Showing papers in "Materials Transactions Jim in 2002"

Development of low rigidity β-type titanium alloy for biomedical applications : Biomaterials and bioengineering

Abstract: The low rigidity type titanium alloy, Ti-29Nb-13Ta-4.6Zr was designed, and then the practical level ingot of the alloy was successfully fabricated by Levicast method. The mechanical and biological compatibilities of the alloys were investigated in this study. The following results were obtained. The mechanical performance of tensile properties and fatigue strength of the alloy are equal to or greater than those of conventional biomedical Ti-6Al-4V ELI. Young's modulus of the alloy is much lower than that of Ti-6Al-4V ELI, and increases with the precipitation of a phase or ω phase in the β matrix phase. The compatibility of the alloy with bone of the alloy is excellent. Low rigidity of the alloy is effective to enhance the healing of bone fracture and remodeling of bone. The bioactive coating layer of hydroxyapatite can be formed on the alloy.

XPS characterization of the surface oxide film of 316L stainless steel samples that were located in quasi-biological environments : Biomaterials and bioengineering

Abstract: The purpose of this study was to characterize the surface oxide films on 316L austenitic stainless steel located in various environments to estimate the reconstruction of the film in human body. Five kinds of specimens were prepared according to the following methods: polished in deionized water, autoclaved, immersed in Hanks' solution, immersed in cell culture medium, and incubated with cultured cells. X-ray photoelectron spectroscopy (XPS) was performed to estimate the compositions of the surface oxide film and substrate and the thickness of the film. Surface oxide film on 316L steel after polished in water consists of iron and chromium oxides containing small amount of nickel, molybdenum, and manganese oxides. The surface oxide contained a large amount of OH - . Calcium phosphate was formed on/in the film after immersion in the Hanks' solution and medium and incubated with the cells. Sulfate is adsorbed by the surface oxide film and reduced to sulfite and/or sulfate in cell culture medium and with culturing cells. The results in this study suggest that nickel and manganese are depleted in the oxide film and the surface oxide changes into iron and chromium oxides containing a small amount of molybdenum oxide in human body.

Effect of isothermal aging on ball shear strength in BGA joints with Sn-3.5Ag-0.75Cu solder : Lead-free electronics packaging

Abstract: The ball shear strength of BGA solder joints during isothermal aging was studied with Sn-3.5Ag-0.75Cu solder on three different pads (Cu, electroless Ni-P/Cu, immersion Au/Ni-P/Cu) at temperature between 70 and 170°C for times ranging from 1 to 100 days. The reliability of solder ball attachment was characterized by mechanical ball shear tests. As a whole, the shear strength of BGA joints decreased with increasing temperature and time. The shear strength for both the immersion Au/Ni-P/Cu and electroless Ni-P/Cu pads was consistently higher than that of the Cu pad for all isothermal aging conditions. The fracture surface showed various characteristics depending on aging temperature, time, and the types of BGA pad. The P-rich Ni layer formed at the interface between (Cu, Ni) 6 Sn 5 and Ni-P deposits layer after aging, but fracture at this interface was not the dominant site for immersion Au/Ni-P/Cu and electroless Ni-P/Cu pad.

Interface reaction and mechanical properties of lead-free Sn-Zn alloy/Cu joints : Lead-free electronics packaging

Abstract: The interfacial reaction and mechanical properties of Sn-Zn lead-free alloys/Cu joints were investigated under thermal exposure conditions. In the solder layer, Zn phases reacted with Cu and were transformed to Cu-Zn compounds with increasing exposure time. The microstructure change caused decreasing Vickers hardness of the solder layer. At the joint interface, although Cu-Zn compounds formed first, the formation of Cu-Sn compounds occurred with increasing exposure time. Simultaneously, the disappearance of Cu-Zn compounds and void formation occurred. The activation energy of the growth of Cu-Zn compounds at the joint interface was determined to be approximately 70 kJ/mol. That value is close to the activation energy of the diffusion of Zn in Sn crystal.

