NL2029369A - High-strength and high-toughness post-processing method for 3d printing biomedical metal tantalum and metal tantalum - Google Patents

Abstract

A high-strength and high-toughness post-processing method for a 3D printing biomedical metal tantalum, comprising the following steps: placing the 3D printed tantalum metal in an argon atmosphere and heating the 3D printed tantalum metal to first threshold temperature; cooling down in a furnace to second threshold temperature; cooling down in the furnace to third threshold temperature; and cooling down quickly to a room temperature, comprising, the first threshold temperature, the second threshold temperature, and the third threshold temperature are in an arithmetic sequence. The invention can effectively realize the transformation of 3D printing metal tantalum columnar crystals to equiaxed crystals, while maintaining the fine crystal grains of 3D printing metal tantalum through the regular arrangement and accumulation of dislocations to form sub-grain boundaries, so as to maintain the high strength of 3D printing metal tantalum. At the same time can significantly improve the elongation of 3D printing metal tantalum.

Description

HIGH-STRENGTH AND HIGH-TOUGHNESS POST-PROCESSING METHOD FOR 3D

PRINTING BIOMEDICAL METAL TANTALUM AND METAL TANTALUM CROSS-REFERENCE TO RELATED APPLICATIONS The application claims priority to Chinese patent application No. 2021107525617, filed on July 2, 2021, the entire contents of which are incorporated herein by reference.

TECHNICAL FIELD The present invention belongs to a technical field of 3D printing post-processing, specifically relates to a high-strength and high-toughness post-processing method for a 3D printing biomedical metal tantalum and the metal tantalum.

BACKGROUND Tantalum metal is currently recognized as the metal element with the best biocompatibility in the biomedical field, and has the function of inducing bone growth. However, the metal tantalum has an ultra-high melting point (2996°C) and a strong oxygen affinity, which makes it difficult to use traditional processing schemes in the processing and forming process. The rise of 3D printing technology has effectively solved the difficult problem of refractory metal forming, and the center temperature of its high-energy laser beam exceeds 3000°C. Therefore, the use of 3D printing technology can realize the effective forming of the metal tantalum with the high melting point. However, a technical bottleneck of the metal tantalum formed by 3D printing technology is how to effectively control the microstructure of the formed metal tantalum workpiece, because the 3D printing process has a very high cooling rate and non-equilibrium solidification characteristics. The microstructure will directly affect the physical and chemical properties of metal tantalum workpieces. Therefore, how to control the microstructure of 3D printed metal tantalum workpieces has been a hot and difficult point in research. At the same time, columnar crystals are easily formed in 3D printed metal tantalum workpieces, and this crystal shape is likely to cause anisotropy. Compared with columnar crystals, equiaxed crystals will bring higher mechanical properties and can also effectively avoid the formation of anisotropy. Moreover, due to the high cooling rate and non-equilibrium solidification characteristics of 3D printing, the prepared metal tantalum workpieces often have high strength but generally low elongation, which severely limits its further promotion and application. Therefore, how to effectively control the microstructure of 3D printed metal tantalum workpieces to obtain fine equiaxed crystal structure is of great significance. However, there is no relevant research report, especially for the microstructure control of 3D printing high biocompatibility and high melting point metal tantalum.

SUMMARY The purpose of this section is to outline some aspects of the embodiments of the present invention and briefly introduce some preferred embodiments. Some simplifications or omissions may be made in this part and the description abstract and the title of the invention in this application to avoid obscuring the purpose of this part, the description abstract and the title of the invention, and such simplifications or omissions cannot be used to limit the scope of the present invention.

In view of the above and/or the problems in the prior art, the present invention is proposed.

The present invention provides a high-strength and high-toughness processing method for 3D printing biomedical metal tantalum. The post-processing method can effectively realize the transformation of 3D printing metal tantalum columnar crystal to equiaxed crystal, and at the same time, through the regular arrangement and accumulation of dislocations to form sub-grain boundaries, the fine crystal grains of 3D printing metal tantalum are maintained, so that the high strength of 3D printing metal tantalum can be maintained, and the elongation of 3D printing metal tantalum can be significantly improved.

