Directional solidification system, method, and high-purity low-oxygen palladium alloy rods for palladium alloys

Abstract

This invention relates to a directional solidification system, method, and high-purity, low-oxygen palladium alloy rod for palladium alloys. The directional solidification system includes a melting apparatus, a melting and solidification apparatus, and a pressure regulating component. The melting apparatus includes an electric arc melting furnace and a vacuum induction melting furnace. The melting and solidification apparatus includes a melting and solidification furnace, a directional solidification rod, and a cooling component. The melting and solidification furnace includes an openable and closable sealed furnace chamber, a melting crucible disposed within the sealed furnace chamber, and a heating and insulation component surrounding the melting crucible. The melting crucible has a bottom opening, and the directional solidification rod is disposed below the melting crucible with its upper end capable of opening / closing the bottom opening, drawing the alloy melt from the bottom opening. The alloy melt is then gradient-directively solidified by the cooling component at a temperature gradient of not less than 100°C / cm. The pressure regulating component connects the melting apparatus and the sealed furnace chamber, providing a switchable vacuum environment and protective atmosphere to the melting apparatus and the sealed furnace chamber.

Description

Technical Field

[0001] This invention relates to the field of directional solidification technology, specifically to a directional solidification system and method for palladium alloys, and a high-purity, low-oxygen palladium alloy rod. Background Technology

[0002] Palladium alloys, due to their excellent electrical conductivity, corrosion resistance, and mechanical properties, have become a core material for micron-scale components such as semiconductor probes and micro-connectors. These components have extremely high requirements for material properties, necessitating uniform compositional distribution and the absence of structural defects (such as segregation and shrinkage cavities) within any micron-scale region to ensure the reliability and stability of the devices at the microscale. Melting technology, as a key process affecting alloy purity, compositional uniformity, and structural integrity, directly influences the quality of the final product through the matching of its process with alloy characteristics. Directional solidification technology is a crucial process in materials preparation. In palladium alloy preparation, the precision of controlling the directional solidification process directly affects the uniformity of the material's microstructure, thus influencing its comprehensive properties such as electrical performance and mechanical strength. Directional solidification technology establishes a unidirectional temperature gradient during metal crystallization, eliminating transverse grain boundaries and allowing crystals to grow along a specific orientation, thereby obtaining castings with columnar or single-crystal structures. This special microstructure significantly enhances the physical or mechanical properties of the material in a specific direction, thus possessing irreplaceable value in the field of high-end materials.

[0003] However, existing electric arc melting processes have limited melt stirring effects, making elemental segregation prone to occur. Vacuum induction melting processes have weak ability to break the oxide film on the melt surface and are difficult to precisely control local temperatures, both of which result in insufficient diffusion and mixing of alloying elements, leading to uneven distribution within a micrometer-scale area. Furthermore, existing melting technologies lack precision in controlling raw material purity and calculating proportions, and environmental control is inadequate. Oxygen and impurity gases are easily introduced during the melting process, causing a decrease in palladium alloy purity and an increase in oxygen content, further reducing the performance stability of micrometer-scale parts.

[0004] Existing casting methods include static solidification in a mold, where the molten palladium alloy is directly poured into a graphite mold and allowed to cool and solidify naturally at room temperature or in a simple insulated box. While this method and equipment are simple, the cooling rate is uncontrollable, the internal temperature gradient of the melt is <20℃ / cm, dendrites are easily formed, solute element segregation is severe, and defects such as bubbles and shrinkage cavities easily appear on the surface and inside the rod. The uniformity of the crystal structure is also poor, making it difficult to meet the stringent requirements of high-end materials such as palladium alloys for high-purity, micron-sized fine parts.

[0005] Furthermore, existing smelting processes lack synergistic design with subsequent directional solidification processes. For example, invention patent CN109226666B discloses a composite cold crucible directional solidification method for high-activity TiAl-based alloys and the TiAl-based alloy components prepared therefrom. This method involves melting metal raw materials to form an alloy ingot; preparing a mold according to the component's shape requirements; fixing the cut alloy ingot inside the mold and placing it in an electromagnetic cold crucible cavity, with the lower end of the mold immersed in liquid metal coolant; evacuating the directional solidification device and then refilling it with argon gas; heating the alloy ingot to melting using electromagnetic induction, and then pulling the mold downwards at a certain speed and temperature. When the pulling distance reaches the required level, the pulling and heating are stopped, and the directional solidified alloy component is obtained after cooling. This invention connects smelting and directional solidification by forming an alloy ingot, which is time-consuming and energy-intensive. Moreover, impurities are easily introduced into the alloy melt during cooling / heating, which is detrimental to obtaining high-purity alloys.

[0006] Continuous casting, which involves directly transferring the alloy melt to the solidification equipment, can improve efficiency. Invention patent CN105710301B discloses a gas protection method for investment casting of high-temperature alloy castings during the investment casting process. This method uses carbon monoxide for gas protection during casting, and the pressure of the carbon monoxide gas in the vacuum melting chamber and the casting chamber is controlled at 10... 2 ~8×10 4 Between Pa; high-temperature alloy castings adopt directional solidification, the steps are as follows: (1) heat the shell, and evacuate the casting chamber and melting chamber, heat the shell to 1500~1600℃, and maintain the vacuum degree of the casting chamber and melting chamber at 10 -3 ~10 - 1 Pa; (2) Introduce carbon monoxide gas into the casting chamber and melting chamber for more than 6 seconds at a flow rate of 30 L / min; (3) Melt the alloy in the melting chamber, let it stand, and then inject the alloy liquid into the mold shell; (4) Move the casting chamber downwards at a speed of 2-10 mm / min until crystal pulling is completed; (5) Start the vacuum pump to remove the carbon monoxide gas from the casting chamber; open the valve to inject air into the casting chamber. This method can reduce the contamination of the metal by the interfacial reaction products during the casting process and improve the surface quality of the casting. However, the transfer of high-temperature melt is difficult and has a high safety risk. Moreover, even with the use of a carbon monoxide protective atmosphere, the temperature drop of the alloy melt during the melt transfer process often exceeds 50°C, which can easily introduce impurities, resulting in insufficient purity and quality of the alloy melt.

[0007] Therefore, existing palladium alloy melting and directional solidification technologies have significant shortcomings in terms of alloy purity and uniformity, temperature gradient control, and process integration, making it difficult to meet the high standards required for palladium alloy rods used in probes, such as micron-level uniformity and ultra-low oxygen content. There is an urgent need in this field to develop a method capable of efficient melting and deoxygenation, and precise temperature-controlled directional solidification, to prepare high-end palladium alloy materials for probes with uniform microstructure and excellent performance. Summary of the Invention

[0008] To meet the comprehensive performance requirements of palladium alloys for probes, including electrical and mechanical properties, this invention provides a directional solidification system and method for palladium alloys, as well as a high-purity, low-oxygen palladium alloy rod. Based on the characteristics of palladium alloy smelting and directional solidification processes, adjustments are made to the system setup, process parameters, and alloy proportions to obtain a high-purity, low-oxygen, uniformly structured, and high-performance high-end palladium alloy material for probes.

[0009] In a first aspect, the present invention provides a directional solidification system for palladium alloys, comprising a melting apparatus, a melting and solidification apparatus, and a pressure regulating component;

[0010] Melting equipment, including electric arc melting furnaces and vacuum induction melting furnaces;

[0011] Melting and solidification equipment, including a melting and solidification furnace, a directional solidification rod, and a cooling assembly;

[0012] The melting and solidification furnace includes an openable and closable sealed furnace chamber, a melting crucible disposed in the sealed furnace chamber, and a heating and heat preservation assembly surrounding the melting crucible.