Recent progress in bulk glassy alloys : Bulk amorphous, nano-crystalline and nano-quasicrystalline alloys IV

Abstract: This paper deals with recent progress in stabilized supercooled liquid and the resulting bulk glassy alloys and focusing on the following factors; alloy composition, forming ability, formation mechanism, computed glass-forming ability, computed glass formation range, atomic configuration, production techniques, mechanical properties, corrosion resistance, soft magnetic properties, micro-forming ability, applications, significance to science and engineering, and future trends for bulk glassy alloys including supercooled liquid. As demonstrated in this review, the high stability of metallic supercooled liquid has already opened up new fields of investigation in basic science and yielded new engineering applications. There is every reason to expect that their importance will continue to increase.

Progress on composites with embedded Shape Memory Alloy wires : Special issue on smart materials-fundamentals and applications

Abstract: Composite materials containing thin Shape Memory Alloy (SMA) wires show great promise as materials able to adapt their shape, thermal behaviour or vibrational properties during service. Tools for designing such materials are however far from being available. The work presented here reports the main achievements of a concerted European effort towards the establishment of a fundamental understanding for manufacturing and design of SMA composites. The following major steps are examined: selection and characterisation of the material constituents, development of manufacturing processes for the production of composites with pre-strained SMA wires, analysis and modelling of the action of the SMA wires in the composite, the contribution of the SMA-resin interface, analysis and modelling of the functional, thermomechanical, impact and durability properties of SMA composites and the development of a simple, large-scale, aerodynamic model. It is argued that the achievements of this research have brought the knowledge on SMA composites to a substantially higher level enabling reliable manufacturing and design, and the emergence of new industrial applications.

Increase in electrical resistivity of copper and aluminum fine lines : Special issue on materials-related issues for Cu interconnects used in ultra high speed large scaled integrated Si devices

Abstract: The resistivities of thin films and fine lines of copper (Cu) and aluminum (Al) were measured by a resistance ratio method (referred to as RR method hereafter), which measures the ratio of room-temperature resistance to liquid-nitrogen-temperature resistance. This method can predict resistivity exactly without the need for precise and detailed line or film dimension measurements. Thinner films and finer lines have higher resistivities in the case of both Cu and Al, with Cu showing larger resistivity increases (films and lines) than Al. From the present data, we estimated the electron mean free path of Cu to be 55 nm, which is close to most of the previously reported values, and that of Al to be 22 nm. Line resistivities depend not only on the line width but also on line thickness. We propose a simple equation for expressing line resistivity in terms of line thickness and width.

Suppression of surface hot shortness due to Cu in recycled steels : Environmental benign manufacturing and material processing toward dematerialization

Abstract: The most serious problem in the recycling of steel is the occurrence of surface hot shortness during hot deformation due to the mixing of Cu from scrap into steels. Tin accelerates the effect of Cu. The surface hot shortness is caused by liquid embrittlement, that is, formation of the liquid Cu-enriched phase through preferential oxidation of Fe atoms at the steel/scale interface during heating for hot deformation and penetration of this Cu-enriched phase into the grain boundaries. Decrease in the amount of the liquid Cu-enriched phase penetrating into grain boundaries can suppress the surface hot shortness. The amount of the liquid Cu-enriched phase penetrating into the grain boundaries can be reduced by the suppression of oxidation, occlusion of the Cu-enriched phase into the scale, back-diffusion of Cu into the steel matrix and suppression of penetration of the liquid Cu-enriched phase. Therefore, the effects of various elements and conditions of heating and deformation on the surface hot shortness, oxidation, amount of the Cu-enriched phase at the interface and the penetration were examined by tensile tests at high temperatures, thermogravimetry and optical microscopy. The conclusion can be summarized as follows. Silicon, Mn, S (+Mn) and B reduce the susceptibility to the surface hot shortness through decreasing the amount of Cu-enriched phase at the steel/scale interface. The effect of Si is significant. Carbon reduces the oxidation rate in LNG combustion gas. Phosphorus, Si, B and C reduce the susceptibility to the surface hot shortness through restraining the penetration of the Cu-enriched phase into grain boundaries. Heating at higher temperatures reduces the susceptibility mainly through a reduction in the amount of the Cu-enriched phase at the steel/scale interface, although the loss of steels by oxidation increases. A large grain size accelerates the surface hot shortness. A small amount of H 2 O in air significantly accelerates the surface hot shortness. Effects of H 2 O in heating atmosphere depend on the steel composition and more detailed research on this is desired. Very slow deformation does not cause liquid embrittlement through dynamical re-crystallization, while at a fast deformation rate the embrittlement is suppressed by an increase in the critical stress for the liquid embrittlement. Multiple methods using physical metallurgy suggested by the present research for suppressing the surface hot shortness should be applied together with other methods through separation, smelting and design of fabrication in order to promote the recycling of steels.

