Bibliographic Information

"Structure-Property Correlations for TiB₂-Based Ceramics Densified Using Active Liquid Metals," V.J. Tennery, C.B. Finch, C.S. Yust, and G.W. Clark, Science of Hard Materials, pp. 891-909 (1983), edited by R.K. Viswanadham, D.J. Rowcliffe, and J. Gurland, published by Plenum Press.

General Materials Processing Notes

"Commercially available TiB₂ powders produced by grinding the product of carbothermic reaction between TiO₂, C, and B₄C (or B₂O₃) were selected as the bases for this work. ... In general, the average particle size varied between 5 µm and 15 µm, while the oxygen content varied between 0.5 and 2 wt%. ... a set of hot pressing conditions was selected in which only the time at hot pressing temperature was the variable. ... Dry TiB₂ and Ni powders were weighed to ±0.05 g and mixed 24 h by tumbling in polyethylene jars. The powder mixtures were loaded into 4.5 cm or 6.0 cm ID graphite die assemblies. The cylindrical surfaces and punch faces of the dies were lined with 0.25 mm thick grafoil or a 0.1 mm thick coating of BN. ... The disks were pressed singly in a vacuum hot press assembly consisting of a vertical graphite resistance heating element furnace surrounding the press assembly. The system was loaded with the dies and evacuated to 10^-3 Pa. The furnace was heated to 1000 °C and held at this temperature until outgassing was complete and the pressure reached 10^-3 Pa. The temperature was then increased to a final hot pressing temperature of 1425 °C. ... Recovery of the pressure to about 10^-3 Pa was usually achieved within 1.0 ks to 1.5 ks... At this time, loading was applied to the die punches via the press rams at a rate of about 3.5 kPa/s until the total pressure was 12 MPa. The charges were maintained under pressure for times ranging from 7.2 ks to 28.8 ks... Specimens of the required geometry and dimensions were cut from the as-pressed disks by electron discharge machining (EDM) or by an oil and water lubricated diamond saw. ... Following EDM cutting, the thin oxidation layer produced on the surface by the cutting was removed with diamond grinding wheels of grit sizes from 60 µm to 6 µm. Final polishing of critical surfaces of some specimens was performed using 0.5 µm diamond on a nylon lap in a vibratory polisher, followed by vibratory polishing with 0.3 µm Al₂O₃."

Measurement Methods

"The densities... were determined by immersion in H₂O and by direct measurement determination of geometric density. The densities generally agreed within ±0.02 g/cm³."

"Fracture toughness was determined by the crack-indent method and by calculation from the measured fracture energies of double cantilever beam specimens and measured values of the elastic moduli and Poisson's ratios."

The authors cite F.F. Lange et al., J. Amer. Ceram. Soc., Vol. 59, 454-458 (1976), and summarize the procedure as follows. "Thermal transport in these ceramics was determined between 25 °C and 1200 °C using the laser flash technique. One side of a thin square plate specimen was flashed with a 50 J Nd-glass laser, and the temperature behavior of the opposite side was sensed with a liquid N₂ cooled infrared detector. Analysis of the thermal transient led to calculation of the thermal diffusivity."

The authors cite W. Mason, Acoustic Properties of Solids, Section IIIF-1, Amer. Inst. of Physics Handbook, pp. 74-79 (1957), and summarize the procedure as follows. "Values of Young's modulus and Poisson's ratio were determined from ultrasonic data on these ceramics..." No additional measurement details were noted.

"... fracture strength was determined at 25 °C using four-point flexure of bars having an outer span of 3.8 cm and an inner span of 1.85 cm." No additional measurement details were noted.

The authors cite G.R. Gessel, "Effect of Minor Alloys on the Strength and Swelling Behavior of Austenitic Stainless Steel," ORNL/TM-6359, pp. 72-75 (1979), and summarize the procedure as follows. "The diamond pyramid hardness (DPH) was determined in vacuum (10^-3 Pa) between room temperature and 800 °C using a diamond indenter and the procedure of Gessel. The polished specimen surfaces typically showed no evidence of oxidation following indentation at high temperature."

Index of Materials and Properties