Toughness prediction method for TiN / TiSiN gradient multilayer coating

Abstract

The invention relates to a TiN / TiSiN gradient multilayer coating toughness prediction method, which comprises the following specific steps: 1) using finite element analysis software to establish a two-dimensional model of a coating indentation experiment; 2) endowing the two-dimensional model with corresponding material attributes; 3) assembling each geometric component; 4) setting an analysis process, and constructing a loading analysis process and an unloading analysis process according to an actual indentation experiment process besides an initial analysis step; 5) defining a contact type and a boundary condition; 6) performing grid division on the two-dimensional model; and 7) performing simulation calculation in the indentation experiment process to obtain a principal stress distribution cloud picture and the maximum principal stress in the coating indentation experiment process. According to the method, the gradient multilayer structure is constructed, the stress distribution condition of the coating is calculated by adopting a finite element analysis method, and an indentation experiment is combined to confirm that a principal stress result calculated by the method is consistent with an actual condition, so that a new solution is provided for designing the TiN / TiSiN gradient multilayer coating with high hardness and high toughness.

Description

Technical Field

[0001] The invention belongs to the technical field of computer-aided design optimization, verification or simulation using a finite element method, and in particular relates to a method for predicting the toughness of a TiN / TiSiN gradient multilayer coating. Background Art

[0002] With the continuous development of industrial automation in my country and the rapid replacement of mechanical parts, higher requirements are placed on the service life and cutting efficiency of cutting tools, and hard-coated tools have emerged. The processing process of hard-coated tools is essentially a confrontation between the hard coating and the workpiece, so the wear rate and service life of the hard coating are more stringent. Hard coatings represented by TiN and TiSiN have extremely high hardness and have great advantages in the field of tool coatings. However, the hardness and toughness of hard coatings are largely in opposition, and high hardness is often accompanied by low toughness. The low toughness of the hard coating will cause the cutting tool to be damaged prematurely during the processing process, or even catastrophically fracture. It can be seen that the hard coating needs to improve its toughness while maintaining high hardness.

[0003] Gradient multilayer structure is currently the main method to improve the hardness and toughness of coatings. The material properties of different components in the multilayer structure determine the different stress characteristics under load, which means that the multilayer structure composed of different materials will affect the stress distribution in the coating, and the stress distribution will affect the adhesion and toughness between the substrate and the coating. In addition, the modulation period of the multilayer coating plays an important role in its mechanical properties, and the stress and damage on the surface and inside of the coating under load are different. Therefore, it is worth studying the effect of setting a variable modulation period with a certain rule in the gradient multilayer coating structure on the mechanical properties of the coating.

[0004] The traditional experimental method can intuitively analyze the mechanical properties of gradient multilayer coatings, but its R&D efficiency is low, the cost is high, and the R&D cycle is long. The present invention predicts the toughness of gradient multilayer coatings based on numerical simulation and theoretical model simulation calculation, which is high in efficiency and low in cost. It is verified by combining experiments, which confirms that the prediction method is more consistent with the actual experimental results. Summary of the invention

[0005] The technical problem to be solved by the present invention is to provide a toughness prediction method for TiN / TiSiN gradient multilayer coatings in view of the deficiencies in the prior art. The prediction method combines indentation experiments and simulation calculations, is close to the experimental test results, and is an efficient and low-cost analysis method.

[0006] To achieve the above object, the technical solution adopted by the present invention is:

[0007] A method for predicting the toughness of a TiN / TiSiN gradient multilayer coating is provided, and the specific steps are as follows:

[0008] 1) Using finite element analysis software, establish a two-dimensional model of the geometric component indenter, coating and substrate during the Vickers indentation test of the TiN / TiSiN gradient multilayer coating, and set the coating structure in the component module;

[0009] 2) Assign corresponding material properties to each component of the 2D model;

[0010] 3) Assemble various geometric components, define the indenter, coating, transition layer and substrate components as non-independent entities and assemble them into a whole;

[0011] 4) Setting up the analysis process, in addition to the initial analysis steps, constructing the loading analysis process and the unloading analysis process according to the actual indentation experiment process;

