Novel cobalt-based high-temperature alloy design method based on combination of laser directional energy deposition and diffusion multi-section

Abstract

The invention relates to a novel cobalt-based high-temperature alloy design method based on combination of laser directional energy deposition and diffusion multi-element knots, which comprises the following steps of: firstly, designing components of cobalt-based high-temperature alloy at each position of the diffusion multi-element knots; selecting proper elementary substance powder and intermediate alloy powder based on preset alloy components, and fully mixing the elementary substance powder and the intermediate alloy powder according to the component proportion; next, the corresponding mixed powder is subjected to laser directional energy deposition according to alloy components at different positions of the diffusion multi-element section, and a diffusion multi-element section test piece is prepared; in the process, uniform distribution and good metallurgical bonding of alloy components are ensured by controlling technological parameters such as laser power, scanning speed and powder feeding rate. And after printing is completed, the diffusion multi-section test piece is subjected to heat treatment, and then composition, structure and performance characterization is carried out. And typical components meeting the target structure and thermophysical properties are preferably selected for printing verification again, so that development of the precipitation-strengthened cobalt-based high-temperature alloy with high solid solution, low density and high performance is realized.

Description

Technical Field

[0001] The present invention relates to the technical field of the design and preparation of cobalt-based superalloys, and specifically to a method for realizing the efficient and precise design and preparation of cobalt-based superalloys by combining laser directed energy deposition technology and diffusion multi-joint technology. Background Art

[0002] Cobalt-based superalloys are a type of superalloys, which have cobalt as the main component, contain a considerable amount of nickel, chromium, tungsten, and a small amount of alloying elements such as molybdenum, niobium, tantalum, titanium, lanthanum, and occasionally contain iron. Cobalt-based superalloys have the characteristics of good high-temperature strength, good oxidation resistance, hot corrosion resistance, and wear resistance, and are widely used in the fields of aerospace, energy, automotive, electronics, and chemical engineering.

[0003] In the prior art, the design and preparation methods of new cobalt-based superalloys mainly rely on the traditional "trial and error method", that is, first, according to the required performance characteristics of cobalt-based superalloys (such as high-temperature strength, oxidation resistance, hot corrosion resistance, etc.), appropriate alloying elements are selected for proportioning, and then melting, casting, and heat treatment are carried out to make alloy specimens, and then the alloy composition is adjusted and optimized in combination with the performance test data of the alloy specimens. This method requires repeated experiments and adjustments, which is time-consuming and inefficient. The complex preparation process and performance testing also increase the manufacturing cost of the alloy, which not only affects the R & D efficiency of the alloy but also limits its application in some fields.

[0004] It should be noted that the information disclosed in this background art section is only intended to deepen the understanding of the overall background art of the present invention, and should not be regarded as an admission or any form of implication that this information constitutes the prior art known to those skilled in the art. Summary of the Invention

[0005] The purpose of the present invention is to provide a new design method for cobalt-based superalloys based on the combination of laser directed energy deposition and diffusion multi-joint. This method couples laser directed energy deposition technology to directly print diffusion multi-joint specimens, reduces the material loss that may be caused during the traditional melting and cutting processes, reduces subsequent processing steps, significantly shortens the preparation cycle and cost, and can realize the online design of the alloy and real-time optimization of the alloy composition and performance by adjusting the composition and energy input of the alloy during the deposition process.

[0006] To achieve the above purpose, the present invention adopts the following technical solutions: In the first aspect, the present invention provides a new design method for cobalt-based superalloys based on the combination of laser directed energy deposition and diffusion multi-joint, including the following steps: S1 Design of the composition of cobalt-based superalloys at each position of the diffusion multi-joint; S2 Select single metal powder or master alloy powder based on the alloy composition designed in S1, and mix them thoroughly according to the composition ratio; S3 uses laser directed energy deposition technology to feed the mixed powder into the laser melting area for heating, so that the powder melts and solidifies to form multiple alloy blocks with preset compositions; by precisely controlling the transportation and deposition of the powder, the alloy blocks with preset compositions are metallurgically bonded during the laser directed energy deposition process to form a diffusion multi-node specimen; S4 heat-treating the prepared diffusion multi-node specimen; S5 The composition test, microstructure and phase analysis methods are used to characterize the composition changes of the diffusion layer at the contact interface and nearby areas of different alloys on the diffusion multi-element specimens after heat treatment, and to establish a "composition-structure-property" database for additively manufactured cobalt-based high-temperature alloys; S6 selects alloy components from the database that meet the target organization and thermophysical properties for reprinting, and conducts microstructure and mechanical property tests on them to achieve the development of high solid solution, low density, high performance cobalt-based high-temperature alloys.