[0013] The melting crucible has a bottom opening, and a directional solidification rod is set below the melting crucible and its upper end can open / close the bottom opening, and draw the alloy melt out from the bottom opening. The alloy melt is then gradient-directionally solidified by a cooling assembly at a temperature gradient of not less than 100°C / cm.

[0014] The pressure regulating component connects the smelting equipment and the sealed furnace chamber of the smelting solidification furnace, providing a switchable vacuum environment and protective atmosphere to the smelting equipment and the sealed furnace chamber.

[0015] The smelting equipment of the present invention can perform composite smelting combining vacuum induction melting and electric arc melting on palladium alloy raw materials to obtain a homogenized melt.

[0016] The electric arc melting furnace includes components such as an electric arc discharge electrode rod and a water-cooled copper crucible.

[0017] As an alloy melting apparatus, the vacuum induction melting furnace and the melting and solidification furnace can be used together or set up separately. However, the melting and solidification furnace must specifically include a melting crucible with an opening at the bottom to cooperate with the directional solidification rod for directional solidification operation.

[0018] This invention achieves seamless integration of composite melting and directional solidification processes through the systematic design of melting and solidification equipment, avoiding the risks of excessive cooling and oxidation during melt transfer. Furthermore, it is equipped with a pressure regulating component capable of rapidly switching and controlling the internal atmosphere of the melting and solidification equipment, providing synergistic support for various aspects such as alloy high-temperature protection, degassing through extraction and pressurization, thereby improving the overall production efficiency and yield of the device.

[0019] Preferably, the heating and heat preservation assembly includes a heating element surrounding the melting crucible, a protective sleeve surrounding the heating element, and an induction coil surrounding the protective sleeve;

[0020] The lower end of the directional solidification rod is connected to a guide drive device that drives it to move up and down. It moves down at a constant speed of 0.2 mm / s to 0.25 mm / s to draw out the alloy melt and directionally solidify it into a casting rod.

[0021] Preferably, the inert gas pressure in the melting and solidification furnace is kept constant as the directional solidification rod moves downward at a uniform speed. This constant pressure suppresses fluctuations in the melt as it is introduced into the cooling pool, ensuring a consistent amount of melt entering the cooling pool per unit time, thereby guaranteeing a constant advance rate at the solidification front. This promotes uniform heat flow distribution at the solid-liquid interface, avoiding localized supercooling or compositional fluctuations caused by flow rate variations, and improving the axial continuity of the solidified structure.

[0022] Preferably, the protective atmosphere is formed by an inert gas, or a mixture of an inert gas and nitrogen; the purity of the gas in the protective atmosphere is above 99.995%.

[0023] Preferably, the volume ratio of inert gas to nitrogen is (95-99):(1-5).

[0024] Preferably, the smelting and solidification equipment includes a thermocouple feedback system:

[0025] Thermocouple: Inserted into the molten alloy in the melting crucible to monitor the temperature; for example, the temperature of the molten alloy in the melting crucible is set at 1200-1300℃;

[0026] Thermocouples are connected to temperature control units (such as PLC controllers) to transmit temperature data in real time.

[0027] Preferably, the upper end of the directional solidification rod is provided with a boss, which matches the opening at the bottom of the melting crucible.

[0028] The fit between the boss and the opening in the melting crucible ensures the crucible's airtightness. The boss accurately opens and closes the discharge port as the directional solidification rod moves, preventing melt leakage or external gas intrusion, thus maintaining the purity of the melt.

[0029] The temperature control unit adjusts the water flow velocity and temperature in the spiral water-cooling pipe and water-cooling jacket based on temperature data from the multi-thermocouple feedback system, creating a sufficient temperature gradient along the downward direction of the directional solidification rod. This invention provides a melting and solidification device adapted to the solidification characteristics of palladium alloys. It integrates a lifting and translation drive system and a cooling control system to construct a gradient liquid metal cooling environment for palladium alloys, achieving precise control of the solidification process and obtaining palladium alloy rods with defect-free appearance, regular grain structure, uniform composition distribution, and no segregation, meeting the performance requirements of micron-sized and micro-fine parts.

[0030] Preferably, the pressure regulating component includes:

[0031] The vacuum unit is connected to the melting equipment and the melting and solidification equipment to evacuate the vacuum induction melting furnace, the electric arc melting furnace and the melting and solidification furnace.

[0032] A protective gas supply unit is connected to the melting and solidification equipment to supply protective gas to the vacuum induction melting furnace, electric arc melting furnace, and solidification furnace.

[0033] Optionally, the pressure regulating assembly further includes a gas filtration and circulation unit connected to the protective gas supply unit, the melting equipment, and the melting and solidification equipment. Optionally, the gas filtration and circulation unit has a filtration accuracy of 0.1-0.5 μm and a circulation flow rate of 5-10 L / min. Gas recycling combined with high-efficiency filtration significantly reduces resource consumption and costs. The filtration system effectively removes particulate and gaseous impurities generated during the process, maintaining a continuously high purity atmosphere.

[0034] Secondly, the present invention provides a method for directional solidification of high-purity, low-oxygen palladium alloy rods, utilizing the aforementioned directional solidification system for palladium alloys, comprising the following steps:

[0035] Step 1: Select palladium alloy raw materials with a purity of 99.99% or higher, and pre-melt a portion of the raw materials to obtain a low-melting-point intermediate alloy with a melting point below 1100℃;

[0036] Step 2: Weigh the low-melting-point master alloy and the remaining raw materials according to the proportion and put them into the melting crucible of the melting and solidification furnace. Perform vacuum induction melting at 1200-1400℃ and hold the temperature.

[0037] During the heat preservation of the alloy melt, the alloy melt is evacuated and filled with inert gas alternately multiple times to remove oxygen and exhaust the alloy melt, so that the oxygen content of the alloy melt is reduced to below 50 ppm.

[0038] Step 3: Keep the alloy melt in the melting crucible at a constant temperature and introduce inert gas into the sealed furnace cavity;

[0039] Step 4: Using the downward-moving directional solidification rod, the alloy melt is drawn out from the bottom opening of the melting crucible, and then the alloy melt is gradient-oriented solidified into a high-purity, low-oxygen palladium alloy rod through the cooling assembly at a temperature gradient of not less than 100℃ / cm.

[0040] This invention utilizes pre-melting, integrating melting, deoxygenation, and venting steps within the melting and solidification furnace. This reduces the oxygen content of the alloy melt to below 50 ppm, providing a fundamental material guarantee for obtaining high-purity, low-oxygen palladium alloy bars through directional solidification. Furthermore, during the molten casting process, inert gas is continuously introduced into the molten material entering the crucible and into the directional solidification outlet to create a positive pressure environment that promotes casting and provides inert gas protection. Finally, immediately after the molten material is transferred, inert gas is introduced into the melting and solidification furnace to rapidly rebuild the protective atmosphere and pressure balance, preventing oxygen infiltration during subsequent directional solidification and ensuring the stability of the solidification interface and the consistency of grain growth.

[0041] Preferably, the palladium alloy raw material comprises, by weight percentage:

[0042] Pd 30-60%,

[0043] Cu 20-40%,

[0044] Ag 5-30%,

[0045] Other elements: 0.01-2%;

[0046] The trace elements are selected from at least one of Zn, Cr, B, Mn, In, Al, Si, Zr, and rare earth elements.

[0047] Preferably, in the low-melting-point master alloy, the mass ratio of trace elements to Cu is (1-10):(90-99).

[0048] Preferably, the trace elements include at least one of the following:

[0049] Zn 0.1%~0.6%;

[0050] Si 0.01%~0.1%;

[0051] Cr 0.1%~0.5%;

[0052] B 50-300ppm;

[0053] Zr 0.1%~0.5%;

[0054] Al 0.01%~0.5%;

[0055] In 0.1%~0.6%.

[0056] Preferably, the trace elements include high melting point elements with a melting point above 1000°C and low melting point elements with a melting point below 1000°C.

[0057] Preferably, the pre-melting in step one adopts a composite melting method, including electric arc melting and vacuum induction melting:

[0058] S1. The trace elements and at least a portion of Cu are mixed and added to an electric arc melting furnace, and the arc current is adjusted to 200-300A to obtain an alloy billet.

[0059] S2. Add the alloy billet to a vacuum induction melting furnace and heat it to 1250-1350℃ at a heating rate of 5-10℃ / s until it is fully melted and held for 5-8 minutes. After cooling, a homogenized low-melting-point master alloy is obtained.

[0060] Arc melting relies on the localized high temperature generated by electric arc discharge, offering advantages such as concentrated temperature and good film-breaking effect. It is suitable for alloying high-melting-point, difficult-to-melt elements, while simultaneously removing impurities during the refining stage. Vacuum induction melting features uniform heating and avoids oxidation, making it suitable for homogenizing the composition of high-purity alloys and ensuring high purity at the melt initiation point. When the two technologies are used in combination, they complement each other, comprehensively improving melting efficiency and quality.

[0061] Preferably, the low-melting-point master alloy is cast to obtain a master alloy billet and then subjected to solution treatment;

[0062] The solution treatment includes: heating the intermediate alloy billet to 600-850°C, holding it at that temperature for 1-2 hours, and then rapidly cooling it to room temperature at a rate of 50°C / s or higher.

[0063] Preferably, the intermediate alloy billet is a thin alloy rod. The diameter of the thin alloy rod obtained by casting is not particularly limited, as long as it facilitates solution treatment of the alloy. The solution-treated low-melting-point intermediate alloy rod is then used as a batching material, placed together with the remaining raw materials into a melting and solidification furnace for subsequent melting and solidification steps. This not only reduces the unwanted consumption of trace elements and improves their uniform dispersion in the alloy, but also facilitates subsequent batching and weighing. During pre-melting, a protective atmosphere of a mixture of inert gas and nitrogen is introduced into the furnace, with argon, for example, serving as the primary protective gas.

[0064] Preferably, after step one, the low-melting-point master alloy is subjected to compositional analysis, and raw materials are replenished based on the analysis results.

[0065] Preferably, in step two, after the material is discharged, the sealed furnace cavity of the melting and solidification furnace is closed and a vacuum is drawn until the vacuum degree is ≤10. -1 Pa, then inert gas is introduced to maintain the furnace pressure at 0.01-0.1 MPa, and vacuum induction melting is carried out at a temperature of 1250-1350℃, and held for 15-30 minutes;

[0066] When the alloy melt is held at a constant temperature, the deoxygenation and venting process includes:

[0067] Vacuuming procedure: The pressure regulating component is used to evacuate the air, reducing the pressure inside the sealed furnace cavity to 10. -1 Below Pa, and maintain at this vacuum level for 1-2 minutes;

[0068] Pressurization step: The pressure regulating component fills the sealed furnace chamber with inert gas, and increases the pressure in the sealed furnace chamber to 0.1-0.2MPa at a rate of 0.02-0.05 MPa / min, and maintains it for 3-13 minutes;

[0069] The vacuuming step and the pressurization step are alternately repeated 2-4 times.

[0070] By alternating between high-purity inert gas and vacuum, the external and internal pressures of the alloy change, which helps to expel the oxygen adsorbed by the alloy, improve the alloy purity, and reduce solidification defects such as porosity and shrinkage cavities.

[0071] The pressurization step preferably includes gradient pressurization degassing:

[0072] Increase the pressure inside the furnace to the first pressure P1 at a pressurization rate V1, and maintain the pressure for 1-5 minutes;

[0073] Increase the pressure inside the furnace to the second pressure P2 at a pressurization rate V2, and maintain it for 1-5 minutes;

[0074] Increase the pressure inside the furnace to the third pressure P3 at a pressurization rate V3, and maintain it for 1-5 minutes;

[0075] Among them, V1≥V2≥V3≥0.02MPa / min, P3>P2>P1≥0.1MPa, preferably V1≥0.04MPa / min, V2≥0.03MPa / min, P2≥0.12MPa, P3≥0.15MPa.

[0076] A high initial pressurization rate can quickly establish a basic gas pressure environment in the melting furnace, accelerating the precipitation of gases in the melt. Subsequent reduction of the pressurization rate and stepwise pressure increases effectively avoid surface disturbance caused by gradual pressure increases, providing a smooth solid-liquid interface for subsequent directional solidification. Staged pressure holding provides sufficient time for gas molecules to diffuse slowly from the melt interior to the surface, reducing the formation of localized supersaturated bubbles and thus lowering the porosity defect rate to an extremely low level, significantly improving the density of the final bar. Through gradient pressurization and degassing, the oxygen content of the alloy melt can be further reduced to below 40 ppm.

[0077] Compared with the prior art, the technical solution of the present invention has at least the following beneficial effects:

[0078] 1. This invention integrates smelting equipment, smelting and solidification equipment, and gas pressure regulation components into a single system. The smelting and solidification furnace serves as both the starting point for alloy smelting and directional solidification. The molten alloy can be quickly extracted after smelting via positive and negative gas pressure regulation, avoiding intermediate transfer steps of the high-temperature alloy melt, significantly shortening the process cycle. Furthermore, since there is no need for casting and transfer, the risk of oxidation is eliminated, which helps improve the yield. Compared with traditional technologies, this invention avoids contamination introduced by the transfer of the melt between process stages, ensuring the purity requirements of materials for micro-parts.

[0079] 2. This invention combines electric arc melting and vacuum induction melting, supplemented by a pressurized deoxygenation and venting step, which can deeply remove gaseous impurities from the melt. This significantly improves the purity of the palladium alloy melt and reduces non-metallic inclusions and bubble defects. The casting rate is precisely controlled by a directional solidification guide drive device, avoiding dendrite coarsening and equiaxed crystal formation, resulting in uniform composition distribution and no segregation defects in the palladium alloy rod within a micron-level region. The gas pressure regulating component allows for flexible switching between vacuum and inert gas environments. During the melting process, oxygen is effectively isolated by evacuating and then filling with inert gas, preventing oxidation of the alloy melt.

[0080] 3. This invention utilizes high-purity alloy raw materials and their reasonable proportions, and through a series of process steps such as composite pre-melting, integrated melting and solidification design, pressurized oxygen removal and degassing, and intermediate component detection, to provide a high-purity palladium alloy with low oxygen content that can meet the requirements for probes. The resulting high-performance palladium alloy is then directionally solidified into palladium alloy rods for subsequent processing into probe products. Attached Figure Description

[0081] Figure 1 This is a schematic diagram of the connection relationship of the directional solidification system of the present invention;

[0082] Figure 2 The present invention describes the process flow of the directional solidification method for high-purity, low-oxygen palladium alloy rods.

