A multi-structured thermal spray composite coating and a method of making and using the same

Abstract

The application discloses a kind of multi-structure thermal spraying composite coating and its preparation method and application, belong to composite coating preparation technical field.The method is by introducing main powder channel and vice powder channel in thermal spraying system, realize the synergic control of different powder in flight trajectory.Through adjusting the gas flow of main, vice channel, nozzle angle and powder track, the spatial distribution regulation of reinforcing phase particles can be realized in one spraying process, so as to prepare the composite coating of dispersion structure, layered structure or gradual transition structure.The application breaks through the process limit of traditional premixed powder or multiple layered spraying, has the advantages of process simplification, efficiency improvement, structure uniformity and the like.The method can be adapted to powder system with large density difference and obvious melting point difference, significantly improve the coating density and interlayer adhesion, reduce the process complexity and cost, and is suitable for surface engineering protection in the fields of aerospace, energy, automobile and the like.

Description

TECHNICAL FIELD

[0001] The present application relates to a multi-structure thermal spraying composite coating and its preparation method and application, in particular to a method for realizing efficient preparation of multi-structure composite coating by one-time spraying using a double-powder feeding system and its application in engineering protective coating. It belongs to the technical field of composite coating preparation. BACKGROUND

[0002] As an important material deposition means in the field of surface engineering, thermal spraying technology is widely used in aerospace, energy, mechanical manufacturing and electronic industry fields to significantly improve the comprehensive performance of the base material in terms of wear resistance, corrosion resistance, thermal shock resistance, etc.

[0003] With higher requirements for coating performance in industrial applications, single-component coatings often cannot balance toughness, corrosion resistance and thermal stability. Multi-structure and multi-functional composite coatings have become a research hotspot because they can integrate different performance advantages in the same coating.

[0004] At present, the commonly used composite coating preparation methods mainly include:

[0005] 1. Pre-mixed powder feeding method: different powders are mixed before spraying, but due to the differences in powder density, particle size and melting point, uneven component distribution is easily produced during the spraying process.

[0006] 2. Multi-layer spraying method: multiple spraying and equipment switching are required, which is complicated and low in efficiency.

[0007] 3. Equipment in series combined spraying: two or more sets of spraying devices are required to work together, which is high in cost and complex in maintenance.

[0008] These methods generally have the following shortcomings:

[0009] 1. Complex process, long spraying time;

[0010] 2. Low freedom of structure control, difficult to accurately control the spatial distribution of reinforcing phase;

[0011] 3. Poor adaptability to powders with large physical property differences;

[0012] 4. High cost, multiple equipment occupation.

[0013] Therefore, there is an urgent need for a high-structure-controllable, highly-adaptable composite coating that can integrate multiple structures in one-time spraying and its preparation method and application. SUMMARY

[0014] The present application provides a multi-structure thermal spraying composite coating, which is highly controllable.

[0015] Meanwhile, the application provides a preparation method of the multi-structure thermal spraying composite coating, which realizes the synergistic control of different powders in the flight trajectory by introducing a main powder feeding channel and a secondary powder feeding channel in a thermal spraying system, and by adjusting the carrier gas flow of the main channel and the secondary channel, the nozzle angle and the powder feeding trajectory, the spatial distribution of the reinforcing phase particles can be regulated in one spraying process, so that the composite coating with a dispersion structure, a layered structure or a gradient transition structure is prepared.

[0016] Meanwhile, the application provides an application of the multi-structure thermal spraying composite coating in surface engineering protection, and the surface engineering protection includes the surface engineering protection in the fields of aerospace, energy, automobile and the like.

[0017] A preparation method of a multi-structure thermal spraying composite coating, the method adopts a thermal spraying device with a double powder feeding system, wherein: the main powder feeding system is used for constant feeding of the main phase powder; the secondary powder feeding system feeds the reinforcing phase powder in combination with an independent adjustable carrier gas system;

[0018] Based on the momentum ratio And the gravity compensation angle formula By adjusting the carrier gas flow of the main channel and the secondary channel, the nozzle angle and the powder feeding trajectory, the intersection of the main phase powder and the reinforcing phase powder in the flight trajectory is realized, so that the composite coating with a dispersion structure, a layered structure or a gradient transition along the thickness direction is formed in one spraying process.

[0019] The secondary powder feeding system is supplied with gas by a single carrier gas bottle and is provided with a gas valve, so that the controllable adjustment of the trajectory, the projection angle and the speed of the reinforcing phase powder in the spraying process can be realized.

[0020] By adjusting the carrier gas flow of the main channel and the secondary channel and the powder feeding trajectory, the composite spraying preparation of different powder systems can be adapted without relying on the difference in physical properties of the powders.

[0021] The composite coating structure of the application includes any one or combination of the following:

[0022] A dispersion structure in which the reinforcing phase particles are uniformly distributed in the main phase;

[0023] A layered structure arranged in multiple layers;

[0024] A gradient transition structure in which the concentration of the reinforcing phase changes along the thickness direction.

