Phase constituents, microstructures and magnetic properties of melt-spun Nd
12−
x
Y
x
Fe
81
B
6
Nb ribbons were investigated systematically. The influence of Y substitution for Nd on the phase ...stability, grain size and magnetic exchange coupling was analyzed. It is found that all the ribbons crystallize in the tetragonal 2:14:1 structure, i.e., with single hard magnetic phase at the roll speed of 25 m·s
−1
. With the increase in Y doping, Curie temperature (
T
C
) increases, while the coercivity decreases monoclinically. However, remanence magnetization (
B
r
) and maximum energy product ((
BH
)
max
) fluctuate and the maximum value is obtained at certain amount of Y. The optimum magnetic properties of intrinsic coercivity of intrinsic coercivity (
H
cj
) = 908.2 kA·m
−1
and (
BH
)
max
= 118.52 kJ·m
−3
are achieved when
x
= 1.0. It can be attributed to the strengthened exchange coupling between the neighboring nanograins in Nd–Y–Fe–B melt-spun powder based on the Henkel curves. Furthermore, Y substitution also significantly improves the temperature stability of magnetic performance. The coercivity temperature coefficient of
β
= − 0.157%·°C
−1
and remanence temperature coefficient of
α
= − 0.32%·°C
−1
are gained, which are greatly reduced compared with those of the undoped Nd–Fe–B compounds.
To get a systematic understanding about dependence of deposition conditions on properties of Gd films, a series of Gd films were prepared under different Ar gas pressures: 0.5, 0.7, 1.0, and 1.5 Pa, ...and another series of Gd films were prepared under different substrate temperatures: 25, 100, 200, 350, and 500 °C. The effects of the deposition time, Ar pressure, and substrate temperature on microstructures and crystal orientation were investigated by grazing-incidence X-ray diffraction (GIXRD) and transmission electron microscopy (TEM). The experimental results show that low Ar pressure and plenty deposition time will contribute to the formation of Gd hcp phase, which has better magnetic properties such as higher Curie temperature and bigger magnetic moment, and high substrate temperature can diminish the inner stress in Gd films and promote lattice parameters closer to those of the ideal Gd hcp-structure.
•Ce addition suppresses the phase decomposition of 2:14:1 main phase due to La doping.•La substitution make grain refining of NdFeB based alloys.•Magnetic properties of La-Ce co-doped alloys are ...superior to single-doped alloys.•The (BH)max of Nd0.5(La0.6Ce0.4)0.52Fe14B reaches 12.4MGOe.•La-Ce co-doped NdFeB alloys can be applied due to its ideal magnetic performance.
Investigation of the phase structure of Nd1−x(LayCe1−y)x2Fe14B (x = 0–0.7, y = 0, 0.2, 0.4, 0.5, 0.6, 0.8, 1.0) melt spun ribbons and their magnetic properties is presented. The La-Ce co-doped Nd-Fe-B alloys are compared with the La doping and Ce doping respectively by controlling the doping ratio of La/Ce. It can be found that the Nd-Fe-B alloys remain single 2:14:1 phase with Ce doping. In contrast, the 2:14:1 phase begins to decompose when the doping content of La reaches 30at.%. The 2:14:1 phase decomposes seriously with the La doping content over 50at.%, accompanied by the rising of secondary phases. The magnetic properties of Nd-Fe-B alloy decrease with the increasing of La, Ce doping content. The performance of La-doped Nd-Fe-B is superior to that of Ce-doped when the addition of La is less than 50at.%. However, severe phase decomposition of 2:14:1 phase with x more than 0.5 leads to the sharp decline of magnetic properties of La-doped Nd-Fe-B. In general, the magnetic properties, especially for the Br and (BH)max of La-Ce co-doped Nd-Fe-B are better than single-doped cases. And the co-doped Nd-Fe-B alloys show greater enhancement of (BH)max with the increasing amount of total doping content. For example, when the total doping concentration reaches 50at.%, the (BH)max of Nd0.5(La0.6Ce0.4)0.52Fe14B still reaches 12.4MGOe, which is much higher than (Nd0.5Ce0.5)2Fe14B ((BH)max = 8.2MGOe).
Melt-spun Y
16
Fe
78
B
6
ribbons were prepared by the melt-spinning technique with pure elements Y, Fe and Fe–B alloy in argon. The ribbons are mainly composed of Y
2
Fe
14
B, YFe
2
and α-Fe phases. ...Amorphous phase appears at the wheel velocity of >35 m·s
−1
. For the ribbons prepared at optimum wheel velocity and heat treatments, the coercivity, remanence and maximum energy product are 239.5 kA·m
−1
, 0.61 T and 32.7 kJ·m
−3
, respectively. By an investigation of Henkel plots of ribbons, it is found that intergrain exchange coupling leads to the enhancement of remanence. The coercivity mechanism of ribbons prepared at 35 m·s
−1
is mainly controlled by inhomogeneous pinning of domain walls. The phase component and magnetic properties change with annealing temperature and time. The optimum magnetic properties are obtained with the ribbon quenched at 35 m·s
−1
and annealed at 700 °C for 10 min.
