The wear of diamonds in impregnated diamond bit drilling

Abstract

The wear of diamonds in impregnated diamond microbits was investigated in the laboratory by drilling a variety of rock types. The wear was studied by optical and scanning electron microscopy after drilling under a range of bit pressures, rates of advance, and rotational velocities using bits of different diamond size and concentration. The nature of the diamond wear modes did not vary with the drilling conditions but the relative proportions of different types of diamond wear changed with drilling performance. For stable drilling in any given rock type a characteristic threshold pressure existed above which desirable microfracture of the exposed diamonds was promoted over undesirable wear flat generation. The flats are produced by a sliding wear mode with the silicate minerals ploughing plastic grooves in the heated surfaces of the diamonds. Microfracture mode is the result of progressive growth and coalescence of cleavage microcracks promoted by the cyclical stresses experienced by the diamonds at pressures sufficient to cause indentation of the rock.