Thermodynamic activities and phase boundaries for the alloys of the Ni3Al-Ni3Ti pseudobinary section in the Ni-Al-Ti system

The pseudobinary section Ni₃Al-Ni₃Ti of the ternary Ni-Al-Ti system has been investigated by ther-mal analysis and Knudsen effusion mass spectrometry. The solidus of the pseudobinary section and the thermodynamic activities of Ni and Al have been determined in the alloys Ni_0.75A1_0.25-xTi_x of the compositionsx = 0.00 to 0.21. Moreover, the thermodynamic activities of Ni and Ti in Ni₃Ti (x = 0.25) as well as the Gibbs energy of mixing of the Ni_0.75Ti_0.25 phase resulted. The ionization cross-sectional ratio Σ(Ni)/Σ(Ti) = 0.77 has been evaluated for the electron impact energy of 50 eV.     

Hydrides based on phases in the Ti2Ni-Zr2Ni section of the Ti-Ni-Zr system

A study has been made on the interaction of hydrogen with a phase based on the intermetallide Zr₂Ni and with the ternary Laves phase occurring in the Ti-Ni-Zr system in the temperature range between room temperature and 700°C. The Laves phase and the phase based on Zr₂Ni form two hydrides: a low-temperature unstable one, which decomposes in air, and a high-temperature one that gives up hydrogen on heating above 400°C. The hydrogen capacities of the two phases can be used to store hydrogen.Materials Science Institute, Ukrainian National Academy of Sciences, Kiev. Translated from Poroshkovaya Metallurgiya, Nos. 1/2(377), pp. 81–84, January–February, 1995.     

Mechanical twinning in Ti50Ni47Fe3 and Ti49Ni51 alloys

Pseudo-twinning and mechanical twinning have been observed in a transmission electron microscopy study of Ti₅₀Ni₄₇Fe₃, and Ti₄₉Ni₅₁ alloys which have the B2(CsCl) structure. Observation of twinning in ordered alloys is rare and this is the first observation of twinning reported in a B2 structure. The twin planes are the {112} and {114} planes. For {112} pseudo-twins, the composition plane is not the twin plane and the pseudo-twin does not have the B2 structure. For {114} mechanical twins, the composition plane is the twin plane and the twin does have the B2 structure. It is shown that a shear on the {114} plane plus a shuffle of the atoms results in the ordered B2 structure in the twinned region.     

Phase transformations in Ti2Ni3 precipitates

The morphology and crystallography of transformation products of Ti₂Ni₃ in an aged Ti-52.0 at. pct Ni alloy have been studied by means of optical and electron microscopy and electron diffraction. Band-shaped surface relief was observed in optical micrographs at room temperature. Needle and antiphase-like domains were observed in electron micrographs at room temperature. The former correspond to the band-shaped relief seen in optical micrographs. The crystal structure of Ti₂Ni₃ at room temperature was confirmed to be monoclinic by electron diffraction. The needle-like domains and matrix are twin-related with respect to the {120} plane of the monoclinic structure. Upon heating, first the needle-like domains (low temperature phase) shrank and disappeared at about 50 °C, and then the antiphase-like domains (intermediate phase) disappeared at about 100 °C. Upon subsequent cooling, antiphase-like domains appeared and then needle-like domains appeared. These transformations are reversible upon thermal cycling. The antiphase-like domains in the intermediate phase disappeared with the growth of the needle-like domains and new antiphase-like domains appeared within the needles. The sequence of transformation events in the Ti₂Ni₃ phase was deduced by electron microscopy and diffraction to be as follows: parent phase (tetragonal) → intermediate phase characterized by antiphase-like domain morphology (orthorhombic) → low temperature phase characterized by needle-like domain morphology (monoclinic). In spite of some differences in crystallographic and morphological changes, the above phenomena are much like theR-phase transition associated with CDW’s in TiNiFe alloys. Formerly with the University of Illinois.     

