Frictional ignition of dispersion-strengthened Ni-Cr alloys

Abstract

Frictional heating of metals at reciprocating or sliding contacts in high-pressure oxygen environments poses a risk of catastrophic metal fires. This phenomenon, known as frictional ignition, has been implicated in several high-profile failures of oxidizer-rich turbopumps, presenting an ongoing challenge in the development of next-generation reusable rocket engines. Early NASA investigations on frictional ignition of candidate turbine materials identified oxide dispersion-strengthened Ni-base superalloys as exceptionally resistant to ignition. In this study, we performed high-speed sliding, frictional ignition experiments on binary Ni-Cr alloys and two oxide dispersion-strengthened Ni-Cr alloys – MA754 and MA758. Analysis of recovered non-ignited samples revealed the in situ growth of oxide tribolayers on rubbing surfaces during sliding. An order of magnitude reduction in friction coefficient during the initial stages of sliding was attributed to the formation of these tribolayers. An abrupt increase in friction coefficient preceding ignition was linked to tribolayer breakdown, exposing the hot underlying metal to high-pressure oxygen. The oxide dispersion-strengthened alloy MA754 was the only material that did not ignite under any test conditions. Its specific content of Cr and Y2O3 dispersoids synergistically promote rapid growth of a thick, adherent oxide tribolayer strengthened by refractory Ni2CrO4 precipitates. These features collectively mitigate tribolayer breakdown, suppressing ignition. The present results highlight the importance of tribolayer stability in achieving frictional ignition resistance and suggest alloy design strategies for tailoring oxidational wear behaviors to develop intrinsically ignition-resistant materials.