Tantalum and tantalum alloys possess excellent properties such as high density, corrosion resistance, superior high-temperature strength, good machinability, and a low ductile-brittle transition temperature. They are primarily used in high-temperature structural materials and corrosion-resistant materials, thus finding wide application in the aerospace and chemical industries. Tantalum and tantalum alloys are formed into parts through powder metallurgy or smelting processes combined with traditional machining methods.
In today's rapidly developing materials science, higher demands are placed on advanced metallic materials. Applications such as hypersonic aircraft, thermal conductive components in the nuclear industry, high-temperature engines, and gas turbines require higher operating temperatures to improve efficiency and stability. However, traditional high-temperature alloys such as cobalt-based and nickel-based alloys have almost reached their performance limits and are insufficient to meet the demands of higher-temperature applications. Refractory metals and their alloys possess characteristics such as high strength, high melting point, and resistance to high-temperature oxidation, especially maintaining high strength and corrosion resistance in high-temperature environments above 1500℃. This makes them the most promising new high-temperature environment metal materials. Among refractory metal materials, tantalum-niobium alloys, being the most challenging to manufacture and possessing the most balanced performance, are increasingly in demand for various high-temperature heat-conducting devices. However, research in this area in China is still in its early stages.
Refractory metals and their alloys mainly refer to tungsten, molybdenum, tantalum, niobium, and their alloys. They have melting points above 2000℃ and good resistance to high-temperature oxidation and corrosion. Currently, the most researched refractory metal materials are generally elemental tungsten, molybdenum, tantalum, niobium, and tungsten alloys. However, the high melting point and strength of refractory metals make them difficult to machine and weld, thus limiting their practical applications. With the development and widespread adoption of additive manufacturing technology, complex metal components can be formed, providing a new approach for the application of tantalum-niobium alloys. However, additive manufacturing technology has high requirements for raw material properties and additive process parameters.
Since tantalum-niobium alloys are sensitive to temperature changes during additive manufacturing, using a titanium alloy substrate with good thermal conductivity can effectively improve the performance of the formed part. It is understood that the titanium alloy substrate is only a preferred embodiment; those skilled in the art can use other substrates with similar good thermal conductivity.
According to the method for preparing tantalum-niobium alloy parts, the substrate and powder are preheated before forming the powder using laser additive manufacturing. Studies have found that the higher the preheating temperature, the fewer warping and cracking occur during additive manufacturing. In a preferred embodiment of the method for preparing tantalum-niobium alloy parts, the powder and substrate are preheated to above 200°C. It is understood that the upper limit of the preheating temperature can be determined based on the equipment, the melting point of the additive manufacturing powder, and the melting point of the substrate. The preheating temperature must not exceed the equipment's tolerance range, the powder's melting point, or the substrate's melting point. In a preferred embodiment, the substrate preheating temperature is 200℃-500℃. The scanning power of the laser additive manufacturing is above 300W. In a preferred embodiment, the scanning power of the laser additive manufacturing is 300W-360W.
Due to the high cost of pure tantalum, in practical applications, considering cost, a certain amount of niobium is added to tantalum as an alloying element. Since tantalum and niobium are mutually infinitely soluble elements, increasing the niobium content can reduce material costs while ensuring that the material performance meets requirements. However, research has found that excessively high niobium content can severely affect the processing performance and overall performance of the alloy product. Research has shown that a composition between Ta40Nb60 and Ta80Nb20, and more preferably between Ta55Nb45 and Ta65N35, is most advantageous for preparing high-performance powder materials using the method of this invention.
The preparation method of tantalum-niobium alloy powder, due to the high melting points of tantalum and niobium, preferably employs arc or electron beam melting to melt the alloy ingots, producing tantalum-niobium alloy ingots. These ingots are then subjected to hydrogenation treatment. In step of the tantalum-niobium alloy powder preparation method, the hydrogenation method involves hydrogenating the ingots using a high-temperature hydrogen atmosphere, achieved through pressure and heating.
The high-temperature hydrogen atmosphere in the tantalum-niobium alloy powder preparation method refers to a hydrogen atmosphere with a temperature above 300°C. More preferably, the high-temperature hydrogen atmosphere refers to a hydrogen atmosphere with a temperature above 340°C. It is understood that the purpose is to hydrogenate the tantalum-niobium alloy; however, a high-temperature, low-pressure method can also be used for hydrogenation crushing, depending on the requirements of the hydrogenation crushing equipment. In step 2 of the tantalum-niobium alloy powder preparation method, the preferred method is to obtain initially crushed hydrogenated tantalum-niobium alloy powder through physical crushing, followed by further crushing using flow milling.
The preparation method of tantalum-niobium alloy powder, in step 2, yields tantalum-niobium alloy powder with a particle size between 10-60 micrometers. The plasma treatment of the hydrogenated tantalum-niobium alloy powder involves feeding the raw powder into a DC plasma spheroidizing device. By adjusting the feeding rate and the length of the feeding tube, the hydrogenated powder is dehydrogenated and spheroidized using high-temperature DC plasma. The powder is then remelted, and the surface tension of the melt causes it to solidify into spherical shapes. The plasma treatment employs a combination of DC layered plasma spheroidizing and high-pressure gas quenching. The combination of high-temperature plasma and room-temperature inert gas cooling maximizes the spheroidization rate of the powder while reducing the nanoparticles generated during vaporization, thus improving product quality.
