CN115026308A

CN115026308A - Method for regulating and controlling laser cladding deposition structure through cold spraying

Info

Publication number: CN115026308A
Application number: CN202210854659.8A
Authority: CN
Inventors: 孙中刚; 焦涛; 郭艳华; 姚杰; 鲁金忠; 李文亚
Original assignee: Nanjing Tech University
Current assignee: Nanjing Tech University
Priority date: 2022-06-10
Filing date: 2022-07-17
Publication date: 2022-09-09
Anticipated expiration: 2042-07-17
Also published as: CN115026308B

Abstract

The invention provides a method for regulating and controlling a laser cladding deposition structure by cold spraying, which is characterized in that the cold spraying and the laser cladding deposition processes are combined, a cladding layer is subjected to cold spraying treatment by printing one layer, the cladding layer is subjected to severe plastic deformation by utilizing high-speed impact of solid metal powder particles, a large number of nucleation sites are provided, the formation of superfine dynamic recrystallization grains is promoted, the local grains are subjected to dynamic recrystallization, the recrystallization grains grow up in the subsequent heating process, the final grains tend to be uniform, the structure of a component is refined, and the mechanical property of the component is improved.

Description

Method for regulating and controlling laser cladding deposition tissue through cold spraying

Technical Field

The invention belongs to the technical field of additive manufacturing, and particularly relates to a method for regulating and controlling laser cladding deposition tissues through cold spraying.

Background

In the additive manufacturing process, the material often has strong physical and chemical changes and a complex physical metallurgy process, and meanwhile, the complex deformation process is accompanied, the above process influence factors are numerous and relate to a plurality of factors such as materials, structural design, technical process, post-treatment and the like, so that the material-process-tissue-performance relation in the additive manufacturing process is often difficult to accurately grasp, and the active and effective regulation and control of the shape are difficult to realize.

The laser cladding deposition is an additive manufacturing technology based on the basic principle of rapid prototype manufacturing, metal powder is used as a raw material, high-energy laser is used as an energy source, and the metal powder synchronously fed is subjected to layer-by-layer melting, rapid solidification and layer-by-layer deposition according to a preset scanning path, so that the direct manufacturing of metal parts is realized. But due to the special metallurgical process, the extremely complex system of multifactor, multi-layer and cross-scale coupling of materials, structures, various physical fields and chemical fields is involved, and the problems of obvious columnar crystal, uneven structure and the like are easily generated in the structure of the obtained part. Around this problem, a great deal of exploratory research has been carried out in the prior art, and attempts are made to solve the problem of metallurgical structure in additive manufacturing from the additive manufacturing process itself, addition of reinforcing particles to refine grains, and regulation and control of microstructure by means of magnetic fields, electric fields and the like.

The U.S. Banerjee et Al successfully prepares Ti-TiB and Ti6Al4V-TiB composite materials by utilizing a laser stereo-forming technology, and TiB reinforcements can be uniformly distributed in a deposited alloy and can refine the structure to a certain degree. The addition of the nucleating agent improves the structure by increasing the number of nucleation sites, but the addition of the nucleating agent affects the alloy composition, and is not suitable for alloys with strict alloy composition requirements.

Researches of Shenhang, Wangwei and the like show that the temperature difference between adjacent layers in the cladding process can be reduced by compound ultrasonic vibration in the cladding process, the molten pool convection is enhanced, the temperature field of the molten pool is more uniform and stable, the cladding layer is uniform in structure, grains are effectively refined, residual stress is reduced, and the size and the number of air holes are obviously reduced. However, the effect of composite ultrasonic vibration in the cladding process is limited, and the grain refining effect is not obvious.

Disclosure of Invention

The invention aims to solve the problems that columnar crystals are obvious and the structure is uneven in the laser cladding deposition process, and the like, and provides a method for regulating and controlling the laser cladding deposition structure by cold spraying.

