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Microhardness profile obtained from MET 231 Laboratory Study of an industrial tractor transmission gear tooth. This gear experience an advanced carburizing process that first pumped high carbon into the surface, followed by surface decarburizing to generate a nearly constant carbon concentration profile to a specified depth. This produced the nearly constant harness profile near the surface of the gear tooth.

Mechanical Properties Laboratory Mentor
Dr. Dana Medlin Office: MI 104

The red circle identifies where the diamond indenter is damaged. The actual cause is unknown. If a user attempted to rotate the indenter/lens turret, before the load was released, it is possible the shear stress on the diamond, as it plows through the metal sample may have caused a chip to break off the diamond. Do not rotate the lens/indenter turret while the load is still applied! A common problem is excessive force is applied to the sample holder. This causes the two fingers that support the top of a sample to bend. Only a gentle force is required to hold the specimen in place. Overstressing of the sample holder causes the following problems. (1) The sample plane is no longer level which produces asymmetrical indentations. (2) The lens can collide with the edge of the sample if it is not level.

Quick Links to BUEHLER MICROMET® Hardness Tester Operation Topics BUEHLER MICROMET® Hardness Tester Calibration Operation Vickers Hardness Measurement Video Illustration of a Typical Test VIA-110 Video Microhardness System VIA-110 Video Operation Instructions

The following several adjustments are required before making any measurements.

Some text and line drawings used in the following section are taken from Buehler's "Operation and Maintenance Instructions" provided with the instrument.

1. Place the HV 700 standard into the micro test table vise. Pay attention to level of the test surface so that it is always perpendicular to the diamond indentor. A bubble level is available if it is suspected the instrument has been moved. Because of the many users of this instrument, it is good practice to make sure the specimen vise is level befor proceeding.
   
   
2. Adjust the visual brightness of the measuring microscope with the brightness adjusting knob located on the right side of the instrument. A visual field that is too bright will cause eye fatigue. Reduce the brightness as desired.
   
   
3. Rotate the table elevating handle slowly to focus on the specimen surface. To prevent the objective lens from being damaged by the specimen surface, raise the specimen surface to a point very close to the objective lens, then lower the specimen until it is in focus while observing through the microscope. For focusing, the 40x measurement lens is usually used. The 10x objective lens for observation may be used first, but must be switched to the 40x lens for final adjustment and indentation.
   
   
4. The diopter adjustment is critical for optimum measuring accuracy and must be adjusted to each operator's eye. Rotate the eyepiece so that the inside edges of the two measurements lines are as sharply in focus as possible.
   
   
5. When the dial on the left side of the measuring microscope is set to zero, the left measurement line will be in the center of the visual field. Move the right measurement line in the visual field with the right dial. The objective is to move the Left and Right lines together until no light is visible between them. This is illustrated in the movie clip below.
   
   
6. Press the SET key for at least two seconds. The digital display is now zeroed. (This operation is necessary only when the main power is off. It is not necessary for normal power-up.)
   
   Note: Do not overlap the right and left measurement lines when operating the right knob.
   
   

   Video of Filer Measurement Centering and Setting the Measurement Zero
   	DSL or Cable Dial Up Modem

   
   
   Operation
   
   Some text and line drawings used in the following section are taken from Buehler's "Operation and Maintenance Instructions" provided with the instrument.
   
   
   1. Rotate the 10x lens so it is vertical. Rotate the focus (table lift control) so there is at least a one or two mm clearance between the top of the tangs and the bottom of the lens.
   2. Placed the polished metallographic specimen into the self-leveling vice and gently secure the specimen by turning the knurled wheel. Please do not used excessive force, the specimen simply needs to be held in place. At least a dozen times last semester the tangs that support the top of the sample has been found bent!
      
      
   3. Center the tangs under the 10x lens and focus.
   4. Select a test load suitable for the material being tested. Loads from 10 g_f to 1000 g_f are set using the dial on the upper right side of the instrument. The load in the image is 300 g_f.
      
      
   5. Set the Dwell time. Use the same dwell time for all tests. If experiments are to be conducted over a long period of time, to ensure consistency the same dwell time must be used during the life of the experiment.
      
      To set the dwell time push the Dwell Time button and hold it until the desired time is displayed. It will cycle between 5 and 50 seconds while the button is held down in steps of one second.
      
      What is dwell time? It is the time the load is applied and/or the time the user allows plastic deformation, as the indenter pushes into the sample. The deformation rate after the constant load has been applied is called creep.
      
