CN109115639A - A kind of superhard material nano hardness measurement method considering pressure head flexible deformation - Google Patents
A kind of superhard material nano hardness measurement method considering pressure head flexible deformation Download PDFInfo
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Abstract
A kind of superhard material nano hardness measurement method considering pressure head flexible deformation, belongs to nano hardness field of measuring technique.Its step: one, it is based on Hertz Elastic Contact Theory, the model of two articles Elastic Contact is established, according to the calculation formula of this model inference hardness；Two, standard fused silica sample is loaded under different pressure depths with pressure head, according to fused silica sample plus unloading data calibration pressure head area function；Three, the sample data obtained by nano indentation test are calculated with the area function that step 2 obtains, can be obtained the hardness of sample.The measurement method established by the present invention for considering superhard material nano hardness when pressure head elastic deformation amount, the hardness calculation formula established consider the elastic deformation amount of pressure head, can more accurately evaluate the hardness of measured material.Area function of the invention is the linear relationship of contact area and maximum pressure depth, and data processing is simpler.
Description
Technical field
The invention belongs to nano hardness field of measuring technique, and in particular to a kind of superhard material for considering pressure head flexible deformation
Nano hardness measurement method, the detection applied to material surface nanoscale mechanical property.
Background technique
Nanoindentation refers to loading sample using the pressure head of standard geometrical shapes, passes through power and position
The power and displacement of displacement sensor record load, to obtain many mechanical performance indexs such as the hardness of material, Young's modulus.Due to
The mechanical property that material can directly be obtained from load-displacement curve using Nanoindentation, without measuring impression
Area.As long as can measure in nanoscale so accuracy of instrument is sufficiently high, the nano hardness of material can be quickly obtained
Etc. parameters.Oliver-Pharr method is most common mechanics parameter calculation method, this method in instrumentation nano indentation
It was proposed by Oliver and Pharr and 1992 year.The application range of Oliver-Pharr method has certain limitation, this method requirement
During entire nano impress, the geometrical morphology of pressure head is remained unchanged, that is, corresponding contact area under different pressure depths is kept to be
Fixed.However for hardness close to the superhard material of even higher than diamond hardness, it is super that these are measured using diamond penetrator
When hard material, diamond penetrator will necessarily generate certain deformation, including flexible deformation and plastic deformation.
Currently, the hardness measurement for superhard material is studied, including the following contents.
Chinese scholar Zong. et al. also observed superhard gold in the subsequent heat treatment research process to diamond cutter
The phenomenon that hard rock surface.Zong. equal scholars survey the mechanical property of tool surface after heat treatment using Nanoindentation
Examination, treated that apparent variation occurs in diamond surface mechanical property for discovery, its hardness and elastic modulus is deep in indentation
Degree is that 6nm reaches maximum value, respectively 650GPa and 24000GPa, about the 6.5 of diamond actual hardness times and actual elastic
12 times of modulus.
The scholar V.D.Blank et al. of Russia has synthesized novel C60The hardness of fullerene polymer, the polymer is super
The hardness of diamond is crossed.They use the atomic force microscope of Knoop diamond penetrator and Diamond tip first to measure
The hardness of the material does not all succeed, because diamond penetrator does not generate impression on the surface of this material.This is that they recognize
One of the reasons why being higher than diamond for this novel fullerene-based material hardness, another reason is the Buddha's warrior attendant for synthesizing this material
Stone high pressure anvil surface has apparent deformation, and the scholars such as V.D.Blank further measure its hardness using scarification,
The hardness for finally measuring this fullerene-based material is 300 ± 40GPa, and as a comparison, they measure natural diamond (100) crystal face
(111) hardness of crystal face, respectively 137 ± 6GPa and 167 ± 5GPa.
Domestic Tian Yongjun academician team is according to Hall-Patch effect, i.e. nanostructure (nanocrystal or nano twin crystal)
The hardness that diamond can be improved has synthesized the nano twin crystal diamond of grain of rice size under high-temperature and high-pressure conditions
(nanotwinned diamond).This material also has excellent temperature stability other than hardness is up to 200GPa.?
