Use of fractals and kinetic equations to model thermally induced hillock formation and growth in thin metal films

We investigated the applicability of a model based on fractals and the Smoluchowski kinetic equations to describe hillock formation in thin metal films. We have previously used this model to analyze cluster and ultrafine particle production. We show how to extract two parameters from measured hillock size distributions which may reveal the scaling of the mobility of clusters and vacancies in films with varying hillock size. On the basis of our application of this model to certain data taken from the literature, the model shows considerable potential for being able to provide an internally consistent quantitative basis for monitoring thermally driven mass redistribution processes in metal films.     

Stress formation and relaxation in amorphous Ta–Cr films

In the present paper, measurements of the intrinsic stress of thin amorphous Ta–Cr alloy films made by magnetron sputtering have been carried out. From the curvature of the substrates and by use of the Stoney formula, the stresses were determined. The bombardment of the growing film with energetic particles is shown to control the magnitude and sign of the intrinsic stress. When changing the deposition parameters, compressive or tensile stresses can be generated in the films in a range from about −2 GPa to +1 GPa. Also the stress relaxation, the change in the stress with time, has been studied for various temperatures. The stress relaxation was measured with a cantilever beam technique using a three-terminal capacitance method to detect the beam (substrate) deflection. The stress-relaxation data have been fitted to a mathematical model for stress relaxation related to inhomogeneous flow in amorphous films. This behaviour is expected to occur in the low-temperature, high-stress regime with deformation taking place along localized shear bands.     

Effect of SiO2 passivation overlayers on hillock formation in Al thin films

Hillock formation in Al thin films with varying thicknesses of SiO₂ as a passivation layer was investigated during thermal cycling. Based on the stress measurements and the number of hillocks, 250 nm thick SiO₂ was thick enough to suppress the hillock formation and the suppression of hillock at 250 nm passivation and the lack of suppression at thinner passivation is related to the presence/absence of protection against the diffusive flow of atoms from the surrounding area to the surface due to the biaxial compressive stresses present in the film through the weak spots in the passivation layer. The stress state of Al films measured during annealing (the driving force for hillock formation) did not vary much with SiO₂ thickness. A small number of hillocks formed during the plasma enhanced chemical vapor deposition of SiO₂ overlayers at 300 °C.     

Study of the formation of chromate conversion coatings on Alclad 2024 aluminum alloy using spectroscopic ellipsometry

The influence of pH of a chromate bath on the morphological and chemical properties of a chromate conversion coating, formed on Alclad 2024-T3 aluminum alloy, has been investigated by variable angle spectroscopic ellipsometry in the visible and infra-red regions. Other techniques such as glow discharge optical emission spectroscopy, transmission and scanning electron microscopy, atomic force microscopy and Auger electron spectroscopy have been used in order to confirm and sustain the results obtained with this technique. The combination of different analytical methods showed a decrease in thickness together with changes in the morphology and chemical composition of the chromate film when the pH is increased from 1.2 to 2.4. Although the complexity of the chromate system and the pronounced roughness of commercial rolled aluminum limit the accuracy of spectroscopic ellipsometry, it is demonstrated that this technique can be usefully applied to the study of thin chromate films formed on industrially relevant aluminum products.     

Cryo-transfer TEM study of vacancy cluster formation in thin films of aluminum and copper elongated at low temperature

Kiritani et al. encountered a large number of vacancy clusters in heavily deformed thin metal films at room temperature. In the present work, thin films of aluminum and copper were loaded to fracture in liquid nitrogen and transferred directly to the TEM without warming up (Cryo-transfer TEM). In thin films of Al and Cu deformed at 78 K, many defect clusters were observed at 120 K. In thin Al films, small defect clusters disappeared by the 120 keV electron irradiation. Upon isochronal annealing, some of the dislocation loops grew in their size, which is much larger than those observed at 120 K. However, in regions that were not exposed to electron irradiation at 120 K, only a large number of stacking fault tetrahedra were observed after room temperature annealing. In copper, the 200 keV electron beam did not significantly change the defect clusters observed at 120 K.     