[0007] The design method of the present invention directly prepares multiple alloy blocks with preset compositions through laser directed energy deposition technology, and enables them to achieve natural diffusion bonding during the metallurgical process to form a diffusion multi-node specimen. By accurately controlling the transportation process of powders of different compositions, it is ensured that the alloys of preset compositions in each part of the diffusion multi-node directly achieve good metallurgical bonding during the printing process, meeting the requirements of high-throughput alloy design. This method not only improves the efficiency of alloy preparation, but also through the design of the diffusion multi-node, it can quickly explore the effects of different alloy compositions on the organization and performance, providing strong support for the development of high-performance cobalt-based high-temperature alloys.

[0008] In a possible implementation of the first aspect, step S5 further includes: adjusting the alloy composition in S1 and the laser energy input in S3 according to the performance test results to achieve online alloy design and real-time optimization. By adjusting the alloy composition and the laser energy input according to the performance test results and adding the steps of online alloy design and real-time optimization, accurate regulation and optimization of alloy performance can be achieved, further improving the performance and preparation efficiency of the alloy.

[0009] In a possible implementation of the above first aspect, in step S1, the preset alloy composition includes Co, Ni, Cr, Al, W, and Ta. Further, the preset alloy composition further includes at least one of Ti, V, Mo, and Nb. The selection of Co, Ni, Cr, Al, W, and Ta elements is based on their important roles in cobalt-based superalloys, such as improving the heat resistance, corrosion resistance, and mechanical properties of the alloy, providing clear guidance for the composition design of cobalt-based superalloys, and helping to develop alloys with better performance. Ti, V, Mo, and Nb elements can further enhance the performance of the alloy, such as improving the strength and hardness of the alloy, providing more choices for the composition design of cobalt-based superalloys, and helping to develop alloys with more excellent performance.

[0010] In a possible implementation of the above first aspect, in step S2, the metal ingot is prepared into elemental metal powder or intermediate alloy powder by gas atomization method, and the powder particles with a particle size range of 75-150 microns are screened and classified for drying and standby. The gas atomization method can prepare powders with uniform particle size and good sphericity, providing high-quality raw materials for the subsequent laser directed energy deposition process, thereby improving the quality and performance of the alloy.

[0011] In a possible implementation of the above first aspect, in step S3, by controlling process parameters such as laser power, scanning speed, and powder feeding rate, ensuring the uniform distribution of alloy components and good metallurgical bonding, the preparation process of the alloy can be precisely controlled, ensuring that the composition and performance of the alloy meet the expected requirements, and improving the preparation accuracy and reliability of the alloy.

[0012] In a possible implementation of the above first aspect, in step S4, the heat treatment process includes solution heat treatment and aging heat treatment. Through heat treatment, the microstructure and performance of the alloy can be further improved, and the heat resistance, strength, and corrosion resistance of the alloy can be enhanced, so as to meet the application requirements in high-temperature environments.

[0013] In a possible implementation of the above first aspect, in step S5, composition testing, microstructure, and phase analysis methods are used to characterize the composition changes of the diffusion layer, the morphology and content of γ' phase, and the content of secondary phases in the contact interface and nearby areas of different alloys, measure the γ' phase dissolution temperature, solidus temperature, liquidus temperature, and alloy mass density, and establish a "composition-structure-property" database for additive manufacturing cobalt-based superalloys. The composition changes of the diffusion layer, the morphology and content of γ' phase, and the thermophysical properties enrich the database of additive manufacturing superalloys, can comprehensively and accurately evaluate the performance and microstructure of the alloy, and provide a scientific basis for the optimization design of the alloy. At the same time, it also provides a theoretical and data basis for the subsequent rapid development of high-performance new materials using methods such as machine learning. The new components screened with excellent comprehensive performance promote the development and application process of new cobalt-based superalloys.

