Effects of Zinc and Calcium Concentration on the Microstructure and Mechanical Properties of Hot-Rolled Mg–Zn–Ca Sheets

Four kinds of Mg alloys with different Zn and Ca concentration were selected to analyze the effect of Zn and Ca concentration on the microstructure and the mechanical properties of Mg–Zn–Ca alloys. It was found that Zn and Ca concentration has a great influence on the volume fraction, the morphology and the size of second phase. The Mg–1.95Zn–0.75Ca(wt%) alloy with the highest volume fraction, continuous network and largest size of Ca2Mg6Zn3 phase showed the lowest elongation to failure of about 7%, while the Mg–0.73Zn–0.12Ca(wt%) alloy with the lowest volume fraction and smallest size of Ca2Mg6Zn3 phase showed the highest elongation to failure of about 37%. It was suggested that uniform elongations of the Mg–Zn–Ca alloys were sensitive to the volume fraction of the Ca2Mg6Zn3 phases, especially the network Ca2Mg6Zn3phases; post-uniform elongations were dependent on the size of the Ca2Mg6Zn3 phase, especially the size of network Ca2Mg6Zn3 phase. Reduction in Zn and Ca concentration was an effective way to improve the roomtemperature ductility of weak textured Mg–Zn–Ca alloys.     

Experimental Investigation of the Mg–Zn–Zr Isothermal Section at 400 °C

Mg-Zn-Zr series Mg alloys(ZK) are one of the most important commercial Mg alloys due to their good comprehensive mechanical properties. The phase equilibria of the Mg-Zn-Zr system at 400 ℃ covering the overall composition range were investigated by X-ray diffraction and electron probe microanalyses on thirteen ternary alloys. Three ternary compounds, τ_1, τ_2 and τ_3, were detected to be thermodynamically stable at 400 ℃, and their homogeneity range was determined to be Mg_((7-17))Zn_((80-88))Zr_((4-6)), Mg_((15-22))Zn_((66-65))Zr_((9-16)) and Mg_9 Zn_(68)Zr_(23)(in at.%), respectively. Eight three-phase regions and four two-phase regions were observed. The maximum solubility of Mg in Zn_(22) Zr, Zn_(39) Zr_5 and Zn_3 Zr phases was measured to be 0.52, 0.37 and 0.99 at.%, respectively, while the solubility of Zr in MgZn_2 and Mg_2 Zn_3 phases is negligible. The isothermal section of the Mg-Zn-Zr system at 400 ℃ was then constructed based on the present experimental data.     

Differential calorimetric analysis of the binary system Sb–Zn

The experimental study of the system Sb–Zn by differential calorimetry made it possible to plot the whole phase diagram. We found the stability domains of existence of the stoichiometric compound SbZn and the solid solutions which extend on both sides from the compositions corresponding to Sb₃Zn₄ (forms γ and β) and Sb₂Zn₃ (forms η and ζ). Sb₃Zn₄ and Sb₂Zn₃ are both congruent melting compounds at 566 and 568 °C respectively with an eutectic transformation at 563 °C:

liquid(43% Zn) ↔ Sb₃Zn₄(γ) + Sb₂Zn₃(η).

Sb₂Zn₃(ζ) is formed at 407 °C starting from Sb₃Zn₄(β) and zinc. The decomposition, by cooling, occurs around 360 °C.     

Subsolidus phase relation in the system ZnO–Li2O–MoO3

The subsolidus phase relation of the system ZnO–Li₂O–MoO₃ has been investigated by X-ray diffraction (XRD) analyses. The phase diagram has been constructed. There are six binary compounds and one ternary compound in this system. The phase diagram comprises nine three-phase regions. The ternary compound Li₂Zn₂(MoO₄)₃ is refined by the Rietveld method. It belongs to an orthorhombic system with space group Pnma and lattice constants a = 5.1114 Å, b = 10.4906 Å, c = 17.6172 Å.     

