SU1193535A1 - Method of inspecting quality of heat conducting coating-to-backing adhesion - Google Patents

Description

The invention relates to a testing technique, and in particular to methods of monitoring the quality of adhesion of heat-conducting coatings to substrates.

The purpose of the invention is to improve the accuracy of quality control of adhesion of heat-conducting coatings to the substrate.

The drawing shows an example of the method.

The method is as follows.

The substrate is coated with one of the known methods, and the surface of the coating is affected by heat flow. In the process of exposure to heat flux, a parameter characterizing the quality of adhesion, for example, the coefficient of reflection of heat flux from the surface of the coating, is measured. In this case, the duration £ of the effect of the heat flux on the surface of the coating and the density P of its power is chosen according to the conditions

'"MIN ^{4 4 with} A \ ax

^ max

where ^ _Min and Р _{myaks are} determined from the system of equations

about. _n: ~ Pmax ^ mitch,

T _x - T _about ----- (1)

o ot ’\ _ Rmeks ^ mmm Pmax 1

0.8 (T _x - T _o ) - - “- p"",

(2)

^a ^ max ^and determined from the system

of equations

20 c1p (T _x - T _o ) = P _min C'max O)

, _ t - 1+ 1I Ί "

ϊχ - That ” ¹⁺ k '

,one . -55 ----- exp - —55—).

I - ' ^to ' (4)

where T _about - the initial temperature of the connection;

Τ _χ is the temperature at which

there is a characteristic change in the measured parameter;

y is the density of the coating material;

c is the heat capacity of the coating material;

k is the coefficient of thermal conductivity of the material of the coating;

X is the coefficient of thermal diffusivity of the coating material;

£ is the coating thickness;

And - thermal conductivity of the boundary of the coating-substrate.

When exposed to a short-duration heat flow, a thin heat-conducting coating applied to the heat-conducting substrate undergoes a local heating of the coating in the area of flow action. The temperature of the surface of the coating depends on such heat flow parameters as the duration of exposure.

10 and the average power density, and thermophysical parameters of the coating material and the substrate, as well as the thermal conductivity of the boundary · coating - substrate, which is determined by the quality of adhesion of the coating to the substrate. The connection of the maximum temperature on the surface of the coating with the thermal conductivity of the boundary appears only in a certain

20 areas of duration of exposure and power density. For specified thermal parameters of the coating material and coating thickness, this area is determined

25 by solving the heat equation for two special cases, between which all possible variants obviously lie. The first system of equations (1) and (2) "characterizes

thirty

the case of bad, thermal wire35

40

45

50

dosing, which corresponds to the poor quality of adhesion of the coating to the substrate.

Equation (1) is a condition for the equality of the temperature on the outer surface of the coating to a certain characteristic temperature, at which a significant change occurs in the reflection coefficient of the heat flux. Equation (2) is a condition that the temperature at the interface with the substrate coating temperature 0,8T _x, where 0.8 numerical parameter formally into account the influence of contact with the substrate boundary coating on the temperature field in the coating.

The second system of equations (3) and (4) characterizes the low thermal resistance of the coating – substrate interface, which corresponds to the good quality of adhesion of the coating to the substrate. Equation (3) sets the ratio between the part of the heat flux going to heat the coating to the temper ature T _y , and the part of the flux that goes to the substrate. Equation (4) determines the temperature on the outer surface of the coating. The value of G _m "COP, semi ·

3

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The system of equations (3) and (4) allows one to work with unsteady heat fluxes, and, therefore, in the region of small durations. The temperature T _x , at which a characteristic change occurs in the coefficient of reflection of the heat flux from the surface of the coating, is characterized by the formation of oxides on the surface of the coating, leading to darkening of the surface of coating Yu. Compare the reflection coefficient with the same coefficient measured on the reference compound, and the results of the comparison are judged on the quality of the adhesion of the coating with a hollow. 15 In this case, the greater the value of the heat flux reflection coefficient from the surface of the coating of the monitored compound coincides with the magnitude of the reflection coefficient of the thermal flux of the reference compound, the better the quality of adhesion of the coating to the substrate in the monitored compound.

Example. The heat flux ⁷ soED-25 is produced by exposure to laser radiation 1 of the GOS-ZOZ model in the free generation mode, and the location of the optical elements - glass plates 2 and 3 - allows to create on the surfaces of 4 and 5 of the reference and controlled samples strictly identical radiation power densities and thereby eliminating the effect of laser instability. The beam of helium-neon laser 6 of the GL-2 model, which passed through the separating plate 7, is used to guide a powerful laser to the coatings 4 and 5, and the beam reflected by the separating plate 7, passing through the system of prizm 8 and 9, hits the surface of the coating 4 controlled sample. Scattered radiation is collected by the collector device 10 on the photodiode 11 of the PD-ZA model, from which the relative change in the reflectance of the surface of the sample under test can be determined. As samples, flat zirconium samples with a copper coating of 20 microns thick, applied by an electrochemical method, are used. In order to reduce reflection losses, the surface of the samples is covered with a graphite layer with a thickness of not more than 1 micron.

From equations (1) - (4) obtained the following restrictions on the parameters of the heat flow:

= 8 · 10- 'ί С ^ _max = 2 - - 7-10 ¹

BT

CM. ² *

t?

The duration of the laser pulse 1 in the free-running mode is 1, 5 ms.

Claims (2)

¹ ~ ---- ^{exp (} " -G + 2 to H ___ where T _about - the initial temperature of the connection; T _x - the temperature at which a characteristic change in the measured parameter occurs; |> - the density of the coating material; c is the heat capacity of the coating material; K - coefficient of thermal conductivity of the coating material; 3> - coefficient of thermal diffusivity of the coating material; Σ is the coating thickness; H - thermal conductivity of the boundary of the coating-substrate. ¹ ^ max ^{and P} mchk we equations T _x Pmin pc ί determine from system20 C1 ^ (T _x - T _in ) = P _miN ^c m "ks" I, T.- " 1. METHOD OF QUALITY CONTROL OF THE GRID OF HEAT CONDUCTING COATINGS WITH SUBSTRATE, which consists in the fact that the surface of the coating is affected by heat flow, measure the parameter characterizing the quality of adhesion, compare it with the same parameter measured on the reference compound, and judging by the results of comparison * , in order to improve the accuracy of control, the duration g of exposure to heat flow and the density P of its power is chosen from the conditions ΐτ <r with * · p <p C G ^{55 1} < ^G MS | KS> where and P _meaks determined from the system of equations r t E'max '^ mik Rmdke · 1 ^g x - To ⁺ -z | --- η I St t> ο, 8ςτ _χ - _{pc1 Sk} " 2. The method according to claim 1, characterized in that as a parameter register the coefficient of reflection of the heat flux from the surface of the coating. 5C, 1193535 > one . 1193535