KR20220027583A - Method for manufacturing metal matrix composite(mmc) coating layer having excellent wear resistance and mmc coating layer manufactured thereby - Google Patents

Abstract

The present invention relates to a method of manufacturing a metal matrix composite (MMC) material. The method includes the following steps of: (a) forming an Ni-P-Si3N4 composite coating layer by performing electroless plating on the surface of a metal base material with a plating solution including a nickel (Ni) precursor, a phosphorus (P) precursor and silicon nitride (Si3N4) nano powder; and (b) thermally treating the Ni-P-Si3N4 composite coating layer. In accordance with the method of manufacturing a metal matrix composite material, an Si3N4 nanoparticles are bound to an Ni-P alloy matrix as a reinforcing agent to manufacture an electroless composite coating layer, and then, thermally treat the coating layer, thereby applying stress from the Si3N4 nanoparticles to Ni and Ni3P grains extracted and grown during the thermal treatment to contract lattice constants of the Ni and Ni3P grains while improving adhesiveness between the Ni and Ni3P grains and the Si3N4 nanoparticles, which can lead to a considerable improvement in mechanical properties such as hardness, wear resistance and the like.

Description

Method for manufacturing a metal matrix composite coating layer having excellent wear resistance and a metal matrix composite coating layer manufactured thereby

The present invention relates to a method for manufacturing a coating layer made of a metal matrix composite material and a coating layer manufactured by the method.

Electroless-plating refers to a self-catalytic process in which metal ions in a plating solution are oxidized and a film is deposited at the same time through oxidation of a reducing agent that supplies an internal current (electrons). The deposited metal ions are reduced by receiving electrons from the surface of the catalyst or the surface of the metal substrate. That is, electroless plating is a self-catalyzed or chemical reduction reaction in which metal ions in a plating solution are coated on a substrate without an external current.

Although various metals such as nickel, copper, gold, silver, palladium and cobalt can be electroless-plated, nickel-based electroless coatings exhibit excellent properties, so they are being actively developed from macro to nano-area applications. In particular, electroless nickel-phosphorus (Ni-P) or nickel-boron (Ni-P) alloy deposition currently accounts for 95% of the total industrial electroless plating.

On the other hand, industrially, the development of materials having various properties such as wear resistance, corrosion resistance and lubricity is required. It is difficult to satisfy all these various properties with a single material, so composite plating methods using materials with different properties are being actively researched and developed recently. The introduced composite plating coating layer is known.

Korean Patent Application Laid-Open No. 10-2013-0136283 (published date: December 12, 2013) Korean Patent Publication No. 10-2019-0071149 (published date: 2019.06.24.)

The present invention relates to a method for manufacturing an electroless composite coating layer formed by introducing a heterogeneous material into a nickel-phosphorus (Ni-P) alloy to improve the physical properties of the existing electroless nickel-phosphorus (Ni-P) coating layer, and An object of the present invention is to provide an electroless composite coating layer prepared by

The present invention is a Ni-P-Si ₃ N ₄ composite by electroless plating on the surface of a metal base material with a plating solution containing (a) a nickel (Ni) precursor, a phosphorus (P) precursor, and a silicon nitride (Si ₃ N ₄ ) nanopowder forming a coating layer; And (b) heat-treating the Ni-P-Si ₃ N ₄ composite coating layer; provides a method for manufacturing a metal matrix composite (MMC) coating layer comprising a.

In addition, the nickel (Ni) precursor is nickel sulfate (NiSO ₄ ·6H ₂ O), the phosphorus (P) precursor is sodium hypophosphite (NaH ₂ PO ₂ ·H ₂ O) Metal matrix composite material, characterized in that A method for manufacturing a coating layer is provided.

In addition, the plating solution, nickel sulfate 25 gL ^-1 , sodium hypophosphite 30 gL ^-1 and silicon nitride nanopowder 0.4 gL ^-1 It provides a method of manufacturing a coating layer of a metal matrix composite material, characterized in that it contains.

In addition, it provides a method of manufacturing a metal matrix composite coating layer, characterized in that the heat treatment for 1 hour at a temperature of 400 ℃ under an inert atmosphere in step (b).

Further, in another aspect of the present invention, there is provided a coating layer of a metal matrix composite material having excellent wear resistance manufactured according to the above manufacturing method.

