ISOTHERMAL SECTION OF Mg-Zn-La SYSTEM IN Mg RICH CORNER AT 350℃

Alloys of Mg-Zn-La system in Mg rich corner at 350℃ have been prepared in this study. Scanning electron microscopy （SEM）, electron probe microanalysis with energy dispersive X-ray spectroscopy （EPMA-EDS）, and X-ray diffraction （XRD） have been used to identify the phase equilibrium and the composition of each phase in the alloys. As a result, the isothermal section of Mg-Zn-La system in Mg rich corner at 350℃ has been determined. The result shows that, in addition to some binary phases, there exists a linear ternary compound called T-phase in Mg-Zn-La system at 350℃, in which the La content is about 8 at. pct ±0.4 at. pct and the Zn content is 8 at. pct- 48 at. pct. The T-phase has a C-centered orthorhombic crystal structure, and the lattice parameters are a=0.965-1.020 nm, b=1.121 1.142 nm, c=0.950-0.977 nm.     

Phase equilibria in the Mg-rich corner of the Mg-Zn-La system at 350℃

The phase equilibria in the Mg-rich comer of the Mg-Zn-La system at 350℃ have been investigated by scanning electron microscopy, X-ray diffraction, and electron probe microanalysis. It has been shown that the linear compound （Mg,Zn）17La2 existed in the Mg-Zn-La system at 350℃. The linear cornpound （so-called Tphase） was with the C-centred orthorhombic crystal structure induced by the solution of significant quantities of the third element. The three-phase region α（Mg） ＋ MgZn（La） ＋ T and the two-phase region composed of the α（Mg） and the linear-compound T phase existed in the Mg-rich comer of the Mg-Zn-La system at 350℃.     

ISOTHERMAL SECTION OF Mg-Zn-La SYSTEM IN Mg RICH CORNER AT 350℃

Alloys of Mg-Zn-La system in Mg rich corner at 350?C have been prepared in this study. Scanning electron microscopy (SEM), electron probe microanalysis with energy dispersive X-ray spectroscopy (EPMA-EDS), and X-ray diffraction (XRD) have been used to identify the phase equilibrium and the composition of each phase in the alloys. As a result, the isothermal section of Mg-Zn-La system in Mg rich corner at 350℃ has been determined. The result shows that, in addition to some binary phases, there exists a li...     

Microstructure of a two-phase titanium alloy by rapid solidification technique

Ribbons of the two-phase titanium alloy were fabricated by single-roller rapid solidification technique, and aged at high temperature. The microstructure of ribbon samples were characterized with X-ray diffractometer （XRD） and environmental scanning electron microscope （ESEM）. The microstructures of the alloy are composed of a phase and supersaturated β phase, and X-ray diffraction results show that all peaks of the a and β phases shift slightly to smaller angles, which can be explained by the disordering growth pattern caused by the rapid solidification process. After aging at 960℃in vacuum, the ribbon is composed of homogeneous a phase and β phase.     

Microstructure of as-extruded 7136 aluminum alloy and its evolution during solution treatment

With the aid of scanning electron microscopy(SEM), energy-dispersive spectroscopy(EDS), X-ray diffraction(XRD), differential scanning calorimetry(DSC)analysis and electron backscatter diffraction(EBSD), the microstructure of the alloy in as-extruded state and various solution-treated states was investigated. The results indicate that second phase of the as-extruded 7136 aluminum alloy mainly consists of Mg(Zn, Cu, Al)_2and Fe-rich phases. The Mg(Zn, Cu, Al)_2phase directly dissolves into the matrix during solution treatment with various solution temperatures. After solution treated at 475 °C for 1 h,Mg(Zn, Cu, Al)_2phases are dissolved into the matrix,while Fe-rich phases still exist. Fe-rich phases could not dissolve into the matrix by prolonging solution time. The mechanical property test and EBSD observation show that two-stage solution treatment makes no significant improvement in mechanical properties and recrystallization of the alloy. The optimized solution treatment parameter is chosen as 475 °C/1 h.     

Phase equilibria of low-Ni side in Nb-Ni-Ti system at 1100℃

The phase equilibria related to liquid phase in low-Ni side of Nb-Ni-Ti system at 1100℃ were investigated through scanning electron microscope(SEM),electron probe micro-analyzer(EPMA),X-ray diffraction(XRD) and differential scanning calorimetry(DSC).The results show that there exists liquid phase in equilibrium with continuous solid solution(Nb,βTi) and compound TiNi in low-Ni side of Nb-Ni-Ti system at 1100℃.The liquid phase region originates from low-Ni side of binary TiNi system and extends t...     

