Thin films of novel superhard composite materials consisting of TiN nanocrystals in an amorphous Si3N4 matrix have been prepared by means of plasma chemical vapor deposition. The films show a high Vickers hardness of 5000 kg/mm2 and elastic modulus of ≳500 GPa, and they are resistant against oxidation in air up to ≥800 °C. The theoretical background of these unusual properties are briefly discussed and practical rules suggested according to which similar properties should be expected for composites of other ternary systems.
Thin films of superhard nanocrystalline nc-W2N/amorphous a-Si3N4 composite have been prepared by plasma chemical vapor deposition at temperatures in the range, 500–550 °C. Maximum hardness of 5200 kg/mm2 (about 51 GPa) and elastic modulus of ≥500 GPa is reached at a silicon content of 7–8 at. %. During the indentation experiment the material shows a large elastic recovery of 80%, which compares favorably with those of hard a-C:H (hardness only about 2000 kg/mm2). The results are similar to those recently obtained with nc-TiN/a-Si3N4 and thus support our concept for the design of novel superhard composite materials with a variety of transition metal nitrides. The question of the upper limit of the strength of these materials is addressed and discussed.
We have developed a theoretical concept for the design of novel superhard materials and verified it experimentally on several systems nc-MenN/a-Si3N4 (nc-MenN is a nanocrystalline transition metal nitride imbedded in a thin amorphous Si3N4 matrix). Hardness in excess of 5000 kg/mm2 (about 50 GPa) and elastic modulus of ≥550 GPa have been achieved [1-3]. Here we address the questions of the universality of the concept for the design of a variety of nc/a systems and the upper limit of the hardness which may be achieved.
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