チタンアルミナイド生成発熱反応を利用したアルミナ粒子/アルミニウム溶湯系の超音波溶浸

Abstract

This study was aimed to realize full incorporation with low applied pressure by means of ultrasonic infiltration accompanying an exothermic reaction between titanium powder and molten aluminum in a non-wetted Al2O3 particle/molten aluminum system as a model composite. Ultrasonic infiltration (resonant frequency=20.5 kHz) was performed with its power of 500 kW/m2 mainly at 1023 K, so as to evaluate the effects of ultrasonic vibration on the threshold infiltration pressure (Pc), non-infiltrated defects and synthetic reaction of titanium aluminides. The Pc of 10.8 kPa obtained in pressure infiltration to 5.3 mass% titanium powder premixed Al2O3 particle preforms with an average diameter of 302 μm, becomes zero in ultrasonic infiltration. The high Pc of 83.5 kPa owing to a small average diameter of 47 μm of Al2O3 particles also becomes zero with ultrasonic vibration, that is, molten aluminum can initiate infiltration into the preform without applied pressure like a wetting composite system. Ultrasonic vibration makes the titanium powder premixed Al2O3 particle preforms infiltrated fully with the applied pressure of 25 kPa for 10 s, although there can be seen non-infiltrated area in pressure infiltration with 25 kPa for 300 s. Non-infiltrated defects appear at the contact points of particles in pressure infiltration, but they disappear with ultrasonic vibration. Exothermic reaction of intermetallic TiAl3 formed around titanium powders is accelerated by ultrasonic vibration, then the molten aluminum temperature increases locally at an infiltration front. The composite systems are changed from non-wetting to wetting apparently by ultrasonic vibration, which arises principally from the hysteresis of contact angles due to molten metal vibration and the generation of ultrasonic pressure in front of a step horn. Hence, the ultrasonic infiltration is extremely useful as a liquid processing for non-wetted hybrid in-situ composite materials without any non-infiltrated defects.