.4. Fracture toughness
Fracture toughness by the indentation technique is the measure of resistance to crack propagation when the material is subjected to applied load. The same micro hardness tester was used for this purpose with a variation in test load from 9.8 to 49 N. The lower limit of load (9.8 N) was selected such that it can generate a visible crack at the corners of indentation marks. Most of the samples were observed to fail above 49 N load, which set the upper limit of applied load. The lengths of the impression diagonals and surface cracks were measured after indentation.