Diagnostics of flaws on metal surfaces

FIELD: metallurgy.

SUBSTANCE: gold cylindrical nanoparticles not over 100 nm in length are sprayed onto surface of tested object, depth of the ply of said particles allowing the filling of cavities of would-be fractures. Then, said surface is dried to remove sprayed ply therefrom. Then, object surface is subjected to non-interlaced scan by fs-laser beam. At a time, intensity of two-photon luminescence signal is registered in every area under analysis to fix the location of said area corresponding to object coordinate. 2D array of two-photon luminescence signal intensities is formed to produce the map of distribution of nanoparticle luminescence intensities excited by laser radiation.

EFFECT: possibility to reveal surface defects for their early detection.

3 cl, 7 dwg

The invention relates to methods of non-destructive testing, in particular, to the determination of defects and cracks on the surface of the metal equipment and pipelines.

There is a method of nondestructive testing, consisting in the preparation of the object of control, shooting and observation of the object on the regions of the optical range from the extreme ultraviolet radiation to the far infrared radiation using ultra-wideband mirror optical lens, and in the process of observation capture an image of the inspection object using at least one matrix of the receiver in at least one camera capable of simultaneous or separate operation of the cameras, and transmit the obtained information about the test object using the interface on the computer, decode and analyze the resulting image, evaluate the results of inspection and determine the technical condition of the object (EN 2394227, 2008).

In a known solution to reduce the influence of the diffraction limit is proposed to obtain an image of the object in the ultraviolet spectral range from 220 nm).

The disadvantage of this method is the technological complexity of manufacturing ultra-wideband mirror optical lens capable of imaging on the matrix receiver with spatial resolution is the group of 220 nm. For imaging in the infrared wavelength range requires the use of specialized detectors, such as cameras. The resolution of the method in the IR range by 2 orders of magnitude lower than in the UV, due to the mentioned fundamental limitations. The disadvantages include the high cost of ultra-wideband mirror optical lens, and a matrix of receiver radiation in the infrared spectral region, low economic efficiency, the need for evacuation path from the test object to a matrix of the receiver.

A known method for detecting defects on the surface, is used to detect on the surface of the controlled objects defects of different origin, namely, that light radiation is directed onto the surface of a floating object, the exposure zone of the controlled object is formed by the intersection of light beams directed radiation with the normal projection area of each of them, a larger area maximum projection of the object from at least three identical sources in space equidistant from each other and from the center of the intersection of light fluxes, a controlled object moving uniformly and rectilinearly through the radiation zone, register the scattered and j the luminous flux of a photodetector with an area of the working surface, equal or greater area of the normal projection of the light flux, each of the photodetectors is located equidistant from the corresponding source in the course of the light flux. Registered luminous flux is converted into discrete electrical signals (for example, the quantization level), measured values of the estimates of the correlation between random values of the signals on each pair of sensors, and thus, the range of estimates of the correlation moments with the number of members determined by the number of possible combinations of pairs of photodetectors. By ranking it in ascending or descending order, receive continuously increasing or continuously decreasing the number of values of the estimates of the correlation moments (EN 2165612, 2000).

The disadvantage of this method is complicated mathematical interpretation of the acquired data, applicable to a perfectly smooth surface, evaluation of the presence of a defect made by the deviation of the values of the estimates of the correlation moments from the values of the estimates of the correlation moments, pre-calculated for a defect-free surface that {deviation} will be present in any surface irregularities (roughness). Another drawback of this method is necessary to calculate the values of the estimates of the correlation of chances for a defect-free surface is t, which differ from the controlled objects of different types. In addition, this method allows the scattering of radiation to establish the existence of a defect on the surface of the test object, but does not allow to estimate the size and position of the defects and their number.

A known method of measuring the topography of nanoscale conducting surface with photon elemental analysis of the material, including the determination of the 3-D profile of a semiconductor or metal surface when approaching along the vertical Z coordinate of the probe with metal nanostream, while the irradiated surface under nanostream probe tunable wavelength optical radiation in the range from IR to UV with a constant spectral power of radiation, fix the value of the wavelength λ_gcorresponding to the boundary, a sharp increase in the magnitude of the tunneling current, and determine the material of the semiconductor or metal on the value of the energy width of the forbidden band of the semiconductor E_gor work output And electrons from the metal in the local region of the surface (RU 2426135, 2010).

The disadvantage of this method is the low speed scanning of the sample surface, due to the complexity of managing nanostream probe and the target speed on the vertical coordinate Z in the nanoscale is assabah (needle should "be able to track the change in height of the surface profile of the moving image, otherwise it will collide with the surface and the needle cantilever down). The speed of scanning devices such as atomic force microscope does not exceed 1 mm/sec.

Known technical solutions closest to the proposed to the technical essence and the achieved result is a method for determining surface defects, which consists in coating the surface of nanopaste of photoluminous, which can be used Gd₂O₃:Eu, (Cd,Sr)TiO₃:Pr, Y₂O₃:Eu, Y₂O₃S:Eu, Zn(Ga,Al)₂O₄:Mn, Y₃(Al,Ga)₅O₁₂:Tb, Y₂SiO₅:Tb, ZnS:Cu,Al, Y₂SiO₅:Ce, ZnGa₂O₄, ZnS:Ag,Cl, after which the excess paste is removed from the surface so that the phosphor paste was only in the depth of the cracks, and then the sample is exposed to x-ray radiation, resulting in particles of the phosphors are excited and lumines cent at the characteristic wavelength. Luminescense radiation is detected with the photodetector and the detection of defects is judged by the presence or absence of luminescense radiation (US 2009180587, 2009).

However, the use of nanolaminates to detect microcracks imposes some limitations on the effective use of this method.

First, the way the Ogre is fullled by the possibility of fixing the cracks and allows to detect defects of large dimensions, i.e. the so-called fatigue cracks.

Secondly, no dependence of the optical properties of particles of phosphorus from their size and geometry is not possible to determine the sizes of cracks.

These shortcomings are a consequence of the fact that the quantum yield of secondary radiation nanoparticles with either method, the excitation will be much higher radiation phosphor.

Thirdly, obtaining photoluminous is quite energy-consuming process, since they are obtained by sintering in a furnace at temperatures above 1000°C for several hours.

The present invention is to provide a method of diagnostics of surface defects, providing early detection of cracks and other defects on metal surfaces.

This object is achieved in that in the method for the diagnosis of defects on metal surfaces beforehand on the surface of the test object is applied by coating the gold nanoparticles cylindrical shape with a length of not more than 100 nm and the thickness of the layer that provides the filling of cavities potential cracks then produce drying of the surface, followed by removing the layer deposition, and then perform row-by-row scanning the surface of an object beam of a femtosecond laser and simultaneously record the signal intensity of two-photon luminescence is ascentii in each study area, recording the location of the specified area, corresponding to the coordinate of the object, then form a two-dimensional array of values of signal intensity of two-photon luminescence with obtaining maps of the distribution of the intensities of luminescence of the nanoparticles generated by laser radiation, there is obtained a map of the area with a maximum value of light intensity, which is judged on the presence of cracks, while the spectra of secondary radiation and the difference of the coordinates of the extreme points of light determine the crack size and the shape of the area of illumination is judged on the crack geometry.

It is preferable to use the femtosecond laser infrared range of the spectrum.

It is advisable progressive scanning the surface of an object to carry out in increments of ~10^-6-10^-7m

Technical result achieved is to expand the functionality of a method for providing detection of cracks minimum size, i.e. at the stage of their origin due to the possibility of fixing the nanoparticles at their small concentrations, obtaining at the same time information about the coordinate of the crack, its size and geometric characteristics, and reducing energy consumption.

The method consists in the following.

To ensure early detection of cracks and other defects using gold nanoparticles cylindrical razmara is not more than 100 nm, thanks to its geometric characteristics and settings are property of the plasmon resonance.

Depending on the size and shape of the nanoparticles, they have characteristic peaks in absorption spectrum. These peaks can be unambiguously determine the presence of microcracks when even a minor content.

The use of gold nanoparticles cylindrical shape with a length of not more than 100 nm, enables you to fill cracks nanometer (sub-micron) size, i.e. at the stage of their origin and to perform early diagnosis of their education.

Due to its chemical nature, the gold nanoparticles are inert to oxidation by oxygen in the air for a long time to maintain its structure. Their reception is held at room temperature, which reduces energy consumption in the process of synthesis compared to fotoluminofore.

Gold nanoparticles have the highest quantum yield and radiation power (the number of photons that are displayed per unit of time).

Nanoparticles have the ability to significantly change the transmission, reflection, absorption and radiation at certain frequencies of the spectrum of electromagnetic radiation. These frequencies are uniquely linked to the size of the nanoparticles having the form of a rod (cylinder), and more precisely with respect to the rod length to its diameter.

Thus, the spectra of p is the absorption, reflection or radiation of the nanoparticles deposited on the surface of the sample, it is possible to identify defects and concentration of nanoparticles of a certain size more accurately (with nanometer/submicron resolution) to determine the size of the nanoparticles, filling defects on the sample surface, and hence the minimum size of the defects.

The method is as follows.

Nanoparticles of gold applied to the surface of the sample by spraying their solution, after which the surface is subjected to drying. Further from the surface mechanically removes the excess nanoparticles attached to the outside of microcracks. As a result, the gold nanoparticles remain only in the microcracks.

The method involves visual inspection of the sample surface (for selection of the study area on the sample), or using a camera, or the eyes of the operator to select the scan area. Then carry out a line-by-line scanning of the surface of the object beam femtosecond laser. Nanoparticles with the above geometrical parameters are excited by the radiation of a femtosecond laser and relax due to the properties of plasmon resonance in its ground state with the emission of photons mainly in the visible part of the spectrum. These photons are detected by a receiver of radiation, and the presence of, l the Bo absence of the optical signal can be concluded that presence on the sample surface microcracks, filled with nanometre gold.

Absorption spectrum of the nanoparticles has two distinct peaks corresponding transverse and longitudinal plasmon resonances. Cluster characteristics (length and aspect ratio of the cylinder) is pre-selected so that the frequency of the plasmon resonance coincided with, or was close to the frequency of the exciting femtosecond laser radiation.

In other words, the wavelength of the laser source should be at the maximum absorption of the nanoparticles. In this case, when the fixed energy of the laser pulse absorbed most of it (than without optimization of the parameters of the clusters under the wavelength of the source)that will provide proportionally more optical response of the nanoparticles in the form of brighter luminescence signal. For example, laser radiation with a wavelength of 1048 nm, pick up the gold nanoparticles, for which the longitudinal fashion on their absorption spectrum tends to this value, which corresponds to the gold nanorods with aspect ratio of length to diameter of the cylinder is about 5.5 to 6.5.

For excitation of the nanoparticles laser radiation focused on the target surface. The size of the focus area is determined by the parameters of laser radiation and an optical system focusing diameter of the laser beam, the wavelength of the s laser radiation, diameters of the optical system, the focal length of the optical system). The required condition of focus is the achievement of the values of power density on the sample surface, providing excitation radiation of two-photon luminescence of the nanoparticles. The diameter of the laser spot on the target surface can take values from hundreds of nanometers to tens of micrometers. The minimum size is determined by the diffraction properties of laser radiation, and the maximum required value of power density.

Use as excitation radiation of a femtosecond laser infrared range of the spectrum allows us to better discriminates the emission of nanoparticles from the spectral composition.

The lens optical system is used to collect radiation of two-photon luminescence emitted by the nanoparticles in the solid angle of 4π steradian. For registration it is recommended to use a lens with numerical aperture close to 1.

Collected radiation nanoparticles focuses on the radiation receiver. The radiation intensity of the nanoparticles determines the amplitude of the signal at the receiver of radiation. While line-by-line scanning of the sample surface with a laser beam, there is a clear correspondence between the coordinates of the laser beam on the sample surface and lying is neither a function of time, registered by the radiation detector with a time resolution.

The step of scanning the surface with a laser beam and the size of the laser spot determines the spatial resolution of the proposed method.

It is preferable to scan with a step equal to the diameter of the laser spot on the sample surface. In this case, the optimum speed of the process and the achieved spatial resolution is determined by the size of the laser spot. To measure the width of the crack factor of several tens to several hundreds of nanometers, is used the analysis of the spectral composition of radiation nanoparticles, described in detail in Example 2.

After the registration of the radiation nanoparticles form a two-dimensional array of values of signal intensity of two-photon luminescence, which is a map of the spatial distribution of intensities of illumination, there is obtained a map of the area with a maximum value of light intensity, which is judged on the presence of cracks. In the absence of cracks card is a uniform (smooth) box, and in the presence of microcracks on the surface of the sample card will contain a bright region, enabling one to obtain information about the location (coordinates), size and shape of the cracks.

Thus the difference of the coordinates of extreme choccolate glow determine the size of the crack, and the shape of the area of illumination is judged on the crack geometry.

The brightness of the light is determined by the concentration of the nanoparticles on the surface of the target.

Femtosecond laser infrared spectrum substantially extends the spectral range of operation (up to 950 nm), because it provides the best spectral selection of the radiation nanoparticles and avoids exposure of the receiver laser radiation.

As the radiation detector nanoparticles can be used in the receiver with a time resolution. The combination of a receiver with analog-to-digital Converter allows you to record the dynamics of the signal from nanolasers (the waveform).

Below are examples of specific implementations of the proposed method, which is illustrated by Fig.1-6.

Figure 1 shows an image of the sample surface with an artificially generated microcinema, Fig.2 shows a micrograph of the surface of the target with artificially generated microenable filled with nanoparticles: a) at the laser impact is outside the scope of micromanage (radiation luminescence nanoparticles absent), b) by laser action in the field of micromanage, figure 3 shows a model sample for the diagnosis of micro-cracks on the metal surface, figure 4 shows quarterspregnant intensity of luminescence of the nanoparticles on the surface of the sample, figure 5 shows a map of the intensity distribution of the illumination of the nanoparticles on the surface of the sample with markers indicating the boundaries of the upper light, figure 6 shows images of nanoparticles with different ratios of length to diameter:-1.5, b-2, C-2.5, figure 7 shows the absorption spectrum For (reflection R=1-K) gold nanoparticles (rods) in relative units with size ratio:-1.5, b-2, C-2.5.

Example 1

To confirm the performance of the method of detecting micro-cracks was conducted point impact of laser radiation in the region of the surface of the plate of steel grade X70 with nanoparticles of gold with the peak of the longitudinal plasmon resonance absorption spectrum in the region of 700 nm, corresponding to the ratio of length to diameter is ~2.3. On the surface of the steel sample by an ion beam were formed micromanage differ in length (from 70 to 100 μm) and width (0.5 to 3 microns).

The image of the sample surface obtained by electron microscope JEOL 2100, shown in Fig.1.

On the surface of the controlled sample was applied by coating the gold nanoparticles cylindrical shape with a thick layer, providing the filling of cavities of potential cracks then deleted the layer of the coating from the surface.

The sample surface was illuminated by a source of visible emitted is I (incandescent). Surface images were recorded on a CCD camera.

Fig.2 (a) shows the image surface in the visible region of the spectrum (rotated 90 degrees). The region of laser irradiation is indicated by the arrow.

Laser excitation of the nanoparticles stimulated the generation of secondary optical radiation (luminescence) nanoparticles in the field of laser exposure. This radiation is focused on the radiation detector (CCD camera). Fig.2 (b) shows that when exposed to laser radiation at micromanage containing nanoparticles, the latter was stimulated by the generation of secondary radiation (Fig.2 (b) is a bright area on the image indicated by the arrow.

Example 2

To obtain two-dimensional distribution of the radiation intensity of two-photon luminescence of gold nanoparticles was scanned model sample, which consisted of a plate of steel grade X70 size 15×10×2.7 mm with artificially generated microenable different width. The metal plate was polished and using focused ion beam cut micromanage sizes 70×0,5, 80×1, 90×2, 100×3 µm. Next, on the surface of the sprayed solution of the synthesized gold nanorods, giving peak longitudinal plasmon resonance absorption spectrum in the region of 700 nm, which corresponds to the ratio of length to diameter of the nano is terina approximately 2.3. The surface of the plate coated with gold nanorods dried, and then mechanically removed were not included in micromanage nanoparticles using filter paper. Figure 3 presents a photograph of the obtained sample for the study.

In our example we have used a femtosecond laser radiation (wavelength 1048 nm, pulse duration of 110 FS, pulse repetition frequency of 71 MHz). Laser radiation was focused on the sample surface in an area with a size of 0.5 micron. The energy density on the surface of the image was 6·10¹⁰W/cm².

The influence of laser radiation on the nanoparticles stimulated the generation of secondary radiation (luminescence) nanoparticles in the visible spectral range. This radiation is focused on a single channel detector is a photomultiplier tube (MELZ, PMT-85), which converts the luminous flux into an electrical signal. The signal amplitude is proportional to the light flux focused on the radiation receiver.

On the surface of the sample was defined research area corresponding to the image boundaries in figure 1, which amounted to 132×100 μm. The study was conducted by scanning the laser beam within the boundaries of the study area.

Scanning the sample with a laser beam was carried out line by line in the horizontal direction. Step scan is of the vertical 0.5 μm (determined by the diameter of the laser spot on the sample surface).

As a result of scanning of one line formed a one-dimensional array containing information about the intensity of secondary radiation nanoparticles. When scanning the specified area with a height of 100 μm in total, there were obtained n=100/0 .5 µm = 200 one-dimensional arrays.

From the received set of one-dimensional arrays formed a two-dimensional array. The number of rows in this two-dimensional array matches the number of the obtained one-dimensional arrays. The generated two-dimensional array to contain the information about the spatial distribution on the sample surface the intensity of the secondary radiation of the nanoparticles. Thus the coordinate of the element of the array is hard wired to the coordinates on the sample surface.

The obtained two-dimensional distribution is a map of the distribution of luminous intensity (figure 4) nanoparticles on the surface of the sample.

Bright areas in the figure correspond to clusters of nanoparticles on the surface of the sample. In this example, the bright regions are in the form of lines and correspond to the grooves on the surface of the investigated sample. The image brightness is proportional to the concentration of the nanoparticles in the appropriate place on the sample surface. Thus, the bright area on the image, you can detect the presence of microcracks.

Estimating the size of the microcracks can be carried out is carried out as follows:

The dimension of the formed two-dimensional array is (264, 200), i.e. 264 200 elements (or pixels) horizontally and vertically, respectively. The size of the scanned area on the sample surface is 132×100 μm. Thus, the increment of the coordinates of the array by one (or by 1 pixel) corresponds to the displacement at the sample surface to 0.5 μm. I.e. the formula to recalculate the coordinates of the element two-dimensional array in the coordinate on the surface of the scanned region of the sample (in microns) as follows

N_mcm=0.5·N_pics,

where N_mcm- coordinate point, expressed in μm, N_pics- coordinate array element, in pixels.

In other words, the scale factor in the conversion of coordinates from pixels to microns equal

K=5 μm/pixel.

Figure 5 markers D1 and D2 indicated at the top point (the least extent), the field of illumination of the nanoparticles. In parentheses are the coordinates of the elements of a two-dimensional array. For the origin of the selected upper left edge of the two-dimensional array representing a map of the intensity distribution of the illumination of the nanorods. So, the point D1 of the array has coordinates 19 and 23 horizontally and vertically, respectively. Point D2 of the array has coordinates 159 and 23 horizontally and vertically, respectively.

The length of the study area and the luminescence is determined by the difference of the coordinates of the extreme points of the region D2-D1 and is 159-19=140 pixels. Using the above scale factor, you can determine the extent of the region of illumination on the sample surface is 70 μm. Therefore, the length of the microcracks having a line shape and filled with nanoparticles, is 70 μm. The width of the considered area of the glow is 1 pixel, which corresponds to 0.5 μm on the surface of the target. Received about the same size as the upper micromanage formed on the surface of the test object.

However, in this example, the size of the laser spot was ~0.5 microns, limiting the spatial resolution of the method at the level of ~0.5 μm, and therefore, cracks smaller size will also have a width of 0.5 μm.

The definition of the transverse size of the crack nanometer size is carried out on the spectra of secondary radiation nanoparticles (absorption, scattering, luminescence), as the spectral composition of the radiation is uniquely correlated with the geometrical characteristics of the nanoparticles.

The surface of the object covered by nanoparticles with different (known in advance) the ratio of length to diameter. Procedure sample preparation is similar to stated previously.

Map is made in the illumination of the sample by the above method. On map luminescence nanoparticles laser beam moves to the crack.

After this poverhnostbyu not excited by the laser radiation, as radiation source a wide spectral range in the visible region (the simplest example is an incandescent lamp).

As the radiation detector is used the receiver with a spectral resolution (e.g., spectrometer), registering the composition of the secondary radiation.

Images of nanoparticles obtained using an electron microscope with a ratio of length to diameter of 1.5 to 2.5, and examples of their absorption spectra are shown in figure 6 and 7 respectively. As can be seen from Fig.7 specific geometry of the nanoparticles corresponds to a certain peak in the recorded spectrum. When applied to the surface of the sample solution containing various nanoparticles, the peaks on the recorded spectra will be blurred. However, the practical interest is the right (far) boundary peak, corresponding to the particle with the highest ratio of length to diameter. This value characterizes most large gold nanoparticles, which by their dimensions were able to penetrate into the crack of nanometer sizes. In the case of application to the surface of gold nanoparticles with a diameter of 15 nm, the rightmost peak in figure 7 corresponds to the length of nanoparticles 37.5 nm. Thus, we can conclude that the crack width is ~40 nm.

1. The way to diagnose defects on metal surfaces, which consists in the fact that PR is varicella on the surface of the test object is applied by coating the gold nanoparticles cylindrical shape with a length of not more than 100 nm and the thickness of the layer, providing for the filling of cavities potential cracks then produce drying of the surface, followed by removing the layer deposition, and then perform row-by-row scanning the surface of an object beam of a femtosecond laser and simultaneously record the signal intensity of two-photon luminescence in each study area, recording the location specified area corresponding to the coordinate of the object, and then form a two-dimensional array of values of signal intensity of two-photon luminescence with obtaining maps of the distribution of the intensities of luminescence of the nanoparticles generated by laser radiation, there is obtained a map of the area with a maximum value of light intensity, which is judged on the presence of cracks, while the spectra of secondary radiation and the difference between the coordinates of the endpoints light determines the size of the crack, and the shape of the area of illumination is judged on its geometry.

2. The method according to claim 1, characterized in that the use of femtosecond laser infrared range of the spectrum.

3. The method according to claim 1, characterized in that the line-by-line scanning of the surface of the object is performed with a scanning step of ~10^-6-10^-7m