Ni-Ti-Ta三元体系的相平衡关系

采用X射线衍射和电子探针显微分析方法,获得Ni?Ti?Ta三元体系在1000和1200℃的全成分范围内等温截面相图.实验结果显示,Ni?Ti?Ta三元体系的1000和1200℃等温截面相图中均存在一个固溶度较小的三元化合物τ相,且通过相平衡可知,该相在1000℃的成分为(16.3～22.4)％Ta,(15.9～24.1...     

Nb-Ti-Co三元系1173K等温截面的研究

采用三元扩散偶技术测定了Nb—Ti-Co三元系富Co，Ti区域在1173K的等温截面，借助电子探针微区成分分析方法测定了Nb-Ti-Co三元扩散偶的相区成分，并对其相关系进行了研究。测得Nb-Ti-Co三元扩散偶富Co，Ti区域在1173K时存在6个二元中间化合物：NbCo3，NbCo2，TiCo3，TiCo2，TiCo和Ti2Co；Nb和Ti形成连续固溶体；在此温度的扩散偶中不形成三元中间化合物。经分析，Nb-Ti—Co三元系在1173K存在6个三相区：（Co）＋TiCo3＋NbCo3，NbCo3＋TiCo3＋NbCo2，NbCo2＋TiCo3＋TiCo2，TiCo2＋NbCo2＋TiCo，NbCo2＋TiCo＋Ti2Co和NbCo2＋Ti2Co＋（Nb，Ti）。     

Mo-Ti-Ru三元系相平衡的实验研究

本研究利用电子探针成分分析和X射线衍射分析等技术建立Mo-Ti-Ru三元系的1100°C和1300°C等温截面相图,实验结果表明：(1)在1100℃等温截面相图中存在三个三相区,而1300℃等温截面相图中存在两个三相区;(2)在1100℃等温截面中,由于Ti的加入,σ-Mo₅Ru₃相被稳定化并形成一个小单相区;(3)在1100℃和1300℃等温截面相图中,(βTi, Mo)相均从富Mo侧一直延伸至富Ti侧,并且具有较大的固溶度。Mo-Ti-Ru三元系相平衡的测定为Ti基合金热力学数据库的建立提供基础理论信息。     

Ti-Mn-Si三元系相图富Ti端800及1100℃等温截面的测定

采用合金法,利用电子探针显微分析(EPMA)及X射线衍射法(XRD),试验测定了Ti-Mn-Si三元系合金相图富Ti端800及1 100℃等温截面中的相关系。结合试验数据和已知子二元系相图,发现Ti-Mn-Si三元系富Ti端800℃时存在3个三相区:BCC(Ti)+HCP(Ti)+SiTi_3、BCC(Ti)+Si_3Ti_5+SiTi_3、BCC(Ti)+Si_3Ti_5+X(X为三元新相); 4个两相区:BCC(Ti)+Si_3Ti_5、BCC(Ti)+SiTi_3、HCP(Ti)+SiTi_3、HCP(Ti)+BCC(Ti);2个单相区:BCC(Ti)、HCP(Ti)。富Ti端1 100℃时存在2个三相区:BCC(Ti)+Si_3Ti_5+SiTi_3、BCC(Ti)+Si_3Ti_5+X; 2个两相区:BCC(Ti)+Si_3Ti_5、BCC(Ti)+SiTi_3; 1个单相区BCC(Ti)。     

Nb-Ni-Ti系低Ni侧1000℃相平衡研究

利用SEM、EPMA、XRD、DSC对Nb-Ni-Ti系低Ni侧1000℃的液相相关相平衡进行了研究。结果表明,1000℃时,在Nb-Ni-Ti系低Ni侧存在着一个可与(Nb,bTi)连续固溶体和TiNi化合物相平衡的液相区;该液相区源自Ti-Ni二元系,延伸至Nb含量3.7%(原子分数)。而二元化合物TiNi在1000℃时则可以溶解约8.0%Nb。1000℃时,Nb-Ni-Ti系低Ni侧等温截面相图中存在2个三相区Liquid+(Nb,bTi)+TiNi和(Nb,bTi)+TiNi+XB,XB是成分为34.0Nb-44.9Ni-21.1Ti的六方结构化合物;这2个三相区之间则是宽阔的(Nb,bTi)+TiNi两相区。在该两相区内,连续固溶体(Nb,bTi)中的Ni含量变化不大、约为3%,Ti含量的变化范围为6.6%~39.9%。而3.7%Nb的溶入未能使二元化合物Ti_2Ni相的稳定存在温度提高到1000℃。     

