A phase-field study of the aluminizing of nickel

A quantitative phase-field approach for multiphase systems that is based upon CALPHAD free energies is used to model the aluminization of nickel wires, wherein vapour-phase alloying is used to deposit Al on the surface of the Ni wire and then the wire is annealed so that to remove all Al gradients and achieve a homogenous Ni-Al alloy. Both processes are modelled and numerical results are compared with experiments. It is found that the kinetics of both processes is controlled by bulk diffusion. During aluminization at 1273 K, formation and growth of intermetallics, Ni₂Al₃ NiAl and Ni₃Al, are strongly dependent on the Al content in the vapour phase. Ni₂Al₃ growth is very fast compared with NiAl and Ni₃Al. It is also found that an intermediate Al content in the vapour phase is preferable for aluminization, since the Ni₂Al₃ coating thickness is difficult to control. Ni₂Al₃ is found to disappear in a few minutes during homogenization at 1373 K. Thereafter, the NiAl phase, in which the composition is highly non-uniform after aluminization, continues growing until the supersaturation in this phase vanishes. Then, NiAl coating disappears concomitantly with the growth of Ni₃Al, which disappears thereafter. Finally, the Al concentration profile in Ni(Al) homogenizes.     

A study on the orientation inheritance in laminated NiAl produced by in situ reaction annealing

In order to promote the performance of B2 NiAl by texture control of orientation during in situ processing, phase transformation in laminated NiAl with bimodal grain size distribution manufactured by reaction annealing of Ni and Al foils has been studied. It turned out that there existed a Kurdjumov–Sachs orientation relationship (K–S OR) between parent Ni and product NiAl by crystallography analysis according to the electron backscatter diffraction (EBSD) results. The parent Ni did not transform to the product NiAl directly but via the formation of Ni₃Al firstly according to the transmission electron microscope (TEM) observation of the interface. This led to a new K–S OR between Ni₃Al and NiAl with a small atomic misfit, which made less residual stress generated through the formation of Ni₃Al than directly from the parent Ni.     

Epitaxial alloyed films out of the bulk stability domain: Surface structure and composition of Ni3Al and NiAl films on a stepped Ni(1 1 1) surface

We have studied by Spot Profile Analysis Low Energy Electron Diffraction (SPA-LEED) and Auger Electron Spectroscopy (AES) Ni–Al alloyed layers formed by annealing, around 780 K, Al deposits on a stepped Ni(1 1 1) surface. The surface structure and composition of the thin epitaxial Ni₃Al and NiAl films, obtained respectively below and above a critical Al initial coverage θ_c, differ markedly from those of corresponding bulk alloys.The Ni₃Al ordered films form in a concentration range larger than the stability domain of the L1₂ Ni₃Al phase. The NiAl films present a marked distortion with respect to the lattice unit cell of the B2 NiAl phase, which slowly decreases when the film thickness increases.It also appears that the value of θ_c depends on the morphology of the Ni(1 1 1) substrate, increasing from θ_c = 4.5 ML for a flat surface to θ_c = 10 ML for a surface with a miscut of 0.4°. This could be directly related to the presence of steps, which favour Ni–Al interdiffusion.     

Distinctive features of the phase composition and structure of the intermetallic compound Ni3Al obtained by self-propagating high-temperature synthesis under pressure

Using x-ray structure analysis and scanning electron microscopy, we studied the phase composition and structure of the intermetallic compound Ni₃Al obtained by self-propagating high-temperature synthesis (SHS) under pressure. We determined experimentally that the structure of the SHS intermetallic compound is similar to the structure the cast intermetallic compound in regard to integrated characteristics. The phase composition of the stoichiometric material is represented by Ni₃Al phases, microinclusions of NiAl phases, and solid solutions of aluminum in nickel.Institute of Strength Physics and Materials Science, Siberian Branch, Russian Academy of Sciences. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 10, pp. 76–80, October, 1995.     