[0083] Explanation of reference numerals in the attached figures:

[0084] 1-Electric arc melting furnace;

[0085] 2-Vacuum induction melting furnace;

[0086] 3- Melting and solidification equipment; 31- Melting and solidification furnace; 32- Directional solidification rod; 33- Cooling assembly; 34- Guided drive device;

[0087] 4-Air pressure regulating component. Detailed Implementation

[0088] Preferred embodiments of the present invention will now be described with reference to the accompanying drawings. Those skilled in the art should understand that these embodiments are merely illustrative of the technical principles of the present invention and are not intended to limit the scope of protection of the present invention.

[0089] It should be noted that in the description of this invention, terms such as "upper," "lower," "vertical," "horizontal," and "inner," indicating directional or positional relationships, are based on the directional or positional relationships shown in the accompanying drawings. These are merely for ease of description and do not indicate or imply that the device or element must have a specific orientation, or be constructed and operated in a specific orientation; therefore, they should not be construed as limitations on this invention. Furthermore, the terms "first," "second," "third," and "fourth" are used for descriptive purposes only and should not be construed as indicating or implying relative importance.

[0090] Furthermore, it should be noted that, in the description of this invention, unless otherwise explicitly specified and limited, the terms "installation," "connection," and "joining" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a direct connection or an indirect connection through an intermediate medium; and they can refer to the internal connection of two components. Those skilled in the art can understand the specific meaning of the above terms in this invention according to the specific circumstances.

[0091] As described in the background section, existing palladium alloys fail to meet the requirements for high-performance probe alloys in terms of purity and oxygen content. The alloy melting process and its connection with directional solidification easily lead to increased impurity levels. Furthermore, directional solidification technology has significant shortcomings in temperature gradient control, cooling efficiency, and process integration. This invention provides a high-purity, low-oxygen palladium alloy for probes, a method for preparing palladium alloy rods, and an apparatus.

[0092] A directional solidification system for palladium alloys, see [link / reference]. Figure 1 It includes smelting equipment, smelting and solidification equipment 3, gas pressure regulating component 4, and control system. Through the coordinated operation of the smelting equipment, smelting and solidification equipment 3, and gas pressure regulating component 4, and the detection and regulation of the control system, the purity and uniformity of the alloy are effectively improved. Among them:

[0093] (1) Melting equipment, including a vacuum induction melting furnace 2 and an electric arc melting furnace 1, to apply a composite pre-melting of palladium alloy raw materials, especially trace elements and some Cu, combining vacuum induction melting and electric arc melting, in order to provide a low-melting-point intermediate alloy melt with uniform composition and no pollution.

[0094] (2) Melting and solidification equipment 3 includes a melting and solidification furnace 31, a directional solidification rod 32 and a cooling component 33. By precisely controlling the temperature gradient and cooling rate, the melt is directionally solidified and forms a columnar crystal structure, thereby significantly improving the physical and mechanical properties of the material. The melting and solidification furnace 31 provides a stable and controllable high-temperature environment for the melt. The directional solidification rod 32 pulls the melt down at a uniform speed to move it relative to the temperature field, controlling the stable advancement of the solid-liquid interface to achieve continuous directional solidification. The cooling component 33 provides forced heat dissipation to the solidification interface.

[0095] (3) Pressure regulating component 4 is connected to the smelting equipment and the smelting and solidification equipment 3 respectively. It is used to precisely control the vacuum degree and inert gas pressure in the smelting equipment and the smelting and solidification equipment 3 to form a vacuum environment or a stable protective atmosphere to prevent the melt from reacting with oxygen.

[0096] Specifically, in the exemplary embodiment, the vacuum induction melting furnace 2 utilizes the principle of electromagnetic induction under vacuum to rapidly and uniformly heat the alloy raw materials, providing a pre-homogeneous alloy for subsequent refining. The electric arc melting furnace 1 generates localized ultra-high temperatures through electric arc discharge, enabling deep refining, vigorous stirring, and purification of the pre-homogeneous alloy, effectively breaking down oxide films and promoting the melting and homogenization of refractory elements. By combining vacuum induction melting and electric arc melting in a sequential and complementary manner, and by progressively processing the alloy from overall homogenization to localized deep refining, the purity, homogeneity, and structural stability of the final alloy melt can be significantly improved.

[0097] The melting and solidification furnace 31 provides a melting space for alloy materials and heats the metal raw materials to a predetermined temperature under vacuum / inert gas protection, allowing them to fully melt and form a homogeneous alloy melt, providing a melt source for the subsequent directional solidification process. In an optional embodiment, the melting and solidification furnace 31 has a vertical cylindrical structure, consisting of an outer shell, an inner lining, and a valve assembly. The outer shell is made of stainless steel, and the inner lining is a multi-layer insulation material of ceramic fiber and graphite to ensure thermal insulation at high temperatures. A specially made melting crucible made of boron carbide or zirconium oxide is provided at the bottom of the melting and solidification furnace 31. Both the bottom of the melting crucible and the bottom of the furnace are equipped with openable and closable discharge ports, which are controlled by the valve assembly. The valve assembly is prior art and will not be described in detail here.

[0098] As an optional embodiment, the vacuum induction melting furnace 2 is equipped with a graphite crucible surrounded by a copper induction coil to melt and electromagnetically stir the alloy raw materials; the electric arc melting furnace 1 serves as a refining unit and is equipped with a water-cooled tungsten electrode.

[0099] Furthermore, in the exemplary embodiment, the melting and solidification furnace 31 includes a sealed furnace cavity that can be opened, closed, and evacuated. A melting crucible is disposed within the sealed furnace cavity. This crucible is made of boron nitride or zirconium oxide through isostatic pressing and high-temperature sintering. Its main body is a cylindrical structure, and the inner wall is polished to reduce melt flow resistance and prevent adhesion. A circular discharge hole, controlled by a directional solidification rod 32, is located at the center of the bottom of the melting crucible. The hole diameter is set according to the diameter of the target bar, for example, 0.5-1.2 mm, preferably 0.8-1.0 mm. The edge of the hole is rounded to avoid stress concentration. The sealed furnace cavity is connected via the aforementioned pressure regulating component 4, thereby regulating the internal pressure of the melting crucible. For example, a negative pressure is created to facilitate oxygen removal before alloy melting; an inert gas is supplied to prevent impurity gases from contacting the alloy melt during holding; and a protective atmosphere and balanced pressure are provided to allow the alloy melt to be smoothly drawn out from the bottom discharge hole along with the directional solidification rod 32.

[0100] Furthermore, in the exemplary embodiment, the melting and solidification furnace 31 also includes a heating and heat preservation assembly. This assembly comprises a heating element surrounding the melting crucible, a protective sleeve surrounding the heating element, and a copper induction coil surrounding the protective sleeve. The coil pitch is 5-10 mm, and the power is 5-10 kW. It is primarily used to provide heat for alloy melting and to maintain the temperature of the molten alloy. The heat preservation sleeve consists of, from the inside out, a high-temperature resistant ceramic fiber felt (10-20 mm thick) and a graphite insulation layer (5-15 mm thick), which work together to slow down heat loss, thereby maintaining the temperature required for melt transfer and settling.