In order to achieve the purpose, the technical scheme adopted by the invention is as follows:

a method for regulating and controlling laser cladding deposition tissues through cold spraying comprises the following steps:

depositing alloy powder on a substrate layer by layer in an upward growth mode from a first layer according to a preset program by adopting a powder feeding additive manufacturing process until a last Nth layer is deposited to obtain a required component;

in the process of depositing the first layer to the Nth layer, cold spraying treatment is carried out on each layer of cladding layer by adopting alloy powder of the same kind as the alloy powder used for printing;

in the process of each cladding layer, recrystallized grains are formed in the ith cladding layer by cold spraying, and the recrystallized grains grow along with the deposition of the (i + 1) th cladding layer, so that the structure of the ith cladding layer along the deposition direction presents a grain gradient of an equiaxed area and a fine grain area, wherein i is 1,2,3, … and N-1.

Preferably, the crystal grain size of the equiaxed crystal area is 30-50 μm.

Preferably, the fine crystalline region has a grain size of 5 to 10 μm.

Preferably, each cladding layer is subjected to cold spray treatment, and the thickness of the resulting sprayed layer on the existing cladding layer is 0.1 to 0.2 mm.

Preferably, when each cladding layer is subjected to cold spraying treatment, the temperature of the sprayed alloy powder is controlled to be 400-700 ℃.

Preferably, the process conditions of the cold spray treatment are as follows:

nitrogen is used as working carrier gas, the pressure of the carrier gas is 2-5MPa, and the flow rate of the carrier gas is 40-50Nm ³ The preheating temperature of the carrier gas is 400-700 ℃, and the rotating speed of the powder feeder is 1-5 r/min.

Preferably, the alloy powder used for spraying has a particle size of 10 to 50 μm.

Preferably, the powder feeding additive manufacturing process is configured to determine the powder feeding speed and the laser power parameter according to the alloy component parameters, and set the printing program according to the parameters so as to print and form the component.

Preferably, the powder feeding additive manufacturing process comprises the following steps:

the powder feeding is 3-10g/min, the laser power is 1000-5000W, the scanning speed is 1-30mm/s, the scanning distance is 1-2mm, and the oxygen content is 200 ppm.

According to the technical scheme, the method for regulating and controlling the laser cladding deposition structure by cold spraying carries out cold spraying treatment on each layer of cladding layer, the sprayed material is the same as the material used for printing, the sprayed material is not melted, the sprayed powder is driven to accelerate in a nozzle by using preheated compressed gas as an accelerating medium to form supersonic gas-solid two-phase flow, the sprayed solid metal powder particles impact on a deposition layer at high speed to cause severe plastic deformation of the cladding layer, so that a large number of nucleation sites are provided, the accumulation and evolution of dislocation are promoted by the extremely large strain and the extremely high strain rate in the particles in the deformation process, the formation of superfine dynamic recrystallization grains is promoted, the local grains are dynamically recrystallized, and when the next layer of cladding layer is deposited, the cold sprayed solid particles are melted by the high temperature generated by laser, and the recrystallized grains generated by plastic deformation grow up, the final grains tend to be uniform, and the structure is refined, so that the mechanical property and the fatigue life of the component are improved.

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

FIG. 1 is a schematic structural diagram of a system for regulating laser cladding deposition tissue by cold spraying.

FIG. 2 is a process flow chart of the method for regulating laser cladding deposition tissue by cold spraying.

FIG. 3 is a schematic diagram of a tissue conditioning process of the method for conditioning laser cladding deposited tissue by cold spray according to the present invention.

Detailed Description

In order to better understand the technical content of the present invention, specific embodiments are described below with reference to 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.

Referring to fig. 1-3, in an exemplary embodiment of the invention, a system for regulating laser cladding deposition tissue by cold spraying is provided, which includes a substrate 10, a 3D printing system 20, a cold spraying system 30, and a powder feeding system 40.

The 3D printing system 20 is a coaxial powder feeding printing system or a paraxial powder feeding printing system, which can be set by a person skilled in the art according to practical situations, and is not limited herein.

In the example shown in fig. 1, a coaxial powder feeding laser cladding 3D printing system is taken as an example.

The powder feeding system 40 may use a commercially available multi-channel powder feeder to feed powder (for example, titanium alloy or aluminum alloy) to the surface of the substrate 10 via the laser cladding head 21 by means of coaxial powder feeding to form a powder spot.

The laser cladding head 21 forms a laser spot on the substrate, and the 3D printing system 20 performs cladding molding on the powder on the substrate according to a preset program, and prints the workpiece in a layer-by-layer printing manner until the printing of the whole component is completed. In fig. 1, reference numeral 22 denotes a molten pool, and reference numeral 23 denotes a cladding layer.

