Iron-based amorphous / nanocrystalline gradient coating and preparation method and application thereof

Abstract

The invention discloses an iron-based amorphous / nanocrystalline gradient coating and a preparation method and application thereof, and belongs to the field of iron-based coatings. The iron-based amorphous / nanocrystalline gradient coating comprises a bottom layer, a middle layer and a surface layer which are the same in composition, the bottom layer is a nanocrystalline enrichment area, the middle layer is an amorphous and nanocrystalline mixing area, the surface layer is an amorphous enrichment area, raw material components of the areas are iron-based amorphous powder, and the iron-based amorphous powder comprises, by mass, 20-24% of Cr, 3-7% of Mo, 3-7% of W, 0.3-0.7% of C, 2-6% of B, 1-5% of Y, 0.3-0.7% of Si and the balance Fe. The preparation method comprises the following steps: (1) pretreating the matrix; (2) preparing iron-based amorphous powder by adopting a vacuum induction melting gas atomization method; and (3) depositing the iron-based amorphous powder on the surface of the substrate by using laser directional energy gradient deposition: sequentially carrying out bottom layer deposition, middle layer deposition and surface layer deposition. The gradient coating provided by the invention can achieve the effects of high-strength combination with a matrix, excellent wear resistance and high corrosion resistance.

Description

Technical Field

[0001] This invention relates to iron-based coatings, and more particularly to an iron-based amorphous / nanocrystalline gradient coating, its preparation method, and its application. Background Technology

[0002] In harsh industrial environments such as energy, chemical, and marine engineering, critical components such as rolls, bearings, molds, and hydraulic plungers often endure the combined effects of severe mechanical wear and intense corrosion, placing extremely high demands on the comprehensive performance of surface protective coatings. To improve the surface properties of these components, surface strengthening technologies are widely used, among which laser-directed energy deposition technology has attracted much attention due to its advantages such as high energy density, controllable heat input, and high coating-substrate bonding strength.

[0003] Iron-based amorphous alloys, due to their long-range disordered atomic arrangement, possess high strength, high hardness, excellent wear resistance, and corrosion resistance, making them ideal surface strengthening materials.

[0004] CN101899663A discloses an iron-based amorphous / nanocrystalline coating using a two-step process of "laser cladding + laser remelting." The limitation of this method lies in its cumbersome process and the strong dependence of the remelting process on the microstructure of the initial cladding layer, making it difficult to achieve a uniform and controllable amorphous / nanocrystalline composite structure across the entire coating thickness. While CN101033543A discloses a plasma-clad iron-based amorphous / nanocrystalline coating that achieves metallurgical bonding between the coating and the substrate, the relatively low energy density of the plasma arc and limited cooling rate of the molten pool result in insufficient amorphous formation capability and generally low amorphous phase content. Consequently, the obtained coating structure is not an ideal amorphous / nanocrystalline composite structure, which limits further improvement in coating performance. CN1730714A uses thermal spraying technology (atmospheric plasma spraying, supersonic flame spraying) to prepare iron-based amorphous / nanocrystalline coatings. The coating and the substrate are mainly mechanically bonded or weakly metallurgically bonded, and the bonding strength is usually low. Under high load or strong impact conditions, it is prone to peeling failure. In order to obtain a nanocrystalline structure, the amorphous coating after spraying needs to be subjected to subsequent heat treatment. This process not only increases energy consumption and process complexity, but may also lead to over-crystallization of the amorphous phase, elemental segregation or redistribution of internal stress in the coating, thereby damaging the original excellent properties of the coating, such as a decrease in corrosion resistance.

[0005] Analysis of existing technologies reveals significant shortcomings in the design of iron-based amorphous or gradient coatings. Current iron-based amorphous coating technologies are either limited by bottlenecks in improving cooling rates and amorphous formation capabilities, or suffer from insufficient coating adhesion strength, reliance on post-treatment that may impair coating performance, and an inability to actively control the microstructure. Summary of the Invention

[0006] Purpose of the invention: The purpose of this invention is to provide a gradient coating that has a high bonding strength with the substrate, excellent wear resistance, and strong corrosion resistance.

[0007] Another object of the present invention is to provide a method for preparing the above-mentioned gradient coating.

[0008] A third objective of this invention is to provide an application of the above-mentioned gradient coating in wear-resistant and corrosion-resistant components.