Structure and mechanical properties of intermetallic magnetron-sputtered coating based on the Ni-Al system

The intermetallic coating phase composition, fine structure, and surface morphology have been investigated by electron microscopy and X-ray diffraction. It is shown that Ni₃Al is the primary phase in the intermetallic coating for all samples studied. The NiAl and AlFe₃C phases are present in small amounts. It is established that ion beam treatment of the coating changes its structural characteristics and radically transforms the character of coating wear.     

Electron microscopic study on interfacial characterization of electroless Ni-W-P plating on aluminium alloy

The interface between electroless plating Ni-W-P deposit and aluminium alloy (Al) matrix at different temperature heated for 1 h was studied using transmission electron microscope. The results show that the interface between as-deposited Ni-W-P deposit and Al matrix is clear. There are no crack and cavity. The bonding of Ni-W-P deposit and Al matrix is in good condition. The Ni-W-P plating is nanocrystalline phase (5-6 nm) in diameter. After being heated at 200 °C for 1 h, the interface of Ni-W-P deposit and Al matrix is clear, without the appearance of the diffusion layer. There exist a diffusion layer and educts of intermetallic compounds of nickle and aluminium such as Al₃Ni, Al₃Ni₂, NiAl, Ni₅Al₃ and so on between Ni-W-P deposit and Al matrix after being heated at 400 °C for 1 h.     

Phase transitions in films prepared from Alnico-type alloys

Phase transitions taking place in films of an alloy based on Fe-Ni-Co-Al-Cu (YuDNK-24) as a result of a thermomagnetic treatment and which lead to a high coercivity state have been investigated. In this state, three phases are detected in the films: a phase with a bcc lattice, and a phase with a fcc lattice, and a phase based on the compound NiAl (or Ni₃Al).     

Surface energy of ordered NiAl and Ni3Al alloys

The surface energies of NiAl alloy with the B2 structure and Ni₃Al alloy with the L1₂ structure for the (100), (110) and (111) faces are calculated by the model electron density functional method. The anisotropy of the surface energy of the alloys is compared with the anisotropy of of the pure metals. It is shown that the value of of NiAl and Ni₃Al is determined by the thermodynamic properties of the alloy and agrees well with the values obtained using Miedema's semiempirical formula.Institute of Physics of Strength and Study of Materials, Russian Academy of Sciences, Siberian Division. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 10, pp. 80–86, October, 1994.     

Adsorption of methanol on Ni3Al(1 1 1) and NiAl(1 1 0): A high resolution PES study

The adsorption of methanol on Ni₃Al(1 1 1) and NiAl(1 1 0) has been studied using high resolution photoemission spectroscopy (HR-PES) and density functional theory (DFT). Both methanol and methoxy are formed on these surfaces after the initial methanol exposure at low temperatures. Heating to 200 K leads to further formation of methoxy. On NiAl(1 1 0) two different methoxy species are observed where the first is formed upon methanol adsorption, and the other results from methanol decomposition during heating. The DFT calculations show that methanol and methoxy interacts with the Al atoms on both surfaces. Methanol is found to bond through the oxygen atom to the Al on-top site on Ni₃Al(1 1 1) and NiAl(1 1 0) with the C–O axis tilted with respect to the surface normal. On Ni₃Al(1 1 1) methoxy is situated in a 2Ni+Al hollow site, whereas on NiAl(1 1 0) the Al–Al bridge site is preferred.     

Growth of Ni-Al alloys on Ni(1 1 1), from Al deposits of various thicknesses: (II) Formation of NiAl over a Ni3Al interfacial layer

