Patent Application
20080128055
1. Field of the Invention
The present invention relates to an alloy film and a process for manufacturing the same, especially to an annealing-induced alloy film and a process for manufacturing the same.
2. Description of the Related Art
Bulk metallic glass (BMG), also called bulk amorphous metal (BAM) or bulk amorphous alloy (BAA), is a new material with distinctive properties for special use. As compared with the traditional amorphous metals formed from melting state rapidly, this material has higher glass-forming ability (GFA). It can be made into amorphous bulk form at extremely low cooling rates and its thermal stability is better than that of the crystalline metals. For example, A. L. Greer (“Metallic Glasses”, Science, 267, 1947 (1995)), A. Inoue (“Stabilization of Metallic Supercooled Liquid and Bulk Amorphous Alloys”, Acta Mater., 48, 279 (2000)) and Y Zhang, D. Q. Ahao, M. X. Pan and W. H. Wang (“Glass Forming Properties of Zr-based Bulk Amorphous Alloys”, J. Non-crystal. Solids, 315, 206 (2003)) et al. summarized various GFA and BMG systems, such as the ternary or quaternary alloys based on Fe, Co, Ni, Pd, Zr, Ti, Mg, or La etc., or alloys with more components.
In addition to controlling the cooling rates, the supercooled liquid region (ΔT), defined by the difference between the glass transition temperature (Tg) and the crystallization temperature (Tx), can be broadened by varying alloy components so that the superplasticity in this temperature range can be utilized. Most BMG have good properties such as mechanical properties, process ability of ΔT, anti-corrosion, hydrogen-stored ability, soft magnetism and other specific optical, electrical, or chemical properties. The examples of actual commercial applications of the material include exercise apparatus and electrodes.
Crystallization generally tends to occur during thermal annealing of amorphous alloy, which is characterized by the distribution of various nano crystallites in the amorphous base and found to strengthen the alloy structures. Researches on this subject have been published by A. Inoue, C. Fan and a. Takeuchi (“High-strength Bulk Nanocrystalline alloys in a Zr-based System containing Compound and Glassy Phases”, J. Non-crystal. Solids, 250-252, 724 (1999)) and A. L. Greer et al. (“Partially or Fully Devitrified Alloys for Mechanical Properties”, Mat. Sci. Eng. A, A304-306, 68 (2001)). Different synthesis processes would influence the distribution, proportion, and routes of crystallization of the nanocrystallites. In other words, if the relationships between components, structures and properties of alloys were found, one could synthesize the materials with desired properties by proper synthesis process for specific applications.
In the solid state, amorphization could be achieved mainly by mechanical alloying, solid-state amorphization (SSA), high pressure and shock loading techniques. In all these solid-state techniques except for the SSA, considerable energy is generally required for ultimate amorphization. Metals can be also induced by hydrogen to form amorphous hydride and proceed to powder metallurgy for the solidification of BMG.
We hope that the characteristics of bulk amorphous metals can be presented in the thin film, i.e. forming a metallic glass thin film (MGTF) to extent the applications of those materials. Similar to bulk alloys, the properties of MGTF can be modified by controlling element components and nanocrystallites. The MGTF presents good properties on mechanical isotropy, structure unity, and have less crystal defects that the size effects should not be existent, and its superplasticity as bulk alloys in the supercooled liquid range is assistant to form three-dimension structures. Therefore, MGTF can be applied in various fields, especially in the fields of MEMS and optical record media.
Though the above-mentioned solid-state technique can successfully synthesize bulk amorphous alloys, it is apparent that the machining-involved technique is not suitable for films formation and the use of SSA in film formations is limited. For example, R. B. Schwarz and w. L. Johnson first proposed that the solid-state amorphization in specific multilayer structures of crystalline metals can be induced due to the annealing-induced diffusion reactions (“formation of an amorphous alloy by solid-state reaction of Pure Crystalline Metals”, Phys. Rev. Lett., 51, 415 (1983)). However, the extent of amorphization in this case is trivial and confined to the reacted interface with the thickness of few nanometers, as shown by B. X. Liu, W. S. Lai and z. J. Zhang (“Solid-State Crystal-to-Amorphous Transition in Metal-Metal Multilayers and Its Thermodynamic and atomistic Modeling” Adv. In Physics, 50, 367 (2001)).
