scholarly journals Carbide Precipitation in a Low Alloyed Steel during Aging Studied by Atom Probe Tomography and Thermodynamic Modeling

Metals ◽  
2021 ◽  
Vol 11 (12) ◽  
pp. 2009
Author(s):  
Mattias Thuvander ◽  
Hans Magnusson ◽  
Ulrika Borggren
Keyword(s):  
Atom Probe Tomography ◽  
Precipitation Hardening ◽  
Atom Probe ◽  
Carbide Precipitation ◽  
Martensitic Structure ◽  
Number Density ◽  
High Number Density ◽  
Molybdenum Carbides ◽  
The Matrix ◽  
Low Alloyed Steel

Carbide precipitation in martensitic low alloyed steels contributes to the mechanical properties through precipitation hardening. A high number density of carbides is desired to maximize the hardening effect, which is achieved through the precipitation of carbides on the dislocations in the martensitic structure. In this study, the nucleation, growth, and coarsening of vanadium and molybdenum carbides during aging at 600 °C for periods up to four weeks were investigated. The work covers characterization with atom probe tomography, which showed that the nucleation of V and Mo rich MC/M2C carbides takes place on dislocations. The growth of these carbides proceeds by the diffusion of elements to the dislocations, which has been modeled using Dictra software, confirming the rate of the reaction as well as the depletion of carbide formers in the matrix. For longer aging times, particle coarsening will decrease the number density of particles with a transition from dislocation-based carbides to separate rounded carbides.

scholarly journals Multiple Influences of Molybdenum on the Precipitation Process in a Martensitic PH Stainless Steel

Metals ◽  
2019 ◽  
Vol 9 (10) ◽  
pp. 1118
Author(s):  
Mattias Thuvander ◽  
Marcus Andersson ◽  
Krystyna Stiller
Keyword(s):  
Electron Microscopy ◽  
Stainless Steel ◽  
Atom Probe Tomography ◽  
Precipitation Hardening ◽  
Atom Probe ◽  
Precipitation Process ◽  
Transmission Electron ◽  
Initial Stage ◽  
The Matrix ◽  
Mo Content

Molybdenum has been found to influence the complex precipitation process in a martensitic precipitation hardening stainless steel during aging at 475 °C in several different ways. Three steels with different Mo content (0, 1.2 and 2.3 at.%) were investigated. Studies of the microstructure were performed with atom probe tomography and energy filtered transmission electron microscopy. It is shown that, at the initial stage of aging, a faster nucleation of Cu-rich clusters takes place with increasing Mo content. The Cu-clusters act as precipitation sites for other solute elements and promote the nucleation of Ni-rich phases. During further aging, a higher Mo content in the material instead slows down the growth and coarsening of the Ni-rich phases, because Mo segregates to the interface between precipitate and matrix. Additionally, Mo promotes decomposition of the matrix into α and α′ regions. After longer aging times (>40 h) quasicrystalline Mo-rich R′ phase forms (to a greater extent in the material having the highest Mo content). The observations serve to understand the hardness evolution during aging.

Atom Probe Tomographic Characterization of Nanoscale Cu-Rich Precipitates in 17-4 Precipitate Hardened Stainless Steel Tempered at Different Temperatures

2017 ◽  
Vol 23 (2) ◽  
pp. 340-349 ◽  
Author(s):  
Zemin Wang ◽  
Xulei Fang ◽  
Hui Li ◽  
Wenqing Liu
Keyword(s):  
Stainless Steel ◽  
Interfacial Energy ◽  
Atom Probe Tomography ◽  
Atom Probe ◽  
Number Density ◽  
The Matrix ◽  
Different Temperatures

AbstractThe formation of copper-rich precipitates of 17-4 precipitate hardened stainless steel has been investigated, after tempering at 350–570°C for 4 h, by atom probe tomography (APT). The results reveal that the clusters, enriched only with Cu, were observed after tempering at 420°C. Segregation of Ni, Mn to the Cu-rich clusters took place at 450°C, contributing to the increased hardening. After tempering at 510°C, Ni and Mn were rejected from Cu-rich precipitates and accumulated at the precipitate/matrix interfaces. Al and Si were present and uniformly distributed in the precipitates that were <1.5 nm in radius, but Ni, Mn, Al, and Si were enriched at the interfaces of larger precipitates/matrix. The proxigram profiles of the Cu-rich precipitates formed at 570°C indicated that Ni, Mn, Al, and Si segregated to the precipitate/matrix interfaces to form a Ni(Fe, Mn, Si, Al) shell, which significantly reduced the interfacial energy as the precipitates grew into an elongated shape. In addition, the number density of Cu-rich precipitates was increased with the temperature elevated from 350 up to 450°C and subsequently decreased at higher temperatures. Also, the composition of the matrix and the precipitates were measured and found to vary with temperature.

