ISSN:
1573-4870
Keywords:
Dynamic densification
;
reactant
;
synthesis
Source:
Springer Online Journal Archives 1860-2000
Topics:
Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
Notes:
Abstract The influence of dynamic densification on the microstructure and properties of reaction synthesized bulk compacts of TiC ceramic was investigated. Self-propagating high-temperature combustion-type chemical reactions were initiated in disk-shaped green reactant compacts, cold pressed from Ti and C elemental powder mixture, by igniting with an electric match. The reaction synthesized mass was instantaneously (within zero to 20 seconds time delay) compacted by high pressure generated by explosive detonation and transmitted through a driver plate. A predictive model, based on heat flow simulation of self-propagating combustion reactions, was developed to provide a quantitative understanding of the process and subsequent cooling of the material from its adiabatic (reaction) temperature, in order to allow better control of the explosive densification step following reaction synthesis. It was determined that in addition to the dynamic-densification pressure, the time delay between reaction completion and densification, was an important variable influencing the density and microstructure (grain size) of the bulk TiC ceramic compacts. With less than the optimum time delay, the reacted and densified compact showed de-lamination and lower densities (due to effects of “after-burn”), and coarse-grain structure (due to slower cooling rate). Likewise, with longer than the optimum time delay, the SHS reacted product cooled below the point where densification to high density and microstructural break-down resulting in fine-grain structure could not be achieved. Under optimized conditions (time delay = 8 s, pressure = 2.5 GPa), bulk titanium-carbide ceramic compacts with densities as high as 95% of theoretical maximum density (T.M.D.) and grain size ≍10 μm were produced. The compacts had microhardness values typically varying between 21.2 to 26.6 GPa, Young's Modulus in the range of 418 ± 20 GPa and 375 ± 14 GPa, compressive strengths between 1.0 ± 0.3 GPa and 0.9 ± 0.2 GPa, and fracture toughness values of 1.51 ± 0.3 MPa√m to 3.69 ± 1.0 MPa√m.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1023/A:1021829215348
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