Thermal Evolution of WC/C Nanostructured Coatings by Raman and In Situ XRD Analysis

• Published in: Plasma processes and polymers Vol. 6; no. S1; pp. S444 - S449
• Main Authors: Mrabet, Said El, Abad, Manuel David, López-Cartes, Carlos, Martínez-Martínez, Diego, Sánchez-López, Juan Carlos
• Format: Journal Article
• Language: English
• Published: Weinheim WILEY-VCH Verlag 01.06.2009; WILEY‐VCH Verlag
• Subjects: annealing; Carbides; Carbon; Coatings; Deposition; Fittings; nanocomposite coatings; Nanostructure; Phases; Polycarbonates; Raman spectroscopy; Thermal stability; Tungsten carbide; X-ray diffraction
• ISSN: 1612-8850; 1612-8869
• DOI: 10.1002/ppap.200931004

In this work, a series of WC/C nanostructured films were deposited on silicon substrates by changing the ratio of sputtering power applied to graphite and WC magnetron sources (PC/PWC: 0, 0.1, 0.5, 1). The thermal stability of WC/C coatings was followed in situ by means of X‐ray diffraction measurements up to 1 100 °C in vacuum (10−1 Pa). Initially, the film microstructure is composed of nanocrystalline WC1−x and W2C phases. As the PC/PWC ratio increases the crystallinity decreases, and WC1−x becomes the predominant phase from PC/PWC = 0.1. The results show that the structural evolution with temperature of all studied layers depends essentially on their initial phase and chemical composition (determined by the synthesis conditions: ratio PC/PWC). The coating deposited at PC/PWC = 0 reveals a transformation of W2C phase into W and W3C phases at 400 °C. However, the samples with PC/PWC greater than 0 exhibits an improved thermal stability up to 600–700 °C where the WC1−x begins to transform into W2C and WC phases. At 900 °C, WC is the predominant phase, especially for those coatings prepared with higher ratios. Further annealing above 1 000 °C yields W as the foremost phase. The thermal behaviour was later studied by means of Raman spectroscopy measurements at certain temperatures where the main changes in phase composition were observed. Particularly, a fitting analysis was carried out on the D and G bands typical of disordered and amorphous carbon. The changes induced during heating are discussed in terms of the positions of D and G lines, and full width at half maximum (FWHM).