[0025] The method of the application is suitable for the composite spraying preparation of different types of powder systems such as metal-ceramic, ceramic-ceramic or metal-polymer.

[0026] The application controls the carrier gas flow of the main channel and the secondary channel by time sequence, realizes the spatial and time controllable deposition of the reinforcing phase powder, and thus constructs a periodic composite or gradient transition functional coating.

[0027] I. Overall device

[0028] This invention provides a plasma spraying device with a dual powder feeding system, which is suitable for one-time forming preparation of multilayer, gradient and functional composite structure coatings.

[0029] like Figure 1 As shown, the device includes: a plasma spraying host, a dual-channel spray gun assembly, a main / auxiliary powder feeding system, an air path control assembly (pressure reducing valve + mass flow meter + OR gate structure + check valve / throttle device) and a control unit.

[0030] Plasma spraying unit: Praxair 3710 (commercially available).

[0031] Dual-channel spray gun: Praxair SG-100 (commercially available) is preferred.

[0032] Main / auxiliary powder feeders: Two sets of Praxair 1264 (commercially available).

[0033] Note: The above product model is a preferred embodiment, and those skilled in the art can use equivalent models to replace it.

[0034] II. Gas Circulation Control Components

[0035] 2.1 Composition

[0036] Two-stage flow stabilization module (two sets): This module consists of a pressure reducing valve and a mass flow meter (MFC) to achieve two-stage flow stabilization of the gas source from high pressure to low pressure and then to precise flow control.

[0037] Level 1: Pressure reducing valve

[0038] Function: Stabilizes the upstream high-pressure gas source to medium-low pressure (e.g., 0.2–0.4 MPa), providing stable operating conditions for downstream precision flow control.

[0039] Example models: SMC AR40 / AR50 or Swagelok / KPR series, with adjustable and stable outlet pressure.

[0040] Features: It can effectively suppress the impact of upstream pressure fluctuations on flow rate, providing a constant gas supply for MFC.

[0041] Secondary: Mass Flow Meter (MFC)

[0042] Function: Under stable gas source conditions, it can achieve precise flow control of carrier gas (SLPM or SCCM), and can set target flow, provide real-time feedback and closed-loop regulation.

[0043] Example model: Alicat MCR / MCS series (0–50 SLPM range selectable), adjustable manually or via programmable control unit (PLC / microcontroller).

[0044] Features: It can counteract the effects of powder resistance, nozzle back pressure and process disturbances on flow rate, and achieve high-precision control of powder ratio in spraying.

[0045] Check valve / throttling device: Each branch is equipped with a check valve before entering the powder feeder to prevent powder backflow; if necessary, a throttling device is installed in the mixing section before the nozzle to adjust the airflow velocity gradient.

[0046] Piping and connectors: The powder delivery hose is made of high-hardness plastic (such as high-hardness polyurethane / nylon) and the end is a copper connector; the air circuit uses stainless steel rigid pipe or wear-resistant plastic pipe connected to metal quick-connect connectors (such as Swagelok 1 / 4" series).

[0047] 2.2 Connection Relationship (from upstream to downstream)

[0048] Air source → (two parallel lines) → Pressure reducing valve A / B → MFC-A / MFC-B → Check valve A / B → Powder feeder (Praxair 1264) carrier air inlet → Powder feeding hose (hard plastic / copper connector) → SG-100 dual-channel spray gun powder inlet / pre-nozzle mixing zone.

[0049] The main and auxiliary powder feeding channels are always open. By adjusting their respective flow rates, the trajectory and deposition area distribution of different powders in the flame can be controlled.

[0050] III. Computable Control Model

[0051] 3.1 Shared Symbols and Basic Relationships

[0052] Main phase powder and reinforcing phase powder: The English word for the subscript m is main, which represents the main phase powder; the English word for the subscript a is aux, which represents the reinforcing phase powder.

[0053] Powder density: ρ p, m ρ represents the density of the main phase powder. p, a This represents the density of the reinforcing phase powder.

[0054] Average particle size: d p, m The average particle size of the main phase powder, d p, a This represents the average particle size of the reinforcing phase powder.

[0055] Carrier gas (plasma / external carrier gas) density and viscosity: μ represents the carrier gas density, and μ represents the carrier gas viscosity.

[0056] Main / secondary channel volumetric flow rate: Represents the volumetric flow rate of the main channel. The volumetric flow rate of the secondary channel (converted to the operating volumetric flow rate based on the SLPM set by single-phase spraying).