The cold spraying system 30 comprises a carrier gas device 31, a powder feeding device 32, a gas heating device 33 and a laval nozzle 34, wherein the gas is divided into two parts by the carrier gas device 31, one part is conveyed to the powder feeding device 32 to be used as carrier gas of powder, the other part is heated by the gas heating device 33 to be used as accelerating gas, the powder feeding gas and the accelerating gas are mixed in a front confluence chamber of the laval nozzle 34, supersonic gas-powder two-phase flow is generated after the powder feeding gas and the accelerating gas are scaled by the laval nozzle 34, and particles impact a deposition layer at extremely high speed.

The cold spray system 30 is configured to be integrally assembled with a control system, and the control system is configured such that after the 3D printing system finishes printing each layer of the cladding layer, the cold spray system 30 performs cold spray on the lower cladding layer 11 with preset parameters, so that the solid metal powder particles collide at high speed to cause severe plastic deformation of the cladding layer, thereby providing a large number of nucleation sites and promoting the formation of ultra-fine dynamic recrystallization grains.

In a preferred embodiment, the carrier gas device 31 can adopt a high-pressure gas device, the carrier gas pressure is 2-5MPa, and the carrier gas flow is 40-50Nm ³ And/min. In a preferred embodiment, the preheating temperature of the carrier gas by the gas heating device 33 is 400 ℃ to 700 ℃.

With reference to fig. 2-3, on the basis of fig. 1, the method for regulating and controlling laser cladding deposition tissues by cold spraying according to the embodiment of the invention comprises the following processes:

In a preferred embodiment, the equiaxed regions have a grain size of 30-50 μm.

In a preferred embodiment, the fine crystalline regions have a grain size of 5-10 μm.

In a preferred embodiment, each cladding layer is subjected to cold spray treatment, and the thickness of the resulting sprayed layer on the current cladding layer is 0.1-0.2 mm.

In a preferred embodiment, when each cladding layer is subjected to cold spraying treatment, the temperature of the sprayed alloy powder is controlled to be 400-700 ℃.

In a preferred embodiment, the process conditions of the cold spray treatment are as follows:

nitrogen is used as working carrier gas, the pressure of the carrier gas is 2-5MPa, and the flow rate of the carrier gas is 40-50Nm ³ Min, preheating temperature of carrier gas is 400-700 ℃, and powder feeding speed of the powder feeding device 32 is 1-5 r/min.

In a preferred embodiment, the alloy powder used for cold spraying has a particle size of 10-50 μm.

In a preferred embodiment, the powder feeding additive manufacturing process is configured to determine the powder feeding speed and the laser power parameter according to the alloy component parameters, and set a printing program according to the parameters so as to print and mold the component.

In a preferred embodiment, the powder feeding additive manufacturing process is as follows:

It should be understood that the method of the present invention is applicable to metal powder or alloy powder, including but not limited to powder materials of titanium alloy, aluminum alloy, stainless steel, etc., and the parameters of the printing process and the cold spraying process can be adjusted appropriately according to actual conditions for different alloy materials.

As shown in fig. 3, by the method of the present invention, the cold sprayed high-speed metal powder (as indicated by reference numeral 1 in b diagram of fig. 3) impacts the cladding layer (a diagram of fig. 3), so that the cladding layer is severely plastically deformed (as indicated by reference numeral 2 in b diagram of fig. 3), a large number of nucleation sites are provided, dynamic recrystallization of the cladding layer (as indicated by reference numeral 3 in b diagram of fig. 3) occurs, and residual stress generated in the cladding layer is eliminated.

During the deposition of the next cladding layer (indicated by reference numeral 1 in c diagram of fig. 3), the high temperature generated by the laser can melt the cold sprayed solid particles, the recrystallized grains generated by plastic deformation grow up (indicated by reference numeral 2 in c diagram of fig. 3) in the subsequent heating process, and the final grains tend to be uniform, so that the structure of the previous cladding layer along the deposition direction has a grain gradient of equiaxed grains (indicated by reference numeral 3 in c diagram of fig. 3) and fine grains (indicated by reference numeral 4 in c diagram of fig. 3).

