micro vicker hardness test


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micro vicker hardness test

  1. 1. Micro Vickers hardness test Micro Vickers hardness test The Vickers hardness test was developed in 1924 by Smith and Sandland. The test evaluates hardness in a manner similar to Brinell taking the ratio between the load applied and the surface area of the resulting impression. It was decided that the indenter shape should be one based on the following  To be capable of producing geometrically similar impressions, irrespective of size.  The resulting impression should have well defined points of measurement.  The indenter should have high resistance to self-deformation. The Vickers hardness test method consists of indenting the test material with a diamond indenter, in the form of a right pyramid with a square base and an angle of 136 degrees between opposite faces subjected to a load of 1 to 100 kgf. The full load is normally applied for 10 to 15 seconds. The two diagonals of the indentation left in the surface of the material after removal of the load are measured using a microscope and their average calculated. The area of the sloping surface of the indentation is calculated. The Vickers hardness is the quotient obtained by dividing the kgf load by the square mm area of indentation. The corresponding units of HV are then kilograms-force per square millimetre (kgf/mm²). To calculate Vickers hardness number using SI units one needs to convert the force applied from kilogram-force to newtons by multiplying by 9.806 65 (standard gravity) and convert mm to m. To do the calculation directly, the following equation can be used HV = 𝐹 1.8544𝐹 𝐴 𝑑2 Where F = applied load in gf D = average of dia n mm In micro Vickers hardness test a load of 1gf – 1000gf is applied. Indenter In this test diamond cone is used as indenter. As diamond has sharp edge so the dia of indenter is easy to find due to sharp edge. Angle between the opposite faces of the indenter is 136o, and use full angle is 120o. pg. 1
  2. 2. Micro Vickers hardness test Figure 1 indenter and impression Micro Vickers Test Method All Vickers ranges use a 136° pyramidal diamond indenter that forms a square indent.  The indenter is pressed into the sample by an accurately controlled test force.  The force is maintained for a specific dwell time, normally 10 – 15 seconds.  After the dwell time is complete, the indenter is removed leaving an indent in the sample that appears square shaped on the surface.  The size of the indent is determined optically by measuring the two diagonals of the square indent.  The Vickers hardness number is a function of the test force divided by the surface area of the indent. The average of the two diagonals is used in the following formula to calculate the Vickers hardness Calculation Applied load = 1.961 N Dwell time = 10 sec First diagonal = d1= 48.78 µm Second diagonal = d2=48.78 µm Average = d = 48.78 µm HV = 1528.26 N/mm2 Advantages The major advantages of the Vickers test method are  Simple conducting of the test pg. 2
  3. 3. Micro Vickers hardness test  Can be used for an extremely broad hardness range  Independent of the hardness value of the test load in the macro range  Suitable for testing small parts, thin sheet material and layers  Can be used to test structural constituents  Determination of case hardening depth possible with the corresponding equipment Disadvantages The major disadvantages of the Vickers test method are  More time required for test surface preparation and the exact measurement of the test impression  Diamond indenter susceptible to damage  Increasing susceptibility to shocks with decreasing test load  Shape deviation of indenter and test surface preparation influence the hardness result with small test impressions pg. 3
  4. 4. Micro Vickers hardness test References:  http://www.instron.us/wa/applications/test_types/hardness/vickers.aspx?ref=https://w ww.google.com.pk/  http://www.instron.us/wa/applications/test_types/hardness/vickers.aspx?ref=https://w ww.google.com.pk/  ASM metals handbook volume 8 mechanical testing and evaluation pg. 4