Product Name: TC4 Titanium Alloy Powder
● Brand:
-TC4 (National Standard)
-TiAl6v4 (ISO)
-Grade F5 (ASTM USA)
-BT6 (TOCT Russia)
-TA6V (NF France)
-TiAl6V4 (DIN Germany)
-YATB640 (JIS Japan)
● Appearance: Grey powdery
● Application: Widely used in aerospace, shipbuilding and marine engineering, chemical equipment, medical devices, etc.

TC4 titanium alloy powder source: Tianjiu Metal
3D printing is one of the rapid prototyping technologies. The technology of using adhesive materials such as powdered plastic or metal, through the principle of discrete stacking, based on a three-dimensional solid model, using layering software to layer according to a certain thickness, converting the three-dimensional digital model into a thin two-dimensional plane model, and then printing layer by layer to form the physical object.
Titanium alloy has the advantages of high strength, low elastic modulus and low density, excellent fatigue resistance and corrosion resistance, and is a rapidly growing material in the laser 3D printing industry, especially favored by the aerospace and medical fields. Titanium alloys are classified into three types based on their annealed microstructure: α - type, B type, and α+β - type. The brand name is "T" followed by A, B, C, and a sequential number, such as TA4~TA8 indicating alpha type; TB1~TB2 represent type B; TC1~TC10 represent the α+β type. The room temperature strength of α - type titanium alloy is relatively low (σ b, about 850 MPa), but its high-temperature (500-600 ℃) strength (σ b, 400 MPa at 500 ℃) and creep strength rank first among titanium alloys; And this type of alloy has stable microstructure, excellent corrosion resistance, good plasticity and processing formability, as well as excellent welding performance and low-temperature performance; β - type titanium alloy has good plasticity and toughness in the quenched state, and good cold formability; But the alloy has a high density, unstable structure, poor heat resistance, and is not widely used; The α+β - type titanium alloy combines the characteristics of both α - and β - type titanium alloys, and has excellent comprehensive performance, making it widely used.
The composition of TC4 titanium alloy is Ti-6AI-4V, which belongs to the (a+β) type titanium alloy. It has good comprehensive mechanical properties, high specific strength, excellent corrosion resistance, good biocompatibility, and is widely used in aerospace, petrochemical, biomedical and other fields. This article compares several main preparation methods for 3D printing titanium alloy powder, selects the plasma rotating electrode method to prepare titanium alloy powder, discusses the spheroidization mechanism of titanium alloy powder, explores the evolution law of its microstructure, and discusses the main heat treatment methods, providing necessary theoretical basis for the application of 3D printing technology TC4 titanium alloy.
Part 1. Preparation Method of TC4 Alloy Powder for 3D Printing Material
There are different types of 3D printing according to different materials, among which metal powder is one of the main raw materials for 3D printing, and high-purity metal powder needs to be used as the raw material. The relevant parameters of the powder, such as chemical composition, particle shape, particle size and distribution, flowability, etc., have a great impact on the quality of 3D printing. Titanium and titanium alloy materials, with their unique properties, can be prepared into powders that meet the requirements of 3D printing metal materials, but the difficulty of preparation is also high. At present, the main mature technologies for preparing 3D printed titanium alloy powder include plasma rotating electrode method, plasma wire material, and gas atomization method.
The products produced by 3D printing of titanium alloy powder have the advantages of high hardness, low thermal expansion coefficient, and good corrosion resistance.
1.1 Comparison of Three Main Preparation Methods for Titanium Alloy Powder
1.1.1 Plasma Rotating Electrode Method
This preparation method uses electrodes made of metal or alloy, and the end face is heated by an arc to melt into a liquid. Under the action of its own high-speed centrifugal force, the liquid is thrown out and crushed into small droplets, and then condensed into powder. This process can adjust the electrode speed to control the powder particle size, and is one of the ideal ways to obtain spherical powder. It has the characteristics of high sphericity, good powder flowability, high loading density, and smooth surface. The printing process control is reliable, and it is not easy to produce defects such as precipitated gases and cracks. However, due to the limitation of centrifugal speed, the titanium alloy powder produced has a coarser particle size and a relatively concentrated particle size distribution range, resulting in higher costs and lower productivity.
1.1.2 Plasma wire atomization method
This preparation method uses different alloy wires as raw materials and processes them into spherical powders* Developed independently by a Canadian company and equipped with self manufactured equipment, it has a certain influence in the industry. The spherical powder produced by this technology has the advantages of high powder yield, low impurities, and high work efficiency, making it suitable for the development of titanium alloy powder. However, there are also trace amounts of "satellite balls" and very little adhesion phenomenon, which have little effect on the performance of use.
1.1.3 Gas atomization method
Gas atomization method is a method that uses high-speed airflow to crush metal liquid flow, rapidly solidify and form powder. This method only needs to overcome the intermolecular forces between liquid metal atoms to disperse it. Basically, any material that can form a liquid can be atomized. Currently, vacuum atomization method and inert gas atomization method are widely used. The titanium alloy powder prepared by gas atomization method has the characteristics of rapid solidification, no hollow particles, and good sphericity, but the powder yield is low and the production cost is high. At present, most of the atomization technology used in China to produce titanium and titanium alloy powders has a low powder yield.
1.2 Comparison of different preparation processes
The above-mentioned methods for preparing spherical titanium and titanium alloy powders are currently the mainstream directions of research and production experiments at home and abroad. The * method has low equipment cost and produces titanium alloy powders with good sphericity, but the resulting powder particle size is relatively coarse. This can be controlled by adjusting parameters to adjust the particle size of the powder. The third type of alloy powder has good sphericity and small particle size, and there are also many types of preparation, but the domestic application technology is not yet very mature. The gas atomization method produces fine powder particles with low oxygen content and no special requirements for raw materials, but the production cost is relatively high.
Several preparation methods have their own advantages and disadvantages. After analysis and comparison, the plasma rotating electrode method was selected for atomization preparation of titanium alloy powder, and the effect was significant.
Part 2: Microstructure and Properties of TC4 Titanium Alloy for 3D Printing Materials
2.1 Experimental Materials and Methods
The experiment used plasma rotating electrode atomization method to prepare TC4 alloy powder, and its chemical composition was analyzed by instruments, as shown in Table 1.