[0012] 5) Define the contact type and boundary conditions. In the calculation model, surface-to-surface contact is used to define the contact relationship between the diamond indenter and the coating. The outer surface of the indenter is set as the active surface, and the coating surface is set as the slave surface. The friction coefficient between the indenter and the coating surface is set to 0. It is assumed that the coating interface is in an ideal state, and three main boundary constraints are set. The first is the left boundary of the model, which is set to be fixed along the x-axis, can only move along the y-axis, and is perpendicular to the z-axis; the second is the bottom of the model, which is set to be completely fixed; the third is the position of the indenter, and the indenter of the model is set to be a rigid body;

[0013] 6) Perform finite element meshing on the two-dimensional model, and perform dense processing on the mesh of the contact area between the indenter and the coating to improve the accuracy of the simulation calculation results;

[0014] 7) The indentation test process is simulated and calculated on the two-dimensional finite element model after fine mesh division to obtain the principal stress distribution cloud map of the coating indentation test process, and the maximum principal stress of the coating at the indentation position is obtained based on the principal stress distribution cloud map.

[0015] According to the above scheme, the TiN / TiSiN gradient multilayer coating is obtained by alternately compounding multiple layers of TiN layers and TiSiN layers on the surface of a Ti-6Al-4V alloy substrate, and a transition layer is provided between the Ti-6Al-4V alloy substrate and the TiN / TiSiN gradient multilayer coating, the transition layer is a Ti layer, the surface of the gradient multilayer coating is a TiSiN layer, and the coating in contact with the transition layer is a TiN layer.

[0016] According to the above scheme, in step 1), the height of the substrate is set to 3 μm, the total thickness of the coating and the transition layer is set to 3 μm, the radius of the substrate is set to 6 μm, the indenter is a conical diamond indenter with a half angle of 70.3°, and the indenter height is set to 1 μm.

[0017] According to the above scheme, in step 2), the pressure head in the model is set as a rigid material, and the substrate, transition layer and coating are set as elastic-plastic materials.

[0018] According to the above scheme, the loading process of the finite element calculation in step 4) is divided into three stages: high load, the indenter penetration depth is 0.3 μm; medium load, the indenter penetration depth is 0.15 μm; low load, the indenter penetration depth is 0.05 μm.

[0019] According to the above scheme, in step 6), the method for fine meshing the two-dimensional finite element model is: the model mesh is set to a two-dimensional quadrilateral unit mesh with 4 nodes, the total number of unit meshes is 500,000 to 2 million, and the nodes within the mesh and the nodes on the upper surface can move freely in space.

[0020] The present invention also includes a screening and design method for high-toughness TiN / TiSiN gradient multilayer coatings based on the above-mentioned toughness prediction method, and the specific steps are: designing a plurality of TiN / TiSiN gradient multilayer coatings with different gradient structures, using the above-mentioned toughness prediction method of the TiN / TiSiN gradient multilayer coating to respectively calculate the maximum stress at the edge of the indentation on the coating surface under high, medium and low loads, and compare them, and select the sample with the lowest maximum stress at the edge of the indentation on the coating surface under high and medium loads, that is, the TiN / TiSiN gradient multilayer coating with the highest toughness.

[0021] The beneficial effects of the present invention are as follows: the present invention first constructs a gradient multilayer structure with a modulation period having a certain regular change, uses a finite element analysis method to calculate the stress distribution of the coating under different loads, and combines indentation experiments to confirm that the maximum principal stress result of the coating at the indentation position calculated by this method is consistent with the actual situation, thereby providing a new solution for designing a TiN / TiSiN gradient multilayer coating that maintains high hardness while improving toughness. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 Schematic diagram of the gradient multilayer coating structure constructed in Examples 1-4 of the present invention;

[0023] Figure 2 The thickness distribution diagram of each layer of the gradient multilayer coating of Examples 1-4;

[0024] Figure 3 A schematic diagram of a two-dimensional model (half edge) constructed in Example 1;

[0025] Figure 4 Comparison diagram of the principal stress distribution cloud diagrams during the indentation process of Examples 1 and 2;

[0026] Figure 5 This is the indentation morphology of the multilayer coating prepared in Comparative Example 1;

[0027] Figure 6 This is the indentation morphology of the multilayer coating prepared in Comparative Example 2. DETAILED DESCRIPTION

[0028] In order to enable those skilled in the art to better understand the technical solution of the present invention, the present invention is further described in detail below using embodiments in conjunction with the accompanying drawings.

