Some standard content:
National Standard of the People's Republic of China
Metallic coatings-Methods of measurement of ductility
GB/T 15821—1995
This standard is equivalent to the international standard IS08401-19864 "Commentary on the measurement of ductility of metallic coatings" 1 Subject content and scope of application
This standard specifies the general measurement method for the ductility of metallic coatings with a thickness not exceeding 200 Å prepared by electroplating, autocatalytic deposition or other processes.
This standard is applicable to the measurement of the ductility of single-layer metallic coatings or multi-layer metallic composite coatings, and can determine the influence of each single-layer metallic coating on the total ductility of the composite layer.
This standard is also applicable to the measurement of the brittleness of the substrate caused by the coating process. When the national standard contains a special test method for a coating, it should be adopted in priority to the method described in this standard and the agreement of both the supplier and the buyer should be obtained in advance.
2 Terminology
2.1 Ductility
The ability of metal or other covering layers to produce plastic deformation or elastic deformation, or both deformations at the same time, without breaking or cracking under stress.
2.2 Linear elongation The ratio of the elongated part of the specimen deformation to the length L before deformation, which is used as a measure of ductility. Usually expressed as a percentage.
3 Overview
The methods for measuring the ductility of metal covering layers can be divided into two categories: one is to measure on the covering layer with a substrate, and the other is to measure on the covering layer foil after the grid is removed. The main measurement methods are to perform tensile or bending tests on the above two types of metal covering layer samples on a certain device until they break or crack, and then calculate their elongation. Usually, the ductility of a material is always measured by extending the specimen in a certain direction. The tensile method is like this, extending in a straight line. Some methods in the bending method also extend the outer layer (i.e., the covering layer) of the test piece in a certain curved direction (see Figure 3), so the ductility can be directly calculated using the linear elongation. However, for some methods in the bending method, such as the cupping test, the entire surface of the foil is extended, and the linear elongation should be calculated using the thickness reduction. If only one axial deformation component is used to calculate the ductility of the material, an incorrect result will be obtained (see Figure 4). In this case, using the increase in surface area to calculate the amount of thinning of the box layer is a better method to measure ductility (see Appendix B (Supplement)). Ductility is a property of the material. It is not affected by the size of the specimen, but the thickness of the covering layer may affect the value of the linear elongation (/L,). The non-thin covering layer exhibits different properties from the relatively thin covering layer. This is because the initially formed residual covering layer is affected by the matrix and produces crystal orientation growth. The internal stress of the merchant may exist in the initial covering layer, thereby affecting the ductility. For the covering layer specimens with uneven thickness, the thinner parts will crack during the test, and the thicker parts will have inconsistent elongation with the thinner parts. Therefore, when preparing the test pieces using this standard, the thickness of the summer covering layer on the entire test piece should be as uniform as possible. National expansion
4 Test of the covering layer foil without matrix
GB/T 15821-1995
The following five test methods are applicable to the covering foil peeled off from the substrate (see Figure 1). The covering foil can be composed of several layers. Therefore, the influence of the bottom layer on the total ductility of the foil interlayer can be measured. The method for preparing the covering foil without the substrate is shown in Appendix A (Supplement). 4.1 Tensile test
4. 1.1 Overview
Use a tensile testing machine to hold the covering box for a linear tensile test until the covering box is stretched to break. Measure the change in the size of the test piece before and after the test, and calculate its ductility.
4.1.2 Apparatus
Tensile testing machine. If the tensile testing machine is equipped with an observation microscope, the experimental results will be more accurate. 4.1.3 Preparation of test pieces
Take the substrate covering box and make a rectangular test piece with widened ends. The purpose of widening the ends is to prevent the test piece from being caught in the claws. Fracture, as shown in (Figure 7). Mark the test piece with equal distances. There should be no unnecessary microcracks at the edge of the cover layer made according to Record A, so as to avoid excessive fracture and unstable results. At the same time, the uniformity of the cover foil should be ensured (see Figure 10). 4.1.4 Test process
First, measure the distance between the marks, then clamp the test piece between the clamps of the tensile testing machine and stretch it at a speed selected according to the total thickness of the test piece. After the test, measure the distance between the marks on the test piece (see Figure 8). 4. 1.5 Expression of results
4.1.5.1 Calculation
The elongation D expressed as a percentage shall be calculated by the following formula: D = L + - × 100%
Where, L - distance between marks before the test, mm L + L - distance between marks after the test, mm. 4.1.5.2 Variation range
The test pieces prepared by mechanical calendering may have a variation range, and the coefficient of variation S/(S - standard deviation, average elongation) may be as high as 20 rings. The variation range of test pieces with more uniform coating is smaller. 4.1. Precautions during the test
4.1.6.1 Due to the shrinkage of the test piece cross section (see Figure 8), it may be necessary to measure smaller length changes. Therefore, it is best to use a microscope with a vernier scale.
4.1.6. 2 If the specimen is thin and brittle, the prestressing of the specimen may be increased by placing it in the jaws of the tensile testing machine, so that the measured value of ductility will be too low.
4.1.6. 3 Distortion of the specimen must be avoided during the test (see Figure 9). 4.1.6.4 When the error factors listed in 4.1.6.1 to 4.1.6.3 cannot be eliminated, other ductility test methods should be used. 4.2 Bend test (micrometer bend test) 4.2.1 Overview
A test method in which a coating is compressed by a micrometer to bend it. It is only suitable for evaluating brittle metal foils. For example, bright nickel plating. 4.2.2 Apparatus
Micrometer.
4.2.3 Preparation of test piece
Remove the base and cover foil to make a 0.5 cm × 7.5 cm test piece strip. The thickness of the box is usually 2~40 μm. Measure the thickness of the test piece at the bending point. The measured thickness is required to accurately reach 5% of its nominal value. The requirements of 4.1.3 are also applicable to this method. 4.2.4
GB/T15821—1995
Bend the test piece into shape and place it between the jaws of the micrometer. Slowly close the jaws of the micrometer and continue to bend the test piece until the test piece foil cracks. This test is carried out at least twice and the number of the micrometer and the thickness of the box are recorded (see Figure 11). 4.2.5 Result Expression
4.2.5.1 Calculation
Calculate the average value of the micrometer reading (see 4.2.4), the elongation expressed as a percentage), and calculate it by the following formula (see Figure 12): D = 2- =- 8100%
Where: Total thickness of the test piece, mm
2F--average value of the micrometer reading, mm. 4.2.5.2 Accuracy
It can be seen from formula (2) that it is important to measure the value with high accuracy. Otherwise, the D value will have a large deviation. 4.3 Bench vise bending test
4.3.1 Overview
A test method for reciprocating bending of the test piece with a bench vise. This method is relatively simple and has certain practicality, but the cold work hardening caused by bending and other factors may affect the test results, so comparative test results are often used. 4.3.2 Test apparatus
A bench vise with jaws (see Figure 13). 4.3.3 Preparation of test pieces
A test piece strip of 1 cm x 5 cm is prepared by removing the base covering layer of the foil. 4.3.4 Test procedure
The test piece is placed in a bench vise, and then the test piece is bent rapidly and continuously in the positive and negative directions at 90°, and repeated several times until the test piece breaks. 4.3.5 Result expression
The ductility result is expressed as the number of bends when the test piece breaks. 4.4 Hydraulic lifting test
4.4.1 Overview
This method clamps the test piece between the bottom of the hydraulic cylinder and a preload plate, on which there is an open circular hole with the same diameter as the cylinder. The water pressure is slowly increased to make the test piece deform steadily to a convex or arched shape until the test piece box bursts (see Figure 14). This method can accurately measure the ductility of the base sheet material, and is particularly suitable for measuring materials with high ductility. 4.4.2 Test apparatus.
See Figure 15.
4.4.3 Test process
Use the device shown in Figure 15, fill the hydraulic cylinder with water to the edge, place the test piece on the water surface, and tighten the test piece with a cover plate with a hollow cone. Draw water from the water and inject it into the hollow cone. The excess water rises to the top of the glass gauge. When the horizontal line exceeds the photosensitive device, the water flow valve of the water storage tank will be closed. Start the motor to slowly raise the photosensitive device. When the device and the meniscus liquid surface are on the same straight line, the light in the device is refracted, which causes the voltage to drop and the motor to be turned off. Use the Duse method to increase the pressure under the test piece. When the meniscus in the glass gauge begins to rise, the motor will start automatically, and the photosensitive device will also rise with the rise of the horizontal surface. The volume increase value is recorded on the XY recorder by potentiometric measurement. The pressure sensor in the hydraulic cylinder also records the pressure under the test piece. In the commercially available device, a pressure-sensitive element is used to turn off the motor at the moment of explosion. In this way, the total discharge of water can be read directly from the digital display of the potentiometer. 4.4.4 Results and Indications
4.4.4.1 Calculation
CB/T 15821—1995
The strength of the foil at break is determined. The specific calculation will be discussed in Appendix C (Supplement). 4.4.4.2 Variation Range
Since the test is carried out at the center of the foil (30 mm), the current density distribution and thickness at this location are relatively uniform during electroplating. The coefficient of variation S/D of 0.05, i.e., 5, is easily achievable. 4.4.5 Test Procedure Notes
Pinholes on the test piece may cause errors in the test results. Before the test, the pinholes can be checked by lighting. That is, a 100 Ω light bulb is placed in a box. There is a hole on the top plate of the box that is slightly smaller than the diameter of the cone opening in the device. The pinholes can be easily found by placing the test piece on the top plate.
When there is a pinhole, a very thin plastic film can be placed at the bottom of the test piece to prevent water from passing through the pinhole. By observing with a microscope, the moment of cracking can be found. At this moment, the motor of the photosensitive device is turned off, and the elongation of the porous foil will be clearly indicated. 4.5 Mechanical bulge test
4.5.1 Overview
The elongation is measured by rotating the micrometer to arch the steel ball to break the test piece, as shown in Figure 16. 4. 5.2 Test equipment
A simple test device can be composed of a micrometer, an upper shaft extension with a steel ball, two circular plates with a circular hole in the center and a clamping frame. The two ends between the main extension and the test piece are connected to a power supply and a light bulb (see Figure 17). 4.5.3 Test process
Place the test piece between the two circular plates and tighten the two circular plates with bolts. Then, turn the micrometer to push the main shaft extension so that the steel ball presses against the test piece foil. When the steel ball contacts the test piece box, the light bulb lights up. Record the reading on the micrometer at this time, and continue to push the steel ball until a crack in the metal foil is detected by a 15x magnifying glass. At this time, record the reading on the micrometer again. 4.5.4 Result expression
Calculate the convex conical surface part of the test piece foil The area change before and after the test, and finally the elongation is calculated using the height of the protrusion at the top of the cone, see Appendix D (supplement).
4.5.5 Special cases
An improved method can be used preferentially, as shown in Figures 18, 19 and 20. In the original device, the steel ball is stationary, and the two clamping plates and the test piece foil are driven downward by a motor until the test piece is cracked. Use a 70x microscope to observe the initial cracking at the observation point of the test piece. At the beginning of the test, when the steel ball forms electrical contact with the test piece, the motor stops: then the circuit is manually disconnected, and the drive motor drives the test piece to continue to move downward. At the moment of cracking, the circuit is closed and the motor is turned off. The height of the protrusion of the test piece is measured by a displacement potentiometer with a resolution of 5m. The motor-driven device is compared It is easier to get good results because: a. During the test, there is no torque generated by turning the micrometer screw between the steel or the test piece. h. It is best to use a Namarski-type microscope, which can more reliably observe the moment when the initial crack appears. c. The height of the protrusion of the potentiometer test piece box is more accurate than the micrometer. d. The improved method improves the lighting during the test and keeps the relative position between the microscope and the top of the protrusion of the test piece unchanged. It has better reproducibility than the above-mentioned micrometer method and is easier to achieve the coefficient of variation S/D=0.05, i.e. 6%. 5 Tests on haze cover with substrate
The following seven test methods are applicable to the testing of ten pairs of covering layers with substrate. These methods require that the micro-cover should have good bonding with the substrate The substrate has better ductility than the covering layer, which is especially important when evaluating very brittle electrodeposited layers. For example, the substrate can be made of annealed brass or suitable ABS plastic materials. This type of method can avoid many defects caused by foil making in the test of styrene covering layers, but when observing the cracking of the covering layer with visual inspection (including corrected vision) or a magnifying glass, it is necessary to find the cracking point very carefully. If the substrate is electroplated ABS plastic, measuring the electrowetting change of the covering layer during the test can accurately find the moment when the cracking occurs (see Figure 21). These methods can sometimes also be used to measure the brittleness of the substrate caused by the electroplating process, such as the nitrogen brittleness of galvanized hoops.
Seven methods are described as follows.
5.1 Tensile test
5. 1.1 Apparatus
See 4.1.2.
5.1.2 Preparation of test piece
GB/T158211995
In order to facilitate the test piece to be installed in the clamp of the tensile machine and avoid misalignment, the test piece is preferably made into a necked shape. The edge of the test piece can be polished to remove the burrs and prevent the edge from cracking.
5.1.3 Test procedure
See 4.1.4.
5.2 Three-point bending test
5.2.1 Overview
The two ends of the test piece are supported by two vertical force points. In the vertical direction of the center of the two force points, a force point is added to the other side of the test piece in the opposite direction, so that the test piece is slowly bent until the coating cracks.
5.2.2 Installation
The three loading methods listed in Figure 2 can be selected. These devices can be installed on a universal testing machine or a special bending device.
5.2. 3 Test process
The three points on the test piece are slowly and continuously loaded in the above manner, and the surface is checked repeatedly regularly to determine the exact moment of cracking of the coating. However, it should be noted that during the entire bending process, the test piece should be constantly observed for distortion or folding during the test (see Figure 23a). This is because distortion or folding of the test piece during the test will cause errors. 5.2.4 Result expression
The elongation D expressed as a percentage is calculated by the following formula 485
where: -- total thickness of the test piece, mm; Www.bzxZ.net
S vertical displacement, mmt
1. Standard length (distance between two support points), mm see Figure 12 and Figure 23b,
5.3 Four-point bending test
5.3.1 Overview
×100%
(3)
This test is similar to the three-point bending test, but the test piece is subjected to loads at two points symmetrical to the center (see Figure 24). The main advantage of this test is that it avoids distortion of the test piece.
5.3.2 Result expression
Express the elongation D in percentage, calculated by the following formula: as
+2L,100%
Where: S-total thickness of the test piece, mn; S-vertical displacement, mm; L-the distance between the two load application points, m; 1+Ig-half the distance between the two support points, mm. See Figure 24.
5.4 Cylindrical mandrel bending
CB/T 15821—1995
The narrow strip test piece or filamentary specimen of the cover to be tested is wound around a group of mandrels with decreasing diameters in turn for bending test 5.4.2 Apparatus
A clamp is provided with a group of mandrels with diameters of 5 to 50 mm and a step size of 3 mm (see Figure 25). 5.4.3 Preparation of test pieces
The substrate thickness and ductility of the test piece must be such that it can be bent around a minimum diameter mandrel without cracking. For example, a plated test piece with a thickness of 1.0 to 2.5 mm, a width of 10 mm and a length of at least 150 mm can be prepared using low carbon steel or ductile pins. 5.4.4 Test procedure
Bend the test piece around a mandrel of decreasing diameter and record the minimum mandrel diameter that does not cause cracking of the coating during bending to determine its ductility. If cracks are not easily observed, the bent test piece can be subjected to a porosity test again, where the cracks will expand into obvious crack lines. 5.4.5 Result Expression
The elongation D expressed as a percentage is calculated by the following formula:8
Dma+a× 100%
Where: —Total thickness of the specimen, nm;
d—Minimum mandrel diameter at which the covering layer does not crack, mm. 5.5 Bending on spiral mandrel
5.5.1 Overview
The test strip with the covering layer is wound around a spiral mandrel with a gradually decreasing curvature to avoid bending test. 5.5.2 Apparatus
Spiral mandrel (see Figure 26).
5.5.3 Test procedure
Bend the test piece along the spiral mandrel in the direction of the smallest curvature until cracks appear in the coating, and record the radius of curvature of the cracking part. If the substrate is a non-conductive body, the moment of cracking can be determined by electrical measurement (see Figure 21). 5.5.4 Result expression
The angle of bending (see Figure 27) can be used as a measure of the relative magnitude of elongation. The elongation expressed as a percentage is calculated according to 5.4, 5. 5.6 Cone mandrel bending
5.6.1 Overview
Bend the square test piece or filamentary specimen with coating around a circular mandrel for bending test (see Figures 28 and 29). This method is not suitable for measuring the elongation of the cover layer specimens with an elongation greater than 11% because the minimum curvature radius of the device is 4 mm and only the specimens with a thickness of less than 0.5 mm can be bent.
5.6.2 Device
Valve cone mandrel.
5.6.3 Test procedure
After the specimen is bent tightly around the cone mandrel, the surface of the specimen is examined with a 10x magnifying glass or microscope to identify the cracking position and the curvature radius of the cone at the position
5.6.4 Result, expression
The percentage of elongation is calculated by formula (5) based on the curvature radius of the cone at the cracking point of the specimen. 5.7 Mechanical protrusion (cupping test)
5.7.1 Overview
The ball (or spherical punch) is pressed evenly against the cover layer specimen clamped in the specified mold to cause cracking. 5.7.2 Apparatus
For the Lintu test machine, see 4.5.5).
GB/T 15821—1995
The test piece generally adopts a thin steel plate with no scratches as the substrate, so as to make the test result more reliable. Because when the substrate of the test bending part is scratched, it will affect the accuracy of the test result. 5.7.4 Test process
Same as 4.5.3.
The diameter of the test device and die hole should ensure that the area where cracks are expected can be observed under the 100x microscope field of view. Reproducible results may be obtained by selecting the matching hole and steel ball (or spherical punch) size according to the thickness of the test piece. 5.7.5 Result expression
For the calculation of the results, see Appendix D.
6 Selection of test method
6.1 It is impossible to recommend a method that can be suitable for measuring the ductility of covering layers of all materials and uses. The guidelines listed in the table in Appendix E (Supplement) will assist in the selection of the test method. However, it should be noted that the results obtained by different methods are rarely comparable. 6.2 Overlays less than 10 μm thick should be tested on a suitable substrate. Brittle deposits are preferably tested by tensile testing, but bending tests (5.4 and 5.5) are also available. Ductile deposits are preferably tested by bending tests (5.3). 6.3 Overlays thicker than 10 μm may be tested in the form of substrate foils. Ductile foils may be tested by the liquid protrusion method (4.4) or the tensile method (4.1). Brittle foils may be tested by the micrometer bend test (4.2) or the mechanical protrusion method (4.5). 6.4 Brittle and/or highly stressed overlays, even if they are more than 1 μm thick, should be tested on a suitable ductile substrate. In this case, although the cylindrical mandrel bending (5.4) or helical mandrel bending (5.5) test can be used, the tensile test (5.1) should be carried out first.
7 Test report
The test report should at least include the following: name, letter and description of the sample to be tested; b.
Standard number and test method used!
Testing device and equipment;
Testing conditions and specimen preparation;
Testing results and calculation formulas; t
Testing date and test personnel.
Metal foil
ryz= (z-dx)(y-dy)(z+de)
ryz =ryr + uydy — ady yedad
Figure 8 Tensile test
Tu (rd)(y - dy)( / d)
GB/T 15821—1995
Figure 4 Cupping test
Material flow
yz =( + dr)y +dy)z -- d)
GB/T 15821—1995
(r+dr)(y+uy) A+aA
Material flow
2(r*) = (z - dz)(r + dr)ty + dy)2A = (α—dA + A)
Figure 6 Cupping test (hydraulic or mechanical)
CB/T15821-1995
Usable dimensions of tensile test piece
Standard length, nm
Width, nm
Micrometer
Clamp bottle
GB/T15821--:1995
Respect the curve
Figure 14
GB/T 158211995
Digital display
Water storage tank
Hollow push,
Pressure group operation.
Xulong line
Glass extraction gauge
Measurement with photosensitive element
A flow surface business
One test piece1).
7 Test report
The test report shall at least include the following: b.
Name, number and description of the tested sample; b.
Standard number and test method used;
Test device and equipment;
Test conditions and test piece preparation;
Test results and calculation formula; t
Test date and test personnel.
Metal foil
ryz= (z-dx)(y-dy)(z+de)
ryz =ryr + uydy — ady yedad
Figure 8 Tensile test
Tu (rd)(y - dy)( / d)
GB/T 15821—1995
Figure 4 Cupping test
Material flow
yz =( + dr)y +dy)z -- d)
GB/T 15821—1995
(r+dr)(y+uy) A+aA
Material flow
2(r*) = (z - dz)(r + dr)ty + dy)2A = (α—dA + A)
Figure 6 Cupping test (hydraulic or mechanical)
CB/T15821-1995
Usable dimensions of tensile test piece
Standard length, nm
Width, nm
Micrometer
Clamp bottle
GB/T15821--:1995
Respect the curve
Figure 14
GB/T 158211995
Digital display
Water storage tank
Hollow push,
Pressure group operation.
Xulong line
Glass extraction gauge
Measurement with photosensitive element
A flow surface business
One test piece1).
7 Test report
The test report shall at least include the following: b.
Name, number and description of the tested sample; b.
Standard number and test method used;
Test device and equipment;
Test conditions and test piece preparation;
Test results and calculation formula; t
Test date and test personnel.
Metal foil
ryz= (z-dx)(y-dy)(z+de)
ryz =ryr + uydy — ady yedad
Figure 8 Tensile test
Tu (rd)(y - dy)( / d)
GB/T 15821—1995
Figure 4 Cupping test
Material flow
yz =( + dr)y +dy)z -- d)
GB/T 15821—1995
(r+dr)(y+uy) A+aA
Material flow
2(r*) = (z - dz)(r + dr)ty + dy)2A = (α—dA + A)
Figure 6 Cupping test (hydraulic or mechanical)
CB/T15821-1995
Usable dimensions of tensile test piece
Standard length, nm
Width, nm
Micrometer
Clamp bottle
GB/T15821--:1995
Respect the curve
Figure 14
GB/T 158211995
Digital display
Water storage tank
Hollow push,
Pressure group operation.
Xulong line
Glass extraction gauge
Measurement with photosensitive element
A flow surface business
One test piece
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