Record Details

Reactive Hot Pressing Of ZrB2-Based Ultra High Temperature Ceramic Composites

Electronic Theses of Indian Institute of Science

View Archive Info
 
 
Field Value
 
Title Reactive Hot Pressing Of ZrB2-Based Ultra High Temperature Ceramic Composites
 
Creator Rangaraj, L
 
Subject Ceramic Composites
Hot Pressing
ZrB2-SiC Composites
Zircomium Boride Composites
Zirconium Carbide
Zirconium Diboride
Titanium Composites
Titanium Nitride
Titanium Diboride
ZrB2-ZrC-SiC Composites
Tin-TiB2 Composites
ZrB2-SiC Composites
ZrB2-ZrC Composites
ZrB2-ZrC Composites
Hot Pressed Composites
Materials Science
 
Description Zirconium- and titanium- based compounds (borides, carbides and nitrides) are of importance because of their attractive properties including: high melting temperature, high-temperature strength, high hardness, high elastic modulus and good wear-erosion-corrosion resistance. The ultra high temperature ceramics (UHTCs) - zirconium diboride (ZrB2) and zirconium carbide (ZrC) in combination with SiC are potential candidates for ultra-high temperature applications such as nose cones for re-entry vehicles and thermal protection systems, where temperature exceeds 2000°C. Titanium nitride (TiN) and titanium diboride (TiB2) composites have been considered for cutting tools, wear resistant parts etc. There are problems in the processing of these materials, as very high temperatures are required to produce dense composites. This problem can be overcome by the development of composites through reactive hot processing (RHP). In RHP, the composites are simultaneously synthesized and densified by application of pressure and temperatures that are relatively low compared to the melting points of individual components.
There have been earlier studies on the fabrication of dense ZrB2-ZrC, ZrB2-SiC and TiN-TiB2 composites by the following methods:
Pressureless sintering of preformed powders at high temperatures (1800-2300°C) with MoSi2, Ni, Cr, Fe additions
Hot pressing of preformed powders at high temperatures (1700-2000°C) with additives like Ni, Si3N4, TiSi2, TaSi2, TaC
Melt infiltration of Zr/Ti into B4C preform at 1800-1900°C to produce ZrB2-ZrC-Zr and TiB2-TiC composites
RHP of Zr-B4C, Zr-Si-B4C and Ti-BN powder mixtures to produce ZrB2-ZrC, ZrB2-SiC and TiN-TiB2 powder mixtures at 1650-1900°C
Spark plasma sintering of powder mixtures at 1800-2100°C
There has been a lack of attention paid to the conditions under which ceramic composites can be produced by simple hot pressing (~50 MPa) with minimum amount of additives, which will not affect the mechanical properties of the composites. There has been no systematic study of microstructural evolution to be able to highlight the change in relative density (RD) with temperature during RHP by formation of sub-stoichiometric compounds, and liquid phase when a small amount of additive is used.
The present study has been undertaken to establish the experimental conditions and densification mechanisms during RHP of Zr-B4C, Zr-B4C-Si and Ti-BN powder mixtures to yield (a) ZrB2-ZrC, (b) ZrB2-SiC, (c) ZrB2-ZrC-SiC and (d) TiN-TiB2 composites. The following reactions were used to produce the composites:
(1) 3 Zr + B4C → 2 ZrB2 + ZrC
(2) 3.5 Zr + B4C → 2 ZrB2 + 1.52rCx- 0.67
(3) (1+y) Zr + C → (1+y) ZrCx- 1/ (1+y) (y=0 to 1)
(4) 2 Zr + B4C + Si → 2 ZrB2 + SiC
(5) 2.5 Zr + B4C + 0.65 Si → 2 ZrB2 + 0.5 ZrCx + 0.65 SiC
(6) 3.5 Zr + B4C + SiC → 2 ZrB2 + 1.5 ZrCx + SiC (5 to 15 vol%)
(7) (3+y) Ti + 2 BN → (2+y) TiN1/(1+y) + TiB2 (y=0 to 0.5)
(a) ZrB2-ZrC Composites:
The effect of different particle sizes of B4C (60-240 μm,
 
Contributor Jayaram, Vikram
 
Date 2010-10-08T09:27:41Z
2010-10-08T09:27:41Z
2010-10-08
2008-12
 
Type Thesis
 
Identifier http://hdl.handle.net/2005/906
 
Language en_US
 
Relation G22886