MICROSTRUCTURAL CHARACTERIZATION OF Nd_(34)Fe_(60)O_(6) ALLOY

The microstructure of Nd_(34)Fe_(60)O_6 alloy was characterized by means of scanning electronmicroscope,Auger electron multiprobe,X-ray diffraction,differential thermal analysesand thermomagnetic analyses.It is found that the equilibrium microstructure of the alloy iscomposed of a Nd_2Fe_(17) matrix,an oxygen-containing Nd-rich phase anda Nd-Fe-O ternary ferromagnetic phase (referred to T_1).This phase forms via aperitectic reaction between Nd_2Fe_(17) and Nd-rich phase at 840 ℃.Its composition isaround Nd_(36)Fe_(54)O_(10),and Curie temperature 180℃.The X-ray diffraction peaks can beindexed on a tetragonal cell with lattice parameter of a=0.771nm and c=2.228nm.Thisstable phase is believed to be transformed from the metastable phase (A_1) in Nd-Febinary system as a result of oxygen introduced.     

Determination of phase equilibria in the Ni-Ta-Zr system at 1223 K

The phase equilibrium relations of the ternary Ni-Ta-Zr system at 1223 K were investigated by means of diffusion triple and electron probe microanalysis (EPMA) techniques. Two ternary compounds were found and a series of tie lines and tie triangles have been determined. The maximum solubility of Ta in NiZr2 is about 13.5% (atom fraction). The corresponding tentative isothermal section at this temperature was constructed based on current experimental information.     

Evolution of intermetallic phases of Al-Zn-Mg-Cu alloy during heat treatment

Al-Zn-Mg-Cu alloy is a favorable choice for aerospace applications requiring good combination of strength and toughness, which is greatly influenced by the coarse intermetallic particles. The evolution of intermetallic particles in an Al-Zn-Mg-Cu alloy during heat treatment was studied by field emission gun scanning electron microscopy （FEG-SEM） and X-ray diffractometry（XRD）. The results show that there are lamellar eutectic structure （α（Al）＋Mg（Zn,Al,Cu）：） and Al7Cu：Fe particles in the solidified structure. The Al7Cu2Fe particles are embedded in the eutectic structure. The content of eutectic structure decreases with the increase of holding time and disappears after 24 h. The size and morphology of Al7Cu：Fe particles exhibit no change during the heat treatment. It is found that the AI：CuMg phase is formed during the treatment at 460 ℃. A transformation process from the primary eutectic phase Mg（Zn,Al,Cu）2 to Al2CuMg is observed, and the transformation mechanism and kinetics are analyzed, The AI：CuMg constituents form in the primary Mg（Zn,Al,Cu）： phase, and grow along the eutectic microstructure.     

STUDY ON THE STABILITY OF T＇ PHASE IN THE Al-Zn-Cu TERNARY SYSTEM

The phase constitutes and phase compositions in the eight alloys designed with different compositions of Al-Zn-Cu system have been determined after the homogenous treatment and then equilibrium cooling to 20~C by use of optical microscope, electron probe microanalysis and X-ray diffraction. It has been found that there existed the T‘phase in the seven alloys. Consequently, it was testified that the T‘ phase was stable at room temperature. At the same time, the phase relationship was not locally right for the isothermal section of 20℃ of Al-Zn-Cu system of the ASM published in 1997.     

Effect of AI content on the phase structure and the hydrogenation characteristic of La（Mg1-xAlx） alloys

La（Mg1-xAlx） （x=0.2, 0.4, 0.6, 0.8） alloys have been prepared using induction melting followed by annealing. It is found that partial substitution of Mg by Al does not lead to a change in crystal structure, and the alloys have a single LaMg phase when x 〈 0.4. The lattice parameter of the LaMg phase decreases obviously after the partial substitution of Mg by Al. However, further substitution of Mg by Al leads to the coexistence of multiple phases when x ≥ 0.6. The alloys consist of the LaMg, LaAl, LaAl2, and La5Al4 phases. The LaMg phase decreases, whereas the La5Al4 phase increases with the increase in x. The Al-substituted La（Mgo.6Al0.4） alloy can be hydrogenated into the tetragonal LaH3, cubic LaH3, MgH2, and LaPd under 5 MPa at 473 K for 5 d.     

