CN106017372B - A kind of method of ultrasonic non-destructive measurement wear-resistant coating thickness and modulus of elasticity - Google Patents
A kind of method of ultrasonic non-destructive measurement wear-resistant coating thickness and modulus of elasticity Download PDFInfo
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Abstract
A kind of method of ultrasonic non-destructive measurement wear-resistant coating thickness and modulus of elasticity, belongs to ultrasonic non-destructive inspection techniques field.This method is based on impulse echo technique and using the echo-signal of single water immersion focusing probe single acquisition wear-resistant coating/metallic matrix sample, you can interface compressional wave and shear wave signal effectively before and after extraction coating.Carry out to shear wave signal the corresponding sound pressure reflection coefficient amplitude spectrum (URCAS) of spectrum analysis acquisition respectively to compressional wave, coating longitudinal wave velocity V is measured simultaneously with reference to the two-parameter inversion technique of cross-correlation analysis2lWith thickness d, pass through inverting thickness d and shear wave URCAS resonant frequency fntCalculate coating transverse wave velocity V2t, with reference to metallographic method count coating porosity to density p2It is modified, the measurement of modulus of elasticity is realized according to modulus of elasticity expression formula.The complex operations of the combination of conventional Ultrasound fado probe or the incidence of multiple angles are the method overcome, also overcome the deficiency that Poisson's ratio is assumed to be definite value by surface wave method, the problem for solving the measurement of coating modulus of elasticity ultrasonic quantitative.
Description
Technical Field
The invention relates to a method for measuring the thickness and the elastic modulus of a wear-resistant coating in an ultrasonic nondestructive mode, and belongs to the technical field of ultrasonic nondestructive testing.
Background
A1 2 O 3 WC, etcThe coating layer has high hardness, strength, elasticity and thermal conductivity, and has extremely high wear resistance and erosion resistance, so that the coating layer has become one of the key points of the technical research on the wear-resistant coating in recent years. Houdkov et al indicate that in small-sized workpieces, particularly in the inner cavity of the workpiece, the coating cannot be sprayed at a vertical angle, which results in unsatisfactory overall properties of the coating, such as microstructure, thickness, elasticity, and the like. Tillmann and p. Chivavibul et al also note that changes in the spray process (granularity, spray angle, etc.) affect the coating thickness, hardness, elasticity, and bond strength, which in turn are closely related to the fracture toughness, wear resistance, erosion resistance of the coating. Chicot et al, in the Application of the interfacial fracture toughness test for addition fracture determination, proposed that the interfacial fracture toughness K is considered ca0 Closely related to the elastic modulus of the coating. Yingke et al indicate that the modulus of elasticity has a significant effect on the contact stress field, the peeling off of the coating, the fracture and the residual stress state inside the coating, and that the coating material generally has different elastic properties than the matrix material before it is sprayed. Therefore, the research on the measurement principle and the detection technology of the elastic modulus of the wear-resistant coating is of great significance to the optimization of process parameters and the quality control in the manufacturing process of the coating.
Currently, researchers have developed many methods to evaluate the elastic modulus of coatings. Such as static nanoindentation, tensile, beam bending test, and dynamic resonance, ultrasonic, etc. The indentation method is to press a indenter into a coating sample under a certain load and calculate the elastic modulus of the coating according to the recorded load-displacement curve. The method is very sensitive to the micro-area tissue structure, the measurement error of a multiphase or composite material coating is large, and the influence of the mechanical property of a matrix on the measurement accuracy cannot be completely eliminated. The tensile method is to peel the coating from the substrate to prepare a sample of the coating alone or attach a strain gauge to the surface of the coated sample, then stretch the sample and record the load-elongation curve, thereby calculating the elastic modulus of the coating. The method has certain destructiveness to the coating and is only suitable for samples with small difference between the Poisson's ratio of the matrix and the coating. The beam bending test method is to calculate the elastic modulus of the coating through three-point or four-point bending test of the coating/matrix composite structure and through curves of load-displacement, load-curvature, load-deflection and the like. The measurement accuracy of the method is greatly influenced by the geometric dimensions of the coating and the substrate. The elastic modulus of the coating is measured by a resonance method, usually, a vibration film sample sheet is used for testing, the coating is uniformly prepared on 2 sides of a metal sheet substrate, and the bending resonance frequency of the coating is measured by an X-ray diffraction method so as to calculate the elastic modulus of the coating. This method is only suitable for thin coatings and films, and is not suitable for coatings of greater thickness. The ultrasonic method is based on the relation between ultrasonic sound velocity and material elasticity, and realizes the measurement of the elastic modulus of the coating material by measuring ultrasonic longitudinal sound velocity and ultrasonic transverse sound velocity. The method has the advantages of no damage, simple and convenient measurement, wide application range and the like. The traditional ultrasonic body wave method needs to adjust the incident angle of the probe for many times or needs the cooperation of a plurality of probes to obtain the longitudinal wave sound velocity and the transverse wave sound velocity of the coating, and the measuring process is complicated. The recently developed ultrasonic surface wave method can realize the measurement of the elastic modulus of the coating by only measuring the sound velocity of the surface wave of the coating once. However, this method requires assuming a constant poisson's ratio of the coating, which makes it difficult to achieve accurate measurement of the elastic modulus of the coating.
Disclosure of Invention
The invention mainly aims at the difficult problem of nondestructive measurement of the elastic modulus of the wear-resistant coating, and provides a method for performing ultrasonic nondestructive measurement on the thickness and the elastic modulus of the wear-resistant coating based on a wave mode conversion principle when ultrasonic waves are obliquely incident to a water/metal matrix/wear-resistant coating/water three-interface structure at a small angle and analysis of reflection and transmission coefficients of each interface. According to the method, only a single probe is needed to perform single sound wave incidence, the simultaneous measurement of longitudinal wave acoustic velocity, transverse wave acoustic velocity and thickness of the coating is realized by adopting a thin-layer sound pressure emission coefficient amplitude spectrum (URCAS) analysis technology and combining a cross-correlation analysis two-parameter inversion method, the coating density is corrected by combining a gold phase observation coating porosity value, and finally the accurate measurement of the elastic modulus of the coating material is realized. The method overcomes the complex operation of multi-probe combination or multi-angle incidence in the conventional ultrasonic method, also overcomes the defect that the Poisson ratio is assumed to be a fixed value in the surface wave method, and solves the difficult problem of ultrasonic quantitative measurement of the elastic modulus of the coating.
The technical scheme adopted by the invention is as follows: a method for measuring the thickness and elastic modulus of a wear-resistant coating in an ultrasonic nondestructive mode adopts a system for measuring the thickness and elastic modulus of the wear-resistant coating by an ultrasonic pulse echo method, wherein the system comprises a water tank, a sample table, a wear-resistant coating sample, a water immersion focusing probe, an X-Y-Z three-dimensional stepping control device, an ultrasonic flaw detector, a digital oscilloscope and a computer, and the method comprises the following steps:
(a) Determining an angle of incidence alpha <5 deg. for a water immersion focusing probe
Placing a stainless steel sample with known thickness on a sample table in a water tank, controlling the relative position between a water immersion focusing probe and the sample by adopting an X-Y-Z three-dimensional stepping device, focusing the focus of the water immersion focusing probe on the surface of the stainless steel sample, exciting the water immersion focusing probe by using an ultrasonic flaw detector, acquiring signal waveform by using a digital oscilloscope, recording the surface echo P of the stainless steel sample at the moment 0 Acoustic time of (a) t 1 And bottom surface reflecting longitudinal wave P 1 Corresponding acoustic time t 2 Knowing the longitudinal acoustic velocity V of the stainless steel sample 1l Longitudinal acoustic velocity V with water 3l Combined with the propagation time t of the ultrasonic longitudinal wave in the stainless steel sample 12 ＝t 2 -t 1 Calculating the incident angle alpha of the water immersion focusing probe by utilizing the Snell's theorem;
(b) When ultrasonic waves are obliquely incident to a water/metal matrix/wear-resistant coating/water multi-interface structure formed by coupling medium water and a coating sample at an angle alpha, an equation of the reflection coefficient of each interface is obtained:
wherein alpha is l And alpha t Angle of reflection, beta, of longitudinal and transverse waves, respectively, at the interface l And beta t Transmission angles, λ, of longitudinal and transverse waves at the interface, respectively 1 、μ 1 And λ 2 、μ 2 Is a materialK is the wave number of the corresponding ultrasonic wave, k =2 pi f/V, V is the sound velocity of the medium, f is the ultrasonic frequency, R is the frequency of the ultrasonic wave l 、R t And T l 、T t The reflection and transmission coefficients of longitudinal waves and transverse waves are respectively; when the ultrasonic waves incident to each interface are in a longitudinal wave mode, the matrix a is:
a＝[-cosα l sinα l k l1 (λ 1 +2μ 1 )cos2α l -k l1 μ 1 sin2α l ]' (2)
determining the sound velocity and density value of elastic parameters at each interface by combining the formulas (1) to (2), and calculating the reflection longitudinal wave coefficient R of the interface l Coefficient of reflected transverse wave R t Coefficient of transmitted longitudinal wave T l And coefficient of transmitted transverse wave T t ；
(c) Focusing the focus of the water immersion focusing probe on the wear-resistant coating/water interface, and effectively identifying and extracting the reflected longitudinal waves P of the front and rear interfaces of the coating by a digital oscilloscope according to the wave mode conversion rule given in the step (b) l1 、P l2 And reflected transverse wave P at front and back interfaces of the coating t1 、P t2 (ii) a Carrying out Fourier transform on the acquired signals by using a computer to respectively obtain a coating longitudinal wave sound pressure reflection coefficient amplitude spectrum and a coating transverse wave sound pressure reflection coefficient amplitude spectrum:
wherein the lower corner marks 1, 2 and 3 respectively represent a metal matrix, a wear-resistant coating and coupling medium water, d is the thickness of the wear-resistant coating, r is 12 、r 23 The sound pressure reflection coefficients of the corresponding interfaces are respectively expressed asRho is the density of the corresponding medium;
(d) Longitudinal wave sound velocity V of coupling medium water 3l And density ρ 3 And the longitudinal acoustic velocity V of the metal substrate 1l And density ρ 1 By acoustic handbooks or by experimentsThe density rho of the wear-resistant coating obtained by measurement 2 Adopting the density value of the material block body, the magnitude spectrum | R (f; d, V) of the longitudinal wave sound pressure reflection coefficient obtained in the step (c) 2l ) I is only the thickness d of the coating with unknown quantity and the sound velocity V of the coating 2l The measured amplitude spectrum | R (f; d, V) of the reflection coefficient of the longitudinal wave sound pressure is measured by the cross-correlation operation shown in the formula (4) 2l ) And the amplitude spectrum | R (f; d, V 2l )| * Carrying out two-parameter inversion in a-6 dB effective frequency band;
wherein, N represents the number of data points in the effective frequency band range of the time domain signal after FFT, and the lower corner mark i represents the ith frequency value;andrespectively the arithmetic mean value of the actually measured and theoretical sound pressure reflection coefficient amplitude spectrum in the effective frequency band; by imparting a thickness d of the abrasion-resistant coating and a longitudinal acoustic velocity V 2l Obtaining theoretical sound pressure reflection coefficient amplitude spectrum matrix by a series of continuous change values, using the theoretical sound pressure reflection coefficient amplitude spectrum matrix as a parent body, carrying out cross-correlation analysis on the actually measured sound pressure reflection coefficient amplitude spectrum one by one, and carrying out d and V corresponding to the maximum positions in the correlation coefficient matrix 2l The optimal inversion result of the thickness of the wear-resistant coating to be measured and the longitudinal wave sound velocity is obtained;
(e) Combining the coating thickness d inverted in the step (d), and reading the transverse wave sound pressure reflection coefficient amplitude spectrum URCAS in the step (c) t Corresponding resonance frequency f nt The value of (c):
wherein V 2t Transverse velocity of sound for coatingN is the order of the resonant frequency, and the thickness d obtained by inversion is substituted into a formula (5) to obtain the shear wave sound velocity value V of the wear-resistant coating 2t The longitudinal wave sound velocity V obtained by calculation 2l Transverse wave sound velocity V 2t And wear-resistant coating density rho 2 Substituting the elastic modulus E into a calculation formula (6), namely calculating the elastic modulus of the coating;
(f) A metallographic analysis technology is adopted to obtain a metallographic picture of a wear-resistant coating section, the porosity p corresponding to a wear-resistant coating sample is counted by a median filtering and binarization image processing method, and the formula rho = rho of the influence of the porosity on the material density is adopted 2 (1-p) correcting the elastic modulus of the wear-resistant coating, wherein the correction result is as follows:
the beneficial effects of the invention are: the method solves the problems that the incident angle of a probe needs to be adjusted for multiple times or multiple probes need to be matched to obtain the longitudinal wave sound velocity and the transverse wave sound velocity of the coating in the traditional ultrasonic bulk wave method, and the process of measuring the elastic modulus is complex; the method also overcomes the defect that the quantitative measurement of the elastic modulus of the coating is difficult to really realize by adopting the ultrasonic surface wave method to assume that the Poisson ratio of the coating is a certain value. According to the method, only a single probe is needed to carry out single sound wave incidence, a thin-layer sound pressure emission coefficient amplitude spectrum (URCAS) analysis technology is adopted, a cross-correlation analysis two-parameter inversion method is combined, the simultaneous measurement of longitudinal wave sound velocity, transverse wave sound velocity and thickness of the wear-resistant coating is realized, the density of the coating is corrected by combining the porosity counted by a gold phase observation result, the measurement of the elastic modulus of the coating material is finally realized, and the result is accurate and reliable. The method has the advantages of mature and simple equipment, convenient operation, low cost and great economic and social benefits.
Drawings
The invention is further described with reference to the following figures and examples.
FIG. 1 is a system for measuring the thickness and the elastic modulus of a wear-resistant coating by ultrasonic pulse echo.
FIG. 2 is a reference waveform for probe excitation: (a) a waveform; (b) a magnitude spectrum.
FIG. 3 is a schematic representation of the propagation of ultrasonic waves at low angle incidence to the water/metal substrate/wear-resistant coating/water multilayer structure.
Fig. 4 is a time domain echo signal of a sample of the WC wear-resistant coating.
Fig. 5 is a spectrum of the sound pressure reflection coefficient amplitude of longitudinal wave and transverse wave of the WC wear-resistant coating.
Fig. 6 is the result of a two-parameter inversion: (a) Experiment | R l (f；d,V 2l ) I and inverted R l (f；d,V 2l )| * (ii) a (b) η is a function of thickness; (c) η varies with the longitudinal sound velocity.
FIG. 7 shows the reversed thickness value d (a) and the metallographic observation thickness (b) of the WC wear-resistant coating sample.
Fig. 8 shows longitudinal wave sound velocity and transverse wave sound velocity measured by all collected data of the WC wear specimens.
Fig. 9 is a SEM photograph of a cross section of a WC wear resistant coating sample.
In the figure: 1. the device comprises a water tank, 2 a sample table, 3 a wear-resistant coating sample, 4 a water immersion focusing probe, 5 an X-Y-Z three-dimensional stepping control device, 6 an ultrasonic flaw detector, 7 a digital oscilloscope, 8 and a computer.
Detailed Description
The method for measuring the thickness and the elastic modulus of the wear-resistant coating in an ultrasonic nondestructive mode adopts a system which comprises a water tank 1, a sample table 2, a wear-resistant coating sample 3, a water immersion focusing probe 4, an X-Y-Z three-dimensional stepping control device 5, an ultrasonic flaw detector 6, a digital oscilloscope 7 and a computer 8 and is used for measuring the thickness and the elastic modulus of the wear-resistant coating in an ultrasonic pulse echo method as shown in figure 1. The specific implementation steps are as follows:
step a, determining an incident angle alpha: thickness h =1.62mmThe stainless steel sample is placed on a sample table 2 in a water tank 1, the relative position between a water immersion focusing probe 4 and the sample is adjusted by adopting an X-Y-Z three-dimensional stepping control device 5, and the focus of the water immersion focusing probe is vertically focused on the surface of the stainless steel sample. And exciting a water immersion focusing probe by using a USIP40 ultrasonic flaw detector 6, wherein the focal length of the water immersion focusing probe is 25.4mm, and the diameter of a wafer is 6mm. The DPO4032 digital oscilloscope 7 is used to acquire signal waveforms as shown in fig. 2 (a). Recording the surface echo P of the stainless steel sample at the moment 0 Acoustic time t of 1 =23.45 μ s and bottom-reflected longitudinal wave P 1 Corresponding acoustic time t 2 =24.03 μ s. The longitudinal wave sound velocity V of a stainless steel sample is known 1l =5890.0m/s, sound velocity of water V 3l =1480.0m/s, propagation time t of reflected longitudinal wave in stainless steel sample 12 ＝t 2 -t 1 =0.58 μ s, and the incident angle α =4.5 ° of the water immersion focusing probe was calculated. The-6 dB effective bandwidth of the water immersion focusing probe is 11.5-27.1 MHz, as shown in FIG. 2 (b).
Step b, identifying longitudinal waves P of front and rear interfaces of the coating based on the wave-type conversion rule l1 、P l2 And transverse wave P t1 、P t2 : putting a WC wear-resistant coating sample into a water tank to form a water/metal matrix/WC wear-resistant coating/water three-interface structure, adjusting the vertical incidence of a water immersion focusing probe on the surface of the sample, and focusing the focus to the position of the coating/water interface, as shown in figure 3. The time domain signal reflected from the WC wear coating sample at this time was collected as shown in fig. 4. The bottom longitudinal wave P can be observed in the time domain signal l1 、P l2 Transverse wave P with the bottom surface t1 、P t2 Moreover, longitudinal waves and transverse waves can be separated in the time domain more easily.
Step c, aligning the bottom surface longitudinal wave P l1 、P l2 Transverse wave P with the bottom surface t1 、P t2 Respectively processing by rectangular windows and carrying out frequency spectrum analysis to obtain a magnitude spectrum | R of a longitudinal wave sound pressure reflection coefficient l (f；d,V 2l ) Amplitude spectrum R of sound pressure reflection coefficient of I and transverse wave t (f；d,V 2t ) As in fig. 5.
Step d, utilizing the cross-correlation operation shown in formula (4) in the claims to measure the amplitude spectrum | R of the reflection coefficient of the longitudinal wave sound pressure obtained by actual measurement l (f；d,V 2l ) I and amplitude spectrum R of reflection coefficient of sound pressure of longitudinal wave obtained by theoretical calculation l (f；d,V 2l )| * The two-parameter inversion is performed within the-6 dB effective band. FIG. 6 shows the magnitude spectrum | R of the reflection coefficient of the sound pressure of the longitudinal wave l (f；d,V 2l ) Data in the effective frequency band and inversion results. By reading the relational numbers eta (d, V) in FIGS. 6 (b) and 6 (c) 2l ) The coordinate of the maximum value position can determine the coating thickness d and the longitudinal wave sound velocity V 2l The best inversion results of (1) are 288 μm and 5140m/s.
FIG. 7 (a) shows the inverted thickness value d of all collected data of WC abrasion-resistant coating samples, the thickness fluctuates between 255 μm and 293 μm, and the coating thickness on the right side of the samples is slightly larger than that on the left side. To avoid errors in ultrasonic and metallographic observations due to positional misalignment, ultrasonic thickness measurements taken throughout the coating are compared with SEM metallographic observations as shown in fig. 7 (b). The result shows that the relative error between the ultrasonic thickness measurement result and the metallographic observation result fluctuates between-9.3% and 4.3%.
Step e, combining the coating thickness d inverted in the step d, and reading the amplitude spectrum | R of the transverse wave sound pressure reflection coefficient in the step c t (f；d,V 2t ) I corresponding to the resonant frequency f 2t Is 12.875MHz. The thickness d obtained by inverting the thickness d is substituted into the formula (5) to obtain the transverse wave sound velocity value V of the WC wear-resistant coating 2t =3226m/s. Fig. 8 shows measured longitudinal wave acoustic velocity and transverse wave acoustic velocity of all collected data of the WC wear specimens. D, averaging the thickness d of the WC wear-resistant coating measured in the steps d and e and the longitudinal wave sound velocity V 2t Mean and transverse velocity V 2t Average value and bulk material density thereof are 14.3kg/m 3 Substituting into the formula (6), the elastic modulus E of the WC wear-resistant coating is calculated to be 331GPa.
Step f, as shown in fig. 9, a metallographic picture of a cross section of the WC wear-resistant coating is obtained through an SEM analysis technology, the porosity p =4.67% corresponding to the metallographic picture of the sample of the WC wear-resistant coating is counted through a median filtering and binarization image processing method, and the formula rho = rho% of the influence of the porosity on the material density is calculated according to the formula rho = rho 2 (1-p) correcting the elastic modulus of the WC wear-resistant coating calculated in the step f, wherein the correction result isE =315GPa. The absolute error between the measurement result and the elastic modulus of 300GPa measured by the nano indentation method is 5%.
Claims (1)
1. A method for measuring the thickness and the elastic modulus of a wear-resistant coating in an ultrasonic nondestructive mode adopts a system for measuring the thickness and the elastic modulus of the wear-resistant coating by an ultrasonic pulse echo method, wherein the system comprises a water tank (1), a sample table (2), a wear-resistant coating sample (3), a water immersion focusing probe (4), an X-Y-Z three-dimensional stepping control device (5), an ultrasonic flaw detector (6), a digital oscilloscope (7) and a computer (8), and is characterized in that: the method comprises the following steps:
(a) Determining an angle of incidence alpha <5 deg. for a water immersion focusing probe
Putting a stainless steel sample with known thickness on a sample table (2) in a water tank (1), controlling the relative position between a water immersion focusing probe (4) and the sample by adopting an X-Y-Z three-dimensional stepping device (5), focusing the focus of the water immersion focusing probe (4) on the surface of the stainless steel sample, exciting the water immersion focusing probe (4) by utilizing an ultrasonic flaw detector (6), acquiring signal waveform by adopting a digital oscilloscope (7), and recording the surface echo P of the stainless steel sample at the moment 0 Acoustic time of (a) t 1 And the bottom surface reflects the longitudinal wave P 1 Corresponding acoustic time t 2 Knowing the longitudinal acoustic velocity V of the stainless steel sample 1l Longitudinal acoustic velocity V with water 3l Combined with the propagation time t of the ultrasonic longitudinal wave in the stainless steel sample 12 ＝t 2 -t 1 Calculating the incident angle alpha of the water immersion focusing probe (4) by utilizing the Snell's theorem;
(b) When ultrasonic waves are obliquely incident to a water/metal matrix/wear-resistant coating/water multi-interface structure formed by coupling medium water and a coating sample at an angle alpha, obtaining a reflection coefficient equation of each interface:
wherein alpha is l And alpha t Angle of reflection, beta, of longitudinal and transverse waves, respectively, at the interface l And beta t Transmission angles, λ, of longitudinal and transverse waves at the interface, respectively 1 、μ 1 And λ 2 、μ 2 Is Lame constant of material, k is wave number corresponding to ultrasonic wave, k =2 pi f/V, V is sound velocity of medium, f is ultrasonic frequency, R is l 、R t And T l 、T t The reflection and transmission coefficients of longitudinal waves and transverse waves are respectively; when the ultrasonic waves incident to each interface are in a longitudinal wave mode, the matrix a is:
a＝[-cosα l sinα l k l1 (λ 1 +2μ 1 )cos2α l -k l1 μ 1 sin2α l ]' (2) determining elastic parameters of sound velocity and density value at each interface by combining the formulas (1) to (2), and calculating the coefficient R of longitudinal wave reflected by the interface l Coefficient of reflected transverse wave R t Coefficient of transmitted longitudinal wave T l And coefficient of transmitted transverse wave T t ；
(c) Focusing the focus of the water immersion focusing probe (4) on the wear-resistant coating/water interface, and effectively identifying and extracting the reflected longitudinal waves P of the front and rear interfaces of the coating by a digital oscilloscope according to the wave type conversion rule given in the step (b) l1 、P l2 And reflected transverse wave P at front and back interfaces of the coating t1 、P t2 (ii) a And (3) carrying out Fourier transform on the acquired signals by using a computer (8) to respectively obtain a coating longitudinal wave sound pressure reflection coefficient amplitude spectrum and a coating transverse wave sound pressure reflection coefficient amplitude spectrum:
wherein the lower corner marks 1, 2 and 3 respectively represent a metal matrix, a wear-resistant coating and coupling medium water, d is the thickness of the wear-resistant coating, r is 12 、r 23 The sound pressure reflection coefficients of the corresponding interfaces are respectively expressed asRho is the density of the corresponding medium;
(d) Longitudinal wave sound velocity V of coupling medium water 3l And density ρ 3 And the longitudinal wave sound velocity V of the metal substrate 1l And density ρ 1 By passingAcoustic handbook or measured by experimental method, density p of abrasion resistant coating 2 Adopting the density value of the material block body, the magnitude spectrum | R (f; d, V) of the longitudinal wave sound pressure reflection coefficient obtained in the step (c) 2l ) L is only the thickness d of the coating and the sound velocity V of the coating 2l The cross-correlation operation shown in formula (4) is utilized to obtain the amplitude spectrum | R (f; d, V) of the reflection coefficient of the sound pressure of the longitudinal wave obtained by the actual measurement 2l ) And the amplitude spectrum | R (f; d, V 2l )| * Carrying out two-parameter inversion in a-6 dB effective frequency band;
wherein, N represents the number of data points in the effective frequency band range of the time domain signal after FFT, and the lower corner mark i represents the ith frequency value;andrespectively the arithmetic mean values of the actually measured and theoretical sound pressure reflection coefficient magnitude spectrums in the effective frequency band; by imparting a wear-resistant coating thickness d and a longitudinal acoustic velocity V 2l Obtaining theoretical sound pressure reflection coefficient amplitude spectrum matrix by a series of continuous change values, using the theoretical sound pressure reflection coefficient amplitude spectrum matrix as a parent body, carrying out cross-correlation analysis on the actually measured sound pressure reflection coefficient amplitude spectra one by one, and carrying out d and V corresponding to the maximum positions in the correlation coefficient matrix 2l The optimal inversion result of the thickness of the wear-resistant coating to be measured and the longitudinal wave sound velocity is obtained;
(e) Combining the coating thickness d inverted in the step (d), and reading the transverse wave sound pressure reflection coefficient amplitude spectrum URCAS in the step (c) t Corresponding resonance frequency f nt The value of (c):
wherein V 2t The transverse wave sound velocity of the coating is obtained, n is the order of the resonant frequency, the thickness d obtained by inversion is substituted into a formula (5) to obtain the transverse wave sound velocity value V of the wear-resistant coating 2t The longitudinal wave sound velocity V obtained by calculation 2l Transverse wave velocity V 2t And wear-resistant coating density rho 2 Substituting the elastic modulus E into a calculation formula (6), namely calculating the elastic modulus of the coating;
(f) Acquiring a metallographic photograph of a section of the wear-resistant coating by adopting a metallographic analysis technology, counting the porosity p corresponding to a wear-resistant coating sample by adopting a median filtering and binarization image processing method, and according to a formula rho = rho of the influence of the porosity on the material density 2 (1-p) correcting the elastic modulus of the wear-resistant coating, wherein the correction result is as follows:
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