Ni3AI–Ni3Cr–Ni3Ta section of Ni–Cr–AI– Ta system

Abstract

The constitution of the 75 at.%Ni section of the Ni–Cr–Al– Ta system has been determined at 1523 and 1273 K. Alloys annealed at these temperatures have been studied using electron probe microanalysis and X–ray diffraction, and their microstructures and associated hardness values have also been examined. The isothermal sections at 1523 and 1273 K contain the following phases: γ+γ′+Ni₃Ta, and Ni₆TaAI, with the following three–phase equilibria between them: γ+γ′+Ni₆TaAI and γ+Ni₃Ta+Ni₆TaAl. The γ′–phase contains up to ~9 at.–%Ta. Some observations on as–cast structures have also been made.

MST/208     

Sputter deposited nanocrystalline Ni-25Al alloy thin films and Ni/Ni3Al multilayers

Thin films of nominal composition Ni-25at%Al have been sputter deposited from a target of the intermetallic compound Ni₃Al at different substrate deposition temperatures. The film deposited on an unheated substrate exhibited a strongly textured columnar growth morphology and consisted of a mixture of metastable phases. Nanoindentation studies carried out on this film exhibited a strong strain hardening tendency. In contrast, the film deposited at 200 °C exhibited a recrystallized non-textured microstructure consisting of grains of a partially ordered Ni₃Al phase. At higher deposition temperatures (∼400 °C), larger grains of the bulk equilibrium, long-range ordered, Ll₂ Ni₃Al phase were observed in the film. Unlike the film deposited on an unheated substrate, the films deposited at elevated temperatures did not exhibit any dependence of the hardness on the indentation depth and, consequently no strain hardening. The average hardness of the film deposited at 200 °C was higher than the one deposited at 400 °C. In addition to monolithic Ni-25Al thin films, multilayered Ni/Ni3Al thin films were also deposited. Multilayers deposited non-epitaxially on unheated substrates exhibited a strong {111} fiber texture while those deposited epitaxially on (001) NaCl exhibited a {001} texture. Free-standing multilayers of both types of preferred orientations as well as of different layer thicknesses were deformed in tension untill fracture. Interestingly, the {111} oriented multilayers failed primarily by a brittle fracture while the {001} multilayers exhibited features of ductile fracture.     

Structure of vacuum-deposited thick films of NiCrAl

Vacuum-deposited thick films for resistors of low sheet resistance cannot be investigated by electron optical techniques because of their thickness. For the X-ray investigation of the structure of NiCrAl films it was necessary to produce very thick films by vapour deposition in a step-by-step manner. These films were deposited at a substrate temperature of 250 °C and subsequently tempered under a high vacuum for 30 min at 300, 400, 500 and 700 °C. It was found that these very thick as-deposited films are amorphous while reflections of the phases Ni₃Al, NiAl and chromium became visible with increasing annealing temperature.Thus the structure of these thick films corresponds to that found by electron optical techniques for thin films of the same composition.     

Investigation on powder metallurgy Cr–Si–Ta–Al alloy target for high-resistance thin film resistors with low temperature coefficient of resistance

The sputtering target for high-resistance thin film resistors plays a decisive role in temperature coefficient of resistance (TCR). Silicon-rich chromium (Cr)–silicon (Si) target was designed and smelted for high-resistance thin film resistors with low TCR. Valve metal tantalum (Ta) and aluminum (Al) were introduced to the Cr–Si target to improve the performance of the target prepared. The measures for grain refining in smelting Cr–Si–Ta–Al target were taken to improve the performance of the prepared target. The mechanism and role of grain refinement were discussed in the paper. The phase structure of the prepared target was detected by X-ray diffraction (XRD). Rate of temperature drop was studied to reduce the internal stress of alloy target and conquer the easy cracking disadvantage of silicon-rich target. The electrical properties of sputtered thin film resistors were tested to evaluate the performance of the prepared target indirectly.     

