scholarly journals Modeling Bainitic Transformations during Press Hardening

Materials ◽  
2021 ◽  
Vol 14 (3) ◽  
pp. 654
Author(s):  
Mingxuan Lin ◽  
Carina Zimmermann ◽  
Kai Wang ◽  
Martin Hunkel ◽  
Ulrich Prahl ◽  
...  
Keyword(s):  
Selection Effect ◽  
Transformation Model ◽  
Reconstruction Technique ◽  
Orientation Relationships ◽  
Mechanical Coupling ◽  
Press Hardening ◽  
Phase Field Models ◽  
Bainitic Microstructure ◽  
External Stresses ◽  
Bainitic Transformations

We revisit recent findings on experimental and modeling investigations of bainitic transformations under the influence of external stresses and pre-strain during the press hardening process. Experimentally, the transformation kinetics in 22MnB5 under various tensile stresses are studied both on the macroscopic and microstructural level. In the bainitic microstructure, the variant selection effect is analyzed with an optimized prior-austenite grain reconstruction technique. The resulting observations are expressed phenomenologically using a autocatalytic transformation model, which serves for further scale bridging descriptions of the underlying thermo-chemo-mechanical coupling processes during the bainitic transformation. Using analyses of orientation relationships, thermodynamically consistent and nondiagonal phase field models are developed, which are supported by ab initio generated mechanical parameters. Applications are related to the microstructure evolution on the sheaf, subunit, precipitate and grain boundary level.

THE BEHAVIOR OF ELECTRODEPOSITED NANOCRYSTALLINE Co–Ni ALLOYS SUBJECTED TO MAGNETIC AND STRESS FIELDS

2010 ◽  
Vol 17 (01) ◽  
pp. 129-134
Author(s):  
R. L. HU ◽  
A. K. SOH ◽  
L. LU ◽  
P. L. TAM ◽  
K. Y. LI
Keyword(s):  
Magnetic Properties ◽  
Ultrafine Particles ◽  
Test System ◽  
Stress Fields ◽  
X Ray ◽  
Mechanical Coupling ◽  
Ni Alloys ◽  
External Stresses ◽  
Nanocrystalline Microstructure ◽  
Pulsed Electrodeposition

Nanocrystalline materials commonly show properties superior to their bulk counterparts. Therefore, they are promising candidates used in the next generation of micro/nanodevices. In the present study, nanocrystalline Co–Ni alloys were fabricated using the pulsed electrodeposition method. The microstructures and components were examined by scanning electron microscopy (SEM) coupled with energy dispersive X-ray spectrometer (EDX). Moreover, the magnetic properties of these alloys subjected to external stresses were studied using a magneto-mechanical coupling test system. The results obtained show that the nanocrystalline microstructure composed of ultrafine particles possessed good magnetic properties, and the saturation magnetization could reach approximately 2 T. In addition, the applied static and varying stresses did slightly affect the magnetic properties of the electrodeposits.

Use of 2½ D imaging in analysis of NiTi martensite

1978 ◽  
Vol 36 (1) ◽  
pp. 610-611
Author(s):  
G. M. Michal
Keyword(s):  
Memory Effect ◽  
Monoclinic Phase ◽  
Reaction Path ◽  
Structural Characteristics ◽  
Salient Feature ◽  
Martensite Phase ◽  
Orientation Relationships ◽  
Low Symmetry ◽  
Hydride Phases ◽  
Unusual Shape

Several TEM investigations have attempted to correlate the structural characteristics to the unusual shape memory effect in NiTi, the consensus being the essence of the memory effect is ostensible manifest in the structure of NiTi transforming martensitic- ally from a B2 ordered lattice to a low temperature monoclinic phase. Commensurate with the low symmetry of the martensite phase, many variants may form from the B2 lattice explaining the very complex transformed microstructure. The microstructure may also be complicated by the enhanced formation of oxide or hydride phases and precipitation of intermetallic compounds by electron beam exposure. Variants are typically found in selfaccommodation groups with members of a group internally twinned and the twins themselves are often observed to be internally twinned. Often the most salient feature of a group of variants is their close clustering around a given orientation. Analysis of such orientation relationships may be a key to determining the nature of the reaction path that gives the transformation its apparently perfect reversibility.

Moire Fringes on Precipitates in Quenched and Aged Beryllium

1968 ◽  
Vol 26 ◽  
pp. 426-427
Author(s):  
F. J. Fraikor ◽  
A. W. Brewer
Keyword(s):  
Ternary Phase ◽  
Volume Fraction ◽  
Age Hardening ◽  
Orientation Relationships ◽  
Solute Content ◽  
Moiré Fringes ◽  
Moire Patterns ◽  
Total Volume Fraction ◽  
Diffraction Patterns ◽  
Moiré Patterns

A number of investigators have examined moire patterns on precipitate particles in various age-hardening alloys. For example, Phillips has analyzed moire fringes at cobalt precipitates in copper and Von Heimendahl has reported on moire fringes in the system Al-Au. Recently, we have observed moire patterns on impurity precipitates in beryllium quenched in brine from 1000°C and aged at various temperatures in the range of 500-800°C. This heat treatment of beryllium rolled from vacuum cast ingots produces the precipitation of both an fee ternary phase, AlFeBe4, and an hcp binary phase, FeBe11. However, unlike a typical age-hardening alloy, the solute content of this material is low (less than 1000 ppm of Fe and 600 ppm of Al) and hence the total volume fraction of precipitates is small. Therefore there is some difficulty in distinguishing the precipitates and their orientation relationships with the beryllium matrix since the weak precipitate spots generally do not appear on the diffraction patterns.