Ti-Fe-Mn三元系热力学评估

通过CALPHAD法,利用相关数据优化了Ti-Fe-Mn三元系,计算了1000℃等温截面图。同时还计算了Ti对Mn在1570℃时液相中活度的影响、TiMn_2-TiFe_2伪二元面、液相投影面和850℃与1150℃富Fe端BCC_A2-FCC_A1相平衡。计算结果与大部分实验结果吻合。     

Cu-Ni-Ti三元系600°C相平衡关系的测定

采用合金相分析法测定了Cu-Ni-Ti三元系在600℃的部分相平衡关系。借助电子探针微区分析方法,对热处理后的Cu-Ni-Ti三元合金的组成相成分进行测定。结果表明,Cu-Ni-Ti三元合金在600℃下生成两个三元化合物,实验检测到3个三相平衡和5个两相平衡;结合三个边际二元系和本文的实验信息,构筑了Cu-Ni-Ti三元系600℃的等温截面。     

相平衡分析在Nb-Si基高温合金制备中应用

在相平衡热力学计算的基础上,利用Scheil-Guilliver模型,计算了Nb-Si-Mo三元体系中不同成分合金的凝固途径.同时,根据Nb-Si-M(M=Ti、Mo、W、Al、Cr、B、Hf)三元系富Nb-M边的液相面投影图及相平衡关系,分析了各合金元素对Nb3Si相的稳定能力,以及对Nbss+Nb5Si3双相区的影响.计算结果与对应合金的显微组织分析相一致,表明相平衡分析有利于设计合金成分、模拟凝固过程、控制合金组织,对于Nb-Si基高温合金的设计与制备具有重要的指导意义.     

ISOTHERMAL SECTION AT 1000 AND 1100℃ OF Fe-Mn-AI SYSTEM PHASE DIAGRAM

利用扩散偶技术和合金法测定了Fe-Mn-Al三元系1000和1100℃等温截面的Fe-Mn侧的相平衡关系,结果表明1000℃有一(α+y+β)三相区,此外,固/气扩散偶被用来测定相平衡成分,表明这种方法对于具有挥发性组元的体系是可行的。     

Mg-Sn-Y三元系富Mg角500℃等温截面的测定

采用合金法,利用XRD、SEM-EDS测定一系列Mg-Sn-Y三元合金在500℃下富Mg角处相平衡关系及各相平衡成分,建立Mg-Sn-Y三元系在500℃下富Mg角处的等温截面相图。结果表明:Mg-Sn-Y三元系富Mg角处存在Mg2Sn、MgSnY、Sn3Y5和Mg24+xY54种化合物与α-Mg固溶体平衡,从而构建3个三相区和4个两相区;Sn在α-Mg基体中的固溶度为2.5%～3.9%(摩尔分数),Y在α-Mg基体中的固溶度为1.1%,但二者不能同时固溶到α-Mg基体中,同时Sn3Y5相中大约可以固溶3.6%～4.1%的金属Mg;由于MgSnY和Sn3Y5等一些高熔点化合物在高温下能够稳定存在,使得Mg-Sn-Y体系有可能成为一种潜在的新型耐热镁合金。     

Phase equilibria in the Co-rich Co-Al-W-Ti quaternary system

We determined phase equilibria in the Co-rich Co-Al-W-Ti quaternary system at a temperature range between 900 °C and 1200 °C with a close attention to the thermodynamic stability of the γ′-Co₃(Al, W, Ti) (L1₂) phase, based on micro-structure observation and electron microprobe analysis on bulk alloy samples heat-treated for periods up to 2000 h. In the quaternary system the single phase field of γ′ extends from the Co-Ti binary edge to a composition of Co-5Al-8.5W-8Ti (in at.%) at 900 °C. At the tip of the single phase field, the γ′ phase is in equilibrium with the γ-Co (A1), Co₂AlTi (L2₁) and Co₃W (D0₁₉) phases. The constructed vertical section of phase diagram between Co-9.4Al-9.6W and Co-16.5Ti indicates that there is a narrow composition range around Co-4.5Al-5.4W-7.5Ti in which the γ single phase field exists at high temperatures above 1200 °C and two-phase of γ+γ′ is thermodynamically stable at low temperatures below 1100 °C.     