　　According to the table, the H, N, and O content in the powder is relatively low, which meets the requirements for printing high-performance products. The shape of the powder particles prepared by this process is very close to spherical, with a smooth surface, good flowability, and no excessive impurities. The SEM image observed under a scanning electron microscope is shown in Figure 1, and the individual powder particles are shown in Figure 2. Through observation, when the geometric shape of TC4 titanium alloy powder particles is spherical, the formability is good, while elliptical powder has poor flowability and formability. Spherical titanium alloy powder has good flowability during laser 3D printing preparation.

　　2.2 Experimental Results and Analysis
2.2.1 Spherical mechanism of TC4 titanium alloy powder
In 3D printing technology, metal powder material is the raw material for metal 3D printing. The basic properties of its powder have a significant impact on the quality of the final product, and it is also one of the material basis and key elements for achieving rapid prototyping. The TC4 alloy powder prepared by plasma rotating electrode atomization method has a particle shape that is very close to spherical, with a smooth surface and good flowability. The mechanism of powder balling mainly consists of three processes, as shown in Figure 3. The process utilizes high-speed airflow to impact the melted alloy droplets, causing them to grow into a wavy liquid film and move away from the gas center at high speed; In the second process, due to the pressure, the elongated alloy droplets are unstable. Under the surface tension of the liquid, they are then blown and broken, forming elliptical droplets; In the third process, the elliptical droplet continues to break again under the action of air pressure and liquid surface tension, and is segmented into several small droplets. Under the action of surface tension, the droplet tends to shrink into a spherical shape during the descent process, and the cooling accelerates, immediately solidifying into a spherical shape.

　This experiment can obtain TC4 titanium alloy particle sizes mainly distributed in the range of 50-160 μ m by controlling the relevant parameters of the experiment. The particle size distribution is narrow and meets the requirements of 3D printing.
2.2.2 Microstructure of TC4 Titanium Alloy Samples
The metallographic structure photo of the cross-section of TC4 titanium alloy sample is shown in Figure 4. When the ion beam acts on the TC4 titanium alloy powder, a circular molten pool is formed. Within the molten pool, the temperature gradually decreases from the center to the edge, showing a Gaussian distribution. The difference in temperature results in varying degrees of melting of TC4 titanium alloy powder, with powders at lower temperatures in the edge region remaining unmelted or insufficiently melted, leading to differences in grain microstructure and size between the melt pool and the edge region. The use of pulse dot mode for metal powder cladding can reduce the influence of temperature gradient on the heat affected zone. When the latter heat source acts on the alloy powder, it also supplements energy to the edge area of the previous spot for remelting. After obtaining the energy, the grains continue to grow along the direction of energy absorption.

　　The metallographic structure photo of the longitudinal section of TC4 titanium alloy sample is shown in Figure 5. Through metallographic microscope observation, the microstructure is coarse β - columnar products. As shown in Figure 5, the grain boundaries can be clearly observed, and the columnar crystals grow along the stacking layer direction, with different growth directions. The growth stops at the β - columnar crystal boundary, and at the same time, the columnar crystals far away from the substrate continue to grow epitaxially, with grain growth phenomenon. After analysis, it was found that the temperature generated during the preparation of TC4 alloy by 3D printing has an impact on the microstructure of titanium alloy. When some of the alloy powder is melted by ion beam, the front part of the alloy is reheated. However, the beta phase self diffusion coefficient of TC4 alloy is relatively large, and smaller energy can promote grain growth. Therefore, columnar crystals are prone to growth and overheating during reheating.

　Therefore, controlling the energy of the heat source can effectively alter the microstructure of TC4 alloy.
2.2.3 Solid solution and aging heat treatment
Figure 6 shows the metallographic structures of TC4 alloy under three different heat treatment states: sedimentary state (a), 970/AC/1h+540/AC/4h (b), and 970/FC/1h (c). The deposited TC4 alloy has a mixed microstructure of alpha solid solution and beta solid solution; After heat treatment at 970 ° C/1h+540 ° C/4h (b), the metallographic structure transformed into a mesh basket structure; After further heat treatment at 970 ° C/FC/1h (c), the structure transformed into a bimodal structure consisting of a basket like structure and spheroidized alpha phase. Among them, the high-temperature creep performance, strength, and plasticity of the basket structure are good, while the plasticity of the bimodal structure is low and the strength is high.

　Through analysis, it is known that solid solution and aging heat treatment can effectively improve the strength and plasticity of TC4 titanium alloy, but the cooling rate has a significant impact on the strength and plasticity of TC4 titanium alloy, and appropriate cooling methods should be adopted in production.
Figure 7 shows the microscopic images of the microstructure of TC4 titanium alloy mesh basket under different cooling methods. When TC4 titanium alloy is air-cooled, a semi diffusion phase transformation occurs. After solid solution and aging treatment, the β phase solid solution between the primary α phase solid solution will appear as small secondary α phase solid solution, as shown in Figure 7 (a); When TC4 titanium alloy is cooled in a furnace, diffusion type phase transformation occurs. After solid solution treatment, a bimodal structure is formed. The β phase solid solution between the primary α phase solid solution in the alloy does not produce secondary α phase solid solution due to the lack of subsequent aging heat treatment, as shown in Figure 7 (b); By comparison, it can be seen that under furnace cooling conditions, the grain boundaries and intragranular alpha phase solid solution are coarser than under air cooling conditions. When TC4 titanium alloy is subjected to external forces, cracks are more likely to initiate and propagate at the grain boundaries, resulting in reduced plasticity, and printing molding is not utilized.

　　Part.3、 conclusion
(1) The TC4 titanium alloy powder prepared by plasma rotating electrode method has a particle shape very close to spherical shape, smooth surface, good flowability, and good powder characteristics, which meet the requirements of 3D printing.
(2) The microstructure of the cross-section of TC4 titanium alloy shows radiating columnar crystals from the temperature center to the edge, while the microstructure of the longitudinal section shows columnar crystals growing along the stacking layer direction. The control of heat source energy can effectively improve the microstructure of TC4 titanium alloy.
(3) The heat treatment method of solid solution+aging and air cooling effectively improves the strength and plasticity of the deposited TC4 titanium alloy, making its performance meet the requirements of TC4 titanium alloy 3D printing.