セラミック粉の金型成形と焼結中における寸法変化機構

概要

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Alumina preforms, d10×h10 mm in size, were made without pressing of a powder having an average particle size of 2.6 μm and containing 0.51-1.5 mass% polyvinyl alcohol. The preforms were pressed under 50-800 MPa with die-wall lubrication, heated in the air for dewaxing and sintering at the rate of 10°C/min to 1600°C, and held at the temperature for 2 hr.<BR>The spring-back of the alumina was larger than those of the iron and copper powders and smaller than those of the spray-dried alumina-based ceramic granules. The axial spring-back by ejection showed the minimum for the optimum binder content. Increased compacting pressure led to increased axial spring-back by the unloading, decreased axial spring-back by the ejecting, and decreased shrinkage during the sintering.<BR>The titanium carbide granules, -140+200 mesh in size, containing 0.5 mass% of polyvinyl alcohol were prepared from a powder with an average particle size of 3.4 μm. They were pressed under 400 and 800 MPa in a die lined with zirconia and having a bore diameter of 10 mm. The electrical conductivity was measured by discharging a constant current to the compacts.<BR>The drop of the conductivity, indicating the occurrence of the microcracking in the ceramic compacts, was larger for the ejecting than for the unloading.