[0014] In a possible implementation of the first aspect above, in step S3, the laser melting deposition parameters used are as follows: laser power 3000 - 4000W, scanning rate 600 - 1000mm / min, powder feeding rate 20 - 30g / min, and spot diameter 3 - 6mm.

[0015] In a second aspect, the present invention provides a cobalt-based superalloy obtained by the design method according to the first aspect above. Its chemical composition by weight percentage includes: Ni 33.29, Cr 5.06, Al 3.94, W 10.43, Ta 5.86, Ti 4.66, and the rest is Co.

[0016] The structure and properties of this alloy meet the following: the volume fraction of γ' phase is 70%, the dissolution temperature of γ' phase is 1196°C, the mass density is 8.63g / cm 3 , the tensile strength at room temperature is 1359MPa, and the elongation is 21.3%.

[0017] In a third aspect, the present invention provides a powder feeding system for the design method according to the first aspect above, which includes a plurality of powder barrels, a plurality of powder mixers, and a plurality of powder feeding channels. The number of the powder mixers matches the number of alloy blocks in the diffusion multi-joint. Each of the powder mixers is used to mix the alloy component powders corresponding to the alloy blocks, and the number of the powder feeding channels matches the number of the powder mixers; wherein, the powder barrels are used to store the elemental alloy powders or intermediate alloy powders, the powder barrels are respectively connected to each powder mixer through powder conveying pipes, and each of the powder mixers is respectively connected to a laser device through a powder feeding channel.

[0018] The use of multiple powder barrels and multiple powder mixers enables precise control of the proportion of elemental powders and intermediate alloy powders. According to the preset alloy zoning printing, diffusion multi-joint specimens can be prepared at one time. The above powder feeding system can achieve precise supply and mixing of alloy powders, providing a stable and reliable raw material supply for the laser directed energy deposition process, and improving the efficiency and quality of alloy preparation. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 According to some embodiments of the present invention, a process flow chart of a novel cobalt-based superalloy design method based on laser directed energy deposition and diffusion multi-joint is shown; Figure 2 According to some embodiments of the present invention, a structural schematic diagram of a powder feeding system is shown; Figure 3 According to some embodiments of the present invention, a deposited structure diagram of the base alloy C printed with selected laser parameters is shown; Figure 4According to some embodiments of the present invention, a schematic diagram of the structure of a diffusion multi-element test piece is shown; Figure 5 According to some embodiments of the present invention, a microstructure diagram of a screened cobalt-based high-temperature alloy after heat treatment is shown. DETAILED DESCRIPTION

[0020] The technical features and advantages of the present invention are described in more detail below in conjunction with the accompanying drawings, so that the advantages and features of the present invention can be more easily understood by those skilled in the art, thereby making a clearer and more definite definition of the protection scope of the present invention.

[0021] See also Figure 1 The present invention provides a novel cobalt-based high-temperature alloy design method based on the combination of laser directional energy deposition and diffusion multi-node, comprising the following steps: S1 Composition design of cobalt-based superalloy at each position of diffusion multi-element node; S2 Select single metal powder or master alloy powder based on the alloy composition designed in S1, and mix them thoroughly according to the composition ratio; S3 uses laser directed energy deposition technology to feed the mixed powder into the laser melting area for heating, so that the powder melts and solidifies to form multiple alloy blocks with preset compositions; by precisely controlling the transportation and deposition of the powder, the alloy blocks with preset compositions are metallurgically bonded during the laser directed energy deposition process to form a diffusion multi-node specimen; S4 heat-treating the prepared diffusion multi-node specimen; S5 The composition test, microstructure and phase analysis methods are used to characterize the composition changes of the diffusion layer at the contact interface and nearby areas of different alloys on the diffusion multi-element specimens after heat treatment, and to establish a "composition-structure-property" database for additively manufactured cobalt-based high-temperature alloys; S6 selects alloy components from the database that meet the target organization and thermophysical properties for reprinting, and conducts microstructure and mechanical property tests on them to achieve the development of high solid solution, low density, high performance cobalt-based high-temperature alloys.

