KR101921281B1 - Method for manufacturing article using additive manufacturing and surface treatment - Google Patents

Abstract

The present invention relates to a method to manufacture a surface-modified additive manufacturing (AM) article, comprising: a step (a) of manufacturing one or more layers or an article by an AM method; and a step (b) of performing ultrasonic nanocrystalline surface modification (UNSM) of the surface of the one or more layers or the article. According to the present invention, UNSM technology is applied to a layer or article manufactured by three-dimensional (3D) printing, and thus a product with remarkably improved hardness and excellent frictional and wearing behaviors more than a conventional article using a bulk material is able to be manufactured at low costs.

Description

TECHNICAL FIELD [0001] The present invention relates to a method for manufacturing a surface-treated laminated article,

The present invention relates to a method of manufacturing an article using a lamination method, and more particularly, to a method of producing an article by performing surface treatment after lamination.

Additive manufacturing (AM), also called 3D printing, refers to the process of manufacturing 3D objects by stacking materials using digital design data.

If the previous manufacturing technique was a subtractive manufacturing method in which a three-dimensional shape material is cut or cut through machining or the like to produce a three-dimensional object, the 3D printing method adopts a lamination method in the opposite direction, and a rapid prototyping ), Additive fabrication, additive fabrication, layer manufacturing, and freeform fabrication. The 3D printing process can be divided into three stages: ① Modeling to produce a 3D digital drawing through a design SW or a 3D scanner, ② Printing, and ③ Finishing process for final commercialization such as removal of the supporter, polishing, dyeing and surface material deposition. Advantages of 3D printing include ① production cost and time saving of prototypes ② small quantity production of various kinds of products, easy customized production ③ contributing to complicated shape production and material cost reduction ④ simplification of manufacturing process during manufacturing and reduction of labor cost and assembly cost . In addition, digital drawings can be distributed instead of products, and output can be made anywhere.

With respect to the method of the lamination method, in the ASTM (American Society for Testing and Materials) F42 and ISO TC261 (Additive Manufacturing), the photo polymerization (PP), the material extrusion (ME) Jetting, BJ), Material Jetting (MJ), Direct Energy Deposition (DED), Powder Bed Fusion (PBF), Sheet Lamination (SL) And 7 types.

In such a laminate manufacturing process, metal 3D printing using metal as a raw material is advantageous because of its properties such as minimizing the use of materials, the ability to make complex shapes with a light structure, and the cost savings in manufacturing mechanical parts with less energy Has received considerable attention.

The metal 3D printing can be performed by a direct energy deposition (DED) method or a powder bed fusion (PBF) method among the lamination method described above. Among them, the metal wire printing method (Metal Wire Arc Additive Manufacturing, MWAAM) and Additive Friction Stirring (AFS).

The MWAAM method is a process of manufacturing an article by stacking wires by feeding a metal filler metal with a heat source such as GMAW, GTAW, or PAW.

The AFS system is a solid-state thermo-mechanical process for the deposition of metal or metal matrix composites (MMCs), in which bulk or powdered fillers are fed through a rotating AFS tool, The material is deposited in the form of a plastic material, which undergoes severe plastic deformation, dynamic recrystallization, compaction (in the case of powder), and deposition, on the substrate.

On the other hand, structures made by layer-by-layer processing of metal 3D printing can compete with bulk materials in terms of mechanical and physical properties. 3D printed machine parts are up to 60% lighter than machined components. In this regard, 3D printing technology is in high demand in terms of economics due to the above-described characteristics of multi-functionality and product complexity of new materials. For example, in the aerospace industry alone, reducing the weight of mechanical components can save billions of dollars. Nowadays, there is 3D printing technology that can print various materials at the same time, which shows the excellent development of metal 3D printing technology. Also, until now, the process of 3D printing technology has progressively achieved a level of accuracy and precision that is satisfactory.

However, there still exist some problems to be solved with respect to the final product manufactured through the metal 3D printing process.

Specifically, one of the major issues in metal 3D printing in terms of mechanical properties is the presence of micro-pores that can cause cracks in mechanical components under cyclic loading. Since the ultimate wear, fatigue, and corrosion properties of a material can be determined by surface and microstructural defects such as cracks, pores, unmelted particles, etc., the relationship between microstructure defects and mechanical properties of the material is very important. For example, 3D-printed AISI H13 tool steels produced by different lamination processes are known to have lower fatigue strength due to the deleterious effects of pores.

In addition, metal 3D printing is known to cause heat-affected zone (HAZ) toughness degradation and residual stress due to latent heat, especially tensile residual stress, as a factor of fatigue strength deterioration.

When the above-described AFS method is applied to metal 3D printing, although the aforementioned problems are alleviated due to the characteristics of the solid state layer bonding (AFS) method, the nonuniformity and residual stress, especially tensile residual stress, It acts as a factor of degradation.

Korean Patent Laid-Open No. 10-2016-0113060 (Disclosure Date: Sep. 28, 2016) Korean Patent Laid-Open No. 10-2016-0076514 (published on June 30, 2016) Korean Patent Laid-Open No. 10-2015-0144503 (Published on Dec. 28, 2015) U.S. Patent No. 5,121,329 (registered on Feb. 09, 1992) U.S. Patent No. 4,575,330 (Registered on Mar. 11, 1986) U.S. Patent No. 5,639,070 (registered on June 17, 1997)

 J.Y. Lee, J. An, C.K. Chul, Fundamentals and applications of 3D printing for novel materials, Appl. Mater. Today 7 (2017) 120-133.  L.Y. Chen, J.C. Huang, C.H. Lin, C.T. Pan, S.Y. Chen, T.L. Yang, D.Y. Lin, H.K. Lin, J.S.C. Jang, Anisotropic response of Ti-6Al-4V alloy fabricated by 3D printing selective laser melting, Mater. Sci. Eng. A 682 (2017) 389-395.  S. Li, X. Wu, S. Chen, J. Li, Wear resistance of H13 and a new hot-work die steel at high temperature, J. Mater. Eng. Perform. 25 (7) (2016) 2993-3006.

SUMMARY OF THE INVENTION The present invention has been made in view of the above problems, and an object of the present invention is to provide a method for improving the mechanical performance including the frictional wear of an article manufactured through a lamination method such as metal 3D printing, Method.

According to an aspect of the present invention, there is provided a method of manufacturing a semiconductor device, comprising the steps of: (a) fabricating one or more layers or articles by additive manufacturing (AM); And (b) performing an ultrasonic nanocrystalline surface modification (UNSM) on the one or more layers or on the surface of the article.

In step (a), photo polymerization (PP), material extrusion (ME), adhesive jetting (BJ), material jetting (MJ), high energy direct Characterized in that a layer or article is manufactured by Direct Energy Deposition (DED), Powder Bed Fusion (PBF) or Sheet Lamination (SL) A method of manufacturing an article is proposed.

Also, in the step (a), a layer or an article made of a metal, a ceramic or a metal matrix composite (MMC) is manufactured, and a method of manufacturing an article using the lamination method is proposed.

In addition, in the step (a), a layer or an article made of metal is manufactured by using a direct energy deposition (DED) method or a powder bed fusion (PBF) method A manufacturing method of articles using a laminated manufacturing method is proposed.

In addition, in the step (a), a layer or an article made of metal is manufactured by using Metal Wire Arc Additive Manufacturing (MWAAM) or Additive Friction Stirring (AFS) By weight based on the total weight of the product.

In the step (a), a layer or an article made of ceramics is manufactured by using an adhesive injection method (Binder Jetting, BJ), a photopolymerization method (PP), or a material extrusion method The present invention also provides a method of manufacturing an article using a lamination method.

In the step (b), ultrasonic nanocrystal surface modification (UNSM) is performed on the surface of each of the one or more layers or on the surface of the article in a state where latent heat generated during additive manufacturing (AM) is present The present invention also provides a method of manufacturing an article using the lamination method.

In the step (b), ultrasonic nanocrystal surface modification (UNSM) is performed while locally heating the surface of each of the one or more layers or the surface of the article. Method.

According to another aspect of the present invention, there is provided a laminate manufacturing apparatus comprising: a laminate manufacturing section including at least one layer or a molding stage in which an article is laminated and formed thereon; An ultrasonic nanocrystalline surface modification (UNSM) processing unit connected in series or in parallel to the laminate manufacturing method unit; And a shaping stage driving unit capable of moving the shaping stage between the lamination manufacturing unit and the ultrasonic nanocrystal surface modification processing unit.

The ultrasonic nanocrystal surface modification treatment unit may further include a heat treatment unit for performing a local heating treatment on a surface of each of the one or more layers transferred from the laminate manufacturing unit or a surface of the article. Lt; / RTI >

The heat treatment unit may include a temperature measurement unit for measuring the temperature of the surface of each of the one or more layers transferred from the lamination production unit or the surface of the article; And a temperature controller connected to the temperature measuring unit for controlling the temperature by determining whether the local heating process is performed according to the temperature measured by the temperature measuring unit.

Further, the present invention further provides a cooling apparatus provided between the laminated production unit and the ultrasonic nanocrystal surface modification treatment unit or at a rear stage of the ultrasonic nanocrystal surface modification treatment unit.

In addition, the present invention proposes an article produced by the above manufacturing method in another aspect of the invention.

It also proposes an article characterized by being made of AISI H13 tool steel.

The method of manufacturing an article using the laminated manufacturing method according to the present invention can be applied to a layer or an article manufactured using 3D printing by using an ultrasonic nanocrystal surface modification (UNSM) A product having remarkably improved hardness and excellent friction and wear behavior can be manufactured at a lower cost.

Furthermore, by performing ultrasonic nanocrystal surface modification in the state where latent heat generated in the lamination manufacturing process exists, or by performing ultrasonic nanocrystal surface modification at the same time as local heating after completion of the layer or final lamination manufacturing process, To eliminate or reduce unmelting defect and porosity, to improve the surface roughness of the layer or article formed by lamination production, to apply compressive residual stress to the layer or article formed by lamination production, Thereby strengthening the crystal grains grown by the latent heat by the laminating process and the brittleness-induced texture.

1 is a schematic diagram of UNSM technology.
2 is a basic parameter diagram of UNSM processing.
Figure 3 shows the EBSD images and mapping results of bulk AISI H13 tool steel specimens (a and b) before and after UNSM treatment and 3D-printed AISI H13 tool steel specimens (c and d).
Figure 4 shows the number of fractions for the misorientation angles of bulk AISI H13 tool steel specimens (a and b) before and after UNSM treatment and 3D-printed AISI H13 tool steel specimens (c and d).
Figure 5 shows the results of surface roughness comparison of bulk AISI H13 tool steel specimens (a and b) before and after UNSM treatment and 3D-printed AISI H13 tool steel specimens (c and d).
Figure 6 shows the results of surface hardness comparison of bulk and 3D printing AISI H13 tool steel specimens before and after UNSM treatment.
Figure 7 is an indent SEM image of bulk AISI H13 tool steel specimens (a and b) before and after UNSM treatment and 3D-printed AISI H13 tool steel specimens (c and d).
Fig. 8 shows the results of comparison of friction coefficient between bulk AISI H13 tool steel specimen (a) before and after UNSM treatment and 3D printing AISI H13 tool steel specimen (b).
9 is a high magnification SEM image of bulk AISI H13 tool steel specimens (a and b) before and after UNSM treatment and 3D-printed AISI H13 tool steel specimens (c and d).
10 (a) to 10 (d) are EDX spectra of the wear tracks of bulk AISI H13 tool steel specimens (a and b) before and after UNSM treatment and 3D printed AISI H13 tool steel specimens (c and d).

In the following description of the present invention, a detailed description of known functions and configurations incorporated herein will be omitted when it may make the subject matter of the present invention rather unclear.

Embodiments in accordance with the concepts of the present invention can make various changes and have various forms, so that specific embodiments are illustrated in the drawings and described in detail in this specification or application. It should be understood, however, that the embodiments according to the concepts of the present invention are not intended to be limited to any particular mode of disclosure, but rather all variations, equivalents, and alternatives falling within the spirit and scope of the present invention.

The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. The singular expressions include plural expressions unless the context clearly dictates otherwise. In this specification, the terms " comprises ", or " having ", or the like, specify that there is a stated feature, number, step, operation, , Steps, operations, components, parts, or combinations thereof, as a matter of principle.

Hereinafter, the present invention will be described in detail.

The present invention relates to a method for improving the mechanical performance including the abrasion and abrasion of an article manufactured through a lamination method to be equal to or higher than that of a bulk material produced through a conventional molding process.

Specifically, a method of manufacturing an article using the laminate manufacturing method according to the present invention includes the steps of: (a) manufacturing one or more layers or articles by additive manufacturing (AM); And (b) performing an ultrasonic nanocrystalline surface modification (UNSM) on the surface of the one or more layers or the article.

In the step (a), a layer or an article made of a composite material such as a metal, a ceramic, or a metal matrix composite (MMC) is manufactured using a lamination method.

