Low‐Temperature Densification of Zirconium Diboride Ceramics by Reactive Hot Pressing

Abstract

Zirconium diboride-silicon carbide ceramics with relative densities in excess of 95% were produced by reactive hot pressing (RHP) at temperatures as low as 16501C. The ZrB 2 matrix was formed by reacting elemental zirconium and boron. Attrition milling of the starting powders produced nanosized (o100 nm) Zr particulates that reacted with B below 6001C. The reaction resulted in the formation of nanoscale ZrB 2 crystallites that could be densified more than 2501C below the temperatures required for conventional ZrB 2 powder. Because of the low-temperature densification, the resulting ZrB 2 grain sizes were as small as 0.570.30 lm for specimens densified at 16501C and 1.571.2 lm for specimens densified at 18001C. Vickers hardness, elastic modulus, and flexure strength of fully dense materials produced by RHP were 27, 510, and 800 MPa, respectively.

Scanning AC nanocalorimetry study of Zr/B reactive multilayers

“…A recent study on reactive hot pressing of Zr and B powders using differential thermal analysis 32 showed that the reaction between Zr and B occurs over a broad temperature range from 300 to 900°C, following a two-step process. It is likely that this process also consists of a combination of interdiffusion and crystallization processes, although diffusion in this case may be controlled by the presence of a native oxide on the Zr grains.…”

Low-Temperature Processing of ZrB2-ZrC Composites by Reactive Hot Pressing

“…[17] It has been recently shown that high energy milling of elemental Zr and B can be used to produce ZrB 2 at temperatures as low as 600°C, and dense ZrB 2 -SiC composites can be obtained at 1700°C. [18] Because boron compounds are cheaper and easier to handle, the present study is undertaken to systematically establish the possibility of lowering the process temperature by reactive densification of ZrB 2 -ZrC composites starting with Zr and B 4 C powders. In an earlier work on processing of TiN-TiB 2 composites, it was shown that a small amount of Ni (1 wt pct) addition to the starting Ti-BN mixture could substantially decrease the densification temperature from 1850°C to 1400°C.…”

Low-Temperature Synthesis of Ultra-High-Temperature Coatings of ZrB2 Using Reactive Multilayers

“…Even though this process is cost-effective, it has been regarded as a lessthan-ideal technique to produce bulk ZrB 2 42 . The rapid heating rate (3,000 -4,000K/s 42,43 ) associated with the process results in incomplete reaction of Zr and B, and in the formation of non-equilibrium phases 42 . Similar observations were made in our previous work on reactive multilayer where impurities in Zr arising from the deposition process prevented complete reaction between B and Zr 21 .…”