[0057] Equivalent cross-sectional area of ​​nozzle: A m A represents the equivalent cross-sectional area of ​​the main channel nozzle. a Representative of the equivalent cross-sectional area of ​​the secondary channel nozzle; airflow exit velocity: U m =Q m / A m U a =Q a / A a U m U represents the airflow exit velocity of the main channel; a This represents the outlet velocity of the secondary channel airflow; the main channel is used for spraying the main phase powder, and the secondary channel is used for spraying the reinforcing phase powder.

[0058] The angle between the nozzle axis and the normal to the substrate: θ m θ represents the angle between the main channel nozzle axis and the normal to the base. a This represents the angle between the axis of the secondary channel nozzle and the normal to the base.

[0059] Normal distance (standoff) between the substrate and the nozzle: S.

[0060] (1) The ratio of axial momentum of the two free jets

[0061]

[0062] This yields the flow ratio:

[0063]

[0064] (2) Particle response time (Stokes approximation)

[0065]

[0066] This formula applies to both the main phase powder and the reinforcing phase powder.

[0067] Stokes number (based on jet characteristic time) Characterization, where D is the equivalent nozzle size and U is the characteristic velocity of the jet:

[0068]

[0069] St Represents the number of Stokes; St i The Stokes number represents the amount of the main phase powder or the reinforcing phase powder; τ p,i Represents τp,m or τ p,a , that is, the particle response time of the main phase powder or the particle response time of the reinforcing phase powder; d p, i Represents d p, m or d p, a .

[0070] 3.2 Spraying Scheme

[0071] Option A: Spraying downwards (ignoring gravity) – Jet confluence model

[0072] A.1 Solving for the confluence axis and incident angle (jet momentum balance)

[0073] After the two jets merge in space, their combined principal axis deflection angle satisfies (momentum is balanced in the transverse component):

[0074]

[0075] Among them, P m The momentum flux of the jet in the main channel. ;P a The momentum flux of the jet in the secondary channel. Select θ m (Usually set to a small angle (≤15°) to ensure normal incidence on the substrate), θ can be solved by inverse equation above. a Or vice versa.

[0076] At a distance S from the nozzle normal, the lateral displacement of the centerlines of the two jets is approximately:

[0077]

[0078] y m This represents the lateral (perpendicular to the main jet axis) displacement of the powder beam in the main channel before it reaches the matrix. a This indicates the lateral displacement of the powder beam in the secondary channel before it reaches the matrix.

[0079] Target points that intersect / coincide on the matrix are required. (To determine the location of layering or enrichment), the following should be satisfied:

[0080]

[0081] This determines the target angle combination ( , θ a ).

[0082] A.2 Structure Formation Criterion (Based on St and Momentum Ratio)

[0083] Dispersed structure: The reinforcing phase needs to diffuse with the flow and embed into the main layer Sta Stm and momentum ratio small, J∈[0.05, 0.3]; angular difference small, |θa-θm|≤10 ∘ .

[0084]

[0085] Layered structure: Two streams are distinguishable but still co-located in the matrix. J∈[0.5, 1.5], the angle difference is medium, ∣θ a -θ m |∈[10°, 25°], and set time segments (S1 / S2 / S3) to maintain their respective dominant segments.

[0086] Time segmentation setting method:

[0087] S1: The main channel is dominant (forming the main layer);

[0088] S2: Two channels are close together (transition layer / diffuse layer; if only a clear cross-section is required, S2 can be omitted).

[0089] S3: Secondary channel dominates (forming a secondary layer).

[0090] Example: Total spraying time T=10 min, S1=6 min, S2=1 min, S3=3 min.

[0091] Gradual structure: Let J(t) change monotonically with time (linear / exponential / S-shaped).

[0092] Recommended linear law:

[0093]

[0094] Where J(t) represents the momentum ratio as a function of time; J0 is the initial momentum ratio; J1 is the target momentum ratio; t is the current spraying time; and T is the total spraying time. This represents the flow ratio as it changes over time, derived from the momentum ratio. It is used in conjunction with small-amplitude synchronous adjustments of θa (within ±5° range) to balance the footprint.

[0095] Note: When gravity is ignored, the structure is mainly determined by the momentum ratio J and the angle difference; the particle Stokes number is used to check whether it can be engulfed / layered by the main flame.

[0096] Verification method:

[0097] If St 1: Particles closely follow the airflow → are easily entrained by the main flame → which is beneficial for the dispersion structure.

[0098] If St 1: Large particle inertia → difficult to deflect with the flow field → easy to remain independent → conducive to layered / stratified structures.

[0099] Option B: Spraying level (gravity must be taken into account) – Add settlement term

[0100] During horizontal spraying, the flight time of particles to the substrate t f Gravitational settlement displacement occurs within S / U:

[0101]

[0102] B.1 Corrected geometric conditions for intersection / overlap

[0103] Set the vertical offset of the target point on the substrate to zero (or a predetermined value). ), thus obtaining the angle-flow-granularity coupling constraint:

[0104]

[0105] in, This represents the gravitational settling displacement of the main phase powder during its flight time to the matrix; This represents the gravitational settling displacement generated by the reinforcing phase powder during its flight time to the matrix.