By carrying out cold spraying treatment on each layer of cladding layer and regulating and controlling the structure form of the laser cladding deposition, the structure of the printed component, whether the surface or the inner structure, is refined and homogenized, the formation of defects is inhibited, the component forms an isometric crystal-fine crystal continuous circulation gradient structure (the state shown in a d diagram of fig. 3), and the mechanical property of the material is greatly improved.

For better understanding, the present invention is further described below with reference to specific examples, but the process is not limited thereto and the present disclosure is not limited thereto.

In the following examples and comparative examples, the printing of the members was performed using TC4 titanium alloy powder as a raw material, the average particle size was 53 to 150 μm, the composition was as shown in Table 1, and the powder used for cold spraying was the same as the printing raw material and the average particle size of TC4 titanium alloy powder used for cold spraying was 10 to 50 μm.

TABLE 1

Al

V

Fe

O

C

Si

N

Ti

6.02wt.％

4wt.％

0.15wt.％

0.16wt.％

0.06wt.％

0.04wt.％

0.03wt.％

Balance of

[ example 1 ]

(1) And drying the TC4 titanium alloy powder, fully mixing and stirring the dried TC4 powder, putting the mixture into an LDM powder feeder, setting a powder feeding process, and conveying nitrogen protection gas while feeding the powder.

(2) And (3) using the processed alloy powder for additive manufacturing, setting laser cladding parameters, printing the additive manufacturing component by adopting a powder feeding process, and stopping printing after the first layer is printed to obtain a coating layer (0.5mm) of TC 4.

The powder feeding speed is 4.5g/min, the powder feeding air flow is 8L/min, the laser power is 1200W, the scanning speed is 10mm/s, the scanning interval is 1.6mm, and the oxygen content is 200 ppm.

(3) And (3) after the printing is stopped, performing cold spraying treatment on the cladding layer formed in the step (2) to obtain a cold spraying coating (controlled to be 0.2 mm).

The particle diameter of TC4 powder is 10-50um, the working carrier gas is nitrogen, the pressure of the carrier gas is 2MPa, and the flow rate of the carrier gas is 45Nm ³ Min, preheating temperature of carrier gas is 400 ℃, and rotating speed of the powder feeder is 4 r/min.

(4) Repeating (2) and (3) on the treated deposition layer, printing layer by layer and cold spraying treatment, wherein the cold spraying treatment is carried out on each printing layer until the whole component (60 multiplied by 30 multiplied by 10mm) is printed.

(5) After the box sealing printing is finished, opening the cabin door and taking out the components after the components are completely cooled (3-4 hours).

[ example 2 ]

The particle diameter of the sprayed powder in the treatment process is 10-50um, the working carrier gas is nitrogen, the pressure of the carrier gas is 3MPa, and the flow rate of the carrier gas is 45Nm ³ Min, preheating temperature of carrier gas is 500 ℃, and rotating speed of powder feeder is 4 r/min.

(4) And (3) repeating the steps (2) and (3) on the treated deposition layer, and performing cold spraying treatment layer by layer each time one layer is printed until the whole component (60 multiplied by 30 multiplied by 10mm) is printed.

(5) After the box sealing printing is finished, opening the hatch door to take out the components after the components are completely cooled (3-4 hours).

[ example 3 ]

(1) And drying the TC4 titanium alloy powder, fully mixing and stirring the dried TC4 powder, putting the mixture into an LDM powder feeder, setting a powder feeding process, and simultaneously feeding nitrogen protection gas.

(2) And (3) using the processed alloy powder for additive manufacturing, setting laser cladding parameters, printing the additive manufacturing component by adopting a powder feeding process, and stopping printing after the first layer is printed to obtain a layer of TC4 cladding (0.5 mm).

The powder feeding speed is 4.5g/min, the powder feeding air flow is 8L/min, the laser power is 1200W, the scanning speed is 10mm/s, the scanning distance is 1.6mm, and the oxygen content is 200 ppm;

The grain diameter of the sprayed TC4 powder in the treatment process is 10-50um, the working carrier gas is nitrogen, the pressure of the carrier gas is 4MPa, and the flow rate of the carrier gas is 45Nm ³ Min, preheating temperature of carrier gas is 600 ℃, and rotating speed of powder feeder is 4 r/min.

