CN110893460B

CN110893460B - Additive manufacturing metallurgical structure regulation and control method based on mismatching degree of titanium alloy and boron carbide particles

Info

Publication number: CN110893460B
Application number: CN201911215049.8A
Authority: CN
Inventors: 孙中刚; 孟欣; 张华健; 张文书; 常辉
Original assignee: Nanjing Tech University
Current assignee: Nanjing Tech University
Priority date: 2019-06-05
Filing date: 2019-12-02
Publication date: 2020-10-02
Anticipated expiration: 2039-12-02
Also published as: CN111644614A; CN110893460A; CN111644614B

Abstract

The invention relates to an additive manufacturing metallurgical structure regulation and control method based on the mismatching degree of titanium alloy and boron carbide particles, and belongs to the technical field of additive manufacturing. Fully mixing a certain proportion B in titanium alloy powder before additive manufacturing₄C particles of which B₄C is different from the titanium alloy powder in median particle diameter, namely mismatching degree, because B is mixed in the titanium alloy powder₄Compared with the prior art without mismatch control, the microstructure of the titanium alloy manufactured by the additive manufacturing method is obviously improved by regulating and controlling the mismatch degree, the initial columnar β crystal grains are changed into equiaxed β crystal grains, and the different β crystal grains with the mismatch degree are refined to different degrees.

Description

Additive manufacturing metallurgical structure regulation and control method based on mismatching degree of titanium alloy and boron carbide particles

Technical Field

The invention belongs to the field of additive manufacturing, relates to a microstructure micro-regulation technology for additive manufacturing titanium alloy, and particularly relates to an additive manufacturing metallurgical structure regulation method based on mismatching degree of titanium alloy and boron carbide particles.

Background

The Additive Manufacturing (AM) technology is a technology for Manufacturing a solid part by a material discrete accumulation method, is Additive Manufacturing by a bottom-up Manufacturing method compared with the traditional material removing and machining technology, can quickly and precisely manufacture parts with any complex shapes, simplifies Manufacturing procedures and shortens the period of finished products. The heat source types include laser, electric arc, plasma, electron beam, etc., and the material forms include powder and wire, although the heat sources and materials used are different, the metallurgical characteristics of the solidification process are substantially the same. The technology is widely applied in a plurality of fields such as automobile industry, aerospace, medical appliances and the like.

Although the additive manufacturing has many advantages, the microstructure of the titanium alloy (taking TC4 as an example) manufactured by the additive manufacturing is coarse beta grains, and the titanium alloy contains a lot of needle-shaped martensite in the grains, so that the mechanical property is poor. How to regulate and control the microstructure of the titanium alloy, refine grains and improve performance becomes the focus of attention of people.

Disclosure of Invention

The invention aims to provide a method for regulating and controlling additive manufacturing metallurgical structure based on mismatching degree of titanium alloy and boron carbide particles.

To improve the texture of the original titanium alloy for better performance, a small amount of B is now introduced into the titanium alloy powder₄C particles, by adjusting titanium alloy powder and different particle size B₄Mixing of C particles (with Ti and B)₄Chemical changes and differences of in-situ autogenous reactions of C in the bathB₄The physical action of C in the bath), the manner of nucleation and growth is altered, thereby improving its organization. Through a large amount of experimental researches, different particle sizes B are found₄C particles, β grains are refined to different degrees, so the concept of mismatching degree is provided.

Titanium alloy powder and B₄The chemical reaction of the C particles to generate TiB + TiC is shown as the following formula:

5Ti+B₄C→4TiB+TiC

definition of degree of mismatch: titanium (Ti) alloy powder and B₄The ratio of the median particle diameter (D50) of the C powder is expressed by phi.

A large number of experimental studies show that: the mismatch phi has two critical values, respectively phi_{Micro critical}1.25 and phi _{Nanocritical point}750. The two critical values are watershed of columnar crystal and isometric crystal, namely, when the mismatching degree phi is larger than or smaller than the corresponding critical value, the crystal grain shapes of the alloy are different. Wherein phi_{Micro critical}For adding B in micron order₄C particle, mismatch threshold at equiaxial transition; phi is a_{Nanocritical point}To add nanoscale B₄C particles, mismatch threshold at equiaxed transition.

When the degree of mismatch phi is less than or equal to phi_{Micro critical}Or phi is more than or equal to phi_{Nanocritical point}When the titanium alloy is additively manufactured, in B₄Under the action of the C particles, the crystal grains are changed into fine isometric crystals from coarse columnar crystals; when phi is_{Micro critical}＜φ＜φ_{Nanocritical point}When the titanium alloy structure is made into columnar crystal by additive manufacturing, B₄The C particles lose the ability to promote equiaxed transformation and the ability to refine the grains.

The technical scheme for realizing the aim of the invention comprises the following steps:

step 1, in a vacuum environment, B₄The C particles and the titanium alloy powder are in a certain mismatch grade as follows: i.e. phi is less than or equal to phi_{Micro critical}Or phi is more than or equal to phi_{Nanocritical point}Fully pre-mixedWherein, 1 to 7 weight percent of B is added according to the mass percent of the titanium alloy powder₄C, particles;

step 2, using the mixed powder for additive manufacturing to obtain the titanium alloy after additive manufacturing, wherein the additive manufacturing comprises a powder laying process and a powder feeding process:

powder spreading technology: the powder spreading thickness is 20-80 μm, and the laser power is 200-500W; the scanning speed is 1-15 m/s;

the powder feeding process comprises the following steps: the powder feeding is 0.2-5r/min, the laser power is 1500-8000W, and the scanning speed is 1-30 mm/s.

Further, the mismatching degree phi is titanium alloy powder and B₄The ratio of the median diameters (D50) of the C particles,

further, the titanium alloy powder has a median diameter D50_TiSatisfies the following conditions: d50 being more than or equal to 25_Ti≤200μm。

Further, B₄Median diameter of C particles

Satisfies the following conditions:

further, 1 to 7 weight percent of B is added according to the mass percent of the titanium alloy powder₄And C, particles.

Further, the titanium alloy powder is a TC4 titanium alloy.

Compared with the prior art, the invention has the remarkable advantages that: (1) the invention regulates and controls the structure of the titanium alloy manufactured by the additive material from the raw material components manufactured by the additive material, and the process method is simple and easy to realize. (2) The invention introduces a small amount of B₄The C particles and Ti are subjected to in-situ self-generated reaction to generate TiC and TiB_xEqual ceramic phases, TiC and TiB_xThe titanium alloy has high melting point, good compatibility with titanium, no interface reaction, stable existence in titanium, 4-5 times of elastic modulus of titanium alloy, and contribution to enhancing the performance of the titanium alloy(ii) a The low thermal expansion coefficient difference caused by the similar Poisson's ratio and density can obviously reduce the thermal residual stress generated in the preparation process of the material and ensure the stability of the workpiece in the printing process.

It should be understood that all combinations of the foregoing concepts and additional concepts described in greater detail below can be considered as part of the inventive subject matter of this disclosure unless such concepts are mutually inconsistent. In addition, all combinations of claimed subject matter are considered a part of the presently disclosed subject matter.

The foregoing and other aspects, embodiments and features of the present teachings can be more fully understood from the following description taken in conjunction with the accompanying drawings. Additional aspects of the present invention, such as features and/or advantages of exemplary embodiments, will be apparent from the description which follows, or may be learned by practice of specific embodiments in accordance with the teachings of the present invention.

Drawings

The drawings are not intended to be drawn to scale. In the drawings, each identical or nearly identical component that is illustrated in various figures may be represented by a like numeral. For purposes of clarity, not every component may be labeled in every drawing. Embodiments of various aspects of the present invention will now be described, by way of example, with reference to the accompanying drawings, in which:

FIG. 1 is based on titanium alloys and B₄And C, a process flow chart of the metallurgical structure regulation and control method for additive manufacturing of particle mismatching degree.

FIGS. 2(a) - (c) are based on titanium alloys and B₄Schematic diagram of additive manufacturing metallurgical structure regulation method of C particle mismatching degree, wherein FIG. 2(a) shows that φ ≦ φ_{Micro critical}Schematic diagram of the following, in which FIG. 2(b) shows_{Micro critical}＜φ＜φ_{Nanocritical point}Schematic view of the following, wherein FIG. 2(c) shows φ ≧ φ_{Nanocritical point}The following schematic diagram.

Fig. 3 is a gold phase diagram under microscope 50X for TC4 direct additive manufacturing titanium alloy.

FIG. 4 is a TC4 titanium alloy and B₄C powder mismatching degree phi is less than or equal to phi_{Micro critical}And (3) a regulated and controlled material increase manufacturing titanium alloy 100 times of gold phase diagram.

FIG. 5 is a TC4 titanium alloy and B₄Degree of mismatch of C powder phi_{Micro critical}＜φ＜φ_{Nanocritical point}And (3) a gold phase diagram of 200 times of the titanium alloy is manufactured through regulated and controlled additive manufacturing.

FIG. 6 is a TC4 titanium alloy and B₄C powder mismatching degree phi is more than or equal to phi_{Nanocritical point}And (3) a 500-time gold phase diagram of the titanium alloy is manufactured through regulated and controlled additive manufacturing.

FIG. 7 is phi_{Nanocritical point}、φ_{Micro critical}And (4) a relation graph with columnar crystals and equiaxed crystals.

Detailed Description

For a better understanding of the technical content of the invention, reference should be made to the following detailed description of the preferred embodiments taken in conjunction with the accompanying drawings.

In this disclosure, aspects of the present invention are described with reference to the accompanying drawings, in which a number of illustrative embodiments are shown. Embodiments of the present disclosure are not necessarily intended to include all aspects of the invention. It should be appreciated that the various concepts and embodiments described above, as well as those described in greater detail below, may be implemented in any of numerous ways, as the disclosed concepts and embodiments are not limited to any one implementation. In addition, some aspects of the present disclosure may be used alone, or in any suitable combination with other aspects of the present disclosure.

With reference to FIG. 1, the present invention provides a titanium alloy and B₄The method for adjusting and controlling the particle size mismatching degree of the titanium alloy metallurgical structure through additive manufacturing comprises the steps of preparing a titanium alloy sample deposition piece through a powder feeding process or a powder laying process, and using mixed titanium gold powder with different mismatching degrees to enable original columnar β crystal grains of the titanium alloy manufactured through additive manufacturing to be equiaxial and refined to different degrees, so that the mechanical property of the titanium alloy manufactured through additive manufacturing is improved.

The invention provides a titanium alloy and B₄C particle size mismatching degree, and a method for regulating and controlling the metallurgical structure of the titanium alloy by additive manufacturing. For better illustration of the invention, the description is explained by the schematic diagrams (fig. 2(a) -2(c)), including:

step 1, the mismatching degree is one of three grades (phi is less than or equal to phi)_{Micro critical}、φ_{Micro critical}＜φ＜φ_{Nanocritical point}、φ≥φ_{Nanocritical point}) B of (A)₄And C, fully premixing the particles and the titanium alloy powder, wherein the particles comprise: in a vacuum environment, adding 1 to 7 weight percent of B according to the mass percent of the titanium alloy powder₄The C particles were mixed well and homogeneously as shown in the first column of FIGS. 2(a) -2(C) (mixing);

step 2, using the uniformly mixed powder for additive manufacturing to obtain the titanium alloy after additive manufacturing, wherein the powder laying process and the powder feeding process can be, for example:

the powder feeding process comprises the following steps: feeding powder at 0.2-5r/min, laser power at 1500-8000W, and scanning speed at 1-30 mm/s;

ti and B in the printing process₄C is subjected to in-situ self-generated reaction to form TiC and TiB_x。

For mismatch phi ≦ phi_{Micro critical}TiC and TiB generated in the molten bath of this grade_xIn B₄C is distributed around the particles and continuously generates dispersion around the particles, increases nucleation particles to improve the nucleation rate and remains large particles B₄The combined action of the C particles for hindering the grain boundary growth refines the structure of the additive manufacturing. I.e. phi is less than or equal to phi_{Micro critical}When the crystal grains are refined, the crystal grains are refined.

For degree of mismatching phi_{Micro critical}＜φ＜φ_{Nanocritical point}TiC and TiB generated in the molten bath of this grade_xAnd residual B₄C particles are dispersed in the molten pool, although nucleation particles are increased, the distribution and the quantity of the C particles are limited in the molten pool, and the structure of the titanium alloy manufactured by the additive plays a certain refining role but is not obvious, namely phi_{Micro critical}＜φ＜φ_{Nanocritical point}In this case, the equiaxial transformation of columnar crystals is not promoted, and the crystal grains are not significantly refined.

