Modification of pitch‐based carbon fibers using a nickel‐catalyzed oxidation treatment: Effect of treatment on fiber‐matrix interfacial shear strength

Pitch‐based carbon fiber surfaces were modified using a nickel‐catalyzed, dry oxygen etch (NCDO) and a dry oxygen etch (DO), both of which were applied using a continuous process. The treatments differed in that DCDO produced preferential pitting on fiber surfaces at nickel particle sites. Tensile strengths of all etched fibers were slightly lower than values for untreated, or “as received” (AR), fibers. Reductions in tensile strength were independent of the type of treatment administered, indicating that most degradation resulted from damage produced by the mechanics of the continuous process, not the etching treatments. Fiber‐matrix interfacial shear strengths (IFSS) of AR and etched fibers were evaluated using the Microbond test. At first glance, Microbond test data indicated that NCDO produced large increases in IFSS. However, inconsistencies in the data raised questions regarding the validity and usefulness of the Microbond test when applied to this system. Only after detailed analysis of the data for this series of fibers was it concluded that NCDO did indeed produce an increase in IFSS over AR fibers and DO fibers.