Solidification of levitated Nd–Fe–B alloy droplets at significant bulk undercoolings

Nd–Fe–B alloys with composition of Nd₁₆Fe₇₆B₈, Nd₁₈Fe₇₃B₉ and Nd₂₂Fe₆₇B₁₁ were melted and solidified using an electromagnetic levitation technique. Two types of solidification behavior were observed depending on the bulk undercooling achieved prior to solidification. The samples with small undercoolings were solidified by the predominant primary formation of the Nd₂Fe₁₄B compound, whereas those with large undercoolings were solidified by the primary formation of the metastable Nd₂Fe₁₇B_x compound (x1) plus the subsequent formation of Nd₂Fe₁₄B. The critical undercooling for the primary Nd₂Fe₁₇B_x formation was determined to be 40, 70 and 130 K in the three alloy compositions, respectively. The liquidus temperature of the metastable Nd₂Fe₁₇B_x compound was estimated to be 1423, 1393 and 1283 K, respectively. The Nd₂Fe₁₇B_x compound was found to decompose into a mixture of Fe plus Nd₂Fe₁₄B due to the slow cooling rates of the samples. It was suggested that the metastable Nd₂Fe₁₇B_x compound may have a lower interfacial energy than that of the stable Nd₂Fe₁₄B compound, hence being favored in nucleation-controlled phase selection at large undercoolings.     

The ytterbium-copper-aluminium system

The isothermal section of the Yb---Cu---Al phase diagram at 870 K over the whole concentration region has been constructed using X-ray structure and phase analysis. We have confirmed the existence of earlier reported ternary compounds: YbCuAl (ZrNiAl type) and YbCu₄Al₈ (CeMn₄Al₈ type); the previously reported compound YbCu₄Al proved to be a solid solution of aluminium in the binary compound YbCu₅ (CaCu₅). New ternary aluminides such as Yb₄(Cu_0.26Al_0.74)₃₃ (new structure type), Yb₂(Cu_0.57Al_0.43)₁₇ (Th₂Zn₁₇), Yb(Cu_0.85Al_0.15)₆ (YbMo₂Al₄)₇ Yb₆(Cu_0.74Al_0.26)₂₃ (Th₆Mh₂₃) and Yb(Cu_0.30Al_0.70)₃ (PuNi₃) have been prepared for the first time and their crystal structures have been determined. The limits of solid solutions of the binary compound YbCu₅ and the homogeneity ranges of the ternary phases Yb(CuAl)₁₂, Yb(CuAl)₁₇ and Yb(CuAl)₂ have been established.     

The 260 °C phase equilibria of the Sn–Sb–Ag ternary system and interfacial reactions at the Sn–Sb/Ag joints

The isothermal section of the Sn–Sb–Ag ternary system at 260 °C has been determined in this study by experimental examination. Experimental results show no existence of ternary compounds in the Sn–Sb–Ag system. Two extensive regions of mutual solubility have been determined. The one located between the two binary isomorphous phases, Ag₃Sn and Ag₃Sb, is labeled as and the other one located between the two binary isomorphous phases, Ag₄Sn and Ag₄Sb, is labeled as ξ. The phase is a very stable phase and is in equilibrium with ξ, Sb, SbSn, Sb₂Sn₃, and liquid Sn phases. Each of the Sb and SbSn phases has a limited solubility of Ag. Only one stoichiometric compound, Sb₂Sn₃, exists. Besides phase equilibria determination, the interfacial reactions between the Sn–Sb alloys and the Ag substrate were investigated at 260 °C. It was found that the phase formations in the Sn–Sb/Ag couples are very similar to those in the Sn/Ag couples.     

Microstructural evolution of Fe3B/Nd2Fe14B nanocomposite magnets microalloyed with Cu and Nb

The microalloying effect of Cu and Nb on the microstructure and magnetic properties of an Fe₃B/Nd₂Fe₁₄B nanocomposite permanent magnet has been studied by transmission electron microscopy (TEM) and atom probe field ion microscopy (APFIM). Additions of Cu are effective in refining the nanocomposite microstructure and the temperature range of the heat treatment to optimize the hard magnetic properties is significantly extended compared with that of the ternary alloy. Combined addition of Cu and Nb is further effective in reducing the grain size. Optimum magnetic properties obtained by annealing a melt-spun Nd_4.5Fe_75.8B_18.5Cu_0.2Nb₁ amorphous ribbon at 660°C for 6 min are B_r=1.25 T, H_cJ=273 kA/m and (BH)_max=125 kJ/m³. The soft magnetic Fe₂₃B₆ phase coexists with the Fe₃B and Nd₂Fe₁₄B phases in the optimum microstructure of the Cu and Nb containing quinternary alloy. Three-dimensional atom probe (3DAP) results show that the finer microstructure is due to the formation of a high number density of Cu clusters prior to the crystallization reaction, which promote the nucleation of the Fe₃B phase. The Nb atoms appear to induce the formation of the Fe₂₃B₆ phase when the remaining amorphous phase is crystallized.     

