High Temperature Squeeze Casting of Nickel Based Metal Matrix Composites with Interpenetrating Microstructure

Abstract

High temperature squeeze casting enables the fabrication of composite structures for alloys with high melting points, suitable for structural and tribological applications at high temperatures. Nickel-chromium alloys with chromium contents of about 20 wt% are extremely resistant to corrosion and exhibit operation temperatures up to 1000 °C due to the high solubility of chromium in nickel and its high melting point. The creep and wear resistance of the metal matrix composite material (MMC) is achieved by a stable ceramic backbone of Alumina with a bimodal pore structure. The fabrication of interpenetrating nickel-chromium/alumina MMCs, namely NiCr8020/Al2O3/50pp, at temperatures above 1550 °C is shown. A special infiltration tool geometry has been used to withstand thermal and mechanical strain, necessary for the infiltration of preforms with 40 mm in height. The infiltration was performed in a unique high temperature squeeze casting device with tool temperatures of about 700 °C. Infiltration duration (pore filling) was as long as about 12 s. For this, the thermal management of the tool is the demanding part. Whereas the inner cavity has to be as hot as possible to enable infiltration and to prevent premature solidification. In contrast the outer side of the infiltration tool has to be as cold as possible to withstand the infiltration pressure applied directly to the squeeze casting tool.