Phase equilibria of low-Y side in Mg-Zn-Y system at 400℃

Phase equilibrium relations of the Mg-Zn-Y system in the low-Y side at 400℃were investigated by alloy-equilibrated method,combined with thermal analysis.The results show that there is a liquid phase which could be in equilibrium with an a-Mg solid solution and an icosahedral quasicrystal I phase in the low-Y side of the Mg-Zn-Y system at 400℃.The liquid phase region originates from the binary Mg-Zn system and extends to 0.4 at%Y in the Mg-Zn-Y system.Besides,the hexagonal structure H phase,fee W...     

Microstructure and mechanical properties of ZA62 based magnesium alloys with calcium addition

As-cast microstructure and mechanical properties of Mg-6Zn-2Al-0.3Mn (ZA62) alloys with calcium addition were investigated.The as-cast microstructure of the base alloy ZA62 consists of the α-Mg matrix and eutectic phase Mg51Zn20.The Mg51Zn20 eutectic was gradually replaced by MgZn phase and Mg32(Al,Zn)49 phase when calcium is added into the base alloy.Further addition of calcium leads to the increase of grain boundary phases and formation of a new quaternary Mg-Zn-Al-Ca eutectic compound.In comparison with the base alloy,the increase of calcium addition to the base alloy results in the reduction of both strength and ductility at ambient temperature,but increase at elevated temperatures due to the thermal stability of Ca-containing phases.At elevated temperatures,the creep resistance of ZA62 based alloys containing calcium is significantly higher than that of AZ91 which is the most commonly used magnesium alloy.     

Microstructural control and hardening response of Mg–6Zn–0.5Er–0.5Ca alloy

The effects of heat treatment on microstructures and hardening response of Mg–6Zn–0.5Er–0.5Ca(wt%) alloy were investigated by optical microscope(OM), scanning electron microscope(SEM), and transmission electron microscope(TEM) in this paper. The results show that the Mg–6Zn–0.5Er–0.5Ca alloy contains Mg_3Zn_6Er_1 quasicrystalline phase(Iphase) and Ca_2Mg_6Zn_3 phase under as-cast condition. Most of the Ca_2Mg_6Zn_3 phases and I-phases dissolve into matrix during heat treatment at 475 ℃ for 5 h. After the as-solution alloy was aged at 175 ℃ for 36 h, a large amount of MgZn_2 precipitate with several nanometers precipitate. It is suggested that the trace addition of Ca results in refining the size of the precipitate, and the presence of the nanoscale MgZn_2 phase is the main factor to improve the peak-aged hardness greatly to 87 HV, which increases about 40 % compared with that of as-cast alloy.     

Thermodynamic modeling of the La-Mg-Y system and Mg-based alloys database

As an example of the La-Mg-Y system, the method how to set up the themaodynamic model of individual phases was introduced in the process of thermodynamic optimization. The solution phases （liquid, body-centered cubic, face-centered cubic, hexagonal close-packed and double hexagonal close-packed） were modeled with the Redlich-Kister equation. The compound energy model has been used to describe the thermodynamic functions of the intermetallic compounds in the La-Mg-Y systems. The compounds Mg2Y, Mg24Y5, Mg12La, Mg17La2, Mg41Las, Mg3La and Mg2La in the La-Mg-Y system were treated as the formulae （Mg,Y）2（La,Mg,Y）, Mg24（La,Mg,Y）4Y, Mg12（La, Y）, Mg17（La,Y）2, Mg41（La,Y）5, Mg3（La,Mg,Y） and Mg2（La, Y）, respectively. A model （La, Mg,Y）0.5（La,Mg,Y）0.5 was applied to describe the compound MgM formed by MgLa and MgY in order to cope with the order-disorder transition between body-centered cubic solution （A2） and MgM with CsCl-type structure （B2） in the La-Mg-Y system. The Gibbs energies of individual phases were optimized in the La-Mg, La-Y and La-Mg-Y systems by CALPHAD technique. The projection of the liquidus surfaces for the La-Mg-Y system was predicted. The Mg-based alloys database including 36 binary and 15 ternary systems formed by Mg, Al, Cu, Ni, Mn, Zn and rare earth elements was set up in SGTE standard.     

