10.1021/jacs.6b02676.s001

Extrinsic Hardening of Superhard Tungsten Tetraboride Alloys with Group 4 Transition Metals

Abstract

Alloys of tungsten tetraboride (WB<sub>4</sub>) with the group 4 transition metals, titanium (Ti), zirconium (Zr), and hafnium (Hf), of different concentrations (0–50 at. % on a metals basis) were synthesized by arc-melting in order to study their mechanical properties. The phase composition and purity of the as-synthesized samples were confirmed using powder X-ray diffraction (PXRD) and energy dispersive X-ray spectroscopy (EDS). The solubility limit as determined by PXRD is 20 at. % for Ti, 10 at. % for Zr, and 8 at. % for Hf. Vickers indentation measurements of WB<sub>4</sub> alloys with 8 at. % Ti, 8 at. % Zr, and 6 at. % Hf gave hardness values, <i>H</i><sub>v</sub>, of 50.9 ± 2.2, 55.9 ± 2.7 and 51.6 ± 2.8 GPa, respectively, compared to 43.3 GPa for pure WB<sub>4</sub> under an applied load of 0.49 N. Each of the aforementioned compositions are considered superhard (<i>H</i><sub>v</sub> > 40 GPa), likely due to extrinsic hardening that plays a key role in these superhard metal borides. Furthermore, these materials exhibit a significantly reduced indentation size effect, which can be seen in the plateauing hardness values for the W<sub>1–<i>x</i></sub>Zr<sub><i>x</i></sub>B<sub>4</sub> alloy. In addition, W<sub>0.92</sub>Zr<sub>0.08</sub>B<sub>4</sub>, a product of spinoidal decomposition, possesses nanostructured grains and enhanced grain hardening. The hardness of W<sub>0.92</sub>Zr<sub>0.08</sub>B<sub>4</sub> is 34.7 ± 0.65 GPa under an applied load of 4.9 N, the highest value obtained for any superhard metal at this relatively high loading. In addition, the WB<sub>4</sub> alloys with Ti, Zr, and Hf showed a substantially increased oxidation resistance up to ∼460 °C, ∼510 °C, and ∼490 °C, respectively, compared to ∼400 °C for pure WB<sub>4</sub>

Similar works

Full text

thumbnail-image
oai:figshare.com:article/3199420Last time updated on 2/12/2018

This paper was published in FigShare.

Having an issue?

Is data on this page outdated, violates copyrights or anything else? Report the problem now and we will take corresponding actions after reviewing your request.