[0101] Furthermore, the cooling assembly 33 includes a water-cooled pool located below the melting and solidification furnace 31. Several spiral water-cooling pipes are installed in the water-cooled pool, and the outer wall of the pool adopts a double-layer structure to form a water-cooling jacket. The cooling assembly 33 can also be a cooling pool containing a liquid metal cooling medium (such as gallium-indium-tin alloy or high-purity molten tin), with the outer layer of the cooling pool being a jacket through which circulating cooling water flows. The top of the cooling pool is sealed to the bottom of the crucible in the melting and solidification furnace 31 via a flange, and a high-temperature resistant graphite gasket is installed at the connection to ensure airtightness. The alloy melt undergoes gradient cooling and solidification as it moves downwards through the directional solidification rod 32 within the cooling pool.

[0102] Furthermore, the cooling water in the water-cooled pool is circulating pure water, and the water temperature is maintained below 35°C.

[0103] Furthermore, the melting and solidification equipment 3 includes a multi-thermocouple feedback system, which includes:

[0104] First thermocouple: Inserted into the alloy melt in the crucible to monitor the temperature; for example, the temperature of the melt in the crucible is set at 1200-1300℃.

[0105] Several second thermocouples: embedded at different heights in the cooling pool to monitor the cooling water temperature at each height within the cooling pool;

[0106] The third thermocouple: A boss is provided at the upper end of the directional solidification rod 32. The boss is matched with the opening at the bottom of the crucible. The third thermocouple is provided on the top of the boss to monitor the temperature of the alloy melt at the bottom of the crucible. It works with the first thermocouple to judge the temperature uniformity of the alloy melt in the crucible, so as to determine the timing of the directional solidification rod 32 moving down to start directional solidification.

[0107] Each thermocouple is connected to the temperature control unit (such as a PLC controller) to transmit temperature data in real time.

[0108] The temperature control unit is connected to the refrigeration unit, which exchanges heat with the cooling component 33 through stainless steel coils. The temperature control unit adjusts the water flow rate and temperature in the spiral water-cooled pipe and water-cooled jacket according to the temperature data of the multi-thermocouple feedback system, forming a sufficient temperature gradient along the downward direction of the directional solidification rod 32.

[0109] When the directional solidification process is started, as the directional solidification rod 32 carries the melt into the water-cooling pool, the temperature control unit adjusts the output power of the refrigeration unit according to the temperature data monitored by the first thermocouple, the second thermocouple and the third thermocouple, so that the temperature of the cooling medium is maintained within the set range, with a temperature gradient of not less than 100℃ / cm, preferably 100℃ / cm to 150℃ / cm, and more preferably 110℃ / cm to 150℃ / cm, to gradient directional solidify the alloy melt into a high-purity low-oxygen palladium alloy rod.

[0110] Furthermore, in the exemplary embodiment, the directional solidification rod 32 is movably inserted into the cooling pool. The upper end of the directional solidification rod 32 can open / close the bottom opening of the crucible and draw the alloy melt out from the bottom opening of the crucible to achieve gradient cooling solidification in the cooling pool.

[0111] Furthermore, in the exemplary embodiment, the directional solidification rod 32 has a hollow cooling channel inside, through which circulating cooling water is circulated to maintain the structural integrity of the rod body during long-term contact with the high-temperature melt. A boss is machined at the upper end of the directional solidification rod 32, the size of which matches the discharge hole at the bottom of the crucible. The vertical displacement of the directional solidification rod 32 achieves the sealing and opening of the discharge hole. The bottom of the directional solidification rod 32 is connected to the guide drive device 34 to realize the vertical movement of the directional solidification rod 32. In the specific working process, the directional solidification rod 32 first rises with the assistance of the pressure difference established by the air pressure regulating component 4, causing its upper boss to tightly fit against the opening at the bottom of the crucible to form a seal. After the melting process is completed and the melt temperature is uniform, the rod body is pulled down at a constant speed according to a preset program. The melt is drawn out from the opening under the combined action of gravity and pressure difference and enters the cooling pool. The uniform movement of the rod body ensures the stable advancement of the solid-liquid interface.

[0112] Compared to the stable movement and precise solidification design of the single-bore directional solidification rod 32, as an optional embodiment, the upper end face of the directional solidification rod 32 can also be provided with multiple bosses, such as 2-4. Correspondingly, the number of discharge ports at the bottom of the crucible is consistent with the position and number of bosses. During operation, the directional solidification rod 32 can open all discharge ports at the bottom of the sealed crucible at once. After melting is completed, the rod is pulled down synchronously at a set speed, and the alloy melt is simultaneously drawn out from multiple discharge ports under the action of pressure difference, entering their respective cooling zones in the cooling pool for independent directional solidification, thereby obtaining multiple alloy rods with highly consistent composition and microstructure at once, improving production efficiency. Due to the precise control of the directional solidification temperature gradient and the stroke of the directional solidification rod 32, the number of bosses can be selected as 2 or 3, and should not be too many. They should be arranged at intervals and symmetrically on the upper end face of the directional solidification rod 32.

[0113] As an optional embodiment, the guide drive device 34 of the directional solidification rod 32 consists of a vertical lifting module and a horizontal translation module. The vertical lifting module is responsible for the up-and-down movement of the rod to control the advancement speed of the solidification interface. The vertical lifting module adopts a ball screw pair driven by a servo motor, and the traction speed is adapted to the traction speed of the directional solidification rod 32, for example, 0.2-0.25 mm / s. The horizontal translation module is connected to the vertical lifting module and is used to drive the entire vertical lifting module and the rod to move horizontally. This module specifically adopts a linear motor guide drive device 34, which works with a horizontal slide rail and a high-precision slider to complete the horizontal movement, ensuring that the deviation of the traction verticality of the directional solidification rod 32 is within 0.05 mm, preferably within 0.03 mm.

[0114] Furthermore, in the exemplary embodiment, the pressure regulating component 4 comprises a vacuum unit, a protective gas supply unit, and a gas filtration and circulation unit, and is integrated into the smelting equipment and the smelting and solidification equipment 3 via pipelines, valves, and sensors.

[0115] Furthermore, the vacuum unit employs a Roots pump to rapidly evacuate the melting chamber and the directional solidification chamber to a vacuum state, thereby removing impurities such as moisture and oxygen.

[0116] Furthermore, the protective gas supply unit is used to fill and maintain a high-purity protective gas in the chamber. Specifically, the protective gas includes an inert gas or a mixture of an inert gas and nitrogen (wherein the nitrogen volume percentage is preferably less than 5%). The device includes a gas storage tank and a pressure control valve, which can stabilize the chamber pressure within a specific range according to process requirements.

[0117] Furthermore, the gas filtration and circulation unit is used to recycle inert gas and reduce operating costs. The unit includes a circulation channel, an induced draft fan as a power source, a multi-stage filtration and purification unit responsible for progressively purifying the gas, and a sensor system for real-time monitoring. The induced draft fan is a corrosion-resistant centrifugal fan, with its flow-through components made of stainless steel, providing stable power for the gas circulation throughout the loop. The multi-stage filtration and purification unit includes a primary filtration unit composed of a sintered metal felt filter, a secondary filtration unit composed of a high-efficiency particulate air filter, and a gas purifier. The gas purifier is filled with a specific adsorbent to achieve chemical adsorption of gaseous impurities. Further, a pressure sensor and a trace oxygen analyzer are installed in the circulation channel to continuously monitor the gas state and purity, ensuring that the quality of the circulating gas always meets process requirements.

[0118] Specifically, in the exemplary embodiment, the control system is used to realize the fully automated operation of the melting equipment, the melting and solidification equipment 3 and the air pressure regulating component 4, to ensure precise control of process parameters and coordinated operation of each subsystem, and ultimately to achieve high-purity melting and directional solidification of the alloy melt.

