Question

Ultrahard and superhard materials are incomepressible solids with high hardness values that can rival that of diamond. They are used in a range of applications from polishing, cutting, to medical implants and heavy industry. Given the concepts you learned in this course, if you were asked to design a material with exceptionally high hardness values, what would be your strategy?

Answer 1

Hardness is a measure of the resistance to plastic deformation induced by either mechanical identation, scratching or abrasion.

Nano-hardness test uses minor loads of about 1 nano-Newton followed by precise measuring depth of indentation. We use following techniques to find the hardness.They are:

• Brinell Hardness Test.
• Rockwell Hardness Test.
• Rockwell Superficial Hardness Test.
• Vickers Hardness Test.
• Knoop Hardness Test.
• Shore Scleroscope Hardness Test.

Approach:

We require materials with exceptionally high hardness for different applications. So first to do any one of the hardness tests mentioned above. Mostly we use Rockwell hardness test for finding hardness of the material.

1)Rockwell hardness test:

The hardness of a material by this Rockwell hardness test method is measured by the depth of Penetration of the indentor. The depth of Penetration is inversely proportional to the hardness. Both ball or diamond cone types of indenters are used in this test. There are three scales on the machine for taking hardness readings.

Scale “A” with load 60 kgf or 588.4 N and diamond indenter is used for performing tests on thin steel and shallow case hardened steel.

Scale “B” with load 100 kgf or 980.7 N and 1.588 mm dia ball indenter is used for performing tests on soft steel, malleable iron, copper and aluminum alloys.

First minor load is applied to over come the film thickness on the metal surface. Minor load also eliminates errors in the depth of measurements due to spring of the machine frame or setting down of the specimen and table attachments. The Rockwell hardness is derived from the measurement of the depth of the impression.

EP = Depth of penetration due to Minor load of 98.07 N.

Ea = Increase in depth of penetration due to Major load.

E = Permanent increase of depth of indentation under minor load at 98.07 N even after removal of Major load.