[0106] Substitution and :

[0107]

[0108] By combining the momentum ratio J with the above equation, θ can be solved simultaneously. a With Q a / Q m .

[0109] B.2 Gravity Correction Criterion for Structure Formation

[0110] For diffuse structures (including gravity): Small J and small angle difference are still required, i.e., J∈[0.05, 0.3]; angle difference |θa-θm|≤10°, but Δz is also required. a -Δz m Not exceeding the layer thickness tolerance h tol :

[0111]

[0112] h tol This indicates the permissible deviation of the sprayed coating. Theoretically, different coatings have different tolerances depending on the working conditions. The coating thickness tolerance is h. tol The allowable deviation of the single-layer thickness H is preferably taken as h.tol =0.05 H (Strict control), more preferably h tol =0.10 H (Conventional industrial) or specified directly in absolute value according to process conditions (e.g., ±50 µm).

[0113] Layered structure (including gravity): allows Δz a -Δz m Intentionally separate to form upper / lower layer arrangement; at this time, choose a medium to large J and a medium angle difference, and relax the above inequality to the designed layer spacing target.

[0114] To form a recognizable layered structure within a single layer thickness H, this invention proposes a normal separation amount Δz a -Δz m Take 0.4H-1.4H; planar separation is determined by both the momentum ratio J and the injection angle difference. In engineering, J ∈ [0.5, 1.5] can be taken (it can be extended to [0.8, 2.0] when stronger stratification is required), and the injection angle difference is taken as |θ. a -θ m |∈[10°, 25°]. During design, Q can be obtained by first selecting J and the angle difference. a / Q m With θ a Then calculate the differential settlement. And using geometric correction formulas Inverse calculation of minute angle compensation, until... It falls within the aforementioned range.

[0115] ;z target This refers to the desired relative normal positions of the two phases in the matrix; for example, if the target is a dispersion coating, z target It's 0; if it's layered, you can select based on the target, such as z. target Set it to 0.2H or 0.3H, etc. If it is a gradient coating, z target It is a value that varies over time from 0 to 0.3H.

[0116] H represents the total thickness of the coating. The required thickness of H varies depending on the coating type, generally around 350 micrometers, but can also be as low as 200 micrometers or even 1000 micrometers. For example, the thickness of a single layer... H To design the target thickness (e.g.) H =350μm).

[0117] Gradual structure (including gravity):

[0118] Gradation adjusts the momentum ratio simultaneously in the time domain. Angle with secondary channel Achieved. The momentum ratio can be determined according to a linear law. or exponential law The parameters are set as follows (a linear law is preferred to ensure structural controllability and reproducibility. An exponential law can be used when the reinforcing phase reacts rapidly on the surface or when rapid establishment of functional layers is required). Where J0 and J1 are the initial / final momentum ratios, respectively. For gradual duration, The time scale is exponential. The secondary channel angle is calculated according to... Alternatively, it can be calculated inversely time-by-time from geometric relationships, where... For the initial angle, The rate of change of angle (which can be derived from...) Obtained and subject to mechanical actuation capacity limitations, engineering recommendations (Controlled within the equipment's allowable range). Simultaneously, the settlement difference is calculated every moment.

[0119]

[0120] and with constraints Ensure that the normal error is within the tolerance range.

[0121] It is a coefficient that maps gas volumetric flow rate to average particle transport velocity. It is a calibration coefficient (obtained as follows: under the same operating conditions, the average particle velocity is measured using a high-speed camera or particle velocimeter (PIV / LDV) and compared with the theoretical gas velocity to obtain the coefficient). ).

[0122] IV. Control Methods

[0123] 4.1 Manual Mode (Current Implementation)

[0124] The operator can set the carrier gas pressure of each branch through the pressure reducing valve according to specific process requirements, and dynamically adjust the flow ratio of the main and auxiliary channels using the MFC knob or panel. Simultaneously, by combining parameters such as powder density, particle size, and powder feed rate, fine distribution of powder can be achieved during the deposition process. Specific effects are as follows (taking a combination of high-density main phase and low-density reinforcing phase as an example, the same applies below):

[0125] When the flow rate in the main channel is high and that in the secondary channel is low, the reinforcing phase powder is evenly distributed along the gap between the main powder layers, forming a dispersed reinforced structure.

[0126] When the flow rate in the secondary channel is high and that in the main channel is low, the main phase powder preferentially deposits on a specific layer, forming a functional layered structure.

[0127] When the flow rates of the main and secondary channels change according to a time pattern, periodic composite or gradient transition structures can be constructed to achieve spatially and temporally controllable deposition of the enhanced phase.