According to the method for manufacturing a metal matrix composite coating layer according to the present invention, by performing heat treatment after manufacturing an electroless composite coating layer by bonding Si ₃ N ₄ nanoparticles as a reinforcement to a Ni-P alloy matrix, precipitation and growth during heat treatment Stress is applied to the Ni and Ni ₃ P grains by Si ₃ N ₄ nanoparticles to contract the lattice constants of Ni and Ni ₃ P crystals, while the adhesion between Ni and Ni ₃ P grains and Si ₃ N ₄ nanoparticles is improved As a result, it is possible to manufacture a composite coating layer with greatly improved mechanical properties such as hardness and abrasion resistance.

1(a) and 1(b) are Ni-P coating surface morphology and cross-sectional images, respectively, and FIGS. 1(c) and 1(d) are Ni-P-nSN coating surface morphology and cross-sectional images, respectively ( The Si ₃ N ₄ bonding coating contained a Ni-P layer (about 5 μm thick) as the nanoparticles were added to the bath 10 min after the Ni-P pre-coating.
2 is an XRD diffraction pattern of a specimen that is not heat treated after plating (as-plated) and a coated specimen that has been heat treated (an amorphous peak of a specimen that is not heat treated after plating is converted into a sharp crystalline peak of a specimen that has been heat treated, , diffraction peaks are associated with Ni or Ni ₃ P phases).
3(a) and 3(b) are the Rietveld analysis results of the XRD spectra observed in the Ni-P(H) specimen and (b) Ni-P-nSN(H) specimen, respectively (in (a) Inset shows unit cells of Ni and Ni ₃ P crystals, with blue and pink spheres representing Ni and P atoms, respectively).
Figure 4 (a) is a schematic diagram showing the Ni-P matrix Si ₃ N ₄ nanoparticles are bonded, Figure 4 (a) is a schematic diagram showing the microstructure change by the formation of Ni and Ni ₃ P crystal grains after heat treatment ( Si ₃ N ₄ nanoparticles exist between the grains and exert stress (indicated by arrows) on the growing Ni and Ni ₃ P grains during heat treatment.
5 (a) and (b) are TEM images and enlarged images (Ni and Ni ₃ P particles are more clearly visible) showing Ni and Ni ₃ P crystal grains precipitated after heat treatment, FIGS. 5 (c) and (d) ) is the SAED pattern for each of the indicated regions (1) and (2) in FIG. 5(b), and FIGS. 5(e) and (f) are HRTEM images on Ni and Ni ₃ P, respectively.
6(a) is an annular high-angle annular dark field (HAADF) image of a Ni-P-nSN(H) specimen, and FIGS. 6(b) to 6(f) are Ni-P-nSN (H) Elemental mapping image of the specimen.
7 is a coefficient of friction versus time curves of Ni-P and Ni-P-nSN specimens as-plated and heat-treated after plating.
8(a) and 8(b) are wear scar images and corresponding depth profile plots of Ni-P and Ni-P-nSN specimens, respectively.
9(a) and 9(b) are wear scar images and corresponding depth profile plots of Ni-P(H) and Ni-P-nSN(H) specimens, respectively.
FIG. 10(a) is a Raman spectrum of the coated surface of each specimen, and FIG. 10(b) is a Raman spectrum of a wear piece of each specimen.

In describing the present invention, if it is determined that a detailed description of a related well-known function or configuration may unnecessarily obscure the gist of the present invention, the detailed description thereof will be omitted.

Since the embodiment according to the concept of the present invention may have various changes and may have various forms, specific embodiments will be illustrated in the drawings and described in detail in the present specification or application. However, this is not intended to limit the embodiment according to the concept of the present invention to a specific disclosed form, and should be understood to include all changes, equivalents, or substitutes included in the spirit and scope of the present invention.

The terms used herein are used only to describe specific embodiments, and are not intended to limit the present invention. The singular expression includes the plural expression unless the context clearly dictates otherwise. In the present specification, terms such as "comprise" or "have" are intended to designate that the described feature, number, step, operation, component, part, or a combination thereof exists, but one or more other features or numbers , it should be understood that it does not preclude the possibility of the existence or addition of steps, operations, components, parts, or combinations thereof.