[0029] Example 1

[0030] A toughness prediction method for a TiN / TiSiN gradient multilayer coating is provided. The designed TiN / TiSiN gradient multilayer coating is prepared on the surface of a Ti-6Al-4V alloy substrate, and a transition layer is provided between the Ti-6Al-4V alloy substrate and the TiN / TiSiN gradient multilayer coating. The transition layer is a Ti layer (thickness 50nm). The total thickness of the TiN / TiSiN gradient multilayer coating and the transition layer is 3μm. The structural schematic diagram is shown in FIG. Figure 1 As shown in G1, the surface of the gradient multilayer coating is a TiSiN layer, and the coating in contact with the transition layer is a TiN layer. The thickness of the TiN layer and the TiSiN layer gradually decreases from the coating surface and the transition layer to the middle. The thickness distribution of each layer is shown in Figure 2 , Figure 2 The horizontal axis is the number of layers, the total number of designed layers is 60 layers, and the vertical axis is the modulation period. Each modulation period represents the total thickness of adjacent TiN layers and TiSiN layers, and the thickness of the TiN layer and the TiSiN layer are the same in each modulation period, that is, the modulation period gradually decreases from the coating surface and the substrate to the middle. The specific steps of the toughness prediction method are as follows:

[0031] 1) Using ABAQUS finite element analysis software, the code was used to establish the two-dimensional model of the geometric component indenter, coating and substrate during the Vickers indentation test of TiN / TiSiN gradient multilayer coating. The coating structure was set in the component module. Considering the symmetry, a 1 / 2 axisymmetric model was established with the central axis as the symmetry axis. The substrate height was 3 μm, the total thickness of the coating and transition layer was 3 μm, the substrate radius was 6 μm, the indenter was a conical diamond indenter with a half angle of 70.3°, and the indenter height was 1 μm. The schematic diagram of the two-dimensional model (half edge) is shown in Figure 3 ;

[0032] 2) Assign corresponding material properties to each component of the two-dimensional model. According to actual needs, the pressure head in the model is set as a rigid material, and the substrate, transition layer and coating are set as elastic-plastic materials. The model material property parameters are shown in Table 1;

[0033] Table 1

[0034]

[0035] In Table 1, Elastic modulus represents elastic modulus, Poisson's ratio represents Poisson's ratio, A represents initial yield stress, B represents hardening modulus, C represents strain rate constant, and n represents strain hardening exponent.

[0036] 3) Assemble various geometric components, define the indenter, coating, transition layer and substrate components as non-independent entities and assemble them into a whole;

[0037] 4) Setting the analysis process. In addition to the initial analysis steps, the loading analysis process and the unloading analysis process are constructed according to the actual indentation experiment process. In order to better compare with the actual experiment, the loading process of the finite element calculation is divided into three stages: high load (indenter penetration depth of 0.3 μm), medium load (indenter penetration depth of 0.15 μm) and low load (indenter penetration depth of 0.05 μm).

[0038] 5) Define the contact type and boundary conditions. In the calculation model of this embodiment, surface-to-surface contact is used to define the contact relationship between the diamond indenter and the coating. Since the diamond indenter is an active surface with great hardness, the outer surface of the indenter is set as the active surface and the coating surface is set as the slave surface. In order to prevent the movement of the nodes in the model from having unnecessary effects on the simulation results, the friction coefficient between the indenter and the coating surface is set to 0. In addition, it is assumed that the coating interface is in an ideal state, and three main boundary constraints are set. The first is the left boundary of the model, which is set to be fixed along the x-axis, can only move along the y-axis, and is perpendicular to the z-axis; the second is the bottom of the model, which is set to be completely fixed; the third is the position of the indenter, and the indenter of the model is set to be a rigid body;

[0039] 6) Finite element meshing of the two-dimensional model. In order to ensure that the calculation process of the model can converge better during the indentation test and obtain detailed mechanical properties, the two-dimensional finite element model is finely meshed. The model mesh is set to a 4-node two-dimensional quadrilateral unit mesh (CAX4R), and the total number of unit meshes is 500,000 to 2 million. The nodes in the mesh and the nodes on the upper surface can move freely in space (no constraints are imposed on the node mesh and node position. When subjected to pressure during the indentation test, these meshes can deform freely). The mesh in the contact area between the indenter and the coating is densely processed to improve the accuracy of the simulation calculation results;

[0040] 7) The two-dimensional finite element model after fine meshing is simulated and calculated to obtain the main stress distribution cloud diagram of the coating indentation test process (see Figure 4), the maximum principal stress of the coating at the indentation position is obtained according to the principal stress distribution cloud diagram: under low load conditions, the maximum stress at the edge of the indentation on the coating surface is 9.8 GPa; under medium load conditions, the maximum stress at the edge of the indentation on the coating surface is 15.8 GPa; under high load conditions, the maximum stress at the edge of the indentation on the coating surface is 16.1 GPa. The statistical data are shown in Table 2.

[0041] Comparative Example 1

[0042] The accuracy of the prediction method in Example 1 above was verified by experiments:

[0043] Under appropriate argon and hydrogen gas flow rates and suitable deposition pressure conditions, a TiN / TiSiN gradient multilayer coating was prepared by a multi-arc ion plating sputtering method. The gradient structure change mode of the gradient multilayer coating was consistent with G1 in the aforementioned Example 1, and an indentation test was performed on the prepared gradient multilayer coating.

[0044] The specific steps for preparing TiN / TiSiN gradient multilayer coating are as follows:

[0045] 1) Install TiSi target (the atomic ratio of the two elements is Ti:Si=75:25) and Ti target of the same specification (purity is 99.9%) on the two target holders of the multi-arc ion plating equipment, and adjust the distance between the rotating frame and the target to 240mm;

[0046] 2) The polished and cleaned Ti-6Al-4V alloy substrate is fixed vertically on a rotating rack, and then the rotating rack is pushed into the coating chamber of the multi-arc ion plating sputtering equipment, and the rotating rack drives the Ti-6Al-4V alloy substrate to revolve at a speed of 3 rpm / min;

[0047] 3) After the vacuum in the coating chamber is pumped to below 1000Pa, the Roots pump, the front valve and the molecular pump are opened in sequence. After the molecular pump is running at full speed, the front valve is turned off, and the roughing valve is opened for roughing until the vacuum in the coating chamber reaches 8Pa. Then, the gate valve is opened and the molecular pump is switched for fine pumping. When the vacuum reaches 5×10 -2 After Pa, turn on the heating tube and heat to 350℃;

[0048] 4) Glow cleaning: In order to improve the bonding strength between the coating and the substrate, it is necessary to clean the impurities adsorbed on the surface of the substrate before depositing the coating. In this process, the argon flow rate is first set to 270sccm, and the deposition pressure is set to 1.9Pa. The bias voltage is set to -600V, -800V and -1000V in sequence, and the substrate surface is bombarded for 20 minutes. Then, the argon flow rate is adjusted to 80sccm, and the deposition pressure is set to 0.46Pa, the bias voltage is set to -160V, and the AEG (Ti target) voltage is set to 40A, so that the argon ions are ionized more fully, and the impurities on the surface of the substrate are further removed. Due to the existence of an electric field in the cavity and the negative bias voltage applied to the rotating frame, the argon gas will be ionized into argon ions. The argon ions are accelerated by the electric field and bombarded to the surface of the substrate. The substrate is bombarded by ions, and the surface roughness increases, thereby achieving cleaning;

[0049] 5) Deposition of transition layer Ti coating: The Ti target current is set to 150A, and the deposition negative bias voltage is set to 150V, so as to bombard the substrate surface with Ti ions and deposit the Ti coating. The deposition time is 2 minutes.

[0050] 6) Deposition of TiN / TiSiN gradient multilayer coating: The turret drives the Ti-6Al-4V alloy substrate to revolve to realize the alternating deposition preparation of TiN layer and TiSiN layer, and the flow rates of argon gas (purity 99.999% by volume) and nitrogen gas (purity 99.999% by volume) are set to 80 sccm and 210 sccm, respectively, and the deposition pressure is controlled to be maintained at 1.1 Pa. Subsequently, the switches of the Ti target and the TiSi target are turned on, the target currents are set to 110 A and 120 A, respectively, and the deposition negative bias voltage is set to 150 V. In addition, the magnetic field is adjusted to achieve stable and uniform arc contraction. Then, the rotation speed of the turret is gradually increased from 1 r / min to 6 r / min, increasing by 1 r / min each time, and then reduced from 6 r / min to 1 r / min, decreasing by 1 r / min each time, for a total of 12 steps, with a deposition time of 240 s for each rotation speed and a total deposition time of 48 min. Finally, the power supply is turned on and the deposition of TiN / TiSiN gradient multilayer coating is started;

[0051] 7) After the deposition is completed, turn off the target power supply, substrate bias, gas and heating tube. In order to prevent the coating from being oxidized, the temperature in the chamber is reduced to at least 100°C before opening the chamber and taking out the gradient multilayer coating sample.

[0052] The coating samples obtained by the above deposition were subjected to Vickers indentation test, which mainly included three processes: loading, holding (peak indentation load was maintained for 12 seconds) and complete unloading. In addition, in order to study the influence of different loads on the experimental results, three loads were applied to the indenter: high (load of 0.3kgf), medium (load of 0.1kgf), and low (load of 0.05kgf). Each group of experiments was repeated five times, and appropriate distances must be maintained between different indentations to avoid interference. Finally, the surface morphology of the coating samples after the indentation tests under three loads was observed under a scanning electron microscope (see Figure 5 ), under low load conditions, no obvious cracks appear on the coating surface; under medium load conditions, short cracks and annular cracks appear around the indentation on the coating surface; under high load conditions, catastrophic annular cracks appear around the indentation on the coating surface.

[0053] Example 2

[0054] A toughness prediction method for a TiN / TiSiN gradient multilayer coating is provided. The designed TiN / TiSiN gradient multilayer coating is prepared on the surface of a Ti-6Al-4V alloy substrate, and a transition layer is provided between the Ti-6Al-4V alloy substrate and the TiN / TiSiN gradient multilayer coating. The transition layer is a Ti layer (thickness 50nm). The total thickness of the TiN / TiSiN gradient multilayer coating and the transition layer is 3μm. The structural schematic diagram is shown in FIG. Figure 1 As shown in g1, the surface of the gradient multilayer coating is a TiSiN layer, and the coating in contact with the transition layer is a TiN layer. The thickness of the TiN layer and the TiSiN layer gradually increases from the coating surface and the transition layer to the middle. The thickness distribution of each layer is shown in Figure 2 , Figure 2 The horizontal axis is the number of layers, the total number of layers is designed to be 60, and the vertical axis is the modulation period. Each modulation period represents the total thickness of adjacent TiN layers and TiSiN layers, and the thickness of the TiN layer and the TiSiN layer are the same in each modulation period, that is, the modulation period gradually increases from the coating surface and the substrate to the middle, and its toughness prediction method is similar to that of Example 1. The maximum principal stress of the coating at the indentation position is obtained according to the principal stress distribution cloud map: under low load conditions, the maximum stress on the coating surface is 11.7 GPa; under medium load conditions, the maximum stress on the coating surface is 12.7 GPa; under high load conditions, the maximum stress on the coating surface is 13.2 GPa, and the statistical data are shown in Table 2.

[0055] Table 2

[0056]

[0057] Comparative Example 2

[0058] The accuracy of the prediction method in Example 2 above was verified by experiments:

[0059] Under appropriate argon and hydrogen gas flow rates and suitable deposition pressure conditions, a TiN / TiSiN gradient multilayer coating was prepared by a multi-arc ion plating sputtering method. The gradient structure change mode of the gradient multilayer coating was consistent with g1 in the aforementioned Example 2, and an indentation test was performed on the prepared gradient multilayer coating.

[0060] The specific steps for preparing the TiN / TiSiN gradient multilayer coating are similar to those in Comparative Example 1, except that: Step 6) the rotation speed of the rotating frame is gradually reduced from 6 r / min to 1 r / min, decreasing by 1 r / min each time, and then increased from 1 r / min to 6 r / min, increasing by 1 r / min each time, for a total of 12 steps, with a deposition time of 240 s at each rotation speed and a total deposition time of 48 min.

