CN110441176B - Method for measuring fracture toughness of large-thickness high-toughness hard film on metal surface - Google Patents
Method for measuring fracture toughness of large-thickness high-toughness hard film on metal surface Download PDFInfo
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Abstract
The invention discloses a method for measuring the fracture toughness of a hard film with large thickness and high toughness on the surface of metal, which comprises the following steps: placing the hard film deposited on the metal surface in the stage of a microhardness meter, regulating and fixing, then sequentially carrying out multiple times of loading-holding-complete unloading prefabrication of short cracks by adopting a small load loading test, carrying out single time of loading-holding-unloading expansion by adopting a large load loading test to form elongated cracks, measuring the length value of the cracks and calculating the fracture toughness KICThe test, measurement and calculation processes are repeated to obtain a plurality of fracture toughness KsICAnd taking an arithmetic mean value after the numerical value to represent the fracture toughness. The method of multiple pressing-in under small load loading and single pressing-in under large load loading is adopted to promote the initiation and the expansion of cracks, obtain effective cracks, realize the quantitative evaluation of the fracture toughness of the hard film with large thickness, solve the problem of difficult induction of the effective cracks and improve the accuracy of fracture toughness results.
Description
Technical Field
The invention belongs to the technical field of material mechanical property testing, and particularly relates to a method for measuring fracture toughness of a hard film with large thickness and high toughness on a metal surface.
Background
The hard film has excellent mechanical performance and good physical and chemical performance, and is widely applied to surface strengthening of knife molds and precision parts. The thickness of the hard film obtained by vapor deposition is usually only several micrometers, which greatly limits the application of the hard film in extreme harsh and severe environments such as nuclear power, aviation, deep sea and the like. But with super powerAnd development and improvement of special coating devices and technologies such as multiple assistance, and the like, the hard film makes great progress in thickness, for example, CrN and Cr prepared by Sproul et al by using a modulated pulse magnetron sputtering device2The thickness of the N film reaches 55 mu m, and the deposition rate is as high as 10 mu m/h; wei et al prepared TiSiCN, ZrSiCN, ZrN, CrN, TiN thick films with thicknesses up to even 80 μm by means of plasma enhanced magnetron sputtering. For the research on the large-thickness hard film exceeding tens of microns, the initial research mainly focuses on the realization path of the thickness, and the micro-structure evolution and the mechanical property are rarely involved.
In the process of preparing the hard film by deposition, internal stress is gradually accumulated along with the increase of the film thickness of the film layer, and the cohesive strength and the fracture toughness of the film are greatly reduced. In practical application, the film with poor toughness is easy to crack under the cyclic action of alternating load, and loses the protection of a metal matrix. The accurate measurement of the fracture toughness of the film can effectively predict the service behavior of the coated parts in advance so as to avoid accidents. At present, a Vickers indentation method is mostly adopted for measuring the fracture toughness of the film, namely a Vickers indenter is adopted to press the film surface with a certain load, the indentation tip cracks due to overhigh contact stress, and the fracture toughness of the film can be calculated by measuring the length of a radial crack and combining the following formula:
in the formula, KICFracture toughness/MPa.m1/2Delta-related constant of the geometric shape of the indenter, E-elastic modulus of the film/GPa, H-hardness of the film/GPa, P-load/N; c-crack length/m.
Musil et al have shown that the fracture toughness of films is also measured to satisfy the requirement that the crack length be greater than the diagonal length of the indentation, which is often difficult to satisfy for high toughness, large thickness hard films.
The measurement of fracture toughness of hard films on metal substrates has been a difficult problem of concern in academic and engineering circles. The biggest difficulty of the indentation method for measuring the fracture toughness of the hard film is that the film material has a crack initiation threshold value, and any indentation smaller than the threshold value can not cause the film to crack. Under the influence of a tough metal matrix, both the Rockwell indenter and the Vickers indenter are difficult to reach the crack initiation threshold in a single pressing mode, and generally, the film is difficult to crack or is mainly characterized by annular cracks, so that the fracture toughness of the film cannot be quantitatively characterized. Many researchers have turned to the deposition of hard thin films on brittle substrates such as single crystal silicon, which also introduce significant variation. For a hard film with a thickness of tens of microns, although the interference of a plastic matrix on the cracking and peeling of the film can be avoided to a certain extent, the critical condition required for judging the fracture toughness can not be met all the time.
The search of documents in the prior art shows that the existing measurement method for the fracture toughness of the hard film with large thickness and high toughness on the metal surface is only reported, and no simple and applicable method can be popularized and applied.
Disclosure of Invention
The invention aims to solve the technical problem of providing a method for measuring the fracture toughness of a hard film with large thickness and high toughness on the surface of metal aiming at the defects of the prior art. The method adopts the method of multiple pressing-in under small load loading and single pressing-in under large load loading to promote the initiation and expansion of cracks, thereby obtaining effective cracks, realizing the quantitative evaluation of the fracture toughness of the hard film with large thickness, obviously reducing the cracking threshold of the hard film, solving the problem that the initiation and expansion of the effective cracks are difficult to induce due to improper loading capacity in the traditional method, and improving the accuracy of fracture toughness results.
