BS ISO 14705:2016 pdf free download.Fine ceramics (advanced ceramics, advanced technical ceramics) — Test method for hardness of monolithic ceramics at room temperature.
Vickers indenter
Indenter In the shape of a rlghi’angle pyramid with a square base and an angle between opposite faces of 136
Note ito entry: See Ithlcl and Figure 1.
3.3
Knoop hardness
value obtained by dMding the applied force by the proected area of the indentation computed from the measurement of the long diagonal of the indentation, assuming that the Indentation is an imprint of the undeformed indenter
Note Ito entry: The Knoop hardness may be expressed In two different units:
a) with units of GPa, obtained by dividing the applied force in N by time prolected area of the Indentation In mmz:
b) Knoop hardness number, obtained by dividing the applied force in kgf by the proec1ed area oltiw indentation
In mmz, without units specified.
3.4
Knoop Indenter
Indenter In the shape cia rhombk.based pyramid wIth the two angles between the opposite edges at
172,5 and 130
Note ito entry: See Iabki and Figure 6.
4 Vickers hardness
4.1 Principle
Forcing a diamond indenter in the farm of a right-angle pyramid with a square base, and with a specifIed angle between opposite faces at the vertex into the surface ala test piece and measuring the length of the diagonals of the indentation left in the surface after removal of the test force. I See Fieure 1 and Figure 2.
4.2 Symbols, abbreviated terms and designations
4.2.1 See Table 1.. FIgure 1 and Figure 2.
4.2.2 The Vickers hardness is denoted by the symbol HV, preceded by the hardness value and followed by a number representing the test force (see Table 2).
Examples:
a) Use olSi unit (GPa):
15.0 GPa HV 9,807 N represents a Vickers hardness of 15.0 GPa, determined with a test force of
9,807 N (1 kgf)
b) Use of the Vickers hardness number (no units specified):
1 500 HV I represents a Vlckers hardness number of 1 500. determined with a test force of 9,807 N (lkgf).
4.4 Apparatus
4.4.1 TestIng machine, capable cii applying a predetermined test force in the range of 4.903 N (0.5 kgf) to 98,07 N (10 kgf), preferably 9,807 N (1 kgf), in accordance with ISO 6507-2. Verification of the test force shall be carried out in accordance with ISO 6507-2.
4.4.2 Diamond indenter, in the shape of a right-angle pyramid with a square base, as specified in ISO 6507-1 and ISO 6507-2. Veritkatlon of the indenter shall be carried out in accordance with lS06507-2.
4.4.3 MeasurIng device, capable of measuring the indentation diagonals with a readout resolution of tO,2 pm or finer. A numerical aperture (NA) between 0,60 and 0.95 for the ob)ectlve lens for the microscope Is recommended. Verification of the measuring device shall be carried out In accordance with ISO 65 07-2.
NOTE Indirect verification can b carried out by means of standardized blocks calibrated In accordance with ISO 6507-3, Iollowlag ISO 6507-2 or other approved and traceable ceramic standard reference blocks.
4.5 Test pieces
4.5.1 The test shall be carried out on a surface which is smooth, flat and free from foreign matter. The test piece shall be polished to permit accurate measurement of the diagonal lengths of the indentation. Preparation shall be carried out in such a way that any alteration of the surface hardness is minimized. Surfaces shall not be thermally or chemically etched. If applicable, residual surface stresses shalt be removed by suitable polishing or annealing procedures.
4.5.2 The thickness of the test piece shall be at least 0.5 mnt It shall be at least 1,5 tImes the diagonal of the indentation. d. and at least 2 times the crack length. c, whichever is greater. No indentation damage shall be visible at the back of the test piece upon completion of the test
4.6 Procedure
4.6.1 In general, the rest shall be carried out at room temperature within the limits of 10 °C to 35 UC. Tests carried out under controlled conditions shall be made at a temperature of 23 C ± 5 C.
4.6.2 The test force shall he 9.807 N (1 kgf). In cases where significant chipping or lateral crack-spallirig occurs or where the impression is too faint, the test forces within the range 4.903 N (0,5 kgf) to 196,1 N (20 kgfl. listed in Table 2. may be used. Other instances where a heavier load maybe required are where the grain structure is very coarse and the indentation area at lower loads may contact only a few grains of the material (e.g. a multiphase material).
