Influence of Transition Metal Type and Sputter Deposition Conditions on the Hardness of Transition Metal Carbide Thin Films

Transition metal carbides (TMCs) are known for their ultrahigh melting temperatures and high hardness making them ideal for coating applications in extreme environments. The present work investigates the role of atomic mass and chamber pressure on the resulting film hardness for a series of Zr, Nb, and Ta TMCs that are synthesized via reactive gas sputter deposition. For all TMCs, for deposition pressures between approximately 7 – 13 mTorr, the hardness varied between 5 – 15 GPa, which is lower than their bulk values as measured from consolidated powder billets. However, at 4 mTorr, ZrC and NbC hardness rose to approximately 20 and 27 GPa, respectively, which is closer to and at their bulk values and TaC rose to a hardness near 47 GPa, which is greater than its bulk value and is within the superhard regime. These collective effects are explained through the changes in crystallite sizes, film texture, and film densification that occur because of atomic peening effects between the different transition metal atomic masses and sputtering pressures that alter the arrival energy during deposition.