Thermoelectric properties of Fe0.98Co0.02Si2 with ZrO2 and rare-earth oxide dispersion by mechanical alloying

The n-type Co-doped β-FeSi₂ (Fe_0.98Co_0.02Si₂) with dispersion of several oxides, such as ZrO₂ or several rare-earth oxides (Y₂O₃, Nd₂O₃, Sm₂O₃ and Gd₂O₃), was synthesized by mechanical alloying and subsequent hot pressing. The effects of these oxide dispersions on the thermoelectric properties of Fe_0.98Co_0.02Si₂ were investigated. ZrO₂ was decomposed in the β phase, and the ZrSi and -FeSi phases, which are metallic phases, were formed in the samples with ZrO₂ addition. The Seebeck coefficient and the electrical resistivity were significantly decreased with increasing amount of ZrO₂, indicating that a part of the Zr atoms was substituted for Fe atoms in the β phase. In the case of the samples with rare-earth oxide addition, a decomposition of a large amount of these added oxides did not occur. However, the rare-earth oxide addition caused a slight increase in the amount of the phase. The Seebeck coefficient was significantly enhanced by the rare-earth oxide addition especially in the low temperature range. These facts indicated that a small amount of rare-earth oxides was decomposed in the β phase, and rare-earth elements were substituted for Fe atoms as a p-type dopant, resulting in the decrease in the carrier concentration. The rare-earth oxide addition was also effective in reducing the thermal conductivity.     

Effects on direct synthesis of large scale mono-disperse Ni0.5Zn0.5Fe2O4 nanosized particles

Mono-disperse Ni_0.5Zn_0.5Fe₂O₄ spinel ferrite particles have been synthesized directly via the hydrothermal method using sodium dodecyl sulfate (SDS) as surfactant. Particle size could be varied from 6 to 19 nm by changing the experiment parameters. X-ray diffraction, high resolution TEM images confirmed the high crystallinity of ferrite nanocrystals. The effects of precursor suspension pH value, reaction temperature and surfactant (SDS) concentration on phase purity, particle size and dispersed property were discussed. The results indicated that mono-disperse Ni_0.5Zn_0.5Fe₂O₄ spinel ferrite nanoparticle had been obtained at pH value range (8–9), reaction temperature (90 °C) and moderate SDS concentration (>0.2 mM). The magnetic measurement shows that as prepared Ni_0.5Zn_0.5Fe₂O₄ nanoparticle possesses good super-paramagnetic behavior. We also put forward a primary experimental model to shed light on the controllability of the monodispersity of the nanosized particles.     

Preparation of neodymium sulphides by the reaction of Nd2(So4)3 with carbon disulphide

The reaction to synthetize neodymium sulphides from neodymium sulphate octahydrate in a stream of carbon disulphide gas was studied. The dehydration of the octahydrate in vacuum was finished at 300 °C. At 1050–1100 °C in air neodymium oxysulphide, Nd₂O₂SO₄, was formed. Neodymium oxysulphide, Nd₂O₂S, was formed upon heating with a reducing agent such as annealed carbon. The reaction of neodymium sulphate with carbon disulphide commenced at 500–600 °C, resulting in formation of the disulphide, NdS₂. The crystal structure of NdS₂ heated at 500 °C was, however, different from that of the sample heated at 600 °C. In the temperature range 800–900 °C -Nd₂S₃ was obtained as a single phase after heating for at least 3 h in high flow rates of gas mixtures of nitrogen and high concentrations of carbon disulphide. The sesquisulphide, γ-Nd₂S₃ (or Nd₃S₄), was formed at temperatures as high as 1100 °C. The reaction conditions for the compounds mentioned above are discussed together with the analysis of their crystal structures by X-ray powder diffractometry.     

Structure and magnetic properties of mechanically milled Nd2xFe100−3xBx (x = 2–6)

The effects of composition and heat treatment on the structure and magnetic properties of mechanically milled Nd_2xFe_100−3xB_x alloys (x = 2–6) have been studied. High remanences have been obtained in isotropic samples consisting of a nanocrystalline mixture of Nd₂Fe₁₄B and -Fe. For optimally heat treated samples, an increase in the volume fraction of -Fe from 14% to 73%, increased the reduced remanence (M_r/M_s) from 0.56 to 0.64. The corresponding coercivities decreased from about 8 kOe to only 1.6 kOe. The magnetic behaviour of these Nd₂Fe₁₄B--Fe alloys is associated with exchange coupling between the hard and soft magnetic phases.     