As a specific method for carrying out the lamination method of the present step (a), a photopolymerization method (PP), a material extrusion method (Material Extrusion method) as a 3D printing method defined in ASTM (American Society for Testing and Materials) F2792-12a, (ME), Binder Jetting (BJ), Material Jetting (MJ), Direct Energy Deposition (DED), Powder Bed Fusion (PBF) And a sheet lamination (SL) method.

The material extrusion method (ME) is a method (FDM or the like) in which a filament material is plasticized through a nozzle and extruded to form a shape, and a material jetting method (MJ) (Polyjet, MJM, etc.) by spraying through a plurality of fine nozzles and then curing, and Binder Jetting (BJ) is a method in which a liquid binder is sprayed through a plurality of fine nozzles to select a powder material (LOM, VLM, etc.) for manufacturing a shape by joining a sheet material to a desired cross-section and bonding the sheet material to a desired cross-section, Photopolymerization (PP) is a method (SLA, DLP, etc.) in which a liquid polymer is selectively cured by using light energy to form a shape. Powder Bed Fusion (PBF) (SLS, DMLS, etc.), which are produced by selectively sintering / dissolving by using a high thermal energy source (laser) in a high energy direct current (MWAAM, LENS, DMT, etc.) that form a pool dissolved in water and form a shape by supplying powder thereto.

The PBF method and the DED method can be cited as preferred methods for producing the metal-made article in the above method. Although there are advantages and disadvantages according to each of these methods, the DED method is superior in stiffness to the PBF method at present, There are many advantages in application and active research and applications are underway.

In addition to PBF and DED, the AFS method described above is also a suitable method for manufacturing metal laminated articles.

In order to produce articles made of ceramics, a BJ method generally known as powder printing, an ME method represented by fused deposition modeling (FDM) and paste extruding deposition (PED), stereolithography (SLA) or dislative light processing ) Is preferably used.

Next, in step (b), ultrasonic nanocrystalline surface modification (UNSM) is performed on the surface of one or more layers or articles formed by the lamination method in the step (a) The UNSM may be performed each time one or more layers are formed by the lamination method, or UNSM may be performed after the shape of the article is completely obtained by the lamination method.

As an example of the UNSM treatment performed in this step, static and dynamic forces are applied by attaching a 1 to 5 mm diameter tungsten carbide (WC) / silicon nitride (Si ₃ N ₄ ) tip to an ultrasonic device The said tip impacts the surface of the 20,000 laminated manufacturing layer or laminate manufactured article at a rate of 20,000 per second to modify the surface, such impact can be regarded as micro-cold-forging, Plastic and elastic deformation to induce deep residual stresses and nanocrystalline structures and also to generate innumerable non-uniform micro-dimples on the surface of the specimen Thereby improving the surface characteristics.

That is, by carrying out this step, not only the removal and minimization of the fine pores and the unmelted powder of the articles produced by the lamination method but also the weak mechanical properties (hardness, friction / wear characteristics, fatigue strength, etc.) have.

Further, in this step (b), the surface of each of the one or more layered layers or the local heating of the surface of the article may be simultaneously performed with the UNSM treatment.

When local heating is performed simultaneously with the UNSM treatment on the laminated layer or article as described above, extreme elasto-plastic strain energy is added to move an element such as carbon or nitrogen from the inside to the surface layer, change the microstructure, The crystal grains can be made fine and a compressive residual stress can be added.

Also, in this step (b), UNSM processing can be performed in a state where latent heat generated during additive manufacturing (AM) exists so that the same effect as that of the local heating can be exhibited.

That is, the surface modification of the ultrasonic nanocrystals may be performed in the state where the latent heat generated in the lamination manufacturing process exists, or the ultrasonic nanocrystal surface modification may be performed simultaneously with local heating after completion of the layer or final lamination manufacturing process, To eliminate or reduce the unmelting defect and porosity caused by the lamination, to improve the surface roughness of the layer or article formed by lamination, to apply compressive residual stress to the layer or article formed by lamination, It is possible to remarkably improve the fatigue strength by changing the crystal grains grown by the latent heat by the laminating process and the brittleness structure.

According to the method of manufacturing an article using the laminate manufacturing method according to the present invention, by applying an ultrasonic nanocrystalline surface modification (UNSM) technique to a layer or an article manufactured using 3D printing, the surface hardness can be increased and the surface roughness And by refining large particles into nano-sized particles, it improves friction and wear behavior and improves material fatigue life. It has a remarkably improved hardness and superior friction and wear behavior compared to conventional bulk materials. And can be manufactured at low cost.

