Zirconium alloyed tungsten borides synthesized by spark plasma sintering

Abstract

Tungsten borides (WBx; x = 2.5 or 4.5) with an increasing substitution of tungsten by zirconium from 0 to 24 at.% were synthesized by spark plasma sintering (SPS) for the first time. The influence of the holding time (2.5–30 min) on the densification behavior, microstructure evolution and development of the properties of W–Zr–B compounds were studied. The samples were characterized using scanning electron microscopy (SEM) for microstructure analysis, X-ray diffraction (XRD) for phase identification, Vickers micro-indentation for microhardness measurements, tribological tests to determine the coefficient of friction and specific wear rate, as well as measurements of electrical conductivity. The XRD results confirm the presence of the WB4 phase in the microstructure, despite the high sintering temperature (1800 °C) and small overstoichiometric excess of boron (4.5) addition in the sintered samples. This is caused by the high heating rate (400 °C/min), short holding time (2.5 min) and addition of zirconium. The Vickers hardness (HV) values measured at 1 N are 24.8 ± 2.0 and 26.6 ± 1.8 GPa for 24 at.% zirconium in WB2.5 and for 0 at.% zirconium in WB4.5, respectively. In addition, the hardest sample (W0.76Zr0.24B2.5) showed electrical conductivity up to 3.961·106 S/m, which is similar to WC–Co cemented carbides. The friction and wear test results reveal the formation of a boron-based film which seems to play the role of a solid lubricant.

Properties of Spark Plasma Sintered Compacts and Magnetron Sputtered Coatings Made from Cr, Mo, Re and Zr Alloyed Tungsten Diboride

“…With an increasing zirconium content, the electrical conductivity of the SPSed specimens increased both in W 1−x Zr x B 4.5 and W 1−x Zr x B 4.5 (0 < x ≤ 0.24). W 0.76 Zr 0.24 B 2.5 sintered at a 24 min holding time is characterized by the highest electrical conductivity of 3.961 × 10 6 S/m, which is similar to the electrical conductivity of WC-Co cemented carbides [9]. In the case WB 4 alloyed with chromium (Cr), Mohammadi et al [13] showed that addition of 10 at.% Cr on a metals basis results in an increase in microhardness (at 0.49 N) from 43.3 ± 2.9 GPa for pure WB 4 to 53.5 ± 1.9 GPa and the defect structure of this material may be responsible for the hardening trends observed for the solid solutions.…”

“…It is clearly seen that the densification process is complete and after 24 min the displacement of punch is nearly constant. Optimal sintering parameters were selected on the basis of [9], where the influence of the holding time (2.5-30 min), sintering temperature and compacting pressure on the densification behavior, microstructure evolution and development of the properties of W-Zr-B compounds were studied. An example of sintering curves (chromium) is presented in Figure 1.…”

“…As it was shown by Garbiec et al [9], it is possible to synthesize in one stage fast process the W 1−x Zr x B 2 ceramic with properties competitive to the widely used WC-4Co sintered compacts. Additionally, until now there has been no information about the use of WB x alloyed by Re, Mo, Cr, Zr as a coatings deposited by magnetron sputtering (MS).…”

“…However, a major challenge remains in that the applications are to produce reliable tool components made of these materials in a relatively simple and time-consuming manner. This challenge is partly resolved by deposition of thin films [5][6][7][8] developing easily machinable materials [3] or new methods of sintering [9]. For better electro machining the good electrical conductivity is needed.…”

“…Additionally, corrosion resistance of WB 2 ceramic was improved. In the case of alloying with zirconium (Zr) [9], the spark plasma sintered compacts are characterized by a specific wear rate in the range of 1 × 10 −6 -3 × 10 −5 mm 3 /Nm. The friction and wear test results reveal the formation of a boron-based film which seems to play the role of solid lubricant.…”