A method for producing nickel-titanium alloy ingots with low oxygen content and low porosity

Abstract

This invention specifically discloses a method for producing nickel-titanium alloy ingots with low oxygen content and low porosity, solving the problems of high porosity and high oxygen content in existing nickel-titanium alloy ingot smelting methods. The method comprises the following steps: Step S1: Weighing sponge titanium and electrolytic nickel according to the alloy composition ratio; Step S2: Placing the sponge titanium and electrolytic nickel into a water-cooled copper crucible, and then starting a vacuum pump to create a vacuum; Step S3: Baking the metal in the water-cooled copper crucible; Step S4: Increasing the induction heating power; Step S5: Refining the molten metal after it has completely melted; Step S6: Pouring the molten metal into a casting mold, and after cooling, removing it to obtain a nickel-titanium alloy ingot. This invention achieves the production of nickel-titanium alloy ingots with low oxygen content and low porosity; the manufacturing process effectively eliminates gas and reduces porosity.

Description

Technical Field

[0001] This invention relates to the field of nickel-titanium alloy production technology, specifically a method for producing nickel-titanium alloy ingots with low oxygen content and low porosity. Background Technology

[0002] Nickel-titanium shape memory alloys possess excellent shape memory effect and superelasticity, are wear-resistant and corrosion-resistant, and have good biocompatibility, making them widely used in electronics, aerospace, and medical devices. High-quality nickel-titanium alloy ingots are the core foundation for producing nickel-titanium shape memory alloy products. The content of impurity elements within the nickel-titanium alloy ingot has a significant impact on the material's performance, with carbon and oxygen being the two most prominent impurity elements. Controlling the carbon and oxygen content helps in the preparation of high-quality nickel-titanium alloy materials.

[0003] Currently, there are three main methods for smelting nickel-titanium alloy ingots: one is vacuum induction melting, which can obtain ingots with better compositional uniformity. However, due to the use of static mold casting, the molten metal is poorly vented during solidification, resulting in high porosity and coarse grains. Excessive porosity and coarse grains can easily cause material cracking and fracture during subsequent processing. The second method is vacuum arc consumable melting, which is difficult to obtain ingots with uniform composition due to the large density difference between nickel and titanium. The third method is a two-step smelting method combining vacuum induction melting and vacuum arc consumable melting. First, a nickel-titanium alloy ingot is obtained by vacuum induction melting. Then, the ends of the ingot are cut off and the surface is machined off. Multiple ingots are welded together and then melted using vacuum arc consumable melting. This method can obtain nickel-titanium alloy ingots with greater weight, but the problem of poor compositional uniformity still exists. Furthermore, the process is complex, energy-intensive, and material-intensive.

[0004] In the production of nickel-titanium alloy ingots, the use of graphite crucibles is usually avoided to effectively reduce carbon content. The commonly used method to reduce oxygen content is to add a certain amount of industrial pure calcium particles as an oxygen scavenger. The principle of this method is that after pure calcium particles combine with oxygen, they generate calcium oxide slag that floats on the surface of the molten metal. During casting, it is easy to become an inclusion inside the nickel-titanium alloy ingot.

[0005] Therefore, it is necessary to propose a method for producing nickel-titanium alloy ingots with low oxygen content and low porosity to solve the above problems. Summary of the Invention

[0006] In order to solve the problems of high porosity and high oxygen content in existing nickel-titanium alloy ingot smelting methods, this invention provides a method for producing nickel-titanium alloy ingots with low oxygen content and low porosity.

[0007] This invention is achieved using the following technical solution:

[0008] A method for producing nickel-titanium alloy ingots with low oxygen content and low porosity, comprising the following steps:

[0009] Step S1: Weigh the sponge titanium and electrolytic nickel according to the alloy composition ratio;

[0010] Step S2: Place the weighed sponge titanium and electrolytic nickel into the water-cooled copper crucible in the vacuum induction melting furnace, close the furnace chamber, and then start the vacuum pump to evacuate the furnace chamber to a vacuum level of 8×10⁻⁶. -3 Pa; At the same time, a heating and heat preservation device is installed on the outside of the casting mold, and the heating and heat preservation device is activated to heat the casting mold to 300℃~600℃;

[0011] Step S3: Start the induction heater and set its power to 5kW~10kW. Then bake the metal in the water-cooled copper crucible for 15min~45min.

[0012] Step S4: Increase the power of the induction heater to 40kw~60kw so that all the metal in the water-cooled copper crucible is melted;

[0013] Step S5: After all the metal has melted, adjust the power of the induction heater to 20kw~45kw, and then refine the molten metal for 5min~30min. Keep the vacuum pump running during the refining process.