[0128] 4.2 Automatic Mode (Preferred Embodiment)

[0129] In the preferred embodiment, the MFC is connected to the control unit to achieve automated proportional regulation. The control unit can be a PLC (such as Siemens S7-1200) or an embedded microcontroller (such as STM32 / Arduino), which achieves closed-loop control by setting the stage sequence, target flow rate, steady-state waiting time, and powder property parameters.

[0130] Control algorithm (implementable examples)

[0131] Input parameters

[0132] Flow procedure list: S1 (main powder bottom layer deposition), S2 (gradient / mixed deposition), S3 (secondary powder reinforcement layer);

[0133] Duration of each phase: T stage (Second);

[0134] Primary / Secondary Channel Target Traffic: Q main-target Q aux-target (SLPM);

[0135] Steady-state waiting time: t settle (Second);

[0136] Flow tolerance: ε (SLPM)

[0137] initialization

[0138] PLC power-on self-test: Reading MFC flow feedback Q main Q aux Check whether the downstream pressure P of the pressure reducing valve is within the set range P. target ± δP; if it deviates, an alarm will sound or the pressure will be adjusted.

[0139] Spraying stage cycle

[0140] S1: Set MFC-A = Q main-target (Recommended range: 6.0-10.0 SLPM), MFC-B = Q aux-target-low (Recommended range: 1.0-3.0 SLPM), wait for t settle Closed-loop reading of feedback and fine-tuning.

[0141] S2: Set MFC-A / B to medium flow rate (recommended range 3.0-6.0 SLPM), wait for steady state, close-loop adjustment, and achieve a gradient or periodic hybrid structure.

[0142] S3: MFC-A low flow rate, MFC-B high flow rate, closed-loop control preferential deposition of reinforcing phase powder to form a functional layer.

[0143] Closed-loop regulation

[0144] Flow feedback is read every Δt (e.g., 100 ms). If the deviation ΔQ > ε, the MFC output is finely adjusted via PID / PI to ensure stable powder ratio and avoid overshoot and oscillation.

[0145] Loop and End

[0146] Press S1→S2→S3 to cycle until the total spraying time or number of layers is completed. When finished, adjust MFC to the safe minimum flow rate and turn off the air source to trigger the spray gun cooling or exhaust program.

[0147] The beneficial effects achieved by this invention are as follows:

[0148] 1. By combining carrier gas flow rate, powder density, and powder delivery rate, precise spatial distribution of powder can be achieved during the deposition process;

[0149] 2. No solenoid valve is required; flow ratio and closed-loop regulation replace on / off switching, resulting in a simple and stable structure.

[0150] 3. It can flexibly form dispersed, layered, periodic composite or gradient transition structures to meet the needs of multifunctional composite coating preparation.

[0151] This invention discloses a method for preparing multi-structured composite coatings based on dual-channel powder delivery. This method achieves coordinated control of different powders along their flight trajectory by introducing a main powder delivery channel and a secondary powder delivery channel into the thermal spraying system. The main powder delivery channel transports the main phase powder, while the secondary powder delivery channel, combined with an independent carrier gas system, enables adjustable delivery of the reinforcing phase powder. By adjusting the carrier gas flow rate, nozzle angle, and powder delivery trajectory of the main and secondary channels, the spatial distribution of reinforcing phase particles can be controlled during a single spraying process, thereby preparing composite coatings with dispersed, layered, or gradually transitioning structures.

[0152] This invention overcomes the limitations of traditional premixed powder feeding or multi-layer spraying processes, offering advantages such as simplified process, improved efficiency, and high structural uniformity. This method is adaptable to powder systems with significant density and melting point differences, significantly improving coating density and interlayer adhesion, while reducing process complexity and cost. It is suitable for surface engineering protection in aerospace, energy, automotive, and other fields. Attached Figure Description

[0153] Figure 1 This is a schematic diagram of the structure of the present invention;

[0154] Figure 2The images show the cross-sectional morphology and tensile fracture morphology of coatings prepared by two different methods: (a) the cross-sectional morphology of the composite coating prepared by the improved method; (b) the cross-sectional morphology of the composite coating prepared by the traditional method; (c) the fracture morphology of the composite coating prepared by the improved method; and (d) the fracture morphology of the composite coating prepared by the traditional method. Detailed Implementation

[0155] The present invention will now be described in further detail with reference to the accompanying drawings and specific embodiments. The following embodiments are for illustrative purposes only and are not intended to limit the scope of the invention.

[0156] Using the technology of this invention, our project team successfully prepared composite coatings with different structures in a manual mode, as detailed below:

[0157] In-situ synthesized TiN-reinforced Fe-based amorphous composite coatings were prepared using plasma spraying technology with both conventional mixed powder feeding methods and an improved dual-channel powder feeding scheme. Figure 2 As shown, Figure 2 (a) The coating prepared for the improved scheme, Figure 2 (b) The coating prepared by the conventional method.

