Environment‐Sensitive Hardness and Machinability of Al ₂ O ₃

Abstract

The influences of water, toluene, and n ‐alcohols on the pendulum hardness of Al 2 O 3 monocrystals and on the ease of drilling of mono‐ and polycrystalline Al 2 O 3 were studied. Adsorption‐induced increases in pendulum hardness were produced by certain alcohol environments; these increases resulted in rates of drilling with diamond‐studded core bits of up to 10 times those measured under water. A correlation between pendulum hardness, machinability, and surface charge (as indicated by ζ‐potential measurements) was established and revealed that Al 2 O 3 is hardest and most effectively drilled with a diamond core bit at its zero point of charge. The possible use of this correlation in developing more cost‐effective and ecologically viable cutting fluids for the machining of Al 2 O 3 is discussed.