decreases, focusing more on the surface finishing of the alloy bar to enhance its surface quality.

[0039] Preferably, each stage of diameter reduction hot forging includes feed forging, rotation angle, and draw forging.

[0040] Preferably, during the feeding forging process, the minor axis direction of the current cross section is perpendicular to the minor axis direction of the elliptical hot forging cavity of the forging die;

[0041] During the drawing and forging process, the minor axis of the current cross-section of the alloy bar is made to be substantially perpendicular to the minor axis of the elliptical hot forging cavity of the forging die.

[0042] Preferably, the rotation angle is 90°. Based on the symmetrical force application of the elliptical hot forging cavity, the bar stock will present a near-elliptical shape after feeding and forging. Rotating it by 90° essentially interchanges the current minor and major axes of the alloy bar stock. During drawing and forging, its major axis is essentially aligned with the minor axis of the elliptical hot forging cavity of the forging die. That is, the minor axis of the current cross-section of the alloy bar stock is basically perpendicular to the minor axis direction of the elliptical hot forging cavity of the forging die. After feeding and drawing forging, the alloy bar stock basically recovers a relatively good circular cross-section.

[0043] Preferably, during hot forging with different grades of diameter reduction, the diameters of the alloy bars that substantially overlap with the short axis of the elliptical hot forging cavity of the forging die are different. Different grades of diameter reduction hot forging target the short and long axes of different groups of bars, i.e., multi-directional forging. This allows the bars to withstand deformation forces in multiple directions, more effectively breaking down anisotropic cast dendritic structures, promoting equiaxed grains, thereby improving the uniformity and density of the forged billet structure. This is beneficial for more comprehensively healing microscopic defects such as pores and loose structures that appear inside the cast bars during casting.

[0044] Preferably, in step one, the high-frequency melting process involves first evacuating the high-frequency melting furnace to a vacuum level of 10.-1 Below Pa, inert gas is then introduced until the furnace pressure is above 0.03 MPa, the smelting power is 8-10 kW, the smelting temperature is not lower than 1850℃, the holding time after melting is not less than 5 min, and the total time from loading the smelting power to completing the casting is 10-25 min.

[0045] By evacuating the high-frequency melting furnace to a high vacuum and filling it with positive-pressure argon, the contamination of the platinum-iridium alloy by residual oxygen and water vapor in the furnace is eliminated, ensuring the high purity of the alloy. At the same time, the melting power and melting temperature are controlled to ensure that the alloy components melt uniformly and diffuse fully. Limiting the holding time and the total melting cycle can not only homogenize the alloy elements and reduce component segregation, but also effectively prevent the loss of precious metals due to overheating or excessive time and grain coarsening.

[0046] Preferably, the high-frequency melting furnace is first evacuated to 10... -1 Keep the pressure below Pa for 2-3 minutes, then fill with argon gas with a purity of ≥99.99%.

[0047] Preferably, during the holding period after melting, the furnace is evacuated and inert gas is introduced alternately multiple times to deoxygenate and vent the casting solution. Preferably, the oxygen content of the alloy melt is reduced to below 50 ppm. The evacuation and inert gas introduction are similar to those in step one; the vacuum is maintained for 1-2 minutes, and the inert gas is introduced to raise the furnace pressure to 0.05-0.10 MPa. This process is repeated 2-4 times to avoid time and energy consumption.

[0048] Preferably, in the preheating and casting of step two, a boron nitride mold is used, with an inner hole diameter of 20-40 mm and a height of more than 100 mm.

[0049] The slow solidification after the molten casting is poured into the mold includes holding at 1000-1200℃ for 1-1.5 hours.

[0050] Boron nitride molds possess excellent high-temperature stability and non-stick properties, ensuring the smoothness of the cast rod surface. Limiting the inner diameter and height of the mold hole according to the target rod size facilitates sequential solidification, reducing shrinkage cavities and porosity. Simultaneous execution of the slow solidification process after casting with homogenization heat treatment helps eliminate rapid solidification stress in the cast rod, promotes full diffusion of elements between dendrites, and reduces compositional segregation, thereby achieving homogenization and stabilization of the as-cast microstructure and improving the internal quality and uniformity of the cast billet.

[0051] Preferably, the surface roughness Ra of the inner wall of the boron nitride mold is ≤0.8μm.

[0052] Preferably, the cold working in step three includes multiple cold rolling and multiple cold drawing;

[0053] In this process, intermediate annealing is performed between multiple cold rolling cycles, and the alloy bar is rotated around the axis at a certain angle. Each cold rolling cycle includes 5-30 rolling passes, with the deformation per pass being less than 10%.

[0054] The intermediate annealing conditions include: heating to 400-800℃ at a rate of 15-30℃ / min, holding at that temperature for 30-60min, and then slowly cooling to room temperature.

[0055] Limiting the deformation amount in each cold rolling pass to below 10%, preferably below 6%, avoids excessive work hardening or surface microcracks caused by excessive deformation in a single pass. Intermediate annealing can promptly eliminate accumulated dislocations and internal stresses, fully restoring the material's plasticity and facilitating the next cold rolling pass. Rotating the bar around its axis ensures uniform deformation in the circumferential direction, effectively eliminating anisotropy. This allows the bar to achieve high hardness and high strength mechanical properties while maintaining excellent plasticity and dimensional stability, ultimately achieving high-surface-quality alloy bars that do not require turning.

[0056] Preferably, the angle of rotation around the axis is 90°.

[0057] Using a fixed 90° rotation can make the deformation direction of the bar stock perpendicular between multiple cold rolling processes, which can effectively disrupt and homogenize the deformation texture formed by the previous rolling direction and reduce the anisotropy of mechanical properties.

[0058] Preferably, intermediate annealing is performed under vacuum or inert gas protection. This prevents surface oxidation of the bars during annealing, thereby ensuring the surface quality of the alloy bars.