In order to solve the technical problems, the invention adopts the technical scheme that: the method for measuring the fracture toughness of the hard film with large thickness and high toughness on the metal surface is characterized by comprising the following steps of:
step one, installing a pressure head of a microhardness meter on the microhardness meter, and then placing a hard film deposited on the surface of metal in a vapor phase on an objective table of the microhardness meter; the thickness of the hard film deposited on the metal surface by vapor deposition is 10-30 μm;
adjusting the position of the objective table until the surface appearance of the hard film deposited on the metal surface by vapor phase can be clearly observed from an ocular lens of a microhardness tester, and then fixing the position of the objective table;
step three, carrying out a small load loading test on the hard film deposited on the metal surface by the vapor phase on the objective table in the step two, and the specific process is as follows: firstly, sequentially loading and holding a hard film which is vapor-deposited on the surface of a metal according to a preset load, then completely unloading, and repeating the loading, holding and unloading processes until a fine crack appears at the tip of an indentation of a pressure head observed from an eyepiece of a microhardometer;
step four, carrying out a large load loading test on the hard film which is subjected to the small load loading test in the step three and is deposited on the metal surface by vapor deposition, wherein the specific process is as follows: sequentially loading and holding the hard film which is subjected to the small-load loading test and is vapor-deposited on the metal surface according to a preset load, and unloading when the crack length of the tip of the indentation of the indenter is larger than the length of the diagonal line of the indentation from the eyepiece of a microhardometer;
step five, measuring the length of the crack at the tip of the indentation in the hard film deposited on the metal surface in the vapor phase after the heavy load loading test in the step four by using a measuring tool of a microhardometer control terminal to obtain a crack length numerical value, taking the preset load of the heavy load loading test as a load numerical value, substituting the crack length numerical value and the elastic modulus and hardness numerical value of the hard film deposited on the metal surface in the vapor phase into a formula (1) for calculation to obtain fracture toughness KICNumerical values:
in the formula (1), KICFracture toughness/MPa.m1/2Delta-related constant of the geometric shape of the indenter, E-elastic modulus of the film/GPa, H-hardness of the film/GPa, P-load/N; c-crack length/m;
the elastic modulus and the hardness are measured by adopting a nano-indenter;
step six, adjusting the position of the objective table through the position adjusting rods in the X-axis direction and the Y-axis direction of the objective table to obtain a new hard film surface test area of vapor deposition on the metal surface, fixing the objective table, and then sequentially repeating the step three to the step five of small load loading test, large load loading test, crack length measurement and fracture toughness KICA numerical calculation process to obtain a plurality of fracture toughness KsICNumerical value of all fracture toughness Ks to be obtainedICThe numerical average value of the numerical values represents the fracture toughness of the hard film deposited on the metal surface by vapor deposition.
The invention divides the process of inducing the hard film which is deposited on the metal surface by vapor phase to crack and form cracks into two stages: in the first stage, a small load test is adopted to carry out multiple times of loading, load retention and complete unloading, so that the pressure of a pressure head acting on the hard film exceeds a crack initiation threshold value to prefabricate a small crack; because the film materials all have a crack initiation threshold, any indentation smaller than the threshold can not cause the cracking of the film, and the critical load of the material for fatigue failure is far smaller than the single loading failure load, when the first stage of the invention adopts the small load to press in for a plurality of times, the deformation is mainly concentrated in the hard film, the stress can not be released through the plastic deformation, so once the crack initiation threshold is reached, the film will crack to generate short cracks, the invention adopts a plurality of times of loading-load retention-complete unloading to greatly reduce the threshold of the conventional method for inducing the cracking of the film; meanwhile, the small load loading is adopted to effectively reduce the occurrence of plastic deformation of the metal matrix, thereby avoiding the generation of annular cracks; in the second stage, a large load test is adopted to carry out single loading-load retention-unloading, and a pressure head acts on the short cracks to further expand the short cracks to form elongated cracks, so that the crack toughness K is suitable for the short cracksICThe formula (1) is calculated, so that the quantitative characterization of the fracture toughness of the film is realized; the measuring method overcomes the defects that the loading capacity is insufficient, the loading capacity is released through the plastic deformation of the metal matrix, the initiation and the expansion of effective cracks are difficult to induce, the effective crack length cannot be obtained for judging the fracture toughness in the traditional method, and the hard material is prevented from being used for judging the hard materialThe error caused by the fact that the film is transferred to the brittle matrix for evaluation enables the fracture toughness result of the hard film to be more accurate and effective.
The method for measuring the fracture toughness of the hard film with large thickness and high toughness on the metal surface is characterized in that in the step one, the pressure head of the microhardness meter is a Vickers pressure head or a Vickers pressure head. The tip of the pressure head is sharper, the thin film is easy to crack, the smooth operation of the measuring process is facilitated, the commercialization degree is high, and the popularization is easy.
The method for measuring the fracture toughness of the hard film with large thickness and high toughness on the metal surface is characterized in that in the step one, the base metal material in the hard film vapor-deposited on the metal surface is steel. The steel is the material which is most widely applied in the industrial field at present, the hard film is mainly used for strengthening the surface of the steel matrix at present, and the general applicability of the invention is improved by taking the steel as the preferred material of the invention.
The method for measuring the fracture toughness of the hard film with large thickness and high toughness on the metal surface is characterized in that the hard film in the hard film deposited on the metal surface in the second step is a TiN film, TiAlN film, CrN film or CrTiAlN film. The four preferable films are typical hard films, have the advantages of wide application range and large performance coverage range, and further expand the applicability of the invention.
