Materials Science Forum Vols. 604-605

Abstract: The present paper reports a microstructure inspection of powder fabrication of regulated structure Ti/Ti-based metal matrix composites (MMC) utilizing sacrificial NaCl particles. Blending, compaction and sintering of Ti and YSZ reinforced Ti compacts containing NaCl resulted in regulated foam structures with porosities between 45 and 70 pct. SEM observations indicated that three pore sizes and morphologies were formed while XRD analysis suggested that the yttria stabilized zirconia (YSZ) reinforcements are unstable at the high temperature sintering conditions considered in this study.

Abstract: The continuous improvement of the applications of duplex stainless steels (DSS) is justified mainly by their excellent corrosion resistance in very aggressive environments and by their mechanical strength, often twice than that of conventional austenitic grades. Therefore more extensive applications have been suggested, like constructions, structural components, automotive applications, etc. However for such not advanced but quantitatively important applications the base cost of the alloy is one of the more constraining features. A way to obtain leaner alloys is to reduce the Ni content and to compensate with manganese and nitrogen additions. In the present paper the structural and mechanical properties of two low Ni duplex grades are analyzed in order to investigate the structural stability of the austenite against its possible transformation to martensite and the secondary phase’s precipitation. The detailed characterization has been performed with SEM-EDS on as received and heat treated (600-850 °C) alloys. A limited precipitation of chromium carbides and nitrides at the grain boundaries has been detected in both grades. The martensite formation has been revealed only in the 2101 grade. With regard to the impact toughness the behaviour of 2101 grade is quite similar to that of the common DSS, while in the 2304 the drastic drop of toughness is avoided. The corrosion behaviour of both grades in aggressive chloride environments is quite similar to that of austenitic AISI 304 grade.