Even various amorphous films can be formed through traditional evaporation or sputtering process, the annealing-induced crystallization reactions in both are quit different and the properties of both are not certainly identical. It is due to that the elemental components of traditional deposition and sputter systems are not necessarily the same with BMG and there are substantial differences between the film and bulk manufacturing process. For example, Y. Liu, S. Hata, K. Wada and A. Shimokohbe et al. successfully sputtered the Pd-based ternary alloy film on the aluminum layer or silicon wafer. They found that the mechanical and thermal properties of obtained MGTF are similar to those of BMG having the same components and those properties of the MGTF are influenced by the sputtering conditions. However, they didn't disclose the variance of crystallization, distribution or properties caused by heating at different temperatures. They only showed that, by way of the time-temperature-transition diagram, the MGTF have good thermal stability while compared to the crystallized, and observed that the resistance of the MGTF decreased apparently when the annealing temperature increased to Tx.
S. Hata, Y. Liu, T. Kato and A. Shimokohbe (“Three-dimensional Micro-Forming Process of Thin Film Metallic Glass in the Supercooled Liquid Region”, Proceeding of 10th International Conference on Precision engineering (ICPE), 3741 (2001)) sputtered the Zr-based ternary alloy films and manufactured a three-dimensional cone spring by utilizing the superplasticity of such films in the supercooled liquid temperature region. According to the time-temperature-transition diagram, they simply confirmed that heating the metals with a long time in the temperature range would not result in crystallization, but they didn't disclose the variance of crystallization, distribution or properties caused by heating with different temperatures.
According to the above-mentioned prior art, a skilled person in this field could not effectively control and anticipate the structures and properties of BMG in the form of films. For example, the distribution of crystalline phase/amorphous phase could not be controlled extensively and uniformly. Thus, the requirement for thin-film alloy utilization, not bulk alloys that have thicker volumes, could not be satisfied yet.
Accordingly, the purpose of this invention is to produce an alloy film based on elements with high glass-forming ability with extensive amorphous structures and, in the meanwhile, effectively control and anticipate its structures and properties so as to satisfy the requirements mentioned above.
In one aspect, the present invention provides an alloy film based on elements with high glass-forming ability, which is deposited as a film from a source composed of desired chemical elements, and annealed in a controllable annealing process to form partly or fully amorphous structures in the film. The alloy film of the invention includes a principal element with high glass-forming ability and at least two secondary elements different from the principal element, wherein the principal elements with high glass-forming ability are selected from a group consisting of iron, cobalt, nickel, palladium, zirconium, titanium, magnesium, and lanthanide series; the secondary elements are selected from aluminum, zirconium, copper, tin, zinc, palladium, titanium, iron, cobalt, nickel, niobium, beryllium, gallium, germanium, chromium, molybdenum, hafnium, lanthanide series, VI˜VIII group transition elements, phosphorus, boron, carbon, silicon or other metal or nonmetal elements.
In a further aspect, the present invention provides a process for manufacturing the above-mentioned alloy film, comprising the following steps: using a alloy composed of desired chemical elements as a film source, depositing the alloy onto a substrate to form a film, and annealing the film to induce partial or full amorphization in the film.
The present invention successfully induced partial or full amorphization in the films, wherein the amorphous structures distributed up to decades of micrometers and over the film extensively. Such controllable extensive amorphization in the thin film is useful to regulate the proportion of amorphous structure to crystalline structure, establish the relationships between the structure and property of the film and thus manufacture a film with specific mechanical, electrical or optical properties.
The details of one or more embodiments of the invention are set forth in the accompanying description below. Other features, objects, and advantages of the invention will be apparent from the detailed description, and the claims.
In one aspect, the present invention provides an alloy film based on elements with high glass-forming ability, which is deposited as a film from a source composed of desired chemical elements, and annealed in a controllable annealing process to form partly or fully amorphous structures in the film.