The method for measuring the fracture toughness of the hard film with large thickness and high toughness on the metal surface is characterized in that in the third step, the preset load in the small load loading test is 10 g-300 g, and the number of times of repeating the loading, load-holding and unloading processes is 5-100. The preset load can not only avoid that the film is not cracked effectively when the load is too small, but also avoid that the metal matrix is subjected to a large amount of plastic deformation when the load is too large, thereby reducing the measurement error; the repeated times are selected to be 5-100 times, so that the test requirement for cracking of the film can be met, the test period can be effectively shortened, and the measurement efficiency is improved.
The method for measuring the fracture toughness of the hard film with large thickness and high toughness on the metal surface is characterized in that the preset load in the large load loading test in the fourth step is 50-500 g, and the preset load in the large load loading test is improved by 50-400% compared with the preset load in the small load loading test in the third step. The numerical relationship of the preset load in the preset load test, the small load loading test and the large load loading test can effectively promote the crack expansion in the second stage of the test.
The method for measuring the fracture toughness of the hard film with large thickness and high toughness on the metal surface is characterized in that the load holding time in the small load loading test in the step three and the large load loading test in the step four is 5-60 s. The setting of the load-holding time can ensure the energy requirement of crack initiation and expansion, can shorten the test period and further improve the measurement efficiency.
The method for measuring the fracture toughness of the hard film with large thickness and high toughness on the metal surface is characterized in that the repetition frequency in the step six is more than 3 times. The repetition times are more than 3, so that the test error caused by local accidental defects of the hard film can be avoided, and the accuracy of the measurement result is improved.
Compared with the prior art, the invention has the following advantages:
1. the invention adopts the small load test to carry out multiple times of loading, load holding and complete unloading to prefabricate the short cracks, and then adopts the large load test to carry out single time of loading, load holding and unloading expansion to form the slender cracks, thereby obtaining effective cracks, realizing the quantitative evaluation of the fracture toughness of the large-thickness hard film, obviously reducing the threshold value of the hard film fracture, solving the problem that the traditional method has improper loading capacity and is difficult to induce the effective cracks to germinate and expand, and improving the accuracy of fracture toughness results.
2. The measuring method can be realized on the existing commercial microhardness tester, does not need to modify instruments and equipment, has simple operation process and stronger popularization.
3. The measuring method of the invention is simple, easy to calculate and accurate in result.
The technical solution of the present invention is further described in detail by the accompanying drawings and examples.
Drawings
FIG. 1a is an indentation pattern of a TiN film vapor-deposited on the surface of M2 high-speed steel after a small load test in example 1 of the invention.
FIG. 1b is an indentation pattern of a TiN film vapor-deposited on the surface of M2 high-speed steel after a large load test in example 1 of the invention.
FIG. 2 is an indentation pattern of TiN film vapor-deposited on the surface of M2 high-speed steel according to comparative example 1 after a single indentation loading test.
FIG. 3 is an indentation pattern of TiN film vapor-deposited on the surface of M2 high-speed steel according to comparative example 2 after a single indentation loading test.
FIG. 4 is an indentation pattern of TiN film vapor-deposited on the surface of M2 high-speed steel according to comparative example 3 after a single indentation loading test.
FIG. 5 is an indentation pattern of TiN film vapor-deposited on the surface of M2 high-speed steel according to comparative example 4 after a single indentation loading test.
FIG. 6 is an indentation pattern of TiN film vapor-deposited on the surface of M2 high-speed steel according to comparative example 5 after a single indentation loading test.
FIG. 7a is an indentation pattern of a TiN film vapor-deposited on the surface of M2 high-speed steel after a small load test in example 2 of the invention.
FIG. 7b is an indentation pattern of TiN film vapor-deposited on the surface of M2 high-speed steel after a large load test in example 2 of the invention.
FIG. 8 is an indentation pattern of a CrN film vapor-deposited on the surface of M2 high-speed steel after a large load test in example 3 of the invention.
FIG. 9 is an indentation pattern of TiAlN thin films vapor-deposited on the surface of stainless steel according to example 4 of the present invention after a large load test.
FIG. 10 is an indentation pattern of a CrTiAlN thin film vapor-deposited on a stainless steel surface according to example 5 of the present invention after a large load loading test.
FIG. 11a is an indentation pattern of a TiN film vapor-deposited on the surface of M2 high-speed steel after a small load test in example 6 of the invention.
FIG. 11b is an indentation pattern of TiN film vapor-deposited on the surface of M2 high-speed steel after a large load test in accordance with example 6 of the present invention.
