Bibliographic Information

"Sintering Behavior and Properties of Si₃N₄ Sintered with Nitrogen-Rich Liquid in the System Y₂O₃-AlN-SiO₂," P.K. Das and J. Mukerji, Advanced Ceramic Materials, Vol. 3 [3], pp. 238-243 (1988), published by American Ceramic Society.

General Materials Processing Notes

"The material used was Si₃N₄ prepared in the laboratory by nitridation of low-Ca (0.004 %, mass fraction) silicon powder and having the following analyses: Ca 0.053%, Mg 0.01%, Na 0.084%, Fe 0.138%, N 38.63±0.52%, O 2.2±0.3%, α 86%. Surface area was 8.7 m²/g. Other raw materials were AlN (C 0.05%, Fe 0.1%, Al 65.5%, and N 32.5%), Y₂O₃ (99.99%), and SiO₂ (optical grade > 99.9%, Fe₂O₃, 0.004%). ... After weighing up to 0.01 g accuracy, 100 g of powder was attrited in n-hexane using alumina balls for 3 h. Alumina pickup in each grinding was about 0.05% (mass fraction). For sintering study, cylindrical pellets 15.5 mm in diameter and 14.5 mm high were prepared from powders at 200 MPa pressure. Dynamic sintering was conducted in a high-temperature dilatometer at an increase rate of 30°C/min. ... Runs were taken up to 1750°C, and the final soaking lasted 20 min at that temperature. For other studies, powders were uniaxially pressured into billets and then isostatically pressed at 285 MPa. The final size of the bars was 67 mm by 17 mm by 15 mm. The bars were generally sintered at 1750°C for 60 min in a graphite resistance furnace with Si₃N₄ packing using BN-coated graphite crucibles. ... Crystallization treatment of the samples was done usually at 1330°C in pure nitrogen atmosphere for 24 h." Processing conditions were: Sintering Sintering Fired temperature time density Batch (°C) (min) (g/cm³) P1 1700 60 2.86 1750 60 3.06 P5 1750 120 3.09 JM2 1700 60 3.21 JM4 1750 120 3.24

Measurement Methods

"Strength measurements at room temperature and at high temperatures were done by four-point bending with a 20 mm constant bending moment span. The bars (45 mm by 4.5 mm by 3.5 mm) were ground using -600 emery powders and finally polished with 2 µm diamond paste. The loading rate was 1.25 N/s."

"Fracture toughness has been measured by four-point single-edge-notched bend specimen technique. The bars of same size were notched with a diamond blade 0.2 mm thick. The notch dimensions generally were a/w = 0.2 to 0.65 and notch width R = 0.25 mm to 0.4 mm, where, a is the notch length; K_c was calculated....Fracture toughness measurements was also done by the indentation technique..."

"The measurement of creep strain rate ... was done under flexure in a creep testing machine using bars of the same dimension as in MOR measurement, ground with -600 emery powder."

Index of Materials and Properties