[0022] The design method of the embodiment of the present invention adopts laser directed energy deposition technology to accurately control the proportion change of single-element powder or intermediate alloy powder, realizes the metallurgical bonding of alloy blocks with preset components during the laser printing process, obtains a diffusion multi-node specimen at one time, and then establishes a "composition-structure-performance" database based on the diffusion multi-node to screen out the alloy components with the best structure and performance, thereby realizing the development of precipitation-strengthened cobalt-based high-temperature alloys with high solid solution, low density and high performance.

[0023] The alloy design method of the present invention will be described in detail based on a specific embodiment below. The embodiment of the present invention provides a method for directly preparing a diffusion multi-joint containing 5 different cobalt-based alloys by laser directed energy deposition technology, which specifically includes the following steps: (1) Design the composition of the cobalt-based superalloy at each position of the diffusion multi-joint, and determine the element types and contents of each alloy as follows: Alloy A: CoNiCrAlWTaTi, where the weight percentage of each element is Ni 30 - 35, Cr 4.5 - 5.5, Al 3.5 - 4.5, W 10 - 12, Ta 5.5 - 6.5, Ti 4 - 5, and the rest is Co.

[0024] Alloy B: CoNiCrAlWTaV, where the weight percentage of each element is Ni 30 - 35, Cr 4.5 - 5.5, Al 3.5 - 4.5, W 10 - 12, Ta 5.5 - 6.5, V 4 - 5, and the rest is Co.

[0025] Alloy C: CoNiCrAlWTa, where the weight percentage of each element is Ni 30 - 35, Cr 4.5 - 5.5, Al 3.5 - 4.5, W 22 - 24, Ta 5.5 - 6.5, and the rest is Co.

[0026] Alloy D: CoNiCrAlWTaMo, where the weight percentage of each element is Ni 30 - 35, Cr 4.5 - 5.5, Al 3.5 - 4.5, W 10 - 12, Ta 5.5 - 6.5, Mo 4 - 5, and the rest is Co.

[0027] Alloy E: CoNiCrAlWTaNb, where the weight percentage of each element is Ni 30 - 35, Cr 4.5 - 5.5, Al 3.5 - 4.5, W 10 - 12, Ta 5.5 - 6.5, Nb 4 - 5, and the rest is Co.

[0028] (2) Construct the powder supply system Please refer to Figure 2 , which is a schematic structural diagram of the powder supply system of the embodiment of the present invention, including multiple powder barrels 1, five powder mixers 3, and five powder feeding channels 4. Among them, the powder barrels 1 are used to store elemental alloy powders or master alloy powders. Each powder barrel 1 is connected to each powder mixer 3 through a powder conveying pipe 2. The five powder mixers 3 correspond to the powder mixing of 5 different cobalt-based alloy blocks respectively. Each powder mixer 3 is connected to the laser head 5 through a powder feeding channel 4. The specific process is as follows: a. Preparation of single substance powder and master alloy powder: CoAl, CoW, Ni, Cr, Ta, Ti, V, Mo, and Nb powders are prepared by gas atomization of metal ingots, and particles with a particle size range of 75-150 μm are graded and screened and dried.

[0029] b. Powder storage and transportation: The dried and deoxidized CoAl, CoW, Ni, Cr, Ta, Ti, V, Mo, and Nb powders are placed in different powder barrels 1. The feed port of each powder barrel 1 is connected to an argon gas source, and a timer is installed at the outlet. The air flow rate of the argon gas is regulated, and each powder is blown out continuously within a certain period of time and sent to each powder mixer 3 through the powder conveying pipe 2. After being fully mixed, cobalt-based alloy powders of five components A, B, C, D, and E are formed.

[0030] (3) Diffusion multi-section specimen printing Preheat the substrate to 200°C and set the printing parameters as follows: laser power 3000-4000W, scanning rate 600-1000mm / min, powder feeding rate 20-30g / min, spot diameter 3-6mm, and bidirectional scanning strategy. First print the basic alloy C to determine the laser parameter combination for high-density forming. At this time, the deposited C alloy has a dense structure without defects such as pores and cracks (see Figure 3 ).

[0031] The diffusion multi-node is prepared by following the deposition sequence from bottom to top and from left to right. The alloy powder corresponding to each position is fed into the laser action area on the substrate 7 through the powder feeding channel 2 and the nozzle 6. The high-energy laser beam heats the alloy powder to melt and solidify, and directly completes the metallurgical bonding between the alloy blocks to form a diffusion multi-node specimen 8, as shown in FIG. Figure 4 shown.