Photocatalytic activity enhancing for TiO2 photocatalyst by doping with La

La doped nanocrystalline TiO2 photocatalyst was developed by sol-gel method. The prepared La-TiO2 photocatalysts with anatase phases were characterized by X-ray diffractometry （XRD）, UV-Vis absorption spectroscopy, and photoluminescence spectra （PL）. The photocatalytic activity was evaluated by the photocatalytic degradation of phenol in solution under sunlight irradiation. The results show that the crystallinity of anatase is improved by La doping. Moreover, La not only suppresses phase transition from anatase to rutile but also exhibits an absorption in the λ≥400 nm range. The photocatalytic activity of La-doped TiO2 photocatalysts exceeds that of pure TiO2 photocatalyst prepared by the same method when the molar ratio of La to Ti is kept at 0.3%.     

Microstructure and elevated-temperature tensile properties of differential pressure sand cast Mg-4Y-3Nd-0.5Zr alloy

The microstructures of an Mg-4Y-3Nd-0.5Zr alloy by differential pressure casting were investigated using scanning electron microscopy(SEM) and transmission electron microscopy(TEM), and its tensile deformation behavior was measured using a Gleeble1500 D themo-simulation machine in the temperature range of 200 to 400 °C at initial strain rates of 5×10-4 to 10-1 s-1. Results show that the as-cast microstructure consists of primary α-Mg phase and bone-shaped Mg5 RE eutectic phase distributed along the grain boundary. The eutectic phase is dissolved into the matrix after solution treatment and subsequently precipitates during peak aging. Tensile deformation tests show that the strain rate has little effect on stress under 300 °C. Tensile stress decreases with an increase in temperature and the higher strain rate leads to an increase in stress above 300 °C. The fracture mechanism exhibits a mixed quasi-cleavage fracture at 200 °C, while the fracture above 300 °C is a ductile fracture. The dimples are melted at 400 °C with the lowest strain rate of 10-4 s-1.     

Static oxidation behaviour of silicide coating on niobium alloy at high temperature

A silicide coating was prepared on the surface of the Nb521 alloy by the complex pack cemented method. The oxidation resistance properties of the present coating were exeamed by the static oxidation tests at 1 700 ℃in air. The compositions and the microstructures of the coating before and after test were characterised and analysed through scanning electron microscopy （SEM）, X-ray diffraction analysis （XRD）, energy dispersive X-ray spectrometry （EDS） and electron probe microanalysis （EPMA）, respectively. The present silicide coating can provide an effective protection for the Nb alloy for 25 h at 1 700 ℃ in air. The results show that the oxidation kinetics of the present silicide coating is parabolic. The diffusion of Si leads to the phase transformation and evolution during the oxidation.     

Determination of isothermal section of Fe-Ti-Zr ternary system at 1173 K

Phase relations in the Fe-Ti-Zr ternary system at 1173 K were investigated by means of diffusion-triple approach together with electron probe microanalysis（EPMA） technique. A series of tie lines and tie-triangles were determined and the isothermal section at 1 173 K was established, which consists of four three-phase fields： β（Ti, Zr）＋FeZr2＋FeTi, FeZr2＋FeTi＋Fe2Zr, FeTi ＋Fe2Zr ＋Fe2Ti and Fe2Zr ＋Fe2Ti ＋Fe. The results show that the largest solubility of Ti in Fe2Zr is about 11.3 %（mole fraction） and the solid solubility of Ti in FeZr2 is about 26.9%, the solid solubility of Zr in Fe2Ti is about 8.1% and the solid solubility of Zr in FeTi is 7.2%. The binary compound FeZr2 is nearly a linear compound. No ternary compound is found.     

Microstructure characterization and mechanical properties of Mg-9Li-5Al-1Zn-0.6RE alloy

Mg-9Li-5Al-1Zn-0.6RE alloy was prepared by vacuum induction heating. The microstructure and phases composition of the alloy were analyzed with optical microscope, scanning electron microscope and X-ray diffractometer. Then the effect of homogenization temperature on microstructure and mechanical properties of the alloy was studied. The hardness of samples under different homogenization temperatures was measured. The results show that, the alloy is composed of a phase, β phase, Mg17Al12 and AlLi. RE added into the alloy is solved in a phase and β phase completely. After homogenization heat treatment, the needle-like a phase disappears. With the increase of homogenization temperature, the shape of a phase is spherical-like first, then vennicular-like, and large block-like finally. The variation of the shape of a phase causes the hardness of sample to change accordingly. The most favorable homogenization temperature for microstructure and mechanical properties is 150 ℃.