      
   6. Select the test area and carefully focus on the sample surface. Since focus is related to the distance the indentor has to travel, the measuring lens must be used before the indentation occurs.
   7. Rotate the turret slowly, making sure that the specimen or vise will not contact the indenter. Clearance between the diamond indenter tip and the specimen surface should be no more than 1.0 mm.
   8. Press the START key on the front panel to start load application. The green LED turns ON. The diamond indenter lowers slowly, touches the specimen surface, and begins to penetrate into the specimen until a preset test load reaches the maximum. The dwell timer is activated when the full load is applied. After preset time has passed, the diamond indenter rises slowly and the load is released. At this time the green LED turns OFF.
      
      The loading LED goes ON when load application begins and is turned OFF when the load is released. It is now safe to rotate the turret to select the 40x objective lens for measurement.
      
      Note: Never rotate the turret while the loading LED is ON!
      
      
   
   Vickers Hardness Measurement
   
   Some text and line drawings are used in the following section are taken from Buehler's "Operation and Maintenance Instructions" provided with the instrument.
   
   
   1. The diagonal length of an indentation is measured as follows:
      1. Bring the inside edges of the two measurement lines and four corners of an indentation into focus.
      2. Rotate the left knob on the filar eyepiece to align the inside of the left measurement line to the left edge of the indentation accurately.
      3. Rotate the right dial on the filar eyepiece to align the inside of the right measurement line to the right edge of the indentation. Press the READ switch on the lower right of the filar eyepiece once. The length dl is displayed on the display unit and fixed. Since Vickers hardness is usually obtained from the average length of the two diagonal lines, rotate the filar eyepiece 90^o to align the measurement lines to the edges of another diagonal line of the indentation and press the READ switch again; length d2 is displayed.
   
   The average of dl and d2 are calculated and HV is displayed, based on the load selected.
   
   Video Illustration of a Typical Test
   
   

   Illustration of Vickers Hardness Measurement The sharpness of the diamond pyramid indention is due to the need for a lens adapter for the video camera -- I hope I can fix this at a later date.
   	DSL or Cable Dial Up Modem

   
   
   VIA-110 Video Operation Instructions
   

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   Two Power Switches Must Be Turned On
   The VIA-110 Controller	The TV Monitor
   	The P1(X) and P2(Y) knobs are used to program the test parameters. PROGRAM CONTROLLER: Move to the screen illustrated below by pushing the SELECT button.
   Start-up Screen The start-up screen provides for setting various parameters.	The appearance of the programming screen after pushing the SELECT button. Note the cursor is located adjacent to the BEGIN line. Go to next panel.
   	Rotate the P1 knob to move cursor so as to select a test parameter. Illustrated here is selecting the Vickers hardness conversion to Rockwell B (HRB), which will be displayed along with the Vickers hardness number on the CRT. To fix this programming selection, push the SELECT button. Repeat this step to select other test parameters as needed. Go to next panel.
   	To select the indentor, load and dwell time move the cursor to the LABEL MENU, then push the SELECT button. Go to next panel.
   	The next objective is to set the LOAD and DWELL time. Go to next panel.
   	Using the P1 knob, move the curser to the LOAD line. Rotate P2 to the digit to be changed. Rotate P1 until correct digit is displayed. Repeat this process until the desired load is displayed. When the correct LOAD is displayed push the SELECT button. Continue the process to change the DWELL time if needed. Go to next panel.
   	With load and dwell properly displayed, move the cursor to MAIN MENU, then push the SELECT button. Go to next panel.
   	With the correct LOAD and Dwell parameters set, the VIA-110 computer will compute and display the correct hardness and other defined outputs. On this screen -- not an actual hardness test -- no Vickers indentation present The two pairs of horizontal and vertical line defining the body diagonals produced by a Vickers indenter are 83.4 and 71.9 µm respectively Load is 500 gf Dwell time is 20 seconds Vickers hardness (HV) is 153.9 Rockwell B hardness number (HRB) is 81.3 Go to next panel.
   	View of actual indentation on the surface of an etched steel specimen. The horizontal and vertical lines surround the body diagonals of the hardness indentation. To accomplish this task, use P1 and P2 knobs and the tilt switch labeled x and y respectively on the VIA–110 controller. .

   
   

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     9.  Link to Quiz and Web Site Evaluation Form
   
   

   If you are enrolled in MET 231, 331 or 441/541 the Username and Password is your student ID number. If you are working on a CAMP or AMP project and enrolled as an graduate or undergraduate student, contact Dr. Medlin via email. Your Password and Username will set as your student ID number. If you are a visitor, email or contact Dr. Medlin directly. A temporary Username and Password will be provided.

   Unsupervised use of this equipment requires personal certification by Dr. Medlin, or passage of the qualifying quiz with a grade of 100%