In order to solve the above technical problems, the present invention provides the following technical solutions: the high-strength and high-toughness post-processing method for 3D printing biomedical metal tantalum, comprising the following: placing a 3D printed tantalum metal in an argon atmosphere and heating the 3D printed tantalum metal to a first threshold temperature; cooling down in the furnace to the second threshold temperature; cooling down in the furnace to the third threshold temperature; cooling down quickly to a room temperature; and the first threshold temperature, the second threshold temperature, and the third threshold temperature are in an arithmetic sequence.

Preferably, the first threshold temperature is 1800°C, the second threshold temperature is 1600°C, and the third threshold temperature is 1400°C.

Preferably, heating the 3D printed tantalum metal to a first threshold temperature and a heating rate is 20°C/s.

Preferably, comprising a heat preservation step; performing the heat preservation step after a temperature is raised to the first threshold temperature, cooling in the furnace to the second threshold temperature, and cooling in the furnace to the third threshold temperature, and a heat preservation time is 1~ 2 hours.

Preferably, the 3D printed tantalum metal is formed by placing a raw material powder in a selective laser melting device for 3D printing to form.

Preferably, for the 3D printing to form, a laser power is 200~300W, a laser scanning speed is 80~150mm/s, a laser scanning distance is 0.23 mm, a scanning layer thickness is 0.03mm, a laser spot size is 100m, and a scanning method adopts a zigzag scanning method with a layer- by-layer rotation of 67°.

Preferably, the density of the 3D printed tantalum metal is higher than 97%.

Preferably, the raw material powder is obtained by vacuum drying metallic tantalum powder with a medium particle size of 30~45um.

Preferably, the metal tantalum powder is smelted by an electric arc or a hydrogenation- dehydrogenation.

Preferably, in mass percentage, the metal tantalum powder includes 0.0012wt% H, 0.15wt% O, 0.0028wt% N, 0.0030wt% C, 0.0041wt% Nb, and Ta balance.

Another abject of the present invention is t provides the metal tantalum prepared by the high- strength and high-toughness post-processing method for the 3D printing biomedical metal tantalum, its tensile strength of the metal tantalum is greater than 600MPa, yield strength is greater than 550MPa, and elongation is greater than 8%.

Compared with the prior art, the present invention has the following beneficial effects: the post-processing method can effectively realize the transformation of 3D printing metal tantalum columnar crystal to equiaxed crystal, and at the same time, through the regular arrangement and accumulation of dislocations to form sub-grain boundaries, the fine crystal grains of 3D printing metal tantalum are maintained, so that the high strength of 3D printing metal tantalum can be maintained, and the elongation of 3D printing metal tantalum can be significantly improved.

The present invention combines the 3D printing process with the post-processing process, which has a greater subversion compared to the traditional forming process, and can effectively improve the difficulty of forming the high melting point metal tantalum with the traditional process, and at the same time, it can effectively improve the problem of low elongation of 3D printing metal tantalum.

BRIEF DESCRIPTION OF DRAWINGS In order to explain the technical solutions of the embodiments of the present invention more clearly, the following will briefly introduce the drawings that need to be used in the description of the embodiments. Obviously, the drawings in the following description are only some embodiments of the present invention. For those of ordinary skill in the art, other drawings can be obtained based on these drawings without creative labor.

FIG. 1 is the heat treatment process flow chart provided by the present invention; FIG. 2 is the 3D printed biomedical metal tantalum with 500um scale microstructure before and after post-processing; FIG. 3 is the 3D printed biomedical metal tantalum with 10pm scale microstructure before and after post-processing; FIG. 4 is the 3D printed biomedical metal tantalum with 100um scale microstructure before and after post-processing; FIG. 5 is the changes in mechanical properties of 3D printing biomedical metal tantalum before and after post-processing.

