Title

Mechanical Properties Of Ultrafine-Grained Titanium Aluminide/Titanium Suicide Composites Prepared By High Energy Milling

Abstract

This study was undertaken to systematically investigate the powder-metallurgical synthesis and mechanical behavior of intermetallic/ceramic composites with grain sizes in the nano- and submicron range. γ-TiAl with 0.5 to 60 vol.% Ti5Si3 content was chosen as a model system. The resulting microstructure was either a fine dispersion of Ti 5Si3 in the γ-TiAl matrix or intermixed grains of γ-TiAl and Ti5Si3, with comparable grain sizes. Four objectives were pursued: (1) measurement of truly grain size-dependent mechanical properties, not affected by any processing flaws, (2) coverage of a wide range of grain sizes, extending from several micrometers down to the nanometer-range, thus ensuring that the results may be related to the data available for materials with conventional grain sizes, (3) clarification, whether the mechanical behavior is governed by chemistry and/or microstructure, and (4) evaluation of the results with respect to the underlying mechanisms. Dense composite material was obtained by high-energy milling and subsequent hot isostatic pressing. At room temperature, the grain size dependence of hardness and yield strength was described by the well-known Hall-Petch relationship. Contrary to the behavior of conventional alloys, the ductility of submicron-grained composites dropped if the grain size was further reduced. This may be attributed to the increasing difficulties for deformation based on single dislocation glide mechanisms. In the high temperature range, the flow stress is strongly reduced. Superplastic deformation became feasible at temperatures ≤800°C, allowing for easy forming of parts. Silicide particles impede grain growth, but they also promote cavitation during tensile straining. Higher silicide content did not change the deformation behavior substantially, indicating that the mechanical behavior is mainly controlled by microstructure rather than chemistry. The mechanisms of deformation are similar to those established for coarse-grained materials, though at significantly reduced temperatures.

Publication Date

12-1-2003

Publication Title

Processing and Properties of Structural Nanomaterial: Proceedings of Symposia held at the Materials Science and Technology 2003 Meeting

Number of Pages

93-100

Document Type

Article; Proceedings Paper

Personal Identifier

scopus

Socpus ID

1542748729 (Scopus)

Source API URL

https://api.elsevier.com/content/abstract/scopus_id/1542748729

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