Method of photometric diagnosis phase transitions in solid bodies based on analysis data of luminance spectra of light reflected from surfaces thereof

FIELD: physics, optics.

SUBSTANCE: invention relates to methods of determining physical conditions at which phase transitions in metals and alloys take place. The method is based on joint analysis of the image of fragments of the surface of analysed material and luminance spectra of visible light reflected from the said surface, taken before and after the external physical action causing the phase transition. The analysis results are processed using special computer software.

EFFECT: invention simplifies diagnosis of phase transitions, increases accuracy and degree of automation of processing experimental results.

11 dwg

 

The present invention relates to methods for determining the physical conditions under which the test material develops a phase transition, and the parameters characterizing the kinetics. In physical science and in practice, thermal, mechanical and thermal processing of structural materials the processing modes through which is formed the desired level of properties is carried out by results of the analysis of the structural condition of the materials, including, according to the phase analysis. Under phase is commonly understood as a homogeneous part of the material system, which is separated from other parts of the interphase boundary. The point of phase transformations of substances are determined by the curves change their structure-dependent characteristics in function of the intensity of the external energy of the impact, which can cause a change in the phase composition of the system. Since the development of the methods of physico-chemical analysis of metal alloys Kournakova NS (NS Kurnakov Introduction to physico-chemical analysis. M: From the USSR, 1940; Anosov VA, Ozerov M.I., Violet YA Basis of physico-chemical analysis. M.: Nauka, 1978. 503 S.) points of phase transitions is determined by the characteristic kinks on the curves of dependence of some physical properties that are distinguished by good reproducibility re is Ulatov measurement, in function of the parameter characterizing the intensity of external influences (temperature, magnetic field strength, the content of the alloying element, the magnitude of plastic deformation and so on). The formation of phases associated with a certain type of interatomic interactions, which determine the type of crystal lattice phase, its chemical composition and, ultimately, all of its physical characteristics. The nature of interatomic bonds is primarily due to the electronic structure of atoms, which entered into cooperation. Reflectivity of light waves from a solid surface as dictated by the electronic structure of the atoms of which they are composed, as an elementary act of reflection incident on the surface of photons is their dispersion in the valence electrons of the material. The angles and intensity of scattering is directly dependent on the surface microrelief solid and chemical nature of the atoms on it. These factors determine the balance of reflection and absorption of light by the object of research. The technical result of the proposed invention is its ability to define the points of phase transitions and kinetic parameters of the transitions with the aid of computer analysis of the reflectance spectra. This result is achieved in that the surface of the examined body is photographed before and after EXT is its physical impact, caller phase transition. Obtain images of the surface are translated into a digital code, is entered into the computer, where they are removed spectra brightness, reflections from external light sources, which are analyzed with the help of special computer programs, decomposing the spectra into separate intervals that characterize a certain intensity acts of his scattering and absorption. These intervals range are ranked according to their degree of brightness that allows you to set the interval with the highest reflective or absorptive capacity and to obtain the appropriate authentic assessment of their spectral density of the brightness of the reflection. On them are built according to the average for the selected range of spectral densities of the brightness of the reflection intensity of external influence. According to the research points excesses and extremes of the dependences indicate phase transitions. Integrated surface condition can be characterized by the range of brightness of the reflection from her visible light or monochromatic components, which can be visualized as a graph in the coordinate spectral density of the brightness of the reflection - brightness (intensity) of the reflection". Correlation analysis of the dependence of the spectral density of the brightness of the reflection in a given interval of brightness from online is newnote external influences allows to detect the interval, most sensitive to changes in external forcing. This gives you the opportunity to build a kinetic curve changes of the spectral density of the brightness of the reflection at the chosen intensity of the external impact or the curve of the dependence of the spectral density of the brightness of the reflection intensity of external influence when it is specified duration. A salient point on these curves indicate the phase transformations occurring in the studied solid, under specified conditions, as the acts of reflection of light waves from solids are implemented by means of free electrons on their surface, and the concentration of the latter directly from the type of crystalline lattice of the material and the electronic structure of its atoms. The experiments showed the high sensitivity of the reflectivity of the light to change settings of external influence, good reproducibility of their measurements, greater simplicity and reliability compared with other methods of physical measurements of properties suitable for the definition of points and intervals of phase transitions (dilatometry, electrical resistivity, x-ray analysis).

The proposed method photometric diagnostic phase transformations is the analysis of the spectra of the brightness of reflected light incident on the investigated surfaces shall be of material from an external source to an external physical impact, caller phase transformations in the material and after each of its modes. According to the results of scanning the sample surface of the sample, represented as a graph of the spectral density of the brightness of the reflection corresponding to the brightness of the reflection using correlation analysis found the interval of the brightness of the subject changes with the highest correlation coefficient with a variable parameter mode external influences ((Tj- the temperature and duration of annealing, plastic deformation, the magnetic field strength, etc). Defines the average value of the relative spectral density of the brightness of the reflection in the selected interval of the brightness of ai(I) for all intensity levels of external influences, which were used in the performed series of experiments. Received two data arrays {i(I)} and {Tj} cost dependence of ai(I)=f(Tj), point breaks which are the values of the parameters of external influence, in which phase transitions occur. As an example, consider the evolution of structural changes in the aluminium alloy AK-8 half-hour isothermal annealing in the temperature range 293-714, 3K.

Figure 1 shows an image of the surface of the sample alloy at room temperature (293 K, painted in accordance with the results of the analysis of the spectrum of the brightness of reflected visible light from an external source (figure 2). The spectrum allocated three intervals brightness: 1 - (highlighted in black) corresponds to the area of the spectrum with an increased absorption of the visible light from the light source, which illuminates a surface of the sample; 2 - (highlighted in white) - corresponds to the area of the spectrum with higher brightness, reflections from the surface of the sample; 3 - (gray) - corresponds to the interval surrounding area of the spectrum maximum brightness of the reflection. Figure 3 shows the surface of the same alloy, but at a temperature of 714, 3K. In comparison with figure 1 you can see qualitative changes in the investigated alloy under the influence of annealing. Not less notable changes under the influence of annealing occurred in the spectrum of the brightness of the reflection (figure 4). In particular, almost completely disappeared the third interval of the spectrum, whereas in the rst interval, the spectral density of the brightness of reflected increased significantly. Figure 5 shows the temperature dependence of the average spectral density of the reflection from the sample surface in intervals 2 and 3, the spectrum of the brightness of the reflection. You can see the non-monotonic nature of these dependencies, which introduces ambiguity in the determination of the temperature at which the possible phase transformations. Unlike data, while the data in figure 5, the temperature dependence of the spectral density of the brightness of the reflection at the first interval is monotonous character, leading to higher values of correlation coefficients between the values of the temperature of annealing and the corresponding increments of the spectral density of reflection. Figure 6 shows the temperature dependence of the rate of change of the spectral density of the brightness of the reflection in the first interval of the spectrum for aluminum alloy AK-8. The figure shows that the fracture is given as a function accounts for T=K and, consequently, it is at this temperature, we should expect the phase transformation. As another example illustrating the present method of determining the critical temperatures of phase transitions, it is possible to bring the temperature evolution of the structural state of nanostructure-based alloy system Zr-Nb-Cu-Fe. When heated in the diffusion processes in this alloy there is a transition from nanocrystalline state in polycrystalline coarse-grained state. 7 shows the structure of the alloy in the initial state, and Fig - range brightness of the reflection of visible light from its surface at room temperature. In figures 9 and 10 show respectively the structure and range of the brightness of the reflection from the surface of the investigated alloy at T=20°C after annealing 360°With the a period of 20 minutes It is seen that the structural state of the alloy has undergone significant quantitative and qualitative changes caused by temperature effects. Figure 11 shows the temperature dependence of the average spectral densities of the brightness of the reflection from the surface of this alloy when heated in the temperature range 20-420°C. At a temperature of 380°C clearly show the sharp change in the slope of these dependencies, which indicates that the phase change alloy in the vicinity of this temperature. This is evident on both dependencies, but more sharp phase transition is expressed for dependencies related to the interval of the spectrum with increased absorption.

The way photometric diagnostic phase transformations in solids according to the analysis of spectra of light reflected from their surfaces, concluding that the surface of the investigated solids before and after the external physical impact on him photographed with a digital camera, the photographic images are removed spectra brightness reflect light from external light sources, which are analyzed by computer programs that divide the range of the brightness of the reflection at separate intervals, opt them out of the interval, the most sensitive to external influences, calling phase transformation, calculate values of spectralinewater the brightness of the reflection for the specified intensity levels of external exposure in the specified interval of reflection and build dependencies of the spectral density of the brightness of the reflection as a function of intensity of external influence, wherein the inflection point and the extrema found by thus dependencies indicate phase transformations and determine the conditions of their implementation.



 

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