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structural, microstructural and magnetic evolution in cryo milled carbon doped mnal

by:Maghard      2020-02-28
Low cost, free of rare earth Tau-
MnAl phase has high potential in partial substitution of bonded Nd2Fe14B rare earth permanent materials. However, the τ-
The phase is substeady state and it is difficult to obtain the powder suitable for the alignment process of permanent experimentally, which requires the powder to have proper microstructure and high τ-phase purity.
In this work, a new method for the preparation of high purity τ-
The phase fine powder is introduced.
High purity τ-phase Mn0. 55Al0. 45C0.
02 alloy was synthesized by drop synthesis.
The drip synthetic material is subjected to freeze grinding and then a flash heating process is performed.
The crystal structure and microstructure of synthetic, frozen grinding and flash heating samples were studied with X-X
X-ray in situ powder diffraction, scanning electron microscopy, X-ray
Ray energy scattering spectrum and electron reverse scattering diffraction.
The magnetic and magnetic structures of the synthesized droplets, frozen grinding, flash heating samples were characterized by magnetic measurements and neutron powder diffraction, respectively.
The results showed that both the 2-hour and 4-hour frozen grinding and flash-heated samples showed high τ-
Phase purity and micron grade
The size of the round particle shape.
In addition, the samples heated by Flash show a high saturation magnetic strength and an increased magnetic strength.
Permanent magnets play a vital role in advanced green energy technologies such as wind turbines, electric vehicles and hybrid vehicles.
However, the market for permanent materials is mainly composed of NdFeB and ferrites, which contain not only Nd, but also Dy and other rare earth elements as additives.
The supply of some heavy rare earth elements such as Dy, Tb and Sm for permanent in high temperature application is quite limited, and the price of rare earth has fluctuated greatly.
Therefore, it is predicted that if alternative materials made from richer elements are not found, these elements will have a supply shortage in the coming decades based on the current consumption rate. Mn-
On the other hand, based on magnetic materials such as MnAl, MnGa, and MnBi, a combination of large magnetic crystal-specific properties, high Curie temperature, and maximum energy products is provided ()
As a result, more attention has been paid recently.
In particular, magnetic materials based on MnAl (~50–60 at. % Mn)with the -Type Structure (τ-phase)
Great potential to become a high-performance permanent material at low cost (
Cost of raw materials about $2/kg)
, If appropriate processing routes can be developed. Off-
Chemical metrology of manganese
To obtain the magnetic properties in MnAl magnetic materials, a rich composition is required.
The theoretical calculation results show that the total magnetic moment of the composition is 1. 98 μ/f. u. (=u20090. 69u2009MA/m)
The temperature of the big Curie point (670u2009K)
The magnetic permeability can be as large as 2. 18 MJ/mu2009.
For mnlc, the experimental results of the push-out to 0 u2009 k show the value of the saturation magnetic strength u2009 = u2009 0.
68 u2009 MA/m and magnetic heterosexual Energy will . . . . . . = u2009 1.
7. MJ/m. , results and theory. However, the τ-
The phase mnel is substeady and can easily be decomposed into more stable β-s in thermodynamics-Mn and γ-phases (AlMn).
Add carbon in the eight-sided gap (½, ½, 0)
It has proved to be an effective way to stabilize the Foursquare structure and follow along.
Our previous studies have also shown the importance of carbon doping for τ-stability
In this study, only carbon-doped samples were used.
In addition, carbon has the effect of increasing the saturation magnetic strength, but reduces the temperature of the Curie point and the asymmetry.
Previous research has shown that,
The stage is through two-
Step process, derived from the parent hexagon hexagonal-
Transition to the middle B19 stagestructure ɛ’-
This in turn translates into phase of τ-
If sufficient undercooling is achieved at 723 k, it is phase.
These transitions are considered to be independent of the composition and are controlled by the Nuclear and growth processes.
It has been shown that this transition is highly dependent on τ-
Phase at the phase-phase interfacephase.
Due to the importance of microstructure to magnetic properties, several processes for manufacturing τ-have been reported
Phase, including nano-crystal powder for mechanical grinding, melting rotation and freezing grinding;
However, the processing of most reports is either complex or the final attribute is not good enough (. . , the ()is too low)
For industrial permanent applications. The ()
The performance of a permanent depends not only on the inherent properties, such (, and )
However, it is also closely related to external factors such as the microstructure, grain size and texture orientation of the .
This means that the constituent particles of the need to be aligned in a specific direction to reach the maximum ()value.
There are two main ways to prepare a textured MnAl .
The first method is extrusion by high temperature, such as deformation or compaction at high temperature, and various work carried out by this method has been reported before.
The second method is to grind the ball/surface active substance of the sample by gas atomization or induction/arc melting, and then carry out magnetic field compaction.
The former method is too expensive, and the latter method produces thin sheets with random crystal orientation due to the large scalability of MnAl, thus hindering the correct orientation of particles in the magnetic field.
Therefore, the preparation of powder composed of regular-shaped single particles is crucial for the success of high-performance heterosexual permanent materials.
This article reports :)
High purity mn1c synthesized using low temperature grinding drops (τ -phase)
Preparation of powder with a particle size of about 20 μm and a round shape; )
Evolution of a function of heating/cooling rate and annealing temperature of a high purity freeze-grinding τ-using synchronous radiationphase powder; )
The relationship between low-temperature grinding time and microstructure, crystal structure and Mn/Al ordering with the evolution of magnetic properties was studied by optical microscopy (LOM)
Scanning electron microscope (SEM)with X-
Ray energy scattering spectrum (EDS)
Electron reverse scattering diffraction (EBSD)
Magnetic Test (M); and )
Effect of short annealing time at 900 °c of rapid cooling (
Flash heating program
Re-acquire the highly crystalline τ-
Phase is carried out within a single particle to maximize and promote the ideal state of one grain per powder particle, thus creating a high-performance MnAl permanent .
These results provide new insights into the impact of the milling process and the negative impact of milling (. .
On-site mixing of Mn and Al)
The magnetic properties can be greatly reversed using the flash heating method we propose.
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