Hereinafter, the present invention will be described in more detail by way of examples.

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

<Example>

Low carbon steel panels were machined to size 20 mm × 15 mm × 0.4 mm and polished with 1200 grit SiC abrasive paper. The polished panel was washed with acetone and rinsed with deionized water. It was then degreased in 10% NaOH (w/w) solution and etched in 10% H ₂ SO ₄ (v/v) solution for 10 min and 2 min, respectively. The substrate panels were properly rinsed with deionized water between each treatment step. All processes of surface treatment were performed at room temperature (25° C.). The treated substrates were immediately transferred to an electroless coating bath and coated through an autocatalytic redox reaction.

The chemical composition of the electroless plating bath was prepared in the same way as in the previous study (DR Dhakal et al.; Surface & Coatings Technology 381 (2020) 125135) except for the added nanoparticles. In this example, the amount of Sodium Dodecyl Sulfate (SDS) was taken as 0.05 gL ^-1 . The pH of the bath measured at 25 °C was 5.0 and the plating temperature was maintained at 80 °C 2 °C throughout the coating process. As the ceramic additive, a commercially available Si ₃ N ₄ nanopowder having an average particle diameter of 20 nm was used. A slurry of Si ₃ N ₄ nanopowder and SDS mixed in a 50 mL bath solution was prepared in a separate container. It was sonicated for 1 hour to disperse the agglomerated nanopowder particles. Before adding the slurry to the bath, the substrate was coated with Ni-P for 10 min to ensure good adhesion between the substrate and the coating. The concentration of Si ₃ N ₄ nanopowder in the bath was 0.4 gL ⁻¹ . The stirring was continued at 250 rpm during the 1 hour coating process. For comparison, two types of plating, that is, a Ni-P composite and a Ni-P-Si ₃ N ₄ composite were prepared.

The two types of coated specimens were heat treated at 400 °C for 1 hour in an inert argon (Ar) atmosphere. In order to distinguish specimens according to plating and heat treatment conditions, the following symbols were adopted for each specimen below.

1. Ni-P → Ni-P coating

2. Ni-P-nSN → Ni-P coating with Si ₃ N ₄ nanoparticles

3. Ni-P(H)→Ni-P coating, heat treatment at 400℃ for 1 hour

4. Ni-P-nSN(H)→Ni-P-nSN coating after heat treatment at 400℃ for 1 hour

<Experimental example>

1. Surface and cross-sectional properties of composites

1 shows the coating surface and cross-sectional views for Ni-P and Ni-P-nSN composite coatings. After bonding the Si ₃ N ₄ particles to the Ni-P matrix, the morphological appearance did not change significantly in the Ni-P-nSN composite coating (Figs. 1a and c). The shape of the nodules observed on the composite surface indicates the uniformity and conciseness of the coating. In addition, the bonded nanoparticles did not change the coating mechanism of nickel and phosphorus because the composite coating did not have irregular growth of cavities, cracks or nodules. The smoothness of the composite coating was also verified by the surface profile test. The average roughness (R _a ) value was 0.02 μm for the Ni-P coating and 0.04 μm for the Ni-P-nSN composite coating, which was not significantly different (Table 1).

The cross-sectional images of Ni-P and Ni-P-nSN shown in FIGS. 1b and 1d show the uniformity of the two coatings, respectively. The thickness of the Ni-P composite coating (20.1 μm) and the thickness of the Ni-P-nSN composite coating (20.3 μm) were both coated for one hour and were virtually identical. The similar coating thickness of the two coatings suggests that the presence of nanoparticles did not affect the catalytic activity of the bath. That is, during the Ni-P coating process, nanoparticles are physically adsorbed to the catalyst surface, but the reduction of Ni ions on the catalyst surface is not affected by the presence of nanoparticles. Therefore, the coating thickness in the one-hour coating process is almost the same for both coatings.