Generally, the usual BMG element systems are all suit for the present invention. As known by those skilled in the art, the principal element with high glass-forming ability includes iron, cobalt, nickel, palladium, zirconium, titanium, magnesium, and lanthanide series etc. Besides those principal elements, the components of the alloy film include at least two secondary elements that are different with the principal elements for assisting in amorphization and forming ternary or quaternary alloys or alloys with more components. The secondary elements include aluminum, zirconium, copper, tin, zinc, palladium, titanium, iron, cobalt, nickel, niobium, beryllium, gallium, germanium, chromium, molybdenum, hafnium, lanthanide series, VI˜VIII group transition elements, phosphorus, boron, carbon, silicon or other metal or nonmetal elements. It is apparent for one skilled person to select and determine the proportion of the above-mentioned elements. Thus the elements used in the invention are not limited to the above-mentioned.
In one preferred embodiment of the invention, the principal element with high glass-forming ability is zirconium. In this embodiment, the secondary elements with high glass-forming ability preferably include copper, aluminum and nickel. Take the Zr—Cu—Al—Ni alloy for example, the atom percentage of the alloy is zirconium 40˜60%, copper 15˜35%, aluminum 5˜20% and nickel 0˜15%; preferably, zirconium 47%, copper 31%, aluminum 13% and nickel 9%, hereafter designated as Zr47Cu31Al13Ni9
In the other preferred embodiment of the invention, the principal element with high glass-forming ability is iron. In this embodiment, the secondary elements with high glass-forming ability preferably include cobalt, nickel, titanium, niobium and boron. Take the Fe—Co—Ni—Ti—Nb—B alloy for example, the atom percentage of the alloy is iron 50˜70%, cobalt 5˜15%, nickel 5˜15%, titanium 5˜15%, niobium 0˜10% and boron 0˜20%; preferably, iron 65%, cobalt 8%, nickel 7%, titanium 13%, niobium 1% and boron 6%, hereafter designated as Fe65Co8Ni7Ti13Nb1B6.
According to the invention, partly amorphous structures are extensively formed in the film, i.e. there are extensive nanocrystallite/amorphous nanophase composite structures formed in the film. According to a preferred embodiment of the invention, for example, the Zr47Cu31Al13Ni9 alloy film annealed at 800 K, the amorphous structures are formed fully and extensively in the film.
In one embodiment of the invention, the thickness of the alloy film is about 0.2 μm˜50 μm. In one preferred embodiment of Zr-based alloy film, the thickness of the film is about 5 μm˜10 μm. In the other preferred embodiment of Fe-based alloy film, the thickness of the film is about 0.5 μm˜10 μm
In a further aspect, the present invention provides a process for manufacturing the above-mentioned alloy film, comprising the following steps: using a alloy composed of desired chemical elements as a film source, depositing the alloy onto a substrate to form a film, and annealing the film to extensively induce partial or full amorphization in the film.
For depositing the thin film alloy, a proper film source (or target) is prepared at first. For example, an alloy ingot with desired chemical compositions is found by the vacuum arc remelting process, and then proceed and heated into the final forms. A proper substrate for deposition is selected according to the film types and its application. The examples of substrates include well-cleaned glass, silicon or other substrates made of different materials.
The deposition process includes, for example, evaporation, sputtering, or cathodic arc, preferably the physical vapor deposition (PVD). The sputtering system used usually includes DC or RF magnetron sputtering system. In one embodiment of the invention, the working pressure and sputtering power during sputtering was maintained at 3×10−3 torr and 100 W respectively, and the sputtering system was in an argon atmosphere for sputtering. The deposition conditions are apparent for one skilled person in the art, thus the deposition conditions are determined in practice without limited to the above-mentioned.
The as-deposited alloy film was then annealed with suitable conditions to induce partial or extensive amorphization in the film. Due to that the behavior of crystallization in the film is influenced by the annealing conditions, the thermal behaviors of those films composed of different elements during the heating process is recorded by, for example, differential scanning calorimeter (DSC) before annealing, establishing the temperature range of supercooled liquid region and the corresponding variation of film structures, whereby determining a preferred annealing condition. The utilization of DSC results to determine annealing conditions is also known by the skilled person.
Annealing can be conducted in any anneal furnace with functions of adjusting parameters such as heating rates, temperatures, etc. According to one embodiment of the invention, the film was annealed in a rapid thermal annealing (RTA) system, such as MILA-3000 RTA system. To prevent contamination, before annealing, the annealing system was pumped down to 10−3 torr range followed by purging with pure argon, such as 99.9995% Ar, for several times to minimize the residual reactive gases, such as oxygen.
The heating rate of annealing is about 5 K/min˜200 K/min. In a preferred embodiment of Zr-based alloy film, the heating rate of annealing is 40 K/min. In the other preferred embodiment of Fe-based alloy film, the heating rate of annealing is 100 K/min. The temperature of annealing is preferably on the range of supercooled liquid region in order to control the reaction rate of amorphization. The supercooled liquid region varies with the components of alloys. For example, the temperature range of annealing is about 400 K˜1200 K. In a preferred embodiment of Zr-based alloy film, the temperature range of annealing is about 550 K˜950 K. In the other preferred embodiment of Fe-based alloy film, the temperature range of annealing is about 673 K˜1073 K. The holding time of annealing is about 10 s˜3600 s, preferably 60 s. The cooling rate of annealing is about 5 K/min˜200 K/min, preferably 20 K/min˜40 K/min.
Zr-based quaternary alloy thin films of thickness 5-10 μm with a nominal composition of Zr47Cu31Al13Ni9 were deposited onto the well-cleaned glass substrate using an RF magnetron sputtering system in an argon atmosphere. The working pressure and RF power during sputtering were maintained at 3×10−3 torr and 100 W, respectively. The compositions of the films were measured using an electron probe for microanalysis (EPMA). The compositional fluctuation at various points on the film surface was also determined and found to be very small, (around 1%) which reveals the uniformity of the deposited films. The films were then annealed in a rapid thermal annealing (RTA) system in Ar at temperatures ranging from 550 to 950 K. To avoid contamination, the RTA system was pumped down to 10−3 torr range followed by purging with pure Ar for several times. For RTA, the samples were kept 60 seconds in holding time with the heating rate of 40 K/min. The crystallization of the film was studied using a differential scanning calorimeter each film was delaminated entirely from the glass substrate for the DSC analysis without the aid of any chemical solutions. The crystal structures of films were examined by a transmission electron microscopy (TEM). Broad-face TEM sample discs were thinned from the substrate side by a dimpler, followed by an ion miller for the final perforation. TEM examinations were performed at 300 keV. Sheet resistance measurements of films were done at room temperature by a four-point probe method. For the mechanical property evaluation, the Knoop ultramicrohardness of film was measured. To eliminate any error due to the substrate effect, the indentation was applied with 25 g loading, 15 second holding time and loading rate of 40 μm/sec.
The DSC study in
Except varying with temperature and light wavelengths, the refractive index varies with elemental components of the material. The refractive indexes of the films annealed at different temperatures v.s. light wavelengths are show in
Annealing at 800 K, in the ΔT region, produces a fully amorphous structure without any observable crystalline phases, as evidenced by the TEM image of
We now discuss the mechanism by which the partly amorphous film dispersed with crystallites is transformed to the fully glassy state during annealing. Since impurities such as hydrogen have been reported to induce amorphization in many alloys under highly pressurized (˜5 MPa) and thermal environment, species in the substrate and residual gases in the RTA system might have possibly played roles to promote the amorphization in our case. However, such possibilities are not likely because the short annealing duration (60 seconds) and relatively low operational pressure are unfavorable to allow the diffusion-driven reactions to occur. Furthermore, oxygen impurity and contamination are known to strongly affect the stability of the amorphous phase in BMG. As Zr and its alloys are known to be susceptible to oxidation, incorporation of oxygen into the film is often very difficult to avoid even in the reduced and protective annealing environment. However, the oxygen effect would be negligible for the annealing temperatures ≦800 K on account of the following reasons. Interaction of Zr with oxygen involves both oxygen dissolution and formation of scale (mainly ZrO2). The scale formation was limited in this study because our X-ray diffraction analysis results (which are not shown here) revealed the presence of oxide phases only at and above 850 K. The oxygen dissolution during annealing is thus considered in this study. In the absence of an exact diffusion coefficient, D, we take an Arrhenius expression, D(in cm2/sec)=5.2exp[−212/(8.314*T)], where T is absolute temperature. This expression has been commonly used for Zr and its alloys to determine the depth of oxygen dissolved into the metal through volume diffusion. Based on X=2√{square root over (Dt)}, where t is the annealing time and X the distance at which the oxygen concentration falls to half the initial value of maximum solubility (28.5%) at the metal oxide interface, and an assumption that the time spent in heating up to 0.8 of annealing temperature makes insignificant contributions to the total amount of diffusion, depths of oxygen dissolution into our annealed films are estimated to be 0.1, 0.3, 0.7, 1.4 μm for 800, 850, 900 and 950 K, respectively. The estimate is consistent with the depth profile of oxygen concentration shown in
To interpret the present results and explain the thermodynamics that govern the structure evolution during annealing, hypothetical free-energy diagrams are shown in
It has been proposed that sufficient thermal-driven diffusions and high interfacial energies between two different phases are prerequisite for the SSA to take place. Our result-thus demonstrates, as we qualitatively hypothesized, the thermal energy supplied by the annealing and the interfacial energy arising from the nanocrystallite/glass interfaces might have imparted significant influences on the amorphization and crystallization of film during annealing. Upon annealing at below the supercooled liquid region, the interfacial energy appears to be predominant because of the presence of nanocrystallites, and hence the growth of nanocrystalline phases is favorable. In addition, the viscosity of glass matrix presumably decreases with the annealing temperature, analogous to that required for the superplasticity behavior of metallic glasses. The glassy matrix with sufficiently low viscosity thus allows the nanocrystalline phases to “move around” in the matrix. Ultimately, nanocrystallites become interconnected and form a network structure. Once this interconnected crystalline network structure is formed, facilitating the flow of electrical current, a decrease in resistivity is thus expected (
In summary, here we show direct experimental evidences that annealing of Zr47Cu31Al13Ni9 film at a temperature within the supercooled liquid region results in extensive amorphization, presumably attributed to sufficient thermal and interfacial energies between nanocrystallites and glassy matrix. The formation of comprehensive amorphous structure gives rise to notable alterations in the electrical and mechanical properties of annealed film. Additional features of the present work are that a prominent strengthening effect is observed due to the improved amorphous matrix dispersed with nanocrystalline phases upon annealing and that one can take this advantage to tailor the film properties by modulating the amorphous content in the annealed films. The controllable amorphization may also serve as a precursor for exciting new nano materials.
The details of above-mentioned Zr-based alloy film have been published on Physical Review B, Vol. 69, page 113410 in March of 2004.
The Fe65CO8Ni7Ti13Nb1B6 (atomic percent, at. %) thin films were prepared by an RF magnetron sputtering method. The Fe—Co—Ni—Ti—Nb—B target was an as-cast alloy. Thin films of thickness 0.5-10 μm were deposited on glass substrate. The deposition was carried out under the following conditions. The base vacuum was 10−7 Torr, Ar gas flow rate was 20 sccm, and the working pressure was 3×10−3 Torr. The power of 100 W was applied during the deposition. The film was annealed in Ar at a heating rate of 100 K/min and a holding time of 60 s at temperatures ranging from 673 to 1073 K. The annealing system was pumped down to the 10−3 Torr range followed by several purging with Ar. Compositions of thin films were determined by Electron Probe Microanalyzer. The thermal behavior of the film was determined using a differential scanning calorimeter (DSC) in Ar at a scanning rate of 100 K/min. The DSC film sample was delaminated from the glass without the aid of any chemical solutions. Sheet resistance and hardness measurements were carried out by four-point probe and Knoop ultramicrohardness methods, respectively. The ultramicrohardness was measured with a 25 g loading, a 15 holding time, and a loading rate of 40 μm/s. The crystal structures of films were examined by a transmission electron microscopy (TEM). TEM examinations were performed at 200 keV. The composition distribution and oxygen content of the films were performed by secondary ion mass spectrometry (SIMS, Cameca IMS6F), depth-profiling studies were carried out by Ar sputtering. The coercive field (Hc) and the saturation magnetization were measured at room temperature by a vibrating sample magnetometer (VSM), using maximum field strength of 7500 Oe.