溅射功率对TaN薄膜电阻电性能的影响

本文利用直流反应磁控溅射技术,通过调节溅射功率于200℃、3％的氮分压条件在Al2O3基片上沉积了一系列TaN薄膜,并使用光刻工艺制备出相应的TaN薄膜电阻,研究了溅射功率对TaN薄膜电阻率、电阻温度系数（TCR）和功率容量的影响。实验结果表明：当溅射功率从200W增大到1000W,TaN薄膜电阻率逐渐减小,TCR绝对值从几百ppm／℃降为几十ppm／℃,功率容量呈现逐渐增大趋势。     

A high-resolution-electron-microscopy study of γ/γ′-α directionally solidified eutectic alloy

A master alloy with eutectic compositions of Ni-30.26Mo-6.08Al-1.43 V (wt%) has been directionally solidified (DS) into γ/γ′-α alloy. The microstructural as-ageing treatment was studied by means of high resolution electron microscopy (HREM). A majority of α fibres still display the Bain orientation relationship with the γ′/γ matrix. In a few cases, however, the so-called Nishiyama-Wasserman (NW) orientation relationship is found in specimens aged at 850 °C for 2000 h. Different microdomain structures of the γ phase, corresponding to different ageing temperatures, were revealed. Orthorhombic Ni₃Mo phase, with a size of tens of nanometres, was found to precipitate inside α fibres after ageing at both 850 and 650 °C. Occasionally, an γ′-Ni₃Al phase with lamellar twin structure was also found to coexist with Ni₃Mo precipitate inside the α fibres. The orientation relationships between the precipitates and the α fibres were determined. Energy dispersive X-ray analysis (EDX) showed that the precipitation of Ni₃Mo and Ni₃Al is due to solid solution of Ni and Al in the α fibres.     

Electrical and structural properties of NiCr thin film resistors reactively sputtered in O2

NiCr thin film resistors have been reactively sputtered using a d.c. diode system in which the anode is formed by a carousel. The substrates are mounted on this carousel and can be rotated through the discharge. For films deposited onto a stationary carousel (the substrates permanently fixed in the discharge), film resistivities range from 150 to 300 μΩ as the oxygen partial pressure is increased from the base pressure to 3 × 10^-5 torr. The TCR values range from 150 to 300 ppm/°C. For carousel rotation at 20 rev/min the corresponding resistivities may be increased by a factor as large as 20 without greatly affecting the TCR. Microprobe analysis indicates that the Ni/Cr concentration ratio is independent of the deposition conditions, but that for a given oxygen partial pressure the film density is less for films deposited onto a rotating carousel than for films deposited onto a stationary carousel. Transmission electron microscopy indicates that the crystallographic structure consists of a metallic phase and an oxide phase which do not change with carousel rotation, but that films deposited onto a stationary carousel have an island structure while those deposited onto a rotating carousel have a worm-like structure. The structural features of films deposited onto a rotating carousel may be due to oblique incidence effects. Measurements of film resistance at low temperatures indicate that conduction in the film may be considered to consist of a metallic conduction mechanism of positive TCR acting in conjunction with an oxide conduction mechanism of negative TCR, with the relative contribution of each mechanism being a function of the physical microstructure of the films. Heat treatment of films deposited onto a rotating carousel produces an increase in resistance which is attributed to oxidation of the film surface, while heat treatment of films deposited onto a stationary carousel produces a resistance decrease which is attributed to thermal annealing effects dominating surface oxidation effects.     

NiAl formation by annealing of infiltrated aluminium-nickel precursors

Samples fabricated by pressure-infiltration of nickel powders with molten aluminium were heat treated at 1200 °C under vacuum or argon isostatic pressure. Reaction and diffusion in the asinfiltrated samples, which contained nickel, aluminium and varying amounts of Ni₂Al₃ and Al₃Ni, resulted in the formation of NiAl as a principal phase with nickel and Ni₃Al as minor phases. All samples exhibited macroporosity due to the formation of an interconnected transient liquid phase during heat treatment. Vacuum-annealed samples also showed extensive Kirkendall porosity in the nickel phase, which was, however, pore-free in hot isostatically pressed samples due to compaction during reaction. Concentration profiles of aluminium in these nickel regions were measured and are in good agreement with predicted values.     