On the other hand, as an example of an apparatus for manufacturing an article for implementing the method of manufacturing articles using the laminated manufacturing method according to the present invention, there is provided an apparatus for producing a laminated product comprising at least one layer or a molding stage in which an article is laminated thereon part; An ultrasonic nanocrystalline surface modification (UNSM) processing unit connected in series or in parallel to the laminate manufacturing method unit; And a shaping stage driving unit capable of moving the shaping stage between the lamination manufacturing method and the ultrasonic nanocrystal surface modification processing unit.

In order to achieve a synergistic effect by the above-described local heating and UNSM treatment, the ultrasonic nanocrystal surface modification treatment section may be configured to perform a local heating treatment on the surface of each of the one or more layers transferred from the lamination production section, And a heat treatment unit for performing the heat treatment.

At this time, the heat treatment unit may include a temperature measuring unit for measuring the temperature of the surface of the one or more layers conveyed from the lamination producing unit or the surface of the article, and a local heating process depending on the temperature measured by the temperature measuring unit. And a temperature control unit for controlling the temperature and connected to the temperature measuring unit.

The article manufacturing apparatus may further include a cooling unit installed between the laminate manufacturing unit and the ultrasonic nanocrystal surface modification treatment unit so that heat can be cooled while the molding stage is moving between the laminated manufacturing unit and the ultrasonic nanocrystal surface modification treatment unit have.

In addition, the article manufacturing apparatus may further include a cooling unit installed at a rear end of the ultrasonic nanocrystal surface modification unit so that the heat can be cooled after the ultrasonic nanocrystal surface modification process.

Hereinafter, the present invention will be described in more detail with reference to examples.

The embodiments according to the present disclosure can be modified in various other forms, and the scope of the present specification is not construed as being limited to the embodiments described below. Embodiments of the present disclosure are provided to more fully describe the present disclosure to those of ordinary skill in the art.

<Examples>

1. Preparation of specimens using 3D printing and UNSM treatment

(1) Specimen fabrication using direct metal tooling (DMT)

In order to compare the properties of the bulk and non-annealed 3D specimens, the bar-shaped AISI H13 steel was selected as the base material that has not been pretreated by quenching and tempering heat treatment processes since no additional annealing process is performed after the 3D printing process.

For reference, AISI H13 tool steels are used in a wide variety of industries due to their high hardenability, excellent abrasion resistance, high temperature toughness and excellent thermal shock resistance. Molybdenum (Cr-Mo) high temperature machined steel which is used as a variety of tools in hot and cold machining such as steel, The hardness of the AISI H13 steel acts as a resistance to thermal fatigue cracks resulting from periodic heating and cooling processes. AISI H13 steel is a preferred material for high temperature working tools than other tool steels due to its high toughness and high resistance to thermal fatigue cracking. Therefore, there is a need to increase the mechanical properties and abrasion resistance to extend the fatigue life of mechanical parts and dies made of AISI H13 steel. From an economic point of view, it is also necessary to lighten these components while maintaining or improving mechanical, physical, chemical and tribological properties. Generally, the material is subjected to heat treatment to improve its mechanical properties. The hardness of AISI H13 ranges from 48-50 HRC after quenching. Molybdenum (Mo) and vanadium (V) act as strengthening agents. Cr helps to increase the softening resistance of AISI H13 steels at high temperatures.

In this embodiment, AISI H13 tool steel is manufactured by 3D printing using a laser-assisted direct metal tooling (DMT) machine (MX-450, InssTak Inc.) operating with a 1 kW Ytterbium fiber laser Respectively. In DMT, the laser energy dissolves the powdered metal in a sealed build chamber to produce fully integrated layers of layers. DMT is a method of building structures by stacking layers as one of the lamination methods that can be applied to rapid prototyping, tooling and functional component manufacturing with selected metals. Depositing a new layer on the previously formed layer by locally fusing the feed powder under a high power laser while blowing an inert gas into the chamber. The H13 tool steel used in this embodiment is a martensitic alloy steel capable of providing high hardenability, excellent abrasion resistance and high temperature toughness, but DMT-treated H13 experiences rapid dissolution, cooling and reheating, Can not be the same as the material properties of the material. In addition, the laser process direction and void affect the properties.

