Excellent mechanical properties of metastable c-WN fabricated at high pressure and high temperature

• Published in: International journal of refractory metals & hard materials 2017-08, Vol.66, p.63-67
• Main Authors: Wang, Changchun, Tao, Qiang, Li, Yan, Ma, Shuailing, Dong, Shushan, Cui, Tian, Wang, Xin, Zhu, Pinwen
• Format: Article
• Language: English
• Subjects: Bulk modulus; Decomposition; Diamond pyramid hardness; Diamonds; Diffraction; Hardness; High temperature; Mechanical properties; Metastable phases; Microhardness; Pressure effects; Protective coatings; Sodium chloride; Studies; Synergistic effect; Synthesis; Tungsten; X-ray diffraction
• ISSN: 0263-4368
• DOI: 10.1016/j.ijrmhm.2017.02.004

Tungsten nitrides (WNs) are promising functional materials with high hardness, but the greatest challenge is to synthesize stoichiometric and bulk materials. In this paper, bulk tungsten mononitride (c-WN) with sodium chloride structure, which is a metastable phase, has been successfully synthesized at high pressure and high temperature (HPHT) using W3N4 as precursor. It is found that synergistic effect of pressure and temperature was useful to control the complete decomposition of W3N4 and to suppress further decomposing of as-synthesized c-WN. The compression ability and Vickers hardness were investigated by in situ high pressure X-ray diffraction (XRD) and Vickers microhardness tests, respectively. It is worth noting that the bulk modulus of c-WN is 422.9 ± 6.7 GPa, which is comparable to diamond. The Vickers hardness, 29 GPa obtained under an applied load of 0.49 N, is nearly 45% higher than that of TiN which is widely used as hard wear protective coatings. The excellent mechanical properties of c-WN may be ascribed to strong psingle bondd hybridization which has been further proved by XPS.