Atomic ordering in Ni3Mn-Ni3Ti microcrystalline alloys

Neutron diffraction is used to determine the concentration dependences of the long-and short-range order parameters and the antiphase-domain size in Ni₃Mn-Ni₃Ti microcrystalline alloys produced by melt quenching and the initial bulk alloys quenched from 1433 K. The dependences of the order parameters on the order-disorder transition temperatures are determined. Microcrystals of the γ’ phase are found to have a high long-range order parameter as compared to this parameter in the bulk alloys. This fact is explained by the high degree of supersaturation of a solid solution with excess vacancies formed during melt quenching and, hence, a sharp increase in the atomic diffusion mobility.     

The B2 To R Transformation in Ti50Ni47Fe3 and Ti49.5Ni50.5 alloys

In near equiatomic NiTi alloys, selected area electron diffraction patterns, obtained by high-angle-tilting, cold-stage experiments, have been used to determine the unit cell dimensions of the R phase and the orientation relationship between the parent B2 and product R phase. Convergent beam electron diffraction patterns establish the point group of the R phase to be 3̄m and hence of rhombohedral symmetry as has been postulated by other investigators. Differential scanning calorimetry shows the B2 to R transformation to be a first-order phase transformation with an enthalpy of transformation of 3.75 J/g.     

An X-ray diffraction study of the oxidation of Ni3Ti

Conclusions A layer-by-layer x-ray diffraction phase analysis was made of the scale formed on Ni₃Ti during atmospheric oxidation over the temperature range 600–1000°C. The scale was found to contain the oxides NiO, NiO · TiO₂, TiO₂ (rutile), Ti₃O₅, and Ti₂O₃ as well as two nickel phases — pure nickel and a nickel solid solution. The pattern of distribution of these phase constituents in consecutive scale layers is outlined.Translated from Poroshkovaya Metallurgiya, No. 5 (137), pp. 57–62, May, 1974.     

Sulfur segregation to grain boundaries in Ni3Al and Ni3(AI,Ti) alloys

The segregation of S to grain boundaries in Ni₃Al and Ni₃(Al, Ti) has been studied using Auger electron spectroscopy. The S concentration at the grain boundaries decreases more slowly with increasing temperature than would be predicted by segregation models based on a single solute binding energy to the grain boundaries. This behavior, which can be interpreted as an increase in the effective solute binding energy for a grain boundary as a function of temperature, is consistent with predictions of a model based on the existence of a spectrum of solute binding energies for grain boundaries. Formerly Professor and Head of the Department of Metallurgical Engineering, Michigan Technological University     

Formation of structural intermetallics by reactive metal penetration of Ti and Ni oxides and aluminates

Alumina-aluminum composites can be prepared by reactive metal penetration (RMP) of mullite by aluminum. The process is driven by a strong negative free energy for the reaction (8 +x)Al + 3Al₆Si₂0₁₃ → 13Al₂O₃ + 6Si + xAl. Thermodynamic calculations reveal that titanium oxide, aluminum titanate, nickel oxide, and nickel aluminate all have a negative free energy of reaction with aluminum from 298 to 1800 K, indicating that it may be possible to form alumina-intermetallic composites by reactions of the type (2 +x)Al + (3/y) MO_y → Al₂O₃ + Al_xM_3/y. Experiments revealed that aluminum reacts with titanium oxide, nickel oxide, and nickel aluminate, but not aluminum titanate, at 1673 K. Reaction with the stoichiometric amount of aluminum (x = 0) leads to the formation of alumina and either titanium or nickel. In some cases, reactions with excess aluminum (x > 0) produce intermetallic compounds such as TiAl₃ and NiAl. This article is based on a presentation made in the “In Situ Reactions for Synthesis of Composites, Ceramics, and Intermetallics” symposium, held February 12–16, 1995, at the TMS Annual Meeting in Las Vegas, Nevada, under the auspices of SMD and ASM-MSD (the ASM/TMS Composites and TMS Powder Materials Committees).     