Room temperature deformation behavior of Zn-22 mass%Al alloy with nanocrystalline structure : Superplasticity and its applications

Abstract: The deformation behavior near room temperature in Zn-22 mass%Al alloy including nanocrystalline structure produced with Thermo Mechanical Controlling Process (TMCP) technology has been characterized over a wide range of strain rates from 10 -6 to 10 -1 s -1 at temperatures from 273 to 473 K. The microstructure of TMCP produced Zn-22 mass%Al alloy had both a random distribution of equiaxed Al-rich and Zn-rich phases with grain size of 1.3 μm and many nanocrystalline Zn particles in Al-rich phases. Since the flow stress in the deformation near room temperature was much larger than that in superplastic deformation and a maximum m value is only 0.3 (n = 3) at low strain rates below 10 -5 s -1 , the pure superplastic behavior may not be observed near room temperature. However it is noted that the large elongation of ∼ 200% was observed at 10 -5 s -1 . From microstructural observations of the specimens tested in the condition with the m value of 0.3 near room temperature, furthermore, it is considered that grain boundary sliding (GBS) is the dominant deformation process, and the specimen may be fractured by cavitation as well as the conventional superplastic materials. Therefore, it seems that the various factors contribute to the deformation flow at room temperature.

Mechanical properties of surface nitrided titanium for abrasion resistant implant materials : Biomaterials and bioengineering

Abstract: In order to verify its application for abrasion-resistant implant materials such as abutment in dental implants and artificial joints, mechanical properties of surface nitrided titanium were evaluated by three different tests, the Vickers hardness test, Martens scratch test and ultrasonic scaler abrasion test. The Vickers hardness of a nitrided layer of 2 μm in the thickness was 1300, about ten times higher than that of pure titanium. The Martens scratch test showed high bonding strength for the nitrided layer with matrix titanium. The abrasion test using an ultrasonic scaler showed very small scratch depth and width, demonstrating extremely high abrasion resistance. The results show that a surface-nitrided titanium has sufficient abrasion resistance if it is used under clinical conditions.

Low-temperature superplasticity in aluminum alloys processed by equal-channel angular pressing : Superplasticity and its applications

Abstract: Equal-channel angular pressing (ECAP) was applied to achieve grain refinement of Al-3 mass%Mg alloys containing 0.2 mass%Sc, 0.2 mass%Fe or 0.1 mass%Zr. The thermal stability of the fine-grained structures was examined by conducting static annealing experiments. The fine grain sizes produced by ECAP were essentially retained up to a temperature of 523 K for the Fe-containing and Zr-containing alloys and up to a temperature as high as 773 K for the Sc-containing alloy. The three alloys with Sc, Fe and Zr additions were pulled to failure in tension at 523 K corresponding to 0.59T m , where T m is the absolute melting point of the alloy, and maximum elongations of ∼ 640%, ∼ 370% and ∼ 390% were obtained at an initial strain rate of 3.3 x 10 -4 s -1 , respectively. Such elongations resulted in more than three times or approximately twice the elongation achieved in a binary Al-3%Mg alloy. It is shown that either Fe or Zr may be used as an alternative element in place of Sc to attain low temperature superplasticity. Tensile testing was also conducted on the Sc-containing ternary alloy at a temperature as low as 473 K corresponding to 0.54T m . A maximum elongation of ∼ 420% was attained at an initial strain rate of 3.3 x 10 -4 s -1 This appears to be the lowest homologous temperature reported to date for superplasticty of Al-based alloys.