[0032] (4) Diffusion layer microstructure characterization and thermal physical properties testing The diffusion multi-node specimen 8 was cut from the substrate 7 and subjected to 1350℃ / 4h solution treatment / air cooling and 800℃ / 500h aging heat treatment / water cooling. The diffusion layers of different alloy contact interfaces and nearby areas were selected to prepare electron probe test samples, and the range of changes in the composition of each element in the diffusion layer was analyzed; the microstructure in the diffusion layer was observed by scanning electron microscopy, and the phase composition was determined by X-ray diffraction results, the critical concentration of the elements causing phase transition was extracted, and the relationship between the composition gradient change and the phase distribution characteristics was established. The microstructure was processed by image measurement software to count the size and content of the γ' phase and secondary phase; the phase transition temperature, including the γ' phase dissolution temperature, solidus temperature, and liquidus temperature, was determined by differential thermal analysis; the alloy mass density was determined by Archimedes drainage method.

[0033] (5) Verification of high-performance new alloys Based on the results of the analysis of the structure and performance of the diffusion layer, an alloy composition with only γ+γ' two phases, no secondary phase precipitation, a γ' phase volume fraction higher than 65%, a γ' phase dissolution temperature higher than 1180 °C, and a mass density lower than 8.8 g / cm 3 was selected for re-printing and forming. After cutting the new alloy sample block from the substrate 7, microstructure and mechanical property tests were carried out, Figure 5 Figure 4 is the microstructure diagram of the alloy sample block after heat treatment. Measure its γ' phase volume fraction, γ' phase dissolution temperature and mass density to ensure that it meets the performance objectives; conduct tensile property tests and summarize the mechanical properties of the new alloy.

[0034] In this part, parameters closely related to engineering applications such as tissue stability, γ' phase thermodynamic stability, alloy density, and high-temperature mechanical properties were characterized, providing positive feedback on the effectiveness of using high-throughput technology to develop multi-component new cobalt-based superalloys in the embodiments of the present invention.

[0035] According to the above method, the components of the new cobalt-based superalloy obtained are as follows: by weight percentage, it includes: Ni 33.29, Cr 5.06, Al 3.94, W 10.43, Ta 5.86, Ti 4.66, and the rest is Co.

[0036] Through performance testing, the performance of the new cobalt-based superalloy is as follows: the γ' phase volume fraction is 70%, the γ' phase dissolution temperature is 1196 °C, and the mass density is 8.63 g / cm 3 , the room temperature tensile strength is 1359 MPa, and the elongation is 21.3%.

[0037] In the description of the embodiments of the present invention, it should be understood that the orientation or positional relationship indicated by the terms "upper", "lower", "front", "rear", "left", "right", "vertical", "horizontal", "center", "top", "bottom", "top part", "bottom part", "inner", "outer", "inner side", "outer side", etc. is based on the orientation or positional relationship shown in the drawings, and is only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as a limitation to the present invention. Among them, the "inner side" refers to the internal or enclosed area or space. The "periphery" refers to the area around a specific component or a specific area.

[0038] In the description of the embodiments of the present invention, the terms "first", "second", "third", and "fourth" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the quantity of the indicated technical features. Thus, features defined with "first", "second", "third", and "fourth" may explicitly or implicitly include one or more of such features. In the description of the present invention, unless otherwise specified, the meaning of "a plurality" is two or more.

[0039] In the description of the embodiments of the present invention, it should be noted that, unless otherwise clearly specified and defined, the terms "installed", "connected", "joined", and "assembled" shall be construed broadly. For example, it may be a fixed connection, a detachable connection, or an integral connection; it may be directly connected or indirectly connected through an intermediate medium, and it may be the internal communication of two components. For those of ordinary skill in the art, the specific meanings of the above terms in the present invention can be understood in specific cases.

[0040] In the description of the embodiments of the present invention, specific features, structures, materials, or characteristics may be combined in a suitable manner in any one or more embodiments or examples.

[0041] In the description of the embodiments of the present invention, it should be understood that "-" and "~" represent the range between two numerical values, and this range includes the endpoints. For example, "A - B" represents a range greater than or equal to A and less than or equal to B. "A ~ B" represents a range greater than or equal to A and less than or equal to B.

