A Deformation Model for Elevated Temperature Including Grain Size Distribution Effects

This paper presents domain and structure studies of bonded magnets made from nanocrystalline Nd-(Fe, Co)-B powder. The structure studies were investigated using scanning electron microscopy (SEM), high-resolution transmission electron microscopy (HRTEM), Mössbauer spectroscopy and X-ray diffractometry. On the basis of performed qualitative and quantitative phase composition studies, it was found that investigated alloy was mainly composed of Nd2(Fe-Co)14B hard magnetic phase (98 vol%) and a small amount of Nd1.1Fe4B4 paramagnetic phase (2 vol%). The best fit of grain size distribution was achieved for the lognormal function. The mean grain size determined from transmission electron microscopy (TEM) images on the basis of grain size distribution and diffraction pattern using the Bragg equation was about ≈130 nm. HRTEM images showed that over-stoichiometric Nd was mainly distributed on the grain boundaries as a thin amorphous border of 2 nm in width. The domain structure was investigated using a scanning electron microscope and metallographic light microscope, respectively, by Bitter and Kerr methods, and by magnetic force microscopy. Domain structure studies revealed that the observed domain structure had a labyrinth shape, which is typically observed in magnets, where strong exchange interactions between grains are present. The analysis of the domain structure in different states of magnetization revealed the dynamics of the reversal magnetization process.

Download Full-text

Influence of bimodal grain size distribution on the corrosion resistance of Mg-4Li-3Al-1Zn (LAZ431)

Journal of Materials Research and Technology ◽

10.1016/j.jmrt.2021.04.078 ◽

2021 ◽

Author(s):

Anna Dobkowska ◽

Boguslawa Adamczyk – Cieślak ◽

Dariusz Kuc ◽

Eugeniusz Hadasik ◽

Tomasz Płociński ◽

...

Keyword(s):

Grain Size ◽

Corrosion Resistance ◽

Size Distribution ◽

Grain Size Distribution ◽

Bimodal Grain Size ◽

Bimodal Grain Size Distribution

Download Full-text

Effect of Strain-Induced Precipitation on the Recrystallization Kinetics in a Model Alloy

Metallurgical and Materials Transactions A ◽

10.1007/s11661-021-06206-8 ◽

2021 ◽

Author(s):

Mo Ji ◽

Martin Strangwood ◽

Claire Davis

Keyword(s):

Grain Size ◽

Size Distribution ◽

Grain Size Distribution ◽

Avrami Exponent ◽

Model Alloy ◽

Size Distributions ◽

Recrystallization Kinetics ◽

Grain Size Distributions ◽

Recrystallized Grain Size ◽

Nb Addition

AbstractThe effects of Nb addition on the recrystallization kinetics and the recrystallized grain size distribution after cold deformation were investigated by using Fe-30Ni and Fe-30Ni-0.044 wt pct Nb steel with comparable starting grain size distributions. The samples were deformed to 0.3 strain at room temperature followed by annealing at 950 °C to 850 °C for various times; the microstructural evolution and the grain size distribution of non- and fully recrystallized samples were characterized, along with the strain-induced precipitates (SIPs) and their size and volume fraction evolution. It was found that Nb addition has little effect on recrystallized grain size distribution, whereas Nb precipitation kinetics (SIP size and number density) affects the recrystallization Avrami exponent depending on the annealing temperature. Faster precipitation coarsening rates at high temperature (950 °C to 900 °C) led to slower recrystallization kinetics but no change on Avrami exponent, despite precipitation occurring before recrystallization. Whereas a slower precipitation coarsening rate at 850 °C gave fine-sized strain-induced precipitates that were effective in reducing the recrystallization Avrami exponent after 50 pct of recrystallization. Both solute drag and precipitation pinning effects have been added onto the JMAK model to account the effect of Nb content on recrystallization Avrami exponent for samples with large grain size distributions.

Download Full-text