[0158] The chemical composition of the iron-based amorphous powder used is Fe. 48 Cr 23 Mo 10 C 14 B5 (atomic percentage), this system has been shown to have good glass-forming ability and amorphous stability in previous preliminary experiments. In the traditional scheme, a single powder feeder and a single-channel spray gun are used, Fe 48 Cr 23 Mo 10 C 14 B5 (atomic percentage) amorphous alloy powder and Ti powder are pre-mixed mechanically in a powder feeder at a mass ratio of 80:20. This mixture is then fed into a plasma spray gun (equivalent nozzle diameter approximately 2 mm, nozzle-substrate distance approximately 100 mm, spraying attitude vertically downwards) along with a single-path carrier gas (nitrogen, 5–9 L / min). During spraying, the powder is entrained in the plasma flame. At high temperatures, some Ti powder reacts with nitrogen to form TiN, which is deposited on the carbon steel substrate to form a composite coating. Because the two powder phases share a single channel, Ti powder may be locally abundant or insufficient, leading to particle agglomeration and high porosity (approximately 7%) in the deposited layer, with a microhardness of approximately 770 Hv. 0.3 The bonding strength is approximately 24–28 MPa.

[0159] In the improved dual-channel powder feeding scheme, the main channel transports FeCrMoCB amorphous powder, and the secondary channel transports Ti powder. The relative spatial distribution of the two jets is determined by the powder-airflow coupling model established in this paper, with the core parameter being the particle relaxation time (also known as particle response time) τ. p,i Stokes number St i The momentum ratio J and the displacement difference Δr at the base.

[0160] 1. Calculation of particle relaxation time and Stokes number

[0161]

[0162] in, Let be the density of the i-th type of powder (which can be m or a). Where μ is the equivalent particle size and μ is the gas viscosity.

[0163] Number of Stokes:

[0164]

[0165] Jet Momentum (Momentum Flow Rate):

[0166]

[0167] Momentum ratio:

[0168]

[0169] Settlement approximation under horizontal spraying (used for normal displacement correction):

[0170]

[0171] Geometric relationship at the base (when the two streams meet at the same height):

[0172]

[0173] When the small angle is approximated:

[0174]

[0175] The instance parameters used in this system are listed below:

[0176] Main phase (FeCrMoCB amorphous): ρ{Fe} = 7.5 g / cm³ 3 = 7.5 × 10 3 kg / m; d50≈89 μm;

[0177] Reinforcing phase (TiN / Ti): Equivalent TiN: ρ{TiN} = 5.4 g / cm³3 = 5.4 × 10 3 kg / m 3 d50≈33μm.

[0178] Carrier gas (nitrogen) equivalent viscosity: μ = 3.0 × 10⁻⁶ -5 Pa·s (example for model calculation); gas density It is a constant in momentum ratio calculations (can be taken as 1.16 kg / m). 3 (If necessary), but can be offset under the "same caliber" approximation.

[0179] The equivalent nozzle diameter D = 2.0 mm Cross-sectional area A = π (1.0 mm) 2 = 3.1416×10 -6 m 2 .

[0180] The nozzle-substrate distance S = 100 mm = 0.1 m. This is an empirical parameter, and the optimal deposition rate is achieved at this distance.

[0181] This study also adopted a powder feeding ratio of 4:1 for the main phase to the reinforcing phase, with 17.6 g / min for amorphous powder and 4.4 g / min for Ti powder.

[0182] Using the momentum ratio J criterion (diffusion: J) 0.05–0.3; Layered: J 0.5–1.5; Gradual change: J(t) varies according to the curve) and Q is determined by empirical parameters. m and Q a Based on previous experiments, a relatively good amorphous coating performance can usually be obtained when the main phase flow rate is 7-9 L / min. Therefore, 8 L / min was chosen, and Qa should be less than 4.4 L / min. Taking 4 L / min, the velocities of the two particles can be obtained using the formula Ui = Qi / A: Um is approximately 42.44 m / s, and Ua is approximately 21.22 m / s. The particle relaxation time for both types of particles is calculated as: τ p，Fe Approximately 0.110 s, τ p，TiN Approximately 0.011 s. Characteristic jet times for the two powders: Calculated result τ for the amorphous phase. f,Fe =D / U Fe Approximately 4.71 × 10 -5 The s, TiN phase is approximately 9.43 × 10 -5 Furthermore, the obtained Stokes numbers for amorphous and TiN are St... Fe Approximately 2335, St TiNThe value is approximately 116, indicating significant particle inertia at the "characteristic time / length at the nozzle scale." However, the St value of TiN is much smaller than that of Fe, suggesting that TiN is relatively easier to be carried by fluid disturbances ("relatively easy to entrain"), which is beneficial for the dispersion of Ti powder in the high-temperature flame and its participation in in-situ reaction to generate TiN. This also verifies the rationality of the flow rate selection.

[0183] Since this invention uses horizontal spraying, a certain amount of settlement difference correction is required.