[0009] Technical solution: The iron-based amorphous / nanocrystalline gradient coating of the present invention includes three regions with the same composition: a bottom layer, a middle layer, and a top layer. The bottom layer is a nanocrystalline enrichment region, the middle layer is a mixed region of amorphous and nanocrystalline materials, and the top layer is an amorphous enrichment region. The raw material composition of the regions is iron-based amorphous powder, which, by mass percentage, includes 20-24% Cr, 3-7% Mo, 3-7% W, 0.3-0.7% C, 2-6% B, 1-5% Y, 0.3-0.7% Si, and the balance is Fe.

[0010] Preferably, the total thickness of the coating is 300-500 μm; the thickness of the bottom layer accounts for 20%-30% of the total coating thickness, the thickness of the middle layer accounts for 30%-40%, and the thickness of the top layer accounts for 30%-40%.

[0011] The method for preparing the iron-based amorphous / nanocrystalline gradient coating of the present invention includes the following steps: (1) Pretreatment of the matrix; (2) Iron-based amorphous powder was prepared by vacuum induction melting gas atomization method; (3) Use laser-directed energy gradient deposition to deposit iron-based amorphous powder onto the substrate surface: perform bottom layer deposition, middle layer deposition and surface layer deposition in sequence.

[0012] The substrate mentioned in step (1) is either 45# steel or 20G steel.

[0013] The powder in step (2) has a particle size of 53-150 μm and should be dried under vacuum at 100-120℃ for more than 2 hours before use.

[0014] The P / V ratios of the bottom layer, middle layer, and surface layer sediments described in step (3) are 83-120 J / mm², respectively. 2 120-175J / mm 2 175-267J / mm 2 The opening degrees of the water-cooled valves for the bottom layer deposition, middle layer deposition, and surface layer deposition in step (3) are 20-40%, 50-70%, and 80-100%, respectively.

[0015] The present invention relates to the application of the iron-based amorphous / nanocrystalline gradient coating in wear-resistant and corrosion-resistant components, wherein the components are one of the following: rolling mill rolls, bearings, molds, and hydraulic plungers.

[0016] Invention Principle: This method aims to provide a gradient coating, which is mainly divided into three regions: a bottom layer, a surface layer, and a middle layer. The bottom layer is a nanocrystalline enrichment region, possessing high toughness, high fracture resistance, and excellent bonding strength with the substrate, effectively buffering external mechanical stress and preventing crack propagation into the substrate. The surface layer is a highly amorphous region, providing extremely high hardness, wear resistance, and ultra-high corrosion resistance, serving as the first barrier against wear and corrosion. The middle mixed region, as a transition area, enables a smooth gradient change in mechanical properties, avoiding interfacial failure caused by abrupt performance changes. This structure allows the coating to achieve a synergistic effect of wear resistance and corrosion resistance when facing complex working conditions where wear and corrosion alternate or occur simultaneously.

[0017] In the composition system designed by this method, Mo, W, and Y act as large atoms, while B and C act as small atoms. Together with Fe, Cr, and Si atoms, they form a topologically disordered packing state with a large atomic mismatch, thereby improving the amorphous formation capability of the entire alloy system. Cr, Mo, and W synergistically ensure corrosion resistance; C and B, as metalloid elements, can reduce the critical cooling rate of the amorphous alloy, which is beneficial to the formation of the amorphous phase; Y plays a role in purifying the melt and refining the microstructure; and Si improves process wettability, thereby enhancing the fluidity of the molten metal and the amorphous formation capability of the system.

[0018] This method utilizes laser-directed energy deposition (EDA) to prepare gradient coatings. An adjustable water-cooling system is introduced to control the ratio of laser power (P) to scanning speed (V) for different deposition layers, actively regulating the molten pool cooling rate. This constructs a continuous gradient microstructure within the coating, from nanocrystalline at the bottom to a highly amorphous surface layer. This effectively solves the problems of low amorphous content, high internal stress, insufficient bonding strength, and uncontrollable microstructure in existing technologies. Specifically, the bottom layer employs a high P / V value and a low cooling water flow rate. Low energy input ensures deep fusion and a strong metallurgical bond with the substrate, while slower cooling promotes the formation of a structure dominated by tough nanocrystalline particles at the bottom. The middle layer uses a medium P / V value and a moderate cooling water flow rate. Reduced energy input and accelerated cooling initiate the formation of a mixed amorphous and nanocrystalline structure. The surface layer uses a low P / V value and a high cooling water flow rate. High heat input and forced rapid cooling maximally suppress crystallization, resulting in a surface layer with a high amorphous content.

