CN104502273A - Method for representing bonding strength of hard film through interfacial stress of elasticoplastic deformation - Google Patents

Abstract

The invention discloses a method for characterizing the bonding strength of a hard film by means of elastic-plastic deformation interface stress, which uses a cyclic indentation tester to perform a cyclic indentation test on a sample with a hard film deposited on the surface of a metal or hard alloy substrate. It causes elastic-plastic deformation of the film-based system and eventually the film peels off from the substrate due to interface fatigue. According to the relevant material properties and actual test conditions, the finite element modeling analysis is carried out, and the shear stress amplitude acting on the film-base interface when the film peels off under different cyclic loads is obtained from the solution results. Finally, the shear stress amplitude-peeling cycle The secondary curve quantitatively characterizes the bonding strength of the film/substrate interface. The method of the present invention for characterizing the bonding strength at the film/matrix interface is more reasonable and feasible; the characterization is more accurate and quantitative; the result is more practical and reliable, and can be applied to the surface of metal or hard alloy widely used in the current industrial field. Characterization and evaluation of bonding strength of hard thin films.

Description

A Method for Characterizing the Bonding Strength of Hard Thin Films by Interfacial Stress of Elastic-Plastic Deformation

technical field

The invention relates to a method for detecting the properties of a hard film on the surface of a metal or hard alloy substrate.

Background technique

As an important performance index to evaluate the quality of the film, the bonding strength between the film and the substrate is a necessary condition for process optimization. As an important field of surface engineering research, the evaluation and characterization of bonding strength has received extensive attention. How to effectively evaluate and characterize the bonding strength of the film base has extremely important guiding significance for further improving the performance and service life of tools and molds.

At present, there are dozens of measurement and evaluation methods for the bonding strength of thin films, mainly including scratch method, indentation method, stretching method, bending method, etc. The influence of interface factors can only be used to qualitatively or semi-quantitatively characterize the bonding strength of thin films. In addition, the above methods are all one-time loading failures, and the characterization results cannot accurately and truly reflect the service conditions of the membrane under actual working conditions. At present, the evaluation and characterization method of thin film dynamic bonding strength has become one of the important evaluation methods of membrane-based bonding strength, and has also been applied in actual industry, but it still has certain limitations. Taking the rolling contact fatigue method, which has been reported more often, as an example, although it characterizes the bonding strength through a situation similar to the failure of the film in a long-term service process, it is often limited to the elastic contact range and does not take into account the plastic deformation of the film/substrate . In the actual industrial environment, the film-based system often undergoes elastic-plastic deformation first during use, and continues to work for a period of time under the action of external loads before gradually peeling off from the substrate due to fatigue failure. A method for characterizing the interfacial bonding strength of a film-based system after elastic-plastic deformation.

Through the search of the existing technical literature, it is found that the method of quantitatively characterizing the bonding strength of the film/substrate interface based on the elastic-plastic deformation of the film-based system under cyclic loading has not been reported so far, and there is no universally applicable method that can be promoted. use.

Contents of the invention

The purpose of the present invention is to provide a method capable of characterizing the interfacial bonding strength of the film-based system after elastic-plastic deformation, that is, using a press-in tester under different loading conditions, using a spherical indenter to deposit a hard film on a metal or Carbide samples were subjected to multiple press-in tests to cause elastic-plastic deformation of the film-based system, and fatigue failure to peel off from the substrate. Record the times when the film peeled off, and calculate the effect on the film when the film peeled off through finite element calculations. The shear stress amplitude at the base interface is used to draw the shear stress amplitude-peeling cycle curve, which is finally used to quantitatively characterize the bonding strength of the hard film.

To achieve the above object, the present invention is achieved by taking the following technical solutions:

A kind of method characterizing the bonding strength of hard thin film with the interfacial stress of elastoplastic deformation, it is characterized in that, comprises the steps:

(1) Use a cyclic indentation tester to conduct multiple cyclic indentation tests on the surface of a metal or hard alloy sample deposited with a film under a certain load of no more than 1000N, so that the sample film-based system undergoes elastic-plastic deformation until the film peels off ;

(2) Record the number of press-in cycles that the film undergoes elastic-plastic deformation and peeling off under the load;

(3) Establish a two-dimensional axisymmetric finite element model for the spherical indenter and membrane-based system, and divide the grid; set the analysis step;

(4) Determine the material properties, elastic modulus, and Poisson's ratio of the indenter and the membrane-based system according to the actual test conditions, and set the peak load, minimum load, and cyclic loading cycles when the shear stress is stable according to the actual stress situation. Input into the finite element model for calculation; wherein, the peak load value is not greater than 1000N;

(5) Through the calculation of the finite element model, the relevant parameters reflecting the deformation of the membrane-based system are obtained: the change trend of the contact radius between the indenter and the membrane-based system with the loading cycle, and the change trend of the indentation shape with the loading cycle , The change trend of the shear stress value and shear stress amplitude of the film-base interface at the contact radius with the loading cycle;

(6) analysis and comparison step (5) said each parameter tends towards the cyclic loading cycle after the stability, choose the shear stress amplitude value of the film-base interface at the contact radius place under this cyclic loading cycle;

(7) According to the actual measured loading cycles of film peeling in steps (1) to (2), and the shear stress amplitude of the film-base interface at the contact radius obtained through step (6), draw the shear stress amplitude——peeling The cycle curve is used to quantitatively characterize the bonding strength of the hard film.

In the above method, the minimum load value is not greater than 90% of the peak load value.

The number of cyclic loading cycles when the shear stress in step (4) is stable is 10. The cyclic loading cycle after each parameter in step (6) tends to be stable is 10 times, and the shear stress amplitude of the film-base interface at the contact radius calculated under the cyclic loading cycle is selected as a characterization parameter to quantify To characterize the bonding strength at the interface of the membrane-based system.

The advantages of the present invention are:

(1) The residual indentation after cyclic pressing is a spherical indentation, and the substrate has residual plastic deformation. The method of the present invention shows that the plastic deformation can be stabilized within 10 cycles, and subsequent cyclic pressing will not cause plastic deformation and stress changes. , the interfacial shear stress amplitude at the contact radius after 10 times can be used to characterize the bonding strength of the film substrate.

(2) The method of the present invention can fix the ratio of the minimum load to the peak value of the load, change the peak value of the load and the minimum value, or change the ratio of the minimum load value to the peak value of the load by means of cyclic pressing, so as to obtain the shear stress amplitude of the film-base interface at the contact radius , thus making the testing method more flexible and convenient.

(3) Since the matrix allows certain plastic deformation during stress calculation, and the indenter can have elastic deformation, the indenter material can be diamond with high elastic modulus and basically no deformation during the test, or diamond with high strength but certain elastic deformation can be used. For ceramic materials, the test conditions are flexible, and the bonding strength can be quantitatively obtained for hard film materials with different thicknesses and elastic moduli.

Description of drawings

Figure 1 shows the geometric shape and size of the indentation of the film-based system at different cycles. Among them: (a) is measured by surface profiler; (b) is obtained by finite element calculation.

Figure 2 is the engineering stress-strain curve of the matrix (GCr15 steel) in the film-based system.

Fig. 3 is the change curve of the plastic deformation of the matrix in the film matrix system with the load cycle obtained by the finite element calculation.

Fig. 4 is the change curve of the contact radius between the indenter and the membrane-based system as a function of the load cycles obtained from the finite element calculation.

Fig. 5 is the change curve of the shear stress value at the interface of the film matrix system with the load cycle obtained by the finite element calculation.

Fig. 6 is the change curve of the shear stress amplitude at the interface of the film matrix system with the load cycle obtained by the finite element calculation under the load of 250N.

Fig. 7 is the shear stress amplitude-peeling cycle curve of the 5.6 μm MoN film under different loads.

Fig. 8 is the shear stress amplitude-peeling cycle curve of the 2.3μm CrN film under different loads.

Detailed ways

The method of the present invention will be further described in detail below in conjunction with the accompanying drawings and specific embodiments.

Example 1

A kind of method characterizing the bonding strength of hard thin film with the interfacial stress of elastoplastic deformation, comprises the steps:

In the first step, the sample is tested using a cyclic press-in tester

(1) A sample of MoN film deposited with a thickness of 5.6 μm and a substrate material of GCr15 steel was used for testing. Using a cyclic indentation tester, a diamond spherical indenter with a radius of curvature of 200 μm was used to perform an indentation test on the surface of the sample film under cyclic loading at a fixed peak value and minimum value. The sample film matrix system undergoes elastic-plastic deformation under external loads. The upper limit of the load peak selection in the cyclic indentation test shall be less than 90% of the load value when one-time indentation causes peeling off. The minimum load should not be greater than 90% of the peak load. In this embodiment, the peeling load of the film once loaded is greater than 1000N, so the peak loads used are 100N, 150N, 200N, and 250N respectively, and the minimum loads are all selected to be 30% of the peak load. In order to illustrate that the finite element simulation calculation results are in good agreement with the actual test results, the actual indentation measurements using a surface profiler are provided when the load is 250N and the indentation cycles are 1, 5, and 10 times. The geometric shape and size of the indentation measured and calculated by finite element simulation are shown in Figure 1. It can be seen from Figure (a) that the sample undergoes obvious plastic deformation under the action of the applied load and leaves a spherical indentation. The geometric shape and size of the indentation are basically stable after the fifth post-indentation, which is consistent with the first The shape and size of the indentation obtained by the ten measurements are almost coincident, indicating that the plastic deformation of the film-based system is basically stable at this time, and the amount of plastic deformation does not increase significantly. It can be seen from Fig. 1(b) that the indentation morphology and geometric dimensions calculated by finite element simulation also do not change significantly after five cycles of indentation testing, which is almost the same as the actual measurement results in Fig. 1. are exactly the same, and the trend of change is the same.

(2) Cyclic indentation tests were carried out on the samples under different loads, which eventually caused the peeling of the film. Using an optical camera to observe and record, the number of cycles that the film peeled off under the load of 250N was 8.0×10 ³ times; under 200N, it was 1.4 ×10 ⁴ times; 4.0×10 ⁴ times at 150N; 1.0×10 ⁵ times at 100N.

The second step is to establish a finite element model

(1) Use the general-purpose ABAQUS software to establish a two-dimensional axisymmetric model of the indenter and the membrane-based system, define the properties of the indenter, film, and matrix materials, and determine the elastic modulus, Poisson's ratio, and yield strength of the membrane-based system. In this embodiment, the diamond indenter is defined as rigid; the MoN film is elastic: the elastic modulus is 540GPa, and the Poisson’s ratio is 0.25; the matrix GCr15 steel is elastic-plastic: the elastic modulus is 210GPa, the Poisson’s ratio is 0.3, and the plastic stress—— The strain input is based on the engineering stress-strain curve of GCr15 steel (Fig. 2).

(2) Limit the rotation of the indenter around the Z coordinate axis and the displacement along the X axis coordinate direction, limit the displacement of the sample symmetry axis along the X coordinate axis direction and the displacement of the sample bottom surface along the Y coordinate axis direction.

(3) The rigid indenter uses the 2-node linear discrete rigid body cell RAX2 for grid division, and the sample uses the 4-node quadrilateral linear reduced integration unit CAX4R for grid division. High-precision fine mesh ensures the accuracy of calculation results.

(4) The contact mode is surface-to-surface contact, in which the main surface is the surface of the diamond indenter, and the secondary surface is the outer surface of the film, and the contact property is hard contact without friction.

(5) Establish an analysis step, and establish a load analysis step in the step module of the ABAQUS software. The minimum increment is defined as 0.01, and the maximum increment is defined as 0.1.

The third step is to select the load parameters according to the actual test

(1) The minimum load value is 30% of the peak load value. Since the shape of the indentation tends to be stable after 10 load cycles, the shear stress should also be stable, so the cycle number is set to 10.

(2) Input the load parameters into the finite element model for solution, and obtain the change curve of the plastic deformation of the film-based system with the load cycle, the change curve of the contact radius of the film-based system with the load cycle, and the shear stress value at the interface with the load cycle. The cycle change curve and the shear stress amplitude at the interface change curve with the load cycle (Fig. 3-6).

It can be seen from Figure 3 that after the first unloading, the matrix has a certain residual plastic deformation, and after each unloading, the plastic deformation increases slightly but the trend slows down, and the plastic deformation basically tends to be stable. After the fifth loading, the change of plastic strain value is relatively small The previous time was less than 5%, and the continuous loading no longer produces obvious plastic deformation, basically entering the elastic deformation stage.

It can be seen from Figure 4 that the contact radius presents a maximum value at the first loading, but due to the work hardening of the matrix, it gradually decreases and tends to be stable, and the value of the contact radius after the fifth loading is basically no longer changes, indicating that the contact between the indenter and the sample is basically stable at this time.

It can be seen from Figure 5 that during the multiple press-in process, as the number of cycles increases, the peak value of the shear stress at the contact interface during the loading and unloading process gradually tends to be stable, and finally tends to be basically constant and no longer increases with the cycle. changes.

It can be seen from Fig. 6 that the change law of the shear stress amplitude is consistent with other parameters, and gradually tends to be stable with the increase of the cycle, and the change of the shear stress amplitude is less than 0.5% after the fifth press-in, so it can be Consider the stress parameter as the final evaluation of the bond strength of the hard film.