Phase equilibria and thermodynamic calculation of the Co–Ta binary system

Experimental investigation and thermodynamic evaluation of the Co–Ta binary phase diagram was carried out. Equilibrium compositions obtained in two-phase alloys and diffusion couples were measured by electron probe microanalyzer (EPMA). A very narrow λ₃(C36) + λ₂(C15) two-phase region is confirmed to be present around 26.5 at.% Ta at temperatures between 950 °C and 1448 °C. Equilibrium relationships above 1500 °C among the liquid, Laves (λ₁(C14), λ₂ and λ₃, whose stoichiometry is described by Co₂Ta), μ(D8_b) and CoTa₂(C16) phases were investigated by microstructural examination in as-cast Co-(24–60 at.%)Ta alloys. The solvus temperature of the γ′ Co₃Ta (L1₂) phase precipitated in the 5.8 at.%Ta γ(Co) and the peritectoid temperature of the Co₇Ta₂ phase in an 8.5 at.%Ta alloy were determined to be 1013 °C and 1033 °C, respectively, by differential scanning calorimeter (DSC). Fine precipitates of the γ′ phase precipitated in the γ (A1) matrix were observed by transmission electron microscope (TEM). Analyzing the present experimental results synthetically, the γ′ Co₃Ta phase was identified to be a metastable phase, of which the γ/γ′ transition temperature of the stoichiometric Co₃Ta alloy was estimated to be 2000 °C. Thermodynamic assessment of the Co–Ta binary system was carried out based on the present results as well as on experimental data in the literature. Calculated results of not only stable but also metastable equilibria were found to be in good agreement with the revised phase diagram. The evaluated stability of the metastable γ′ Co₃Ta coincides with the enthalpy of formation (ΔH(γ'Co₃Ta) = −23.44 kJ/mol) calculated by the ab initio method.     

Partition behavior of alloying elements and phase transformation temperatures in Co–Al–W-base quaternary systems

The phase equilibria among γ (A1), γ′ (L1₂), χ (D0₁₉), β (B2) and μ (D8₅) phases and the γ′ solvus and γ solidus temperatures were investigated in the Co–Al–W-based quaternary systems with alloying elements of Ti, V, Nb, Ta, Cr, Mo, Mn, Fe, Ni, Si, Zr, Hf, Ru and Ir by electron probe microanalysis (EPMA) using multiphase alloys and by differential scanning calorimetry (DSC). It was found that Ta, Nb, Ti, V, Mo and W are partitioned to the γ′ or χ phase rather than to the γ phase, while Cr, Mn and Fe tend to be distributed to the γ phase. The correlation between the partition coefficient of alloying elements between γ/γ′, γ/χ and γ/β phases and ab initio formation energy of Co₃X (L1₂), Co₃X (D0₁₉) and CoX (B2) was respectively obtained. It was also found that the γ′ solvus temperature increases by the addition of the γ′ former elements such as Ta, Nb and Ti, which decreases the γ solidus temperature.     

Experimental investigation of phase equilibria and microstructure in the Co–Ti–V ternary system

The phase equilibria in the Co–Ti–V ternary system have been investigated by means of optical microscopy (OM), electron probe microanalyzer (EPMA), differential scanning calorimetry (DSC), field emission scanning electron microscope (SEM) and X-ray diffraction (XRD). The mechanical properties were measured by compressive tests. Four isothermal sections of the Co–Ti–V ternary system at 800 °C, 1000 °C, 1100 °C and 1200 °C were experimentally established. The results show that: (1) there is no ternary compound in this system; (2) the CoTi₂ phase and Co₃Ti phase stabilized by the V addition; (3) a large solubility of Ti in the σ-Co₂V₃ phase was observed at all isothermal sections of 800 °C, 1000 °C, 1100 °C and 1200 °C; (4) The alloy with the distribution of fine cuboidal Co₃Ti (L1₂) in (αCo) phase was observed. (5) The compressive strength of Co_77.29Ti_5.83V_16.88 (at.%) alloy at room temperature was measured to be about 1985 MPa. The newly determined phase equilibria in this system will provide useful information for the development of Co-based and Ti-based materials.     