Detailed Description
Example 1
The method of the embodiment comprises the following steps:
mounting a Vickers pressure head on a microhardness meter, and then placing a TiN film which is vapor-deposited on the surface of M2 high-speed steel on an objective table of the microhardness meter; the thickness of the TiN film deposited on the surface of the M2 high-speed steel by vapor deposition is 25.6 mu M;
adjusting the position of the objective table until the surface appearance of the TiN film deposited on the surface of the M2 high-speed steel by vapor deposition can be clearly observed from an eyepiece of a microhardometer, and then fixing the position of the objective table;
step three, carrying out small load loading test on the TiN film deposited on the surface of the M2 high-speed steel by the vapor phase on the objective table in the step two, and the specific process is as follows: firstly, sequentially loading and holding a TiN film which is vapor-deposited on the surface of M2 high-speed steel according to a preset load, then completely unloading, and repeating the loading, holding and unloading processes until tiny cracks appear at the indentation tip of a pressure head observed from an eyepiece of a microhardometer; in the small load loading test, the preset load is 300g, the load holding time is 10s, and the loading, load holding and unloading processes are repeated for 20 times;
step four, carrying out a large load test on the TiN film which is subjected to the small load test in the step three and is vapor-deposited on the surface of the M2 high-speed steel, wherein the specific process is as follows: sequentially loading and holding the TiN film which is subjected to the small-load loading test and is vapor-deposited on the surface of the M2 high-speed steel according to a preset load, and unloading when the crack length of the tip of the indentation of the indenter is larger than the length of the diagonal line of the indentation observed from an eyepiece of a microhardometer; in the large load loading test, the preset load is 500g, and the load retention time is 10 s;
step five, carrying out the large-load loading test on the vapor deposition on the surface of the M2 high-speed steel in the step four by using a measuring tool of a microhardness tester control terminalMeasuring the crack length of the indentation tip in the TiN film to obtain a crack length value, taking the preset load of a large load loading test as a load value, substituting the crack length value and the elastic modulus and hardness values of the TiN film vapor-deposited on the surface of the M2 high-speed steel into a formula (1) for calculation to obtain fracture toughness KICNumerical values:
in the formula (1), KICFracture toughness/MPa.m1/2Delta-related constant of the geometric shape of the indenter, E-elastic modulus of the film/GPa, H-hardness of the film/GPa, P-load/N; c-crack length/m;
the elastic modulus and the hardness are measured by adopting a nano-indenter;
step six, adjusting the position of the objective table through the position adjusting rods in the X-axis direction and the Y-axis direction of the objective table to obtain a new hard film surface test area of vapor deposition on the metal surface, fixing the objective table, and repeating the small load loading test, the large load loading test, the crack length measurement and the fracture toughness K of the step three to the step five for 4 times in sequenceICThe numerical calculation process obtains 5 fracture toughness KsICNumber of values, for the 5 fracture toughness K obtainedICThe numerical value is calculated as an arithmetic mean value, and the fracture toughness of the TiN film which is vapor-deposited on the surface of the M2 high-speed steel is 2.8 MPa.m0.5。
FIG. 1a is an indentation pattern of a TiN film vapor-deposited on the surface of M2 high-speed steel according to the embodiment after a small load test, and it can be seen from FIG. 1a that short radial cracks can be observed at the tips of the indentations, which indicates that the small load test has effectively induced film cracking.
FIG. 1b is an indentation morphology graph of the TiN film vapor-deposited on the surface of the M2 high-speed steel after a large load loading test, and it can be seen from FIG. 1b that a slender radial crack has been generated at the indentation tip, and the conditions required for fracture toughness determination are satisfied.
Comparative example 1
This comparative example comprises the following steps:
mounting a Vickers pressure head on a microhardness meter, and then placing a TiN film which is vapor-deposited on the surface of M2 high-speed steel on an objective table of the microhardness meter; the thickness of the TiN film deposited on the surface of the M2 high-speed steel by vapor deposition is 25.6 mu M;
adjusting the position of the objective table until the surface appearance of the TiN film deposited on the surface of the M2 high-speed steel by vapor deposition can be clearly observed from an eyepiece of a microhardometer, and then fixing the position of the objective table;
thirdly, performing single press-in loading test on the TiN film deposited on the surface of the M2 high-speed steel by the vapor phase deposition on the objective table in the second step according to a preset load, sequentially performing loading, load retention and complete unloading, and observing the indentation condition of the pressure head from an eyepiece of a microhardometer; the preset load of the single press-in loading test is 50g, and the load retention time is 10 s.
Comparative example 2
This comparative example differs from comparative example 1 in that: the preset load for a single press-in load test was 100 g.
Comparative example 3
This comparative example differs from comparative example 1 in that: the preset load for a single press-in load test was 200 g.
Comparative example 4
This comparative example differs from comparative example 1 in that: the preset load for a single press-in load test was 300 g.
Comparative example 5
This comparative example differs from comparative example 1 in that: the preset load for a single press-in load test was 500 g.
Fig. 2 to 6 are impression topography images of TiN films vapor-deposited on the surface of M2 high-speed steel according to comparative examples 1 to 5 of the present invention after a single indentation loading test, respectively, and it can be seen from fig. 2 to 6 that no crack is observed at the tip of the indentation, which indicates that no observable crack can be formed on a hard film with large thickness and high toughness of a metal matrix by single indentation, and thus the fracture toughness of the film can not be measured by the crack length according to the conventional test method.