Structural characterisation and mechanical properties of nanocomposite Al-based alloys : Bulk amorphous, nano-crystalline and nano-quasicrystalline alloys IV

Abstract: Nanocomposite Al-based alloys can be obtained with a combination of amorphous, crystalline and quasicrystalline phases. In order to understand the correlation between the nanostructure and the mechanical behaviour, four nanocomposite alloys with different characteristics were studied: two alloys from the Al-Fe-Cr-Ti system consisting of a spherical nanoquasicrystalline phase in an α-Al matrix; one alloy from the Al-Fe-V-Ti system consisting of a mixture of amorphous and α-Al phases; and one alloy from the Al-Mn-Cr-Cu system consisting of nanocrystalline particles embedded in an α-Al matrix. Melt-spun samples were prepared and the structure was characterised by means of X-ray diffraction and transmission electron microscopy. Differential scanning calorimetry was used to study the thermal stability and the transformation processes. Tensile tests, fractographic analysis and Vickers microhardness at room temperature were performed in order to evaluate the mechanical behaviour. A combination of solid solution, particle dispersion and grain refinement strengthening was responsible for the high strength of the alloys. The microstructure of the alloy Al 93 Fe 3 Cr 2 Ti 2 (at%) remained acceptably stable up to 703 K, due to the slow coarsening rate of the icosahedral phase.

Low temperature swelling in beta-SiC associated with point defect accumulation : Special issues on radiation-induced effects by high energy particle/solid interaction

Abstract: An experimental technique to characterize irradiation-induced swelling, or isotropic volume expansion, through a combined utilization of medium-to-high energy accelerators and interferometric surface profilometry, was established. The technique was successfully applied to a characterization of swelling behavior in beta-silicon carbide arising from the accumulation of point defects at relatively low temperatures, i.e., 333-873 K, as a function of fluence level, displacement damage rate and irradiation temperature. Swelling rate and swelling at any given fluence level exhibited a negative dependence on irradiation temperature. The saturated low temperature swelling fell on the lower edge of neutron irradiated swelling data band. The influence of displacement damage rate appeared unremarkable. An additional study on the synergistic effect of atomic displacement damage and helium production revealed an enhancement of low temperature swelling in silicon carbide in the presence of helium.

Melting and joining behavior of Sn/Ag and Sn-Ag/Sn-Bi plating on Cu core ball : Lead-free electronics packaging

Abstract: We fabricated Cu core Sn-Ag solder balls by plating pure Sn and Ag on Cu balls and clarified that Sn/Ag plating began to melt at a rather low temperature, the eutectic temperature of Sn-Ag-Cu. This early melting at the eutectic temperature was ascribed to the diffusion of Cu and Ag into the Sn plating during the heating process. We investigated the solderability of the BGA joint with the Ni/Au coated Cu pad to compare it with that of the commercial Sn-Ag and Sn-Ag-Cu balls. After reflow soldering, we observed a eutectic microstructure composed of β-Sn, Ag 3 Sn, and Cu 6 Sn 5 phases in the solder, and a η'-(Au,Cu,Ni) 6 Sn 5 reaction layer was formed at the interface between the solder and the Cu pad. The BGA joint using Cu core solder balls could prevent the degradation of joint strength during aging at 423 K because of the slower growth rate of the η'-(Au, Cu, Ni) 6 Sn 5 reaction layer formed at the solder-pad interface. Furthermore, we were able to fabricate Cu-cored, multicomponent Sn-Ag-Bi balls by sequentially coating binary Sn-Ag and Sn-Bi solders onto Cu balls. The coated balls also exhibited almost the same melting and soldering behaviors as those of the previously alloyed Sn-2Ag-0.75Cu-3Bi solders.