Electrical characterisation of AlCuMo thin films prepared by DC magnetron sputtering

Thin film resistors have been manufactured to evaluate the electrical performance characteristics of AlCuMo thin films. The films were prepared on Al2O3 substrates at room temperature as a function of Mo concentration by DC magnetron sputtering and were then annealed at various temperatures in air and N2 atmospheres. The effect of annealing temperature on the electrical properties of the films was systematically investigated. Increase in Mo content produced a decrease in temperature coefficient of resistance (TCR), an increase in resistivity (r) and an improvement in long term stability (DV/V) of the films. TCR varied from negative to positive and further improvements in resistance stability of the films were also achieved through increasing annealing temperature in both air and N2 atmospheres. A temperature region is proposed where `near zero? TCR (ppm/8C) and long term stability of better than 0.2% can be realised.     

Two-Phase Coexistence and Multiferroic Properties of Cr-Doped BiFeO3 Thin Films

Pure BiFeO ₃ (BFO) and Cr-doped BiFe _0.97 Cr _0.03 O ₃ (BFCO) thin films were successfully prepared on F-doped SnO ₂ conductive film (FTO)/glass (SnO ₂: F) substrates by a sol–gel method. The effect of Cr doping on the structure, ferroelectric, and ferromagnetic properties of the BFO and BFCO thin films have been investigated. X-ray diffraction, Rietveld refined X-ray diffraction (XRD) patterns, and Raman spectroscopy results clearly reveal that the BFCO thin film is characterized by the coexistence of two phases (trigonal and tetragonal). Moreover, the various leakage mechanisms of both thin films have also been studied. The improved ferroelectricity with remnant polarization (Pr) of about 2Pr = 68.68 μC/cm ² under an applied electric field of 1,181.8 kV/cm and enhanced ferromagnetism with saturation magnetization (M _s) of M _s = 0.93 emu/cm ³ have been observed in the BFCO thin film. The improved electrical properties of the BFCO thin film are ascribed to the coexistence of trigonal and tetragonal phase and high valence of Cr ⁶⁺, and the Fe–O ₆ octahedron distortion is enhanced due to the overlap and hybridization of Fe _3d/Cr _3d and O _2p orbits by Cr doping.     

Experimental determination of nickel-rich corner of Ni–Al–Ta phase diagram

Abstract

Liquid–solid and solid–state phase equilibria have been studied in the Ni–NiAl–Ni₃Ta triangle of the Ni–AI–Ta system, using a combination of several experimental techniques. Five primary phases occur in this region, including the ternary compound, π, Ni₆TaAI, which enters into equilibrium with each of the other four. Another compound, Ni₈Ta, forms in the solid state by decomposition of Ta–rich Ni solid–solutions and occurs in equilibrium with the γ, π, and δ (Ni₃ Ta) phases. The extent of these different phase fields has been determined at 1250°C and particular attention has been paid to the γ-γ′ solvus surface which has been shown to be accurately described by a second–order polynomial function of the atomic concentrations.

MST/321     

Fabrication of Ta3N5-Ag nanocomposite thin films with high resistivity and near-zero temperature coefficient of resistance

In this study, we investigate as-deposited Ta₃N₅-Ag nanocomposite thin films with near-zero temperature coefficients of resistance (TCRs) that are fabricated by a reactive co-sputtering method; these films can be used in thin-film embedded resistors. In these films, the TCR approaches zero due to compensation between Ag (+TCR) and Ta-N (−TCR) at resistivities higher than 0.005 Ω-cm.Taking into account the fact that Ag counterbalances the resistivity of the Ta₃N₅-Ag thin film, we performed reactive co-sputtering at a nitrogen partial pressure of 55%, corresponding to a resistivity of 0.384 Ω-cm. The resistivity and power density changed, respectively, from 1.333 Ω-cm and 0.44 W/cm² for silver to 0.0059 Ω-cm and 0.94 W/cm² for the Ta₃N₅-Ag thin film. A near-zero TCR of + 34 ppm/K was obtained at 0.94 W/cm² in the Ta₃N₅-Ag thin film without heat treatment.     