[0014] Step S6: Fill the water-cooled copper crucible with 99.999% pure argon gas to make the vacuum degree in the furnace cavity reach 300Pa; at the same time, connect an ultrasonic vibration device to the support plate at the bottom of the casting mold, start the ultrasonic vibration device and set the ultrasonic vibration frequency to 20kHz~40kHz; then pour the molten metal into the casting mold, and after cooling, remove it to obtain a nickel-titanium alloy ingot.

[0015] This invention features a reasonable and reliable structural design. The use of a water-cooled copper crucible effectively avoids the problem of increased carbon and oxygen content in materials when using graphite or oxide crucibles for melting. Low-power baking effectively removes gases adsorbed on the material surface, especially on the surface of sponge titanium, preventing the formation of stable compounds that are difficult to eliminate after the sponge titanium reacts with oxygen after the metal melts. Refining under vacuum further promotes the removal of gases from the molten metal, reducing its gas content. Injecting high-purity argon gas and pouring under a certain pressure removes residual gases from the molten metal, reducing porosity. A heating and insulation device outside the mold effectively controls the solidification rate of the alloy melt, allowing sufficient time for gases to rise and escape. Simultaneously, the addition of an ultrasonic vibration device to the casting mold promotes gas removal and loose closure, further reducing porosity. Furthermore, the ultrasonic vibration device can break up coarse dendritic grains, resulting in a denser ingot structure. Attached Figure Description

[0016] Figure 1 This is a micrograph of the pore size of the nickel-titanium alloy ingot in this invention. Detailed Implementation

[0017] Example 1

[0018] A method for producing nickel-titanium alloy ingots with low oxygen content and low porosity, comprising the following steps:

[0019] Step S1: Weigh sponge titanium and electrolytic nickel according to the alloy composition ratio of 50:50;

[0020] Step S2: Place the weighed sponge titanium and electrolytic nickel into the water-cooled copper crucible in the vacuum induction melting furnace, close the furnace chamber, and then start the vacuum pump to evacuate the furnace chamber to a vacuum level of 8×10⁻⁶. -3 Pa; At the same time, a heating and heat preservation device is installed on the outside of the casting mold, and the heating and heat preservation device is activated to heat the casting mold to 300℃;

[0021] Step S3: Start the induction heater and set its power to 5 kW. Then bake the metal in the water-cooled copper crucible for 15 minutes.

[0022] Step S4: Increase the power of the induction heater to 40kw so that all the metal in the water-cooled copper crucible is melted;

[0023] Step S5: After all the metal has melted, adjust the power of the induction heater to 20kw, and then refine the molten metal for 5 minutes. Keep the vacuum pump running during the refining process.

[0024] Step S6: Fill the water-cooled copper crucible with 99.999% pure argon gas to make the vacuum degree in the furnace cavity reach 300Pa; at the same time, connect an ultrasonic vibration device to the support plate at the bottom of the casting mold, start the ultrasonic vibration device and set the ultrasonic vibration frequency to 20Hz; then pour the molten metal into the casting mold, and after cooling, remove it to obtain a nickel-titanium alloy ingot.

[0025] The casting mold in step S2 is made of high-strength, high-purity, and high-density graphite.

[0026] Example 2

[0027] A method for producing nickel-titanium alloy ingots with low oxygen content and low porosity, comprising the following steps:

[0028] Step S1: Weigh sponge titanium and electrolytic nickel according to the alloy composition ratio of 50.2:49.8;

[0029] Step S2: Place the weighed sponge titanium and electrolytic nickel into the water-cooled copper crucible in the vacuum induction melting furnace, close the furnace chamber, and then start the vacuum pump to evacuate the furnace chamber to a vacuum level of 8×10⁻⁶. -3 Pa; At the same time, a heating and heat preservation device is installed on the outside of the casting mold, and the heating and heat preservation device is activated to heat the casting mold to 450℃;

[0030] Step S3: Start the induction heater and set its power to 8 kW. Then bake the metal in the water-cooled copper crucible for 30 minutes.

[0031] Step S4: Increase the power of the induction heater to 50kw so that all the metal in the water-cooled copper crucible melts.

[0032] Step S5: After all the metal has melted, adjust the power of the induction heater to 30kw, and then refine the molten metal for 15 minutes. Keep the vacuum pump running during the refining process.