Phase diagram study of the formation and crystallization of Ge-metal amorphous alloy films

The Ge-Au and Ge-Ag alloy films were deposited in vacuum at room temperature and then systematically observed in the TEM. The maximum metallic concentrations in the alloy films,C _max, which form the stable amorphous alloy phases of germanium with gold and silver, were obtained. The annealed crystallization temperatureT _c, which falls with increasing metallic content in these films was also found. The structures of these films and their annealed specimens were also studied. There are various factors which influence the formation of amorphous alloy films deposited in vacuum for Ge-metal systems. A new formula forC _max has been derived. The annealed crystallization character has been explained by means of the variation of the free energy and the activation energy of crystallization. The activation energy of crystallization,E _a, can be obtained from the data values ofT _c. For Ge-Au films,E _a (Au)=E _a ^o /(–18.66C _Au ² +16.83C _Au+1)±3.3 (kcal mol^–1); for Ge-Ag films,E _a (Ag)=E _a ^o /(–2.754C _Ag ² +3.815C _Ag+ 1)±2.6 (kcal mol^–1). In order to explain all these results, two kinds of phase diagram for the alloy films have been introduced. One is the three-dimensional relationship diagrams of phase formation in semiconductor-metallic alloy films; it was introduced to explain the influencing factors. The other is the three-dimensional phase diagrams of annealed semiconductor-metallic films systems. From this diagram all the phase transitions can be found.     

Comparative study of direct and indirect forging processes for rheological material of A356 aluminium alloy

Abstract

Using a vacuum electromagnetic stirring system, a high quality rheological material is developed in order to fabricate the engineering components without defects like internal porosities, which are caused by the entrapment of external air into the melt and impurities arising from the penetration of surface oxides by vacuum electromagnetic stirring. For practical application in vehicle industry, forming of the knuckle component that is used in automobiles was demonstrated by both direct and indirect type rheoforging processes. Here, insufficient filling behaviour occurred during direct forging processes, whereas indirect rheoforging of material with a solid fraction of 30–40% produced a completely formed knuckle component; thus, an indirect forging process may be suitable for forming the knuckle part. Through microstructural investigations and tensile tests before and after T6 heat treatment of the material, mechanical properties were characterised. By obtaining data about the rheoforging process and material properties of the rheoforged product associated with microstructural features, feasibility for future practical application was investigated. Moreover, the die structure for direct and indirect rheological forging processes was comparatively studied.     

一种新的铝合金晶界检测算法及应用

晶粒度检测是金相检验中的一个重要问题，在应用图像处理方法时体现为边缘检测，原有的边缘检测算法的各向同性的特点导致边缘提取的效果不理想，本文通过对图像边缘的分析，提出一种新的边缘检测算法，设计出一种各向异性，权重合理的边缘检测算子。与传统的边缘检测算法实验结果的比较显示了其优良的性能，在铝合金的晶界检测中取得了较好的效果。     

Atomic layer deposition of tantalum nitride based thin films from cyclopentadienyl type precursor

Tantalum nitride based thin films have been deposited on p-Si (100) and SiO₂/Si by thermal Atomic Layer Deposition (ALD) using either the Ta(= N^tBu)(NEt₂)₃ or a derivative, in which one dialkylamido ligand is substituted by a η⁵-cyclopentadienyl (η⁵-Cp), as metal organic precursors with ammonia as reducing agent. TaN_xC_y self-limiting temperature dependent ALD growth was achieved for the TaCp(= N^tBu)(NEt₂)₂/NH₃ process with a growth rate of 0.51-0.91 Å cycle⁻¹ in the 400-425 °C temperature range while between 240 and 280 °C, the growth of TaN based films from the Ta(= N^tBu)(NEt₂)₃ was accompanied by a partial decomposition of the precursor. The η⁵-cyclopentadienyl type compound allows lower nitrogen content in the precursor and thereafter in the deposited film. Although N/Ta ratio is close to one at temperatures of 390 and 400 °C, as analyzed by Rutherford Back Scattering and Nuclear Reaction Analysis, films were amorphous independently of the deposition temperature. Since Ta-C bonds are present in the Cp derivative, the TaCp(= N^tBu)(NEt₂)₂ tends more likely to form tantalum carbide compared to Ta(= N^tBu)(NEt₂)₃, which leads to lower thin film resistivity. For both precursors, employed in their respective ALD window, films were smooth with a root-mean-square roughness close to 1 nm.     

Influence of constitutional liquation on corrosion behaviour of aluminium alloy 2017A

The purpose of this work was to investigate microstructural aspects of constitutional liquation in the aluminium alloy 2017A and to determine its effect on corrosion behaviour of this alloy. Non-equilibrium melting of the alloy in the naturally aged condition was provoked by rapid heating above the eutectic temperature and immediate cooling in air. Corrosion testing was performed by exposure to a marine onshore atmosphere. The microstructure examinations were carried out using light microscopy, scanning electron microscopy, X-ray energy dispersion and X-ray diffraction analysis. It was found that, due to rapid heating rate, coarse θ (Al₂Cu) particles were melted by constitutional liquation and this way introduced strong susceptibility of 2017A alloy to intergranular corrosion.     

