Colloidal Processing of Zirconium Diboride Ultra‐High Temperature Ceramics

Abstract

Defence Materials Technology Centre, VIC 3122, AustraliaColloidal processing of the Ultra-High Temperature Ceramic (UHTC) zirconium diboride (ZrB 2 ) to develop nearÀnet-shaping techniques has been investigated. The use of the colloidal processing technique produces higher particle packing that ultimately enables achieving greater densification at lower temperatures and pressures, even pressureless sintering. ZrB 2 suspension formulations have been optimized in terms of rheological behavior. Suspensions were shaped into green bodies (63% relative density) using slip casting. The densification was carried out at 1900°C, 2000°C, and 2100°C, using both hot pressing at 40 MPa and pressureless sintering. The colloidally processed materials were compared with materials prepared by a conventional dry processing route (cold pressed at 50 MPa) and subjected to the same densification procedures. Sintered densities for samples produced by the colloidal route are higher than produced by the dry route (up to 99.5% relative density by hot pressing), even when pressureless sintering is performed (more than 90% relative density). The promising results are considered as a starting point for the fabrication of complex-shaped components that can be densified at lower sintering temperatures without pressure. W.-C. Wei-contributing editor Manuscript No. 31878.

Pressureless Sintering of ZrB2Prepared by Colloidal Processing: Particle Packing, Sintering Conditions, and Additives

“…Carbon [in the form of carbon black powder (Printex 60, D 50 = 20 nm, specific surface area = 120 m 2 /g, Degussa, Frankfurt, Germany), novolac‐type phenolic resin (Rezicure 3056, Schenectady, NY)] and boron carbide (B 4 C; grade HD15, D 50 = 0.8 μm, specific surface area = 19 m 2 /g, H. C. Starck) were selected as sintering additives. Previous characterization of the powders was in a good agreement with manufacturer's data . Upon thermal degradation, phenolic resin yields ~40 wt% carbon …”

Fabrication of ZrB2 ceramics by reactive hot pressing of ZrB and B

“…The ZrB 2 grains resulted from the "multiple" nucleation-growth processes presumably helped refine microstructure of the ZrB 2 ceramic, while a transient eutectic liquid formed at T > 1661°C enhanced densification of the ZrB 2 by liquid phase sintering. 27 ZrB þ B ¼ ZrB 2 Solid state reaction at T<1250 C Liquid state reaction at T>1661 C…”

“…Methods for making dense ZrB 2 ceramics were reviewed by Fahrenholtz and Hilmas in 2007 . Briefly, effective methods for increasing ZrB 2 ceramic density include (a) application of optimized processing techniques, (b) refinement of ZrB 2 starting powder, (c) additions of various sintering aids, and (d) reactive sintering. In the last category, ZrB 2 ceramics were densified by reactive sintering of Zr+B, ZrO 2 +B, ZrO 2 +B 4 C, and ZrO 2 +B 4 C+C powder compacts, exploiting Reactions .…”

“…1 Briefly, effective methods for increasing ZrB 2 ceramic density include (a) application of optimized processing techniques, [2][3][4] (b) refinement of ZrB 2 starting powder, (c) additions of various sintering aids, [5][6][7][8][9][10][11][12][13][14][15][16] and (d) reactive sintering. In the last category, 1,17,18 ZrB 2 ceramics were densified by reactive sintering of Zr+B, ZrO 2 +B, ZrO 2 +B 4 C, and ZrO 2 +B 4 C+C powder compacts, exploiting Reactions (1)(2)(3)(4). However, Reaction (1) was extremely exothermic and heating rate had to be carefully controlled in order to avoid igniting combustion synthesis.…”

Ice templating of ZrB2–SiC systems

“…The potential of these compounds was initially explored for dense massive ceramics, however, UHTC porous bodies may also have applications in aerospace, as well as in energy sectors or hot gases and molten metal filtration and catalysis [2,3]. Processing of porous UHTC is possible thanks to wet forming techniques [2,[4][5][6].…”