Phase relationships in Nb - 18. 7 a/o Si in-situ composite

Journal Article · Sun Sep 01 04:00:00 EDT 1991 · Scripta Metallurgica; (United States)

OSTI ID:5703923

Cockeram, B; Lipsitt, H A; Srinivasan, R; Weiss, I ^[1]

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1. Dept. of Mechanical and Materials Engineering, Wright State Univ., Dayton, OH (US)

This paper reports that many intermetallic compounds based on refractor metals such as Nb, Mo and W have high melting temperatures (above 1700{degrees}C) and retain their strength and stiffness to high temperature ({gt}1000{degrees}C), thus, making them good candidate materials for very high temperature applications. Most of the above intermetallic compounds are extremely brittle in nature, and successful implementation of these compounds in engine applications depends on improved room temperature and elevated temperature toughness. One possible method is to produce in-situ composites consisting of a brittle compound and a metallic phase formed during eutectic or eutectoid reaction. The distribution and physical disposition of the brittle intermetallic and ductile metallic phases are of great importance since in-situ composites attain their toughness from the morphological distribution of the phases present. The Nb-Si binary system has been chosen as a model system for this class of materials. Upon solidification at normal cooling rates, the microstructure of the eutectic composition (18.7 a/o Si) consists of the terminal Nb phase ({lt}1 a/o Si) distributed in a matrix of metastable Nb{sub 3}Si, which is the dark phase, has a tetragonal structure with 32 atoms per unit cell, consisting of 24 Nb and 8 Si atoms (tP32, space group No. 86). The distribution and morphology of the phases can be altered by changing composition or through different thermomechanical processing routes. Figures 1,2 and 3 show SEM micrographs of the eutectic alloy in the cast, the cast and hot extruded, and the directionally solidified (DS) conditions, respectively. The morphologically aligned nature of the eutectic niobium particles is exemplified in both the DS and extruded material as compared to the as-cast eutectic alloy.

• OSTI ID: 5703923
• Journal Information: Scripta Metallurgica; (United States), Journal Name: Scripta Metallurgica; (United States) Vol. 25:9; ISSN 0036-9748; ISSN SCRMB
• Country of Publication: United States
• Language: English

Related Subjects

36 MATERIALS SCIENCE
360102* -- Metals & Alloys-- Structure & Phase Studies
ALLOYS
CHEMICAL COMPOSITION
COMPOSITE MATERIALS
CRYSTAL STRUCTURE
CRYSTALLOGRAPHY
ELECTRON MICROSCOPY
ENERGY LEVELS
EUTECTICS
EXCITED STATES
FABRICATION
HEAT RESISTANT MATERIALS
HEAT RESISTING ALLOYS
HEAT TREATMENTS
INTERMETALLIC COMPOUNDS
MATERIALS
MATERIALS WORKING
METASTABLE STATES
MICROSCOPY
MICROSTRUCTURE
MOLYBDENUM COMPOUNDS
NIOBIUM ALLOYS
NIOBIUM BASE ALLOYS
NIOBIUM COMPOUNDS
PHASE TRANSFORMATIONS
REFRACTORY METAL COMPOUNDS
SCANNING ELECTRON MICROSCOPY
SILICON ALLOYS
THERMOMECHANICAL TREATMENTS
TRANSITION ELEMENT COMPOUNDS
TUNGSTEN COMPOUNDS