[0059] When the cold rolling deformation is relatively low, the dislocation density is relatively low. Annealing at a lower temperature mainly relies on the recovery mechanism to eliminate stress while retaining some work hardening effect, which is beneficial for subsequent processing. When the deformation is relatively high, the dislocation density is high. Annealing at a higher temperature can induce sufficient recrystallization, forming fine and uniform new grains, thereby optimizing the mechanical properties of the alloy bar.

[0060] Preferably, the cooling rate to room temperature is no more than 50°C / h. This avoids the generation of new stress due to excessively rapid cooling, ensures complete and stable annealing, and thus guarantees the comprehensive performance of the alloy bar.

[0061] Preferably, the total deformation from the alloy casting rod to the high-hardness, high-strength, non-machining platinum-iridium alloy rod is above 90%, wherein:

[0062] The deformation amount in diameter-reduced hot forging is over 50%;

[0063] The deformation rate after multiple cold rolling processes is 50-80%.

[0064] The deformation after multiple cold drawing operations is over 50%.

[0065] By setting a large deformation amount of over 50% in hot forging with reduced diameter, the as-cast crystalline structure can be fully broken up and internal pores welded together, significantly improving the density of the bar and laying the foundation for subsequent processing. Subsequently, multiple cold working processes combining cold rolling and cold drawing are adopted to refine the grains and increase the dislocation density, thereby improving the hardness and strength of the bar. By controlling the deformation amount of each process and the total deformation amount, work hardening cracks caused by excessive single deformation amount are avoided, ensuring that the bar can maintain good elongation while obtaining high hardness and high strength, and directly obtain a smooth surface. This comprehensively realizes the high hardness and high strength platinum-iridium alloy bar forming without turning.

[0066] By alternating deoxygenation and venting of the melt and preheating the casting mold to a high and uniform temperature, the alloy molten metal can slowly solidify after being injected into the mold, significantly improving the purity and surface quality of the cast rod, reducing the number and depth of surface defects and pits, and providing a basic guarantee for machining without machining. Subsequently, multi-stage diameter reduction hot forging is used to effectively break up the as-cast structure and weld internal defects, greatly improving the density and uniformity of the material. The multi-stage hot forging of this invention can be carried out at a lower hot forging temperature, ensuring material performance while saving energy. Through the synergistic combination of cold rolling and cold drawing, while avoiding the risk of cracking due to excessive deformation in a single operation, grain refinement and dislocation strengthening are achieved, enabling the rod to directly obtain excellent comprehensive properties such as high surface finish, high hardness, high strength, and good elongation without any turning or polishing.

[0067] Secondly, the present invention provides a high-hardness, high-strength, non-machining platinum-iridium alloy rod, which is prepared by the aforementioned method. The platinum-iridium alloy rod has a diameter of 0.6~6.0mm, a hardness of 180HV or higher, a tensile strength of 550MPa or higher, and an elongation of 6% or higher.

[0068] Compared with the prior art, the present invention has at least the following beneficial effects:

[0069] 1. This invention addresses the characteristics of high-melting-point materials such as platinum-iridium alloys by employing a multi-stage forging die with an elliptical cavity for diameter reduction hot forging. It combines heavy hammer forging, light hammer finishing, and stress-relief annealing in a cyclic process to improve the as-cast microstructure and densify internal defects. Subsequently, through multiple cold workings with small deformations, and by introducing intermediate annealing and bar rotation, grain refinement and dislocation strengthening are achieved while avoiding machining cracks. This results in bars that possess excellent mechanical properties such as high hardness, high strength, and high elongation, as well as high-quality surface properties, without the need for turning.

[0070] 2. This invention utilizes high-vacuum and positive-pressure inert gas protection, along with high-frequency melting technology involving alternating deoxygenation and venting, combined with a synergistic process of preheating the mold and high-temperature holding and slow cooling after casting. This process yields high-purity, smooth-surfaced, and dense alloy castings during casting, providing billets with excellent surface properties for subsequent diameter-reducing hot forging, multiple cold rolling processes, and cold drawing. Attached Figure Description

[0071] The invention will now be described with reference to the accompanying drawings. In the drawings:

[0072] Figure 1 The process flow diagram for preparing high-hardness, high-strength, non-machining platinum-iridium alloy rods according to the present invention is shown below.

[0073] Figure 2 This is a schematic diagram of the diameter-reducing forging die with an elliptical hot forging cavity according to the present invention;

[0074] Figure 3 Photograph of the bar sample of Embodiment 3 of the present invention;

[0075] Figure 4 Photograph of the bar sample of Embodiment 7 of the present invention;

[0076] Figure 5 This is a photograph of the bar sample in Comparative Example 1, which shows severe peeling and defects on its surface.

[0077] Figure 6 The image shows a bar sample from Comparative Example 2, which exhibits numerous peeling cracks on its surface. Detailed Implementation

[0078] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be described in further detail below. Obviously, the described embodiments are merely some embodiments of this invention, and not all embodiments. Based on the embodiments of this invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this invention.

[0079] The terminology used in the embodiments of this invention is for the purpose of describing particular embodiments only and is not intended to limit the invention. The singular forms “a,” “the,” and “the” as used in the embodiments of this invention and the appended claims are also intended to include the plural forms, and “multiple” generally includes at least two unless the context clearly indicates otherwise.

[0080] As described in the background section, existing technologies rely on surface treatment processes such as polishing and turning to ensure the surface quality of platinum-iridium alloy bars, which not only increases costs but also leads to material waste. Therefore, there is an urgent need to develop a preparation technology for platinum-iridium alloy bars that can directly obtain bars with smooth surfaces and dense internal structures through process innovation, without any polishing or turning surface treatments, thus overcoming the shortcomings of existing technologies. This invention considers both surface forming and internal structure control at every stage, from melting protection and mold selection to hot forging finishing and cold working parameter design. This ensures that the bars have a smooth surface from the moment they are cast and maintains and optimizes it during subsequent plastic processing, ultimately directly obtaining high-quality products with excellent internal and external properties.