Magnetic properties of novel compounds R3(Fe,Cr)29Xy (R=Nd, Sm and X=N, C)

The novel ternary rare-earth iron-rich interstitial compounds R₃(Fe,Cr)₂₉X_y (R=Nd, Sm and X=N, C) with the monoclinic Nd₃(Fe,Ti)₂₉ structure have been successfully synthesized. Introduction of the interstitial nitrogen and carbon atoms led to a relative volume expansion ΔV/V of about 6% and an enhancement of Curie temperatures T_c about 268 K for the nitride and about 139 K for the carbide, respectively. The Nd₃Fe_24.5Cr_4.5X_y compounds have a planar anisotropy at room temperature. A first-order magnetization process (FOMP) with critical field B_cr=4.4 T and 3.1 T at room temperature were observed for the Nd-nitride and carbide compounds, respectively. The Sm₃Fe₂₄Cr₅X_y compounds were found to have a large uniaxial anisotropy of about 18 T at 4.2 K and about 11 T at 293 K. A FOMP with B_cr=2.3 T was also observed in the Sm-nitride compounds at 4.2 K. Magnets with coercivity of μ_OjH_c0.8 T at 293 K has been successfully developed from the Sm₃Fe₂₄Cr₅X_y (X---N and C) phases.     

Precipitation phenomenon in stoichiometric Nd2Fe14B alloys modified with titanium and titanium with carbon

Precipitation phenomenon has been investigated in stoichiometric Nd₂Fe₁₄B alloys modified with Ti and Ti with C. Precipitates can be used to inhibit grain growth and understanding the precipitation process is important in order to form the most effective dispersion. In the Nd---Fe---B---Ti system, TiB₂, and in the Nd---Fe---B---Ti---C system. TiC are found to be the precipitating phases. Depending on composition, the precipitates can form at high temperatures in the liquid, during cooling after solidification, and during heat treatment. The precipitates form on grain or phase boundaries. The TiC precipitates typically form as discrete particles while the TiB₂ precipitates form generally in a globular bunched-up fashion. After a homogenization heat treatment, the equilibrium solubilities of Ti and Ti with C in the Nd₂Fe₁₄B phase are found to be 0.47 wt.% and 0.06 wt.% respectively. This means that almost all of the alloyed Ti and C can be precipitated as TiC which returns the excellent intrinsic magnetic properties of the hard magnetic phase. Both the carbides and the borides are found to have excellent high-temperature stability and resist coarsening and dissolution at least to 1000°C. Since Ti and C react to form TiC the amount of hard magnetic phase is not reduced while Ti addition alone reacts with boron and reduces the amount of hard magnetic phase if extra boron is not added.     

Thermodynamic assessments of the Cu–Th and Mo–Th systems

The thermodynamic assessments of the Cu–Th and Mo–Th binary systems were carried out by using Calculation of Phase Diagrams (CALPHAD) method on the basis of the experimental data including the thermodynamic properties and phase equilibria. The Gibbs free energies of the liquid, bcc, and fcc phases are described by the subregular solution model with the Redlich–Kister equation and those of the four intermetallic compounds Cu₆Th, Cu_3.6Th, Cu₂Th and CuTh₂ in the Cu–Th binary system were described by the sublattice model. A set of self-consistent thermodynamic parameters are obtained, and the calculated phase diagrams and thermodynamic properties are presented and compared with the experimental data from literatures. The calculated thermodynamic properties as well as phase diagrams are in good agreement with the experimental data.     

ICP-MS direct determination of trace amounts of rare earth impurities in various rare earth oxides with only one standard series

An inductively coupled plasma mass spectrometry (ICP-MS) method with just one standard series for direct determination of trace rare earth impurities in various rare earth oxides was developed. The spectral interference in ICP-MS analysis of high-purity neodymium (Nd₂O₃) was thoroughly estimated. For the investigation of matrix effect, high-purity Y₂O₃ was used as model sample and the experimental results showed that the maximal matrix tolerant amount obtained by stepwise dilution method is comparable to that obtained by conventional method with the use of higher purity Y₂O₃ as matrix. Under the selected conditions, no obvious matrix effect can be found with the matrix (Y) concentration of less than 500 μg mL⁻¹. For real sample analysis, 100 μg mL⁻¹ of matrix was chosen as the sample concentration. The proposed method was applied to the analysis of trace rare earth impurities in different high-purity rare earth oxides (Y₂O₃, Pr₆O₁₁, Nd₂O₃, Dy₂O₃, Er₂O₃), and the analytical results obtained were in good agreement with the recommended values. The detection limits of the method for rare earth elements were 1–21 ng L⁻¹ with the R.S.D varying between 2.9 and 7.8%, and the percentage recovery ranged from 93 to 115% for the spiked samples. This method was characterized with simplicity, rapidity, sensitivity, small sample amount required, and no internal standard/matrix matching requirements.     

