A major concern for 17-4PH steels operating at elevated temperatures is embrittlement due to Fe-rich (α) and Cr-enriched (α′) phase separation, along with precipitation of other detrimental phases. In this study the sequence of microstructural changes at the atomic scale in a 17-4PH steel is characterized by atom probe tomography (APT) at two different ageing temperatures, 480 °C and 590 °C. In the earliest stages of heat treatment at both temperatures, APT reveals that dislocations and matrix defects are highlighted by the segregation of NbN/CrN ionic species, providing heterogeneous nucleation sites for subsequent Cu-rich precipitates (CRPs) and Nb-rich precipitates, respectively. At the lower temperature, Cr-rich α′-phase also nucleates and ultimately a Mn, Ni, and Si-rich (MNS) phase was observed to form. The evolution in number density and fraction of CRPs and Cr-rich α′-phase, the latter of which was not observed at the higher temperature, has been quantified and their respective contributions to the overall precipitation hardening of the material has been estimated

Carlin-type gold deposits are one of the most important gold mineralization styles in the world. Despite their economic importance and the large volume of work that has been published, there remain crucial questions regarding their metallogenesis. Much of this uncertainty is due to the cryptic nature of the gold occurrence, with gold occurring as dispersed nanoscale inclusions within host pyrite rims that formed on earlier formed barren pyrite cores. The small size of the gold inclusions has made determining their nature within the host sulfides and the mechanisms by which they precipitated from the ore fluids particularly problematic. This study combines high-resolution electron probe microanalysis (EPMA) with atom probe tomography (APT) to constrain whether the gold occurs as nanospheres or is dispersed within the Carlin pyrites. APT offers the unique capability of obtaining major, minor, trace, and isotopic chemical information at near-atomic spatial resolution. We use this capability to investigate the atomic-scale distribution of trace elements within Carlin-type pyrite rims, as well as the relative differences of sulfur isotopes within the rim and core of gold-hosting pyrite. We show that gold within a sample from the Turquoise Ridge deposit (Nevada) occurs within arsenian pyrite overgrowth (rims) that formed on a pyrite core. Furthermore, this As-rich rim does not contain nanonuggets of gold and instead contains dispersed lattice-bound Au within the pyrite crystal structure. The spatial correlation of gold and arsenic within our samples is consistent with increased local arsenic concentrations that enhanced the ability of arsenian pyrite to host dispersed gold (Kusebauch et al., 2019). We hypothesize that point defects in the lattice induced by the addition of arsenic to the pyrite structure facilitate the dissemination of gold. The lack of gold nanospheres in our study is consistent with previous work showing that dispersed gold in arsenian pyrite can occur in concentrations up to ~1:200 (gold/arsenic). We also report a method for determining the sulfur isotope ratios from atom probe data sets of pyrite (±As) that illustrates a relative change between the pyrite core and its Au and arsenian pyrite rim. This spatial variation confirms that the observed pyrite core-rim structure is due to two-stage growth involving a sedimentary or magmatic-hydrothermal core and hydrothermal rim, as opposed to precipitation from an evolving hydrothermal fluid.

We study surface kinetic roughening of TiN films grown on Si(100) substrates by dc reactive sputtering. The surface morphology of films deposited for different growth times under the same experimental conditions were analyzed by atomic force microscopy. The TiN films exhibit intrinsic anomalous scaling and multiscaling. The film kinetic roughening is characterized by a set of local exponent values ${\alpha }_{\mathrm{loc}}=1.0$ and ${\beta }_{\mathrm{loc}}=0.39$, and global exponent values $\alpha =1.7$ and $\beta =0.67$, with a coarsening exponent of $1∕z=0.39$. These properties are correlated to the local height-difference distribution function obeying power-law statistics. We associate this intrinsic anomalous scaling with the instability due to nonlocal shadowing effects that take place during thin-film growth by sputtering.