This paper presents results on the evolution of microstructure (both matrix and precipitates) of an ASME Grade 91 steel that has been creep tested for 113,431h at 600°C under a load of 80MPa.The microstructure was investigated using transmission electron microscopy (TEM) and revealed chromium rich M 23 C 6 carbides, MX-type precipitates, Laves phases and modified Z-phases. Only a small amount of modified Z-phase was found. In order to quantify coarsening of precipitates and growth of new phases during creep, the size distributions of the identified precipitates were determined by analysis of TEM images. In addition to this, the size distribution of Laves phases was determined by image analysis of scanning electron micrographs.Substructure modifications and creep damage were investigated on cross sections of the creep specimen using Electron Backscatter Diffraction and Scanning Electron Microscopy. *Please cite this article in press as: Panait CG, et al., Study of the microstructure of the Grade 91 steel after more than 100,000 h of creep.

a b s t r a c tThere are rather few quantitative data on the microstructure of the 9-12%Cr heat resistant steels after long-term creep. This paper presents results of the quantitative measurement of the size of MX precipitates, subgrain size and dislocation density in a P91 steel that had been creep tested for 113,431 h at 600 • C. The same measurements were conducted in the same P91 steel in the as received conditions.Transmission electron microscopy investigations were conducted using thin foils and revealed a decrease in dislocation density and an increase in subgrain size after creep exposure. MX carbonitrides are very stable during thermal and creep exposure of P91 steel at 600 • C up to 113,431 h.Electron backscatter diffraction (EBSD) investigations also revealed a significant change in the substructure of the steel after creep exposure.

The synthesis of few-layered graphene is performed by ion implantation of carbon species in thin nickel films, followed by high temperature annealing and quenching. Although ion implantation enables a precise control of the carbon content and of the uniformity of the in-plane carbon concentration in the Ni films before annealing, we observe thickness non-uniformities in the synthesized graphene layers after high temperature annealing. These non-uniformities are probably induced by the heterogeneous distribution/topography of the graphene nucleation sites on the Ni surface. Taken altogether, our results indicate that the number of graphene layers on top of Ni films is controlled by the nucleation process on the Ni surface rather than by the carbon content in the Ni film.