Both heat-treated specimens were observed to have morphological characteristics similar to those of as-plated specimens after plating. In general, the presence of ceramic additives in the Ni-P matrix results in irregular coating deposition. Thus, Ni-P-Ceramic composite coating surfaces typically consist of large, improperly grown nodules, inter-nodular gaps, craters, and kinks, resulting in a much rougher coating surface. . Heat treatment mainly affects the smoothing of the surface by rearranging the structure through Ni and P diffusion. This structural rearrangement reduces the coating thickness to some extent in the Ni-P-Ceramic composite coating after heat treatment. However, in this example, a decrease in the coating thickness of the heat-treated specimen was not observed (see Table 1). There was no appreciable change in surface asperities due to heat treatment as there were no voids, cavities, or inappropriate nodule growth in the coating.

<Table 1> Coating property parameters

2. Vickers hardness

The hardness of the Ni-P-nSN coating did not improve but rather decreased compared to the reference Ni-P coating (see Table 1). Particle-matrix adhesion plays an important role in improving hardness. Therefore, the weak adhesion of Si ₃ N ₄ nanoparticles in the amorphous coating matrix could be the reason for creating a soft composite coating. However, the hardness of Ni-P (H) and Ni-P-nSN (H) coatings that were subjected to heat treatment were significantly improved after plating compared to the as-plated specimens.

The increase in microhardness of Ni-P(H) is associated with precipitation hardening due to the hard Ni ₃ P phase, and the microhardness of Ni-P-nSN (H) coatings is firmly between grains (Ni and Ni ₃ P). It is further increased by the attached Si ₃ N ₄ nanoparticles. after heat treatment. The understanding of the improved microhardness of Ni-P-nSN(H) compared to Ni-P(H) in terms of structural change will be discussed below.

3. Microstructure and Phase Analysis

(1) XRD analysis

The XRD patterns of the as-plated Ni-P and Ni-P-nSN specimens and the heat-treated specimens after plating are shown in FIG. 2 . The broad peaks ranging from 37° to 55° in both coated specimens that were not as-plated after plating suggest that the coated material is short-range ultrafine nanocrystals or amorphous. On the other hand, no additional diffraction peaks were detected in the two coated specimens that were not heat treated after plating (as-plated). The peak related to the incorporated Si ₃ N ₄ nanoparticles did not appear clearly, indicating that the Si ₃ N ₄ nanoparticles provided in this example exhibit short-period crystallinity and the amount contained in the coating was not sufficient to detect by X-ray. seems to be because it is not. Fiolek et al. reported a similar XRD pattern for Si ₃ N ₄ nanopowders with sizes ranging from 15 to 30 nm, where a diffuse SAED ring pattern of the nanopowders was also observed.

It can be seen that the amorphous phase is converted into a crystalline phase in the Ni-P(H) and Ni-P-nSN(H) specimens. When the coating is heat treated at 400 °C for 1 hour, the microstructure changes from amorphous to crystalline. Rietveld refinement of the diffraction data of Ni-P(H) and Ni-P-nSN(H) to obtain information on the phase composition of the Ni-P electroless coating system and the influence of Si ₃ N ₄ nanoparticles. ) was carried out. 3 is an XRD spectrum of Ni-P(H) and Ni-P-nSN(H) specimens after Rietveld refining, and it can be seen that the overall diffraction pattern calculated from the refining parameters is almost identical to the experimental diffraction pattern. The sharp diffraction peaks of the crystalline phase are for Ni and Ni ₃ P nanoparticles, no other phases are observed. Therefore, Rietveld purification confirmed that the Ni-P electroless coating system heat treated at 400 °C for 1 hour was composed of pure Ni and Ni ₃ P phases with space groups Fm-3m and I-4 , respectively. Table 2 presents the results of purification. The high astringency of the tablets is indicated by a low R coefficient. The lattice constants of Ni and Ni ₃ P crystal structures of the Ni-P(H) electroless coating system are in good agreement with those of pure Ni and Ni ₃ P crystal structures presented in other previous studies. However, the lattice constant and unit cell volume of Ni and Ni ₃ P crystals decreased in the Ni-P-nSN(H) system. The contraction of the lattice constant is believed to be due to the presence of Si ₃ N ₄ nanoparticles in the Ni-P-nSN(H) system. Heat treatment of amorphous Ni-P electroless coating without Si ₃ N ₄ nanoparticles induces diffusion and rearrangement of Ni and P atoms, leading to free grain growth of Ni and Ni ₃ P crystal phases. However, when Si ₃ N ₄ nanoparticles dispersed in the amorphous coating layer are present in the amorphous coating layer as schematically shown in FIG _. do. As the Ni and Ni ₃ P particles become larger and larger, the bound Si ₃ N ₄ nanoparticles exert more and more stress on the surrounding Ni and Ni ₃ P particles, and two direct results can be expected. First, the lattice constants of Ni and Ni ₃ P crystals decreased in the Ni-P-nSN(H) system due to the residual stress of Si ₃ N ₄ nanoparticles, which was confirmed through Rietveld purification. Second, Si ₃ N ₄ nanoparticles generate a kind of tight binding effect between grains, resulting in improved mechanical properties such as microhardness and abrasion resistance behavior of the Ni-P-nSN(H) coating system. create a microstructure. Therefore, as can be seen in Table 1, the increase in microhardness of the Ni-P-nSN(H) coating compared to the Ni-P(H) coating was the result of the lattice constants of Ni and Ni ₃ P crystals in Ni-P-nSN(H). This can be attributed to the decrease in