[0081] A high-hardness, high-strength, non-machining platinum-iridium alloy rod, wherein the purity of the raw material for the platinum-iridium alloy rod is higher than 99.95% by mass percentage, comprising:

[0082] Iridium 9.5-10.5 wt%, balance platinum and unavoidable impurities;

[0083] The raw material for platinum-iridium alloy bars is obtained by high-frequency melting and preheating casting to obtain alloy cast bars, which are then subjected to diameter reduction hot forging and cold working to obtain high-hardness and high-strength platinum-iridium alloy bars that do not require turning. The cold working includes multiple cold rolling and multiple cold drawing. The total deformation from the alloy cast bars to the high-hardness and high-strength platinum-iridium alloy bars is over 90%, of which: the deformation from diameter reduction hot forging is over 50%; the deformation from multiple cold rolling is 50-80%; and the deformation from multiple cold drawing is over 50%.

[0084] The diameter of the high-hardness, high-strength platinum-iridium alloy rod is 0.6-6.0 mm, the hardness is above 180 HV, the strength is above 550 MPa, and the elongation is above 6%.

[0085] Reference Figure 1 A method for preparing a high-hardness, high-strength, non-machining platinum-iridium alloy rod includes the following steps:

[0086] S1 High-Frequency Melting

[0087] The high-frequency melting furnace was evacuated to 10°C. -1 Keep the pressure below 0.03 MPa for 2-3 minutes, then fill with an inert gas (such as argon) with a purity of ≥99.99% until the pressure inside the furnace is above 0.03 MPa.

[0088] Platinum-iridium alloy raw material (iridium content 9.5-10.5 wt%, balance platinum and unavoidable impurities, raw material purity higher than 99.95%) is subjected to high-frequency melting under inert gas protection. The melting power is controlled at 8-10 kW, the melting temperature is not lower than 1850℃, the holding time after the raw material is completely melted is not less than 5 min, and the total time from applying the melting power to the completion of casting is controlled at 10-25 min to obtain the cast molten liquid.

[0089] During the melting process, an inert gas positive pressure environment is maintained. During the holding period after melting, the furnace is alternately evacuated and filled with inert gas multiple times (e.g., alternated 2-4 times) to deoxygenate and vent the casting solution, reducing the oxygen content of the alloy melt to below 50 ppm.

[0090] Vacuum up to 10 -1 Keep below Pa for 1-2 minutes;

[0091] Inert gas is introduced to increase the pressure inside the furnace to 0.05-0.10 MPa.

[0092] S2 Preheating Casting

[0093] Boron nitride molds with good high-temperature stability are used. The inner diameter of the mold is 20-40 mm, the height is more than 100 mm, and the surface roughness of the inner wall Ra is less than 0.8 μm.

[0094] Preheat the mold to above 500℃ and hold for 20-60 minutes;

[0095] Under the protection of positive pressure of inert gas, the molten casting is injected into the preheated mold. After casting, the alloy rod is obtained by slow solidification process (holding at 1000-1200℃ for 1-1.5h and then cooling naturally with the mold) to promote the diffusion of elements between dendrites, reduce composition segregation, and obtain a rod with a smooth surface and dense interior.

[0096] S3 Reduced Diameter Hot Forging

[0097] The alloy casting rod is heated in stages:

[0098] Heat to 400-600℃ at a rate of 30-40℃ / min and hold for 10-30min;

[0099] The temperature is increased to 800-1000℃ at a rate of 25-35℃ / min and held for 10-30min. The specific holding time for the first and second stages is determined according to the diameter D of the casting rod. For example, the holding time T (unit: min) is numerically equal to K×D, where 0.4≤K≤0.7.

[0100] The temperature is increased to above 1100℃ at a rate of 10-25℃ / min and held for at least 100min (optionally, after the temperature reaches 1000℃, the heating rate is further reduced to 10-15℃ / min). The entire heating process is carried out under vacuum or high-purity inert gas protection to avoid surface oxidation;

[0101] At least three levels of forging dies are used for diameter reduction hot forging, with a total hot forging deformation of more than 50%. Each level of forging die has an elliptical hot forging cavity (the ratio of the major axis to the minor axis is between 12:10 and 18:10), and the diameter reduction ratio is controlled at 8-25%. Each level of hot forging includes heavy hammer forging, light hammer finishing, and stress-relieving annealing (annealing temperature 800-1000℃, annealing time 45-90min). The force ratio of heavy hammer forging to light hammer finishing is in the range of (20-40):(5-15), and the force ratio and the force of the heavy hammer gradually decrease as the number of forging die levels increases.

[0102] Both heavy hammer forging and light hammer finishing include feed forging and draw forging:

[0103] Before feeding and forging, place the short axis of the current cross section of the alloy bar perpendicular to the short axis of the elliptical hot forging cavity of the forging die;

[0104] After feeding and forging and before pulling and forging, the alloy bar is rotated 90° so that the minor axis of the current section of the alloy bar is basically perpendicular to the minor axis of the elliptical hot forging cavity of the forging die. After the last stage of hot forging, it is cooled to below 600°C by furnace cooling or by controlling the cooling rate to no more than 100°C / h, and then air-cooled to room temperature to obtain the alloy bar.

[0105] S4 multiple cold rolling

[0106] The hot-forged alloy bars are subjected to multiple cold rolling passes, each pass consisting of 5-30 passes. The deformation per pass is controlled below 10%, preferably below 6%, and the total deformation is below 80%. Intermediate annealing is performed between the cold rolling passes.

[0107] The temperature of intermediate annealing is adjusted according to the total deformation of cold rolling (400-650℃ when the total deformation is less than 40%, and 550-800℃ when the total deformation reaches more than 40%). The annealing time is 30-60 minutes, and the temperature is slowly cooled to room temperature at a rate of no more than 50℃ / h under vacuum or inert gas protection.

[0108] After each cold rolling, the alloy bar is rotated around the axis by a certain angle (such as 90°) to ensure uniform deformation and obtain a cold-rolled bar.

