Tolga Tavsanoglu

Abstract:

Boron carbide (B4C) is the third hardest material at room temperature, surpassing even diamond and cubic boron nitride at temperatures over 1100 °C. It has many other attractive properties such as good wear resistance, high modulus, high chemical and thermal stability. These properties make boron carbide a promising candidate as hard and protective coatings for cutting tools, automobile parts, hard disk drives and other wear–resistance applications. Despite of these significant properties, boron carbide has not been investigated extensively in thin film form. In this study, we present our results on the deposition of boron carbide thin films by focusing on the micro/nanostructural properties of the coatings obtained. Boron carbide thin films were deposited by DC magnetron sputtering of a B4C target on Si (100) and steel substrates. Nanostructural observations conducted by TEM, HRTEM and EFTEM showed that columnar morphologies of B4C films deposited without heating and at floating potential formed by 20-25 nm thick single columns and 2-3 nm thick nano-voids at the column boundaries where impurity oxygen was present. Microstructural analyses realized by FE-SEM demonstrated the densification and the transition from columnar to non-columnar, featureless morphologies of the coatings with the increase in the bias voltages and temperature. Chemical analyses realized by EPMA demonstrated that films with columnar structures had excess amount of impurity oxygen in their composition. Boron carbide films obtained were amorphous according to FFT patterns. Hardness of films obtained from nanoindentation studies increased from 20±2 GPa to 40±2 GPa with the increase in the bias voltages and temperature, demonstrating that ultrahard boron carbide films with superior mechanical properties can be obtained by DC magnetron sputtering.