THE EFFECT OF APPLIED STRESS ON THE GRAPHITIZATION OF PYROLYTIC GRAPHITE

Conference · Sat Jun 15 04:00:00 EDT 1963

OSTI ID:4875462

Bragg, R H; Crooks, D D; Fenn, Jr, R W; Hammond, M L

Metallographic and x-ray diffraction studies were made of the effect of applied stress at high temperature on the structure of pyrolytic graphite (PG). The dominant factor was whether the PG was above or below its graphitization temperature, which, in turn, was not strongly dependent on applied stress. Below the graphitization temperature, the PG showed a high proportion of disordered layers (0.9), a fairly large mean tilt angle (20 deg ) and a small crystailite size (La --150 A). Fracture occurred at low stress and strain and the materiai exhibited a high apparent Young's modulus ( approximates 4 x 10/sup 6/ psi). Above the graphitization temperature, graphitization was considerably enhanced by strain up to about 8%. The disorder parameter was decreased from a zero strain value of 0.3 to 0.l5 with strain, the mean tilt angle was decreased to 4 deg , and a fivefold increase in crystallite size occurred. When the strainenhanced graphitization was complete, the material exhibited a low apparent modulus ( approximates 0.5 x 10/sup 6/ psi) and large plastic strains (>100%) for a constant stress ( approximates 55 ksi). Graphitization was shown to be a spontaneous process that is promoted by breaking cross-links thermally, and the process is furthered by chemical attack and plastic strain. (auth)

• Research Organization: Lockheed Missiles and Space Co., Palo Alto, CA (United States)
• NSA Number: NSA-17-032649
• OSTI ID: 4875462
• Report Number(s): CONF-73-3; AED-Conf--63-061-7
• Country of Publication: United States
• Language: English

Related Subjects

CONFERENCE
DEFECTS
DEFORMATION
DIFFRACTION
FAILURES
GRAIN SIZE
GRAPHITE
GRAPHITIZATION
HIGH TEMPERATURE
LATTICES
METALLOGRAPHY
METALS, CERAMICS, AND OTHER MATERIALS
PYROLYSIS
STRESSES
TEMPERATURE
TENSILE PROPERTIES
X RADIATION