[0109] S5 multi-pass cold drawing

[0110] The cold-rolled bar is drawn in multiple passes, with the deformation per pass controlled within an appropriate range, such as below 6%, and the total deformation above 50%, ultimately yielding high-hardness, high-strength, non-machining platinum-iridium alloy bars with a diameter of 0.6-6.0 mm.

[0111] Example 1

[0112] Example 1 describes a method for forming high-hardness, high-strength, non-machining platinum-iridium alloy bars without turning, comprising the following steps:

[0113] S1 High-Frequency Melting

[0114] The high-frequency melting furnace was evacuated to a vacuum level of 5×10. -2 The pressure was set at 0.05 MPa for 2.5 minutes, and then argon gas with a purity of ≥99.99% was introduced until the furnace pressure reached 0.05 MPa.

[0115] Platinum-iridium alloy raw material (iridium content 10.0 wt%, balance platinum and unavoidable impurities, raw material purity higher than 99.95%) was subjected to high-frequency melting under argon protection. The melting power was controlled at 9 kW, the melting temperature at 1870℃, and the material was held at that temperature for 8 minutes after complete melting. The total time from applying the melting power to casting completion was controlled at 20 minutes to obtain the cast molten metal. A positive pressure argon environment was maintained during the melting process.

[0116] S2 Preheating Casting

[0117] Boron nitride molds are used, with an inner hole diameter of 30 mm, a height of 120 mm, and an inner wall surface roughness Ra of 0.6 μm.

[0118] Preheat the mold to 550℃ and hold for 40 minutes.

[0119] Under positive pressure protection of argon gas, the molten casting is poured into a preheated mold, and after casting, it is held at 1150℃ for 1.2 hours for slow solidification to obtain an alloy casting rod with a diameter of 30mm.

[0120] S3 Reduced Diameter Hot Forging

[0121] The alloy casting rod is heated in stages:

[0122] Heat to 500℃ at a rate of 35℃ / min and hold for about 15 minutes (the holding time is calculated based on the diameter of the casting rod D=30mm, K is taken as 0.5, and the holding time = 0.5×30=15min).

[0123] Heat to 900℃ at a rate of 30℃ / min and hold for about 15 minutes (the holding time is calculated based on the diameter of the casting rod D=30mm, K is taken as 0.5, and the holding time = 0.5×30=15min).

[0124] The temperature was increased to 1150℃ at a rate of 20℃ / min. Once the temperature reached 1000℃, the heating rate was reduced to 15℃ / min, and the temperature was held for 120 minutes. The entire heating process was carried out under argon protection.

[0125] Five-stage forging dies are used for diameter reduction hot forging, with a total hot forging deformation of approximately 53%. Each stage of the forging die has an elliptical hot forging cavity (the ratio of the major axis to the minor axis is 15:10). The minor axis dimensions and diameter reduction ratios of each stage of the forging die are as follows:

[0126] First grade: Diameter from 30mm to 24mm, with a reduction ratio of approximately 20%;

[0127] Second grade: Diameter from 24mm to 20mm, with a reduction ratio of approximately 16%;

[0128] Grade 3: Diameter from 20mm to 17.5mm, with a reduction ratio of approximately 12.5%;

[0129] Grade 4: Diameter from 17.5mm to 15.5mm, with a reduction in diameter of approximately 11.4%;

[0130] Grade 5: Diameter from 15.5mm to 14.2mm, with a reduction ratio of approximately 8.4%.

[0131] Each stage of hot forging includes heavy hammer forging, light hammer finishing, and stress-relief annealing. The heavy hammer forces of the five stages are 38Kg, 34Kg, 30Kg, 25Kg, and 22Kg, respectively. The light hammer finishing force is constant at 10Kg. The force ratio of heavy hammer forging to light hammer finishing is 38:10, 34:10, 30:10, 25:10, and 22:10, respectively.

[0132] Both heavy hammer forging and light hammer finishing include feed forging and pull forging.

[0133] Each stage of heavy hammer forging involves two cycles of feeding forging and pulling forging:

[0134] Before the first feeding and forging, the minor axis of the current cross section of the alloy bar is placed perpendicular to the minor axis of the elliptical hot forging cavity of the forging die.

[0135] After feeding and forging and before pulling and forging, rotate the alloy bar by 90° so that the minor axis of the current section of the alloy bar is basically perpendicular to the minor axis of the elliptical hot forging cavity of the forging die.

[0136] Before the second feeding and forging, the alloy bar is reversed and forged again in a similar manner as described above.

[0137] Each stage of light hammer finishing involves two cycles of feeding forging and pulling forging. Unlike heavy hammer forging, light hammer finishing involves continuously rotating the bar stock, thereby uniformly forging and finishing the entire outer surface of the bar stock.

[0138] After light blowing and finishing, stress-relief annealing is performed at a temperature of 900℃ for 60 minutes, followed by the next stage of hot forging.

[0139] After the final stage of hot forging, the temperature is controlled to be below 600℃ by a cooling rate not exceeding 100℃ / h, and then air-cooled to room temperature to obtain an alloy bar with a diameter of approximately 14.2mm.

[0140] S4 multiple cold rolling

[0141] The hot-forged alloy bar is cold-rolled three times to obtain a square cross-section cold-rolled bar with a size of approximately 5.5mm × 5.5mm. Each cold rolling process includes eight rolling passes, with the deformation per pass controlled at approximately 4%, and the total deformation of the cold rolling process is approximately 62%.

[0142] Intermediate annealing is performed between multiple cold rolling cycles: after the first cold rolling, the deformation is less than 40%, and the intermediate annealing temperature is 500℃; after the second cold rolling, the intermediate annealing temperature is 700℃; the annealing time is 45min, and the medium is slowly cooled to room temperature at a rate not exceeding 50℃ / h under argon protection.

[0143] After each cold rolling, the alloy bar is rotated 90° around the axis to ensure uniform deformation.

[0144] S5 multi-pass cold drawing

[0145] The cold-rolled bar was drawn in 15 passes, with the deformation per pass controlled at about 5% and the total deformation at about 53%, to obtain a high-hardness, high-strength platinum-iridium alloy bar with a diameter of 2.6 mm.

[0146] Example 2

[0147] Example 2 describes a method for forming high-hardness, high-strength, non-machining platinum-iridium alloy bars without turning, comprising the following steps:

[0148] S1 high-frequency melting is the same as in Example 1;

[0149] S2 Preheating Casting

[0150] Boron nitride molds are used, with an inner hole diameter of 25 mm, a height of 100 mm, and an inner wall surface roughness Ra of 0.6 μm.

[0151] Preheat the mold to 500℃ and hold for 30 minutes.

[0152] Under positive pressure protection of argon gas, the molten casting is poured into a preheated mold. After casting, it is held at 1150℃ for 1.0h for slow solidification to obtain an alloy casting rod with a diameter of about 25mm.

[0153] S3 Reduced Diameter Hot Forging

[0154] The alloy casting rod is heated in stages:

[0155] Heat to 500℃ at a rate of 35℃ / min and hold for 10 min (the holding time is calculated based on the diameter of the casting rod D=25mm, K is taken as 0.4, and the holding time = 0.4×25=10min).

[0156] Heat to 900℃ at a rate of 30℃ / min and hold for 10min (the holding time is calculated based on the diameter of the casting rod D=25mm, K is taken as 0.4, and the holding time = 0.4×25=10min).

[0157] The temperature was increased to 1150℃ at a rate of 20℃ / min. Once the temperature reached 1000℃, the heating rate was reduced to 10℃ / min and held for 100min. The entire heating process was carried out under argon protection.

[0158] Five-stage forging dies are used for diameter reduction hot forging. Each stage of the forging die has an elliptical hot forging cavity (the ratio of the major axis to the minor axis is 15:10). The minor axis dimensions and diameter reduction ratios of each stage of the forging die are as follows:

[0159] First grade: Diameter from 25mm to 20mm, with a reduction ratio of approximately 20%;

[0160] Second grade: Diameter from 20mm to 16.5mm, with a reduction ratio of approximately 17.5%;

[0161] Grade 3: Diameter from 16.5mm to 14mm, with a reduction ratio of approximately 15%;

[0162] Grade 4: Diameter from 14mm to 12.2mm, with a reduction in diameter of approximately 13%;

[0163] Grade 5: Diameter from 12.2mm to 11.0mm, with a reduction ratio of approximately 10%.

[0164] Each level of hot forging includes heavy hammer forging, light hammer finishing and stress-relieving annealing. The heavy hammer forces of the five levels are 35Kg, 32Kg, 28Kg, 24Kg and 22Kg respectively, and the light hammer finishing force is constant at 10Kg.

[0165] Both heavy hammer forging and light hammer finishing include feed forging and pull forging.

[0166] Each stage of heavy hammer forging involves two cycles of feeding forging and pulling forging:

[0167] Before the first feeding and forging, the minor axis of the current cross section of the alloy bar is placed perpendicular to the minor axis of the elliptical hot forging cavity of the forging die.

[0168] After feeding and forging and before pulling and forging, rotate the alloy bar by 90° so that the minor axis of the current section of the alloy bar is basically perpendicular to the minor axis of the elliptical hot forging cavity of the forging die.

[0169] Before the second feeding and forging, the alloy bar is reversed and forged again in a similar manner as described above.

[0170] Each stage of light hammer finishing involves two cycles of feeding forging and pulling forging. Unlike heavy hammer forging, light hammer finishing involves continuously rotating the bar stock, thereby uniformly forging and finishing the entire outer surface of the bar stock.

[0171] After light blowing and finishing, stress-relief annealing is performed at a temperature of 900℃ for 40 minutes, followed by the next stage of hot forging.

[0172] After the final stage of hot forging, the temperature is controlled to be below 600℃ by a cooling rate not exceeding 100℃ / h, and then air-cooled to room temperature to obtain an alloy bar with a short shaft diameter of about 11mm.

[0173] S4 multiple cold rolling

[0174] The hot-forged alloy bar is subjected to three cold rolling processes, each of which includes eight rolling passes. The deformation per pass is controlled at 5%, and the total deformation of the cold rolling is 70%.

[0175] Intermediate annealing is performed between multiple cold rolling cycles: when the total deformation of the first cold rolling is less than 40%, the subsequent intermediate annealing temperature is 500℃; the intermediate annealing temperature after the second cold rolling is 700℃; the annealing time is 40 min for each cycle, and the temperature is slowly cooled to room temperature at a rate not exceeding 50℃ / h under argon protection.

[0176] After each cold rolling, the alloy bar is rotated 90° around the axis to ensure uniform deformation, resulting in a cold-rolled bar with a square cross-section of 3.5mm × 3.5mm.

[0177] S5 multi-pass cold drawing

[0178] The cold-rolled bar is drawn in 20 passes, with the deformation per pass controlled at 6% and the total deformation at 70%, to obtain a high-hardness, high-strength, non-machining platinum-iridium alloy bar with a diameter of 1.0 mm.

[0179] Example 3

[0180] Example 3 describes a method for forming high-hardness, high-strength, non-machining platinum-iridium alloy bars without turning, comprising the following steps:

[0181] S1 high-frequency melting is the same as in Example 1;

[0182] S2 Preheating Casting

[0183] Boron nitride molds are used, with an inner hole diameter of 36 mm, a height of 120 mm, and an inner wall surface roughness Ra of 0.6 μm.

[0184] Preheat the mold to 600℃ and hold for 40 minutes.

[0185] Under positive pressure protection of argon gas, the molten casting is poured into a preheated mold, and after casting, it is held at 1150℃ for 1.0h for slow solidification to obtain an alloy casting rod with a diameter of 36mm.

[0186] S3 Reduced Diameter Hot Forging

[0187] The alloy casting rod is heated in stages:

[0188] Heating to 500℃ at a rate of 35℃ / min and holding for 20min (the holding time is calculated based on the diameter of the casting rod D=36mm, K is taken as 0.55, and the holding time = 0.55×36≈20min).

[0189] Heating to 900℃ at a rate of 30℃ / min and holding for 20min (the holding time is calculated based on the diameter of the casting rod D=36mm, K is taken as 0.55, and the holding time = 0.55×36≈20min).

[0190] The temperature was increased to 1150℃ at a rate of 20℃ / min. Once the temperature reached 1000℃, the heating rate was reduced to 10℃ / min and held for 100min. The entire heating process was carried out under argon protection.

[0191] Five-stage forging dies are used for diameter reduction hot forging. Each stage of the forging die has an elliptical hot forging cavity (the ratio of the major axis to the minor axis is 15:10). The minor axis dimensions and diameter reduction ratios of each stage of the forging die are as follows:

[0192] First grade: Diameter from 36mm to 28mm, with a reduction ratio of approximately 22%;

[0193] Second grade: Diameter from 28mm to 23mm, with a reduction ratio of approximately 18%;

[0194] Third grade: Diameter from 23mm to 20mm, with a reduction ratio of approximately 13%;

[0195] Grade 4: Diameter from 20mm to 17.5mm, with a reduction ratio of approximately 12.5%;

[0196] Grade 5: Diameter from 17.5mm to 16.0mm, with a reduction ratio of approximately 8.5%.

[0197] The other conditions for each stage of hot forging were the same as in Example 1, resulting in alloy bars with a short shaft diameter of approximately 16 mm.

[0198] S4 multiple cold rolling

[0199] The hot-forged alloy bar is subjected to three cold rolling processes, each of which includes seven rolling passes. The deformation per pass is controlled at 4%, and the total deformation of the cold rolling is 55%.

[0200] Intermediate annealing is performed between multiple cold rolling cycles: when the total deformation of the first cold rolling is less than 40%, the subsequent intermediate annealing temperature is 500℃; the intermediate annealing temperature after the second cold rolling is 700℃; the annealing time is 45 min for each cycle, and the temperature is slowly cooled to room temperature at a rate not exceeding 50℃ / h under argon protection.

[0201] After each cold rolling, the alloy bar is rotated 90° around the axis to obtain a cold-rolled bar with a square cross-section of 7.2mm × 7.2mm.

[0202] S5 multi-pass cold drawing

[0203] The cold-rolled bar was drawn in 20 passes, with the deformation per pass controlled at 4%, and the total deformation was about 56%, to obtain a high-hardness and high-strength platinum-iridium alloy bar with a diameter of about 3.2 mm.

[0204] Example 4

[0205] Example 4 describes a method for forming high-hardness, high-strength, non-machining platinum-iridium alloy bars without turning, comprising the following steps:

[0206] S1 high-frequency melting is the same as in Example 3;

[0207] S2 preheating and casting, the same as in Example 3, yielded an alloy casting rod with a diameter of 36 mm;

[0208] The difference between S3 and Example 3 is that the reduction ratios at each stage are different:

[0209] Five-stage forging dies are used for diameter reduction hot forging. Each stage of the forging die has an elliptical hot forging cavity (the ratio of the major axis to the minor axis is 15:10). The minor axis dimensions and diameter reduction ratios of each stage of the forging die are as follows:

[0210] First grade: Diameter from 36mm to 28mm, with a reduction ratio of approximately 22%;

[0211] Second grade: Diameter from 28mm to 24mm, with a reduction ratio of approximately 14%;

[0212] Grade 3: Diameter from 24mm to 21mm, with a reduction ratio of approximately 12.5%;

[0213] Grade 4: Diameter from 21mm to 18mm, with a reduction ratio of approximately 14.3%;

[0214] Grade 5: Diameter from 18mm to 16.0mm, with a reduction ratio of approximately 11%.

[0215] The other conditions for each stage of hot forging were the same as in Example 3, resulting in alloy bars with a short shaft diameter of approximately 16 mm.

[0216] S4 multiple cold rolling, the same as in Example 3;

[0217] The S5 multi-pass cold drawing process, the same as in Example 3, yields a high-hardness, high-strength platinum-iridium alloy bar with a diameter of approximately 3.2 mm.

[0218] Example 5

[0219] Example 5 describes a method for forming high-hardness, high-strength, non-machining platinum-iridium alloy bars without turning, comprising the following steps:

[0220] S1 high-frequency melting is the same as in Example 3;

[0221] S2 preheating and casting, the same as in Example 3, yielded an alloy casting rod with a diameter of 36 mm;

[0222] The difference between S3 and Example 3 is that the reduction ratios at each stage are different:

[0223] Three-stage forging dies are used for diameter reduction hot forging. Each stage of the forging die has an elliptical hot forging cavity (the ratio of the major axis to the minor axis is 15:10). The minor axis dimensions and diameter reduction ratios of each stage of the forging die are as follows:

[0224] Grade 1: Diameter from 36mm to 27.5mm, with a reduction ratio of approximately 23%;

[0225] Second grade: Diameter from 27.5mm to 21mm, with a reduction in diameter of approximately 23%;

[0226] Third grade: Diameter from 21mm to 16mm, with a reduction ratio of approximately 23%;

[0227] The other conditions for each stage of hot forging were the same as in Example 3, resulting in alloy bars with a short shaft diameter of approximately 16 mm.

[0228] S4 multiple cold rolling, the same as in Example 3;

[0229] The S5 multi-pass cold drawing process, the same as in Example 3, yields a high-hardness, high-strength platinum-iridium alloy bar with a diameter of approximately 3.2 mm.

[0230] Example 6

[0231] Example 6 describes a method for forming high-hardness, high-strength, non-machining platinum-iridium alloy bars without turning, comprising the following steps:

[0232] S1 high-frequency melting is the same as in Example 3;

[0233] S2 preheating and casting, the same as in Example 3, yielded an alloy casting rod with a diameter of 36 mm;

[0234] The difference between S3 and Example 3 is that S3 shrinking hot forging does not use segmented heating, but instead uses a rate of 30℃ / min to preheat the casting rod to 1150℃ in one go and hold it for 120min.