Thermal annealing results in variations of microstructure/crystal structure in the film and thus film properties such as hardness and electrical resistivity have been altered. Annealing of the Fe-based films at low temperatures yields the release in the residual stress present in the as-deposited condition and thus causes the decrease in film hardness, as seen in
Since impurities such as hydrogen have been reported to induce amorphization in many alloys as mentioned in the previous example of Zr-based film,
In this example, qualitatively, the thermal energy supplied by the annealing and the interfacial energy arising from the nanocrystalline/matrix interfaces have significant influences on the amorphization and crystallization of film during annealing. Upon annealing, our films clearly show a structure development sequence of metastable sputtered structure→metastable nanocrystallite/amorphous nanophase composite→single metastable amorphous phase→stable crystalline structure. To interpret the present results and explain the thermodynamics that govern the structure evolution during annealing, hypothetical free energy diagrams are shown in
In addition to the thermodynamic factor, the thermal energy at elevated temperatures and the interfacial energy arising from the nanocrystallite/glass interfaces are kinetically favorable for the amorphization, as proposed previously in SSA. At low temperatures, the large interfacial energy drives coarsening of the metastable crystalline phase through a process analogous to Ostwald ripening. Further, the viscosity of the glass matrix presumably decreases with temperature, analogous to that required for the superplasticity behavior of metallic glasses. The amorphous matrix, with a sufficiently low viscosity, allows the metastable nanocrystalline phases to “move around” and reorient in the matrix. An extensive amorphization occurs as the metastable nanocrystallites are thermally annihilated and “liquefied” into the amorphous matrix due to the combined effects of sufficient thermal energy and excessive interfacial energy. In contrast to the planar interfacial area in SSA multilayer films, the single layer films in this study are considered to yield much higher interfacial energies since nanocrystallite/amorphous matrix interfaces are present through the film thickness. As a result, wide spread amorphization could take place in the film. Above Tx, the amorphous structure is no longer thermodynamically favorable and crystallization readily proceeds.
In this example, the Fe-based film shows the extensive amorphization phenomenon, presumably attributed to sufficient thermal and interfacial energies between nanocrystallites and amorphous matrix. The extensive amorphization gives rise to distinct variation in the electrical, mechanical and magnetic properties of annealed Fe-based film within supercooled liquid region. However, Fe-based film did not form fully amorphous structure as Zr-based film did. This might be due to the fact that Zr-based film has better glass-forming ability than Fe-based film. Some important results are summarized as follows.
(1) The electrical resistivity result indicates that Fe-based film has the high resistivity (˜228 μΩ-cm) within the supercooled liquid region.
(2) The Fe-based film has low ultra-microhardness (˜866.6 HK) with in the supercooled liquid region.
(3) TEM results show the Fe-based film has the amorphization taking place at 923 K.
(4) The VSM result shows the Fe-based film has low coercivity (˜33 Oe) and maximum saturated magnetization (˜0.027 emu/g) within the supercooled liquid region. Cyclic variation of coercivity and saturated magnetization with annealing temperature are observed.
(5) The MFM result (
All of the features disclosed in this specification may be combined in any combination. Each feature disclosed in this specification may be replaced by an alternative feature serving the same, equivalent, or similar purpose. Thus, unless expressly stated otherwise, each feature disclosed is only an example of a generic series of equivalent or similar features.
From the above description, one skilled in the art can easily ascertain the essential characteristics of the present invention, and without departing from the spirit and scope thereof, can make various changes and modifications of the invention to adapt it to various usages and conditions. Thus, other embodiments are also within the scope of the following claims.
| Number | Date | Country | Kind |
|---|---|---|---|
| 92121265 | Aug 2003 | TW | national |
This application is a divisional of patent application Ser. No. 10/898,240 filed Jul. 26, 2004.
| Number | Date | Country | |
|---|---|---|---|
| Parent | 10898240 | Jul 2004 | US |
| Child | 12068146 | US |