The fourth step is to synthesize the parameter analysis of the third step. In order to ensure that the test results are more reliable and the evaluation characterization is more accurate, the present invention finally selects the shear stress amplitude at the interface calculated after the tenth loading as 3650MPa as the test load peak value of 250N To quantitatively characterize the bonding strength at the interface of the film-based system by using the characteristic parameters of time. The same process of quantitatively characterizing the bonding strength at the interface of the film-based system with the characterization parameters when the load is 250N, the interface shear stress amplitudes at the contact radius when the film peels off when the peak load is 100N, 150N, and 200N are respectively 2770MPa and 3190MPa , 3390MPa.

According to the variation curve of shear stress amplitude with load cycles obtained by finite element calculation in Figure 6, the shear stress amplitude under different loads-peeling cycle curves (Figure 7) can be obtained, which can quantitatively evaluate and characterize the bonding strength of the film.

Example 2

The sample was changed to a 2.3 μm CrN thin film, and the operation steps were the same as in Example 1.

The first step is to use a cyclic indentation testing machine to test the sample with a diamond spherical indenter with a radius of curvature of 200 μm

(1) Use a cyclic indentation tester to perform an indentation test on the surface of the sample film under cyclic loading with a fixed 60N load peak value. The minimum load values are respectively 15N, 20N, 30N and 40N (the ratio of the minimum load value to the maximum value is 25% respectively. , 33%, 50%, 66%).

(2) Under the above-mentioned four load ratios, the sample is subjected to a cyclic press-in test and finally the peeling of the film is caused. The observation record shows that the number of cycles that the film peels off under the action of 25% load ratio is 9.0× ¹⁰² times; 1.5×10 ³ times; 1.8×10 ⁴ times at 50%; 5.0×10 ⁵ times at 66%.

The second step is to establish a finite element model with Example 1. This example defines the diamond indenter as rigid; the CrN film is elastic: the modulus of elasticity is 400GPa, and Poisson's ratio is 0.25; the base GCr15 steel is elastoplastic: the modulus of elasticity It is 210GPa, Poisson's ratio is 0.3, and the plastic stress-strain input is based on the engineering stress-strain curve of GCr15 steel (Figure 2).

The third step is to select the load parameters according to the actual test

(1) The minimum load value is 25%, 33%, 50%, and 66% of the peak load value, and the number of cycles is set to 10.

(2) Input the load parameters into the finite element model for solution, and obtain the change curve of the shear stress amplitude at the interface with the load cycle.

The fourth step, based on the parameter analysis of the third step, select the shear stress amplitude at the interface calculated after the tenth loading, and the contact radius at which the film peels off under the load ratios of 25%, 33%, 50% and 66%. The amplitudes of interfacial shear stress are 3330MPa, 2710MPa, 2050MPa, 1330MPa respectively. Combined with peeling cycles, the shear stress amplitude-peeling cycle curves under different loads can be obtained (Figure 8).

Example 3

Sample and operating steps are the same as in Example 1.

In the first step, use a cyclic indentation tester, the indenter is a Si ₃ N ₄ ceramic spherical indenter with a curvature radius of 400 μm, and perform an indentation test on the surface of the sample film under cyclic loading with a fixed peak and minimum load.

(1) The peak loads used in this embodiment are 150N and 200N respectively, and the minimum load is selected as 30% of the peak load.

(2) Under the above two loads, the sample was subjected to a cyclic press-in test and eventually the film peeled off. The observation records showed that the number of cycles that the film peeled off under the peak load of 200N was 1.3×10 ⁵ times; under 150N it was greater than 1.0× 10 ⁶ times.

The second step is to establish a finite element model with Example 1. In this example, the Si ₃ N ₄ ceramic indenter is defined as elastic: the modulus of elasticity is 210GPa, and Poisson’s ratio is 0.23; the MoN film is elastic: the modulus of elasticity is 540GPa, Poisson's ratio is 0.25; the base GCr15 steel is elastic-plastic: the elastic modulus is 210GPa, Poisson's ratio is 0.3, and the plastic stress-strain input is based on the engineering stress-strain curve of GCr15 steel (Figure 2).

The third step is to select the load parameters according to the actual test

(1) The minimum load value is 30% of the peak load value, and the number of cycles is set to 10.

(2) Input the load parameters into the finite element model for solution, and obtain the change curve of the shear stress amplitude at the interface with the load cycle.

