Microstructural design of hard coatings

The technique of atom probe tomography (APT) is reviewed with an emphasis on illustrating what is possible with the technique both now and in the future. APT delivers the highest spatial resolution (sub-0.3-nm) three-dimensional compositional information of any microscopy technique. Recently, APT has changed dramatically with new hardware configurations that greatly simplify the technique and improve the rate of data acquisition. In addition, new methods have been developed to fabricate suitable specimens from new classes of materials. Applications of APT have expanded from structural metals and alloys to thin multilayer films on planar substrates, dielectric films, semiconducting structures and devices, and ceramic materials. This trend toward a broader range of materials and applications is likely to continue.

Invited review article: Atom probe tomography.

Strategies for fabricating atom probe specimens with a dual beam FIB.

On the effect of alloy composition on martensite start temperatures and latent heats in Ni–Ti-based shape memory alloys

The influence of deformation-induced excess vacancies on segregation and on precipitation is discussed within a phenomenological framework. During high temperature deformation, vacancies are mainly generated by the non-conservative movement of thermal jogs. Sinks for these vacancies are dislocations and grain boundaries. The excess vacancy concentration increases with strain rate and inverse temperature. Stronger effects are expected in f.c.c. materials because of their comparatively low diffusivities; in austenitic steels, the concentrations of deformation-induced vacancies are predicted to be significant, even at temperatures as high as 0.75 of the melting temperature. At the high strain rates (> 10 s −1 ) used in industrial rolling, the vacancy concentration may attain levels 2–3 orders-of-magnitude higher than the equilibrium one. One consequence of the presence of deformation-induced vacancies is the non-equilibrium segregation of boron observed e.g. in austenitic Nb-B steels, where it stimulates the nucleation of Nb borocarbonitrides.

Modelling the effect of deformation-induced vacancies on segregation and precipitation

Overview no. 63 Non-equilibrium grain boundary segregation of boron in austenitic stainless steel—I. Large scale segregation behaviour

Overview no. 63 Non-equilibrium grain boundary segregation of boron in austenitic stainless steel—IV. Precipitation behaviour and distribution of elements at grain boundaries

A recently developed technique for viewing wire specimens in the electron microscope has been used in a search for a suitable electrolyte for preparation of tungsten specimens for the field-ion microscope. Clean specimens which yield good transmission electron micrographs can be produced and the amount of back-polishing can be monitored with an electronic timer.

http://iopscience.iop.org/article/10.1088/0950-7671/44/12/428/pdf

Preparation of contamination-free tungsten specimens for the field-ion microscope

Observations of the field-evaporation end form of tungsten.

The significance of field-ion studies of high angle grain-boundary structure is reconsidered in the light of the limitations of resolution and crystallographic accuracy inherent in the technique. All available data for high angle boundaries are compared with the predictions of the coincident site lattice model which is shown not to apply to the majority of observations. One boundary is analysed in detail to show how facets, ledges and grain-boundary dislocations are recognized. Combined electron and field-ion microscopy are used to investigate the nature of grain-boundary dislocations.

H. Norden

Papers

Overview no. 63 Non-equilibrium grain boundary segregation of boron in austenitic stainless steel—I. Large scale segregation behaviour

Overview no. 63 Non-equilibrium grain boundary segregation of boron in austenitic stainless steel—IV. Precipitation behaviour and distribution of elements at grain boundaries

Preparation of contamination-free tungsten specimens for the field-ion microscope

Observations of the field-evaporation end form of tungsten.

Field-ion and electron microscopy of grain-boundary structure