The effects of x-beam irradiation with different doses on microhardness and its related physical constants on
[Ky(NH4)1-y]2ZnCl4 mixed crystals with concentrations, y equals 0.000, 0.232, 0.644, 0.859 or 1.000 has been
studied. The tests were performed for x-doses from 0.2 kGy up to 1.6 kGy for loads from 20 to 160 g. The
variation of hardness on (010) faces of orthorhombic [Ky(NH4)1-y]2ZnCl4 mixed crystals with load were
studied. The experimental results showed that, the hardness decreased as the x-doses increased. Variation of
the microhardness follows the normal ISE trend for low x-doses and un-irradiated crystals, then follows the
reverse ISE trend for high x-doses. Analysis of the experimental results revealed that: the radial cracks length,
indentation size and applied indentation load are mutually related, and these dependences related with fracture
mechanics are the basis of Meyer's empirical law. Indentation size effect (ISE) can be explained satisfactory
by Hays-Kendall's approach and proportional specimen resistance model. Brittleness of two cracks system are
applicable for characterizing cracks around indentation impression (i.e. radial cracks) and another is (lateral
cracks) for [Ky(NH4)1-y]2ZnCl4 mixed crystals, crystals in the load range 60 – 160 g. It is shown that
indentation induced microhardness decreases, whereas the length of radial cracks induced on indentation
increases with the increase of x-doses.