Excessive thermodynamic properties of praseodymium in a gallium-indium alloy

The equilibrium potentials of praseodymium-diluted homogeneous Pr-Ga-In alloys in a (Li-K-Cs)Cl_eut-based salt electrolyte were measured between 573–1073 K by the emf method. These potentials are used to calculate the activity coefficients of α-praseodymium in liquid Ga-In eutectic alloys. PrIn₃ alloy with well-known thermodynamic characteristics and without phase transitions in the temperature range 428–1483 K was employed as the reference electrode.     

Rapid solidification of Al-Cu eutectic alloy by laser remelting

Rapid surface resolidification using a high powered CO₂-laser has been performed on eutectic Al-32.7 wt% Cu at speeds between 0.2 and 8 m/s. By means of longitudinal cuts through the centre of the laser trace, the local growth rate has been measured by observation of the orientation of the microstructure using transmission electron microscopy. The various microstructures as a function of growth rate, are:

• 1.(a) regular lamellar eutectic α-Al/θ-Al₂Cu structure for growth rates below 20 cm/s with interlamellar spacing as fine as 17 nm;
• 2.(b) a new wavy eutectic α-Al/θ'-Al₂Cu morphology for growth rates of between 20 and 50 cm/s;
• 3.(c) a banded structure formed by alternating supersaturated α-Al solid solution and the wavy eutectic for growth rates greater than 50 cm/s.

A recent analytical model for eutectic growth under rapid solidification condition is compared to the experimental results. Contrary to the classical λ²V_s = const. relationship, which predicts a continuous decrease in spacing as the growth rate increases, this new theoretical model clearly predicts a limit for the coupled eutectic growth which finds its analogy in single phase solidification in the limit of absolute stability.     

Halo formation in eutectic alloy systems

Halo formation was studied in several faceted-nonfaceted and faceted-faceted eutectic systems. Ascribing halo formation to the amount of thermal, under cooling of the secondary phase in the presence of a primary phase is shown incorrect. Rather it is proposed that halo formation is due to growth rate phenomena of the phases involved.     

Directional solidification in a AgCuSn eutectic alloy

An experimental study of microstructures in a directionally solidified, near-eutectic Ag-Cu-Sn alloy has been completed. This material is an important candidate for use as a lead-free solder, and the studies show the origin and velocity dependence of some of the microstructures seen in solder joints. Quantitative stereology and microstructural observation were completed for directional solidification experiments where the sample was moved through a gradient furnace at velocities between 0.826 and 500 μm/s.     

Creep behavior of Ni-Cr lamellar eutectic alloy

The structural changes that occur during creep deformation at 625° and 760°C, with creep and creep rupture data of a directionally solidified Ni-Cr lamellar eutectic alloy are presented and discussed. It is shown that the characteristic features of stage I deformation are the formation of dislocation tangles in the nickel-rich phase and shearing of the cellular structure; these features are then carried into stage II without any additional changes. The onset of accelerated creep is associated with the fracture of the chromium-rich lamellae. During this stage well-defined dislocation cells are formed. More than an order of magnitude increase in lifetime over cast specimens is obtained in the lamellar material with intermediate results for partially dendritic specimens. The activation enthalpy for creep is strain dependent, increasing from about 40 kcal per mole at low strains to a constant value of 80 kcal per mole at about 2 pct plastic strain. Stress dependence of steady-state creep for both test temperatures conforms to the expression έ =Aσ ⁿ witha − 7 for the lamellar eutectic anda − 5 for cast specimens.     

同位素稀释质谱法测定铀铌合金中铀含量

根据同位素稀释质谱法原理,推导了铀铌合金中铀含量的计算公式。研究了铀铌合金的分解方法,优化了取样量和稀释剂用量,探讨了质谱谱线干扰和合金元素干扰对测量结果的影响。加入硝酸和氢氟酸定量溶解铀铌合金,再定量加入铀同位素稀释剂,直接制备成混合试样溶液,应用质谱法测定混合溶液、铀铌合金试样的铀同位素比,最后计算出铀铌合金中铀含量。确定的方法无需定量分离铀。为了对分析结果的准确性进行验证,应用XRF法、ICP-AES法和元素分析法测量铀铌合金中铌含量和杂质元素总量,反推得到相应的铀含量,其结果同实验方法的结果是一致的。对铀铌合金样品进行分析,测定结果的相对标准不确定度为0.2%（6次测定）,扩展不确定度为0.5%（95%置信水平）。     