Example 2
The method of the embodiment comprises the following steps:
mounting a Vickers pressure head on a microhardness meter, and then placing a TiN film which is vapor-deposited on the surface of M2 high-speed steel on an objective table of the microhardness meter; the thickness of the TiN film deposited on the surface of the M2 high-speed steel by vapor deposition is 25.6 mu M;
adjusting the position of the objective table until the surface appearance of the TiN film deposited on the surface of the M2 high-speed steel by vapor deposition can be clearly observed from an eyepiece of a microhardometer, and then fixing the position of the objective table;
step three, carrying out small load loading test on the TiN film deposited on the surface of the M2 high-speed steel by the vapor phase on the objective table in the step two, and the specific process is as follows: firstly, sequentially loading and holding a TiN film which is vapor-deposited on the surface of M2 high-speed steel according to a preset load, then completely unloading, and repeating the loading, holding and unloading processes until tiny cracks appear at the indentation tip of a pressure head observed from an eyepiece of a microhardometer; in the small load loading test, the preset load is 200g, the load holding time is 30s, and the times of repeating the loading, load holding and unloading processes are 10 times;
step four, carrying out a large load test on the TiN film which is subjected to the small load test in the step three and is vapor-deposited on the surface of the M2 high-speed steel, wherein the specific process is as follows: sequentially loading and holding the TiN film which is subjected to the small-load loading test and is vapor-deposited on the surface of the M2 high-speed steel according to a preset load, and unloading when the crack length of the tip of the indentation of the indenter is larger than the length of the diagonal line of the indentation observed from an eyepiece of a microhardometer; in the large load loading test, the preset load is 300g, and the load retention time is 20 s;
step five, measuring the length of the crack at the tip of the indentation in the TiN film deposited on the surface of the M2 high-speed steel in a vapor phase mode after the large load loading test in the step four by a measuring tool of a microhardometer control terminal to obtain a crack length value, and then taking the preset load of the large load loading test as a load value, and the crack length value deposited on the M2 high-speed steel meter in the vapor phase modeSubstituting the elastic modulus and hardness values of the TiN film of the surface into the formula (1) for calculation to obtain the fracture toughness KICNumerical values:
in the formula (1), KICFracture toughness/MPa.m1/2Delta-related constant of the geometric shape of the indenter, E-elastic modulus of the film/GPa, H-hardness of the film/GPa, P-load/N; c-crack length/m;
the elastic modulus and the hardness are measured by adopting a nano-indenter;
step six, adjusting the position of the objective table through the position adjusting rods in the X-axis direction and the Y-axis direction of the objective table to obtain a new hard film surface test area of vapor deposition on the metal surface, fixing the objective table, and repeating the small load loading test, the large load loading test, the crack length measurement and the fracture toughness K of the step three to the step five for 4 times in sequenceICThe numerical calculation process obtains 5 fracture toughness KsICNumber of values, for the 5 fracture toughness K obtainedICThe numerical value is calculated as an arithmetic mean value, and the fracture toughness of the TiN film which is vapor-deposited on the surface of the M2 high-speed steel is 2.5 MPa.m0.5。
The fracture toughness of TiN thin film vapor-deposited on the surface of M2 high-speed steel with a thickness of 25.6 μ M was measured in both of the examples and example 1, and the results show that the measurement results in the two examples are closer, which indicates that the method of the present invention has higher accuracy.
Fig. 7a is an indentation pattern of the TiN film vapor-deposited on the surface of the M2 high-speed steel according to the embodiment after the small load test, and it can be seen from fig. 7a that short radial cracks can be observed at the tips of the indentations, which indicates that the small load test has effectively induced the film cracking.
Fig. 7b is an indentation morphology graph of the TiN film vapor-deposited on the surface of the M2 high-speed steel after a large load loading test, and it can be seen from fig. 7b that a slender radial crack has been generated at the indentation tip, and the conditions required for fracture toughness determination are satisfied.
Example 3
The method of the embodiment comprises the following steps:
step one, mounting a Vickers pressure head on a microhardness meter, and then placing a CrN film which is vapor-deposited on the surface of M2 high-speed steel on an objective table of the microhardness meter; the thickness of the CrN film deposited on the surface of the M2 high-speed steel by vapor deposition is 15.5 mu M;
adjusting the position of the objective table until the surface appearance of the CrN film deposited on the surface of the M2 high-speed steel in a vapor phase can be clearly observed from an eyepiece of a microhardness tester, and then fixing the position of the objective table;
step three, carrying out a small load loading test on the CrN film deposited on the surface of the M2 high-speed steel by the vapor phase on the objective table in the step two, wherein the specific process is as follows: firstly, sequentially loading and holding a CrN film which is vapor-deposited on the surface of M2 high-speed steel according to a preset load, then completely unloading, and repeating the loading, holding and unloading processes until tiny cracks appear at the indentation tip of a pressure head observed from an eyepiece of a microhardometer; in the small load loading test, the preset load is 100g, the load holding time is 5s, and the times of repeating the loading, load holding and unloading processes are 5 times;
step four, carrying out a large load loading test on the CrN film which is subjected to the small load loading test in the step three and is vapor-deposited on the surface of the M2 high-speed steel, wherein the specific process is as follows: sequentially loading and holding the CrN film which is subjected to the small-load loading test and is vapor-deposited on the surface of the M2 high-speed steel according to a preset load, and unloading when the crack length of the tip of the indentation of the indenter is larger than the length of the diagonal line of the indentation from the eyepiece of a microhardometer; in the large load loading test, the preset load is 300g, and the load retention time is 15 s;
step five, measuring the length of the crack at the tip of the indentation in the CrN film which is subjected to the large-load loading test and is vapor-deposited on the surface of the M2 high-speed steel in the step four by using a measuring tool of a microhardometer control terminal to obtain a crack length value, and then taking the preset load of the large-load loading test as a load value, the crack length value and the elasticity of the CrN film which is vapor-deposited on the surface of the M2 high-speed steelThe modulus and hardness values are substituted into the formula (1) for calculation to obtain the fracture toughness KICNumerical values:
in the formula (1), KICFracture toughness/MPa.m1/2Delta-related constant of the geometric shape of the indenter, E-elastic modulus of the film/GPa, H-hardness of the film/GPa, P-load/N; c-crack length/m;
the elastic modulus and the hardness are measured by adopting a nano-indenter;
step six, adjusting the position of the objective table through the position adjusting rods in the X-axis direction and the Y-axis direction of the objective table to obtain a new hard film surface test area of vapor deposition on the metal surface, fixing the objective table, and then repeating the small load loading test, the large load loading test, the crack length measurement and the fracture toughness K of the step three to the step five for 5 times in sequenceICThe numerical calculation process obtains 6 fracture toughness KsICNumber of values, for the 6 fracture toughness K obtainedICThe average value of the numerical values is calculated to obtain the CrN film with the fracture toughness of 3.3 MPa.m deposited on the surface of the M2 high-speed steel by vapor deposition0.5。
FIG. 8 is an indentation morphology graph of a CrN film vapor-deposited on the surface of M2 high-speed steel after a large load loading test, and it can be seen from FIG. 8 that a slender radial crack has been generated at the indentation tip, and the conditions required for fracture toughness determination are satisfied.