Effect of Cu on Nanoscale Precipitation Evolution and Mechanical Properties of a Fe–NiAl Alloy

2017 ◽  
Vol 23 (2) ◽  
pp. 350-359 ◽  
Author(s):  
Qin Shen ◽  
Hao Chen ◽  
Wenqing Liu
Keyword(s):  
Mechanical Properties ◽  
Atom Probe Tomography ◽  
Diffusion Rate ◽  
Atom Probe ◽  
Peak Hardness ◽  
Dramatic Improvement ◽  
Number Density ◽  
Cu Alloy ◽  
Tension Tests ◽  
Nial Alloy

AbstractThe microstructural evolution of precipitation in two model alloys, Fe–NiAl and Fe–NiAl–Cu, was investigated during aging at 500°C for different times using atom probe tomography (APT). The APT results reveal that the addition of Cu effectively increases the number density of NiAl precipitates. This is attributed to Cu promoting the nucleation of NiAl particles by increasing the chemical driving force and decreasing the interfacial energy. The NiAl precipitates of the Fe–NiAl–Cu alloy grow and coarsen at a slower rate than that of the Fe–NiAl alloy, mainly due to the slower diffusion rate of the Cu atoms. The mechanical properties of the two alloys were characterized by Vickers hardness and tension tests. It was found that the addition of Cu results in the formation of core–shell precipitates with a Cu-rich core and a NiAl shell, leading to a dramatic improvement of peak hardness and strength. The effect of Cu on precipitation strengthening is discussed in terms of chemical strength and coherency strength.

scholarly journals Atom Probe Tomographic Studies of Precipitation in Al-0.1Zr-0.1Ti (at.%) Alloys

2007 ◽  
Vol 13 (6) ◽  
pp. 503-516 ◽  
Author(s):  
Keith E. Knipling ◽  
David C. Dunand ◽  
David N. Seidman
Keyword(s):  
Atom Probe Tomography ◽  
Local Thermodynamic Equilibrium ◽  
Atom Probe ◽  
Atomic Ratio ◽  
Chemical Compositions ◽  
Ti Alloys ◽  
The Matrix ◽  
Solute Atoms ◽  
Interfacial Segregation ◽  
Zr Alloys

Atom probe tomography was utilized to measure directly the chemical compositions of Al3(Zr1−xTix) precipitates with a metastable L12 structure formed in Al-0.1Zr-0.1Ti (at.%) alloys upon aging at 375°C or 425°C. The alloys exhibit an inhomogeneous distribution of Al3(Zr1−xTix) precipitates, as a result of a nonuniform dendritic distribution of solute atoms after casting. At these aging temperatures, the Zr:Ti atomic ratio in the precipitates is about 10 and 5, respectively, indicating that Ti remains mainly in solid solution rather than partitioning to the Al3(Zr1−xTix) precipitates. This is interpreted as being due to the very small diffusivity of Ti in α-Al, consistent with prior studies on Al-Sc-Ti and Al-Sc-Zr alloys, where the slower diffusing Zr and Ti atoms make up a small fraction of the Al3(Sc1−xTix/Zrx) precipitates. Unlike those alloys, however, the present Al-Zr-Ti alloys exhibit no interfacial segregation of Ti at the matrix/precipitate heterophase interface, a result that may be affected by a significant disparity in the evaporation fields of the α-Al matrix and Al3(Zr1−xTix) precipitates and/or a lack of local thermodynamic equilibrium at the interface.