[0184] Δz was calculated Fe 2.543 mm; Δz TiN 0.403 mm; Difference Δz a -Δz m -2.14 mm (i.e., Fe sinks / displaces more).

[0185] This indicates that under horizontal spraying conditions and at this flow rate, the sedimentation difference is on the order of mm, which will clearly separate the two-phase deposition locations. Angle compensation or flow / distance adjustment must be used to control the thickness within the allowable tolerance range. The target thickness in this study is 350 μm, with an error within 50 μm. This can be obtained using the small-angle approximation formula:

[0186] Statistical analysis of the microstructure of the sprayed coating cross section showed that the volume fraction of TiN particles in the coating was stable at 28-30%, and the particles were uniformly distributed and mainly formed a strip-like structure.

[0187] Performance test results show that the porosity of the new composite coating is only 4.23% (measured according to the ASTM E2109-01 image analysis method), which is nearly half that of the 8.36% porosity obtained by conventional spraying methods; its density is significantly improved, and the corresponding microhardness reaches 900 Hv. 0.3 (HV-1000 microhardness tester, load 0.3 kg, hold time 15 s), the improved coating shows an increase of approximately 130 Hv compared to conventional methods. Bond strength, determined by tensile testing (ASTM C633), reaches 34-36 MPa for the improved coating, significantly higher than the 28-32 MPa of conventional coatings.

[0188] In summary, the improved scheme achieves overall performance improvements such as high density, uniform dispersion of TiN particles, enhanced microhardness, and strengthened interfacial bonding strength.

[0189] Furthermore, based on relevant calculations, parameters can be determined to prepare a clearly defined layered composite coating.

[0190] A layered coating

[0191] Select J Regarding angle: To ensure discernible layers, the angle is determined based on experience / models. J ∈[0.5,1.5] and ∈[10°, 25°]. Determine Q. m Then, use the formula Calculate Qa in reverse. Calculate and verify the settlement difference Δz: if Δz_rel exceeds the acceptable range, fine-tune according to the geometric formula. (Or reduce the nozzle-substrate distance, or appropriately increase the flow rate of the reinforcing phase). The main parameters for spraying are the same as above; the specific correction parameters are calculated as follows: Q m =8, Q a When = 6.3 L / min, J With a slope of 0.62, a settlement difference of approximately 2.2 mm, and an angle compensation of approximately 12.6°, a clear layered structure can be obtained.

[0192] B Gradient Structure

[0193] To achieve a continuous transition from "dispersed" to "layered" in the thickness direction, a time law J(t) is used to control the momentum ratio of the main / auxiliary channels, with a linear law being preferred:

[0194]

[0195] And adopt Q a (t)=Q m (J(t)) 1 / 2

[0196] This serves as the control relationship of the auxiliary channel's volumetric flow rate over time (approximately at the same diameter). Simultaneously, in cases of horizontal spraying or sensitivity to layer thickness tolerance, the settlement difference is calculated at each moment and a small angle compensation θa(t) is performed to ensure that the arrival displacement difference at the substrate meets the design tolerance.

[0197] Q m Also fixed at 8 L / min, based on the previous calculation results. J Start, End: J 0 = 0.30 (diffusion end) J 1 = 0.90 (towards the lamellar end), single occurrence.

[0198] Depend on J 0、 J 1. Calculate Q a Start and end values ​​(approximate caliber) Q a (0) is approximately 4.38 L / min, Q a (1) Approximately 7.59 L / min, converted to velocity, the mainstream characteristic velocity U mIt is a fixed 42.44 m / s, and the starting / ending velocity of the auxiliary flow is U. a (0) is approximately 23.25 m / s, U a (1) Approximately 40.26 m / s, particle relaxation time results are the same as above, and the calculated settlement displacement Δz m Approximately 2.543 mm, Δz a (0) is approximately 0.460 mm, Δz a (1) is approximately 0.265 mm, therefore the difference in settlement at the beginning and end points is Δz. a (0)-Δz m Approximately -2.083 mm, Δz a (1)-Δz m The angle is approximately -2.278mm. Based on this, the angle compensation should start at -0.99° and end at -1.11°, and the speed should be adjusted during the spraying process.

[0199] In the foregoing description of exemplary embodiments of the invention, various features of the invention are sometimes grouped together in a single embodiment, figure, or description thereof. However, this disclosure should not be construed as reflecting an intention that the claimed invention requires more features than expressly recited in each claim. Rather, as reflected in the claims, the inventive aspect lies in fewer than all features of the foregoingly disclosed embodiments. Therefore, the claims, following the detailed description, are hereby expressly incorporated into that detailed description, wherein each claim itself is a separate embodiment of the invention.