[0119] The control system's hardware components include a central processing unit (CPU), a signal acquisition module, and a drive output module. The CPU processes signals from the signal acquisition module and outputs commands to the drive output module. The signal acquisition module includes multiple types of sensors: platinum resistance temperature sensors distributed around the melting furnace, cooling pool, and directional solidification rod 32; pressure sensors installed in the melting chamber and directional solidification chamber; and oxygen content sensors that detect the oxygen content of the inert gas in real time. The drive output module controls the aforementioned actuators: including a servo motor driving the lifting and translation of the directional solidification rod 32, a frequency converter adjusting the speed of the induced draft fan and the delivery pump, and solenoid valves managing the on / off state of the gas pipeline.

[0120] As an optional implementation, the control system can integrate an artificial intelligence module to optimize process parameters through machine learning algorithms. For example, a neural network model can be trained based on historical production data to predict the optimal combination of melting temperature, holding time, and pull-down speed to minimize component segregation and defect rate. Simultaneously, remote monitoring and predictive maintenance are supported, uploading equipment status data via an IoT interface to achieve cloud-based analysis and fault warnings.

[0121] Based on the aforementioned directional solidification system, this invention also provides a method for the directional solidification of high-purity, low-oxygen palladium alloy rods, see [link to relevant documentation]. Figure 1-2 It includes the following steps:

[0122] Step 1: Composite Pre-melting

[0123] 1. Raw Material Selection and Formulation: Select raw materials with a purity of 99.99% or higher, specifically including, by mass percentage: 30%~60% palladium, 5%~30% silver, 20%~40% copper, and 0.01-2% trace elements (such as at least one of the following: 0.1%~0.6% zinc, 0.01%~0.1% silicon, 0.1%~0.5% chromium, 50-300ppm boron, 0.1%~0.5% zirconium, 0.1%~0.6% indium, and 0.01%~0.5% aluminum). First, mix a portion of the copper (e.g., 70%~97%) with the trace elements to form an intermediate alloy raw material;

[0124] 2> Arc melting: The intermediate alloy raw material is placed in the arc melting furnace 1. After evacuation, a mixed atmosphere of argon and nitrogen (argon content ≥95%) is introduced into the melting furnace. The pressure of the protective atmosphere in the furnace is maintained at 0.01-0.1MPa. The melting furnace is started and the arc current is 200-300A to obtain the alloy billet.

[0125] 3> Vacuum induction melting: The alloy billet is added to the vacuum induction melting furnace 2 and heated to 1250-1350℃ at a heating rate of 5-10℃ / s to fully melt and hold for 5-8 minutes to obtain a homogenized low melting point intermediate alloy with a melting point below 1100℃.

[0126] 4> Cast the low-melting-point master alloy to obtain a master alloy billet (such as a fine alloy rod) and perform a solution treatment. The solution treatment includes: heating the master alloy billet to 600-850°C, holding it at that temperature for 1-2 hours, and then rapidly cooling it to room temperature at a rate of 50°C / s or higher.

[0127] 5. Perform composition analysis on the low-melting-point master alloy and supplement raw materials based on the analysis results;

[0128] Step 2: Weigh the low-melting-point master alloy, optional supplementary raw materials, and remaining raw materials according to the proportion and put them into the melting crucible of melting and solidification furnace 31. Perform vacuum induction melting at 1200-1400℃ and hold for 15-30 minutes.

[0129] During the holding period of the alloy melt, the alloy melt is alternately evacuated and purged with inert gas multiple times to remove oxygen and exhaust the gas, reducing the oxygen content of the alloy melt to below 50 ppm. Specifically, this includes:

[0130] Vacuuming procedure: Control the air pressure regulating component 4 to evacuate the air, reducing the pressure inside the sealed furnace cavity to 10. -1 Below Pa, and maintain at this vacuum level for 1-2 minutes;

[0131] Pressurization step: The pressure regulating component 4 fills the sealed furnace cavity with inert gas, and increases the pressure in the sealed furnace cavity to 0.1-0.2MPa at a rate of 0.02-0.05 MPa / min, and maintains it for 3-13 minutes;

[0132] The pressurization step includes gradient pressurization degassing:

[0133] Increase the pressure inside the furnace to the first pressure P1 at a pressurization rate V1, and maintain the pressure for 1-5 minutes;

[0134] Increase the pressure inside the furnace to the second pressure P2 at a pressurization rate V2, and maintain it for 1-5 minutes;

[0135] Increase the pressure inside the furnace to the third pressure P3 at a pressurization rate V3, and maintain it for 1-5 minutes;

[0136] Among them, V1≥V2≥V3≥0.02MPa / min, P3>P2>P1≥0.1MPa, preferably V1≥0.04MPa / min, V2≥0.03MPa / min, P2≥0.12MPa, P3≥0.15MPa.

[0137] Repeat the vacuuming and pressurization steps alternately 2-4 times.

[0138] Step 3: Keep the alloy melt in the melting crucible at a constant temperature and introduce inert gas into the sealed furnace cavity, maintaining the inert gas pressure at 0.1MPa-0.2MPa;

[0139] Step 4: Using the downward-moving directional solidification rod 32, the alloy melt is drawn out from the bottom opening of the melting crucible, and then the alloy melt is gradient-directedly solidified into a high-purity, low-oxygen palladium alloy rod through the cooling assembly 33 at a temperature gradient of not less than 100℃ / cm. Specifically:

[0140] The directional solidification rod 32 is moved downward at a constant speed of 0.2 mm / s to 0.25 mm / s while the inert gas pressure in the melting and solidification furnace 31 remains constant. The alloy melt is drawn out from the bottom opening of the crucible. A temperature gradient of 100℃ / cm to 150℃ / cm is formed along the downward direction of the directional solidification rod 32 by several spiral water-cooling pipes in the water-cooling pool and water-cooling jacket set on the outer wall of the pool, so as to directionally solidify the alloy melt into a high-purity low-oxygen palladium alloy rod.

[0141] Example 1

[0142] Example 1 describes the preparation of high-purity, low-oxygen palladium alloy rods using the palladium alloy directional solidification system and method of the present invention, comprising the following steps:

[0143] Step 1: Pre-melting and composite melting:

[0144] 1. Raw Material Selection and Mixing: Select 100g of raw materials with a purity of 99.99% or higher, specifically including, by theoretical mass percentage: 55% palladium (55g), 6.97% silver (6.97g), 37.5% copper (37.5g), 0.5% zinc (0.5g), and 0.03% silicon (0.03g). First, mix approximately 30g of copper (accounting for 80% of the total copper mass) and zinc to form an intermediate alloy raw material;

[0145] 2> Arc melting: The intermediate alloy raw material is placed in the arc melting furnace. After evacuation, a mixed atmosphere of argon and nitrogen (argon volume ratio of about 96%) is introduced into the melting furnace. The pressure of the protective atmosphere in the furnace is maintained at 0.05MPa. The melting furnace is started and the arc current is 250A to obtain the alloy billet.

[0146] 3> Vacuum induction melting: The alloy billet is added to a vacuum induction melting furnace and heated to 1300±10℃ at a heating rate of 8℃ / s to fully melt and hold for 6 minutes to obtain a homogenized low melting point master alloy.

[0147] 4> Cast the low-melting-point master alloy to obtain a master alloy fine rod with a diameter of approximately φ0.8mm, and perform a solution treatment. The solution treatment includes: heating the master alloy billet to 750°C, holding it at that temperature for 1.5h, and then rapidly water-cooling it to room temperature.