For mismatching degree phi is more than or equal to phi_{Nanocritical point}TiC and TiB generated in the molten bath of this grade_xAnd residual nanoscale minute B₄The C particles are dispersed in the molten pool fully and uniformlyFine TiC and TiB_xThe reinforcing phase as nucleation particles increases the nucleation rate and refines the crystal grains to obtain refined structure. The above process is shown in FIGS. 2(a) -2(c) for the second column (TiC and TiB)_xAnd B₄C distributed within the bath, multimedia) and the third column of fig. 2(a) -2(C) (improved as-deposited microstructure, microstrure). I.e. phi is more than or equal to phi_{Nanocritical point}At this time, equiaxed transformation of the crystal grains occurs and a thinning effect is produced.

Through a large number of experimental researches, the invention respectively manufactures additive manufacturing small samples by adjusting a series of parameters of the mismatching degree phi from 0.2, 0.3, 0.5, 0.8, 1.0, 1.2, 1.5, 2, 3, 5, 10, 15, 20, 50, 100, 200, 300, 500, 800, 1000, 2000 … … and the like, and researches B₄When the C particles have the effect of refining the crystal grains of the TC4 titanium alloy after additive manufacturing, the crystal grains are equiaxial crystals when phi is less than or equal to 1.2 or phi is more than or equal to 800; when phi is more than or equal to 1.5 and less than or equal to 500, the crystal grains are columnar crystals.

Further, more detailed metallographic tests were conducted in the ranges of 1.2 ± 0.5 and 800 ± 150, and the values of the degree of mismatch Φ were adjusted to 0.70, 0.80, 0.90, 1.00, 1.15, 1.20, 1.25, 1.30, 1.40, 1.50, 1.60, 1.70, 650, 700, 725, 750, 775, 800, 825, 850, 875, 900, 950, and the like, respectively, and small samples of titanium alloy were printed out and subjected to metallographic observation. When phi is less than or equal to 1.25, the crystal grains are isometric crystals, and when phi is more than or equal to 750, the crystal grains are isometric crystals; and when the phi is more than 1.25 and less than 750, the crystal grains are columnar crystals. Thus, it is finally determined that the two critical values are respectively phi_{Micro critical}1.25 and phi_{Nanocritical point}＝750。

[ MEANS FOR IMPLEMENTING I ]

(1) The titanium alloy adopted is TC4 powder with median grain diameter (D50)_Ti) At 150 μm, B was added₄Median diameter of C particles (D50)_B4C) Is 150 μm, B₄The addition amounts of the C particles are 1 wt% and 3 wt%, respectively. The mismatching degree phi is 150/150 is 1, phi < phi_{Micro critical}1.25, it was uniformly mixed with TC4 titanium alloy powder under a vacuum environment.

(2) The mixed titanium alloy powder is used for additive manufacturing, a powder feeding process is adopted, the laser power is 1000W, the scanning speed is 360mm/s, the powder feeding amount is 0.8r/min, and the flow of argon protective gas is 15L/min.

(3) And observing the microstructure of the titanium alloy after additive manufacturing.

The results are shown by comparing FIG. 3 with FIG. 4, it can be seen that the titanium alloy produced by direct additive manufacturing has a deposited structure morphology of β grains which are originally coarse and have a mismatching degree of phi ≦ phi_{Micro critical}The structural morphology of the additive manufacturing titanium alloy prepared by regulation and control is changed, β crystal grains are equiaxial to different degrees and become smaller with B₄The increase in the amount of C introduced increases the degree of grain refinement (1 wt% in the left panel of FIG. 4 and 3 wt% in the right panel of FIG. 4).

[ PREPARATION II ]

(1) The titanium alloy adopted is TC4 powder with median grain diameter (D50)_Ti) At 120 μm, B was added₄Median diameter of C particles (D50)_B4C) Is 5 μm, B₄The addition amounts of the C particles are 1 wt% and 3 wt%, respectively. The mismatch phi between them is 120/5 and 24, and phi is_{Micro critical}＝1.25＜φ＜φ_{Nanocritical point}In the range of 750, the titanium alloy powder is uniformly mixed with TC4 titanium alloy powder in a vacuum environment.