In order to avoid generation of stress due to heat generation and change of microstructure, the material was cut into a plate shape having dimensions of 10 × 10 × 3 mm ³ by using a wire cut having a wire diameter of 0.14 mm. The chemical composition and mechanical properties of the two specimens are shown in Tables 1 and 2, respectively. The surface of the specimen was polished using silicon carbide (SiC) sand (max # 2000) to obtain a similar average surface roughness of about 0.1 μm. For the analysis of the surface characteristics, a mirror-like specimen surface was obtained using a 1 μm diamond suspension.

Bulk and 3D Printed AISI  H13 Chemical composition of tool steel (weight % ). Material C V Si Mo Mn Cr Fe Bulk 0.32 1.0 1.0 1.33 0.25 5.13 Honey 3D Printing 0.41 0.90 1.0 1.4 0.35 5.35

 Bulk and 3D Printed AISI  H13 Mechanical properties of tool steel Material Yield strength, MPa Elastic modulus, GPa Poisson`s ratio UTS,
GPa Elongation,% Bulk 1650 210 0.30 1990 9 3D Printing 1720 218 2010 8

(2) UNSM  process

UNSM technology is a patented material strengthening technology. UNSM technology uses a 2.38 mm diameter tungsten carbide (WC) / silicon nitride (Si3N4) tip to impact the specimen surface up to 20,000 times per second, transforming coarse particles into nano-sized particles from the surface of the material to a certain depth. A schematic of a built-in house UNSM device is shown in FIG. In this UNSM process, not only the static load ( P _st ) but also the dynamic load (P _dy = P sin2πft ) are applied to the surface. The oscillator and the piezoelectric transducer shown in Fig. 1 emit ultrasonic waves at 20 kHz. The waves are amplified as they pass through an acoustic booster. The dimensions of the vibrating part in contact with the surface are such that a vibration amplitude of 10 to 100 μm can be obtained to achieve a uniform treatment on the surface to be treated. The principle of UNSM is based on the conversion of a harmonic oscillation of an acoustically tuned body into a resonant impulse of ultrasound frequency. The acoustically tuned body is energized by supplying power to the ultrasonic transducer. The UNSM technical apparatus may be installed at different positions on any numerical control (NC) and / or computer numerical control (CNC) machine. In this embodiment, the UNSM treatment process was carried out in a complex CNC machine tool machine capable of planar processing and annular wobbling. The trajectory of the UNSM processing is depicted in FIG.

The specimens were subjected to UNSM according to the process parameters listed in Table 3. The optimum conditions should be determined according to the surface condition of the material, and the optimum condition should be found after analyzing the mechanical properties of the surface state of the treatment results. As shown in Table 3, the static loads applied to bulk and 3D-printed AISI H13 steel specimens were 30 and 70 N, respectively, taking into account the initial surface hardness of the specimens. Prior to UNSM treatment, specimens were cleaned in an ultrasonic bath with ethanol and deionized water for 10 minutes to maintain a clean, dust-free surface.

Bulk and 3D Printed AISI  H13 In tool steel  applied UNSM  Process variable and application value Material Frequency, kHz Amplitude, ㎛ Static load, N Speed, mm / min Feed-rate, ㎛ Ball diameter, mm Ball material Bulk 20
30
30 2000 70 2.38 WC 3D Printing 70

2. Microstructure analysis of specimen

Figure 3 shows the geometry of the tissue with the mapping of bulk and 3D printed specimens using EBSD technology. From FIG. 3 (a), it can be seen that the average particle diameter of the bulk specimen is in the range of 5 to 30 μm in the longitudinal direction. From FIG. 3 (b), it can be confirmed that the UNSM treatment fine-grained the coarse particles to fine particles of 1 to 10 μm in the length direction. Minimizing the particle size of the specimen treated with UNSM may be due to subsequent impacts occurring in the UNSM process, which induces severe plastic deformation on the upper surface within a certain depth. As shown in Figures 3 (c) and (d), in the case of 3D-printed specimens, the presence of micronized particles between coarse particles due to heating during lamination was observed and the distribution of particle sizes was found to be broad. Coarse particles are further refined by UNSM treatment, with an average particle size of less than 50 nm. The UNSM technology has previously been reported to be able to produce nanostructured materials with particle sizes less than 100 nm. According to the SPD method, the dislocation accumulation occurs first, followed by the formation of sub-grains, and a part of the dislocation accumulates in the sub- At the boundary, it is extinguished to increase the misorientation angle. Finally, a balance is established between the formation of the dislocation by the SPD and the absorption of the dislocation in the grain boundaries. The number of grain boundaries increases considerably as the coarse grains are refined into nanocrystalline grains. It can also be explained that a large amount of dislocations are formed in the crystal grains, dislocations are rearranged to lower the energy level, and a large amount of grain boundary is formed during UNSM processing.