A computational study of kinetic phase diagrams for CoPt alloy films during epitaxial growth

We have studied the kinetic processes of the epitaxial growth for CoPt alloy films using the master equation method. The kinetic phase diagrams of CoPt alloy films which show the phase formation conditions during the epitaxial growth are determined. From the kinetic phase diagrams, we find that the [001] ordered structure is much easy to be grown at high temperature while the [100] ordered structure is easy to be grown at low temperature although both the [001] and [100] ordering could be the equilibrium ground states. The atomic deposition, ordering and surface segregation lead to a rich variety of phases in epitaxial growth. The surface segregation is found to enhance the [001] ordering and leads to the formation of the [001] ordered phase at high temperature.     

Surface morphology, composition and thermal behavior of tungsten-containing anodic spark coatings on aluminium alloy

Anodic spark coatings on aluminium alloy were prepared in aqueous electrolytes with sodium tungstate. The influence of boric acid addition in the electrolyte on the surface morphology, elemental and phase composition of the coatings was investigated. In both cases the coatings contained O, Al and W. The coatings obtained in electrolyte with boric acid and sodium tungstate contain also B at approximately 1 at.%. Scanning electron microscopy indicated that the coatings had three layers: the grey underlayer of anodic alumina, the second black layer of crystalline or amorphous aluminium tungstate agglomerated into fibers and the outer green layer of WO₃. It was proposed that isopoly- and heteropolyanions in the electrolyte used take part in the coating growth.     

铁磁形状记忆合金Ni-Mn-Ga薄膜制备工艺研究

铁磁形状记忆合金（FSMA）是种新型智能材料，Ni—Mn—Ga合金是这种材料的典型代表。本文使用ECR磁控溅射方法在NaCl晶片上制备出了Ni—Mn—Ga薄膜，并对其制备溅射功率进行了探讨。通过对薄膜成分和表面性质的分析，知22．5W为其制备的最佳功率。对沉积在玻璃片上的薄膜进行衍射分析各其为有序化程度不高的晶态。     

Some metallurgical aspects of chip formation in cutting Ti-6wt.%Al-4wt.%V alloy

Adiabatic shear banding is a phenomenon observed in machining titanium and some other metals and alloys as well. The shear localized chips are important in the chip disposal process, machined surface integrity and the automation of machining operations. It is therefore necessary to understand the mechanisms of metal cutting such as the formation of shear banding in the produced chips. In this paper, the behaviour of the chip formation is investigated using various metallurgical analysis techniques. It was found, in cutting Ti-6wt.%Al-4wt.%V titanium alloy, that some non-diffusional phase transformation took place in the shear localized chips. The process of chip formation with shear banding and the effects of cutting conditions on shear banding frequency were also studied. The results of these tests are presented in this paper.     

Electrical stability of polyimide siloxane films for interlayer dielectrics in multilevel interconnections

Electrical stability of a polyimide siloxane (PSI) film for ultra-large scale integrated circuit (ULSI) multilevel interconnections is studied. The PSI films, modified by p-aminophenyltrimethoxysilane (APTMS), are designed to have three-dimensional polymer structures through Si–O bonds. It has been revealed that the PSI films are more stable in electrical properties at higher temperatures than 150°C, as compared to the conventional polyimide (PI) films. The electrical conduction mechanism study for the PSI films has revealed that Schottky emission is dominant. Barrier height φ_B obtained from the electrical property for the PSI film was 0.460 eV in the temperatures ranging from 25–250°C. On the other hand, barrier height of 0.422 eV at lower temperatures than 150°C and activation energy of 1.09 eV at higher temperatures than 150°C were obtained for the conventional PI film. The difference in polymer structure is very sensitive to the electrical conduction at high temperature, due to sodium ion migration. The ideal band diagrams of metal-insulator-semiconductor (MIS) structures were also discussed. The optical band gaps for PSI and conventional PI films were 3.320 eV and 3.228 eV, respectively. This result suggests that the band gap of PI films can be enlarged by modification with Si–O components. The differential barrier height between the PSI and conventional PI films is 0.038 eV, and is close to the difference in half of optical band gaps (0.046 eV).     