[0148] Step 2: Weigh the low-melting-point master alloy and the remaining raw materials according to the proportion and put them into the melting crucible of the melting and solidification furnace. Perform vacuum induction melting at 1250±10℃ and hold for 25 minutes.

[0149] During the holding period of the alloy melt, the alloy melt is alternately evacuated and purged with inert gas multiple times to remove oxygen and exhaust the gas, reducing the oxygen content of the alloy melt to below 50 ppm. Specifically, this includes:

[0150] Vacuuming procedure: Control the pressure regulating component to evacuate the air, reducing the pressure inside the sealed furnace cavity to 10. -2 Below Pa, and maintained at this vacuum level for approximately 1 minute;

[0151] Pressurization step: The pressure regulating component introduces inert gas into the sealed furnace cavity, and degassing is performed by gradient pressurization.

[0152] The pressure inside the furnace is increased to the first pressure P1 = 0.1 MPa at a pressurization rate of V1 = 0.05 MPa / min, and held for about 3 minutes.

[0153] The pressure inside the furnace is increased to a second pressure P2 = 0.15 MPa at a pressurization rate of V2 = 0.03 MPa / min and maintained for about 3 minutes;

[0154] The pressure inside the furnace was increased to the third pressure P3 = 0.2 MPa at a pressurization rate of V3 = 0.02 MPa / min and maintained for about 4 minutes.

[0155] Repeat the vacuuming and pressurization steps alternately twice.

[0156] Step 3: Keep the alloy melt in the melting crucible at a constant temperature and introduce inert gas into the sealed furnace cavity to maintain the inert gas pressure at approximately 0.15 MPa;

[0157] Step 4, Directional Solidification: Using a directional solidification rod moving downwards at a speed of 0.25 mm / s, the alloy melt is drawn out from the bottom opening (0.6 mm inner diameter) of the crucible. At the same time, the inert gas pressure in the melting and solidification furnace is kept constant. The alloy melt is gradient directionally solidified into a high-purity, low-oxygen palladium alloy rod with a diameter of 0.6 mm through the cooling components at a temperature gradient of 115 ± 2 °C / cm.

[0158] Examples 2-6

[0159] The main difference between Examples 2-6 and Example 1 lies in the different alloy element composition and / or mass percentage, as shown in Table 1.

[0160] Table 1 Alloying elements and proportions in Examples 1-6

[0161]

[0162] Example 7

[0163] The main difference between Example 7 and Example 1 lies in the directional solidification in step four:

[0164] Step 4, Directional Solidification: Using a directional solidification rod moving downwards at a speed of 0.2 mm / s, the alloy melt is drawn out from the bottom opening (0.8 mm inner diameter) of the crucible. At the same time, the inert gas pressure in the melting and solidification furnace is kept constant. The alloy melt is gradient directionally solidified into a high-purity, low-oxygen palladium alloy rod with a diameter of 0.8 mm through the cooling components at a temperature gradient of 120 ± 2 °C / cm.

[0165] Example 8

[0166] The difference between Example 8 and Example 1 is that, after step one, the composition of the low-melting-point master alloy is analyzed, including:

[0167] Based on the composition analysis, it is necessary to supplement the raw materials with 0.5g palladium, 0.6g silver and 0.05g zinc. Put the solution-treated intermediate alloy rod and the supplementary raw materials into the mixer and mix for 20 minutes to ensure a uniform mixture.

[0168] Then proceed to step two, which involves placing the aforementioned mixture and remaining raw materials into a melting and solidification furnace for vacuum induction melting and heat preservation.

[0169] Example 9

[0170] The difference between Example 9 and Example 1 is that in step one, the pre-melting only involves arc melting to obtain an intermediate alloy; in step two, the intermediate alloy and the remaining raw materials are subjected to subsequent vacuum induction melting and other steps.

[0171] Example 10

[0172] The difference between Example 10 and Example 1 is that in step two, the alternating deoxygenation and venting process does not include a gradient pressurization degassing step. Specifically, the alloy melt is held at 1250°C, and the furnace is alternately evacuated and filled with inert gas twice to deoxygenate and vent the alloy melt, reducing the oxygen content to below 50 ppm. This includes:

[0173] Vacuuming procedure: Control the pressure regulating component to evacuate the furnace and reduce the internal pressure to 10. -2 Pa, and maintained at this vacuum level for approximately 1.5 minutes;

[0174] Pressurization step: Control the gas pressure regulating component to introduce inert gas into the furnace, and increase the furnace pressure to 0.2 MPa at a rate of 0.05 MPa / min, and maintain it for 10 min.

[0175] Repeat the vacuuming and pressurization steps alternately twice.

[0176] Comparative Example 1

[0177] The difference between Comparative Example 1 and Example 1 is that no pre-melting is performed. Comparative Example 1 includes the following melting steps.

[0178] Step 1, Arc Melting: Place the alloy raw material into the arc melting furnace and evacuate to a vacuum level of approximately 10. -2 Pa, then a mixed atmosphere of argon and nitrogen (argon volume percentage of about 96%) is introduced into the melting furnace, maintaining the pressure of the protective atmosphere in the furnace at 0.05 MPa, the melting furnace is started, the arc current is 280 A, and the alloy billet is obtained by cooling.

[0179] Step 2: Place the alloy billet into the melting crucible of the melting and solidification furnace, close the sealed furnace chamber, and evacuate to 10°C. -2 Pa, then fill with a mixture of argon and nitrogen (volume ratio 96:4) to maintain the pressure of the protective atmosphere inside the furnace at 0.15 MPa, and perform vacuum induction melting at 1250±10℃ and hold for 25 min;

[0180] During the heat treatment of the alloy melt, deoxygenation and venting are performed, and steps three and four are the same as in Example 1.

[0181] Comparative Example 2

[0182] The difference between Comparative Example 2 and Example 1 is that in step two, the alloy melt is not subjected to alternating oxygen removal and degassing. That is, after the alloy melting in the melting and solidification furnace is melted and held at a temperature for 25 minutes, it enters steps three and four.

[0183] Comparative Example 3

[0184] The difference between Comparative Example 3 and Example 1 is that, in directional solidification, the cooling assembly directionally solidifies the alloy melt with a temperature gradient of 90±5℃ / cm.

[0185] Tests and Results

[0186] 1. Hardness test

[0187] The samples of Examples 1-10 and Comparative Examples 1-3 were tested using a Vickers hardness tester, with the load set to 200 gf and the indentation time set to 10 seconds.

[0188] 2. Mechanical property testing

[0189] Mechanical properties were tested using samples from Examples 1-10 and Comparative Examples 1-3.

[0190] Tensile strength was determined according to the national standard GB / T228.1-2021 "Metallic materials, tensile testing - Part 1: Test method at room temperature". Using a universal testing machine, samples were taken along the length of the final obtained bar and processed into standard tensile specimens. Tensile tests were conducted at room temperature until the specimens broke. The software automatically recorded and calculated the tensile strength parameters.

[0191] 3. Resistivity test

[0192] The resistance of each sample in Examples 1-10 and Comparative Examples 1-3 was measured using a ohmmeter, and the resistivity was calculated from the cross-sectional area and length of the sample.

[0193] The test results for hardness, tensile strength, and resistivity are shown in Table 2.