In the hardness measurement of this material, the scholars such as Tian. measure the hardness of this material using Vickers indenter under conditions of 4.9N,
The hardness of the higher material of some other hardness is also measured under the same conditions as a comparison simultaneously.They think that 4.9N is carried
Measured material hardness can accurately show the hardness of this material under lotus, although the hardness of diamond penetrator is twin lower than nanometer
The hardness of diamond, but pattern of the pressure head before and after hardness measurement is observed by SEM (scanning electron microscope), do not see
The deformation generated to pressure head pattern.
In the above-mentioned research to superhard material, require to measure the hardness of material.The method of measurement includes pressure
Trace method and two kinds of scarification, wherein the precision of indentation method is higher.But either indentation method or scarification measure the hard of material
Degree requires that the hardness of pressure head is higher than the hardness of measured material in existing hardness evaluation method, guarantees that pressure head can be effective
Indentation sample.And in above-mentioned superhard material hardness measurement process, all do not account for the hardness of diamond penetrator
Less than the hardness of measured material, flexible deformation will necessarily occur during measurement and be even plastically deformed for pressure head, so that pressure head
Geometrical morphology change, corresponding contact area under different pressure depths can not be accurately obtained, so cannot obtain accurately
Hardness.
Summary of the invention
Not accounting for pressure head flexible deformation the purpose of the present invention is to solve existing method causes hardness measurement to generate
The problem of certain error, provides a kind of superhard material nano hardness measurement method for considering pressure head flexible deformation.
To achieve the above object, the technical solution adopted by the present invention is as follows:
A kind of superhard material nano hardness measurement method considering pressure head flexible deformation, the method and step are as follows:
Step 1: it is based on Hertz Elastic Contact Theory, the model of two articles Elastic Contact is established, according to this model inference
The calculation formula of hardness；
Step 2: using nano indentation test, load standard fused silica sample under different nano impress depth with pressure head,
According to fused silica sample plus unloading data calibration pressure head area function；
Step 3: the sample data obtained by nano indentation test are carried out with the area function that step 2 obtains
It calculates, can be obtained the hardness of sample.
The beneficial effect of the present invention compared with the existing technology is: hardness calculation formula established by the present invention, pressure head only
When flexible deformation occurs, it is contemplated that the elastic deformation amount of pressure head can more accurately evaluate the hardness of measured material.Face of the invention
Product function is the linear relationship of contact area and maximum pressure depth, and data processing is simpler.
Detailed description of the invention
Fig. 1 is the curved surface profile schematic diagram of two articles Elastic Contact；
Fig. 2 is the load comparison's figure for loading fused silica sample before and after loading diamond under identical pressure depth twice；
Fig. 3 is diamond Bo Shi Tip area function matched curve figure when considering pressure head elastic deformation amount；
Fig. 4 is hardness balance's figure that conventional method and improved method of the present invention measure the deep lower diamond sample of small pressure.
Specific embodiment
Further description of the technical solution of the present invention with reference to the accompanying drawings and examples, and however, it is not limited to this,
All to be modified to technical solution of the present invention or equivalent replacement, range without departing from the spirit of the technical scheme of the invention should all
Cover within the protection scope of the present invention.
Specific embodiment 1: present embodiment record is that a kind of superhard material nanometer for considering pressure head flexible deformation is hard
Measurement method is spent, the method and step is as follows:
Step 1: it is based on Hertz Elastic Contact Theory, the model of two articles Elastic Contact is established, according to this model inference
The case where calculation formula of hardness, specifically, formula 1-7 are the contact of two rigid bodies, do not consider flexible deformation, can be used to calculate；
Compared with prior art, which is no longer considered as the changeless rigid body of geometrical morphology for pressure head, but considers the bullet of pressure head
Property deformation；
Step 2: using nano indentation test, load standard fused silica sample under different nano impress depth with pressure head,
According to fused silica sample plus unloading data calibration pressure head area function；Compared with prior art, pressure head face of the invention
Product function is the linear relationship for contacting projected area and maximum pressure depth, rather than contacts projected area and contact deep square of pressure with practical
Linear relationship；
Step 3: the area function obtained with step 2 is (outer to the sample data obtained by nano indentation test
The relationship of power P and maximum nano impress depth h) it is calculated and (is calculated using formula 1-1~1-7), it can be obtained sample
Hardness.
In the present invention, relevant calculation model is established first with step 1, then step 2 obtains the pressure head face of calibration
Product function, step 3 carry out nano-indentation experiment to tested superhard material, obtain external force and maximum nano impress depth, last base
External force, maximum nano impress depth in step 3, the calibration Tip area function of step 2 substitute into them the public affairs of step 1
Formula can calculate the nano hardness of tested superhard material.
Specific embodiment 2: superhard material is received when a kind of consideration pressure head elastic deformation amount described in specific embodiment one
The measurement method of rice hardness, in step 1, the calculation formula of the hardness is as follows:
In formula, PmaxFor maximum load, A is contact projected area.
Specific embodiment 3: superhard material is received when a kind of consideration pressure head elastic deformation amount described in specific embodiment two
The measurement method of rice hardness, the function expression of the contact projected area A stated are as follows:
A=π Rh
In formula, R is indenter tip blunt round radius, and h is that the pressure of nano-hardness tester record is deep.
Specific embodiment 4: superhard material is received when a kind of consideration pressure head elastic deformation amount described in specific embodiment three
The measurement method of rice hardness, the function expression of the contact projected area A are only applicable to pressure head and flexible deformation only occur
It presses in deep range.
Specific embodiment 5: superhard material is received when a kind of consideration pressure head elastic deformation amount described in specific embodiment one
The measurement method of rice hardness, in step 2, the area function refers to the contact projected area of pressure head and the line of maximum pressure depth
Sexual intercourse (i.e. formula 1-6).
Embodiment 1:
A kind of superhard material nano hardness measurement method considering pressure head flexible deformation, the specific steps are as follows:
One, the hardness calculation model for considering pressure head elastic deformation amount is established
As shown in Figure 1, the model be two object Elastic Contacts when contour of object curved surface schematic diagram.Two objects are outside
Contact model under the action of power, last only the radius of curvature of one of contour surface need to be set as infinity can be obtained pressure
Contact model between head and plane.
Point S when two objects just contact, on two articles curved surface profile1And S2Distance S can with formula (1-1) indicate:
In formula, R is the inverse of the sum of radius of curvature inverse of two articles contour surface contact point, and r is any in contact surface
A little arrive the distance at contact surface center.
uz1And uz2Point S on respectively two curved surfaces1And S2Flexible deformation displacement under pressure P effect, h1And h2For two articles
On not by flexible deformation influence area point displacement, a be contact radius of circle.Postulated point S1And S2After being respectively positioned on flexible deformation
Contact area, then elastic deformation amount and maximum press deep relationship are as follows:
uz1+uz2+ S=h1+h2=h (1-2)
In formula, h is the relative displacement of two articles, is the depth of cup of instrument record in nano-indentation experiment.
Again according to the deep relationship with maximum crushing stress in contact surface of the available pressure of Hertz Elastic Contact Theory are as follows:
In formula, p0For Max.contact stress in contact surface, a is the radius of contact surface circle, and r is that any point is arrived in contact surface
The distance at contact surface center, ErFor nominal Young's modulus.
Wherein nominal Young's modulus ErIt can be indicated with following formula:
In formula, E0For the elasticity modulus of pressure head, v0For the Poisson's ratio of pressure head, EiFor the elasticity modulus of measured material, viFor quilt
It measures and monitor the growth of standing timber the Poisson's ratio of material.
Pressure suffered by entire contact surface can be acquired by integral:
To obtain external force P and press the relationship of depth h, may further be analyzed according to power-displacement curve of nano impress
The mechanical property of material.
In formula (1-3), since the distance at any point to contact surface center in pressure depth h and contact surface is unrelated, simplified
It arrives:
That is A=π Rh (1-6)
From formula (1-6) as can be seen that cross-sectional area and maximum pressure plutonic linear relationship.Hardness calculation expression formula is as follows:
Hardness calculation expression formula is same as the prior art, and difference is that the calculating of area function is different.
Two, area function is calibrated with standard fused silica
It is generated within the scope of the pressure depth of flexible deformation since the present invention is only applicable to pressure head, to determine that pressure head generates elasticity
The pressure depth range of deformation.By loading fused silica sample first under identical pressure depth, superhard material is reloaded, finally reloads and melts
Quartz specimen, after the deep point-by-point load of different pressures, the magnitude of load for loading fused silica sample under the identical pressure depth of comparison twice is determined
The pressure depth range that pressure head flexible deformation allows.Fig. 2 is before loading single crystal diamond sample with diamond Bo Shi pressure head under identical pressure depth
Load the magnitude of load comparison of fused silica sample twice afterwards, it can be seen that when 0~200nm presses deep, load fused silica sample twice
The magnitude of load of product is identical, shows that pressure head is in regime of elastic deformation always, when pressure is greater than 200nm range deeply, loads superhard
Pressure head produces plastic deformation after material, so that load becomes larger under identical pressure depth.
It is fitted the cross-sectional area of pressure head and the relationship that maximum pressure is deep again, obtains the area function of pressure head, is illustrated in figure 3 gold
Hard rock Bo Shi pressure head considers area function when pressure head elastic deformation amount.
Three, with the method measurement material hardness for considering pressure head elastic deformation amount
With the hardness of Buddha's warrior attendant Bo Shi pressure head measurement single-crystal diamond, pressed in deep range in 0~50nm, pressure head only produces bullet
Property deformation, the diamond sample hardness that measures of the comparison prior art and the present invention consider the gold that pressure head elastic deformation amount method measures
The hardness of hard rock sample, as shown in figure 4, it can be found that the diamond hardness number that measures of method of the invention is bigger than normal and closer
The true value of diamond sample hardness.
Claims (5)
1. a kind of superhard material nano hardness measurement method for considering pressure head flexible deformation, it is characterised in that: the method step
It is rapid as follows:
Step 1: it is based on Hertz Elastic Contact Theory, the model of two articles Elastic Contact is established, according to this model inference hardness
Calculation formula；
Step 2: using nano indentation test, load standard fused silica sample under different nano impress depth with pressure head, according to
Fused silica sample plus unloading data calibration pressure head area function；
Step 3: the sample data obtained by nano indentation test are counted with the area function that step 2 obtains
It calculates, can be obtained the hardness of sample.
2. a kind of measurement method for considering superhard material nano hardness when pressure head elastic deformation amount according to claim 1,
It is characterized by: the calculation formula of the hardness is as follows in step 1:
In formula, PmaxFor maximum load, A is contact projected area.
3. a kind of measurement method for considering superhard material nano hardness when pressure head elastic deformation amount according to claim 2,
It is characterized by: the function expression of the contact projected area A is as follows:
A=π Rh
In formula, R is indenter tip blunt round radius, and h is that the pressure of nano-hardness tester record is deep.
4. a kind of measurement method for considering superhard material nano hardness when pressure head elastic deformation amount according to claim 3,
It is characterized by: the function expression of the contact projected area A is only applicable to the pressure depth model that flexible deformation only occurs for pressure head
In enclosing.
5. a kind of measurement method for considering superhard material nano hardness when pressure head elastic deformation amount according to claim 1,
It is characterized by: the area function refers to the contact projected area of pressure head and the linear relationship of maximum pressure depth in step 2.
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