Disordering of the Ni3Si intermetallic compound by mechanical milling

The ordered f c c intermetallic compound Ni₃Si was mechanically milled in a high-energy ball mill. The severe plastic deformation produced by milling induced transformations with increasing milling time as follows: ordered f c c disordered f c c nanocrystalline f c c. The structural and microstructural evolution with milling time was followed by X-ray diffraction, TEM, hardness tests, and differential scanning calorimetry (DSC). Complete disordering occurred at milling times of 2 h and kept the saturated H of the DSC peak in the range of estimated enthalpy even after 60 h milling. The structural development during milling of the f c c solid solution for Ni₃Si was presumably dominated by the formation and refinement of a dislocation cell structure into microcrystallites which eventually reached nanometre dimensions.     

Processing and electrochemical characterization of Ni2Si intermetallic compound produced by vacuum sintering

In this study, a powder metallurgy approach for fabrication of Ni₂Si intermetallic compound was utilized. In this regard, mechanically activated Ni-33 at.% Si powders were used as feedstock. The powders were investigated by differential scanning calorimetry to study phase transformations that occurred during heating in the calorimeter. It was shown that the milled powders reacted after heating up to 850 °C. In order to fabricate bulk Ni-33 at.% Si, the as-milled powders were cold-pressed and subsequently sintered at 900 °C for 1 h in a vacuum furnace. X-ray diffraction results indicated that the phase composition of sintered materials consisted of only δ-Ni₂Si intermetallic. Consolidated samples exhibit 12% porosity and microhardness up to 773 HV_0.05. Further investigations showed the corrosion rate of sintered compound is higher than that of Ni–Si alloys reported in the literature. Here, anodic dissolution near the surface pores seems to be corrosion mechanism which resulted in increase in surface porosity up to 27% after corrosion.     

Compressive deformation of CoZr and (Co,Ni)Zr intermetallic compounds with B2 structure

B2 type (Co,Ni)Zr compounds which were prepared by arc-melting were deformed in compression at temperatures from liquid nitrogen temperature to 973 K. Their flow stress was anomalously dependent on the testing temperature, decreasing with increasing temperature up to room temperature and then increasing with temperature up to about 673 K, followed by a decrease. The peak of the flow stress was higher for PE specimens than for PA ones which were machined perpendicular and parallel to the direction of grain growth of the ingot, respectively. It is considered that this behaviour of the flow stress is caused, not by the phase transition but by the motion of superlattice dislocations. The ductility of CoZr was lowered by cracking at grain boundaries at which secondary phases were observed. The substitution of nickel for cobalt suppressed the grain boundary cracking and (Co,Ni)Zr had a higher ductility than CoZr.     

Permanent deformation of (Co,Ni)Zr intermetallic compounds through phase transformation

(Co, Ni)Zr intermetallic compounds, which have B_f structure at room temperature and B2 structure at elevated temperatures, were heated and cooled repeatedly in the temperature range between room temperature and 1223 K. This process produced the large permanent deformation in Co₃₀Ni₂₀Zr₅₀. Permanent elongation by as much as 0.2 to 0.3% per cycle was observed for the specimen parallel to the columnar structure, which grew from the bottom to the top of the button ingot, and permanent shrinkage by as much as 0.2% per cycle was observed for the specimen perpendicular to the columnar structure. For example, permanent elongation of about 30% was obtained after 93 cycles of the heating and cooling process in the former specimen, but no permanent elongation nor shrinkage was observed in the specimen parallel and perpendicular to the columnar structure for Co₃₆Ni₁₄Zr₅₀. The latter alloy had a different preferred orientation of the columnar structure from the former. These facts show that the crystal orientation influenced the permanent deformation caused by this transformation.     

Hydrogenation of Zr3Al2 in hydrogen and ammonia

We have identified conditions for the formation of Zr₃Al₂-based intermetallic hydrides through reactions with hydrogen and ammonia at temperatures from 150 to 300°C. The use of ammonia is shown to reduce the onset temperature for the formation of a hydride phase by 100°C compared to hydrogenation with hydrogen. Increasing the ammonia-Zr₃Al₂ reaction temperature to 500°C in the presence of NH₄Cl as an activator leads to the decomposition of the intermetallic compound and the formation of finely dispersed zirconium hydride and zirconium nitride powders.     

Hydrogenation of Zr6MeX2 intermetallic compounds: Absorption and desorption characteristics, crystal structure, and magnetic properties (Me-Fe, Co, Ni; X-Al, Ga, Sn)

We study the process of formation of the hydrides of Zr₆MeX₂ ternary intermetallic compounds (Me-Fe, Co, Ni; X-Al, Ga, Sn). It is shown that they are characterized by high hydrogen-storage capacity (9.4–10.8 atoms of hydrogen per formula unit). In the process hydrogenation, by the method of X-ray powder diffraction analysis, we revealed the transition of the crystal structure of Zr₆MeX₂ from the {ie528-1} space group of symmetries into {ie528-2} with doubling of the unit cell in the [001]-direction. The analysis of the crystal structure of Zr₆NiAl(Sn)₂H _x hydrides by using the Rietveld improvement of the data of X-ray powder diffraction analysis shows that it is identical to the structure of Zr₆FeAl₂D₁₀ deuteride studied earlier by the method of neutron diffraction analysis. The thermal desorption of hydrogen from the synthesized Zr₆MeX₂ hydrides was observed in the temperature range 400–900°K. The dependence of the magnetic susceptibility of the Zr₆FeAl₂ compound on temperature is characterized by the presence of a peak at 50°K. The character of these curves undergoes significant changes in the processes of hydrogenation and dehydrogenation of the specimen. These results were presented by the author at the 5th International Conference “Hydrogen Materials Science and Chemistry of Metal Hydrides” held on September 2–8, 1997 in Katsiveli (Crimea, Ukraine). Karpenko Physicomechanical Institute, Ukrainian Academy of Sciences, L'viv. Published in Fizyko-Khimichna Mekhanika Materialiv, Vol. 34, No. 4, pp. 71–78, July–August 1998.     

Quenched-in vacancies in B2-structured intermetallic compound FeAl

The concentrations of quenched-in vacancies retained in B2 intermetallic compound Fe_1-cAl_c were obtained as functions of composition (0.39 < c < 0.51) and quenching temperature (773–1273 K) from lattice constant and density measurements. Obtained vacancy concentration indicates rather gradual increase with composition in lower Al content region, while it increased rapidly as the composition approaches to stoichiometric composition. Further, the data for slow-cooled (1 K min⁻¹) samples showed that retained vacancy concentration is higher than that for samples annealed at and quenched from 773 K. Observed lattice constant for each composition decreases linearly with vacancy concentration, which is interpreted in terms of atomic size effect. From changes in vacancy concentration with quenching temperature, apparent vacancy formation energies were estimated. The relation between vacancy concentration and microhardness was also examined. Present results of dependency of lattice constant on heat treatment condition confirm the hardening effect due to retained vacancy. Further, the proposed linear relation of hardness to the square root of vacancy concentration is supported by the present study.     

Orientation and temperature dependence of the flow stress in the intermetallic compound Ni3Ge single crystals

Tensile tests on Ni₃Ge single crystals were carried out to make clear the mechanism of the positive temperature dependence of the CRSS and the work-hardening rate as a function of the tensile axis orientation below room temperature. Both the CRSS () and the maximum work hardening rate ( _M) show positive temperature dependence even below room temperature. The increments of and _M are satisfactorily expressed by the Schmid factor ratio of the cube cross slip system to the primary octahedral one,N=(010) [¯101]/(111) [¯101 ]. Then, the positive temperature dependence of both the CRSS and the maximum work-hardening rate is thought to be governed by two mechanisms. One arises from the Kear—Wilsdorf mechanism, which depends on the orientation. The other seems to arise from the orientation-independent factor, although it is obscure at present.     

High-temperature strength and ductility of L12-type Ni3Al-Ni3Mn intermetallic compound

The mechanical properties of L1₂-type pseudobinary intermetallic compound Ni₃Al-Ni₃Mn were investigated in relation to testing temperature and alloy composition. A positive temperature dependence of yield stress was found in manganese compositions lower than 15 at %, suggestive of the Kear-Wilsdorf mechanism, while a negative dependence was found in the high manganese alloys. The composition dependence of yield stress at room temperature in the low manganese alloys was attributed to the solid solution hardening while that in the high manganese alloys was attributed to imperfect ordering. The elongation exhibited a maximum around 700 K irrespective of compositions, while the maximum and minimum were observed approximately in 9 and 12 at % manganese alloys, respectively. The high values of elongation obtained in 20 and 25 at % manganese alloys were probably due to imperfect ordering. Both the temperature and composition dependences of UTS were quite similar to those of elongation. The fractographic observation showed that the more ductile specimen tended to fracture more transgranularly.     

Microstructure and tensile properties of aged Superalpha 2 intermetallic compound

Abstract

Specimens of commercially available Superalpha 2 were solution heat treated at 1060°C in the (α₂ + β phase field, air cooled, then aged at temperatures between 650 and 950°C followed by air cooling. During aging, the B2 phase was more stable than expected from earlier work. The aged specimens were tensile tested to failure at room temperature and microstructural studies were carried out using optical microscopy, scanning electron microscopy, and analytical transmission electron microscopy. It was found that the strength of Superalpha 2 could be dramatically increased by aging at low temperatures, which refines the β matrix. The ductility at room temperature was observed to depend on the volume fraction of retained B2 phase.

MST/1578     

Interaction of hydrogen with the intermetallic compounds Sc2Al and Sc2Ni

The reactions of the intermetallic compounds Sc₂Al and Sc₂Ni with hydrogen have been investigated. The results demonstrate that Sc₂Ni reacts with hydrogen even at room temperature, to form amorphous Sc₂NiH₅. The reaction is irreversible at room temperature. Vacuum extraction of hydrogen between room temperature and 900°C leads to partial decomposition of Sc₂NiH₅ and the formation of crystalline ScH₂ and ScNi₂. Sc₂Al is nonreactive with hydrogen at room temperature. Heating at a hydrogen pressure of 5 MPa leads to Sc₂Al hydrogenolysis starting at 225°C and the formation of ScH₂ and metallic Al.     

The de Haas-van Alphen effect in the intermetallic compound Cu2Sb

The de Haas-van Alphen effect has been studied in the intermetallic compound Cu₂Sb (tetragonal structure) by the modulation method in fields up to 100 kG. Numerous frequency branches have been obtained in the (100), (110), and (001) planes, and several cyclotron effective masses have been determined. The results show some compatibility with the nearly-free-electron model in the single- or double-zone scheme. The lattice parameters have been determined at room temperature and at liquid-helium temperatures.     

再流条件对Ni颗粒增强复合钎料组织形态的影响

主要针对不同的再流次数带来的不同热输入对Ni颗粒增强复合钎料IMC形态的影响进行了深入研究。由前一阶段研究表明，决定Ni颗粒增强复合无铅钎料组织变化的关键因素是钎料的钎焊温度与钎料熔点的温度差△T以及在熔点以上保温时间t。其本质即外界对钎料的热输入量的大小。随着热输入的增加，Ni颗粒周围的IMC以及钎料/基板界面处的IMC都相应变化发展。由于Ni颗粒的加入。基板＼钎料界面层的结构形态均与Sn-Ag共晶钎料有较大不同，Ni与cu6Sn5的相互作用起到了关键影响。界面层厚度的变化随再流次数增加呈现线性增长。     

Mechanochemical synthesis of a La0.67Ce0.21Nd0.08Pr0.04Ni5 intermetallic compound

The mechanochemical synthesis of a La_0.67Ce_0.21Nd_0.08Pr_0.04Ni₅ intermetallic is studied. The intermetallic is synthesised from a mixture of LaNi₅ and La_0.25Ce_0.52Nd_0.17Pr_0.06Ni₅. The processes controlling the mechanical alloying are characterised as a function of integrated milling time (t_m). Effects of fracture and cold welding on the sample are identified by scanning electron microscopy. Compositional, microstructural and structural changes are analysed by energy dispersive spectroscopy and X-ray diffraction. The powder obtained has a particle size distribution of 9 ± 1 μm with an average crystallite size of 370 ± 10 Å and strain >10%. The intermetallic compound is annealed in Ar to increase crystallite size and to release strain. The structure is refined by the Rietveld method. Cell parameters are a = 4.982(2) Å and c = 3.980(9) Å, respectively. The advantage of the synthesis method using intermetallics instead of metals/alloys is discussed along with the characteristics of the powder obtained.     

Tensile behaviour of Ni3Al+B intermetallic compound: influence of cold deformation and annealing

Nickel aluminide, intermetallic compound Ni₃Al, is a promising structural material on account of its high strength at elevated temperatures. The influence of cold deformation on the tensile behaviour of an Ni₃Al alloy containing zirconium and boron is presented. The undeformed material, in the as-cast condition, was subjected to varying levels of cold deformation ranging from 11.4%–61.4%, and tensile tests performed. The tensile properties and fracture behaviour of the cold-deformed material are compared with undeformed material to highlight the influence of cold deformation on strength, ductility and fracture behaviour. Tensile tests were performed on cold-deformed plus annealed samples and properties compared with the cold-deformed counterpart in order to elucidate the influence of annealing on tensile behaviour. The intrinsic effects of cold deformation and annealing on microstructure, tensile properties and fracture behaviour are highlighted.     

Rapid Growth of TiNi intermetallic compound within undercooled Ti50Ni50 alloy under electrostatic levitation condition

The undercooling dependence of the solidification mechanism was systematically explored by the elec-trostatic levitation(ESL)facility.During the experiments,the maximum undercooling reached up to 406 K(0.26 TL)and the growth velocity of the primary TiNi phase was in-situ determined at various undercool-ings.At the initial increase of alloy undercooling,the value of growth velocity sluggishly rose followed by a power function.In this case,the primary TiNi phase preferentially developed as the equiaxed dendrite,then the remnant liquid participated as Ti2Ni and α-Ti phases on the grain boundary.Once the under-cooling exceeded the critical value of 350 K,the growth velocity of the primary phase displayed a sharply increase tendency.Meanwhile,the TEM results demonstrated that the precipitation of the intermetallic Ti2Ni compound was gradually restrained during the rapid solidification and the R-phase existing in the TiNi matrix at large undercooling implied that the martensitic transformation was incomplete.     

Effect of cooling rate on the 3D morphology of the proeutectic Al_3Ni intermetallic compound formed at the Al/Ni interface after solidification

Effect of cooling rate on the 3 D morphology and the growth mechanism of the proeutectic Al_3Ni intermetallic compound(IMC) that forms at the Al/Ni interface after solidification was investigated by synchrotron X-ray microtomography in combination with EBSD analysis. The proeutectic Al_3Ni phase that forms under an average cooling rate of 0.1 Ks~(-1) shows a characteristic faceted growth behavior and presents a typical 3 D morphology as partially hollow quadrangular prisms. On the contrary, that forms under an average cooling rate of 10 Ks~(-1) shows complicated dendritic morphology with asymmetrically distributed arms and faceted V-shape groove at the distal end, indicating a gradual transition of the growth behavior from non-faceted to faceted during the solidification process. These results reveal that the morphology of the proeutectic Al_3Ni is highly sensitive to the solidification condition so that fine control of the desired morphology may be achieved by carefully manipulating the cooling profile.