CN102520058A - Metal magnetic memory detection method based on metal in-situ crystallography and magnetic domain characterization - Google Patents

Abstract

The invention discloses a metal magnetic memory detection method based on metal in-situ crystallography and magnetic domain characterization, belonging to the research field of metal magnetic memory nondestructive detection. The method is characterized by using a metal material itself as a research object, acquiring the corresponding magnetic domain images by bitter powder pattern method under different stress states (different stretching stages or different fatigue cycle numbers), and acquiring SEM morphology, orientation and other crystallographic information by using an SEM-EBSD system, so as to acquiring the relationship among the crystallographic information, magnetic domain and stress of the metal material. According to the method, by combining the metal material itself, the material microscopic dimension magnetic signal magnitude, magnetic moment direction and crystallographic information are acquired, and the influence of other factors aside from the material itself is removed, thus the method has good reliability and overcomes the errors in the particle application.

Description

A kind of method based on in-situ metal crystallography and magnetic domain characterizing metal magnetic memory detection

Technical field

The present invention relates to method, belong to the nondestructive test with metal magnetic memory research field based on metal " original position " crystallography and magnetic domain characterizing metal magnetic memory detection.

Background technology

At present, metal material is widely used in industries such as Aeronautics and Astronautics, electric power, petrochemical industry, railway, boilers and pressure vessel.Hardware and equipment in use very easily destroy under stress corrosion, and as easy as rolling off a log causing a serious accident.So effective Dynamic Non-Destruction Measurement is the emphasis of studying at present.Conventional lossless detection method (like ray, ultrasonic, magnetic and infiltration detection etc.) can only detect the gross imperfection of certain size, is difficult to find microdefect.And metal magnetic memory detection technology can detect the stress that possibly bring out damage or destroy (like undercarriage, aircraft crossbeam, locomotive, rail, station boiler and pressure vessel, pipeline etc.) and concentrates the position, for the early diagnosis of equipment provides foundation.Therefore, it has caused vast Non-Destructive Testing worker's very big interest.Metal magnetic memory detection technology is based on the magnetic leakage signal that the concentrated zone of component stress occurs; Its tangential component Hp (x) has maximal value, and normal component Hp (y) changes direction and has the zero passage point value, and promptly the area of stress concentration on the detected object surface generates such theory of stray field gradient; But in the applying detection of reality, find; Be not the certain zero crossing of value of the Hp (y) of region of stress concentration,, remain further research so should theory also need constantly perfectly.And at present the research majority of this method is rested on macroscopical field, seldom it is studied from microscopic fields (micro/nano level).Effective microexamination method has good promote significance to the development of this technology.At present SEM-EBSD (scanning-EBSD) system is successfully to apply to microscopic fields analysis such as material crystals; And bitter powder pattern method successfully applies to the metal material magnetic domain and observes, and this magnetic domain pattern can reflect the size and Orientation of metal surface magnetic.Based on these two possible technique conditions, the present invention proposes under different stress, the relevance of metal material microcrystallography and magnetic domain is introduced the magnetic memory study.Under the different stress effect, the magnetic domain of original position research metal material and the Changing Pattern between the crystallography reach the purpose of characterizing metal magnetic memory detecting method, and reliable theoretical foundation are provided for the magnetic accumulating method.

Summary of the invention

The purpose of this invention is to provide a kind of brand-new " original position " research metal material stress state, crystallography and magnetic domain Changing Pattern and remember the method for Non-Destructive Testing with characterizing metal magnetic.

