RU2499244C1 - Method to determine residual stresses and energy characteristics of gas thermal coatings - Google Patents

Abstract

FIELD: electricity.

SUBSTANCE: sample is loaded with a gas thermal coating arranged on supports with a coating down, with static load according to a 4-point scheme. The sample is loaded gradually, to the value of the load that does not exceed the resilience limit of the coating material, serially unloaded to the value of tension deformation equal to zero, at the same time the residual force is measured, unloading is continued to produce the force value equal to zero, and the residual deformation of compression is measured. According to the produced deformation hysteresis, the residual stresses are calculated in the coating, as well as its energy characteristics that include the following: energy of internal stress release (J); energy required for complete relaxation of residual stresses (J); density of energy required for complete relaxation of residual stresses (J/m³).

EFFECT: provision of a complex of mechanical characteristics of a gas thermal coating, which make it possible to monitor its quality and to create a perfect process for its production.

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Description

The invention relates to mechanical testing of thermal coatings, and more specifically relates to the determination of residual stresses in the coating and the energy necessary for their release. The invention can be used to control the quality of thermal coatings in the development of new technologies and the current control of serial technologies.

A known method for determining the deformation of thermal coatings [A. Kucuk, S.S. Bemdt, U. Senturk, R.S. Lima, C.R. Lima Influence of plasma spray parameters on mechanical properties ofyttria stabilized zirconia coatings. I: Four point bend test // Materials Science and Engineering, 2000, A284, p.29-40], carried out loaded on a 4-point scheme of the sample with the coating located on top so that when loading the coating in the middle of the sample was compressed . This method does not allow to determine the value of residual stresses and energy released during unloading of the sample, as it uses a softer than tension type of loading of the sample.

A known method for determining the strength of a thermal coating [United States Patent 4876148, "Ceramic bodies having a plurality of stress zones", 10/24/1989], carried out loaded on a 4-point pattern of the sample with a coating located below so that when loading the coating in the middle part of the sample was subjected to stretching. Loading is carried out until the coating is destroyed. However, this method does not use loads that would form elastic deformations in gas-thermal coatings, which allow determining residual stresses, as well as the energy required to relieve them.

The technical result is to obtain a set of mechanical characteristics of a thermal spray coating, which allow to control its quality and create a perfect technological process for its production.

The technical result is achieved by the fact that in the method for determining the residual stresses and energy characteristics of the thermal spray coating, which includes loading the sample with a thermal spray, placed on the supports with the coating down, with a static load according to a 4-point circuit, it is new that the sample is loaded smoothly to a value loads not exceeding the elastic limit of the coating material are successively unloaded to a tensile strain value of zero, while the residual force is measured, continue unloading until a force value of zero is obtained, and the residual deformation of compression is measured, the residual stresses in the coating and its energy characteristics are calculated from the obtained deformation hysteresis, including: release energy of internal stresses (J); energy necessary for complete relaxation of residual stresses (J); energy density necessary for complete relaxation of residual stresses (J / m ³

Figure 1 presents a diagram of a 4-point bend, where 1 is a rectangular metal sample (plate); 2 - sublayer; 3 - coating; 4 - strain gauge; 5 - strain gauge; 6- device for loading.

Figure 2 presents examples of diagrams of deformation of samples with a thermal coating.

Figure 3 presents a diagram of the deformation hysteresis of the thermal coating, where: S ₁ is the energy spent on deformation of the sample; S ₂ - energy released during unloading of the sample; And - part of the energy S ₂ spent on the relaxation of residual stresses.

The essence of the method is as follows. A sample with a thermal coating, located on the supports coated down, is loaded according to a 4-point circuit to a load value not exceeding the elastic limit of the coating material. Then, they are successively unloaded to a tensile strain value of zero, while the residual force P ₀ (H) is measured. Then, unloading is continued until a force value of zero is obtained and the residual compressive strain - L, (microns) is measured. Based on the measurement results, a diagram is constructed in the coordinates: “Load - P, (H) - displacement (absolute deformation) - L, (μm), which is a deformation hysteresis. Based on the obtained deformation hysteresis, residual stresses in the coating and its energy characteristics are calculated, including: the energy of release of internal stresses (J); energy necessary for complete relaxation of residual stresses (J); energy density necessary for complete relaxation of residual stresses (J / m ³ ).

1. The release energy of internal stresses S, (J) is calculated as the difference of the energy S ₁ spent on the process of deformation of the thermal coating and the energy S ₂ released during unloading of the coating.

$$\text{S}={\text{S}}_{\text{one}}-{\text{S}}_{\text{2}}\left(\text{one}\right)$$

The calculation of these areas can be carried out according to formulas (2) and (3):

$${\text{S}}_{\text{one}}={\displaystyle \sum _{\text{i}=\text{one}}^{\text{n}}{\text{L}}_{\text{i}}\cdot {\text{P}}_{\text{n1}}}\left(\text{2}\right)$$

$${\text{<figure-callout id="2" label="S" filenames="00000010.png" state="{{state}}">S</figure-callout>}}_{\text{2}}={\displaystyle \sum _{\text{i}=\text{one}}^{\text{n}}\left|{\text{L}}_{\text{i}}\right|\cdot {\text{P}}_{\text{n2}}}\left(\text{3}\right)$$

where P _n1 - loading, N; P _n2 - unloading, N; L, - displacement, microns.

2. The energy A (J) necessary for the complete relaxation of the residual stresses in the coating is calculated by the formula:

where: F- force, N; a - displacement in the compression region, μm, P _o - residual force, N.

In the hysteresis diagram, the energy A (J) corresponds to the area of a right triangle in the compression region.

3. The residual stress σ (MPa) is calculated by the formula:

$$\text{σ}=\frac{{\text{3P}}_{\text{0}}\cdot \text{C}}{\text{B}\cdot {\text{H}}^{\text{2}}}\left(\text{5}\right)$$

where P ₀ is the residual force at which the deformation becomes equal to zero; In - the width of the sample, mm; H is the total thickness of the sample, mm; C is the distance between the loaded and the supporting beam, 10 mm

4. The energy density of the relaxation of residual stresses, J / m ^{3 is} calculated by the formula:

U $$\text{U '}=\frac{\text{U}}{\text{Fl}}=\frac{{\text{<figure-callout id="2" label="σ" filenames="00000010.png" state="{{state}}">σ</figure-callout>}}^{\text{2}}}{\text{2E}}\left(\text{6}\right)$$

U

where σ = P _m / F is tensile stress. The elastic modulus E of the three-layer system (base-sublayer-coating), using the additivity rule, we find by the formula:

$$\text{E}=\frac{\text{E}{}_{\text{main}\text{.}}\text{h}{}_{\text{main}\text{.}}+{\text{E}}_{\text{sublayer}}+{\text{h}}_{\text{sublayer}}+{\text{E}}_{\text{PC}\text{.}}{\text{h}}_{\text{PC}}}{\text{N}}\left(\text{7}\right)$$

where: E _DOS. , E _sublayer , E _pc. , are the elastic moduli of the base, sublayer, and gas-thermal coating, respectively, MPa; h _main , h _sublayer , h _pc. - the thickness of the base, sublayer and thermal coating, respectively, microns. As a result, a complex of mechanical characteristics of a thermal spray coating is obtained, which makes it possible to control its quality by comparing the results of similar thermal spray coatings and create a perfect process for producing thermal spray coatings.

Claims (1)

A method for determining the residual stresses and energy characteristics of a thermal spray coating, including loading a specimen with a thermal spray coating, placed on the supports downward, with a static load according to a 4-point circuit, characterized in that the loading of the specimen is carried out smoothly, up to a load value not exceeding the elastic limit of the material coatings are subsequently unloaded to a tensile strain value of zero, while the residual force is measured, unloading is continued until a value is obtained forces equal to zero, and measure the residual deformation of compression; Based on the obtained deformation hysteresis, residual stresses in the coating and its energy characteristics are calculated, including: internal stress release energy (J); energy necessary for complete relaxation of residual stresses (J); energy density necessary for complete relaxation of residual stresses (J / m ³ ).

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