Lattice imaging of precipitates in Al-Zn-Mg alloy

1986 ◽  
Vol 44 ◽  
pp. 412-413
Author(s):  
C. K. Wu
Keyword(s):  
Grain Boundaries ◽  
Homogeneous Nucleation ◽  
Alloy System ◽  
Mg Alloy ◽  
List Type ◽  
Lattice Structures ◽  
Type Number ◽  
Orientation Relationships ◽  
Lattice Imaging ◽  
The Matrix

The precipitation phenomenon in Al-Zn-Mg alloy is quite interesting and complicated and can be described in the following categories:(i) heterogeneous nucleation at grain boundaries;(ii) precipitate-free-zones (PFZ) adjacent to the grain boundaries;(iii) homogeneous nucleation of snherical G.P. zones, n' and n phases inside the grains. The spherical G.P. zones are coherent with the matrix, whereas the n' and n phases are incoherent. It is noticed that n' and n phases exhibit plate-like morpholoay with several orientation relationship with the matrix. The high resolution lattice imaging techninue of TEM is then applied to study precipitates in this alloy system. It reveals the characteristics of lattice structures of each phase and the orientation relationships with the matrix.

In situ TEM observations of melting in nanosized eutectic Pb-Cd inclusions embedded in Al

1996 ◽  
Vol 54 ◽  
pp. 986-987
Author(s):  
S. Hagège ◽  
U. Dahmen ◽  
E. Johnson ◽  
A. Johansen ◽  
V.S. Tuboltsev
Keyword(s):  
Electron Microscope ◽  
Melt Spinning ◽  
Ternary Alloys ◽  
Solid Matrix ◽  
Eutectic System ◽  
In Situ Tem ◽  
In Situ Observation ◽  
Orientation Relationships ◽  
Transmission Electron

Small particles of a low-melting phase embedded in a solid matrix with a higher melting point offer the possibility of studying the mechanisms of melting and solidification directly by in-situ observation in a transmission electron microscope. Previous studies of Pb, Cd and other low-melting inclusions embedded in an Al matrix have shown well-defined orientation relationships, strongly faceted shapes, and an unusual size-dependent superheating before melting.[e.g. 1,2].In the present study we have examined the shapes and thermal behavior of eutectic Pb-Cd inclusions in Al. Pb and Cd form a simple eutectic system with each other, but both elements are insoluble in solid Al. Ternary alloys of Al (Pb,Cd) were prepared from high purity elements by melt spinning or by sequential ion implantation of the two alloying additions to achieve a total alloying addition of up to lat%. TEM observations were made using a heating stage in a 200kV electron microscope equipped with a video system for recording dynamic behavior.

Direct imaging of order-disorder and antiphase domain structures in Ti3Al intermetallic compound

1990 ◽  
Vol 48 (4) ◽  
pp. 480-481
Author(s):  
H. Q. Ye ◽  
T.S. Xie ◽  
D. Li
Keyword(s):  
Intermetallic Compound ◽  
Volume Fraction ◽  
Fundamental Problem ◽  
Antiphase Domain ◽  
Atomic Scale ◽  
Orientation Relationships ◽  
Domain Structures ◽  
Α Phase ◽  
Diffraction Patterns ◽  
Two Phases

The Ti3Al intermetallic compound has long been recognized as potentially useful structural materials. It offers attractive strength to weight and elastic modulus to weight ratios. Recent work has established that the addition of Nb to Ti3Al ductilized this compound. In this work the fundamental problem of this alloy, i.e. order-disorder and antiphase domain structures was investigated at the atomic scale.The Ti3Al+10at%Nb alloys used in this study were treated at 1060°C and then aged at 700°C for 2 hours. The specimens suitable for TEM were prepared by standard jet electrolytic-polishing technique. A JEM-200CX electron microscope with an interpretable resolution of about 0.25 nm was used for HREM.The [100] and [001] projections of the α2 phase were shown in Fig.l.The alloy obtained consist of at least two phases-α2(Ti3Al) and β0 structures. Moreover, a disorder α phase with small volume fraction was also observed. Fig.2 gives [100] and [001] diffraction patterns of the α2 phase. Since lattice parameters of the ordered α2 (a=0.579, c=0.466 nm) and disorder α phase (a0=0.294≈a/2, c0=0.468 nm) are almost the same, their diffraction patterns are difficult to be distinguished when they are overlapped with epitaxial orientation relationships.

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