Example 4
The method of the embodiment comprises the following steps:
step one, mounting a Vickers pressure head on a microhardness meter, and then placing a TiAlN film vapor-deposited on the surface of stainless steel on an objective table of the microhardness meter; the thickness of the TiAlN film deposited on the surface of the stainless steel by vapor deposition is 10.2 mu m;
adjusting the position of the objective table until the surface appearance of the TiAlN film deposited on the stainless steel surface in a vapor phase can be clearly observed from an ocular lens of a microhardometer, and then fixing the position of the objective table;
step three, carrying out a small load loading test on the TiAlN film deposited on the stainless steel surface in the gas phase on the objective table in the step two, and specifically comprising the following steps: firstly, sequentially loading and holding a TiAlN film vapor-deposited on the surface of stainless steel according to a preset load, then completely unloading, and repeating the loading, holding and unloading processes until tiny cracks appear at the indentation tip of a pressure head observed from an eyepiece of a microhardometer; in the small load loading test, the preset load is 50g, the load holding time is 60s, and the times of repeating the loading, load holding and unloading processes are 100 times;
step four, carrying out a large-load loading test on the TiAlN film which is subjected to the small-load loading test in the step three and is vapor-deposited on the surface of the stainless steel, wherein the specific process is as follows: sequentially loading and keeping the load of the TiAlN film which is subjected to the small-load loading test and is vapor-deposited on the surface of the stainless steel according to a preset load, and unloading when the crack length of the tip of the indentation of the indenter is larger than the length of the diagonal line of the indentation from the eyepiece of a microhardometer; in the large load loading test, the preset load is 200g, and the load retention time is 20 s;
step five, measuring the length of the crack at the tip of the indentation in the TiAlN film vapor-deposited on the surface of the stainless steel after the heavy-load loading test in the step four by using a measuring tool of a microhardometer control terminal to obtain a crack length value, taking the preset load of the heavy-load loading test as a load value, substituting the crack length value and the elastic modulus and hardness value of the TiAlN film vapor-deposited on the surface of the stainless steel into a formula (1) for calculation to obtain the fracture toughness KICNumerical values:
in the formula (1), KICFracture toughness/MPa.m1/2Delta-related constant of the geometric shape of the indenter, E-elastic modulus of the film/GPa, H-hardness of the film/GPa, P-load/N; c-crack length/m;
the elastic modulus and the hardness are measured by adopting a nano-indenter;
step six, adjusting the position of the objective table through the position adjusting rods in the X-axis direction and the Y-axis direction of the objective table to obtain a new hard film surface test area of vapor deposition on the metal surface, fixing the objective table, and repeating the small load loading test, the large load loading test, the crack length measurement and the fracture toughness K of the step three to the step five for 6 times in sequenceICThe numerical calculation process obtains 7 fracture toughness KsICNumber of values, for the 7 fracture toughness K obtainedICThe numerical value is calculated as an average value, and the fracture toughness of the TiAlN film vapor-deposited on the surface of the stainless steel is 2.9 MPa.m0.5。
FIG. 9 is an indentation morphology graph of the TiAlN thin film vapor-deposited on the surface of the stainless steel after a large load loading test, and it can be seen from FIG. 9 that a slender radial crack is generated at the indentation tip, and the conditions required for fracture toughness determination are met.