Hydrogen permeable Ta–Ti–Ni duplex phase alloys with high resistance to hydrogen embrittlement

Crystal structures, microstructures and hydrogen permeability Φ of as-cast Ta–TiNi alloys on the line connecting the compositions of the primary (Ta, Ti) and the ternary eutectic phases have been investigated to find out highly hydrogen permeable duplex phases alloys with high resistance to the hydrogen embrittlement. The alloys on this line show microstructures of (1) the eutectic {(Ta, Ti) + TiNi} phase, (2) the primary (Ta, Ti) phase + the eutectic {(Ta, Ti) + TiNi} phase, and (3) the (Ta, Ti) solid solution, although a little amount of unidentified (impurity) phases are included in these samples. The value of Φ increases with increasing Ta content and the volume fraction of the primary (Ta, Ti) phase, which indicates that the primary phase contributes mainly to the hydrogen permeation. The Ta₅₆Ti₂₃Ni₂₁ alloy, containing the 61 vol.% primary phase, shows the highest Φ of 2.18 × 10⁻⁸ mol H₂ m⁻¹ s⁻¹ Pa^−0.5 at 673 K, which is 1.3 times higher than that of the previous most high Φ alloy (Ta₅₃Ti₂₈Ni₁₉). The more Ta-rich alloys on this line, i.e., containing a small amount of the eutectic phase, are broken down by the hydrogen embrittlement, suggesting that the eutectic phase suppresses the hydrogen embrittlement.     

Phase Equilibria and Ternary Intermetallic Compound with L1<Subscript>2</Subscript> Structure in Co-W-Ga System

Phase equilibria and stabilities of intermetallic phases appearing in the Co-rich portion of the Co-W-Ga ternary alloys were investigated and isothermal section diagrams at 1200, 1100, 1000, and 900 °C were determined. A fine cuboidal phase with an L1₂ structure was observed at 900 and 800 °C, where the composition of the new ternary compound obtained by aging at 900 °C for the Co-7.4W-12.0Ga alloy was Co-11.2W-11.4Ga (at.%). It was confirmed that this compound is metastable at 900 °C but is more stable at 800 °C. These results mean that the thermodynamic stability of the metastable Co₃W L1₂ phase, especially in the low temperature region, increases by the addition of Ga.     

Alloyed W–(Co,Ni,Fe)–C phases for reaction sintering of hardmetals

It has been shown that W–Co–C phases could dissolve a substantial amount of metals such as V, Cr and Ta, which are known to positively influence the microstructure of hardmetals with respect to uniform grain size distribution and fine grain size. This offers a tool to circumvent the conventional doping of hardmetals with individual carbides. In the present study we used double- and triple-alloyed κ-W₉Co₃C₄ (i.e. κ-(W,V,Cr)₉Co₃C₄ and κ-(W,V,Cr,Ta)₉Co₃C₄) and applied a variety of sintering experiments to obtain WC–Co, WC–(Ti,Ta,Nb)C–Co and WC–(Ti,Ta,Nb)(C,N)–Co hardmetals. We also prepared κ-W₉Fe₃C₄, alloyed κ-W₉Ni₃C₄, and κ-W₉(Fe/Ni)₃C₄, and used the latter for sintering.     