[0061] The Vickers indentation test was performed on the coating sample obtained by the above deposition using the method of Comparative Example 1. Finally, the surface morphology of the coating sample after the indentation test under three loads was observed under a scanning electron microscope (see Figure 6 ), under low load conditions, short cracks will appear on the coating surface close to the center point; under medium load conditions, short cracks will appear around the indentation on the coating surface; under high load conditions, short cracks will also appear around the indentation on the coating surface, but no catastrophic annular cracks will occur.

[0062] Example 3

[0063] A toughness prediction method for a TiN / TiSiN gradient multilayer coating is provided. The designed TiN / TiSiN gradient multilayer coating is prepared on the surface of a Ti-6Al-4V alloy substrate, and a transition layer is provided between the Ti-6Al-4V alloy substrate and the TiN / TiSiN gradient multilayer coating. The transition layer is a Ti layer (thickness 50nm). The total thickness of the TiN / TiSiN gradient multilayer coating and the transition layer is 3μm. The structural schematic diagram is shown in FIG. Figure 1 As shown in G2, the surface of the gradient multilayer coating is a TiSiN layer, and the coating in contact with the transition layer is a TiN layer. The thickness of the TiN layer and the TiSiN layer gradually increases from the transition layer to the coating surface. The thickness distribution of each layer is shown in Figure 2 , Figure 2 The horizontal axis is the number of layers, and the designed total number of layers is 60 layers. The vertical axis is the modulation period. Each modulation period represents the total thickness of adjacent TiN layers and TiSiN layers, and the thickness of the TiN layer and the TiSiN layer are the same in each modulation period, that is, the modulation period gradually increases from the substrate to the coating surface, and its toughness prediction method is similar to that in Example 1.

[0064] A TiN / TiSiN gradient multilayer coating was prepared by a multi-arc ion plating sputtering method. The structure of the gradient multilayer coating was consistent with that of G2, and an indentation test was performed on the prepared gradient multilayer coating. The experimental results show that the prediction method of Example 3 is consistent with the actual experimental results.

[0065] Example 4

[0066] A toughness prediction method for a TiN / TiSiN gradient multilayer coating is provided. The designed TiN / TiSiN gradient multilayer coating is prepared on the surface of a Ti-6Al-4V alloy substrate, and a transition layer is provided between the Ti-6Al-4V alloy substrate and the TiN / TiSiN gradient multilayer coating. The transition layer is a Ti layer (thickness 50nm). The total thickness of the TiN / TiSiN gradient multilayer coating and the transition layer is 3μm. The structural schematic diagram is shown in FIG. Figure 1 As shown in g2, the surface of the gradient multilayer coating is a TiSiN layer, and the coating in contact with the transition layer is a TiN layer. The thickness of the TiN layer and the TiSiN layer gradually decreases from the transition layer to the coating surface. The thickness distribution of each layer is shown in Figure 2 , Figure 2 The horizontal axis is the number of layers, and the designed total number of layers is 60 layers. The vertical axis is the modulation period. Each modulation period represents the total thickness of adjacent TiN layers and TiSiN layers, and the thickness of the TiN layer and the TiSiN layer are the same in each modulation period, that is, the modulation period gradually decreases from the substrate to the coating surface. The toughness prediction method is similar to that in Example 1.

[0067] A TiN / TiSiN gradient multilayer coating was prepared by a multi-arc ion plating sputtering method. The structure of the gradient multilayer coating was consistent with that of g2 above. An indentation test was performed on the prepared gradient multilayer coating. The experimental results showed that the prediction method of Example 4 was consistent with the actual experimental results.