<Table 2> Ni and Ni calculated after Rietveld analysis ₃ P-phase decision information

(2) TEM, HRTEM and SAED pattern analysis of composite coatings

TEM, HRTEM and SAED images of Ni-P-nSN(H) heat treated in FIG. 5 are shown.

The crystal grains of the Ni and Ni ₃ P phases can be clearly seen in the TEM micrographs (FIGS. 5(a) and (b)). In order to confirm the phase of the observed grains, a selected area electron diffraction (SAED) pattern was analyzed in both regions 1 and 2 of FIG. 5(b). The SAED patterns corresponding to grains 1 and 2 are shown in FIGS. 5(c) and 5(d), respectively. In region 1, (111) and (200) reflections with lattice spacing of 0.205 nm and 0.238 nm, respectively, are obtained, which correspond to Ni grains. Similarly, region 2 was identified as grains on Ni ₃ P with grating spacing of 0.397 nm for (101) reflection and 0.286 nm for (310) reflection. In addition, the crystal plane is clearly observed in the HRTEM images of FIGS. 5(e) and (f). A (111) plane corresponding to a Ni crystal with a lattice spacing of 0.207 nm is found in the HRTEM image, which is consistent with that obtained from the SAED pattern. Fig. 5(e) also shows the (141) plane associated with Ni ₃ P along with the Ni crystal plane. As a result of HRTEM and SAED pattern analysis, no other metastable phase of nickel phosphide was observed. In addition, a phosphorus interface separating Ni and Ni ₃ P particles can also be seen in FIG. 5(e) (indicated by a red dotted line). However, the crystal planes overlap in some parts of the interface and some parts consist of a semi-crystalline structure, which is thought to be related to the Ni ₃ P crystals. The HRTEM image taken in region 2 shown in FIG. 5(f) further confirms the crystal grains of the Ni ₃ P phase. Clear and ordered grating planes appeared (see Fig. 5(f)), some of which were identified as (101) and (121) planes with grating spacings of 0.393 nm and 0.299 nm, respectively.

(3) EDS analysis of the composite coating microstructure

6 shows the elemental composition of Ni-P-nSN(H) analyzed by EDS. In the HAADF image of FIG. 6( a ), small spheroids represent crystal grains developed after heat treatment. In addition, the Ni-rich region and the P-rich region clearly identified in the elemental mapping images (Figs. 6(c) and (d)) suggest the formation of nanocrystalline phases of Ni and Ni ₃ P. A P-deficient region with a large Ni concentration belongs to Ni grains, and a region with a relatively high P concentration compared to Ni indicates Ni ₃ P grains. Obviously, the Ni concentration of Ni grains is higher than that of Ni ₃ P grains. EDS mapping of Si (Fig. 6(b)) shows that Si ₃ N ₄ nanoparticles are bound. The concentration of Si ₃ N ₄ nanoparticles in the plating bath is 0.4 gL ⁻¹ . The volume percentage of reinforcing nanoparticles should be similar in the composite coating. According to the EDS quantitative mapping result, the weight% of Si and N are 0.9% by weight and 1.3% by weight, respectively. Although this concentration is low, it is important for improving microhardness compared to Ni-P(H) coatings by causing shrinkage of Ni and Ni ₃ P crystal unit cells in Ni-P-nSN(H) composite coatings.