Tensile properties of Sn-3.5Ag and Sn-3.5Ag-0.75Cu lead-free solders : Lead-free electronics packaging

Abstract: The tensile properties of Sn-3.5Ag and Sn-3.5Ag-0.75Cu lead-free solders were investigated. The effect of annealing at 100°C for 1 h before the tensile test on mechanical properties was small in both solders. The tensile strength decreased with decreasing strain rate, and with increasing test temperature. However, the ductility of each solder was relatively constant in the strain rate ranging from 1.67 x 10 -4 s -1 to 1.67 x 10 -2 s -1 and in the test temperature ranging from -40 to 120°C. From the results of the strain-rate-change tests, the strain sensitivity for Sn-3.5Ag and Sn-3.5Ag-0.75Cu were found to be 0.077 and 0.078, respectively.

Preparation of calcium phosphate coatings on titanium using the thermal substrate method and their in vitro evaluation : Biomaterials and bioengineering

Abstract: Hydroxyapatite (Ca 10 (PO 4 ) 6 (OH) 2 , HAp) and dicalcium phosphate anhydrous (Ca(H 2 PO 4 ) 2 , DCPA) were coated onto titanium substrates using the thermal substrate method in an aqueous solution containing calcium and phosphate ions at 150°C with pH values in the range 4-8. Specimens with the HAp and DCPA layer were immersed in a simulated body fluid (SBF) to examine the dissolution and induced HAp growth behaviour of the coated layers in the SBF. No precipitation occurred on the coated DCPA layer after 7 days immersion in the SBF, and also the DCPA did not dissolve in the SBF. On the other hand, a new precipitate, which was identified as HAp, nucleated after 1 day and grew in a spherical manner on soaking the HAp substrate specimens in the SBF. The influence of small quantities of DCPA in the HAp layer on the coating's bioactive property in the SBF was negligible as the DCPA was not on the surface of the coated layer.

Modelling and material design of SMA polymer composites : Special issue on smart materials-fundamentals and applications

Abstract: Material design has recently become one of the key topics in the development of smart adaptive composites. In particular, different material constituents of the hybrid polymer composites with embedded Shape Memory Alloy elements (SMA composites) have to be combined and positioned in such a way that predetermined functional properties are obtained. Due to the complexity arising from the inherently nonlinear and hysteretic thermomechanical response of SMA elements, modelling of the functional behaviour of SMA composites has become an indispensable part of the SMA composite technology. In this paper, design of SMA polymer composites using a recently developed SMA composite model is demonstrated. The simulations carried out in a preliminary stage of the smart composite design help to find optimal material parameters of the SMA wires (Young's modulus and coefficient of thermal expansion of austenite and martensite, transformation temperature, strain, hysteresis, entropy, etc.) and of the polymer matrix (longitudinal Young's modulus, coefficient of thermal expansion), as well as optimal composite fabrication parameters (layout of the composite, volume fraction of wires, prestrain given to the SMA wires when hybridising it with the matrix).

Solid-state recycle processing for magnesium alloy waste via direct hot forging : Environmental benign manufacturing and material processing toward dematerialization

Abstract: A solid-state recycle processing for magnesium alloy waste has been developed by combining cyclic plastic working and direct hot forging under the short thermal explosion. AZ91D machined chips, which were employed as wasted materials in this study, were consolidated to the green compact with fine microstructures via bulk mechanical alloying (BMA) process, where the compaction and forward extrusion in the closed die were repeated at room temperature. To keep fine microstructures after hot forging, that is, to prevent from the matrix softening due to the grain and/or intermetallic growth, the thermal damage on the green compact in pre-heating before forging was controlled by using the infrared gold image rapid heating furnace. The hot forged AZ9 ID alloy showed superior mechanical properties such as hardness and ultimate tensile strength (UTS) to the cast one used as input raw materials. The same effects were recognized in the case of wasted Al-Si alloys via this process. The developed solid-state recycle processing revealed a possibility to improve the mechanical properties of the consolidated light alloys even in employing their wasted materials.

Aluminum-alloyed cast iron as a versatile alloy : Environmental benign manufacturing and material processing toward dematerialization

Abstract: The feasibility of intelligent utilization of iron-aluminum scraps is explored in this work. Through adding aluminum which is contained in the scraps to cast iron, the changes in wear resistance, heat resistance and damping property of aluminum-alloyed cast irons were systematically investigated. Superior properties were obviously manifested in the cast irons with certain aluminum contents. Iron-aluminum mixed scraps are expected to be utilized as a raw material for high quality cast irons.

Effect of nitrogen addition on shape memory characteristics of Fe-Mn-Si-Cr alloy : Special issue on smart materials-fundamentals and applications

Abstract: Nitrogen-microalloying and partial substitution of Cr for Mn have been employed to enhance the shape memory effect and corrosion resistance of Fe-Mn-Si based alloys. Typically, the tested alloys with nominal composition Fe-25Mn-6Si-5Cr-(0.12-0.14)N in mass% exhibit perfect shape recovery for a 3% pre-strain after only one cycle of thermomechanical training. The related mechanism has been discussed, taking account of the effect of nitrogen on the stacking fault energy (SFE) or the stacking fault probability (P sf ) of the alloy and the strengthening of the austenite matrix. Thermodynamic calculation and P sf measurement showed that the SFE increases with increasing N-content in the concentration range investigated, e.g. less than 0.3 mass%. Thus, the critical stress for the formation of stress-induced martensite increases with N-content. It is believed that the interstitial strengthening of the matrix by nitrogen predominantly contributes to the improvement of shape memory effect. Besides, nitrogen-microalloying remarkably improves the corrosion resistance of the alloys in aqueous solutions containing NaOH and NaCI, but not in HCI solution as indicated by the long-term immersion tests.

Magnetostrictive properties of galfenol alloys under compressive stress : Special issue on smart materials-fundamentals and applications

Abstract: Fe-Ga alloys, in which the α-Fe structure is maintained, are rich sources of high strength, low cost magnetostrictive alloys for transducer and vibration reduction applications. Although the magnetostriction of Fe itself is very low, when a relatively small fraction of the Fe atoms are replaced by Ga, the magnetostriction, (3/2)λ 100 , increases greatly. Until recently, the highest magnetostriction was found with the replacement of Fe by Al (Alfenol). In this paper, we present our measurements of magnetostriction on Fe 1-x Ga x , 0.13 ≤ x ≤ 0.24, (Galfenol). With the substitution of 19% Ga for Fe in Fe 1-x Ga x , a 12-fold increase in magnetostriction to ∼ 400ppm occurs, even though Ga is non-magnetic. In these alloys, the saturation magnetizations remain high, M s ≅ 1.7 T, and the Curie temperatures are far above room temperature, T C ≅ 700°C. In most alloys studied, the magnetostrictions and magnetizations are fully saturated in fields less than 24 kA/m, even under compressive stresses > 100MPa. For x = 0.24 (near Fe 3 Ga), an anomalous increase in magnetostriction with temperature occurs with a peak magnetostriction above room temperature. Small additions of Ni and Mo to the binary Fe-Ga alloys decrease the room temperature value of λ 100 .

Direct comparison between critical cooling rate and some quantitative parameters for evaluation of glass-forming ability in Pd-Cu-Ni-P alloys : Bulk amorphous, nano-crystalline and nano-quasicrystalline alloys IV

Abstract: The quantitative parameters such as supercooled liquid region or several reduced glass transition temperatures were applied for evaluating the glass-forming ability of Pd-based metallic glasses. A distinct proportional tendency was recognized between measured critical cooling rates and reduced glass transition temperature by liquidus temperature rather than eutectic temperature. Significance and physical meanings of the quantitative parameters for evaluating of glass-forming ability were also discussed. Furthermore, a new concept of a modified reduced glass transition temperature was proposed to evaluate the glass-forming ability. The modified reduced glass transition temperature as a function of critical cooling rate was found to exhibit a much clear linearity.

