Structure, magnetization, and magnetostriction of Sm-R-Fe （R = Pr, Nd） thin films

The structure, magnetization, and magnetostriction of Sm0.9Pr0.1Fex and Sm1-xNdxFel.9 thin films have been investigated using X-ray diffraction, vibrating sample magnetometer, and optical cantilever method. It is found that the structure of Sm0.9Pr0.1Fex thin films consists of an Sm-Pr-Fe amorphous phase when x≤2.69 and that of Sm1-xNdxFel.9 thin films consists of an Sm-Nd-Fe amorphous phase. The in-plane magnetization of Sm0.91Pr0.1Fex thin films increases with increase in the Fe content, and low values of the in-plane coercivity occur in the range of 1.62≤ x≤ 2.28. The magnetostriction value of Sm0.91Pr0.1Fex thin films increases with increasing the Fe content when x ≤ 1.94 and decreases when x 〉 1.94. The in-plane magnetostriction of Sm1-xNdxFe1.9 thin films under low magnetic fields has been improved by the substitution of Nd for Sm when x = 0.2.     

Microstructures and tensile properties of as-extruded Mg-Sn binary alloys

The microstructure and mechanical properties of Mg-xSn(x=3,7 and 14,mass fraction,%) alloys extruded indirectly at 300℃ were investigated by means of optical microscopy,scanning electron microscopy and tensile test.The grain size of theα-Mg matrix decreases from 220,160 and 93μm after the homogenization treatment to 28,3 and 16μm in the three alloys after extrusion,respectively.The results show that the grain refinement is most remarkable in the as-extruded Mg-7Sn alloy.At the same time,the amount of the Mg2Sn particles remarkably increases in the Mg-7Sn alloy with very uniform distribution in theα-Mg matrix.In contrast,the Mg2Sn phase inherited from the solidification with a large size is mainly distributed along grain boundary in the Mg-14Sn alloy.The tensile tests at room temperature show that the ultimate tensile strength of the as-extruded Mg-7Sn alloy is the highest,i.e.,255 MPa,increased by 120%as compared with that of as-cast samples.     

Effect of gadolinium on aged hardening behavior,microstructure and mechanical properties of Mg-Nd-Zn-Zr alloy

Mg-3.4Nd-0.1 Zn-0.40Zr alloy samples with and without containing gadolinium(0.6%,mass fraction)were prepared by sand casting.The aged hardening behavior,solidification microstructures and mechanical properties of the alloys were investigated by using the analysis methods of OM,XRD,TEM,hardness tests and mechanical property tests.The main research results are as follows.1)Compared with the alloy without the addition of gadolinium.the alloys with the addition of gadolinium shows the more remarkable age-hardening response.2) The as-cast microstructure of the alloy with and without containing gadolinium consists of α-Mg grains with Mg12Nd phase on the grain boundary.After solution heat-treatment,Mg12Nd phase of the alloy without containing gadolinium is dissolved in the matrix,however,there iS still discontinued Mg12Nd phase at grain boundary of the alloy with containing gadolinium.The more finely dispersed precipitates in Mg matrix are formed in the alloy with containing gadolinium during age-treatment.3)The room temperature and high temperature mechanical properties ofthe alloy are satisfactory.with σb=280 MPa,σ0.2=165 MPa at RT and aσb=215 MPa,σ0.2=155 MPa at 250℃.The high temperature mechanical properties decrease slightly with the increase of temperature.     

Magnetostriction of 〈100〉 oriented Fe–Ga rods with large diameter

The Fe83Ga17 alloy rods with h100 i preferential orientation was prepared by directional solidification method.The dimension of oriented Fe83Ga17 rods is large up to 40 mm greater than diameter in previous investigations of3–10 mm.The growth direction of columnar grain is nearly parallel to the solidification direction of rods.The deviation angle between axial direction and h100 i direction of columnar crystal was investigated by method of electron backscattering diffraction, and the deviation is smaller than10°.The large columnar grain and h100 i preferential orientation along axial direction of rods could be attributed to the calm solid–liquid interface during solidification process that is difficultly formed due to electromagnetism agitation in induction heating zone-melting method.The corresponding magnetostriction is large up to 290 9 10-6under pre-compressive press of 15 MPa.     

Mechanical and magnetostrictive properties of Tb0.36Dy0.64（Fe1-xMnx）1.9 alloys

The magnetization, magnetostriction and compressive strengths of arc-cast polycrystalline and directionally solidified Tb0.36Dy0.64（Fe1-xMnx）1.9 （x=0, 0.05, 0.10, 0.15, 0.20） rods were investigated by VSM, standard strain gauge method and compressive tests, respectively. The results show that the magnetostriction λs, saturation magnetization Ms and magnetocrystalline anisotropy constant K1 decrease with increasing the Mn concentration. The optical micrographs and XRD patterns show that the Tb0.36Dy0.64（Fe1-xMnx）1.9 alloys are composed of MgCu2-type Laves phase as matrix and a small amount of rare-earth rich phase. It is found that the distribution of the rare-earth rich phase has an important effect on mechanical property of Tb0.36Dy0.64（Fe1-xMnx）1.9 samples. For the arc-cast samples, smaller equal-axial grains are arranged irregularly, which results in higher compressive strengths. However, the rare-earth rich phase is arranged as parallel arrays in the directionally solidified samples, which leads to smaller compressive strengths.     

MICROSTRUCTURE AND ELECTROCHEMICAL CHARACTERISTICS OF Zr_(0.9)Ti_(0.1)(Ni_(1.1)Mn_(0.7)V_(0.2))_x METAL HYDRIDE ELECTRODE

The crystal structure, the phase composition and the electrochemical characteristics of Zr0.9Ti0.1(Ni1.1Mn0.7V0.2)x (x=0.90, 0.95, 1.00, 1.05) alloys were investigated by means of XRD, SEM, EDS and electrochemical measurements. It was shown that all alloys are multiphase with C15 Laves phase as a main phase along with C14 phase and some secondary phases. And the amounts of the C14 phase and secondary phases in the four alloys increases with decreasing x. The results indicated that the various stoichiometric ratios have great effects on the electrochemical characteristics such as the maximum discharge capacity, discharge rate capability and self-discharge properties etc. for Zr0.9Ti0.1(Ni1.1Mn0.7 V0.2)X (x=0.90, 0.95, 1.00, 1.05) alloys. The hyper-stoichiometric Zr0.9 Ti0.1(N1.1Mn0.7 V0.20)1.05 exhibits the maximum discharge capacity of 332mAh-g-1. The C14 phase and secondary phases seems to improve discharge rate capability of the alloys.     

Synthesis and co-luminescence properties of Tb3+-methacrylic acid-1,10-phenanthroline complexes doped with Eu3+

A series of rare earth complexes Tb1-xEux(MAA)3phen (x=0.00,0.01,0,03,0.05,0.07,0.09,0.10,0.30,and 0.50) were synthesized with MAA as the first ligand and phen as the second ligand.The complexes were characterized by means of FT-IR,thermogravimetry-differential scanning calorimetry (TG-DSC),XRD,UV absorption spectra,and photoluminescence spectra (PL).The results show that the luminescence intensity of Eu3+ increases as Tb3+ transfer the absorbed energy to Eu3+ in the complexes.The emission of Tb3+ at 545 nm is observed and increasing with x decreasing.When x=0.01,the luminescence intensity reaches the maximum value,and the emission intensity ofTb3+ at 545 nm and Eu3+ at 614 nm are almost equal.It realizes the co-luminescence ofEu3+ and Tb3+.We can obtain complexes with different colors by adjusting the ratio of Eu3+ to Tb3+.     

Coercivity enhancement mechanism of Tb-diffusion Nd-Fe-B sintered magnets studied by magneto-optical Kerr optical microscope

The coercivity,microstructure,and magnetic domain structure of Nd-Fe-B sintered magnets by grain boundary diffusion process(GBDP) with TbH_3 nanoparticles were systematically investigated.Compared to the original magnet,the coercivity(H_(ci)) of the GBDP magnets improved from 1702 to 2374 kA·m~(-1) with few remanence reduced from 1.338 to 1.281 T.Electron probe microanalysis(EPMA) analysis showed that Tb diffused along grain boundary,mainly concentrated in the boundary layer of the main phase,and formed a core-shell structure.Magneto-optical Kerr optical microscope(MOKE) analysis showed that there were two types of magnetic domain reversal in one grain:gradual reversal(GR) and abrupt reversal(AR).When the applied field decreased from saturated magnetic field,the reversal magnetic domain nucleated and then spread over the whole grain gradually,which was called GR.However,some grains kept the single domain state until Hh which was a value of reverse direction applied field in second quadrant in hysteresis loops.When the applied field increased above H_h,reversed magnetic domain would suddenly appear and occupy most of the area of the grain,which was called AR.That is because AR grains have higher reversed magnetic domain nucleation field(H_(RN2)) than GR grains(H_(RN1)).After GBDP,the area of AR region increased obviously and GR region decreased accordingly,indicating that the core-shell structure could change GR grain into AR grain.The coreshell structure could suppress flipping of the magnetization of the grains due to the large magnetic anisotropy of Tbrich shell.Therefore,large AR area led to high coercivity.     

Microstructure of explosively compacted Nd-Fe-B magnet by TEM

The microstructure of an explosively compacted Nd-Fe-B permanent magnet(Nd-Fe-B) was investigated by means of TEM and XRD. It is shown that there are three kinds of phases: Nd2 Fe14 B matrix phase, O-rich phases and Nd-rich phase with different structures and compositions in the magnet. The hard magnetic phase Nd2Fe14 B is tetragonal, which lattice parameters are determined to be a=0.88 nm and c=1.22 nm. The O-rich phase locates at the grain boundaries and the triple junctions has fcc structure whose lattice parameter is a=0. 559 nm. A dislocation is observed in this phase. It is also found that a large number of the block-shaped Nd-rich phases with hcp structure are embedded in the Nd2 Fe14 B matrix or at grain boundary. Their lattice parameters are determined to be a= 0. 395 nm and c=0. 628 nm.     

Effects of Sb Content on Solidification Pathways and Grain Size of AZ91 Magnesium Alloy

The phase constitution and solidification pathways of AZ91+xSb(x = 0, 0.1, 0.5, 1, in wt%) alloys were investigated through ways of microstructure observation, thermal analysis technique, and thermodynamic calculation. It was found that the non-equilibrium solidification microstructure of AZ91+xSb(x = 0.1, 0.5, 1) is composed of a-Mg matrix, b-Mg17Al12 phase, and intermetallic compound Mg3Sb2. The grain size of the alloys with different Sb contents was quantitatively determined by electron backscattered diffraction technique which shows no grain refinement in Sb-containing AZ91 alloy. Thermodynamic calculations are in reasonable agreement with thermal analysis results, showing that the Mg3Sb2 phase forms after a-Mg nucleation, thus impossible acts as heterogeneous nucleus for a-Mg dendrite. Besides,the solid fraction at dendrite coherency point(fDCPs) determined from thermal analysis decreases slightly with increasing Sb content, which is consistent with the fact that Sb does not refine the grain size of AZ91 alloy.     

Effect of partial pressure of reactive gas on chromium nitride and chromium oxide deposited by arc ion plating

The effects of reactive gas partial pressure on droplet formation, deposition rate and change of preferred orientation of CrN and Cr2O3 coatings were studied. For CrN coatings, as nitrogen partial pressure increases, the number and size of droplets increases, the deposition rate initially increases obviously and then slowly, and the preferred orientation of CrN changes from high-index plane to low-index one. For Cr2O3 coatings, with the increase of oxygen partial pressure, the number and size of droplets decreases, the deposition rate decreases and the （300） becomes the preferred orientation. These differences are ascribed to the formation of CrN （with a lower melting point） and Cr2O3 （with a higher melting point） on the surface of Cr target during the deposition of CrN and Cr2O3. Complete coatings CrN or Cr2O3 film can be formed when reactive gas partial pressure gets up to 0. l Pa. The optimized N2 partial pressure for CrN deposition is about 0.1-0.2 Pa in order to suppress the formation of droplets and the suitable 02 partial pressure for Cr2O3 deposition is approximately 0.1 Pa for the attempt to prevent the peel of the coating.     

Magnetocaloric effect of （Gd1-xNdx）Co2 alloys in low magnetic field

The phases and magnetocaloric effect in the alloys （Gd1-xNdx）Co2 with x = 0, 0.1, 0.2, 0.3, and 0.4 were investigated by X-ray diffraction analysis and magnetization measurement. The samples are single phase with a cubic MgCu2-type structure. The To decreases obviously with increasing Nd content from 404 K of the alloy with x = 0 to 272 K of the alloy with x = 0.4; forx = 0.3, the To is 296 K, which is near room temperature. In the samples （Gd1-xNdx）Co2 with x = 0.0, 0.1, 0.2, 0.3, and 0.4, the maximum magnetic entropy change is 1.471, 1.228, 1.280, 1.381 and 1.610 J·kg^-1·K^-1, respectively, in the applied field range of 0-2.0 T. The results of Arrott plots confirmed that the transition type were second order magnetic transition forx = 0, 0.3, and 0.4.     

Effect of microstructure on impact toughness of TC21 alloy

The impact toughness of TC21 alloy after different types of forging and heat treatments was studied. The results show that heat treatment at 915℃ for 1 h followed by air-cooling can achieve the highest impact toughness. The crack propagation path of bimodal microstructure is different from that of lamellar microstructure. Boundaries of primary a grain are observed to be preferential sites for microcrack nucleation. With the increase of heat treatment temperature, the volume fraction of primary a phase decreases and the nucleation sites of microcrack at the primary α phase boundaries also decrease, the impact toughness value is effectively improved. The microcracks of lamellar microstructure are located on α/β interface, or the boundary of colony, and/or grain boundary a phase. The crack propagates cross the colony, or along the colony boundary, and/or along β grain boundary. The crack propagation path of lamellar microstructure is dependent on the size, direction of colony. The crack path deflects at grain boundaries, colony boundaries, or arrests and deviates at α/β interface because of crisscross a lamellar. Therefore the impact toughness value of basket microstructure is higher than that of Widmanstatten microstructure.     

TEM STUDIES OF THE W PHASE AND ITS ORDERED W'PHASE IN RARE EARTH Mg ALLOYS

By means of transmission electron microscopy(TEM),the W phase and its ordered W'phase in as-cast Mg-Zn-Zr-Y system alloys were studied.The W phase,which distributes alongthe grain boundaries in the form of a lamellar eutectoid with Mg,is of FCC structure with α=0.865 nm.The W'phase,which is an ordered structure of the W phase with α=2.055 nm,was found in the alloy with lower Y content.The W and W'phases have a simple orientationrelationship of(100)_W//(100)_(W'),(010)_W//(010)_(W'),and(001)_W//(001)_W;but they do nothave an orientation relationship with the α-Mg matrix.The results of convergent electroncliffractions(CBD)on these phases show that their point group is m3m and that the space group isFm3m.     

Brittleness and fracture mechanism of sintered Dy-doped NdFeB magnets

The brittleness and fracture behaviors of the sintered and the two-stage aged Dy-doped NdFeB magnets were studied by a unique method of acoustic emission testing and Vickers hardness indentation method in this paper.A detailed analysis on the crack propagation mechanism along the grain boundary of the main grain phase(Nd,Dy)₂ Fe₁₄B was done.By comparing the acoustic emission energy count value(E_n) with the Vickers hardness indentation load(P),it is shown that the...     

EFFECTS OF MODIFICATION OF THE CARBIDE CHARACTERISTICS THROUGH GRAIN BOUNDARY SERRATION ON CREEP-FATIGUE LIFE IN AUSTENITIC STAINLESS STEELS

Modification of the carbide characteristics through the grain boundary serration is investigated, using an AISI 316 and 304 stainless steels. In both steels, triangular carbides were observed at straight grain boundaries while planar carbides were observed at the serrated grain boundaries. The serrated grain boundary energy is observed to be much lower than that of the straight one. Therefore, the carbide morphology is found to be changed from triangular to planar along the serrated boundary to reduce the interfacial energy between the carbide and the matrix. The creep-fatigue properties of these steels at 873K have been investigated. The creep-fatigue life of the sample with planar carbide at the serrated grain boundary was found to be much longer than that with triangular carbide at the straight one. These results imply that the planar carbides with lower interfacial energy have higher cavitation resistance, resulting in the retardation of cavity nucleation and growth to increase creep-fatigue life.     

Modification of computer simulation of normal grain growth

A set of principles on transition probability was supplied for the physical process of grain growth. In accord with these principles, a modified transition probability considering the influence of temperature was put forward to simulate the normal grain growth relying on temperature and second phase particles. The modified transition probability correctly reflects the dependence of grain growth on the temperature. The effect of different shapes of second phase particles on the grain growth process was taken into account using the modified transition probability. The relationship between the area fraction of second phase particles and the limit of grain size of the matrix was given. The microstructural evolution patterns employed to 2-D were given. The results agree well with the real grain growth process. All these suggest that the modified transition probability is better than the conventional one.     

Influence of columnar grain boundary on fracture behavior of as-cast fully lamellar Ti-46Al-0.5W-0.5Si alloy

The fracture behavior of fully lamellar γ-TiAl alloys depends on the angle between the lamellar orientation and loading axis,but the role of the presentation of grain boundary cannot be ignored.To investigate the influence of the grain boundary on the initiation and propagation of cracks,the tensile test of the alloy was conducted at room temperature with loading axis parallel and perpendicular to the lamellar orientation,respectively.The cracks adjacent to the fracture zone of the tensile specimens have been investigated to analyze the fracture behavior.Results show that the grain boundary has dual influences on the fracture behavior.When the loading axis is parallel to the lamellar orientation,cracks are preferentially initiated at and propagate along the grain boundaries.When the loading axis is perpendicular to the lamellar orientation,the grain boundaries can prevent the propagation of cracks from running across.Additionally,serrated-shape grain boundaries have a better inhibiting effect on the propagation of cracks than planar boundaries.     

Grain refinement of W-Ni-Fe heavy alloys by tantalum element adding

90W-TNi-3Fe and (90-x)W-xTa-7Ni-3Fe (x= 1,3,5,7,10) specimens were attained by liquid phase sintering. A model describing the process of liquid forming and spreading was proposed to point out the differences between alloys doped with tantalum and traditional tungsten heavy alloys. Tantalum priority of entering matrix and a relative high solubility in liquid matrix depress tungsten solubility in liquid matrix, which decreases kinetic rate constant K and consequently results in the reduction of W grain size. The grain refinement is influenced by Ta content and becomes more obvious when Ta content is over 5%. The sample with less than 3%Ta has dominant W and matrix phases. While besides W and matrix phases, intermetallic phases emerge in 85W-5Tai-TNi-3Fe sample. Ta is superfluous and forms a new tantalum phase when more than 7% Ta is added into alloys.     

Influence of Sn substitution for Co in RCo2 （R = Gd, Tb, Dy） alloys on the structure and magnetocaloric effect

The phases and the magnetocaloric effect in the alloys R(Co1-xSnx)2 with x=0, 0.025, 0.050, 0.075, and 0.100 were investigated by X-ray diffraction analysis and magnetization measurement. The substitution of Sn in RCo2 is limited. The cubic MgCu2-type structure for the alloys of RCo2 was confirmed by X-ray powder diffraction and the remaining alloys mainly consisted of the RCo2 phase, along with some RCo3 and R5Sn3 impurity phases. The impurity phases increase with the increase of Sn content. The Tc of the alloys is not very sensitive to the Sn substitution for Dy(Co1-xSnx)2 and Tb(Co1-xSnx)2, whereas in Gd(Co1-xSnx)2, the Curie temperatures significantly increase. The maximum magnetic entropy changes in the alloys Dy(Co1-xSnx)2 (x=0,0.025, 0.050, 0.075) are 5.78, 5.43, 3.88, and 2.98 J·kg-1·K-1, respectively, and those in the Tb(Co1-xSnx)2 (x =0,0.025) are 3.44, and 2.29 J·kg-1·K-1 respectively in the applied field change of 0-2.0 T.