Abstract
During the routine testing of a cryogenic engine, failure of a copper alloy (Cu-Cr-Ti-Zr) liner was noticed which led to the test abort. On close inspection of the liner, a circumferential crack with a length of 78 mm was observed on the divergent side of the thrust chamber. Roughening of the inner wall of the thrust chamber was noticed at the cracked location and extended circumference. Thinning of the copper liner wall was observed at the location of the crack indicating plastic yielding of the material at the location of failure. Fracture surface observations by scanning electron microscopy revealed features of material flow and softening at many locations indicative of exposure of fracture surface to high temperature after failure. Further, striation marks were noticed on the fracture surface indicative of fatigue. Very fine recrystallized grains were noticed in optical microscopy at the location of the crack. This is attributed to dynamic recrystallization occurring during deformation at high temperatures. Strain markings and slip bands were noticed in the interior of grains near the fracture edge. Based on extensive microstructural analysis of the failed hardware, it is concluded that the throat of thrust chamber failed due to “thermal ratcheting.”