The effect of long-term thermal exposure on the carbide evolution in a Ni-16Mo-7Cr base superalloy was investigated. The results show that M₁₂C carbides are mainly precipitated on the grain boundaries during thermal exposure, and the primary massive M₆C carbides can be completely transformed to M₁₂C carbides in situ at temperatures above 750 °C for long-term thermal exposure. The transformation from M₆C carbides to M₁₂C carbides is attributed to the release of C atoms from M₆C, which results in the morphology changes of massive carbides, and stabilization of the sizes of M₁₂C carbides precipitated on the grain boundaries.

The mechanism of ferromagnetism in carbon-based materials, which contain only s and p electrons in contrast to traditional ferromagnets based on 3d or 4f electrons, is important but unclear. Here, by means of near-edge x-ray-absorption fine-structure (NEXAFS) and bulk magnetization measurements, we demonstrate that the origin of ferromagnetism in 12C+ ion implanted highly oriented pyrolytic graphite (HOPG) is closely correlated with the defect electronic states near the Fermi level. The angle-dependent NEXAFS spectra imply that these defect-induced electronic states are extended on the graphite basal plane. We attribute the origin of electronic states to the vacancy defects created under 12C+ ion implantation. The intensity of the observed ferromagnetism in HOPG is sensitive to the defect density, and the narrow implantation dosage window that produces ferromagnetism is optimized.