Structure, mechanical properties, and oxidation behavior of nanolayered MoSi[sub 2]/SiC coatings

Conference · Wed Jan 01 00:00:00 EST 1992

OSTI ID:6828392

Hirvonen, J-P; Kattelus, H; Likonen, J; Suni, I ^[1]; Lappalainen, R ^[2]; Kung, H; Jervis, T R; Nastasi, M ^[3]

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1. Technical Research Centre of Finland, Espoo (Finland)
2. Helsinki Univ. (Finland). Dept. of Physics
3. Los Alamos National Lab., NM (United States)

Structure, hardness, elastic properties, and oxidation of nanolayered MoSi[sub 2]/SiC were examined. DC-magnetron and rf -diode sputtering were used to deposit MoSi[sub 2] and SiC, respectively. Total number of sublayers of each kind was 90. Nominal thickness of MoSi[sub 2] sublayers was 10 and that of SiC 3 nm. As-deposited microstructure was amorphous whereas annealing at 500C for 1 h resulted in transformation of MoSi[sub 2] into C40 type hexagonal structure. However, silicon carbide remained still amorphous. Hardness of 11.6 and 20.8 GPa were obtained for as-deposited and annealed structure; Young moduli were 220 and 290 GPa, which yield 232 and 332 GPa for Young moduli of amorphous and crystalline MoSi[sub 2]. Oxidation tests were carried out in wet conditions at 400 and 500C; degree of oxidation was determined using the reaction [sup 16]O(d,p)[sup 17]O at 950 keV. The MoSi[sub 2]/SiC coating gave a good protection against oxidation for unalloyed steel. As compared to a single MoSi[sub 2] coating, a slightly higher degree of oxidation and a significantly different mechanism of oxidation was observed. This was also supported by secondary ion mass spectroscopy. Cracking of the coating caused by a thermal mismatch and transformation stresses was worse in the case of the single MoSi[sub 2] layer than in the case of the composite coating. Thus cracking of the coating can be significantly reduced by using a nanolayered structure.

• Research Organization: Los Alamos National Lab., NM (United States)
• Sponsoring Organization: USDOE; USDOE, Washington, DC (United States)
• DOE Contract Number: W-7405-ENG-36
• OSTI ID: 6828392
• Report Number(s): LA-UR-92-4298; CONF-921101-50; ON: DE93005472
• Resource Relation: Conference: 16. Material Research Society international symposium on the scientific basis for nuclear waste management fall meeting, Boston, MA (United States), 30 Nov - 5 Dec 1992
• Country of Publication: United States
• Language: English

Related Subjects

36 MATERIALS SCIENCE
MOLYBDENUM SILICIDES
PROTECTIVE COATINGS
SILICON CARBIDES
ANNEALING
CRACKS
HARDNESS
LAYERS
MICROSTRUCTURE
OXIDATION
YOUNG MODULUS
CARBIDES
CARBON COMPOUNDS
CHEMICAL REACTIONS
COATINGS
CRYSTAL STRUCTURE
HEAT TREATMENTS
MECHANICAL PROPERTIES
MOLYBDENUM COMPOUNDS
REFRACTORY METAL COMPOUNDS
SILICIDES
SILICON COMPOUNDS
TRANSITION ELEMENT COMPOUNDS
360200* - Ceramics
Cermets
& Refractories
360105 - Metals & Alloys- Corrosion & Erosion