The present invention with metal material itself as research object; Under different stress (stretching different phase or tired different number of times); Utilize bitter powder pattern method to record corresponding magnetic domain figure, utilize the SEM-EBSD system to record crystallography information such as SEM pattern and orientation.Thereby obtain the crystallography information of metal material, the relation of magnetic domain and stress, this method specifically comprises the steps:

1) with metal material as research object; With the sample under different stretch or the fatigue state, sample is carried out 100-2000 sand paper by roughly grinding correct grinding, until almost there not being cut; Use 8% perchloric acid acetate electropolishing then, glossing is: anodic current density is 71.4A/dm ², polishing time is 50s-60s; With 3% nitric acid alcohol corrosion sample 3s-5s, obtain initial sample in apparent good order and condition at last; Obtain the magnetic domain figure of sample through Bitter powder pattern method, thereby obtain the direction of sample surfaces magnetic signal size and magnetic moment, and then set up the one-to-one relationship of the direction of sample interior stress under different stretch stage or the different fatigue state-magnetic signal size and magnetic moment;

2) with the SEM original position that is equipped with EBSD (observing the same research microcell of magnetic domain in (1)) measure with corresponding draw stage of step (1) or fatigue state under tissue topography, grain orientation crystallography information, and then the one-to-one relationship of the corresponding stress-tissue topography of sample, grain orientation crystallography information under foundation and different stretch stage or the different fatigue state;

3) integrating step (1) and (2); Direction, tissue topography and the grain orientation crystallography information of the stress under same draw stage or the fatigue state, magnetic signal size and magnetic moment is corresponding one by one; Obtain the one-to-one relationship of microcrystallography and magnetic information under the different stress, finally obtain the purpose of characterizing metal magnetic memory Non-Destructive Testing.

Above-mentioned steps 2) and 3) described grain orientation crystallography preferably adopts the crystal grain average orientation difference GAM of whole analyzed area to represent that its formula is following:

The quantity m of the inner misorientation data of each crystal grain is determined by following formula:

$m=\frac{1}{2}\underset{i=1}{\overset{n}{\mathrm{\Σ}}}{p}_i$ Wherein n refers to the pixel number that crystal grain is inner, and pi refers to count with the i adjacent pixels;

The inner average orientation difference β of crystal grain is defined as:

$\mathrm{\β}=\frac{1}{m}\underset{j=1}{\overset{m}{\mathrm{\Σ}}}{\mathrm{\θ}}_j$ θ j refers to consecutive point misorientation numerical value;

The crystal grain average orientation difference GAM of whole analyzed area is:

$\mathrm{GAM}=\left\{\underset{K=1}{\overset{N}{\mathrm{\Σ}}}\left({\mathrm{\β}}_k{A}_k\right)\right\}/\underset{K=1}{\overset{N}{\mathrm{\Σ}}}{A}_k$

Wherein N is the number of crystal grain in the analyzed area, and Ak is the area of crystal grain K.

Metal magnetic memory detection technology is based on the magnetic leakage signal that the concentrated zone of component stress occurs; Its tangential component Hp (x) has maximal value; And normal component Hp (y) changes direction and has the zero passage point value, but in the applying detection of reality, finds, is not the certain zero crossing of value of the Hp (y) of region of stress concentration; The present invention introduces the magnetic memory with the relevance of metal material microcrystallography and magnetic domain, has overcome the error in the above-mentioned practical application.

The present invention has following advantage:

1. the present invention is easy and simple to handle, and is simple and clear, and magnetic signal under the different stress conditions of metal material is showed the memory of characterizing metal magnetic through the magnetic domain pattern, novel in design and reasonable.

2. the present invention combines metal material itself to obtain the direction and the crystallography information of material micro-scale magnetic signal size and magnetic moment, and the interference of having removed other factors beyond the material itself has good reliability.

3. the present invention adopts " original position " research method, more helps continuity research is carried out at same position.

4. along with STRESS VARIATION or produce stress and concentrate sample surfaces magnetic domain pattern to change, also can image express stress concentrate with magnetic sample signal magnitude and magnetic moment direction between Changing Pattern, can be accurately from microscopic fields characterizing metal magnetic memory detection.

Description of drawings

Fig. 1: the scintigram when selected materials Q235 steel is differently strained;

(a)-(d) being respectively strain is 0.0%, 0.3%, 0.6%, 0.9% o'clock SEM figure;

Fig. 2: EBSD was orientated to image pattern when selected materials Q235 steel was differently strained;

(a)-(d) being respectively strain is 0.0%, 0.3%, 0.6%, 0.9% o'clock EBSD grain orientation figure;

Fig. 3: magnetic domain picture when selected materials Q235 steel is differently strained;

(a)-(d) being respectively strain is 0.0%, 0.3%, 0.6%, 0.9% o'clock magnetic domain picture.

Embodiment

Concrete research method of the present invention is following: following examples adopt iron and steel as research material, according to GB under stretching different phase and tired different number of times, with uniaxial tension machine or fatigue machine to the metal material stress application, preparation stretching or fatigue samples.

1. stretch or the fatigue samples preparation: look into GB, hot rolled steel plate is designed stretching or the fatigue testing specimen of length and width size＜40mm * 10mm on request, stress relief annealing under the technology that is fit to then reaches the service state of material.Sample is carried out 100-2000 sand paper by roughly grinding correct grinding, until almost there not being cut, use 8% perchloric acid acetate electropolishing then, glossing is: anodic current density is 71.4A/dm ², polishing time is 50s-60s.With 3% nitric acid alcohol corrosion sample 3s-5s, obtain initial sample in apparent good order and condition at last.

2. a small electron microscopic impression is stamped on the initial sample surface; So that study the variation of this microcell (below be called regional A); In the SEM-EBSD system, record earlier regional A sweep figure and be orientated to image pattern, add at sample surfaces that magnetic flaw detection ink covers then and take the magnetic domain shape appearance figure below the microslide light microscopic.

3. sample is carried out uniaxial tension or torture test, under different stretch degree or times of fatigue, the scintigram of measured zone A and be orientated to image pattern adds that at sample surfaces magnetic flaw detection ink covers shooting area A magnetic domain shape appearance figure below the microslide light microscopic then.

4. finally obtain the scanning picture under different stretch degree or the times of fatigue, EBSD is orientated to crystallography information and magnetic domain shape appearance figures such as image pattern.

If the quantity m of the inner misorientation data of each crystal grain is determined by following formula:

$m=\frac{1}{2}\underset{i=1}{\overset{n}{\mathrm{\Σ}}}{p}_i$

Wherein n refers to the pixel number that crystal grain is inner, and pi refers to count with the i adjacent pixels.The inner average orientation difference β of crystal grain is defined as:

$\mathrm{\β}=\frac{1}{m}\underset{j=1}{\overset{m}{\mathrm{\Σ}}}{\mathrm{\θ}}_j$

θ j refers to consecutive point misorientation numerical value.The crystal grain average orientation of whole analyzed area poor (Grain average misorientation GAM) is defined as:

$\mathrm{GAM}=\left\{\underset{K=1}{\overset{N}{\mathrm{\Σ}}}\left({\mathrm{\β}}_k{A}_k\right)\right\}/\underset{K=1}{\overset{N}{\mathrm{\Σ}}}{A}_k$

Wherein N is the number of crystal grain in the analyzed area, and Ak is the area of crystal grain K.

Through more also can exploring crystallography under the different stress-magnetic domain Changing Pattern, thereby the memory of characterizing metal magnetic detects.

Embodiment 1

With a kind of ferrous materials, apply drawing stress

Select typical steel iron material Q235; Adopt above method to prepare sample, stamp the electron microscopic impression as survey region B, original state (not carrying out tension test) records the area B scintigram in the SEM-EBSD system; See Fig. 1 (a) and be orientated to image pattern; See Fig. 2 (a), magnetic flaw detection ink covers shooting area B magnetic domain shape appearance figure below the microslide light microscopic under light microscopic, sees Fig. 3 (a); Then sample being stretched to strain on the uniaxial tension machine is 0.3% o'clock, and the scintigram of measured zone B is seen Fig. 1 (b) and is orientated to image pattern, and see Fig. 2 (b), the magnetic domain shape appearance figure is seen Fig. 3 (b); In like manner respectively sample was stretched to dependent variable at 0.6%, 0.9% o'clock, records the scintigram of area B, see Fig. 1 (c), (d) be orientated to image pattern; See Fig. 2 (c), (d), the magnetic domain shape appearance figure is seen Fig. 3 (c); (d), above-mentioned through GAM calculate can be 0.0%, 0.3%, 0.6% in tensile strain; Get GAM 0.9% time and be respectively 0.325471 °, 0.415463 °, 0.487463 °, 0.536524 °.

Test findings shows; Under different tensile strain conditions; Variation has taken place in the microstructure pattern and the crystalline orientation of material, and great changes have also taken place the pattern of magnetic domain, explains that different stretch stress is influential to the size and the magnetic moment direction of the crystallography information of material and material magnetic signal thereof; And variation along with drawing stress; Material microcrystallography and magnetic domain information change demonstrate certain rules property, and study its regularity and can probe into the influence of drawing stress sample crystallography and magnetic information, thus the well-characterized metal magnetic memory.

Embodiment 2

With a kind of ferrous materials, apply fatigue stress

Compare with embodiment 1, embodiment 2 has changed the mode of stress application, adopts fatigue loading mode (promptly periodically loading).Because one of main failure forms that the fatigue failure of ferrous materials is a hardware lost efficacy, the Changing Pattern characterizing metal magnetic memory of crystallography and magnetic information highly significant under the research fatigue loading mode.For making the fatigue stress that applies meaningful, the present invention is set at 0.7 σ s (σ s is a YIELD STRENGTH) with tired maximum load simulation steel part military service process, and stress ratio is 0.1 to draw fatigue loading mode.Under different times of fatigue, measure the SEM figure of material, orientation maps, the magnetic domain picture, all the other steps and analytical approach are with embodiment 1.

Claims (2)

1. the method based on in-situ metal crystallography and magnetic domain characterizing metal magnetic memory detection is characterized in that, comprises the steps:

1) with metal material as research object; With the sample under different stretch or the fatigue state; Obtain the magnetic domain figure of sample through Bitter powder pattern method; Thereby obtain the direction of sample surfaces magnetic signal size and magnetic moment, and then set up the one-to-one relationship of the direction of sample interior stress under different stretch stage or the different fatigue state-magnetic signal size and magnetic moment;

2) with the SEM in-site detecting that is equipped with EBSD and the tissue topography under corresponding draw stage of step (1) or the fatigue state, grain orientation crystallography information, and then the one-to-one relationship of the corresponding stress-tissue topography of sample, grain orientation crystallography information under foundation and different stretch stage or the different fatigue state;

3) integrating step (1) and (2); Direction, tissue topography and the grain orientation crystallography information of the stress under same draw stage or the fatigue state, magnetic signal size and magnetic moment is corresponding one by one; Obtain the one-to-one relationship of microcrystallography and magnetic information under the different stress, finally obtain with crystallography and magnetic domain characterizing metal magnetic memory Non-Destructive Testing; Wherein the original position of step (2) refers to and the middle same research microcell of magnetic domain of observing of step (1).

2. according to the method for claim 1, it is characterized in that step 2) and 3) described grain orientation crystallography information preferably adopts the crystal grain average orientation difference GAM of whole analyzed area to represent that its formula is following:

The quantity m of the inner misorientation data of each crystal grain is determined by following formula:

wherein n refers to the pixel number that crystal grain is inner, and pi refers to count with the i adjacent pixels;

The inner average orientation difference β of crystal grain is defined as:

θ j refers to consecutive point misorientation numerical value;

The crystal grain average orientation difference GAM of whole analyzed area is:

Wherein N is the number of crystal grain in the analyzed area, and Ak is the area of crystal grain K.

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