DETAILED DESCRIPTION OF THE EMBODIMENTS In order to make the above-mentioned objects, features and advantages of the present invention more obvious and understandable, the specific embodiments of the present invention will be described in detail below in conjunction with the embodiments of the specification.

In the following description, many specific details are explained in order to fully understand the present invention, but the present invention can also be implemented in other ways different from those described here. Those skilled in the art can make similar promotion without violating the connotation of the present invention. Therefore, the present invention is not limited by the specific embodiments disclosed below.

Secondly, the "one embodiment” or "embodiment" referred to herein refers to a specific feature, structure, or characteristic that can be included in at least one implementation of the present invention. The appearances of "in one embodiment" in different places in this specification do not all refer to the same embodiment, nor are they separate or selective mutually exclusive embodiments with other embodiments.

Embodiment 1 (1) Selecting a spherical tantalum powder with a medium particle size of 38.3um prepared by arc melting, which, by mass percentage, includes 0.0012wt% H, 0.15wt% O, 0.0028wt% N,

0.0030wt% C, 0.0041wt% Nb, and Ta balance.

(2) Drying the spherical tantalum powder obtained in (1) in a vacuum drying oven at 50°C for 24 hours as raw material powder for 3D printing.

(3) Placing the dried raw material powder in the BLT-S210 selective laser melting equipment for forming. The forming base material is metal tantalum plate. The forming process parameters are: laser power 250W, laser scanning speed 100mm/s, scanning distance 0.23mm, scanning layer thickness 0.03mm, scanning mode is layer-by-layer rotation 67°, and the density of the workpiece formed by the above process conditions is 98.3%, which is higher than 97%.

Dividing the formed workpieces into two groups, one group for post-processing, and the other group without processing.

(4) Placing the post-processing sample in a tube furnace protected by argon, and heating up to 1800°C with a heating rate of 20°C/s, and keep it at 1800°C for 2h.

(5) Then it is cooled to 1600°C in the furnace and kept warm for 2h.

(6) Then it is cooled to 1400°C in the furnace and kept warm for 2h.

(7) Then take out the air from the furnace and cool it down to room temperature to obtain the high-strength and high-toughness post-processing metal tantalum.

The 500um scale microstructure before and after the 3D printing biomedical metal tantalum is shown in FIG. 2, including the Figure 2(c) is the 500um scale microstructure of the spherical tantalum powder 3D printing without post-processing; Figure 2(d) is a 500um-scale microstructure diagram of spherical tantalum powder 3D printed and post-processing; and it can be seen that the columnar crystals formed in the process of 3D printing metal tantalum are transformed into equiaxed crystals.

The 10pm-scale microstructure before and after the 3D printing biomedical metal tantalum is 5 shown in FIG. 3. Among them, Figure 3(c) is the 10pm-scale microstructure of the spherical tantalum powder 3D printing without post-processing; Figure 3(d) is a 10um-scale microstructure diagram of spherical tantalum powder 3D printed and post-processing; it can be seen that the post-processing process can arrange randomly distributed dislocations in a regular manner.

The microstructure of 100nm scale after 3D printing biomedical metal tantalum is shown in FIG. 4. It can be seen that after the post-processing process makes the regularly arranged dislocations gradually accumulate to form sub-grain boundaries, a uniformly distributed short- range ordered equiaxed crystal structure is formed through the dislocation walls, which plays a role in grain refinement. At the same time, the sub-grain boundaries play a role in hindering the further slippage of dislocations, thereby maintaining the high strength of the workpiece at room temperature.

The above-mentioned high-strength and high-toughness post-processing metal tantalum and the un-post-processing workpiece were subjected to a tensile test at room temperature using the Instron 3369 universal electronic mechanics testing machine. The results are shown in FIG. 5. The results show that the strength of the 3D printed metal tantalum without high-strength and high-toughness post-processing is 740MPa, the elongation is only 1.7%, and there is almost no work hardening. After the high-strength and high-toughness post-processing, the strength of the workpiece is increased to 750MPa, the elongation is increased to 12%, and the work hardening phenomenon is obvious.

