Accession Number:

ADA371725

Title:

Microscale Plasticity and Fracture Toughness of Ti3SiC2 at Ambient and High Temperatures

Descriptive Note:

Final rept. 1 May-31 Dec 97

Corporate Author:

DREXEL UNIV PHILADELPHIA PA DEPT OF MATERIALS ENGINEERING

Personal Author(s):

Report Date:

1999-11-01

Pagination or Media Count:

32.0

Abstract:

The goal of this work was to develop a science-based understanding of the structure property relationships in Ti3SiC2. Late in 1995 we synthesized for the first time dense, bulk single phase samples of Ti3SiC2. Preliminary characterization has shown it to be a ternary compound with a unique set of properties, machinability similar to that of graphite, excellent oxidation resistance, relatively low density 4.5 gmcu cm and non-susceptibility to thermal shock. A brittle-to-ductile transition occurs at 1200 deg C, and at 1300 deg C the material is plastic with very respectable yield points 100 and 500 MPa in flexure and compression, respectively. This combination of properties renders Ti3SiC2 an attractive candidate for a variety of high temperature structural applications of interest to the Air Force and creates the immediate need for a detailed characterization study to understand the physical origin of these properties. The evolution of deformation-microfracture damage below Hertzian contacts in a coarse-grain Ti3SiC2 was studied. The Hertzian indentation stress-strain response deviates strongly from linearity beyond a well-defined maximum, with pronounced strain-softening, indicating exceptional deformability in this otherwise elastically stiff ceramic. Surface and subsurface ceramographic observations reveal extensive quasi-plastic microdamage zones at the contact sites. The ternary carbide, Ti3SiC2, fabricated by a reactive hot press route was investigated by transmission electron microscopy, TEM. The material consists mainly of large elongated grains with planar boundaries and is characterized by a low defect density. Dislocations are observed in the grains and at grain boundaries. Perfect dislocations with b 13 1120 lying in 0001 basal planes are present.

Subject Categories:

  • Ceramics, Refractories and Glass

Distribution Statement:

APPROVED FOR PUBLIC RELEASE