Core-Shell Structure of Intermediate Precipitates in a Nb-Based Z-Phase Strengthened 12% Cr Steel

2017 ◽  
Vol 23 (2) ◽  
pp. 360-365 ◽  
Author(s):  
Masoud Rashidi ◽  
Hans-Olof Andrén ◽  
Fang Liu
Keyword(s):  
Phase Transformation ◽  
Shell Structure ◽  
Atom Probe Tomography ◽  
Atom Probe ◽  
Core Shell ◽  
The Core ◽  
The Matrix ◽  
Core Shell Structure ◽  
Cr Steels

AbstractIn creep resistant Z-phase strengthened 12% Cr steels, MX (M=Nb, Ta, or V, and X=C and/or N) to Z-phase (CrMN, M=Ta, Nb, or V) transformation plays an important role in achieving a fine distribution of Z-phase precipitates for creep strengthening. Atom probe tomography was employed to investigate the phase transformation in a Nb-based Z-phase strengthened trial steel. Using iso-concentration surfaces with different concentration values, and subtracting the matrix contribution enabled us to reveal the core-shell structure of the transient precipitates between MX and Z-phase. It was shown that Z-phase forms by diffusion of Cr into NbN upon ageing, and Z-phase has a composition corresponding to Cr1+xNb1−xN with x=0.08.

Atom probe tomography evidence of nitrogen excess in the matrix of nitrided Fe–Cr

2010 ◽  
Vol 90 (11) ◽  
pp. 793-800 ◽  
Author(s):  
P. Jessner ◽  
M. Gouné ◽  
R. Danoix ◽  
B. Hannoyer ◽  
F. Danoix
Keyword(s):  
Atom Probe Tomography ◽  
Atom Probe ◽  
The Matrix ◽  
Nitrogen Excess

APT Investigation of Effect of Minor Zr on Precipitation Strength of Al-Sc Alloy

2016 ◽  
Vol 877 ◽  
pp. 245-250 ◽  
Author(s):  
Na Xue ◽  
Hui Song ◽  
Chang Bing Zhou ◽  
Xiao Jiao Wang ◽  
Wen Qing Liu
Keyword(s):  
Aging Time ◽  
Atom Probe Tomography ◽  
Diffusion Rate ◽  
Atom Probe ◽  
Precipitation Strengthening ◽  
Number Density ◽  
Zr Addition ◽  
Zr Alloy ◽  
Zr Alloys

As-cast Al-Sc alloys and Zr-containing Al-Sc-Zr alloys were aged at 300°C for different times, the Al-Sc-Zr alloy showed more excellent precipitation strengthening. The atom probe tomography (APT) was applied to characterize the precipitates in the two alloys, the results show that the precipitates in Al-Sc-Zr alloy is smaller in size and is higher in number density than that in the Al-Sc alloy at same aging time, it is because that the Zr addition reduces the diffusion rate of Sc, and which retains the growth of precipitates and results in the excellent precipitation strengthening of Al-Sc-Zr alloy.

PosgenPy: An Automated and Reproducible Approach to Assessing the Validity of Cluster Search Parameters in Atom Probe Tomography Datasets

2021 ◽  
pp. 1-10
Author(s):  
Przemysław Klupś ◽  
Daniel Haley ◽  
Andrew J. London ◽  
Hazel Gardner ◽  
James Famelton ◽  
...  
Keyword(s):  
Atom Probe Tomography ◽  
Spatial Clustering ◽  
Atom Probe ◽  
Parameter Selection ◽  
Material System ◽  
Number Density ◽  
Cluster Number ◽  
Simulated Material ◽  
Parameter Values ◽  
Selection Of

One of the main capabilities of atom probe tomography (APT) is the ability to not only identify but also characterize early stages of precipitation at length scales that are not achievable by other techniques. One of the most popular methods to identify nanoscale clustering in APT data, based on the density-based spatial clustering of applications with noise (DBSCAN), is used extensively in many branches of research. However, it is common that not all of the steps leading to the selection of certain parameters used in the analysis are reported. Without knowing the rationale behind parameter selection, it may be difficult to compare cluster parameters obtained by different researchers. In this work, a simple open-source tool, PosgenPy, is used to justify cluster search parameter selection via providing a systematic sweep through parameter values with multiple randomizations to minimize a false-positive cluster ratio. The tool is applied to several different microstructures: a simulated material system and two experimental datasets from a low-alloy steel . The analyses show how values for the various parameters can be selected to ensure that the calculated cluster number density and cluster composition are accurate.

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