Embodiment 2 (1) Selecting a spherical tantalum powder with a medium particle size of 43.7um prepared by hydrogenation-dehydrogenation, which, by mass percentage, includes 0.0005wt% H, 0.21wt% O,

0.0033wt% N, 0.0027wt% C, 0.0035 wt% Nb, and Ta balance.

(2) Drying the spherical tantalum powder obtained in (1) in a vacuum drying oven at 50°C for 24 hours as raw material powder for 3D printing.

(3) Placing the dried raw material powder in the BLT-S210 selective laser melting equipment for forming. The forming base material is metal tantalum plate. The forming process parameters are: laser power 275W, laser scanning speed 100mm/s, scanning distance 0.23mm, scanning layer thickness 0.03mm, scanning mode is layer-by-layer rotation 67°, and the density of the workpiece formed by the above process conditions is 97.9%, which is higher than 97%.

Dividing the formed workpieces into two groups, one group for post-processing, and the other group without processing.

(4) Placing the post-processing sample in a tube furnace protected by argon, and heating up to 1800°C with a heating rate of 20°C/s, and keep it at 1800°C for 2h.

(5) Then it is cooled to 1600°C in the furnace and kept warm for 2h.

(6) Then it is cooled to 1400°C in the furnace and kept warm for 2h.

(7) Then take out the air from the furnace and cool it down to room temperature to obtain the high-strength and high-toughness post-processing metal tantalum.

The 500um scale microstructure before and after the 3D printing biomedical metal tantalum is shown in FIG. 2, including the Figure 2(a) is the 500um scale microstructure of the polygonal tantalum powder 3D printing without post-processing; Figure 2(b) is a 500um-scale microstructure diagram of polygonal tantalum powder 3D printed and post-processing; and it can be seen that the columnar crystals formed in the process of 3D printing metal tantalum are transformed into equiaxed crystals.

The 10um-scale microstructure before and after the 3D printing biomedical metal tantalum is shown in FIG. 3. Among them, Figure 3(a) is the 10pm-scale microstructure of the polygonal tantalum powder 3D printing without post-processing; Figure 3(b) is a 10um-scale microstructure diagram of polygonal tantalum powder 3D printed and post-processing; it can be seen that the post-processing process can arrange randomly distributed dislocations in a regular manner.

The above-mentioned high-strength and high-toughness post-processing metal tantalum and the un-post-processing workpiece were subjected to a tensile test at room temperature using the Instron 3369 universal electronic mechanics testing machine. The results are shown in FIG. 5. The results show that the strength of the 3D printed metal tantalum without high-strength and high-toughness post-processing is 610MPa, the elongation is only 1.3%, and there is almost no work hardening. After the high-strength and high-toughness post-processing, the strength of the workpiece is increased to 690MPa, the elongation is increased to 9.3%, and the work hardening phenomenon is obvious.

Embodiment 3 The difference between embodiment 3 and embodiment 1 is that the post-processing conditions are: placing the post-processing sample in a tube furnace protected by argon, and heating up to 1800°C with a heating rate of 20°C/s, and keeping it at 1800°C for 2h, and then cooling it down to room temperature in the furnace to obtain a coarse equiaxed crystal structure, whose strength is 330MPa, and the elongation rate is 25%. Compared with the direct 3D printing sample, the elongation is significantly increased, but the strength is significantly reduced.

Embodiment 4 The difference between embodiment 4 and embodiment 1 is that the post-processing conditions are: placing the post-processing sample in a tube furnace protected by argon, and heating up to 1800°C with a heating rate of 20°C/s, and keep it at 1800°C for 2h, and then cooling it down to 1600°C in the furnace and keeping warm for 2h, and then cooling it down to room temperature in the furnace to obtain a workpiece, whose strength is 350MPa, and the elongation rate is 16%. Compared with the direct 3D printing sample, the elongation is significantly increased, but the strength is significantly reduced.