The number of fractions for the azimuthal angle of the bulk and 3D-printed specimens obtained using the EBSD technique are shown in FIG. As shown in FIGS. 4 (a) and (b), it was clearly shown that the number of specimens after UNSM treatment increased in bulk specimens. The amount of low angle grain boundary (LAGB) increased from 21 to 34% while the amount of high angle grain boundary (HAGB) decreased from 79 to 66%. For the 3D-printed specimen shown in Figures 4 (c and d), the amount of LAGB increases from 8 to 17%, while the amount of HAGB decreases from 92 to 83%. This change in grain boundaries may be due to an increase in grain boundaries by UNSM treatment. The grain refinement can greatly increase the mechanical properties such as the hardness of the material.

3. Measurement and analysis of specimen surface roughness and surface hardness

The surface roughness of the specimen before and after the UNSM treatment was measured as in FIG. The mean surface roughness of bulk specimens after UNSM treatment increased from 0.445 to 0.563 μm, while the mean surface roughness of 3D-printed untreated and UNSM treated specimens were 0.451 and 0.454 μm, respectively, indicating no significant change. It can be seen in FIG. 5 (b) that UNSM-treated tracks are clearly generated on the surface of the specimen having a distance of 70 μm as shown in Table 3. These corrugated surfaces are generated by the forward and backward movement of the UNSM treatment. Untreated and UNSM treated Top surface images of the specimens confirm the formation of micro-dimples on the specimen surface due to UNSM treatment. There are some surface modification techniques available for producing micro dimples on the surface, which have beneficial effects on the friction characteristics of the material. For example, the desired micro dimple may be fabricated with laser surface texturing (LST) technology, but the micro dimple size in this case is relatively large compared to the micro dimple size produced by the UNSM process.

The surface hardness of the specimen before and after the UNSM treatment was measured, and the effect of particle refinement after the UNSM treatment on the surface hardness and the comparison of the surface hardness value are shown in Fig. All UNSM treated specimens showed significantly higher hardness compared to bulk specimens and 3D printed specimens. The surface hardness of bulk specimens and 3D printed specimens were increased to 45, 58 HRC and 52, 66 HRC, respectively, after UNSM treatment.

The difference in the indentation sizes of the two specimens before and after the UNSM treatment is shown in FIG. The finer particles after UNSM treatment are directly responsible for the increase in surface hardness, which can be explained by the Hall-Petch relation. Previous studies on TEM observation have shown that the increase in surface hardness can be due to the increased dislocation density and the area fraction of the grain boundaries.

4. Measurement and Analysis of Friction and Wear Behavior

A dry sliding friction test was performed on bulk and 3D-printed untreated and UNSM treated specimens to investigate the effect of UNSM treatment on friction and wear behavior. Figure 8 shows the friction behavior of the specimen for sliding times up to 70 minutes. In both specimens, the UNSM treated specimen showed a lower coefficient of friction than the untreated specimen. In the case of bulk specimens, the friction behavior increases sharply at the beginning of the slip due to surface contamination such as water absorbed from the atmosphere and initial true contact between the substrate and the counter surface. After reaching the peak, it gradually decreased with time and stabilized to a coefficient of friction of 0.41 and 0.36, respectively, for untreated and UNSM treated bulk specimens. In runnig-in and steady-state sections, the coefficient of friction of untreated specimens was about 14% higher than the coefficient of friction of UNSM treated specimens. For three - dimensionally printed specimens, frictional behavior increased sharply when sliding began. On the other hand, specimens treated with UNSM showed a reduction rate of about 20% higher than untreated specimens, due to the reduced contact area at the interface due to the presence of corrugated surfaces.

The high frictional behavior of the untreated specimens during the initial stage of the test is due to the planarization of the initial surface roughness. On the contrary, the friction behavior was relatively stable and relatively stable. However, the friction behavior of specimens treated with UNSM began to fluctuate in the runnig-in and transition to steady-state. This rubbing behavior of the specimen generally occurs due to the plastic deformation of the asperity at the contact surface due to the initial contact surface roughness and high contact stress. That is, when the reciprocating sliding is continued, the contact area increases and a wear track is formed on the surface of the specimen. The decrease in the coefficient of friction of the specimens treated with UNSM can be attributed mainly to changes in surface roughness and the presence of deformed surfaces by the UNSM technique.