[0235] The five-stage hot forging conditions were the same as in Example 3, resulting in an alloy bar with a short shaft diameter of approximately 16 mm.

[0236] S4 multiple cold rolling, the same as in Example 3;

[0237] The S5 multi-pass cold drawing process, the same as in Example 3, yields a high-hardness, high-strength platinum-iridium alloy bar with a diameter of approximately 3.2 mm.

[0238] Example 7

[0239] The difference between Example 7 and Example 3 is that in the high-frequency melting process, deoxygenation and venting are performed during the holding period after melting. The melting process includes:

[0240] The high-frequency melting furnace was evacuated to a vacuum level of 5×10. -2 Pa, and maintain for 2.5 min, then fill with argon gas with a purity ≥99.99% until the furnace pressure is 0.05 MPa;

[0241] Platinum-iridium alloy raw material (iridium content 10.0 wt%, balance platinum and unavoidable impurities, raw material purity higher than 99.95%) was subjected to high-frequency melting under argon protection. The melting power was controlled at 9 kW, the melting temperature at 1870℃, and the argon positive pressure environment was maintained during the melting process. After the raw material was completely melted, it was held at that temperature for 8 minutes. The total time from applying the melting power to completing the casting was controlled at 20 minutes, resulting in the cast molten liquid.

[0242] During the holding period after complete melting, the furnace is evacuated and argon is introduced twice alternately to deoxygenate and exhaust the casting solution, reducing the oxygen content of the alloy melt to below 50 ppm; this includes:

[0243] The first vacuuming was performed until the gas pressure inside the furnace reached 5 × 10⁻⁶. -2 Pa, and maintain for 1.5 min;

[0244] The first argon purging was performed until the pressure inside the furnace reached 0.10 MPa.

[0245] The second vacuuming was performed until the gas pressure inside the furnace reached 5 × 10⁻⁶. -2 Pa, and hold for 1 minute;

[0246] The furnace was filled with argon gas a second time until the pressure inside the furnace reached 0.05 MPa.

[0247] Comparative Example 1

[0248] The difference between Comparative Example 1 and Example 3 is that the diameter reduction hot forging was omitted, and the alloy casting bar with a diameter of 36 mm was cold-worked, with a total deformation of approximately 91%.

[0249] (1) Multiple cold rolling processes, with a total cold rolling deformation of approximately 80%.

[0250] The alloy casting rod is cold rolled three times, each cold rolling process consisting of 10 passes, with the deformation per pass controlled at approximately 5%.

[0251] Intermediate annealing was performed between multiple cold rolling cycles: the intermediate annealing temperature after the first cold rolling and the second cold rolling was 700℃, the annealing time was 45min, and the temperature was slowly cooled to room temperature at a rate not exceeding 50℃ / h under argon protection.

[0252] After each cold rolling, the alloy bar is rotated 90° around the axis to obtain a cold-rolled bar with a square cross-section of 7.2mm × 7.2mm.

[0253] (2) Multi-pass cold drawing

[0254] The cold-rolled bar was drawn in 20 passes, with the deformation per pass controlled at 4%, and the total deformation was about 56%, to obtain a high-hardness and high-strength platinum-iridium alloy bar with a diameter of about 3.2 mm.

[0255] Comparative Example 2

[0256] The difference between Comparative Example 3 and Example 3 is that a three-stage forging die is used for the diameter reduction hot forging, and the specific parameters are as follows:

[0257] Grade 1: Diameter from 36mm to 26.5mm, with a reduction ratio of approximately 26%;

[0258] Second grade: Diameter from 26.5mm to 19.5mm, with a reduction ratio of approximately 26%;

[0259] Grade 3: Diameter from 19.5mm to 16mm, with a reduction ratio of approximately 18%.

[0260] Comparative Example 3

[0261] The difference between Comparative Example 3 and Example 3 is that, in the preheating casting, the mold was preheated to 450°C and held for 15 minutes.

[0262] Comparative Example 4

[0263] Traditional commercially available products.

[0264] Tests and Results

[0265] The bar samples obtained in Examples 1-7, Comparative Examples 1-3, and the commercially available bar (φ3.2mm × 100mm length) in Comparative Example 4 were subjected to the following tests:

[0266] 1. Mechanical property testing:

[0267] Yield strength, tensile strength, and elongation were determined according to the national standard GB / T228.1~2021 "Metallic materials, tensile testing—Part 1: Test at room temperature". A universal testing machine was used to take samples along the length of the final obtained bar, process them into standard tensile specimens, and conduct tensile tests at room temperature until the specimens fractured. The software automatically recorded and calculated the various mechanical property parameters.

[0268] The mechanical property test results are shown in Table 1:

[0269] Table 1:

[0270]

[0271] The mechanical property test results show that the samples in Examples 1-7 all simultaneously meet the requirements for high-hardness, high-strength platinum-iridium alloy rods: a hardness of ≥180HV, tensile strength ≥550MPa, and elongation of 7-10%. Samples in Examples 1-3, 5, and 7 can further improve the hardness to ≥190HV and the strength to ≥580MPa. Without turning, the preparation process of this invention can achieve a relatively satisfactory surface quality of the rods. See [link to relevant documentation]. Figure 3 (Example 3) can also impart good mechanical properties to the alloy rod. Among them, Example 7, which uses alternating deoxygenation and venting, has better overall mechanical properties and surface quality than Example 3 due to the further improvement in alloy purity under the same process conditions. See [link to example]. Figure 4 (Example 7). However, due to the lack of diameter reduction hot forging in Comparative Example 1, insufficient control of the diameter reduction ratio during hot forging in Comparative Example 2, and insufficient mold preheating during casting in Comparative Example 3, the macroscopic mechanical properties exhibited a significant decrease, and numerous surface defects were also observed, for example… Figure 5 The sample surface was severely peeling and damaged (Comparative Example 1). Figure 6 The sample surface showed peeling and cracking (Comparative Example 2). Commercially available products achieved better surface quality through processes such as turning, and their comprehensive mechanical properties basically met the requirements, but they had significant raw material waste and high costs.

