JPH0534214A - Method for measuring residual stress of ceramic member - Google Patents

Abstract

PURPOSE:To obtain an nondestructive residual-stress measuring method for a ceramic member which can accurately measure the residual stress at the minute part of the ceramic member whose surface to be measured is the curved surface. CONSTITUTION:X rays are cast on the curved surface to be measured of a ceramic member. The residual stress of the ceramic member is measured based on the obtained diffracted X rays. With respect to the X rays which are cast on the curved surface of the ceramic member, the ratio d/D between the diameter (d) of a the region, on which the X rays are cast, and D, which is the value twice the radius of curvature of the curved surface is 1/15 or less.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a residual stress measuring method for a ceramic member having a curved surface.

[0002]

2. Description of the Related Art In recent years, ceramic members have been used for various component materials including electric / electronic component materials and structural component materials. Residual stress is measured as one means for evaluating the reliability of such a ceramic member.

That is, a ceramic member is often joined to a metal member and used as a composite member. However, if the difference in coefficient of thermal expansion between the ceramic member and the metal member is large, residual stress is generated in the vicinity of the bonding interface between the ceramic members. This residual stress causes a crack in the ceramic member and causes a destruction of the bonded body, or has a bad effect such that the bonding strength is lowered even if the bonded body is not broken. Therefore, measurement of residual stress is an important method for evaluating the reliability of the ceramic-metal bonded body.

The measurement of the residual stress of such a ceramic member is not limited to the application to the ceramic-metal bonded body,
The measurement of the residual stress caused by the manufacturing process such as the shape of the ceramic member and the sintering process and the processing process is also an important method as an evaluation method of the ceramic member.

As a method of measuring the residual stress of the ceramic member as described above, the lattice plane spacing of the crystal which changes in proportion to the magnitude of the residual stress is measured by X-ray diffraction.
The in ² ψ method and the like are known. This method using X-ray diffraction has been attracting attention as a reliability evaluation method because the residual stress can be measured nondestructively and the residual stress in a minute portion can be measured by making the X-ray flux fine.

[0006]

By the way, the above-mentioned X
The residual stress measurement method by line diffraction gives good results when the measurement surface of the ceramic member to be measured is a flat surface. When the measurement surface is a curved surface, there is a problem that the residual stress cannot be accurately measured.

That is, when the surface to be measured is a curved surface, especially when the radius of curvature is small, it becomes impossible for the diffracted X-rays to sufficiently satisfy the Bragg reflection condition, and the intensity of the diffracted X-ray peak decreases. Or, another reflection peak appears due to the interference effect or the like, and it becomes difficult to specify the diffracted X-ray peak used for the measurement, so that the residual stress value cannot be accurately determined. Therefore, the intensity of the diffracted X-ray peak has been increased by increasing the irradiation X-ray dose, etc., but this method also increases the peak intensity that becomes noise, and therefore the S / N ratio decreases, It has not been possible to obtain a reliable residual stress value.

On the other hand, when residual stress measurement is used as a quality evaluation means for the above-mentioned ceramic-metal bonded body, the generated stress differs depending on the distance from the bonding interface of the ceramic member and the position in the bonding interface direction, and Since it is known that the maximum principal stress of residual stress acts near the outer periphery of the bonded body near the interface, it is possible to confirm the reliability by measuring the residual stress of the minute part corresponding to each stress generation position. It is also important for reflection in design and manufacturing processes. Therefore, even for a ceramic member having a curved surface, there has been a strong demand for the development of a method capable of accurately obtaining the residual stress of a minute portion in a nondestructive manner.

The present invention has been made to address such a problem, and enables nondestructive and accurate measurement of residual stress in a minute portion of a ceramic member whose surface to be measured is a curved surface. An object of the present invention is to provide a method for measuring residual stress of a ceramic member as described above.

[0010]

That is, the method for measuring residual stress of a ceramic member according to the present invention comprises irradiating the curved surface of a ceramic member having a curved surface as a surface to be measured with X-rays,
In the method of measuring the residual stress of the ceramic member from the obtained diffracted X-rays, the X-ray radiated on the curved surface of the ceramic member has a diameter d in the irradiation region of this X-ray and is twice the radius of curvature of the curved surface. When the value is D, these ratios d / D are characterized by being 1/15 or less.

[0011]

In the residual stress measuring method of the present invention, the ratio d / D of the irradiation area diameter d of the X-rays radiated to the curved surface to be measured of the ceramic member and the value D which is twice the radius of curvature of the curved surface. To
1/15 or less. As described above, by defining the X-ray irradiation area diameter according to the curvature of the curved surface to be measured, it is possible to accurately obtain the diffraction X-ray peak. That is, when the curvature of the surface to be measured is small, the influence of the curvature of the surface to be measured can be almost eliminated by reducing the diameter of the X-ray irradiation region, and an accurate diffraction X-ray peak can be obtained. .. As a result, it becomes possible to accurately measure the residual stress in a minute portion corresponding to the irradiation area even in the ceramic member whose measured surface is a curved surface.

[0012]

Embodiments of the present invention will now be described with reference to the drawings.

FIG. 1 is a block diagram showing an example of a measuring apparatus to which the residual stress measuring method of the present invention is applied. In the figure, 1 is an X-ray tube which serves as an X-ray source for diffraction. The target material of the X-ray tube 1 is appropriately selected according to the ceramic member to be measured and the measurement depth, and the diffraction peak used is also the same. For example, if the sample is β-Si ₃ N
_In the case of ₄ sintered bodies, the diffraction peak of (411) plane by V-Kα ray (2θ = 152.67deg), the diffraction peak of (212) plane by Cr-Kα ray (2θ = 131.47deg), Cu-Kα By line (323)
In the case of α-Al ₂ O ₃ sintered body, the diffraction peak (2θ = 141.45 deg) of the plane is the diffraction peak (2θ = 135.03 deg) of the (1,1,10) plane due to the Cr-Kα line. Diffraction peak (2θ = 136.11deg) of (416) plane by Cu-Kα ray is ZrO ₂ sintered body (Y-TZP)
In the case of, the diffraction peak (2
θ = 152.09deg), the diffraction peak (2θ = 140.22deg) of the (026) plane due to Cu-Kα rays, etc.
Diffraction peak of (116) plane by Kα ray (2θ = 121.69deg),
Diffraction peak of (306) plane by Cu-Kα ray (2θ = 134.09de
g) etc. are used.

The X-rays 2 emitted from the X-ray tube 1 pass through the filter 3 and are extracted as single-wavelength X-rays 4.
The single-wavelength X-rays 4 that have passed through the filter 3 are collimated to a predetermined spot having a small diameter by a collimator 5 having a double pinhole, and the minute X-rays 6 are the center of the goniometer 7. The measured object arranged at the position, that is, the ceramic member 8 having a curved surface as the measured surface is irradiated.

Here, the single wavelength X-ray 4 is, as shown in FIG. 2, a curved surface 8a which is a surface to be measured of the ceramic member 8.
The diameter of the irradiation area A of the minute X-rays 6 on the upper side is d, the radius of curvature of the curved surface 8a which is the surface to be measured is r, and the radius of curvature r
When the doubled value is D, the collimator 5 collimates the ratio d / D so that the ratio d / D becomes 1/15 or less. The value of D is the diameter of the measured ceramic member 8 when it has a circular cross section. Fine X-rays 6 so that the above-mentioned d / D ratio is less than 1/15
By setting the irradiation area diameter d of 1, it is possible to almost eliminate the influence of the curvature of the surface to be measured, and an accurate diffraction X-ray peak can be obtained. That is, the above d / D ratio is 1 /
When it exceeds 15, the Bragg reflection condition cannot be accurately satisfied due to the influence of the curvature of the surface to be measured. The more preferable value of the above-mentioned d / D ratio is to satisfy 1/20 or less. The diameter d of the irradiation area A of the minute X-rays 6 will be described in detail later.

As described above, if the irradiation area diameter d of the minute X-rays 6 satisfies the value of the above d / D ratio, the effect of the present invention can be obtained, but the radius of curvature of the curved surface 8a which is the surface to be measured. When r is large and the residual stress in a minute portion is measured, the area of X-ray irradiation area A is 0.2 mm after satisfying the above conditions.
Is preferably set to be ² or less, more preferably be 0.1 mm ² or less.

The ceramic member 8 to be measured is not limited to a spherical or cylindrical ceramic member as long as it has a curved surface as the measured surface, and a flat ceramic having a partially curved surface. Various ceramic members such as members can be applied. In particular,
Applicable to various ceramic parts, from single parts such as spherical ceramic parts such as bearing balls, cylindrical ceramic parts such as long links, to composite parts such as cylindrical ceramic-metal bonded parts such as turbo rotor shafts. be able to.

An X-ray detector for measuring the intensity and diffraction angle of the diffracted X-rays 9 diffracted by the curved surface 8a of the ceramic member 8 to be measured is provided on the outer peripheral portion of the above-mentioned goniometer 7, for example. A position sensitive proportional detector (PSPC) 10 is arranged. This position-sensitive proportional detector 10 has a diffraction X
The diffraction angle and intensity of a line can be quickly measured without scanning the detector. The filter 3 described above may be installed immediately before the position-sensitive proportional detector 10.

The residual stress measuring device having the above structure measures residual stress as follows. The residual stress generated in the ceramic member changes the lattice plane spacing (d value) of the crystal in proportion to the magnitude of this stress. When the generated residual stress is a tensile stress, the surface distance d in the direction parallel to the stress becomes small, and the surface distance d in the direction perpendicular to the stress becomes large. In the case of compressive stress, the opposite is true. Utilizing this property, the angle (X-ray incident angle) ψ formed by the object measurement surface normal N and the lattice surface normal N ′ is calculated as shown in FIGS. 3 (a), (b), and (c). The residual stress σ is obtained from the following equation by changing the X-ray irradiation while changing the diffraction angle (2θ) of a specific diffraction peak within the X-ray penetration depth.

[0020]

[Equation 1]

(Where σ is residual stress (kgf / mm ² ), E is Young's modulus (kgf / mm ² ), ν is Poisson's ratio, θ ₀ is standard Bragg angle) K is dependent on material and measurement wavelength Since it is a stress constant that is determined, a graph of 2θ and sin ² ψ is created from the measured values (ψ and 2θ) as shown in Fig. 4, and the gradient is obtained by, for example, the least-squares method. The stress σ is uniquely obtained.

Here, when the residual stress is measured by the sin ² ψ method, the X-ray is irradiated by changing the X-ray incident angle ψ as described above. Therefore, when irradiating X-rays in parallel with the normal line N to the object measurement surface, the irradiation area A of the minute X-rays 6 becomes circular as shown in FIG. When irradiating the minute X-rays 6 with an angle ψ from the line N, as shown in FIG.
Becomes oval. Therefore, the X-ray irradiation area diameter d in the present invention refers to the major axis of the elliptical irradiation area A when the X-ray incident angle ψ is maximized.

Next, a specific measurement example using the residual stress measuring method of the present invention will be described.

Example 1 First, a cylindrical ceramic-metal bonded body was manufactured as an object to be measured by the following procedure. As shown in FIG.
10 mm diameter x 0.2 mm thick copper to be a stress buffer layer between a cylindrical ceramic member 11 made of ₃ N ₄ sintered body and having a diameter of 10 mm and a length of 10 mm, and a steel material (S45C) 12 having the same shape. A brazing filler metal 14 with a member 13 interposed and a Ag-Cu foil with a thickness of 60 μm and a Ti foil with a thickness of 3 μm between the surfaces to be joined
Inserted as. The laminate is then placed under vacuum at about 830
The ceramic member 11, the steel material 12 and the copper member 13 were heat-bonded by heat treatment under the condition of 6 ° C. for 6 minutes to produce a columnar ceramic-metal bonded body 15.

Cylindrical ceramics obtained in this way
For the metal bonded body 15, the axial direction (z direction) component σ _z and the circumferential direction (θ direction) component σ _θ of the residual stress of the ceramic member 11 were measured. The measurement conditions are as follows.

As a specific X-ray, 50 kV, 160 mA of Cr-Kα
X-ray irradiation diameter was set to 0.15 mm at φ = 0 degrees.
The X-ray incident angle ψ is 5 degrees, 15 degrees, 20 degrees, 25 degrees, 30 degrees and
It was set to 35 degrees (parallel tilt method). The X-ray irradiation area diameter d (ellipse major axis) was 0.32 mm when the X-ray incident angle ψ was 35 degrees. Therefore, the d / D ratio is 1/31.

For the measurement, a diffraction peak on the (212) plane at 2θ = 131.47 deg was used, and a graph of 2θ-sin ² ψ was created from the deviation of the diffraction peak, and the gradient and stress constant (K = -883) of this graph.
(MPa / deg) was used to calculate each residual stress.
The measurement positions were set at several positions in the axial direction from the vicinity of the bonding interface with a predetermined gap.

FIG. 7 shows the measurement results of the axial component σ _z and the circumferential component σ _θ of the residual stress. As is clear from FIG. 7, it was found that the residual stress could be accurately measured from the bonding interface in units of 0.1 mm at the minimum. Further, the shear stress τ _θz could be analyzed from the axial component σ _z and the circumferential component σ _{θ of} these residual stresses. This shear stress τ
_θz is indicated by a dashed line in the figure. The dotted line in the figure is an axially symmetric model for elasto-plastic analysis by the finite element method (FEM) and corresponds to the axial component σ _z of residual stress. From this, it can be inferred that the measurement result of the residual stress by X-ray diffraction shows an accurate value.

Further, the following is clarified from the measurement results shown in FIG. That is, a large tensile stress remains in the vicinity of the bonded interface in the axial direction, but since the material strength of the ceramic member is not exceeded, the bonded body has not been destroyed. From the consideration of the measurement results, it is clear that the residual stress measuring method of the present invention is a very effective means for evaluating a ceramic member having a curved surface.

As a comparison with the present invention, the irradiation diameter of X-ray was changed to 0.1 mm, and the residual stress of the cylindrical ceramic-metal bonded body 11 was measured in the same manner as in the above-mentioned embodiment. It is not possible to obtain an accurate residual stress value.
It was not possible to accurately obtain the stress curve as shown in. In this comparative example, the X-ray irradiation area diameter d (major axis of ellipse) is 1.77 mm when the X-ray incident angle ψ is 35 degrees.
Therefore, the d / D ratio was 1 / 5.6.

Example 2 As shown in FIG. 8, the diameter of the cross section near the joint was 6 mm.
Between two steel materials (S45C) 21, a cylindrical ceramic member 22 made of a Si ₃ N ₄ sintered body and having a diameter of 6 mm and a width of 5 mm is interposed, and a diameter of 6 mm serving as a stress buffer layer is formed between these joint surfaces. Each copper member 23 having a thickness of 0.2 mm was interposed. Then, a brazing filler metal (not shown) similar to that used in Example 1 is inserted between the surfaces to be joined, and heat-bonded under the same conditions as in Example 1 to form a cylindrical ceramic-metal bonded body 2.
4 (tensile test piece) was produced.

Cylindrical ceramics obtained in this way
For the metal bonded body 24, the axial direction (z direction) component σ _z of the residual stress of the ceramic member 22 was measured. The measurement conditions were the same as in Example 1. When the X-ray incidence angle ψ is 35 degrees, the X-ray irradiation area diameter d (ellipse major axis) is 0.32.
It was mm. Therefore, the d / D ratio is 1 / 18.8.

FIG. 9 shows the measurement result of the axial component σ _z of the residual stress. As is clear from FIG. 9, it was found that the residual stress could be accurately measured from the bonding interface in units of 0.1 mm at the minimum.

As a comparison with the present invention, when the X-ray irradiation diameter was changed to 1.0 mm and the residual stress of the cylindrical ceramic-metal bonded body 24 was measured in the same manner as in the above embodiment, An accurate residual stress value cannot be calculated, and
It was not possible to obtain the stress curve as shown in. In this comparative example, when the X-ray incidence angle ψ was 35 degrees, the X-ray irradiation area diameter d (major axis of ellipse) was 1.77 mm, and the d / D ratio was 1 / 3.4.

[0035]

As described above, according to the residual stress measuring method for a ceramic member of the present invention, the residual stress in a minute portion can be measured with high accuracy even when the measurement surface is curved. Becomes Therefore, it is possible to precisely measure the residual stress due to various factors such as the manufacturing process of the ceramic member, and to perform reliable quality evaluation.

[Brief description of drawings]

FIG. 1 is a diagram schematically showing a configuration of an example of a measuring apparatus to which a residual stress measuring method of the present invention is applied.

FIG. 2 is a diagram for explaining a relationship between an X-ray irradiation area diameter and a curvature of a measurement curved surface in the present invention.

FIG. 3 is a diagram showing a principle of measuring residual stress by X-ray.

FIG. 4 is a diagram for explaining a method of calculating a residual stress by X-ray.

FIG. 5 is a diagram for explaining an X-ray irradiation area diameter in the present invention.

FIG. 6 is a perspective view showing a cylindrical ceramic-metal bonded body used for measuring residual stress in one example of the present invention.

7 is a graph showing measurement results of residual stress of the cylindrical ceramic-metal bonded body shown in FIG.

FIG. 8 is a perspective view showing a cylindrical ceramic-metal bonded body used for measuring residual stress in another example of the present invention.

9 is a graph showing measurement results of residual stress of the cylindrical ceramic-metal bonded body shown in FIG.

[Explanation of symbols]

 1 ... X-ray tube 2 ... X-ray emitted from X-ray tube 3 ... Filter 4 ... Single wavelength X-ray 5 ... Collimator 6 ... Micro X-ray 7 ... Goniometer 8 ...... Ceramic member with curved surface 9 ...... Diffracted X-ray 10 ... Position-sensitive proportional detector A ...... X-ray irradiation area d ...... X-ray irradiation area diameter r ...... Curve radius D ...... Twice the curvature radius The value of the

Claims (1)

Claim: What is claimed is: 1. A method of irradiating an X-ray on a curved surface of a ceramic member having a curved surface as a surface to be measured, and measuring the residual stress of the ceramic member from the obtained diffracted X-ray. The X-rays that irradiate the curved surface of the member are
The ratio d / D of these values is 1/15 or less, where d is the diameter of the irradiation area of the line and D is the radius of curvature of the curved surface. ..