Structure formation in a titanium-nickel alloy of eutectic composition

Conclusions The mechanism of structure formation in a titanium-nickel alloy of eutectic composition during sintering consists in the dissolution of nickel particles in a titanium matrix, which leads to the formation of the intermetallic compound TiNi and generation of pores, in TiNi Ti₂Ni transition, and in the appearance, at -Ti/Ti₂Ni contacts, of a liquid, which crystallizes in the form of a eutectic at a temperature below 1228°K and undergoes eutectoid decomposition at a temperature below 1043°K. Produced by sintering in the presence of a solid and a liquid phase, the alloy is characterized by high density, strength, and hardness. Its angle of contact on diamond during heating to 1523°K is 72°. In order to be able to use such an alloy in diamond-containing composites, it will be necessary to lower its sintering temperature and increase its adhesion to diamond.Translated from Poroshkovaya Metallurgiya, No. 1(253), pp. 66–71, January, 1984.     

Hydrogen solubility in a titanium aluminide alloy

The dissolution of hydrogen in a titanum aluminide alloy based on Ti₃Al, Ti-24 Al-11 Nb, has been measured as a function of temperature and hydrogen pressure. Both the terminal solubility and the overall solubility, or total uptake of hydrogen, were determined. The terminal solubility of hydrogen in the α₂ matric phase increases with temperature, while the overall solubility decreases with increasing temperature in the high-temperature region. The partial molar heat of solution in the α₂ phase was determined to be−(21.97 ± 1.46) kJ/mol [H], while the partial molar heat of formation of the hydride phase was −(70.29 ± 2.34) kJ/mol [H]. The standard partial molar free energy of hydrogen in the α₂ phase in equilibrium with the hydride was −(74,060 ± 2000) + (87.8 ± 2.1) T J/mol [H].     

A novel method for the determination of the hydrogen solubility in aluminum and aluminum alloy melts

The CHAPEL method, which was developed for the direct and continuous determination of the hydrogen activity in aluminum melts by measuring the equilibrium hydrogen pressure, has been modified for the determination of the hydrogen solubility in aluminum and aluminum alloy melts. The change of the hydrogen equilibrium pressure due to addition or removal of a given amount of hydrogen from a melt of known mass yields directly the Sieverts constant. Such experiments provide reliable data only if no additional gas exchange takes place between the melt and the gas phase. In the present work, a quasi-impermeable interface between the melt and the surrounding hydrogen atmosphere has been realized by maintaining the hydrogen pressure above the melt continuously at the level of the hydrogen equilibrium pressure. By this technique, which is performed by a relatively simple experimental setup, fast determination of the hydrogen solubility is possible. The main advantage of this novel method is the fact that it can be applied also for aluminum alloys without protective oxide layer on the surface. Preliminary results on pure aluminum and Al-Cu alloy melts show good agreement with the data obtained by the classical method of Sieverts that is not well suited for routine determinations on a wide range of alloy composition and temperature since it is very time-consuming. The method can also be applied for the investigation of other metal and alloy melts.     

Radioscopic visualization of isothermal solidification of eutectic Ga-ln alloy

R. DEREBAIL, formerly Research Associate, Department of Aerospace Engineering Sciences, University of Colorado.     

Microstructure and crystallography of unidirectionally solidified Ni-W eutectic alloy

A Ni-W eutectic alloy was subjected to a process of unidirectional solidification (UDS) by the Bridgman-Stockbarger technique. Three phases were identified by transmission electron microscopy, namely: W fibers, a solid solution matrix of W in Ni, and Ni₄W precipitates of the Dla structure in the matrix. The growth axis of the W-fibers was found to be <111> and the orientation relationship between them and the Ni(N) matrix was identified as the Bain type, so that (100)_bcc ‖ (100)_fcc. The shape of the Ni₄W precipitates varies from equiaxial at high solidification rates to elongated plates at low rates. The orientation relationship between the precipitates and the matrix is the same for all solidification rates. The microstructure of specimens subjected to creep deformation was studied and the deformation modes were identified. These include dislocations and microtwins that originate mainly at the boundary between the Ni(W) matrix and the W-fibers. In some specimens the creep test was carried out after solution treatment at 1030 °C followed by quenching, which resulted in a Ni(W) matrix reinforced with W-fibers without Ni₄W precipitates. The microstructural changes during this creep process and the fracture surface were studied by SEM and TEM.