Embodiment 5 The difference between embodiment 5 and embodiment 1 is that the post-processing conditions are: placing the post-processing sample in a tube furnace protected by argon, and heating up to 1800°C with a heating rate of 20°C/s, and keep it at 1800°C for 2h, and then cooling it down to 1600°C in the furnace and keeping warm for 2h, then cooling it down to 1400°C in the furnace and keeping warm for 2h and then cooling it down to 1200°C in the furnace and keeping warm for 2h and then taking out the air from the furnace and cooling it down to room temperature in the furnace to obtain a workpiece, whose strength is 620MPa, and the elongation rate is 10%. Compared with the direct 3D printed sample, the strength is slightly decreased and the elongation is significantly improved, but the obtained strength and elongation are lower than the high-strength and high-toughness processing method provided in embodiment 1. Embodiment 6 The difference between embodiment 6 and embodiment 1 is that the 3D printing process conditions are different, and the 3D printing process is: laser power 200W, laser scanning speed 100mm/s, scanning distance 0.23mm, scanning layer thickness 0.03mm, scanning mode is layer- by-layer rotation 67°. The above process condition will obtain a workpiece, whose density is 96%. After the post-processing in the embodiment 1 of the workpiece, the final strength of the workpiece is 630MPa and the elongation rate is 8.2%. Embodiment 7 The difference between embodiment 7 and embodiment 1 is that the post-processing conditions are: placing the post-processing sample in a tube furnace protected by argon, and heating up to 2000°C with a heating rate of 20°C/s, and keep it at 2000°C for 2h, and then cooling it down to 1800°C in the furnace and keeping warm for 2h, then cooling it down to 1600°C in the furnace and keeping warm for 2h and then taking out the air from the furnace and cooling it down to room temperature in the furnace to obtain a workpiece, whose strength is 450MPa, and the elongation rate is 13%. Embodiment 8 The difference between embodiment 8 and embodiment 1 is that the post-processing conditions are: placing the post-processing sample in a tube furnace protected by argon, and heating up to 1400°C with a heating rate of 20°C/s, and keep it at 1400°C for 2h, and then cooling it down to 1200°C in the furnace and keeping warm for 2h, then cooling it down to 1000°C in the furnace and keeping warm for 2h and then take out the air from the furnace and cooling it down to room temperature in the furnace to obtain a workpiece, whose strength is 670MPa, and the elongation rate is 4%.

Embodiment 9 The difference between embodiment 9 and embodiment 1 is that the post-processing conditions are: placing the post-processing sample in a tube furnace protected by argon, and heating up to 1800°C with a heating rate of 20°C/s, and keep it at 1800°C for 4h, and then cooling it down to 1800°C in the furnace and keeping warm for 4h, then cooling it down to 1400°C in the furnace and keeping warm for 4h and then take out the air from the furnace and cooling it down to room temperature in the furnace to obtain a workpiece, whose strength is 530MPa, and the elongation rate is 12%.

The present invention places the post-processing sample in a tube furnace protected by argon, and heating up to 1800°C with a heating rate of 20°C/s, and keep it at 1800°C for 2h. After the columnar crystals formed in the process of 3D printing metal tantalum are transformed into equiaxed crystals, while eliminating the anisotropy of 3D printing metal tantalum, the room temperature elongation of the workpiece is improved by obtaining equiaxed crystals, and then cooled to 1600°C in the furnace, and keep warm for 2h. After the randomly distributed dislocations are arranged regularly, the equiaxed crystals are then cooled to 1400°C in the furnace and kept for 2 hours, and after the regularly arranged dislocations gradually accumulate to form sub-grain boundaries, a uniformly distributed short-range orderly equiaxed structure is formed through the dislocation walls, which plays a role in grain refinement. At the same time, the sub-grain boundary plays a role in hindering the further slippage of dislocations, and then quickly air-cooled to room temperature to prevent abnormal swelling of the crystal grains and reduce the strength, thereby maintaining the high strength of the workpiece at room temperature.