Example 5
The method of the embodiment comprises the following steps:
step one, mounting a Vickers pressure head on a microhardness meter, and then placing a CrTiAlN film vapor-deposited on the surface of stainless steel on an objective table of the microhardness meter; the thickness of the CrTiAlN film vapor-deposited on the surface of the stainless steel is 29.2 mu m;
adjusting the position of the objective table until the surface appearance of the CrTiAlN film deposited on the surface of the stainless steel in a vapor phase can be clearly observed from an eyepiece of a microhardness tester, and then fixing the position of the objective table;
step three, carrying out a small load loading test on the CrTiAlN film deposited on the surface of the stainless steel by the vapor phase on the objective table in the step two, and specifically comprising the following steps: sequentially loading and holding a CrTiAlN film vapor-deposited on the surface of stainless steel according to a preset load, then completely unloading, and repeating the loading, holding and unloading processes until tiny cracks appear at the tip of an indentation of a pressure head observed from an eyepiece of a microhardometer; in the small load loading test, the preset load is 10g, the load holding time is 30s, and the times of repeating the loading, load holding and unloading processes are 50 times;
step four, carrying out a large load loading test on the CrTiAlN film which is subjected to the small load loading test in the step three and is vapor-deposited on the surface of the stainless steel, wherein the specific process is as follows: sequentially loading and keeping the load of the CrTiAlN film which is subjected to the vapor deposition on the surface of the stainless steel after the small-load loading test according to a preset load, and unloading when the crack length of the tip of the indentation of the indenter is larger than the length of the diagonal line of the indentation from the eyepiece of a microhardometer; the preset load in the large load loading test is 50g, and the load retention time is 60 s;
step five, measuring the length of the crack at the tip of the indentation in the CrTiAlN film which is subjected to vapor deposition on the surface of the stainless steel after the heavy load loading test in the step four by using a measuring tool of a microhardometer control terminal to obtain a crack length value, taking the preset load of the heavy load loading test as a load value, substituting the crack length value and the elastic modulus and hardness value of the CrTiAlN film which is vapor deposited on the surface of the stainless steel into a formula (1) for calculation to obtain fracture toughness KICNumerical values:
in the formula (1), KICFracture toughness/MPa.m1/2Delta-related constant of the geometric shape of the indenter, E-elastic modulus of the film/GPa, H-hardness of the film/GPa, P-load/N; c-crack length/m;
the elastic modulus and the hardness are measured by adopting a nano-indenter;
step six, adjusting the position of the objective table through the position adjusting rods in the X-axis direction and the Y-axis direction of the objective table to obtain a new hard film surface test area of vapor deposition on the metal surface, fixing the objective table, and then repeating the steps three to five of the small load loading test, the large load loading test, the crack length measurement and the fracture toughness K for 10 times in sequenceICThe numerical calculation process obtains 11 fracture toughness KsICNumber of fracture toughness K for 11 pieces obtainedICTaking the arithmetic mean value of the numerical values to obtainThe fracture toughness of the CrTiAlN film vapor-deposited on the surface of the M2 high-speed steel is 3.7 MPa.m0.5。
FIG. 10 is an indentation morphology diagram of a CrTiAlN thin film vapor-deposited on a stainless steel surface according to the embodiment after a large load loading test, and it can be seen from FIG. 10 that a slender radial crack has been generated at the indentation tip, and the conditions required for fracture toughness determination are satisfied.
Example 6
The method of the embodiment comprises the following steps:
step one, mounting a glass pressure head on a microhardness meter, and then placing a TiN film which is vapor-deposited on the surface of M2 high-speed steel on an objective table of the microhardness meter; the thickness of the TiN film deposited on the surface of the M2 high-speed steel by vapor deposition is 25.6 mu M;
adjusting the position of the objective table until the surface appearance of the TiN film deposited on the surface of the M2 high-speed steel by vapor deposition can be clearly observed from an eyepiece of a microhardometer, and then fixing the position of the objective table;
step three, carrying out small load loading test on the TiN film deposited on the surface of the M2 high-speed steel by the vapor phase on the objective table in the step two, and the specific process is as follows: firstly, sequentially loading and holding a TiN film which is vapor-deposited on the surface of M2 high-speed steel according to a preset load, then completely unloading, and repeating the loading, holding and unloading processes until tiny cracks appear at the indentation tip of a pressure head observed from an eyepiece of a microhardometer; in the small load loading test, the preset load is 200g, the load holding time is 30s, and the times of repeating the loading, load holding and unloading processes are 20 times;
step four, carrying out a large load test on the TiN film which is subjected to the small load test in the step three and is vapor-deposited on the surface of the M2 high-speed steel, wherein the specific process is as follows: sequentially loading and holding the TiN film which is subjected to the small-load loading test and is vapor-deposited on the surface of the M2 high-speed steel according to a preset load, and unloading when the crack length of the tip of the indentation of the indenter is larger than the length of the diagonal line of the indentation observed from an eyepiece of a microhardometer; in the large load loading test, the preset load is 300g, and the load retention time is 5 s;
step five, measuring the length of the crack at the tip of the indentation in the TiN film which is subjected to vapor deposition on the surface of the M2 high-speed steel after the large-load loading test in the step four by using a measuring tool of a microhardometer control terminal to obtain a crack length value, taking the preset load of the large-load loading test as a load value, substituting the crack length value and the elastic modulus and hardness value of the TiN film which is vapor deposited on the surface of the M2 high-speed steel into a formula (1) for calculation to obtain the fracture toughness KICNumerical values:
in the formula (1), KICFracture toughness/MPa.m1/2Delta-related constant of the geometric shape of the indenter, E-elastic modulus of the film/GPa, H-hardness of the film/GPa, P-load/N; c-crack length/m;
the elastic modulus and the hardness are measured by adopting a nano-indenter;
step six, adjusting the position of the objective table through the position adjusting rods in the X-axis direction and the Y-axis direction of the objective table to obtain a new hard film surface test area of vapor deposition on the metal surface, fixing the objective table, and repeating the small load loading test, the large load loading test, the crack length measurement and the fracture toughness K of the step three to the step five for 4 times in sequenceICThe numerical calculation process obtains 5 fracture toughness KsICNumber of values, for the 5 fracture toughness K obtainedICThe numerical value is calculated as an arithmetic mean value, and the fracture toughness of the TiN film which is vapor-deposited on the surface of the M2 high-speed steel is 2.7 MPa.m0.5。
In the present example and examples 1-2, the fracture toughness of the TiN thin film vapor-deposited on the surface of the M2 high-speed steel with a thickness of 25.6 μ M was measured, and the results show that the measurement results of the three examples are relatively close, which indicates that the method of the present invention has high accuracy.