[0033] Step S6: Fill the water-cooled copper crucible with 99.999% pure argon gas to make the vacuum degree in the furnace cavity reach 300Pa; at the same time, connect an ultrasonic vibration device to the support plate at the bottom of the casting mold, start the ultrasonic vibration device and set the ultrasonic vibration frequency to 33KHz; then pour the molten metal into the casting mold, and after cooling, remove it to obtain a nickel-titanium alloy ingot.

[0034] The casting mold in step S2 is made of high-strength, high-purity, and high-density graphite.

[0035] Example 3

[0036] A method for producing nickel-titanium alloy ingots with low oxygen content and low porosity, comprising the following steps:

[0037] Step S1: Weigh sponge titanium and electrolytic nickel according to the alloy composition ratio of 50.5:49.5;

[0038] Step S2: Place the weighed sponge titanium and electrolytic nickel into the water-cooled copper crucible in the vacuum induction melting furnace, close the furnace chamber, and then start the vacuum pump to evacuate the furnace chamber to a vacuum level of 8×10⁻⁶. -3 Pa; At the same time, a heating and heat preservation device is installed on the outside of the casting mold, and the heating and heat preservation device is activated to heat the casting mold to 600℃;

[0039] Step S3: Start the induction heater and set its power to 10 kW. Then bake the metal in the water-cooled copper crucible for 45 minutes.

[0040] Step S4: Increase the power of the induction heater to 60kw so that all the metal in the water-cooled copper crucible melts.

[0041] Step S5: After all the metal has melted, adjust the power of the induction heater to 45kw, and then refine the molten metal for 30 minutes. Keep the vacuum pump running during the refining process.

[0042] Step S6: Fill the water-cooled copper crucible with 99.999% pure argon gas to make the vacuum degree in the furnace cavity reach 300Pa; at the same time, connect an ultrasonic vibration device to the support plate at the bottom of the casting mold, start the ultrasonic vibration device and set the ultrasonic vibration frequency to 40KHz; then pour the molten metal into the casting mold, and after cooling, remove it to obtain a nickel-titanium alloy ingot.

[0043] The casting mold in step S2 is made of high-strength, high-purity, and high-density graphite.

[0044] The table below shows the test results of nickel-titanium alloy ingots from Examples 1-3:

[0045] Nickel-titanium alloy ingots Carbon content (wt%) Oxygen content (wt%) Porosity (%) Example 1 0.0024 0.0154 ＜0.2 Example 2 0.0028 0.0149 ＜0.2 Example 3 0.0031 0.0162 ＜0.2 conventional methods 0.02~0.06 0.04~0.08 0.4~0.6

[0046] While specific embodiments of the present invention have been described above, those skilled in the art should understand that these are merely illustrative examples, and the scope of protection of the present invention is defined by the appended claims. Those skilled in the art can make various changes or modifications to these embodiments without departing from the principles and essence of the present invention, but all such changes and modifications fall within the scope of protection of the present invention.

Claims

1. A method for producing a low-oxygen, low-porosity ingot of nickel-titanium alloy, the method comprising: The method is realized by the following steps: ​ Step S1: according to the alloy composition ratio, the titanium sponge and the electrolytic nickel are weighed; Step S2: Put the weighed titanium sponge and electrolytic nickel into the water-cooled copper crucible in the vacuum induction melting furnace, close the furnace chamber, then start the vacuum pump to vacuum, so that the vacuum degree in the furnace chamber reaches 8x10 -3 Pa; at the same time, configure a heating and heat preservation device outside the casting mold, and start the heating and heat preservation device to heat the casting mold to 300℃~600℃; Step S3: start the induction heater, and set the power of the induction heater to 5kw~10kw, then roast the metal in the water-cooled copper crucible, the roasting time is 15min~45min; Step S4: increase the power of the induction heater to 40kw~60kw, so that the metal in the water-cooled copper crucible is completely melted; Step S5: after the metal is completely melted, adjust the power of the induction heater to 20kw~45kw, then refine the metal liquid, the refining time is 5min~30min, and the vacuum pump is kept in working state during the refining process; Step S6: fill the water-cooled copper crucible with argon with a purity of 99.999%, so that the vacuum degree in the furnace cavity reaches 300Pa; at the same time, connect the ultrasonic vibration device on the supporting plate at the bottom of the casting mold, start the ultrasonic vibration device and set the ultrasonic vibration frequency to 20kHz~40kHz; then pour the melted metal liquid into the casting mold, and get the nickel-titanium alloy ingot after cooling and taking out.

2. The method of claim 1, wherein the ingot has a low oxygen content and a low porosity. The material of the casting mold in step S2 is graphite.

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