New aspects of structural and magnetic behaviour of martensites in Ni-Mn-Ga alloys : Special issue on smart materials-fundamentals and applications

Abstract: The structural changes and magnetic anomalies accompanying martensitic transformations in Ni-Mn-Ga alloys are briefly discussed. The role of lattice tetragonality of martensite in the reduction of magnetic field needed for the observation of large magnetostrain effect is theoretically analyzed, considering the compensation of the magnetic anisotropy. The possibility of the field reduction is based on the previously observed lattice parameter dependence on the temperature and proper fit of the alloy specimen shape. The model shows that a significant reduction of the magnetic field needed for the giant MSE can take place in martensites with 0.98 < c/a < 1.04.

The effect of 800 MeV proton irradiation on the mechanical properties of tungsten : Special issues on radiation-induced effects by high energy particle/solid interaction

Abstract: For the Accelerator Production of Tritium (APT) and the Accelerator Driven Transmutation Facility (ADTF), tungsten is being proposed as a target material to produce neutrons. Previous work has shown that the mechanical properties of tungsten are degraded from irradiation in a fission neutron flux but little work has been performed on the irradiation of tungsten in a high energy proton beam. In this study, tungsten rods were irradiated at the 800 MeV Los Alamos Neutron Science Center (LANSCE) proton accelerator for six months. To avoid corrosion during irradiation, the rods were slip fit with thin (0.25mm thick) 304L stainless steel (SS) or (0.125 mm thick) annealed Alloy 718 tubing. After irradiation to a maximum dose in the tungsten of 23.3 dpa at T irr = 50-270°C, the clad rods were opened in the hot cells and the tungsten was removed. The tungsten was then sliced into short compression specimens (∼ 3 mm long). Hardness tests and compression tests were performed on the tungsten rods to assess the effect of irradiation on their mechanical properties. Results show an increase in hardness with dose and irradiation temperature and an increase in yield stress with dose.

Effect of annealing atmosphere on void formation in copper interconnects : Special issue on materials-related issues for Cu interconnects used in ultra high speed large scaled integrated Si devices

Abstract: In order to understand the void formation mechanism in electroplated Cu interconnects used in Si-semiconductor devices, microstructure of Cu/CuO/Cu layered films which were prepared on the Si 3 N 4 /Si substrates by the sputter-deposition technique was observed by transmission electron microscopy (TEM) and scanning ion microscopy (SIM). A high density of macro and micro voids were observed in the samples annealed in atmosphere containing hydrogen, whereas no voids were observed in the samples annealed in Ar atmosphere. TEM observation suggested that a small amount of oxygen contained in the Cu films (even a native oxide layer) formed water vapor at elevated temperatures, causing formation of the micro-voids when the samples were annealed in hydrogen atmosphere. The present result suggested that the void formation in the electroplated Cu films was induced by existence of impurities such as oxygen in the Cu films, and that the void growth was strongly enhanced by annealing in hydrogen atmosphere.

Developments of aluminum- and magnesium-based nanophase high-strength alloys by use of melt quenching-induced metastable phase : Bulk amorphous, nano-crystalline and nano-quasicrystalline alloys IV

Abstract: The stabilization of supercooled metallic liquid occurs for a number of alloys where the constituent elements have the following three rules, i.e., multi-component of more than three elements, significant mismatches of atomic size above 12% among the main three elements, and negative heats of mixing among their main elements. The use of the stabilized supercooled liquid has enabled us to synthesize a number of novel advanced metallic materials. In this review, we present the alloy components, fabrication processings, structures, mechanical properties and applications of high-strength Al- and Mg-based alloys with glassy, nanocrystalline or nanoquasicrystalline phase which were developed on the basis of the concept of the utilization of stabilized supercooled liquid for the last one decade.