[0200] Although the invention has been described with reference to a limited number of embodiments, those skilled in the art will understand from the foregoing description that other embodiments are conceivable within the scope of the invention described herein. Furthermore, it should be noted that the language used in this specification has been chosen primarily for readability and instructional purposes, and not for the purpose of interpreting or limiting the subject matter of the invention. Therefore, many modifications and variations will be apparent to those skilled in the art without departing from the scope and spirit of the appended claims. The disclosure of the invention is illustrative and not restrictive, and the scope of the invention is defined by the appended claims.

[0201] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A method for preparing a multi-structure thermal spray composite coating, characterized in that, Includes the following steps: A dual powder feeding system is adopted. The main powder feeding system is used to transport the main phase powder, and the auxiliary powder feeding system is used to transport the reinforcing phase powder. By adjusting the carrier gas flow rate, nozzle angle and powder feeding trajectory of the main and auxiliary channels, the main phase powder and the reinforcing phase powder can be made to converge in the flight trajectory, thereby forming a dispersed structure, a layered structure or a composite coating that gradually changes along the thickness direction in a single spraying process. When the main and auxiliary powder feeding systems spray downwards, gravity can be ignored. In this case, the parameters for obtaining a dispersed structure coating are: the reinforcing phase powder diffuses with the flow and embeds into the main phase powder, Sta Stm and momentum ratio J∈[0.05, 0.3]; angle difference |θa-θm|≤10°, where Sta represents the Stokes number of the reinforcing phase powder, Stm represents the Stokes number of the main phase powder, θa represents the angle between the axis of the secondary channel nozzle and the normal to the matrix, and θm represents the angle between the axis of the main channel nozzle and the normal to the matrix. When the main powder feeding system and the auxiliary powder feeding system spray downwards, gravity can be ignored. At this time, the parameters for obtaining the layered coating structure are: J∈[0.5, 1.5], angle difference |θa-θm|∈[10°, 25°]. When the main and auxiliary powder feeding systems spray downwards, gravity can be ignored. In this case, the parameters for obtaining the gradient structure coating are: Let J(t) change linearly with time: Linearity: ； Where J(t) represents the momentum ratio as a function of time; J0 is the initial momentum ratio; J1 is the target momentum ratio; t is the current spraying time; and T is the total spraying time. The flow ratio, representing the change in flow rate over time, is derived from the momentum ratio; the balance footprint is adjusted synchronously with a small amplitude of θa, within a range of ±5°; A m A represents the equivalent cross-sectional area of ​​the main channel nozzle. a This represents the equivalent cross-sectional area of ​​the secondary channel nozzle.

2. The preparation method according to claim 1, characterized in that, When the main powder feeding system and the auxiliary powder feeding system are used for horizontal spraying, gravity and a settling term are taken into account. In this case, the parameters for obtaining the dispersion structure coating are: J∈[0.05, 0.3]; angle difference |θa-θm|≤10°, Δz a -Δz m Not exceeding the layer thickness tolerance h tol , where Δz a Δz represents the gravitational settling displacement of the reinforcing phase powder during its flight time to the matrix. m h represents the gravitational settling displacement of the main phase powder during its flight time to the matrix. tol This represents the allowable deviation of the total thickness H of the coating.

3. The preparation method according to claim 1, characterized in that, When the main powder feeding system and the auxiliary powder feeding system are used for horizontal spraying, taking gravity and settling into account, the parameters for obtaining the layered coating structure are: Δz a -Δz m Take a value between 0.4H and 1.4H, where H represents the total thickness of the coating; J∈[0.5, 1.5], angle difference∣θa-θm∣∈[10°, 25°].

4. The preparation method according to claim 1, characterized in that, When the main powder feeding system and the auxiliary powder feeding system are used for horizontal spraying, gravity and settling are taken into account. The parameters for the gradient structure coating are then obtained as follows: the gradient structure adjusts the momentum ratio simultaneously in the time domain. Angle with secondary channel Achieve; momentum ratio follows a linear law or exponential law Set; where J0 and J1 are the initial / final momentum ratios, respectively. For gradual duration, The time scale is exponential; the secondary channel angle is based on... Alternatively, it can be calculated inversely time-by-time from geometric relationships, where, For the initial angle, The rate of change of angle, and at each interval Δ t Calculate the differential settlement at all times and use constraints Ensure that the normal error is within the tolerance range. This represents the relative normal positions of the desired reinforcing phase powder and the main phase powder in the matrix.

5. The preparation method according to claim 4, characterized in that, Rate of change of angle The calculation method is as follows: ,in, represent At time t, the angle between the axis of the secondary channel nozzle and the normal to the base; represent t At time t, the angle between the axis of the secondary channel nozzle and the normal to the base.

6. A multi-structure thermal spray composite coating obtained by the preparation method according to any one of claims 1 to 5.

7. The application of a multi-structure thermal spray composite coating according to claim 6 in surface engineering protection, characterized in that, Surface engineering protection includes surface engineering protection in the aerospace, energy, and automotive fields.

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