The Systems Tantalum (Niobium)-Cobalt-Boron

Constitution of the ternary systems Nb-Co-B and Ta-Co-B was studied, employing optical and electron microscopy, x-ray powder, single crystal diffraction, electron probe microanalysis, DTA and Pirani melting point measurements. Ternary phase equilibria were determined within an isothermal section at 1100 °C. For the Co-rich part (≥50 at.% Co) of the system, a liquidus surface projection and a corresponding Schulz-Scheil reaction scheme were constructed in combination with data for primary crystallization from as-cast samples determined by SEM and EPMA measurements. The crystal structures of novel ternary compounds have been elucidated by x-ray powder and single crystal diffraction and were supported by TEM. {Nb,Ta}CoB with NbCoB-type exhibits a high temperature modification (ZrAlNi-type, a = 0.5953 nm, c = 0.3248 nm; a = 0.5926 nm, c = 0.3247 nm for Nb and Ta respectively), which was only present in as-cast alloys, but found to be stabilized by the addition of Fe to annealing temperatures of 1400 °C. Ta₃Co₄B₇ (a = 0.3189 nm, b = 1.8333 nm, c = 0.8881 nm) was proven to be isotypic with Nb₃Co₄B₇. The novel orthorhombic compounds {Nb,Ta}Co₂B₃ (TaCo₂B₃-type with space group Pnma; a = 0.53628 nm, b = 0.32408 nm, c = 1.24121 nm for TaCo₂B₃; a = 0.53713 nm, b = 0.32442 nm, c = 1.2415 nm for NbCo₂B₃) adopt unique structure types with branched boron zig-zag chains. {Nb,Ta}Co₂B were found to crystallize in a unique monoclinic structure type (space group P2 ₁/c; a = 0.9190 nm, b = 0.64263 nm, c = 0.63144 nm; β = 109.954°, for Nb) very close to an orthorhombic setting (Cmce, a = 0.63162 nm, b = 1.72810 nm, c = 0.64270 nm, for Nb). Substitution of Co by Ni stabilizes a smaller orthorhombic lattice with Re₃B-type structure (Cmcm) although no homologue compound in the Ni-system exists. The crystallographic relations among the structure types of Re₃B and pseudo-orthorhombic as well as monoclinic {Nb,Ta}Co₂B were defined in terms of a Bärnighausen scheme. DFT calculations revealed very close stabilities for the three competing structure types for {Nb,Ta}Co₂B. Detailed transmission electron microscopy (TEM) for Nb(Co,Fe)B, {Nb,Ta}Co₂B,  {Nb,Ta}(Co,Ni)₂B, and Ta₃Co₄B₇ confirmed lattice geometries and crystal symmetry. Vickers hardness was measured for {Nb,Ta}Co₂B, {Nb,Ta}(Co,Ni)₂B, {Nb,Ta}_2?x Co_21+x B₆ and {Nb,Ta}Co₂B₃ exhibiting the highest value of hardness of HV = 22.4 ± 1.1 GPa for TaCo₂B₃. Magnetic, specific heat and electrical resistivity measurements on the compounds TaCo₂B and Ta₂Co₂₁B₆ reveal paramagnetic and ferromagnetic metallic ground states, respectively.     

Remarks on the Co-rich region of the Co-Sm diagram

The Co-rich region (0 to 30 at.% Sm) of the Co-Sm phase diagram was reevaluated. The homogeneity range of Co₅Sm was redetermined with optical metallography, Curie temperature measurements, and lattice parameters data. Some comments on the phases Co₇Sm₂, Co₁₉Sm₅, Co₅Sm, and Co₁₇Sm₂ are presented. The homogeneity range of other Co₅RE and Co₁₇RE₂ (RE = rare-earth) compounds is discussed.     

Phase equilibria in the Co-Ti portion of the Co-Al-Ti ternary system

Phase equilibria of 900, 1000, and 1100 °C in the Co-Ti portion of the Co-Al-Ti system were mainly determined by energy dispersion x-ray spectroscopy. On the Ti-Al side, the β-Ti (A2) phase region is extended by the addition of Co and the β-Ti + AlTi₃ (D0₁₉) two-phase region appears in the ternary equilibrium, while the AlTi (L1₀), AlTi₃, and β-Ti phases show very low solubility of Co. It was found that the two ternary intermetallic compounds, Co₂AlTi (L2₁) and CoAl₂Ti (D8 _a ), exist over a wide solubility range along the CoAl(B2)-CoTi (B2) and CoAl₃-CoTi₃ sections, respectively. The ordering transition and the phase separation due to ordering of the β-Ti, CoAl, or CoTi and Co₂AlTi phases fundamentally possessing the bcc structure are also discussed.