Aging behaviour of cobalt free chromium containing maraging steels

Abstract

This paper reports an investigation of the aging behaviour of two Co free Cr containing maraging steels (Fe–1·0Si–11·2Cr–1·3Mo–9·1Ni–1·2Al–1·0Ti and Fe–0·8Si–17·2Cr–6·1Ni–0·4Al–0·9Ti, all at.-%), using hardness measurements, electron microscopy of replicas and thin foils, atom probe field ion microscopy (APFIM), and thermochemical calculations. Two different families of intermetallic phases (Ti₆Si₇Ni₁₆G phase and η Ni₃Ti) have been found to contribute to age hardening. The composition and morphology of these precipitates were studied in deformed and undeformed alloys after aging at 420–570°C for various times. In addition, reverted austenite has been found in the aged structure. Results obtained using APFIM are compared with equilibrium thermodynamic calculations and previous APFIM studies of conventional Cr free low Al and Si maraging steels having higher Mo contents.

MST/1558     

Crystallization mechanism of amorphous Ni65Cr16P19 metallic alloys

Two large exothermic reaction peaks at 658 and 690 K are observed in the differential scanning calorimetric (DSC) curve for the amorphous metallic alloy, Ni₆₅Cr₁₆P₁₉. Extensive DSC and X-ray diffractometer measurements were carried out for pre-annealed samples, and it is concluded that the two peaks are due to crystallization of Ni and stable Ni₃P phases, respectively. The expanded lattice constants of these phases can be explained by assuming that a small amount of Cr atoms were dissolved in these crystalline phases. As for the metastable Ni₃P phase, confirmation of its presence by X-ray measurement could not be obtained. These results may be interpreted by considering that the metastable phase appears only in the thin film region of the sample.     

Reaction of Al/Mo thin films

Intermixing and compound formation by means of annealing have been studied for Al/Mo thin films. With annealing at 300° C, only intermixing between aluminium and molybdenum films occurs due to mutual diffusion. With annealing at over 350° C, Al₁₂Mo and AlMo₃ compounds were formed. The electrical resistivity of the film increases with intermixing and compound formation. The electrical resistivity increase is proportional to the annealing time,t ^1/2. In low vacuum annealing, molybdenum oxide film forms on aluminium film. It is assumed that molybdenum atoms diffuse through the aluminium film due to their chemical affinity with oxygen in the atmosphere.     

TaAlN thin film resistors with improved electrical properties

When TaAl films are sputtered in the presence of nitrogen they exhibit a high sheet resistivity of the order of 2000–4000 μΩ cm. To understand their performance as resistive elements, the properties of TaAlN films covering a wide range of aluminium and nitrogen compositions were investigated. The increase in sheet resistivity and the changes in the structure of the film due to increases in the aluminium and nitrogen concentrations were studied. The variation in the temperature coefficient of resistance and the change in resistance for different aging temperatures for films with sheet resistances of 50–100 Ω/? and 600 Ω/? were also studied. The formation voltage limits in anodizing the TaAlN films are presented. The results are compared with data reported by other investigators. We suggest a suitable range of sputtering conditions with reference to the aluminium area in the TaAl target and the nitrogen partial pressure to fabricate thin film resistors of optimum performance for use in hybrid circuits.     

Hardening of ordered γ′-Ni3(Al,Ti) by precipitation of disordered γ

• 1.(1) A uniform solid solution of γ′-L1₂ ordered Ni₃(Al,Ti) supersaturated with disordered γ can be obtained by solution annealing at a suitable temperature.
• 2.(2) The initial shape of γ precipitated from supersaturated γ′ on aging is spherical or round-cubic. The γ precipitates grow into platelets as aging proceeds. The γ-precipitates are completely coherent with the matrix γ′ as long as the γ-precipitates are plates.
• 3.(3) The γ′-L1₂ ordered Ni₃(Al, Ti) hardens appreciably by fine precipitation of disordered γ.