The results were obtained: as can be seen by comparing fig. 3 with fig. 5: through a degree of mismatching of phi_{Micro critical}＜φ＜φ_{Nanocritical point}The titanium alloy prepared by regulating and controlling has a structure which is more refined but not obvious to a certain extent than the titanium alloy prepared by directly increasing the material still takes the original columnar β grains as the main part, and B is carried out₄The increased amount of C incorporation did not result in any more significant refinement of the grains (1 wt% in the left panel of fig. 5 and 3 wt% in the right panel of fig. 5).

[ MEANS FOR CARRYING OUT III ]

(1) The titanium alloy adopted is TC4 powder with median grain diameter (D50)_Ti) At 120 μm, B was added₄Median diameter of C particles (D50)_B4C) Is 0.10 μm (i.e.100nm)，B₄The addition amounts of the C particles are 1 wt% and 3 wt%, respectively. The mismatch degree phi of the two is 120/0.10 to 1200, and phi is more than or equal to phi _{Nanocritical point}750, it is mixed with TC4 titanium alloy powder uniformly under vacuum environment.

(3) And observing the microstructure of the titanium alloy in a deposition state after additive manufacturing.

The results show that the titanium alloy manufactured by direct additive manufacturing has the deposition structure morphology of original thick β grains and the mismatching degree of phi is more than or equal to phi through comparing the graph shown in the graph 3 with the graph in the graph 6_{Nanocritical point}The structural morphology of the additive manufacturing titanium alloy prepared by regulation and control is obviously changed, β grains are obviously refined to obtain a plurality of fine equiaxed and fishbone-shaped β grains₄The increase in the amount of C incorporated also further increases the degree of grain refinement (1 wt% in the left panel of FIG. 6 and 3 wt% in the right panel of FIG. 6).

From the above examples, it can be seen that B is added to the titanium alloy powder by controlling the degree of mismatching₄C particles, so that the microstructure of the additive manufacturing titanium alloy is obviously improved, the original columnar β grains are changed into equiaxed β grains, and different β grains with mismatching degrees are refined to different degrees.

Although the present invention has been described with reference to the preferred embodiments, it is not intended to be limited thereto. The above rules are also followed for titanium alloys of other compositions, such as pure titanium, TB5, TB6, etc. Those skilled in the art can make various changes and modifications without departing from the spirit and scope of the invention. Therefore, the protection scope of the present invention should be determined by the appended claims.

Claims

1. The additive manufacturing metallurgical structure regulating and controlling method based on the mismatching degree of the titanium alloy and the boron carbide particles is characterized by comprising the following steps of:

step 1, in a vacuum environment, B₄C granuleThe particles and the titanium alloy powder are graded according to any one of the following mismatching degrees: namely, it isφ≤φ _{Micro critical}Orφ≥φ _{Nanocritical point}Fully premixing, wherein 1 is added according to the mass percentage of the titanium alloy powderwt%~7wt% of B₄C particles of a mixture of, wherein,φ _{has a microcritical value of}Addition of micron-sized B₄C particle, mismatch threshold at equiaxial transition;φ _{nanocritical point}To add nanoscale B₄C particle, mismatch threshold at equiaxial transition; wherein the degree of mismatchingφIs titanium alloy powder and B₄The ratio of the median diameter D50 of the C particles is expressed as follows:

；

and 2, using the mixed powder for additive manufacturing to obtain the titanium alloy after additive manufacturing, wherein the additive manufacturing comprises a powder laying process and a powder feeding process.

2. The method of claim 1, wherein the dusting process parameters are as follows: the powder spreading thickness is 20-80 μm, and the laser power is 200-500W; the scanning speed is 1-15 m/s.

3. The method of claim 1, wherein the titanium alloy powder has a median particle diameter D50_TiSatisfies the following conditions: d50 with the particle size of 25 mu m or less_Ti≤200μm。

4. The method of claim 1, wherein B is₄Median diameter D50B of C particles₄C satisfies: D50B with the particle size of 0.01 mu m or less₄C≤200μm。

5. The method of claim 1, wherein the titanium alloy powder is TC4 titanium alloy.

6. The method of claim 1,φ _{micro critical}=1.25，φ _{Nanocritical point}=750。