In addition, the phosphorus (P) content of the two coatings is about 11% by weight, while the oxygen content of the Ni-P-nSN coating surface decreases compared to the Ni-P coating surface. Therefore, the coating can be viewed as a coating with a high P content, and the microstructure is amorphous in the plated state. Iron and carbon are also deposited as impurities come from the clips holding the sample and from organic compounds in the bath. The effect of the presence of carbon in the coating will be discussed below.

4. Friction and wear behavior of coatings

(1) coefficient of friction

To investigate the effect of nanoparticles bound to the coating matrix, the friction and wear behavior of the coating was investigated. 7 shows plots of the coefficient of friction (COF) versus sliding time recorded during the sliding of a bearing steel ball on the surface of an as-plated and heat treated specimen after plating. Surface roughness is an important parameter that directly affects the friction and wear behavior of coatings. As mentioned earlier, both the plated and annealed coatings have similar average roughness parameters. Therefore, it is expected that the COF and wear behaviors of the coated specimens are purely due to the material properties and not the surface irregularities. Initially, the as-plated specimens after plating show a similar progression in the COF curve during the first minute of sliding. In the Ni-P coating, the COF continued to decrease until the sliding time approached 1.2 min, and then remained almost constant until the sliding time of 5 min. Then, the COF value of the curve showed a change until the sliding process was finished. The COF curve also showed a similar trend in the Ni-P(H) specimen. Initially, the COF curve of Ni-P(H) starts at a lower value than that of Ni-P and continues to follow a similar trend for Ni-P until the sliding time exceeds 6 min, and as the sliding progresses, at the end of the sliding process There were significant fluctuations in COF. On the other hand, the Ni-P-nSN coating shows a higher COF value at first but a steady curve after 2 min. Since the hardness of the Ni-P-nSN composite is lower than that of the Ni-P coating, the high friction provided by the composite can lead to immediate tearing of the soft coating. As the sliding process continues, debris begins to form on the shattered coating, reducing the COF. The debris generated from the composite coating is composed of Si ₃ N ₄ nanoparticles, which further lowers the COF compared to that of the Ni-P coating. A typical COF curve is observed for Ni-P-nSN(H) composite coatings, starting with low COF values and increasing slightly as the sliding process progresses. The stability of the COF values was observed after 2 min and maintained until the end. 7, it can be seen that both the non-heat-treated composite material and the heat-treated composite material after plating exhibited low COF values. The matching curve after 2 min of sliding is the effect of nanoparticle binding.

(2) Analysis of wear scars through SEM and profilometer

8 shows an image of a wear scar and a corresponding depth profile plot. As can be seen in the image, the wear scar width of Ni-P-nSN (~495 μm) is slightly larger than the wear scar width formed in Ni-P (~460 μm). Likewise, the maximum depth of wear scars on flat surfaces is greater for Ni-P-nSN than for Ni-P. The Ni-P-nSN coating has wider and deeper wear scars (Figs. 8(a) and (b)), and relatively more wear debris accumulation occurs around the wear marks. Therefore, the wear rate of Ni-P-nSN (3.37 × 10 ^-5 mm ³ N ^-1 m ^-1 ) is higher than that of Ni-P (2.26 × 10 ^-5 mm ³ N ^-1 m ^-1 ). The wear rate for each specimen is calculated using the following equation:

where V is the amount of wear ( mm ³ ), S is the sliding distance ( m ), and F is the applied vertical load ( N ). The wear amount and wear rate of all specimens are shown in Table 3.

In contrast, the heat treated specimens showed improved wear resistance behavior. The wear rates of Ni-P(H) and Ni-P-nSN(H) were 0.39×10 ⁻⁵ mm ³ N ⁻¹ m ⁻¹ and 0.07×10 ⁻⁵ mm ³ N ⁻¹ m ⁻¹ , respectively. 9(a) and (b) show the wear marks and corresponding depth profile images of Ni-P (H) and Ni-P-nSN (H) specimens, compared with the as-plated specimens after plating. Appropriate reduction was shown in the width and depth of the wear scar. In addition, it can be seen that the Ni-P-nSN(H) composite coating among the two heat treatment specimens has improved wear resistance compared to the Ni-P(H) coating. This improvement in coating abrasion resistance behavior is due to the shrinkage of the lattice constants of Ni and Ni ₃ P crystals by the presence of Si ₃ N ₄ nanoparticles.