[0068] The gradient multilayer coating combines the structural advantages of multilayer and gradient. The present invention first constructs a gradient multilayer coating with a certain regular change in the modulation period, uses the finite element analysis method to calculate the stress distribution of the coating under load, and verifies the simulation calculation results in combination with the indentation experiment, thereby providing a new solution for the gradient multilayer coating to maintain high hardness while improving its toughness. The results of Examples 1-2 of the present invention and Comparative Examples 1-2 show that the crack evolution of different gradient structures under the indentation experiment is consistent with the stress evolution results in the finite element calculation:

[0069] 1. Under low load conditions, the present invention knows from the finite element calculation results that the maximum stress at the edge of the indentation on the surface of the G1 structure coating is 9.8GPa; the maximum stress at the edge of the indentation on the surface of the g1 structure coating is 11.7GPa; the present invention knows from the indentation test results that no obvious cracks are generated on the surface of the G1 structure coating, and a short crack is generated on the surface of the g1 structure coating at a distance of 4.2μm from the center point. Combining the experimental and simulation calculation results, this is because the indentation depth is small under low load conditions (the designed indentation depth in the finite element calculation process of the embodiment is 50nm, the thickness of the coating sublayer on the surface of the structure G1 of embodiment 1 is 75nm, and the thickness of the coating sublayer on the surface of the structure g1 of embodiment 2 is 15nm), the indentation depth is less than the thickness of the sublayer on the surface of the G1 structure coating, and is much larger than the thickness of the sublayer on the surface of the g1 structure coating. At this time, the advantages of the g1 gradient structure are not shown, resulting in a large maximum stress at the edge of the indentation on the surface of the g1 structure coating, and short cracks are generated on the coating surface. However, the maximum stress at the edge of the indentation on the surface of the G1 structure coating is small, and no cracks are generated on the coating surface;

[0070] 2. Under medium load conditions, the present invention learned from the finite element calculation results that the maximum stress at the edge of the indentation on the surface of the G1 structure coating is 15.8 GPa; the maximum stress at the edge of the indentation on the surface of the g1 structure coating is 12.7 GPa; the present invention learned from the indentation test results that short cracks appeared on the surface of the G1 structure coating at a distance of 4.2 μm and 7.4 μm from the center point, and catastrophic annular cracks appeared at the edge of the indentation, and the g1 structure coating only produced short cracks at a distance of 4.3 μm and 5.7 μm from the center point on the surface, showing the advantages of the g1 structure under medium load conditions;

[0071] 3. Under high load conditions, the present invention learned from the finite element calculation results that the maximum stress at the edge of the indentation on the surface of the G1 structural coating is 16.1 GPa; the maximum stress at the edge of the indentation on the surface of the g1 structural coating is 13.2 GPa; according to the indentation test results, the present invention learned that short cracks appeared on the surface of the G1 structural coating at 5.5μm, 7.4μm and 10.5μm from the center point, and catastrophic annular cracks appeared at the edge of the indentation, and the g1 structural coating only produced short cracks at the positions of 4.5μm, 5.7μm and 7.6μm from the center point on the surface, showing the advantages of the g1 structure under high load conditions.

[0072] Combining the analysis of the experimental and simulation calculation results, due to the large indentation depth under medium load and high conditions, it has exceeded the sub-layer thickness of the surface of the G1 and g2 structural coatings, and the advantage of the g1 gradient structure is shown at this time. The stress at the edge of the indentation of the G1 structural coating is large, which causes not only short cracks but also catastrophic annular cracks on the coating surface. The maximum stress at the edge of the indentation on the surface of the g1 structural coating is still small, so only short cracks are generated. This shows that the g1 gradient structure can better reduce the maximum principal stress on the coating surface when the coating is subjected to an applied load, thereby inhibiting the generation of cracks on the coating surface, and then enhancing the toughness of the coating, which shows that the gradient structure coating in Example 2 has better toughness. In addition, during the transition from low-medium-high load to external load, the stress evolution results of the finite element calculation in Example 1 and Example 2 are consistent with the crack evolution results of the gradient multilayer coating actually tested under different indentation conditions.

[0073] In addition, the present application can design TiN / TiSiN gradient multilayer coatings with different structures and modulation periods, and can compare and screen out coating structures that meet the toughness requirements through finite element simulation calculations, thereby eliminating the manual labor consumption of actual experiments and accelerating the screening process.

[0074] The above description is only a preferred embodiment of the present invention and does not limit the present invention in any way. Any simple modification, change and equivalent structural change made to the above embodiment based on the technical essence of the present invention still falls within the protection scope of the technical solution of the present invention.