[ example 4 ]

(1) Drying TC4 titanium alloy powder, fully mixing and stirring the dried TC4 powder, putting the mixture into an LDM powder feeder, setting a powder feeding process, and simultaneously feeding nitrogen protection gas;

The particle diameter of TC4 powder is 50um, the working carrier gas is nitrogen, the carrier gas pressure is 5MPa, and the carrier gas flow is 45Nm ³ Min, preheating temperature of carrier gas is 700 ℃, and rotating speed of powder feeder is 4 r/min.

Comparative example 1

(2) And (3) using the processed alloy powder for additive manufacturing, setting laser cladding parameters, printing the additive manufacturing component by adopting a powder feeding process, stopping printing after printing the first layer to obtain a TC4 cladding layer (0.5mm), and continuously depositing until the whole component (60 multiplied by 30 multiplied by 10mm) is printed.

(3) after the box sealing printing is finished, opening the cabin door and taking out the components after the components are completely cooled (3-4 hours).

The TC4 titanium alloy members of examples 1-4, as well as comparative example 1, were tested for yield strength, tensile strength, and elongation, with the results shown in the table below.

Sample (I)	Tensile strength MPa	Yield strength MPa	Elongation percentage%
				Example 1	1140	916	8.3
Example 2	1215	950	8.9
				Example 3	1175	941	8.6
Example 4	1153	925	8.4
				Comparative example 1	970	850	7.8

The results show that the samples of examples 1 to 4 improve the stress inside each cladding layer and among the multiple cladding layers through the cold spraying treatment of each cladding layer and multiple cold spraying treatments, refine the grain structure and improve the mechanical properties. The comparative example did not use a cold spray treatment cladding layer and the mechanical properties of the resulting member were not as good as the cold spray treated samples.

The metal powder particles directly act on the cladding layer for a plurality of times through high-speed impact, so that the matrix is subjected to severe plastic deformation, opportunities and time are provided for recombination and appreciation of dislocation in the alloy structure, the more reasonable and uniform dislocation structure is formed in the alloy structure, the internal structure is improved, and the comprehensive performance is improved.

Although the present invention has been described with reference to the preferred embodiments, it is not intended to be limited thereto. 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. A method for regulating and controlling laser cladding deposition tissues through cold spraying is characterized by comprising the following steps:

in the process of each cladding layer, recrystallized grains are formed in the current i-th cladding layer through cold spraying treatment, and the recrystallized grains grow along with the deposition of the i + 1-th cladding layer, so that the structure of the current cladding layer along the deposition direction presents a grain gradient of an equiaxed crystal area and a fine crystal area, wherein i is 1,2,3, …, N-1.

2. The method for regulating laser cladding deposition structure through cold spraying according to claim 1, wherein the crystal grain size of the equiaxed crystal area is 30-50 μm.

3. The method for regulating the deposition structure by laser cladding through cold spraying according to claim 1, wherein the grain size of the fine crystalline region is 5-10 μm.

4. The method for regulating the laser cladding deposition structure through cold spraying according to claim 1, wherein each cladding layer is subjected to cold spraying treatment, and the thickness of the sprayed layer obtained on the current cladding layer is 0.1-0.2 mm.

5. The method for regulating and controlling the laser cladding deposition structure through cold spraying according to claim 1, wherein the temperature of the sprayed alloy powder is controlled to be 400-700 ℃ when each cladding layer is subjected to cold spraying treatment.

6. The method for regulating and controlling the laser cladding deposition structure through cold spraying according to claim 1, wherein the process conditions of the cold spraying treatment are as follows:

7. The method for regulating the laser cladding deposition structure through cold spraying according to claim 1, wherein the grain diameter of the alloy powder used for spraying is 10-50 μm.

8. The method for regulating and controlling the laser cladding deposition structure through cold spraying according to claim 1, wherein the powder feeding additive manufacturing process is configured to determine powder feeding speed and laser power parameters according to alloy component parameters, and set a printing program according to the parameters to perform printing and forming of the component.

9. The method for regulating and controlling the laser cladding deposition structure by cold spraying according to claim 1, wherein the powder feeding additive manufacturing process comprises the following steps: