Isothermal fatigue mechanisms in Ti-based metal matrix composites. Final report

Technical Report · Wed Sep 01 04:00:00 EDT 1993

OSTI ID:6002788

Majumdar, B S; Newaz, G M

Stress-controlled isothermal fatigue experiments were performed at room temperature (RT) and 548 C (in argon) on (0)8 SCS6/Ti 15-3 metal matrix composites (MMC's) with 15 and 41 volume percent SCS6 (SiC) fibers. The primary objectives were to evaluate the mechanical responses, and to obtain a clear understanding of the damage mechanisms leading to failure of the MMC's. The mechanical data indicated that strain ranges attained fairly constant values in the stress-controlled experiments at both RT and 538 C, and remained so for more than 85 percent of life. The fatigue data for MMC's with different volume fraction fibers showed that MMC life was controlled by the imposed strain range rather than the stress range. At RT, and at low and intermediate strain ranges, the dominant fatigue mechanism was matrix fatigue, and this was confirmed metallurgically from fractographic evidence as well as from observations of channel type dislocation structures in the matrix of fatigued MMC specimens. Reaction-zone cracks acted as important crack initiating sites at RT, with their role being to facilitate slip band formation and consequent matrix crack initiation through classical fatigue mechanisms. MMC life agreed with matrix life at the lower strain ranges, but was smaller than matrix life at higher strain ranges. Unlike the case of monotonic deformation, debonding damage was another major damage mechanism during fatigue at RT, and it increased for higher strain ranges. At high strain ranges at RT, fractography and metallography showed an absence of matrix cracks, but long lengths of debonds in the outer layers of the SCS6 fibers. Such debonding and consequent rubbing during fatigue is believed to have caused fiber damage and their failure at high strain ranges. Thus, whereas life was matrix dominated at low and intermediate strain ranges, it was fiber dominated at high strain ranges. At 538 C, the mean stain constantly increased (ratchetting) with the number of cycles.

• Research Organization: Battelle Memorial Inst., Columbus, OH (United States)
• OSTI ID: 6002788
• Report Number(s): N-94-12594; NASA-CR--191181; E--8086; NAS--1.26:191181; CNN: NAS3-26494; RTOP 510-01-50
• Country of Publication: United States
• Language: English

Related Subjects

36 MATERIALS SCIENCE
360603* -- Materials-- Properties
CARBIDES
CARBON COMPOUNDS
CRACKS
ELEMENTS
FAILURES
FATIGUE
FIBERS
FRACTURE PROPERTIES
ISOTHERMAL PROCESSES
MATERIALS
MATRIX MATERIALS
MECHANICAL PROPERTIES
METALS
REINFORCED MATERIALS
SILICON CARBIDES
SILICON COMPOUNDS
STRAINS
STRESSES
TEMPERATURE RANGE
TEMPERATURE RANGE 0273-0400 K
TEMPERATURE RANGE 0400-1000 K
TITANIUM
TRANSITION ELEMENTS