Molybdenum silicide material with high strength

Details Molybdenum silicide material with high strength Molybdenum silicide material with high strength

2000-10-18

2002-11-19

Group, Karl (Department: 1755)

Compositions: ceramic

Ceramic compositions

Refractory

C501S092000, C501S103000

Reexamination Certificate

active

06482759

ABSTRACT:

FIELD OF THE INVENTION
The present invention relates to a molybdenum silicide material with high strength even at lower temperatures, such as at room temperature, and high strength at high temperatures, as well as good oxidation properties.
BACKGROUND OF THE INVENTION
Metallic materials have very good physical properties at lower temperatures, but have worse physical properties at higher temperatures. This is valid even for alloyed metallic material. In practice metallic materials cannot be used at temperatures higher than approximately 1100° C.
Ceramic materials such as SiC have good high temperature properties, but are for brittle in the whole range of temperatures.
Intermetallic materials, such as Ni-, Ti- and Fe-aluminides have good high temperature properties, but their practical application temperature is below 1000° C.
Silicides, such as molybdenum silicides, are attractive intermetallic materials with very good physical properties at high temperature. They have also very good oxidation and corrosion properties due to that a layer of glass is formed on the surface, which forms a protective film.
However, like most intermetallic materials, these have low ductility and low rupture strength at room temperature. The brittle-ductile transformation temperature (BDTT) for suicides is normally high, for instance above 1000° C. for MoSi
2
. Below the transformation temperature suicides are extremely brittle and have low impact strength. Above the transformation temperature silicides outperform metals with regard to elongation properties and tension reducing properties. Since suicides undergo creep and plastic deformation above the transformation temperature, an increase in the strength at high temperatures should make them more competitive for applications at high temperature.
Different ways to increase RT (room temperature) hardness and HT (high temperature) strength of silicides have been tested. Thus, molybdenum silicide has been alloyed with V, Ti, Nb, Ta and Al in order to modify the microstructure and thereby increase the strength.
Further, MoSi
2
—ZrO
2
-composites have been studied. ZrO
2
has three well-defined crystalline conditions, namely monoklinisk (M), tetragonal (T), and cubic (C). The M-phase is stable up to 1170° C., where it will be transformed to the T-phase. The T-phase is stable up to 2370° C., whereafter the C-phase is stable up to the melting point of 2680° C. stabilizers in the form of Y
2
O
3
, MgO, CaO or CeO
2
have also been added to such materials. By the addition of such stabilizers, the material could be made tougher at a temperature below 1170° C.
However, corrosion and oxidation tests have shown that such materials have poorer properties than monolithic molybdenum silicide and material which is commercially available under the trademark KANTHAL SUPER.
SUMMARY OF THE INVENTION
The present invention solves the above-mentioned problems, and others, by providing a material having oxidation and corrosion properties which are comparable to monolithic molybdenum silicide or KANTHAL SUPER, but additional has high RT-H
V
and RT-K
C
values.
According to a first aspect, the present invention provides a composite material with high strength at both room temperature and high temperatures, the material comprising a mixture including MoSi
2
; 5-30 vol-% ZrO
2
; 5-15 vol- % MoB; and an oxygen content, in the form of SiO
2
on or in particles of MoSi
2
, below 0.5 weight-%.


REFERENCES:
patent: 4970179 (1990-11-01), Petrovic et al.
patent: 5063182 (1991-11-01), Petrovic et al.
patent: 5382553 (1995-01-01), Petrovic
patent: 5708408 (1998-01-01), Sundberg
patent: 5990025 (1999-11-01), Suyama et al.

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