FIG. 11a is an indentation pattern of the TiN film vapor-deposited on the surface of the M2 high-speed steel after the small load test, and it can be seen from FIG. 11a that short radial cracks can be observed at the indentation tip, which shows that the small load test has effectively induced the film cracking.
Fig. 11b is an indentation morphology graph of the TiN film vapor-deposited on the surface of the M2 high-speed steel after a large load loading test, and it can be seen from fig. 11b that a slender radial crack has been generated at the indentation tip, and the conditions required for fracture toughness determination are satisfied.
The above description is only for the preferred embodiment of the present invention, and is not intended to limit the present invention in any way. Any simple modification, change and equivalent changes of the above embodiments according to the technical essence of the invention are still within the protection scope of the technical solution of the invention.
Claims (6)
1. The method for measuring the fracture toughness of the hard film with large thickness and high toughness on the metal surface is characterized by comprising the following steps of:
step one, installing a pressure head of a microhardness meter on the microhardness meter, and then placing a hard film deposited on the surface of metal in a vapor phase on an objective table of the microhardness meter; the thickness of the hard film deposited on the metal surface by vapor deposition is 10-30 μm;
adjusting the position of the objective table until the surface appearance of the hard film deposited on the metal surface by vapor phase can be clearly observed from an ocular lens of a microhardness tester, and then fixing the position of the objective table;
step three, carrying out a small load loading test on the hard film deposited on the metal surface by the vapor phase on the objective table in the step two, and the specific process is as follows: firstly, sequentially loading and holding a hard film which is vapor-deposited on the surface of a metal according to a preset load, then completely unloading, and repeating the loading, holding and unloading processes until a fine crack appears at the tip of an indentation of a pressure head observed from an eyepiece of a microhardometer; the preset load in the small load loading test is 10 g-300 g, and the times of repeating the loading, load-holding and unloading processes are 5-100 times;
step four, carrying out a large load loading test on the hard film which is subjected to the small load loading test in the step three and is deposited on the metal surface by vapor deposition, wherein the specific process is as follows: sequentially loading and holding the hard film which is subjected to the small-load loading test and is vapor-deposited on the metal surface according to a preset load, and unloading when the crack length of the tip of the indentation of the indenter is larger than the length of the diagonal line of the indentation from the eyepiece of a microhardometer; the preset load in the large load loading test is 50 g-500 g, and the preset load in the large load loading test is improved by 50% -400% compared with the preset load in the small load loading test in the step three;
step five, measuring the length of the crack at the tip of the indentation in the hard film deposited on the metal surface in the vapor phase after the heavy load loading test in the step four by using a measuring tool of a microhardometer control terminal to obtain a crack length numerical value, taking the preset load of the heavy load loading test as a load numerical value, substituting the crack length numerical value and the elastic modulus and hardness numerical value of the hard film deposited on the metal surface in the vapor phase into a formula (1) for calculation to obtain fracture toughness KICNumerical values:
in the formula (1), KICFracture toughness/MPa.m1/2Delta-related constant of the geometric shape of the indenter, E-elastic modulus of the film/GPa, H-hardness of the film/GPa, P-load/N; c-crack length/m;
the elastic modulus and the hardness are measured by adopting a nano-indenter;
step six, adjusting the position of the objective table through the position adjusting rods in the X-axis direction and the Y-axis direction of the objective table to obtain a new hard film surface test area of vapor deposition on the metal surface, fixing the objective table, and then sequentially repeating the step three to the step five of small load loading test, large load loading test, crack length measurement and fracture toughness KICA numerical calculation process to obtain a plurality of fracture toughness KsICNumerical value of all fracture toughness Ks to be obtainedICThe numerical value is taken as the average value of the numerical values to represent the fracture toughness of the hard film deposited on the metal surface by vapor deposition.
2. The method for measuring the fracture toughness of the hard film with large thickness and high toughness on the metal surface as claimed in claim 1, wherein the indenter of the microhardness meter in the step one is a Vickers indenter or a Bohr indenter.
3. The method for measuring the fracture toughness of the large-thickness high-toughness hard film on the metal surface according to claim 1, wherein the base metal material in the hard film vapor-deposited on the metal surface in the step one is steel.
4. The method for measuring the fracture toughness of the hard film with large thickness and high toughness on the metal surface according to claim 1, wherein the hard film in the hard film vapor-deposited on the metal surface in the second step is a TiN film, TiAlN film, CrN film or CrTiAlN film.
5. The method for measuring the fracture toughness of the hard film with large thickness and high toughness on the metal surface according to claim 1, wherein the load holding time in the small load loading test in the step three and the large load loading test in the step four is 5s to 60 s.
6. The method for measuring the fracture toughness of the high-thickness and high-toughness hard film on the metal surface according to claim 1, wherein the number of times of the repetition in the step six is more than 3.
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