The present invention can effectively realize the transformation of 3D printing metal tantalum columnar crystal to equiaxed crystal through the post-processing method. At the same time, the present invention also maintains the fine crystal grains of 3D printing metal tantalum through the regular arrangement and accumulation of dislocations to form sub-grain boundaries, so as to maintain the high strength of 3D printing metal tantalum, and at the same time, it can significantly improve the elongation of 3D printing metal tantalum.

It should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention rather than limiting, although the present invention has been described in detail with reference to the preferred embodiments, those of ordinary skill in the art should understand that modifications or equivalent replacements can be made to the technical solutions of the present invention without departing from the spirit and scope of the technical solutions of the present invention should be covered by the claims scope of the present invention.

Claims (10)

CONCLUSIONS A post-processing method for obtaining a 3D printed biomedical tantalum metal with high strength and high rigidity, the method comprising the steps of: - placing a 3D printed tantalum metal in an argon atmosphere and heating the 3D printed tantalum metal to an first threshold temperature; — cooling in an oven to a second threshold temperature; — cooling in the oven to a third threshold temperature; and — rapid cooling to room temperature; — wherein the first threshold temperature, the second threshold temperature and the third threshold temperature are in an arithmetic sequence. The post-processing method for obtaining high strength and high rigidity 3D printed biomedical tantalum metal according to claim 1, wherein the first threshold temperature is 1800°C, the second threshold temperature is 1800°C, and the third threshold temperature is 1400°C. The post-processing method for obtaining high strength and high rigidity 3D printed biomedical tantalum metal according to claim 1, wherein the 3D printed tantalum metal is heated to the first threshold temperature and the heating rate is 20°C/s. The post-processing method for obtaining high strength and high rigidity 3D printed biomedical tantalum metal according to claim 3, comprising the following heat preservation step, which is performed after the temperature is raised to the first threshold temperature: cooling in the furnace to the second threshold temperature, and cooling in the oven to the third threshold temperature, the heat preservation time is 1 ~ 2 hours. The post-processing method for obtaining 3D printed biomedical tantalum metal with high strength and high rigidity according to claim 1, wherein the 3D printed tantalum metal is formed by placing raw powder raw material in a selective laser melting device to form by 3D printing. The post-processing method for obtaining high strength and high rigidity 3D printed biomedical tantalum metal according to claim 5, wherein for 3D printing forming, the laser power is 200~300W, the laser scanning speed is 80~150mm/s, the laser scanning distance 0.23 mm, the scanning layer thickness is 0.03 mm, the laser spot size is 100 µm, and the scanning method adopts a zigzag scanning method with a layer-by-layer rotation of 67°. The post-processing method for obtaining high strength and high rigidity 3D printed biomedical tantalum metal according to claim 6, wherein the density of the 3D printed tantalum metal is higher than 97%. The post-processing method for obtaining high strength and high rigidity 3D printed biomedical tantalum metal according to claim 6, wherein tantalum metal powder is melted by electric arc or hydrogenation - dehydrogenation. The post-processing method for obtaining high strength and high rigidity 3D printed biomedical tantalum metal according to claim 8, wherein the tantalum metal powder contains 0.0005 ~ 0.0012 wt% H, 0.15 ~ 0.21 wt% O, 0.0028 ~ 0.0033 wt% N , 0.0027 ~ 0.0030 wt% C, 0.0035 ~ 0.0041 wt% Nb, and the remainder includes Ta. The post-processing method for obtaining high strength and high rigidity 3D printed biomedical tantalum metal according to claim 8, wherein the tensile strength of the tantalum metal is greater than 750 MPa, the yield strength of the tantalum metal is greater than 650 MPa, and the elongation of the tantalum metal is greater than 12%.