This paper describes the second part of a study devoted to the growth of thin Ni-Al alloys after deposition of Al on Ni(1 1 1). In the previous paper [S. Le Pévédic, D. Schmaus, C. Cohen, Surf. Sci. 600 (2006) 565] we have described the results obtained for ultra-thin Al deposits, leading, after annealing at 750 K, to an epitaxial layer of Ni₃Al(1 1 1). In the present paper we show that this regime is only observed for Al deposits smaller than 8 × 10¹⁵ Al/cm² and we describe the results obtained for Al deposits exceeding this critical thickness, up to 200 × 10¹⁵ Al/cm². Al deposition was performed at low temperature (around 130 K) and the alloying process was followed in situ during subsequent annealing, by Auger electron spectroscopy, low energy electron diffraction and ion beam analysis-channeling measurements, in an ultra-high vacuum chamber connected to a Van de Graaff accelerator. We evidence the formation, after annealing at 750 K, of a crystallographically and chemically well-ordered NiAl(1 1 0) layer (whose thickness depends on the deposited Al amount), over a Ni₃Al “interfacial” layer (whose thickness—about 18 (1 1 1) planes—is independent of the deposited Al amount). The NiAl overlayer is composed of three variants, at 120° from each other in the surface plane, in relation with the respective symmetries of NiAl(1 1 0) and Ni₃Al(1 1 1). The NiAl layer is relaxed (the lattice parameters of cc-B2 NiAl and fcc-L1₂ Ni₃Al differ markedly), and we have determined its epitaxial relationship. In the case of the thickest alloyed layer formed the results concerning the structure of the NiAl layer have been confirmed and refined by ex situ X-ray diffraction and information on its grain size has been obtained by ex situ Atomic Force Microscopy. The kinetics of the alloying process is complex. It corresponds to an heterogeneous growth leading, above the thin Ni₃Al interfacial layer, to a mixture of Al and NiAl over the whole Al film, up to the surface. The atomic diffusion is very limited in the NiAl phase that forms, and thus the progressive enrichment in Ni of the Al film, i.e. of the mean Ni concentration, becomes slower and slower. As a consequence, alloying is observed to take place in a very broad temperature range between 300 K and 700 K. For annealing temperatures above 800 K, the alloyed layer is decomposed, Al atoms diffusing in the bulk of the substrate.     

二元Ni-Al合金极端条件下的弹性和热力学性能：全电子准谐波近似 cited: 1)

通过在原子尺度上建模来研究Al、NiAl和Ni₃Al合金在极端高温和高压下的点阵常数、弹性常数、弹性模量、泊松比和弹性各向异性因子等性质．计算得到的弹性常数均满足相应的力学稳定条件．由于NiAl和Ni₃Al具有较高的B=G值,在0～30 GPa内都属于延展性材料．通过包含电子热运动对体系吉布斯自由能贡献的全电子准谐近似方法,得到了高温高压下Al、NiAl和Ni₃Al合金的热膨胀系数、体积模量、热容和熵等．计算值与已有的实验值和理论值符合较好     

Effect of alloying and temperature of deformation on the grain structure and phase composition of Ni3Al intermetallic

The structure of Ni₃Al intermetallic alloyed with boron and hafnium is studied at various temperatures of deformation by means of diffraction and scan electron microscopy. The alloy was produced through self-propagating synthesis. The phase composition of the alloy is determined. The effect of doping with boron and hafnium on the alloy structure morphology is revealed.     

MICROSTRUCTURE AT THE INTERFACE OF TITANIUM CARBIDE AND NICKEL ALUMINIDES

Microstructure at the interface of titanium carbide and nickel aluminides in the samples obtained by infiltration of molten Ni₃Al alloy has studied by a scanning electron microscopy (SEM) and an analytical transmission electron microscopy (ATEM) with an energy dispersive spectrometer (EDS). It is found that the morphology at the interfaces between hard phase skeleton of TiC_0.7 and metallic phases depends on the ratio of Ti/C in carbide. Some periodic zigzag fringes are observed at a smooth interface between metallic phase and carbides in the sample of Ni₃Al/TiC_0.7. The results of analysis using EDS show that Ti in TiC_0.7 carbide is easier than that in TiC_0.7 to dissolve into the molten alloy during solid-liquid reaction. The formation of this periodic zigzag fringe,which may be a growth zone of a new Ti-Ni-Al phase,in the interface of TiC_0.7/Ni₃Al would occur during the initial stage of solidification.     