溅射钽靶材用高纯钽粉工艺研究

分析了高纯钽粉生产的技术特点,介绍了一种改进的钽靶材用高纯钽粉的生产方法。采用高温脱氢(900~950℃)和低温脱氧(700~800℃)分步进行的工艺,有利于钽粉氧、氢、镁含量及粒度的控制,所得样品兼具低氧和小粒度的特点。采用真空热处理(700~800℃)工艺可以有效除去脱氧后残余的金属镁、酸洗带入的H、F等杂质,确保颗粒不长大,同时使杂质含量得到了很好的控制。     

Extrusion of EN AW-2014 alloy in semisolid state

Abstract

The potential of forming EN AW-2014 alloy in semisolid state was investigated. The EN AW-2014 slugs were partially melted at 610°C, to a liquid fraction of ～15%, before they were extruded into a solid bar with a diameter of 16 mm. The ram speed used in this process was much lower than that employed in thixoforging of the same alloy to maximise heat removal from the slug and to fully solidify the liquid fraction by the time the extruded bar exits the die. The high solid fraction employed was also of help in this regard. Forming during extrusion under these conditions took place largely via rotation of the α-Al globules over one another, producing a remarkable microstructure of predominantly uniform globular α-Al grains. The forming load was at least an order of magnitude smaller with respect to that measured during hot extrusion of the same alloy, underlining the benefits of extruding the hard to form 2XXX alloys in semisolid state. Having been largely drained of its liquid, the final part of the preheated slug, however, failed to enjoy extrusion under such favourable conditions. The large extrusion deformation and temperatures well above the liquidus point have led to dynamic recrystallisation, which is responsible for the equiaxed, instead of fibrous, grain structure in this region.     

Effect of heat treatment on small scale fragmentation of aluminium alloy

Abstract

Small scale explosions, using a detonator, of 7075 aluminium alloy cylinders, 15–100 mm outside diameter, were carried out to investigate the effects of heat treatment on fragmentation. This was the finest for the strongest as received alloy and coarsest for the softest overaged alloy. This effect was similar to that seen in investigations of the fragmentation of steel. Cylinders of 50 and 100 mm in diameter did not fragment but plastically deformed with maximum deformation at the cylinder bottom. Fragmentation of 33 and 42 mm diameter cylinders produced long fragments typical of the break-up of thick walled cylinders. At smaller diameters, break-up gave fragments of several shapes, finer fragments being largely associated with the smallest diameter cylinders and the highest strength alloys. Results followed those seen in large scale studies of cylinder break-up and suggest the possibility of using small scale fragmentation experiments in the investigation of the effects of composition, heat treatment and processing on natural fragmentation.     

Synthesis of anodic films in the presence of aniline and TiO2 nanoparticles on AA2024-T3 aluminium alloy

Coatings, comprising an inner porous anodic alumina film and an outer polyaniline/TiO₂ nanoparticle layer, were electrochemically synthesised on an AA2024-T3 aluminium alloy by single-step, anodic polarisation in an oxalic acid-based electrolyte. The morphology and composition of the coatings were examined by TEM, SEM and XPS, with the size and zeta-potential of the TiO₂ nanoparticles in the oxalic acid solution also measured. Observation of the growth of the coating during of anodic polarisation revealed that a distinct, two-layered coating is formed from the early stages of polarisation, with the anodic film forming at a constant rate and the outer layer developing at a rate that decreases markedly with times beyond about 30 min. Nanoparticles, agglomerated in the electrolyte, migrate to the anode due to the negative zeta-potential and form the nanoparticle-containing layer at the surface of anodic film. Such particles are not incorporated in the pores due to agglomeration and disordered film porosity at the outer layer of the anodic film.     

Microstructural influence on the intrinsic fatigue properties of Al---Li 8090 alloy

A study has been made to investigate the influence of microstructure on the extrinsic and intrinsic fatigue properties of the Al---Li alloy, 8090. Two types of microstructure have been produced to compare the relative fatigue properties, one with a δ′ phase dominant microstructure and the other with a S′ + δ′ microstructure. Crack closure loads measured by the crack-opening displacement method have been used to obtain intrinsic fatigue resistance of the δ′ and S′ + δ′ microstructures. Results have shown that the extrinsic fatigue resistance of the δ′ microstructure was considerably higher than that of the S′ + δ′ microstructure, especially at lower growth rate, which was mainly due to the more severe crack path tortuosity and associated high levels of crack closure. In addition, the intrinsic fatigue resistance of the δ′ microstructure was also observed to be higher than that of the S′ + δ′ microstructure, presumably due to greater slip reversibility in the δ′ microstructure.