Figure 9 shows a wear track image of untreated and UNSM treated bulk and 3D printed specimens. Obviously, the SEM image shows that the wear track formed on the surface of the UNSM treated specimen is very different from the wear track of the untreated specimen. In addition, it can be seen that there is a large difference in surface roughness of the specimen after the friction test. However, for specimens treated with UNSM, the wear track was partially formed by the corrugated surface, which prevented the specimen from fully contacting the mating surface. In the case of untreated specimens, some exfoliated particles are observed on the surface due to the true contact area and the initial surface roughness, which is relatively smoother than the UNSM treated specimens. The specific wear rate was quantified according to the cross-sectional profile of each wear track and wear test conditions, and the non-abrasion rates of untreated and UNSM treated bulk and 3D-printed specimens were 5.6 × 10 ^-6 mm ³ / Nm and 3.4 × 10 ^-6 mm ³ / Nm, 2.4 10 ^-6 mm ³ / Nm, and 1.3 10 ^-6 mm ³ / Nm. It is clear that bulk specimens have low abrasion resistance compared to 3D printed specimens. The wear mechanism of the untreated specimen was adhesive wear mainly due to plastic deformation during sliding contact, as shown in Figs. 9 (a) and (c). While there was no crack in the wear track of the specimen treated with UNSM, the presence of microcracks (indicated by arrows) within the untreated wear track, as shown in Figures 9 (b and d), was confirmed by a high magnification SEM image. The abrasion wear can be observed on the surface of the UNSM treated specimen, mainly due to the separation of the initial protrusions derived from the rough surface induced by the UNSM treatment. The occurrence of adhesive wear can be explained by the fact that the oxide layer on the protrusions is easily broken due to the contact stress causing direct metal-to-metal contact.

To investigate the chemical state of the wear track, EDS was performed on the wear track of each specimen and the results are shown in Figs. 10 (a) to 10 (d). It has been found that during the dry sliding of the material in relative motion, as shown in Figures 10 (a and b), an oxide is formed which has a special influence on the friction and wear mechanisms. As shown in Figs. 10 (c and d), oxidative wear was found to be dominant in 3D printed specimens. However, the degree of oxidation was much higher at the interface where the untreated specimen contacted the mating surface compared to the interface where the UNSM treated specimen contacted the mating surface in the dry state. Also, the presence of the oxide film at the interface showed a slip Resulting in a lack of steady-state behavior of the friction for a period of time. Therefore, the oxide layer is not particularly advantageous for reducing the coefficient of friction and also lowers the abrasion resistance of the material.

Claims (14)

(a) fabricating one or more layers with additive manufacturing (AM); And
(b) performing an ultrasonic nanocrystalline surface modification (UNSM) on the surface of the one or more layers,
Wherein the ultrasonic nanocrystal surface modification (UNSM) is performed on the surface of each of the one or more layers in the presence of latent heat generated during additive manufacturing (AM) in the step (b) A method of manufacturing an article using a manufacturing method. The method according to claim 1,
In the step (a), a layer is formed by photopolymerization (PP), material extrusion (ME), adhesive jetting (BJ), material jetting (MJ) , Direct Energy Deposition (DED), Powder Bed Fusion (PBF), and Sheet Lamination (SL). Method of manufacturing articles using laminated fabrication method. The method according to claim 1,
Wherein the layer in step (a) is one selected from metal, ceramic, and metal matrix composites (MMC). The method according to claim 1,
Wherein a layer made of a metal is manufactured by using a direct energy deposition (DED) method or a powder bed fusion (PBF) method in the step (a) A method of manufacturing a used article. The method according to claim 1,
Wherein the layer made of metal is manufactured by using Metal Wire Arc Additive Manufacturing (MWAAM) or Additive Friction Stirring (AFS) in the step (a) A method of manufacturing an article using a manufacturing method. The method according to claim 1,
In the step (a), a layer made of a ceramic may be formed by any one method selected from Binder Jetting (BJ), Photo polymerization (PP), and Material Extrusion (ME) Wherein the method comprises the steps of: delete delete delete delete delete delete An article produced by the method of any one of claims 1 to 6. 14. An article according to claim 13 consisting of AISI H13 tool steel.

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