Growth of Ni-Al alloys on Ni(1 1 1): (I) Formation of epitaxial Ni3Al from ultra-thin Al deposits

In this paper we describe the alloying process of ultra-thin Al layers (below 8 × 10¹⁵ Al/cm²) deposited on Ni(1 1 1). For this purpose Auger electron spectroscopy, low energy electron diffraction, and ion beam analysis-channelling measurements have been performed in situ in an ultra-high vacuum chamber. Al deposits formed at low temperature (about 130 K) are strained defective crystalline layers retaining the substrate orientation. Alloying takes place, with very progressive Ni enrichment, in a very broad temperature range between 250 K and 570 K. This feature shows that diffusion of the alloy species is more and more difficult when the Ni concentration increases. At 570 K a crystallographically and chemically ordered Ni₃Al phase is formed, and its order continuously improves upon annealing, up to 750 K. We have shown by ion beam methods that this alloy is three-dimensional, extending up to 16 (1 1 1) planes for the thickest deposits. The Ni₃Al phase can also be obtained directly by Al deposition at 750 K, but its crystalline quality is lower and the layer is probably formed of grains elongated along 〈1 1 −2〉 directions. The Al content of the thin Ni₃Al layers formed mostly dissolves in the bulk above 800 K. However a small amount of Al remains segregated at the Ni crystal surface.     

Crystallization behaviour in a new multicomponent Ti16.6Zr16.6Hf16.6Ni20Cu20Al10 metallic glass developed by the equiatomic substitution technique

A new amorphous Ti_16.6Zr_16.6Hf_16.6Ni₂₀Cu₂₀A1₁₀ alloy has been developed using the novel equiatomic substitution technique. Melt spinning Ti_16.6Zr_16.6Hf_16.6Ni₂₀Cu₂₀A1₁₀ forms an amorphous phase with a large supercooled liquid region, ΔT=70°C. After isothermal annealing within the supercooled liquid region for 3 h at 470°C, the amorphous alloy crystallizes to form a fine-scale distribution of 2–5 nm nanocrystals, and the supercooled liquid region increases to ΔT=108°C. Atomic-scale compositional analysis of this partially crystalline material using a three-dimensional atom probe (3DAP) is unable to detect any compositional difference between the nanocrystals and the remaining amorphous phase. After annealing for 1 hr at 620°C, the amorphous alloy crystallizes to form 20–50nm equiaxed grains of a hexagonal-type C14 Laves phase with lattice parameters a = 5.2Å and c = 9.0 Å. 3DAP analysis shows that this Laves phase has a composition very close to that of the initial amorphous phase, suggesting that the alloy crystallizes via a polymorphic rather than a primary crystallization mechanism, despite the complexity of the alloy composition.     

Diffusion research between Ni3Al coating and titanium alloy produced by plasma spraying process

A Ni₃Al coating was prepared by plasma spraying technique on the surface of titanium alloy. Ni-Al mixed powders, coatings and reaction products were investigated by scanning electron microscope, EDS, DSC and XRD. A tight bonding between the coating and the substrate was formed. The X-ray diffraction analysis of the patterns showed that the coating not only had Ni₃Al phase, but also had NiO and Al₂O₃ phase microcontent. Comparing Ni coated Al to Ni₃Al at 900 °C, the diffusion was stronger and the diffusion layer was thicker. A minute pore structure was formed at 1200 °C in the front edge of solid-state reaction layer. So Ni₃Al restrained the solid-state reaction of the coating with the substrate, and as a whole weakened the entry of oxygen atoms into the substrate and quenched the out-diffusion of titanium.     

用磁分析法观察某些铁-镍-铝合金的脱溶过程

用热磁分析方法较仔细地观测了Fe-Ni-Al三元系合金沿β+β′两相区内某一结线上的几个不同成分的合金样品。淬火所得的成分接近Fe₂NiAl的过饱和固溶体在较高温度(～850℃)分解甚快,在一分钟内脱溶基本上完成。在850℃分出的β′相还含铁约35at.％,其居里点在400℃附近。在850℃经短时间回火继以水淬的合金,在600—700℃再经适当的回火,则首次回火所生成的β′相继续迅速分解,在不超过十分钟内损失大量的铁而变成非铁磁性的;其在室温的H_c可增到500奥斯特。这和Б.Г.Лившнц所提出的“继续脱溶”的假设相符。磁性观测的结果证明:β′相的继续脱溶是“可逆的”,就是说,把曾在600—700℃回火的合金重热至850℃时β′相能在几分钟内恢复850℃的平衡成分。Fe₂NiAl过饱和固溶体在较低温度(70O℃以下)分解极慢,并且其过程是明显地“不均匀”的。因此,这种合金不能通过高温淬火继以较低温度(600—700℃)回火的处理来获得高H_c的事实可以用单畴粒子的理论加以解释。     