(3) Characteristics of wear fragments and the role of wear fragments on COF and wear rate

After plating, sheet-shaped fragments are accumulated around the wear marks of the two coatings that are not heat treated (as-plated) (FIGS. 8(a) and (b)). However, the sheet size of the Ni-P-nSN coating is larger than that of the Ni-P coating and accumulates in large quantities. The hardness measurement results show that the Ni-P-nSN composite coating is softer than the Ni-P coating. The low adhesion between the nanoparticles and the matrix suggests that a soft coating was formed in the presence of the nanoparticles. Many dislocations are generated at the contact surface due to plastic deformation during the sliding process. As the dislocation density continues to accumulate in the surface layer, cracks and voids can be created in the sliding surface. In the composite coating system, the strong adhesion between the particles and the matrix prevents the particles from propagating cracks. However, when the particles are loosely attached to the matrix, the plastic flow of the matrix around the rigid particles creates voids. The combination of crack propagation and void growth can lead to the formation of loose wear particles that can dislodge from sub-layers as shear stresses continue to accumulate during the sliding process. The incorporation of cracks or voids makes the strength of the underlying layer weaker than the shear stress applied to the interface between the slider and the surface, and in this way the loosely bound rigid Si ₃ N ₄ nanoparticles in the Ni-P-nSN coating prevent delamination of the coating. and the formation of sheet-like fragments. Therefore, the number of sheet-like fragments of Ni-P-nSN is higher than that of Ni-P coating. As soon as a sheet of debris is created, some can become trapped between the two surfaces of the sliding track and break into small pieces. The rolling of small fragments containing bound nanoparticles may have reduced the COF of the Ni-P-nSN composite coating as the sliding of the two surfaces further proceeded. On the other hand, both heat-treated specimens consisted of hard Ni ₃ P precipitates, resulting in a relatively hard coating. If the contact stress on the harder surface is sufficient to generate localized dislocations, then successive accumulation of dislocations can create cracks in the harder metal. Although a large number of cracks must be created to form wear flakes, hard surfaces exhibit very little plastic shear deformation. Thus, the wear rate is much lower for hard materials than for soft materials. As suggested by Rietveld analysis, Ni ₃ P precipitation and strain induction by Si ₃ N ₄ nanoparticles improved the hardness of Ni-P-nSN (H) specimens, and damage and separation of the surface layer were slower Therefore, less wear fragments occur in the heat treated specimen. The Ni-P-nSN(H) coating has much less wear debris compared to the Ni-P(H) coating because after heat treatment a harder coating is produced compared to the silver Ni-P(H) coating (Fig. b) see).

<Table 3> Wear volume and wear rate of each specimen

(4) Raman analysis of wear pieces

Structural and chemical properties of laminated thin films are extensively characterized by Raman measurements, and Raman measurements are an excellent tool for understanding the oxidation behavior of Ni thin films, for example. However, it has been rarely used to analyze electroless Ni-P coating systems. In previous studies, the presence of a NiO layer on the surface of the Ni-P electroless coating system even at room temperature was revealed by temperature-dependent Raman measurement of the coating surface. In this example, the oxidation behavior of the wear pieces is studied and differentiated from the properties of the coating in the steady state. The Raman bands of the wear pieces accumulated around the wear marks during the wear test are shown in FIG. 10 .