Preparation of Fe65Co10Ga5P12C4B4 bulk glassy alloy with good soft magnetic properties by spark-plasma sintering of glassy powder : Bulk amorphous, nano-crystalline and nano-quasicrystalline alloys IV

Abstract: With the aim of developing a large size bulk glassy Fe-based alloy with good soft magnetic properties by the powder metallurgy technique, we have applied the spark-plasma sintering technique to a Fe 65 Co 10 Ga 5 P 12 C 4 B 4 glassy alloy powder with a large supercooled liquid region of 50 K before crystallization. The existence of the supercooled liquid region enabled us to form a large size bulk glassy alloy of 20 mm in diameter and 5 mm in thickness with a high relative density of 99%. The resulting bulk glassy alloy exhibits good soft magnetic properties, i.e., 1.20 T for saturation magnetization, 14 A/m for coercive force and 6000 for maximum permeability. The good soft magnetic properties for the multicomponent Fe-based bulk alloy are attributed to the combination of the high relative density and the maintenance of the single glassy structure. The success of forming the large size bulk glassy alloy with good soft magnetic properties by the powder metallurgy techniques is promising for future use as practical soft magnetic materials.

The effect of Ta content on phase constitution and aging behavior of Ti-Ta binary alloys : Biomaterials and bioengineering

Abstract: Using Ti-Ta alloy to which Ta was added systematically, i.e. Ti-5 mass%Ta, 10 mass%Ta, 20mass%Ta, 30mass%Ta, 40 mass%Ta and 50 mass%Ta alloys, the effect of Ta concentration on phase constitution in the solution treated and quenched state and aging behavior is studied by electrical resistivity and Vickers hardness measurements and X-ray diffactometry. All alloys were solution treated at 1173 K for 3.6 ks and then quenched into ice water (STQ). STQed specimens were isochronally heat treated from 323 to 1173 K. STQed specimens of Ti-50 mass%Ta alloy were isothermally aging at five different temperatures, 573 K, 623 K, 673 K, 723 K and 773 K. In the solution treated and quenched state, only reflections of hexagonal martensite, a' were obserevd by XRD in Ti-5Ta to 30Ta alloys, whereas only orthorhombic martensite, α, was identified by XRD in Ti-40Ta and 50Ta alloys. a in Ti-50Ta alloy is reversely transformed into β upon isochronal heat treatment: the starting temperature is situated at a temperature between 623 K and 673 K. Isothermal aging of this alloy shows that a directly decomposes to a and β phases without reverse transformation of a at 573 K and 623 K aging. On isothermal aging above 673 K, a reversely transforms into β and then isothermal ω phase precipitates in the reversed β.

Tungsten nitride deposition by thermal chemical Vapor deposition as barrier metal for Cu interconnection : Special issue on materials-related issues for Cu interconnects used in ultra high speed large scaled integrated Si devices

Abstract: A CVD-WN film is deposited as a barrier metal for copper interconnection using thermal CVD (Chemical Vapor Deposition) of WF 6 /NH 3 /SiH 4 gases. Deposition of CVD-WN film with a resistivity of less than 300μΩ.cm at a temperature of 400°C or less has been realized for the first time in the world. The deposited WN film is proved to be excellent in barrier properties and able to prevent Cu diffusion even with the film thickness of 6 nm as well. It is also proved that the CVD film is superior to a sputtered barrier metal in coverage and ECD (Electro-chemical deposition) filling properties. XPS analysis showed that adhesion of the CVD film to low-k materials is deteriorated by the existence of F at the interface between the WN film and low-k. Chemical surface pretreatment for low-k materials proves to restrain the pile-up of F at the interface and improve adhesion.

Theoretical formation energy of oxygen-vacancies in oxides : Special issue on grain boundaries, interfaces, defects and localized quantum structures in ceramics

Abstract: Formation energies of neutral and charged oxygen vacancies in MgO, ZnO, Al 2 O 3 , In 2 O 3 and SnO 2 have been calculated by a first principles plane-wave pseudopotential method. Two kinds of polymorphs, i.e., an ordinary phase and a high-pressure or an hypothetical negative pressure phase, have been chosen in order to see the effects of crystal structure. Supercells composed of 54 to 96 atoms were employed, and structural relaxation around the vacancy within second nearest neighbor distances was taken into account. Defect levels were obtained from the difference in total energies of the neutral and charged supercells that contain a vacancy. Ionization energies of the vacancy were calculated as the difference in the bottom of the conduction band and the defect levels. They are found to be proportional to band-gaps with a factor of approximately 0.5, which are prohibitively large for the n-type conduction.