Claims

1. A method for predicting toughness of a TiN / TiSiN gradient multilayer coating, characterized in that: The specific steps are as follows: 1) Using finite element analysis software, establish a two-dimensional model of the geometric component indenter, coating and substrate during the Vickers indentation test of the TiN / TiSiN gradient multilayer coating, and set the coating structure in the component module; 2) Assign corresponding material properties to each component of the 2D model; 3) Assemble various geometric components, define the indenter, coating, transition layer and substrate components as non-independent entities and assemble them into a whole; 4) Setting up the analysis process, in addition to the initial analysis steps, constructing the loading analysis process and the unloading analysis process according to the actual indentation experiment process; 5) Define the contact type and boundary conditions. In the calculation model, surface-to-surface contact is used to define the contact relationship between the diamond indenter and the coating. The outer surface of the indenter is set as the active surface, and the coating surface is set as the slave surface. The friction coefficient between the indenter and the coating surface is set to 0. It is assumed that the coating interface is in an ideal state, and three main boundary constraints are set. The first is the left boundary of the model, which is set to be fixed along the x-axis, can only move along the y-axis, and is perpendicular to the z-axis; the second is the bottom of the model, which is set to be completely fixed; the third is the position of the indenter, and the indenter of the model is set to be a rigid body; 6) Perform finite element meshing on the two-dimensional model, and perform dense processing on the mesh of the contact area between the indenter and the coating to improve the accuracy of the simulation calculation results; 7) The indentation test process is simulated and calculated on the two-dimensional finite element model after fine mesh division to obtain the principal stress distribution cloud map of the coating indentation test process, and the maximum principal stress of the coating at the indentation position is obtained based on the principal stress distribution cloud map.

2. The toughness prediction method of the TiN / TiSiN gradient multilayer coating according to claim 1, characterized in that: The TiN / TiSiN gradient multilayer coating is obtained by alternately compounding a TiN layer and a TiSiN layer on the surface of a Ti-6Al-4V alloy substrate, and a transition layer is provided between the Ti-6Al-4V alloy substrate and the TiN / TiSiN gradient multilayer coating, the transition layer is a Ti layer, the surface of the gradient multilayer coating is a TiSiN layer, and the coating in contact with the transition layer is a TiN layer.

3. The toughness prediction method of the TiN / TiSiN gradient multilayer coating according to claim 1, characterized in that: Step 1) Set the height of the substrate to 3 μm, the total thickness of the coating and the transition layer to 3 μm, the radius of the substrate to 6 μm, the indenter to be a conical diamond indenter with a half angle of 70.3°, and the indenter height to 1 μm.

4. The method for predicting toughness of TiN / TiSiN gradient multilayer coating according to claim 1, characterized in that: Step 2) The pressure head in the model is set as a rigid material, and the substrate, transition layer and coating are set as elastic-plastic materials.

5. The method for predicting toughness of TiN / TiSiN gradient multilayer coating according to claim 1, characterized in that: Step 4) The loading process of the finite element calculation is divided into three stages: high load, the indenter penetration depth is 0.3 μm; medium load, the indenter penetration depth is 0.15 μm; Low load, the indenter penetration depth is 0.05μm.

6. The method for predicting toughness of TiN / TiSiN gradient multilayer coating according to claim 1, characterized in that: Step 6) The method for fine meshing the two-dimensional finite element model is as follows: the model mesh is set to a two-dimensional quadrilateral unit mesh with 4 nodes, the total number of unit meshes is 500,000 to 2 million, and the nodes within the mesh and the nodes on the upper surface can move freely in space.

7. A screening and design method for a high-toughness TiN / TiSiN gradient multilayer coating based on the toughness prediction method for the TiN / TiSiN gradient multilayer coating according to any one of claims 1 to 6, characterized in that: The specific steps are as follows: design a variety of TiN / TiSiN gradient multilayer coatings with different gradient structures, use the above-mentioned toughness prediction method of the TiN / TiSiN gradient multilayer coating to calculate the maximum stress at the edge of the indentation on the coating surface under high, medium and low loads, respectively, and compare them, and select the sample with the lowest maximum stress at the edge of the indentation on the coating surface under high and medium loads, which is the TiN / TiSiN gradient multilayer coating with the highest toughness.

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