Strengthening and ductilization of Ni3Si by the addition of Ti elements

The mechanical properties of Ni₃Si polycrystals alloyed with Ti and doped with boron were investigated by compressive and tensile tests. The yield stress increased with increasing Ti concentration and with decreasing Ni concentration at all testing temperatures. The peak temperature in the yield stress increased with increasing Ti concentration. The activation energy for the thermal stress term producing the positive temperature dependence decreased with increasing Ti concentration and was correlated with the phase stability of L1₂(Ni₃Si) relative to D0₂₄(Ni₃Ti). Ductility was obtained by the addition of Ti. Higher elongation values were observed in the alloys consisting of higher Ti concentration and higher Ni concentration. Further improvement of the tensile elongation was found by the addition of a small amount of boron. The variation of the elongation with temperature showed a peak at intermediate temperature. The elongation behavior correlated well with the variation of the fracture patterns. The ductilization of the Ni₃Si observed in this work verified the alloying method to improve the grain boundary cohesion of L1₂ type ordered alloys which has been proposed by the present authors.     

The precipitation sequence of Ni3Ti in Co-free maraging steel

TEM, microdiffraction, and X-ray microanalysis were used to study the precipitation processes in Co-free maraging steel. Austenite crystals were found to nucleate in the martensite matrix as the first step in the precipitation sequence of Ni₃Ti. The austenite reversion is a result of Ni segregation. Ni₃Ti nucleates in the austenite. The shape and orientation of Ni₃Ti is determined by the austenite precursor. The same sequence occurs for heterogeneous nucleation on dislocations and grain boundaries. At the later stages of growth Mo is incorporated in the Ni₃Ti lattice.     

石墨/Ni+Ti体系润湿性研究

陶瓷/金属润湿性研究对于陶瓷-金属连接以及金属陶瓷复合材料的制取有重要意义。采用座滴法研究了石墨/Ni+Ti体系的润湿性。测定了不同成分的焊料与石墨基体的接触角,并研究了界面结构和成分。1340℃时,在真空中石墨/Ni平衡接触角为78°,保温时间对接触角没有显著影响。添加剂Ti的质量分数达到40%后,能显著改善润湿性,在这种情况下,接触角随保温时间延长而减小。润湿界面存在明显的元素互扩散现象。     

Microstructural observations of pressure cast Ni3Al/Al2O3 and Ni/Al2O3 composites

Pressure castings of Ni₃Al(IC218)/Al₂O₃ and Ni/Al₂O₃ composites, made with continuous DuPont FP α-Al₂O₃ and DuPont PRD166 α-Al₂O₃+20 wt pct partially stabilized ZrO₂ 20 μm diameter fibers, were examined by optical, scanning electron microscope (SEM), and transmission electron microscope (TEM) techniques. According to optical magnifications, excellent infiltration took place. However, in SEM and TEM magnifications, small gaps were found adjacent to regions where bonding had taken place between fibers. On the basis of available evidence, the gap formation was attributed to trapped gases and microshrinkage. Titanium was added to the metal to promote infiltration. Diffusion of Ti into the fibers of the Ni/Al₂O₃ composites occurred, but similar diffusion into the fibers of the IC218/Al₂O₃ composites did not take place. The qualitatively higher bond strength of the interfaces of the Ni/Al₂O₃ composites was ascribed to the diffusion of Ti into Al₂O₃. No interface reaction layer was found in any of the composites. Very little grain growth was found to take place in either the FP or PRD 166 fibers after casting and after a subsequent ten day anneal at 1150 °C.     

Ti2AlNb合金金相试样的制备方法

介绍了Ti2AlNb合金金相试样的制备方法,并描述了试样制备过程中研磨、抛光、浸蚀的技巧和辅材的选择方法。实验结果表明：在抛光过程中采用短绒毛的平绒织物和超细纤维眼镜布,并配合使用合适粒度的加有洗洁精的Cr2O3,抛光液进行粗抛和精抛,可快速制备高质量的金相试样;采用合适浓度的化学腐蚀液氢氟酸＋硝酸或氢氟酸＋过氧化氢溶液进行浸蚀后,可获得晶界轮廓清晰的加工态组织（口单相组织）或清晰的热处理组织（晶内的网篮组织和魏氏组织）。