Four bands corresponding to the NiO phase can be seen in both the plated Raman spectra of the two types of coatings (Fig. 10(a)). The bands of ~ 535 cm ^-1 , 800 cm ^-1 , 920 cm ^-1 and 1090 cm ^-1 are respectively a first order longitudinal optical (LO) mode, a second order longitudinal optical (2TO) (second order) transverse optical (2TO) mode, the primary longitudinal and transverse optical combination (LO + TO) mode, and the secondary longitudinal optical (2LO) mode. The heat-treated specimen also showed similar bands except for the 2LO band, and the position of the LO was slightly changed to 515 cm ^-1 (see Fig. 10(a)). The band shift and disappearance may be related to the existing crystalline behavior of the coating. The other bands appearing at 1350 cm ^-1 and 1580 cm ^-1 are identified as the D and G bands of graphitic carbon. A marked increase in the strength of these bands suggests that the graphitic carbons are more ordered in the annealed specimens. Signals from lattice vibrations of graphitic carbon are very sensitive to the degree of structural disorder. As the EDS data show, carbon can be deposited on the electroless Ni-P coating system as an impurity sourced from organic compounds. Heat treatment may have caused impure organic matter to escape from the coating in gaseous form, leaving carbon in the coating. Thus, graphitic carbon bands appear deeper in the annealed specimens. Graphite is inherently lubricious and can reduce friction. For this reason, the Ni-P(H) coating exhibits a relatively lower COF than that of Ni-P at the initial stage of sliding. However, the COF versus time curve (FIG. 7) shows that the variation in COF over time is associated with large obstacles caused by voids and adhered wear debris due to failure of the coating. In contrast, rather low friction is observed in the composite coating to which the nanoparticles are bonded. Debris mixed with nanoparticles may have rolled between sliding surfaces instead of sticking to the sliding tracks.

Similarly, the Raman spectrum of the wear piece consistently shows four NiO bands and D and G bands (see Fig. 10(b)). After plating, the fragments associated with the as-plated specimens had the same characteristic bands that appeared on the surface, suggesting that the coating was weaker and separated easily without further oxidation. Debris detached from the coating too early, so further oxidation by continuous surface sliding did not occur. On the other hand, fine fragments generated from heat-treated specimens show different oxidation behaviors. A sharp rise in the LO band was observed in all fragments of the heat treated specimen, while the 2TO band disappeared (see Figs. 9(a) and (b0)).

In summary, it was confirmed that the incorporation of Si ₃ N ₄ nanoparticles to the Ni-P coating matrix was effective in preventing wear after heat treatment. Strain applied by nanoparticles during the growth of Ni and Ni ₃ P grains in Ni-P-nSN(H) coated specimens caused shrinkage of the lattice constants of Ni and Ni ₃ P crystals, and after heat treatment, the nanoparticles The mechanical properties such as hardness and abrasion resistance behavior of Ni-P-nSN(H) coatings were improved due to the improved adhesion between the particles and the precipitated particles. In addition, according to the Raman measurement results, the degree of oxidation of the wear fragments generated from the heat treated specimen was higher than that of the as-plated specimen after plating. In addition, the Raman bands of 1350 cm ^-1 and 1580 cm ^-1 showed that Ni and P atoms as well as carbon impurities from organic compounds were deposited during the autocatalytic process in the electroless Ni-P coating system. After the heat treatment, the band peak of the impurity carbon became more pronounced like the graphitic carbon material.

The present invention is not limited to the above embodiments, but can be manufactured in various different forms, and those of ordinary skill in the art to which the present invention pertains can take other specific forms without changing the technical spirit or essential features of the present invention. It will be understood that it can be implemented as Therefore, it should be understood that the embodiments described above are illustrative in all respects and not restrictive.

Claims (5)

(a) Electroless plating on the surface of a metal base material with a plating solution containing a nickel (Ni) precursor, a phosphorus (P) precursor, and a silicon nitride (Si ₃ N ₄ ) nanopowder to form a Ni-P-Si ₃ N ₄ composite coating layer making; and
(b) heat-treating the Ni-P-Si ₃ N ₄ composite coating layer; including
Method of manufacturing a metal matrix composite (MMC) coating layer. The method of claim 1,
The nickel (Ni) precursor is nickel sulfate (NiSO ₄ ·6H ₂ O),
The phosphorus (P) precursor is sodium hypophosphite (NaH ₂ PO ₂ ·H ₂ O) Method for producing a coating layer of a metal matrix composite material, characterized in that. 3. The method of claim 2,
The plating solution is
25 gL ^-1 of nickel sulfate, 30 gL ^-1 of sodium hypophosphite, and 0.4 gL ^-1 of silicon nitride nanopowder A method of manufacturing a coating layer for a metal matrix composite material. The method of claim 1,
Method for producing a metal matrix composite coating layer, characterized in that heat treatment for 1 hour at a temperature of 400 ℃ under an inert atmosphere in step (b). A metal matrix composite coating layer prepared by the method of any one of claims 1 to 4.

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