Precipitation and fracture behaviour of Fe–Mn–Ni–Al alloys

The effects of Al addition on the precipitation and fracture behaviour of Fe–Mn–Ni alloys were investigated. With the increasing of Al concentration, the matrix and grain boundary precipitates changed from L1₀ θ-MnNi to B2 Ni₂MnAl phase, which is coherent and in cube-to-cube orientation relationship with the α′-matrix. Due to the suppression of the θ-MnNi precipitates at prior austenite grain boundaries (PAGBs), the fracture mode changed from intergranular to transgranular cleavage fracture. Further addition of Al resulted in the discontinuous growth of Ni₂MnAl precipitates in the alloy containing 4.2?wt.% Al and fracture occurred by void growth and coalescence, i.e. by ductile dimple rupture. The transition of the fracture behaviour of the Fe–Mn–Ni–Al alloys is discussed in relation to the conversion of the precipitates and their discontinuous precipitation behaviour at PAGBs.     

Modifying the structural phase state of fine-grained titanium under conditions of ion irradiation

The results from quantitative investigations into the structural phase state of finely dispersed titanium before and after implantation with aluminum ions are presented. Two types of ??-Ti grains differing by phase composition, defect structure, and size are distinguished in the structure: fine grains in the range of 0.1?C0.5 ??m and coarse grains in the range of 0.5?C5 ??m. The presence of two types of TiO₂ particles in the material, i.e., rounded particles found at dislocations in the bulk of the ??-Ti grains and lamellar particles found only inside coarse ??-Ti grains, is established. The formation of the Ti₃Al phase is observed in the form of lamellar inclusions along the grain boundaries and rounded particles in triple joints. It is found that the particles of the TiAl₃ phase are isolated with a smaller volume fraction than the Ti₃Al phase; they are localized along the boundaries of coarse grains of the titanium matrix. It is established that the granular state and defect structure of the material change substantially after ion irradiation; i.e., the dislocation density and the fields of internal stresses in fine grains grow considerably, relative to the initial state of titanium.     

Growth of thin, crystalline oxide, nitride and oxynitride films on metal and metal alloy surfaces

This paper reviews the current knowledge of the properties of ultrathin, well-ordered oxide, nitride and oxynitride films grown on metal and metal alloy surfaces. Different modes of preparation are discussed and the vibrational and structural properties are summarized. The focus will be put onto Al-oxides grown on surfaces of the intermetallic alloys NiAl, Ni₃Al and FeAl. The properties of Ga₂O₃ grown on surfaces of the intermetallic alloy CoGa are also described. In these cases Al- and Ga-atoms, respectively, segregate from the substrate and react with adsorbed oxygen. The grown Al- and Ga-oxide films, respectively, order at elevated temperatures. Systems are also discussed where Al-oxide is grown by oxidation of Al-atoms which are evaporated on surfaces of the transition metals Re and Ru. The growth of transition metal oxides CoO (1 1 1)/Co (0 0 0 1), CoO (1 0 0)/Co (1 1 2 0), NiO (1 0 0)/Ni (1 0 0), NiO/Ni (1 1 1) and Cr₂O₃/Cr (1 1 0) are also presented. Thin films of Al- and Ga-nitride, respectively, can be grown on the base of the intermetallic alloy NiAl and CoGa by low-temperature adsorption of ammonia. These nitride films order at elevated temperatures. Al- and Ga-oxynitride, respectively, can be grown on surfaces of NiAl and CoGa substrates by adsorption on nitric oxide. An ordering of these ultrathin oxynitride layers is observed at elevated temperatures.