JPS62503052A - hardness measurement - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

[Detailed description of the invention] Engraving (contents (no changes)) Hardness measurement The present invention is based on the hardness of conductive materials such as metals and the hardness of conductive materials coated with a thin metal layer. Suitable for measuring the hardness of electrically conductive materials (e.g. ceramics and plastics) material by measuring the contact resistance between a conductive indenter and a metal object. The present invention relates to a method for measuring the hardness of.

A method for measuring the hardness of materials by measuring contact temperature resistance is H, J. Goldsmid and J. , N. Johnston (J, N. J. Ohnston) Kuss Electrical Scientific Instrument Journal ( J, Phys, E, Set Instrument, ) Volume 14 of J (1981) ) page 1329 and “Materials Science Journal” by the above two authors. le (J.

Materials S fence) J Volume 17 (1982) No. 101 It is introduced on page 2. However, the method is limited by the thermal conductivity of the test material. It is effective only when the quality is very high. Heat loss is more than heat transfer across the contact area Therefore, when testing materials with low thermal conductivity, the sensitivity will be poor, and metals will be Even when testing, it is necessary to make corrections to provide thermal conductivity; In order to do this, it is necessary to know its thermal conductivity in advance through another experiment.

Instead of temperature resistance, measure the electrical resistance between the conductive indenter and the metal sample. It seems that these problems will be resolved if this is established. The entire current flows through the contact area. It is easy to ensure that the electrical resistivity of the metal Even if it is much smaller than that of the material, you do not need to know it in advance (1° resistance Rate ρ4. When ρ2, the electrical resistance between the solids is (ρ1+ρ2)/4r(3) is equal to Therefore, when ρ1〉〉ρ2, the resistance becomes ρ, /4r, so It is only necessary to examine the resistivity of one of the two solids.

The problem with using electrical measurements to measure contact area is that they cannot compete with temperature measurements. oxide layers and other surface contaminants. . Furthermore, in both cases, the actual contact area has a microscopic appearance of There is no guarantee of proximity to the area, i.e. the area of macroscopic impression formation. While I'm struggling , in some cases, F.P. Bovden (F.P. Bovden) and De. Written by T. Abor, Oxford University “Friction and Lubrication of Solids” published by City Press in 1950, Volume 1 (The F r1ctlon and Lubrica, tion of’ 5o11ds , Part I) J, page 28, two solid conductors It appears possible to achieve close electrical contact between the two. hard conductive material As a result of investigating the electrical contact resistance between an indenter made of The use of hard semiconducting materials such as silicon carbide as dental implants Therefore, it was found that effective hardness measurement is possible. silicone carver According to the Mohs hardness, id is the second hardest substance after diamond and is a semiconductor. , its resistivity is considerably higher than that of metals, but not so high that resistance measurement becomes difficult. do not have.

Therefore, the present invention measures the electrical resistance between a conductive indenter and a conductive sample. A method for measuring the hardness of an arbitrary substance by The method consists of a hard semiconducting material, such as silicon carbide. The above index Preferably, the center has a composition such that its thermal conductivity is substantially independent of temperature.

In addition, the indenter has a contoured shape so that it can be used in conventional hardness testers. Preferably, it is the same as the spire-shaped diamond indenter of Kars. in this way The major advantage of this is that it is easier to calibrate than the Witzkers hardness scale. bring significant benefits.

Furthermore, in order to improve the reproducibility of contact resistance when conducting hardness tests, A pre-test operation consisting of discharging the contact between the material and the material shall be carried out. preferable.

Next, the present invention will be explained with reference to the drawings.

Figure 1 shows the electrical resistance versus temperature of silicon carbide used in indenters. Show rate. Furthermore, “Journal of Applied Physics (J, Appl, Phys. , ) As described in J Vol. 50 (1979), p. 5790, Bourguet Of the samples measured by Burgemeistr et al. The following shows data regarding two of the following.

Figure 2 shows the indenter and steel before and after discharging the capacitor. shows the relationship between electrical resistance and voltage between the sample and the sample. The load is 0.2 kg, + and - indicate the polarity of silicon carbide during resistance measurement.

Figure 3 shows the effect of voltage on the capacitor at 15 for various samples. It shows the electrical resistance after a nF capacitor is discharged. The load is 1.0 kg.

Figure 4 shows the capacitor before and after discharge for a typical steel sample. The relationship between the electrical resistance after electric current and the reciprocal of the diagonal measurement value of the indentation is shown.

Figure 5 shows 0.2 kg and 10 companies for all the samples studied. The relationship between the electrical resistance and the reciprocal of the diagonal line for loads between is shown.

Figure 6 shows the hardness measured from resistance measurements and conventional Vickers for various metals. Comparison with the case hardness is shown. The load is 1.0 kg.

Figure 7 shows Perspex coated with metal and Relative hardness (proportional to the square of resistance) and time for indentation in CR-39 Indicates the relationship between

The experiment was conducted using a Zwick hardness tester model 23.2A. It was. This testing machine typically performs Vickers hardness tests using loads up to 10 kg. It is used to carry out. For electrical measurements, indenters and A conductor is attached to the metal test sample and the latter receives electricity from the rest of the test machine. isolated.

In the Vickers hardness test, the indenter is a diamond pillar with a facing angle of 1366 mm. Consists of mid. In this experiment, the diamond indenter was initially Heat-pressed high-density silicone carver supplied as bars by the National Bureau of Standards replaced by id. This indenter is available in standard Vickers shape or was a conical shape with a half-width of 60". The result is that for all indenters The data presented here are qualitatively similar for silicon carbide. The standard pyramid shape is made of a specific bar made of wood and has a well polished surface. It's about one thing. All measurements on the indenter are 300' It was held in

The electrical resistance between the indenter and the metal test sample is By observing the voltage drop for various current values using a digital voltmeter Measured. The only significant voltage change occurs at the contact between the two materials. was proven. As will be described later, the capacitor is discharged at the contact point. Ta.

Table 1 shows the Vickers hardness numbers measured by a diamond indenter. The test samples studied using These tests, like normal hardness tests The surface of the sample was polished to remove oil, but no special cleaning was required. .

As mentioned above, the resistivity ρ of the indenter is much smaller than the resistivity of the metal being tested. It is preferable that it be large. Figure 1 shows a method using a four-point contact technique using a rectangular rod-shaped body. The obtained resistivity ρ in the range from 300'K to 450'K is shown. 30 The resistivity at 0' is 0.37 ohm, while metals and metal alloys is 10-self ohm-meter to 104 ohm-meter. In this way, you need This condition is easily satisfied.

Furthermore, FIG. Figure 2 shows the resistivity change versus temperature for two quartz samples studied in this study. heating press The negative temperature coefficient of resistivity - (dρ/dT)/ρ for silicon carbide is , which is smaller than that of crystal sample N+14, is 6.9×10−″K″1. It has a relatively high value. However, the crystal sample Nα1 has a temperature coefficient of almost zero. , and its resistivity is still several orders of magnitude greater than that of metals. Therefore , an indenter made of material similar to Burgemeister sample No. 1 is , has the important advantage of being virtually independent of temperature.

The resistivity of the semiconductor must not be too high, otherwise the resistance experienced in semiconductor rectifiers will You may encounter barrier issues such as: Preferably, semiconductor inden The resistivity of the conductive sample is at least 100 times that of the conductive sample, but Preferably it is less than or equal to ohmmeter.

The lower curve in Figure 2 shows the typical change in contact resistance measured over a wide range of voltages. show. Its distinct characteristics are: (1) Resistance based on whether the indenter is positive or negative for metals The difference is small; (11) there is an increase or decrease in resistance depending on polarity at low voltages; (ill) There is a substantial reduction at high voltages.

Figure 2 shows a steel sunglass with a load of 0.2 kg applied to the indenter. Regarding pull, no matter what the test metal or load is, The plateau includes measurements at a potential difference of 1'OmV. Therefore, measurements were always performed using this voltage value. Low including polarity effects Changes in voltage indicate interfacial barrier effects, and trends at high temperatures are due to Joule heating. Ru.

The resistance value at constant load was not initially thought to be particularly reproducible. . However, after switching the current on and off while applying a load, It was found that results with less variation were obtained. In this way, the The discharge effect of capacitors has been investigated, and effective pre-test operations have been developed. Ta. The lower curve in Figure 2 shows the discharge of a 15nF capacitor charged to 100V. This was obtained later. After this discharge, the resistance becomes smaller and more renewable. , no longer depended on the polarity of the indenter for one test sample.

It must be emphasized that the energy of the group 2 electricity is only about 100 joules. This means that there will be no adhesion between the two surfaces. indenter The electrical discharge was effective in removing contaminants from the surface, as both the metal and the metal had not been thoroughly cleaned. I think it is effective to do so.

FIG. 3 shows various samples as the voltage on the 15 nF capacitor increases. It shows how the contact resistance for pull has decreased. Regarding gold sample (G1) had little or no total heat change, but significant effects for other samples. There was a sound. After the capacitor voltage reaches 100V, the resistance decreases very little. It didn't progress. In this way, the discharge from the capacitor at this voltage was adopted as a standard pretest manipulation.

Of course, there is no reason why 15nF capacitance is better than anything else. , further research on optimization of discharge will be possible.

It has been found that the resistance of a planar circular contact of radius r is proportional to 1/r. however , the contact between the indenter and the sample is square and non-planar. in addition Nevertheless, we still know that the resistance is inversely proportional to the linear dimension of the indentation. The expected diagonal length d) measured with a microscope is taken as a parameter. Mojiro H-1,8544L/d... Vickers hardness H in the relationship of (1) It is this quantity that is used to define v. This is because the Vickers hardness is spire-shaped. Indicates the load ratio to the contact area. Hardness value is usually) cg/a+m2 expressed.

There is geometric similarity between all contact parts for different loads and samples. If so, the resistance R is considered to be proportional to 1/d. Therefore, in Figure 4, a typical The relationship between R and 1/d for a steel sample is shown. Steps before pre-test operations The results obtained were dispersed, but the origin was not found at the stage after the pre-test operation. The result was very close to a straight line. If appropriate test procedures are taken, The contact resistance appears to be inversely proportional to the length of the diagonal line across the indentation.

Figure 5 shows that all samples listed in Table 1 are subjected to loads between 0.2 kg and 10 kg. The relationship between R and 1/d when multiplied by 0.083 ohm meter slope unit A straight line satisfies all data with a standard deviation of less than 10%.

This slope is called the indenter constant (C). Contact resistance measurements are based on constant load The diagonal length of the indentation at Ru.

After recognizing the above-mentioned indenter constant (C), the hardness determined from the resistance measurement value is The degree is H-1,8544・R2L/C (1).

There is no reason why Vickers hardness should be dependent on load; Therefore, in Figure 6, the nine samples shown in Table 1 are ・Shows the relationship between HR and Witzkers hardness when a load of 1 kg is applied . The dashed line in Figure 6 indicates HR-Hv, and the experimental results closely correspond to this condition. It is clear that The largest difference for very soft gold samples is that the indentation is This may be due to the fact that it reached a width similar to that of the center.

Of course, the hardness test method described above is only suitable for good electrical conductors. deer However, the method is also applicable to insulators coated with conductive materials. I understand. Therefore, this means that ceramics and glasses can be Microhardness testing of viscoelastic substances under continuous load is now possible. This has the significance of making it possible to measure hardness over time.

Gold-coated Perspex (polymethyl methacrylate) and CR-39 ( Some preliminary tests were carried out on the (diallyl diglycol carbonate) samples. . A continuous chart record showing the change in resistance over time under a constant load is shown in Figure 7. sea urchin was used to calculate the relative hardness value (proportional to R2 under constant load) . The resistance of gold is time dependent, but is similar to CR-39 and Perspex. It turns out that it takes several minutes for the value to approach a constant value. clear Important information regarding the time-dependent mechanical properties of these materials is obtained by a relatively simple technique in a shorter time compared to optical microscopy methods be able to.

If the contact part is circular in plan, the indenter constant (C) is equal to ρ/2. In this case, (d) is the diameter of the circle, and the two surfaces are (R, Holm), New York Springer-Verlag (Springer-Verlag) "Theory and Applications of Electrical Contact" published in 1967. cts, T theory and A applications) J 4th See edition. In practice, we think that the indenter constant is somewhat larger than p/2. Toi This is because the square with diagonal line d has a smaller area than the circle with diameter d, and the area of the square with diagonal line d is smaller than that of the spire part within the indentation. This is because there is extra resistance involved. A constant number of indenters is applied to the contact between two surfaces. This is further exacerbated by defects in the In fact, the measured value between a constant number of indenters is 0.083 ohm even though p/2 is 0.185 ohm It's just a meter. The only possible cause for this error is the indentation The silicon carbide resistivity near the tip of the rectangular bar is cut into an indenter. This would mean that the resistivity would have to be less than the measured value for . Said The rods were found to be fairly uniform on a microscopic scale, but microscopically different. It may be of high quality. Indenter made of re-polished silicon carbide The proof is that a certain number has been obtained. In any case, the indenter The constants are clearly of the same order of magnitude as the expected values, and the two surfaces are at least as good as after the pre-test manipulation. This suggests that they must be electrically close to each other.

Hardness tests based on electrical resistance measurements now seem feasible. like this Testing could be done quickly in the laboratory or in the field. Hardness test loaded Being done in-state is a clear advantage. Because this removes the load This is because it eliminates problems caused by changes in the shape of the indentation that often occur after recovery 4. Ru. Additionally, a specific penetration depth rather than a specific load, i.e. a preset The control contact area determined by the minimum contact resistance It is simple and results in more reproducible results. The above test technique The technique can be applied to existing indentation hardness testers by attaching accessories. By maintaining the Vickers spire shape, calibration is greatly simplified. It becomes simple. The fact that continuous measurements can be performed on viscoelastic substances is an advantage of the present invention. This is the most attractive feature of the technology.

Table 1 Samples used for measurement C1 copper 88 B1 Brass 131 A1 Aluminum 140 S1 Steel 148 S2 Steel 330 83 Steel 594 S4 Steel 654 S5 Steel 718 F/θ, l Procedural amendment (formality) 1986 4B

Claims (1)

[Claims] [1] By measuring the electrical resistance between the indenter and the conductive sample In the method of measuring the hardness of a substance, the sample is made of the substance or a coating of the substance. a covering, wherein the indenter is made of a hard semiconductive material. Law. [2] Discharge the contact portion between the indenter and the sample at least once. and then measuring the electrical resistance between the indenter and the sample. The method according to claim 1. [3] Ensure that multiple cycles of the discharge are performed before measuring the contact resistance. A method according to claim 2, characterized in that: [4] A claim characterized in that the hard semiconductive substance is silicon carbide. The method according to any one of the ranges 1 to 3. [5] Claims 1 to 4, wherein the sample is metal. The method described in any one of the above. [6] The substance is an electrical insulator, and the sample is a coating of the substance. A method according to any one of claims 1 to 5, characterized in that: [7] After the indenter penetrates the sample to a predetermined depth, the electrical connection Claims 1 to 6, characterized in that contact resistance is measured. The method described in any one of the above. [8] The indenter is characterized in that it comes into contact with the sample under a constant load. A method according to any one of claims 1 to 5. [9] Resistivity of the indenter at standard temperature or near the standard temperature is substantially independent of temperature. The method described in any one of the above. [10] The resistivity of the indenter is at least 10 of the resistivity of the conductive sample. Any one of claims 1 to 9, characterized in that it is 0 times How to put it on. [11] The resistivity of the indenter is 100 ohm or less. 11. The method according to claim 10, wherein the method comprises: