TEM study of structural hardening in a new martensitic steel for aeronautic application

Abstract

A new generation of high performance martensitic steel hardened by FeNiAl intermetallic nanoprecipitates has been investigated using conventional and advanced Transmission Electron Microscopy (TEM). Cs-corrected high resolution TEM has been used to provide a fine and accurate microstructural characterization: the shape, size and crystallographic characteristics of the nanoprecipitates have been identified. TEM in situ straining tests have been performed to determine the relevant parameters, which control the deformation. The nanoprecipitates are observed to create anchor lines acting against the propagation of the mobile dislocations and to be crossed by shearing process. In addition, in situ TEM experiments have allowed to measure directly the average distance between these nanoprecipitates along the dislocation lines. This value is of great interest as it is the more accurate data to be used in the calculation of the stress associated with the structural hardening. The strength of the alloy due to these nanoprecipitates has been also determined. It is in good agreement with the value deduced from macroscopic mechanical tests.

Thermomechanical Fatigue Testing of Dual Hardening Tool Steels

“…It is assumed that the improved tempering resistance and therefore the increased TMF lifetime of the dual hardening alloy is caused by the combination of secondary hardening carbides and intermetallic precipitates. Upon ageing, the intermetallic particles precipitate very fast and homogeneously distributed due to their coherency to the iron matrix, expanding the preferred precipitation sites for secondary hardening carbides from dislocations and grain boundaries to interfaces between the NiAl particles and the iron matrix . This leads to an increased amount of precipitation sites, thus a more homogeneous distribution and size refinement of the secondary hardening carbides, resulting in an increased tempering resistance.…”

Short-term creep approach to redefining the role of 17-4PH stainless steel for high-temperature applications

“…( 10 ) denotes the self-diffusion coefficient. For iron, D 0L = 3.71 × 10 –4 m 2 s −1 , Q L = 269 kJ mol −1 31 , b = 2.5 × 10 –10 m 32 , while the shear modulus was obtained from Ref. 33 .…”