[0272] 2. Dimensional error detection

[0273] The diameter of the bar samples from Examples 1-7 and Comparative Examples 1-4 was tested. Three samples were selected for each group, and the average diameter of the three samples along the length direction (front end, midpoint, and rear end) was taken as the sample diameter. The maximum error value was calculated based on the diameter of each sample. The results are shown in Table 2.

[0274] Table 2:

[0275]

[0276] The dimensional error detection results show that, without machining or other mechanical treatments, the maximum error of samples 1-7 in Examples 1-7 can be controlled within 0.020. Although some samples have slight surface defects, such as a small number of burrs and rough edges that are easily generated along a certain diamond-shaped edge after drawing from a square-section cold-rolled bar, these do not affect subsequent processing and use. However, the alloy bars of Comparative Examples 1-3 have many surface defects, see... Figure 5 and Figure 6 The overall dimensional error is also large, and both the macroscopic quality of the bar stock and the microscopic morphology cannot meet the requirements for subsequent use, resulting in a serious waste of raw materials and energy. Commercially available products achieve better surface quality and higher bar stock precision through processes such as turning, but this results in greater material loss and higher costs.

[0277] Although preferred embodiments of the invention have been described, those skilled in the art, upon learning the basic inventive concept, can make other changes and modifications to these embodiments. Therefore, the appended claims are intended to be interpreted as including both the preferred embodiments and all changes and modifications falling within the scope of the invention. Clearly, those skilled in the art can make various alterations and modifications to the invention without departing from its spirit and scope. Thus, if these modifications and modifications of the invention fall within the scope of the claims and their equivalents, the invention is also intended to include these modifications and modifications.

Claims

1. A method for preparing a high-hardness, high-strength, non-machining platinum-iridium alloy rod, characterized in that, The raw material of the platinum-iridium alloy rod has a purity of more than 99.95% by mass percentage, comprising: 9.5-10.5 wt% iridium, with the balance being platinum and unavoidable impurities; The preparation method includes the following steps: Step 1, Melting and Casting: The raw materials are melted at high frequency to obtain a casting molten liquid, which is then poured into a mold that has been preheated to above 500°C and held for 20-60 minutes. The molten liquid is then slowly solidified to obtain an alloy casting rod. Step 2, Diameter Reduction Hot Forging: The alloy casting rod is heated in sections to above 1100℃ and held for more than 100 minutes. Diameter reduction hot forging is performed using at least three forging dies, with the diameter reduction ratio between each forging die being 8-25%, to obtain the alloy rod material. Each forging die has an elliptical hot forging cavity. The diameter reduction ratio is the same or gradually decreases based on the minor axis of the elliptical hot forging cavity of each forging die. Each stage of diameter reduction hot forging includes heavy hammer forging, light hammer finishing, and stress-relieving annealing in sequence. Step 3: Cold work the alloy bar to obtain a non-machining platinum-iridium alloy bar with a diameter of 0.6~6.0mm. The platinum-iridium alloy bar has a hardness of 180HV or higher and a tensile strength of 550MPa or higher. The cold working includes multiple cold rolling and multiple cold drawing. In this process, intermediate annealing is performed between multiple cold rolling cycles, and the alloy bar is rotated around the axis at a certain angle. Each cold rolling cycle includes 5-30 rolling passes, with the deformation per pass being less than 10%. The intermediate annealing conditions include: heating to 400-800℃ at a rate of 15-30℃ / min, holding at that temperature for 30-60min, and then slowly cooling to room temperature.

2. The preparation method according to claim 1, characterized in that, In step two, the segmented heating of the alloy casting rod includes at least three stages of heating: First stage of heating: Heat to 400-600℃ at a rate of 30-40℃ / min, and hold for 10-30 minutes; Secondary heating: Heat to 800-1000℃ at a rate of 25-35℃ / min, and hold for 10-30 minutes; Three-stage heating: Heat to above 1100℃ at a rate of 10-25℃ / min, and hold for more than 100 minutes.

3. The preparation method according to claim 1, characterized in that, The ratio of the force of heavy hammer forging to light hammer finishing is (20-40): (5-15).

4. The preparation method according to claim 1, characterized in that, The stress-relief annealing temperature is 800-1000℃, and the annealing time is 45-90min.

5. The preparation method according to any one of claims 1-4, characterized in that, In the high frequency melting of Step 1, the high frequency melting furnace is first vacuumed to 10 -1 Pa or less, the inert gas is then filled to the pressure in the furnace to be 0.03 MPa or more, the melting power is 8-10 kW, the melting temperature is not less than 1850℃, the holding time after melting is not less than 5 min, and the total time from loading the melting power to the completion of casting is 10-25 min.

6. The preparation method according to claim 5, characterized in that, During the heat preservation period after melting, the furnace is evacuated and filled with inert gas alternately several times to remove oxygen and exhaust the casting solution.

7. The preparation method according to claim 5, characterized in that, In step one, a boron nitride mold is used, with an inner hole diameter of 20-40mm and a height of over 100mm. After preheating the mold to above 550°C and holding it at that temperature for 20-60 minutes, the molten casting liquid is poured into the mold. The slow solidification includes: holding at 1000-1200℃ for 1-1.5 hours and then allowing it to cool naturally with the mold.

8. The preparation method according to any one of claims 1-4, characterized in that, The total deformation rate from alloy casting to high-hardness, high-strength, non-machining platinum-iridium alloy rods exceeds 90%, of which: The deformation amount in diameter-reduced hot forging is over 50%; The deformation rate after multiple cold rolling processes is 50-80%. The deformation after multiple cold drawing processes exceeds 50%.

9. A high-hardness, high-strength, non-machining platinum-iridium alloy rod, characterized in that, It is prepared by the preparation method according to any one of claims 1-8.

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