[0019] Beneficial effects: Compared with the prior art, the present invention has the following significant advantages: (1) The layers of the gradient coating are metallurgically bonded and the coating and the substrate are bonded together, and the bonding force between the coating and the substrate is strong; (2) The surface of the gradient coating is a high amorphous region with extremely high hardness, wear resistance and corrosion resistance, amorphous content ≥95%, microhardness ≥850HV, corrosion rate ≤0.07mm / a, and maximum wear depth ≤3.0μm; (3) The present invention achieves its advantages through composition design, especially the composition design of the three key small atoms that form amorphous materials, B, C and Si. This makes the alloy system tend to form a topological disordered stacking state, thereby reducing the free volume of the system and hindering element diffusion, thus obtaining excellent amorphous formation ability; (4) This method uses laser directional energy deposition process to perform gradient deposition of coating on the substrate surface. The entire process does not require post-heat treatment and can actively construct an ideal amorphous / nanocrystalline gradient structure, avoiding the risk of amorphous phase crystallization or performance degradation that may be caused by heat treatment; (5) This method is suitable for components to resist corrosion and wear damage under complex working conditions and has broad industrial application prospects. Attached Figure Description

[0020] Figure 1 This is a schematic diagram of the gradient coating structure described in this invention; Figure 2 The XRD pattern of the gradient coating described in Example 1; Figure 3 The XRD pattern of the gradient coating described in Comparative Example 1; Figure 4 The XRD pattern of the gradient coating described in Comparative Example 2; Figure 5 The image shows the XRD pattern of the gradient coating described in Comparative Example 3. Detailed Implementation

[0021] The technical solution of the present invention will be further described below with reference to the embodiments.

[0022] Example 1 like Figure 1 The iron-based amorphous / nanocrystalline gradient coating of the present invention comprises three regions with the same composition: a bottom layer, a middle layer, and a top layer. The bottom layer is a nanocrystalline enrichment region, the middle layer is a mixed region of amorphous and nanocrystalline materials, and the top layer is an amorphous enrichment region. The raw material composition of the regions is iron-based amorphous powder, which, by mass percentage, comprises 22% Cr, 5% Mo, 5% W, 0.5% C, 4% B, 3% Y, 0.5% Si, and the balance is Fe.

[0023] The method for preparing the iron-based amorphous / nanocrystalline gradient coating of the present invention includes the following steps: (1) Pretreatment of the substrate: The substrate is 45# steel. The surface is ground to remove the oxide layer, and then preheated to 400℃.

[0024] (2) Prepare iron-based amorphous powder according to the above composition. The powder is prepared by vacuum induction melting gas atomization method. After sieving, select a particle size range of 53-150μm and dry it in a vacuum drying oven at 100℃ for 2 hours to obtain iron-based amorphous powder.

[0025] (3) Using laser-guided energy gradient deposition, iron-based amorphous powder is deposited onto the substrate surface: First, deposit the substrate: laser power P1 = 1000W, scanning speed V1 = 12mm / s, then P / V = 83J / mm. 2 The powder feeding rate is 16g / min, the overlap rate is 40%, and the water cooling inlet valve is adjusted to 30% opening to provide a low-speed water flow. Re-deposition of the intermediate layer: Laser power P2 = 1300W, scanning speed V2 = 9mm / s, then P / V = 144J / mm 2 The powder feeding rate is 16g / min, the overlap rate is 40%, and the water cooling inlet valve is adjusted to 60% opening to provide a medium-speed water flow. Finally, the surface layer is deposited: laser power P3 = 1500W, scanning speed V3 = 7mm / s, then P / V = 214J / mm. 2 The powder feeding rate is 16g / min, the overlap rate is 40%, and the water cooling valve is adjusted to 80% opening to provide high-speed water flow.

[0026] During the deposition process, the flow rate of the protective argon gas was maintained at 5 L / min.

[0027] In this embodiment, the total thickness of the gradient coating is approximately 350 μm, of which the thickness of the bottom layer is approximately 100 μm, the thickness of the middle layer is approximately 125 μm, and the thickness of the top layer is approximately 125 μm.

[0028] Example 2

[0029] The similarities between this embodiment and Embodiment 1 will not be repeated here. The difference is that the deposition parameters for each layer in step (3) are different: P1=1200W, V1=10mm / s, then P / V=120J / mm 2 The water-cooled valve opening is 25%; P2=1400W, V2=8mm / s, then P / V=175J / mm 2 The water-cooled valve opening is 55%; P3=1600W, V3=6mm / s, then P / V=267J / mm 2 The water-cooled valve opening is 95%.