The fourth step, based on the parameter analysis in the third step, select the shear stress amplitude at the interface calculated after the tenth loading, and the interface shear stress amplitude at the contact radius are: 2180MPa when the peak load is 200N, and 2180MPa when the peak load is 150N 1910 MPa.

Example 4

The sample was changed to a TiN film with a thickness of 9.6 μm on an M2 high-speed steel substrate, and the operation steps were the same as in Example 1. The indenter was changed to a diamond spherical indenter with a radius of curvature of 500 μm, and the indentation test was carried out on the surface of the sample film under cyclic loading with a fixed peak value and minimum value.

(1) The peak loads used in this embodiment are 800N and 200N respectively, and the minimum load is 10N.

(2) Under the above two loads, the sample was subjected to a cyclic press-in test and finally caused the peeling of the film. The observation records showed that the number of cycles that the film peeled off under the peak load of 800N was 15 times; 160 times per week;

In the second step, the finite element model is established as in Example 1. The TiN film is elastic: the elastic modulus is 450GPa, and the Poisson's ratio is 0.25; the matrix M2 high-speed steel is elastic-plastic: the elastic modulus is 210GPa, and the Poisson's ratio is 0.3.

The third step is to select the load parameters according to the actual test

(1) The minimum load value is 10N, and the number of cycles is set to 10.

(2) Input the load parameters into the finite element model for solution, and obtain the change curve of the shear stress amplitude at the interface with the load cycle.

The fourth step, based on the parameter analysis of the third step, select the shear stress amplitude at the interface calculated after the tenth loading, and the interface shear stress amplitude at the contact radius are: 4480MPa when the peak load is 800N, and 4480MPa when the peak load is 200N 3120 MPa.

The above descriptions are only specific implementation cases of the present invention, and do not represent limitations to the present invention. Under the same circumstances as the inventive concept of the above-mentioned embodiment cases of the present invention, the technical solutions have no substantive transformation, improvement or equivalent replacement, all should be considered within the protection scope of the present invention.

Claims (4)

1. characterize a method for ganoine thin film bond strength with the interfacial stress of elastic-plastic deformation, it is characterized in that, comprise the steps:

(1) adopt circulation indentation test machine repeatedly to circulate to the metal or hardmetal samples surface that deposit film under a certain load being not more than 1000N and be pressed into test, make sample film matrix system elastic-plastic deformation occur until film separation;

(2) the recording sheet press-in cycle that elastic-plastic deformation occurs under this load and peels off;

(3) to the finite element model of spherical indenter and film base Establishing two-dimensional axial symmetric, and grid division; Analysis step is set;

(4) according to material properties, elastic modulus, the Poisson ratio of actual test condition determination pressure head and film matrix system, and according to actual loading situation arrange load peaks, load minimum value, shearing stress is stablized time CYCLIC LOADING cycle, be input in finite element model and calculate; Wherein, described load peaks is for being not more than 1000N;

(5) by calculating finite element model, the associated arguments reflecting film matrix system deformation is obtained: the contact radius of pressure head and film matrix system is with loading the variation tendency of cycle, vickers indentation with loading the variation tendency of cycle, contact radius place film base interfacial shear stress value and shearing stress amplitude with the variation tendency loading cycle;

(6) the described each parameter of com-parison and analysis step (5) all tend towards stability after CYCLIC LOADING cycle, choose the shearing stress amplitude at film base interface, contact radius place under this CYCLIC LOADING cycle;

(7) according to the loading cycle of the actual film separation recorded in step (1) ~ (2), and the contact radius place film base interfacial shear stress amplitude to be obtained by step (6), draw shearing stress amplitude---peel off cycle curve, for quantitatively characterizing ganoine thin film bond strength.

2. the method characterizing ganoine thin film bond strength with the interfacial stress of elastic-plastic deformation as claimed in claim 1, it is characterized in that, described load minimum value is not more than 90% of load peaks.

3. the method characterizing ganoine thin film bond strength with the interfacial stress of elastic-plastic deformation as claimed in claim 1, it is characterized in that, CYCLIC LOADING cycle when step (4) described shearing stress is stablized is 10.

4. the method characterizing ganoine thin film bond strength with the interfacial stress of elastic-plastic deformation as claimed in claim 1, it is characterized in that, CYCLIC LOADING cycle after the described each parameter of step (6) all tends towards stability is 10 times, and the shearing stress amplitude at the film base interface, contact radius place calculated under being chosen at this CYCLIC LOADING cycle carrys out quantitatively characterizing film matrix system interface bond strength as characterization parameter.