The physical metallurgy of steels

Transmission electron microscopy and high-resolution electron microscopy investigations of the structure of Cu precipitates in the size range 4–30 nm were carried out as part of a wider investigation into Cu precipitation from thermally aged Fe-Cu and Fe-Cu-Ni ferritic model alloys. A twinned 9R structure was found to be present in precipitates slightly larger than 4nm in diameter, following transformation from b.c.c. Two twin-related 9R variants were observed in all the smallest 9R particles studied. The 9R precipitates were observed to grow subsequently as spherical, multiply twinned particles up to approximately 17 nm, indicating that further twinning must occur during growth in the 9R phase. At sizes larger than 17 nm, a second transformation to the more stable 3R structure takes place. Observations on these 3R particles indicate that, following transformation from 9R, the precipitates are untwinned and have a distorted f.c.c. structure. The particle-matrix orientation is close to, but not ex...

High-resolution electron microscopy studies of the structure of Cu precipitates in α-Fe

Nanometer-scale multilayer materials exhibit a wealth of interesting structural and mechanical property behaviors. Physical-vapor-deposition technology allows almost unlimited freedom to choose among elements, alloys, and Compounds as layering constituents and to design and produce materials with compositional and structural periodicities approaching the atomic Scale. These materials have tremendous interface area density, approaching 106 mm/mm3, so that a Square centimeter area of a one-micron-thick multilayer film with a bilayer period of 2 nm has an interface area of roughly 1,000 cm2. Hence interfacial effects can dominate multilayer structure and properties leading to unusually large strains and frequently stabilization of metastable structures. The atomic-scale layering of different materials also leads to very high hardnesses and good wear resistance. These materials are a test-bed for examination of the fundamental aspects of phase stability and for exploring mechanical strengthening mechanisms. They are also becoming increasingly interesting for applications such as hard coatings, x-ray optical elements, in microelectromechanical Systems (MEMS), and in magnetic recording media and heads.In this article, we review some of the interesting structures and mechanical properties that have been observed in nanometer-scale artificial multilayer structures.Superlattice thin films are readily deposited by vapor-phase techniques such as sputter deposition, evaporation, and chemical vapor deposition, as well as by electrochemical deposition. Superlattice deposition Systems are similar to conventional film deposition Systems, except for the provision to modulate the fluxes and thereby produce alternating super-lattice layers.

Structure and strength of multilayers

Conventional transmission electron microscopy (TEM) and high-resolution electron microscopy (HREM) experiments have been carried out on thermally-aged binary Fe 1·30 wt% Cu and ternary Fe 1·28 wt% Cu 1·43 wt.% Ni alloys to study the structure of small (7–15 nm) copper precipitates in the α-Fe matrix. The experiments show that the precipitates have a twinned 9R close-packed structure, rather than the expected f.c.c. structure. It is believed that this structure is generated initially by a martensitic transformation from the metastable b.c.c. phase.

Transmission electron microscope investigations of the structure of copper precipitates in thermally-aged Fe—Cu and Fe—Cu—Ni

http://nucapt.northwestern.edu/refbase/files/IsheimCuPPTActaMat2005.pdf

Interfacial segregation at Cu-rich precipitates in a high-strength low-carbon steel studied on a sub-nanometer scale

The size and number density of precipitates formed during the early stage of precipitation of copper from Fe-1.4 at. pct Cu at 500°C was determined with the field-ion microscope (FIM). While particles of less than 50 × 10−8 cm remain invisible in the electron microscope (ETM) they are clearly resolved with the FIM; particles as small as 8 × 10−8 cm in diameter could be detected. The growth rate of the particles can be accounted for by normal bulk diffusion. At its peak strength, the alloy contains approximately 1018 particles per cu cm with an average diameter of 24 × 10−8 cm. The alloy reaches its peak strength well before precipitation is complete.

S. R. Goodman

Papers

An FIM-atom probe study of the precipitation of copper from lron-1.4 at. pct copper. Part I: Field-ion microscopy