[0030] In this embodiment, the total thickness of the gradient coating is approximately 400 μm, of which the thickness of the bottom layer is approximately 100 μm, the thickness of the middle layer is approximately 150 μm, and the thickness of the top layer is approximately 150 μm.

[0031] Example 3

[0032] The similarities between this embodiment and Embodiment 1 will not be repeated here. The difference is that the iron-based amorphous / nanocrystalline gradient coating described in this embodiment, by mass percentage, includes 20% Cr, 3% Mo, 3% W, 0.3% C, 2% B, 1% Y, 0.3% Si, with the balance being Fe.

[0033] Example 4

[0034] The similarities between this embodiment and Embodiment 1 will not be repeated here. The difference is that the iron-based amorphous / nanocrystalline gradient coating described in this embodiment, by mass percentage, includes 24% Cr, 7% Mo, 7% W, 0.7% C, 6% B, 5% Y, 0.7% Si, with the balance being Fe.

[0035] Comparative Example 1 The similarities between this comparative example and Example 1 will not be repeated here. The difference is that the deposition parameters in each region in step (3) are the same: P=1500W, V=7mm / s, then P / V=214J / mm 2 Fixed high-speed water cooling, valve opening 90%.

[0036] The deposited coating consists mainly of crystalline phases from the bottom layer to the top layer, with a total coating thickness of approximately 350 μm.

[0037] Comparative Example 2 The similarities between this comparative example and Example 1 will not be repeated here. The difference is that the iron-based amorphous powder does not contain yttrium. That is, the iron-based amorphous / nanocrystalline gradient coating, by mass percentage, includes 22% Cr, 5% Mo, 5% W, 0.5% C, 4% B, 0.5% Si, and the balance is Fe.

[0038] The deposited coating consists mainly of crystalline phases from the bottom layer to the top layer. The total thickness of the gradient coating is about 350 μm, of which the bottom layer is about 100 μm thick, the middle layer is about 125 μm thick, and the top layer is about 125 μm thick.

[0039] Comparative Example 3 The similarities between this comparative example and Example 1 will not be repeated here. The difference is that the chromium content in the iron-based amorphous powder is greater than 24wt%. That is, the iron-based amorphous / nanocrystalline gradient coating, by mass percentage, includes 30% Cr, 5% Mo, 5% W, 0.5% C, 4% B, 3% Y, 0.5% Si, and the balance Fe.

[0040] The deposited coating consists mainly of crystalline phases from the bottom layer to the top layer. The total thickness of the gradient coating is about 350 μm, of which the bottom layer is about 100 μm thick, the middle layer is about 125 μm thick, and the top layer is about 125 μm thick.

[0041] The performance of the coatings prepared in each experiment was tested. XRD patterns of the bottom, middle, and top layers of the coatings were measured using an X-ray diffractometer. Figure 2-5 As shown, the content of the corresponding amorphous phase was calculated using the pseudo-Voigt semi-quantitative method. The electrochemical corrosion experiment was conducted using a CS2350 electrochemical workstation with a three-electrode system: a platinum sheet as the auxiliary electrode, saturated calomel as the reference electrode, and the test sample as the working electrode. The corrosion electrolyte was an aqueous solution containing 3.5 wt.% NaCl, and the sample surface area was 1 cm². 2 The open circuit potential (OCP) was set for 60 minutes, and dynamic potential polarization testing was performed at a scan rate of 1 mV / s, with a scan range of -0.25 to +1.6 V. The corresponding corrosion rate was calculated from the corrosion current density. The hardness of each coating was tested using an HXD-1000TC microhardness tester with a load of 300 g and a holding time of 15 s. The wear of the coatings at room temperature was tested using an HT-1000 friction and wear testing machine manufactured by Lanzhou Zhongke Kaihua Technology Development Co., Ltd., with a test speed of 15.9 rpm and a load of 600 g. The results are shown in Table 1.