[0194] Table 2

[0195]

[0196] The test results show that, in Examples 1-6, due to significant differences in element content, the resulting palladium alloy rod samples exhibited considerable variations in hardness, tensile strength, and resistivity. In practical applications, these variations can be adjusted according to performance requirements. The palladium alloys in Examples 1 and 7-10 have essentially the same composition, with an overall hardness exceeding 470 HV, a tensile strength exceeding 1200 MPa, and a resistivity below 8.6 μΩ·cm. Compared to Comparative Examples 1-3, they demonstrate better overall performance.

[0197] 4. Elemental uniformity and oxygen content

[0198] Samples from Examples 1, 7-10, and Comparative Examples 1-4 were used. Three samples were taken from the head, middle, and tail of each sample to analyze the elemental uniformity and oxygen content. The results are shown in Table 3.

[0199] Table 3

[0200]

[0201] 5. Straightness error

[0202] Straightness error tests were performed on the samples of Examples 1-10 and Comparative Examples 1-3, with 5 samples selected for each group. The results are shown in Table 4.

[0203] Table 4

[0204]

[0205] 6. Dimensional accuracy error

[0206] The diameter of the samples from Examples 1-10 and Comparative Examples 1-3 was tested. Three samples were selected for each group, and the diameter of each sample was measured at the front end, midpoint and rear end along the length direction. The average value was taken. The results are shown in Table 5.

[0207] Table 5:

[0208]

[0209] In terms of elemental uniformity, oxygen content, straightness error, and dimensional accuracy error, the above test results are related to material composition and process control. Examples 1-10 are generally better than Comparative Examples 1-3. Furthermore, in Example 8, the alloy was tested after the intermediate alloy was melted in step one, and raw materials Pd, Ag, and Zn were added to make it more consistent with the composition of the target alloy.

[0210] 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 directional solidification of high-purity, low-oxygen palladium alloy rods, characterized in that, A directional solidification system for palladium alloys is employed, the directional solidification system comprising melting equipment, melting and solidification equipment, and a gas pressure regulating component; Melting equipment, including electric arc melting furnaces and vacuum induction melting furnaces; Melting and solidification equipment, including a melting and solidification furnace, a directional solidification rod, and a cooling assembly; The melting and solidification furnace includes an openable and closable sealed furnace chamber, a melting crucible disposed in the sealed furnace chamber, and a heating and heat preservation assembly surrounding the melting crucible. The smelting crucible has a bottom opening, and a directional solidification rod is located below the smelting crucible with its upper end capable of opening / closing the bottom opening. A pressure regulating component connects the smelting equipment and the sealed furnace chamber of the smelting solidification furnace, providing a vacuum environment and a protective atmosphere to the smelting equipment and the sealed furnace chamber in a switchable manner; The directional solidification method includes the following steps: Step 1: Select palladium alloy raw materials with a purity of 99.99% or higher, and pre-melt a portion of the raw materials to obtain a low-melting-point intermediate alloy with a melting point below 1100℃; The low-melting-point intermediate alloy is cast to obtain an intermediate alloy billet and then subjected to a solution treatment. The solution treatment includes heating the intermediate alloy billet to 600-850°C, holding it at that temperature for 1-2 hours, and then rapidly cooling it to room temperature at a rate of 50°C / s or higher. Step 2: Weigh the low-melting-point master alloy and the remaining raw materials according to the proportion and put them into the melting crucible of the melting and solidification furnace. Perform vacuum induction melting at 1200-1400℃ and hold the temperature. During the heat treatment of the alloy melt, the alloy melt is alternately evacuated and purged with inert gas multiple times to deoxygenate and exhaust the oxygen, reducing the oxygen content of the alloy melt to below 40 ppm; the deoxygenation and exhaust includes: Vacuuming procedure: The pressure regulating component is used to evacuate the air, reducing the pressure inside the sealed furnace cavity to 10. -1 Below Pa, and maintain at this vacuum level for 1-2 minutes; Pressurization step: The pressure regulating component fills the sealed furnace chamber with inert gas, and increases the pressure in the sealed furnace chamber to 0.1-0.2MPa at a rate of 0.02-0.05 MPa / min, and maintains it for 3-13 minutes; The vacuuming step and the pressurization step are alternately repeated 2-4 times; The pressurization step includes gradient pressurization degassing: Increase the pressure inside the furnace to the first pressure P1 at a pressurization rate V1, and maintain the pressure for 1-5 minutes; Increase the pressure inside the furnace to the second pressure P2 at a pressurization rate V2, and maintain it for 1-5 minutes; Increase the pressure inside the furnace to the third pressure P3 at a pressurization rate V3, and maintain it for 1-5 minutes; Wherein, V1≥V2≥V3≥0.02MPa / min, and V1≥0.04MPa / min, V2≥0.03MPa / min, P3>P2>P1≥0.1MPa, and P2≥0.12MPa, P3≥0.15MPa; Step 3: Keep the alloy melt in the melting crucible at a constant temperature and introduce inert gas into the sealed furnace cavity; Step 4: Using the downward-moving directional solidification rod, the alloy melt is drawn out from the bottom opening of the melting crucible, and then the alloy melt is gradient-oriented solidified into a high-purity, low-oxygen palladium alloy rod through the cooling assembly at a temperature gradient of not less than 100℃ / cm.

2. The directional solidification method as described in claim 1, characterized in that, The heating and heat preservation assembly includes a heating element surrounding the melting crucible, a protective sleeve surrounding the heating element, and an induction coil surrounding the protective sleeve; The lower end of the directional solidification rod is connected to a guide drive device that drives it to move up and down. It moves down at a constant speed of 0.2 mm / s to 0.25 mm / s to draw out the alloy melt and directionally solidify it into a casting rod.

3. The directional solidification method as described in claim 1 or 2, characterized in that, The protective atmosphere is formed by an inert gas, or a mixture of an inert gas and nitrogen. The purity of the gas in the protective atmosphere is above 99.995%.

4. The directional solidification method as described in claim 1, characterized in that, The palladium alloy raw materials, by weight percentage, include: Pd 30-60%, Cu 20-40%, Ag 5-30%, Trace elements 0.01-2%; The trace elements are selected from at least one of Zn, Cr, B, Mn, In, Al, Si, Zr, and rare earth elements.

5. The directional solidification method as described in claim 4, characterized in that, The trace element includes at least one of the following: Zn 0.1%~0.6%; Si 0.01%~0.1%; Cr 0.1%~0.5%； B 50-300ppm; Zr 0.1%~0.5%； Al 0.01%~0.5%； In 0.1%~0.6%.

6. The directional solidification method as described in claim 4 or 5, characterized in that, The pre-melting in step one adopts a composite melting method, including electric arc melting and vacuum induction melting: S1. The trace elements and at least a portion of Cu are mixed and added to an electric arc melting furnace, and the arc current is adjusted to 200-300A to obtain an alloy billet. S2. Add the alloy billet to a vacuum induction melting furnace and heat it to 1250-1350℃ at a heating rate of 5-10℃ / s until it is fully melted and held for 5-8 minutes. After cooling, a homogenized low-melting-point master alloy is obtained.

7. The directional solidification method as described in claim 6, characterized in that, In step two, after the material is discharged, the sealed furnace cavity of the melting and solidification furnace is closed and a vacuum is drawn until the vacuum degree is ≤10. -1 Pa, then inert gas is introduced to maintain the furnace pressure at 0.01-0.1 MPa, and vacuum induction melting is carried out at a temperature of 1250-1350℃, and held for 15-30 minutes.

8. A high-purity, low-oxygen palladium alloy rod for use as a probe, characterized in that, It is prepared by the directional solidification method of the high-purity low-oxygen palladium alloy rod according to any one of claims 1-7.

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