Ba4In2−x(CO3)1+xO6−2.5x and Ba4In0.8Cu1.6(CO3)0.6O6.2—new indium oxycarbonates closely related to n=3 Ruddlesden–Popper phases

Investigations of phase relations in the Ba-rich part of the In₂O₃–BaO(CO₂)–CuO pseudo-ternary system at 900 °C have revealed the existence of new indium–copper oxycarbonate – Ba₄In_0.8Cu_1.6(CO₃)_0.6O_6.2. Rietveld refinement of the X-ray powder diffraction data combined with infrared studies gives evidence that this phase is a oxycarbonate crystallising in the tetragonal structure (space group I4/mmm) with unit cell parameters: a=4.0349(1) Å and c=29.8408(15) Å. In the binary part of the In₂O₃–BaO(CO₂) system we have identified the occurrence of Ba₄In_2−x(CO₃)_1+xO_6−2.5x oxycarbonate solid solution showing a crystal structure also described by I4/mmm space group, but with the unit cell parameters: a=4.1669(1) Å and c=29.3841(11) Å for x=1. The existence range of this phase, −0.153<x<0.4, includes chemical compositions of earlier found phases: Ba₅In_2+xO_8+0.5x with 0≤x≤0.45 (known as the -solid solution), as well as the binary Ba₄In₂O₇ phase. The crystal structures of both new oxycarbonates are isomorphic and related to n=3 member of the Ruddlesden–Popper family.     

The phase equilibria in the quasi-ternary Ag2Se---Ga2Se3---GeSe2 system

Eight polythermal sections of the quasi-ternary Ag₂Se---Ga₂Se₃---GeSe₂ system are investigated by the methods of differential thermal, X-ray phase and microstructural analyses and microhardness measurement. The projection of the liquidus surface and the isothermal section of the phase diagram at 720 K over the whole concentration region have been constructed. The character and the temperatures of 15 nonvariant processes (11 binary and 4 ternary eutectics) have been established. The γ-phase, the maximum on the liquidus surface of AgGaGe₃Se₈ have also been established. Another intermediate quaternary phases are not found. On the basis of the components and the ternary compounds the extended solid solutions have been established.     

Phase equilibria in the Al---Cr system

The Al---Cr system has been reviewed for Cr content up to 40 at.%. In this system several intermetallic compounds are formed by peritectic reactions. From the temperature of transformation and the composition of the phases, the nature of the invariant transformations is discussed. Transmission electron microscopy studies were performed on samples forming these compounds. A detailed structural interpretation is given for the phase θ-Al₇Cr. A new structure is proposed for Al₄Cr similar to that of the μ-Al₄Mn phase of which the crystal structure is known. The phase Al₅Cr (or Al₁₁Cr₂) was found to be orthorhombic and not monoclinic, as had been previously proposed. The existence of a cubic structure for the Al₉Cr₄ phase was confirmed.

On account of previous results, we should point out that the phases θ-Al₇Cr, Al₄Cr and Al₅Cr present characteristic features of pseudoicosahedral symmetry of the Al₄Cr icosahedral phase: it has been verified in the case of θ and μ that the same type of atomic cluster may be considered in order to describe these structures, i.e. 12 atoms located at the vertices of deformed icosahedra (either 12Al or 11Al + 1Cr or 10Al + 2Cr) whose centres are occupied by a Cr atom.

The reason for such an investigation originated from a study of the Al---Cr---Ni system for which the observed ternary structures appeared incoherent with those given for the binary Al---Cr system. This second study will be reported elsewhere.     

Influence of Zn Content on Microstructures,Mechanical Properties and Stress Corrosion Behavior of AA5083 Aluminum Alloy

To enhance the stress corrosion cracking (SCC) resistance, Zn was utilized as an alloy element to add in the AA5083 aluminum alloys. The effects of Zn content on the microstructures, mechanical properties and SCC resistance were systematically evaluated. The results demonstrate that in the studied range adding Zn can significantly improve the SCC resistance of the AA5083 alloys. This is related to the relatively low amount of continuous β (Al₃Mg₂) phase along grain boundary and the formation of Zn-containing phase such as Al₅Mg₁₁Zn₄ phase. Based on the results, the optimal Zn content with respect to SCC resistance is approximately 0.50 wt.%. Further increasing Zn content results in coarse precipitates discontinuously distributed along grain boundaries.