[0042] Table 1 Performance test results of each coating sample Microhardness (HV) Corrosion rate (mm / a) Maximum wear depth (μm) Example 1 925 0.05 2.2 Example 2 934 0.06 2.8 Example 3 887 0.07 2.3 Example 4 896 0.06 2.6 Comparative Example 1 856 0.07 4.7 Comparative Example 2 843 0.10 4.2 Comparative Example 3 823 0.09 3.9 As shown in Table 1, using the layered energy control strategy of "low P / V value in the bottom layer + medium P / V value in the middle layer + high P / V value in the surface layer" described in this invention, combined with water cooling adjustment from weak to strong, coatings with iron-based amorphous / nanocrystalline gradient structures were successfully prepared (Examples 1-4). The continuous gradient structure, consisting of a bottom nanocrystalline enrichment region, a middle mixing region, and a surface amorphous enrichment region, achieves both metallurgical bonding with the substrate and synergistically improves the wear resistance and corrosion resistance of the coating. The excellent performance of the gradient coating prepared by this invention under wear and corrosion resistance conditions proves the effectiveness and advancement of the composition design, gradient structure concept, and innovative preparation process proposed in this invention. It solves the problems of insufficient bonding strength, structural control, and comprehensive performance in existing iron-based amorphous coating technologies, and has broad application prospects in the field of surface protection of key components under harsh working conditions. In contrast, the comprehensive performance of a single amorphous structure with microcracks is far lower than that of gradient structure coatings.

[0043] When a layered gradient deposition strategy is not employed in laser-directed energy deposition (LDED) and the same deposition parameters are used (Comparative Example 1), the resulting coating is predominantly amorphous, such as... Figure 3As shown, the amorphous content of each part of the coating is higher than 95%, there is an incompletely fused area at the bottom, and the internal stress of the coating is relatively large, resulting in microcracks. In corrosion and wear performance tests, the cracks propagate rapidly and cause the coating to peel off prematurely, and its performance is far lower than that of the gradient coatings prepared using this method (Examples 1-4). When yttrium is not added to the iron-based amorphous powder (Comparative Example 2), the resulting coating has a lower amorphous content, with the surface amorphous content being about 39.6%. Figure 4 As shown, this is because the lack of yttrium purifies the melt and refines the grains, leading to increased impurities and defects, larger grain size, and consequently, poor coating hardness, corrosion resistance, and wear resistance. When the chromium content in the iron-based amorphous powder is too high (Comparative Example 3), the surface amorphous content is approximately 44.4%, such as... Figure 5 As shown, the coating performance is limited by the presence of a large number of grain boundaries, and the improvement in corrosion resistance does not reach the ideal level that the chromium content should provide. This indicates that the amorphous / nanocrystalline gradient microstructure obtained through process control is more effective in improving performance than simply increasing the content of alloying elements.

Claims

1. An iron-based amorphous / nanocrystalline gradient coating, characterized in that, The coating comprises three layers with same components, the bottom layer is a nanocrystalline enrichment zone, the middle layer is a non-crystalline and nanocrystalline mixed zone, and the surface layer is a non-crystalline enrichment zone; the raw material components of the layers are iron-based non-crystalline powder, including 20-24% Cr, 3-7% Mo, 3-7% W, 0.3-0.7% C, 2-6% B, 1-5% Y, 0.3-0.7% Si, and the balance of Fe.

2. The iron-based amorphous / nanocrystalline gradient coating of claim 1, wherein, The total thickness of the coating is 300-500 μm.

3. The iron-based amorphous / nanocrystalline gradient coating of claim 2, wherein, The thickness of the bottom layer accounts for 20-30% of the total thickness of the coating, the thickness of the middle layer accounts for 30-40%, and the thickness of the surface layer accounts for 30-40%.

4. A method of producing the iron-based amorphous / nanocrystalline gradient coating according to claim 1, characterized in that, The method comprises the following steps: (1) pretreating the substrate; (2) preparing iron-based non-crystalline powder by vacuum induction melting gas atomization; (3) depositing the iron-based non-crystalline powder onto the surface of the substrate by using laser directional energy gradient deposition, and sequentially depositing the bottom layer, the middle layer, and the surface layer.

5. The preparation method according to claim 4, characterized in that, The substrate in step (1) is one of 45# steel and 20G steel.

6. The preparation method according to claim 4, characterized in that, The powder particle size in step (2) is 53-150 μm, and the powder is dried at 100-120 °C under vacuum for more than 2 hours before use.

7. The preparation method according to claim 4, characterized in that, The P / V of the bottom layer deposition, the middle layer deposition and the surface layer deposition in step (3) is respectively 83-120 J / mm 2 , 120-175 J / mm 2 , 175-267 J / mm 2 .

8. The preparation method according to claim 4, characterized in that, The water cooling valve opening degrees of the bottom layer deposition, the middle layer deposition, and the surface layer deposition in step (3) are 20-40%, 50-70%, and 80-100%, respectively.

9. Application of the iron-based non-crystalline / nanocrystalline gradient coating of claim 1 in wear-resistant and corrosion-resistant components.

10. Use according to claim 9, characterized in that, The components are one of a roller, a bearing, a die, and a hydraulic plunger.

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