     

Synthesis of Al-Cr-O-N thin films in corundum and f.c.c. structure by reactive r.f. magnetron sputtering

Advanced PVD coatings for metal cutting applications must exhibit a multifunctional property profile including high hardness, chemical inertness and high temperature stability. Recently, ternary Al-Cr-O thin films with mechanical properties similar or superior to conventional aluminium oxide thin films have been suggested as potential materials meeting such demands. These coatings can be deposited at moderate temperatures in PVD processes. In this work, new quaternary Al-Cr-O-N coatings are suggested as alternative for offering thin film materials of high strength, hardness and even toughness. A combinatorial approach to the synthesis of Al-Cr-O-N thin films by means of reactive r.f. magnetron sputtering is presented. A thorough phase analysis of deposited coatings covering a wide range of elemental compositions revealed a well-defined phase transition from a corundum-type α-(Al_1 − x,Cr_x)_2 + δ(O_1 − y,N_y)₃ structure to a CrN-type f.c.c.-(Al_1 − x,Cr_x)_1 + θ(O_1 − y,N_y) structure as a function of the Al/Cr ratio and the nitrogen gas flow ratio. Detailed results on the coatings composition, constitution and microstructure are discussed compared to ternary Al-Cr-O thin films deposited by reactive r.f. magnetron sputtering under nearly identical conditions.     

Pack codeposition of Al and Cr to form diffusion coatings resistant to high temperature oxidation and corrosion for γ-TiAl

Abstract

Thermochemical analyses were carried out for a series of pack powder mixtures formulated for codepositing Al with Cr to form diffusion coatings on γ-TiAl resistant to high temperature oxidation by the pack cementation process. Based on the results obtained, experimental studies were undertaken to identify optimum pack powder mixtures for codepositing Al with Cr to form diffusion coatings with an adherent and coherent coating structure. The results of the thermochemical calculations performed indicated that codeposition of Al and Cr is possible with CrCl₃.6H₂O and AlCl₃ activated pack powders containing elemental Al and Cr as depositing sources. However, experimental results obtained at 1100°C revealed that CrCl₃.6H₂O is not suitable for use as an activator for codepositing Al with Cr on γ-TiAl. It caused a significant degree of degradation indicated by weight losses instead of coating deposition to the substrate. However, adherent coatings with excellent structural integrity consisting of an outer Cr doped TiAl₃ layer containing Al₆₇Cr₈Ti₂₅ phase and an inner layer containing TiAl₃ and TiAl₂ phases were successfully codeposited at 1100°C using pack powder mixtures activated by AlCl₃. It is suggested that such coatings were formed via a sequential deposition mechanism through inward diffusion of aluminium and chromium. Conditions that affect the pack codeposition process, and hence need to be carefully controlled, are discussed in relation to the mechanism of the formation of diffusion coatings with an integral structure free from microcracking on γ-TiAl.     

Study on behavior of NiAl coating with different Ni/Al ratios

β-NiAl coatings with different Ni/Al ratios were deposited on K403 superalloy substrates via magnetron sputtering. The phase transformation and diffusion phenomenon of the NiAl/Ni-based superalloy system after vacuum annealing at 900 and 1000 °C were analyzed using X-Ray diffraction (XRD), field emission scanning electron microscope (FE-SEM) and energy dispersive X-ray spectrometry (EDS). The effect of coating concentrations on the outward diffusion behavior of substrate elements was discussed. The high Cr concentrations in the Al-rich NiAl coatings were caused by the intense interdiffusion between Al and Cr. The Ti, W and Mo partitioned to γ′-Ni₃Al in the coatings. Several possible reasons for the formation of γ′-Ni₃Al at the surface of Ni-rich NiAl coating were identified, including: diffusion behavior of W and Mo in β-NiAl, destabilizing effect of substrate elements on β-NiAl, and diffusion rates of Ni and Al in β-NiAl. The volume change in β ⇛ γ′ transformation process shows Ni uphill diffused to the γ′-Ni₃Al islands at the surface of Ni-rich NiAl coatings. The IDZ (interdiffusion zone) thickness and precipitates in IDZ were related to the Al initial concentrations in the coatings.