The effect of annealing temperature (
T
A
) at 600–900 °C on structure and magnetic properties of the melt-spun Sm
8.6
Fe
85.9
Co
4.3
Zr
1.2
alloys and its nitrides was investigated. Results show ...that the melt-spun powder is TbCu
7
-type SmFe
9
single phase. X-ray diffractometer (XRD) Rietveld refinement shows that the lattice parameter
a
increases,
c
and
c/a
decrease with the increase in
T
A
at 600–700 °C. This is due to the tendency of nitrogen entering into the 3f site (1/2, 0, 0) during the nitridation process, which is good for the magnetic properties. The phase transforms from TbCu
7
-type SmFe
9
to Th
2
Zn
17
-type Sm
2
Fe
17
at above 800 °C. Scanning electron microscopy (SEM) images show that the amount of surface defects of melt-spun powder which are harmful for magnetic properties decreases at first and then increases as
T
A
increases. The coercivity (
H
cj
) and maximum magnetic energy product ((
BH
)
max
) of its nitrides increase first and then decrease as a function of
T
A
. And the remanence (
B
r
) always shows a decrease. The optimal magnetic properties of
H
cj
= 748 kA·m
−1
,
B
r
= 0.92 T, (
BH
)
max
= 118 kJ·m
−3
are obtained by annealing at 675 °C for 2 h and then nitriding at 460 °C for 10 h.
It is approved that grain boundary diffusion is an effective method to increase the coercivity of hot-deformed NdFeB magnet. In this paper, a new rare earth-free grain boundary diffusion source of ...hot-deformed magnet was studied. AlCuZn powders blended with commercial NdFeB powders were hot-compacted to obtain fully dense magnets, hot-deformed into anisotropic magnets and finally annealed to gain better homogeneity. Initially, the influences of annealing temperature and time on the magnetic properties of the specimens were studied and the optimal parameters of 600 °C and 60 min were achieved. Then, by changing the proportions of AlCuZn grain boundary diffusion, the coercivity, remanence and maximum energy product of the hot-deformed NdFeB magnets were examined. The result showed that with 1.0 wt% AlCuZn grain boundary diffusion and annealing at 600 °C for 60 min, the coercivity rose from 828 to 987 kA·m
−1
without deteriorating the remanence. Microstructural analysis confirmed that AlCuZn diffused into the intergranular boundaries and the magnet diffused with AlCuZn possessed finer grains than that of without AlCuZn grain boundary diffusion.
A systematical investigation was carried out on structure and magnetic properties in SmFe
9−
x
V
x
(
x
= 0.4, 0.8, 1.2) compounds prepared by a single-roller quenching method. The high cool-down ...rate leads to metastable TbCu
7
phase in the parent compound, which gradually transforms into equilibrium ThMn
12
structure with V-doping content increasing. The Curie temperature increases from 470 to 590 K with V doping, which is consistent with the phase transformation. Surprisingly, simultaneous increase in both coercivity and remanence is resulted by V doping, reaching the highest value of 685 kA·m
−1
and 44.8 × 10
−3
A·m
2
·g
−1
in
x
= 1.2 compound, respectively. This phenomenon can be explained by the combination of phase transformation and intergranular exchange coupling through
δM-H
plots.
The surface of Tb
0.3
Dy
0.7
Fe
2
alloys was modified by microwave electron-cyclotron-resonance chemical vapor deposition (MW-ECR-CVD) and ion implantation technology, respectively. The ...microstructure and corrosion resistance of nitrided layers were investigated by means of optical microscope (OM), X-ray diffractomer (XRD), auger electron spectroscopy (AES), and electrochemical workstation. After modified by MW-ECR-CVD, the nitrogen concentration of the nitrided layers decreases gradually with the depth increasing, while the nitrogen concentration modified by ion implantation process exhibits Gaussian distribution. The self-corrosion electric potential of the sample modified by ion implantation is higher than that modified by MW-ECR-CVD, which reveals that the samples modified by ion implantation process have a better resistance to corrosion. The magnetostrictions are assessed for the samples placed in the air for one year, which further confirms that the ion implantation process is more helpful to maintain the magnetostrictions.
Abstract
Electrochemical corrosion behavior of Sn-containing Al–Zn–Mg aluminum alloy has been studied in detail. The localized corrosion behaviors were studied by electrochemical impedance ...spectroscopy (EIS) analysis, and the potentiodynamic polarization measurements. The grain structure, grain-boundary microstructure, grain-boundary microchemistry, pitting and intergranular corrosion morphology were characterized and observed using SEM, EDS, TEM, SAED and HRTEM analyses. Based on these tests, the effects of grain-boundary on the corrosion resistance in our Sn-containing Al–Zn–Mg alloys before/after bake hardening were analyzed systematically. Finally, the relationship between chemical composition, microstructure evolution and corrosion behaviour was revealed. The results indicate that the bake hardening process improves the corrosion resistance compared to the pre-aging state. The grain size has little effect on the electrochemical corrosion bahavior.
SmFe
10−
x
Nb
x
(
x
= 0, 0.1, 0.2, 0.3) ribbons and their nitrides were prepared by melt-spinning, followed by annealing and subsequent nitriding. The structure and magnetic properties were ...investigated by means of X-ray diffraction (XRD) using the Rietveld method, vibrating sample magnetometer (VSM), transmission electron microscope (TEM) and Mössbauer spectroscopy. XRD analysis shows that the addition of Nb can impede the precipitation of Sm
2
Fe
17
and α-Fe phases and the Nb atoms occupy 2e site in the alloys. At 300 K, the mean hyperfine fields of 2e site are 29.58 T with Nb doping at
x
= 0.1 and the corresponding Curie temperature is 552 K. The optimal properties of remanence of
B
r
= 0.9 T, intrinsic coercivity of
H
cj
= 741.5 kA·m
−1
, and maximum magnetic energy product of (BH)
max
= 124.2 kJ·m
−3
are gained at
x
= 0.10 in the nitrides.