[0042] In the description of the embodiments of the present invention, the term "and / or" herein is merely a description of the association relationship of the associated objects, indicating that there can be three relationships. For example, A and / or B may represent: A exists alone, A and B exist simultaneously, and B exists alone. In addition, the character " / " herein generally represents an "or" relationship between the associated objects before and after.

[0043] Although the embodiments of the present invention have been shown and described, for those of ordinary skill in the art, it can be understood that various changes, modifications, substitutions, and variations can be made to these embodiments without departing from the principles and spirit of the present invention. The scope of the present invention is defined by the appended claims and their equivalents.

Claims

1. A novel design method of cobalt-based superalloy based on the combination of laser directed energy deposition and diffusion multiple joints, characterized in that, The following steps are involved: S1 Composition design of cobalt-based superalloy at each position of diffusion multi-element node; S2 Select single metal powder or master alloy powder based on the alloy composition designed in S1, and mix them thoroughly according to the composition ratio; S3 uses laser directed energy deposition technology to feed the mixed powder into the laser melting area for heating, so that the powder melts and solidifies to form multiple alloy blocks with preset compositions; by precisely controlling the transportation and deposition of the powder, the alloy blocks with preset compositions are metallurgically bonded during the laser directed energy deposition process to form a diffusion multi-node specimen; S4 heat-treating the prepared diffusion multi-node specimen; S5 The composition test, microstructure and phase analysis methods are used to characterize the composition changes of the diffusion layer at the contact interface and nearby areas of different alloys on the diffusion multi-element specimens after heat treatment, and to establish a "composition-structure-performance" database for additively manufactured cobalt-based high-temperature alloys; S6 selects alloy components from the database that meet the target organization and thermophysical properties for reprinting, and conducts microstructure and mechanical property tests on them to achieve the development of high solid solution, low density, high performance cobalt-based high-temperature alloys.

2. The design method according to claim 1, characterized in that Step S5 also includes: adjusting the alloy composition in S1 and the laser energy input in S2 according to the performance test results to achieve online alloy design and real-time optimization.

3. The design method according to claim 1, characterized in that In step S1, the preset alloy components include Co, Ni, Cr, Al, W, and Ta.

4. The design method according to claim 1, characterized in that, It also includes at least one of Ti, V, Mo, and Nb.

5. The design method according to claim 1, wherein In step S2, the metal ingot is prepared by gas atomization to form a single metal powder or an intermediate alloy powder, and powder particles with a particle size range of 75-150 microns are graded and screened to be dried for later use.

6. The design method according to claim 1, characterized in that, In step S3, the uniform distribution of alloy components and good metallurgical bonding are ensured by controlling process parameters such as laser power, scanning speed, and powder feeding rate.

7. The design method according to claim 1, characterized in that In step S4, the heat treatment process includes solution heat treatment and aging heat treatment.

8. The design method according to claim 1, characterized in that In step S5, composition testing, microstructure and phase analysis are used to characterize the composition changes of the diffusion layer, γ' phase morphology and content, and secondary phase content at the contact interface of different alloys and nearby areas, and the γ' phase dissolution temperature, solidus temperature, liquidus temperature and alloy mass density are measured to establish a "composition-structure-performance" database for additively manufactured cobalt-based high-temperature alloys.

9. A cobalt-based superalloy obtained by the design method according to any one of claims 1-8, characterized in that, Its chemical composition by weight percentage includes: Ni 33.29, Cr 5.06, Al 3.94, W 10.43, Ta 5.86, Ti4.66, and the rest is Co.

10. A powder supply system for the design method according to any one of claims 1-8, characterized in that, It includes multiple powder barrels, multiple powder mixers and multiple powder feeding channels, the number of the powder mixers matches the number of alloy blocks in the diffusion multi-node, each of the powder mixers is used to mix the alloy component powders of the corresponding alloy block, and the number of the powder feeding channels matches the number of the powder mixers; wherein the powder barrels are used to store the single alloy powder or the intermediate alloy powder, the powder barrels are connected to each powder mixer through a powder feeding pipe, and each of the powder mixers is connected to a laser device through a powder feeding channel.

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