4.6.3 The following Items shall be confirmed before the test.
a) Check the zero of the measuring system.
b) £heck the measuring system using a calibrated scale or certified indentation in a test block
c) Check the operation of the loading system by performing a test on a certified Lest block.
d) Check the condition of the Indenter by examining the Indentation made in the test block. Replace the indenter, If necessary, by taking into account the conditions given in 4A10.
e) A test block with high hardness has to be used in order to obtain Impressions in the same size range as expected during tests on ceramics.
4.6.4 The indenter shall be cleaned prior to and during the test series, as ceramic powders or fragments from the ceramic test piece can adhere to the diamond indenter.
5.6.5 the test piece shall be placed on a rigid support. The support surface shall be clean and free from foreign matter. It is important that the test piece lie firmly on the support, so that displacement cannot occur during the test. The surface of the test piece being tested shall be on a plane normal to the axis of the indenter.
5.6.6 Carefully adjust the illumination and focusing conditions to obtain the optimum view and clarity of the indentation. Both Indentation tips shall be in focus at the same time, Do not change the locus when measuring the distance from tip to tip.
5.6.7 Bring the indenter Into contact with the test surface and apply the test Force in a direction perpendicular to the surface, without shock or vibration, until the applied force attains the specified value. The time from the Initial application of the force until the full test force is reached shall not be less than 1 s nor greater than S s. The duration of application of the test force shall be ISs.
5.6.8 Throughout the test, the apparatus shall be protected from shock or vibration.
5.6.9 Allow a distance of at least 1.5 times the long diagonal length between the Indentations as shown in Figure 8. If there is evidence of interaction between lateral cracking (from the sides of the indentation). then the spacing shall be increased. The minimum distance between the limit of any indentation and the edge of the test piece shall be at least IS times the long diagonal of the indentation.
5.6.10 the satisfactory condition of the indenter shall be verified frequently. Any irregularities in the shape of the indentation may indicate chipping, cracking or other poor conditions of the indenter. If the examination of the indenter confirms this, then the test shall be rejected and the indenter replaced.
5.6.11 If there Ls excessive cracking from the indentation sides, the Indentation shall be rejected and go unmeasured. 11 one of the tips of an indentation falLs into a pore, the indentation shall be rejected. If the indentation lies in or on a large pore, the indentation shall be rejected. Figure 9 provides guidance in this assessment
5.6.12 Measure the length of the long diagonal to within 0,2 pm for less than 50 pm, or to within 0.5 tm for equal to or more than 50 pm. The length is used for the calculation of the Knoop hardness number. Ii one leg (one.half) of the long diagonal is more than 10 % longer than the other (see Figurf 9). or if the ends of the diagonals are not both in the field of focus, the surface of the test piece may not be normal to the axis of the indenter. Align the test piece surface properly and make another indentation. Follow the manufacturer’s instructions very carefully with regards to the proper usage of the measuring crosshairs. Figure lOis provided for guidance.
5.6.13 At least five valid Indentations shall be made for obtaining a mean result in accordance with this document.
5.6.14 Calculate the Knoop hardness, HK, for each valid Indentation, using the formula in Table 3.
Calculate the mean hardness for all valid Indentations and the standard deviation. The calculated Knoop
hardness shall be expressed with three significant numbers (e.g. 15,4 GPa KK 9.807 N or 1520 BK 1)
5.6.15 See ISO 4545-4 for a table of values for use In tests made on flat surfaces.
5.7 Accuracy and uncertainty
The Knoop test is conducted in the same manner as the Vidcers test, except that only the long diagonal is measured. Since the indentation is much shallower than the Vickers indentation, the angle of intersection of the indentation surfaces with the original surface is small, and the optical contrast this produces in conventional measurement systems tends to be poorer than in the Vickers case. Possible measurement errors and biases are thus much larger and as the round’robin exerciseltl demonstrated. the fractional error in the test results is similar to or greater than that for Vickers tests at the same.