J.P. Chu

Nanoimprint of gratings on a bulk metallic glass

The authors demonstrate that optical gratings with 600 and 1500nm periods on a Pd40Ni40P20 bulk metallic glass (BMG) can be faithfully imprinted in air from Si dies. Results of scanning electron microscopy, atomic force microscopy, and optical diffraction analysis show the fine line feature of ∼150nm. The gratings have smooth and uniform surface profiles with comparable optical properties as the original Si dies. The BMG gratings can be further used to imprint the second-generation replicas on polymethylmethacrylate. Thereby, BMG is a suitable material not only for imprinting nanostructured parts such as gratings, but also as a good die material for nanoimprints.

Laser-shock processing effects on surface microstructure and mechanical properties of low carbon steel

Abstract The effects of laser-shock processing (LSP) on the microstructure, microhardness, and residual stress of low carbon steel were studied. Laser-shock processing was performed using a Nd:glass phosphate laser with≈600 ps pulse width and up to 120 J pulse energy at power densities above 10 12 W cm −2 . The effects of shot peening were also studied for comparison. Laser-shock induced plastic deformation caused the surface to be recessed by≈1.5 μm and resulted in extensive formation of dislocations. Surface hardness increased by up to 80% after the LSP. The microstructure and mechanical properties were altered up to≈100 μm in depth. The LSP strengthening effect on low carbon steel was attributed to the presence of a high dislocation density. Shot peening resulted in a relatively higher compressive residual stress throughout the specimen than did LSP.

Superplasticity in a bulk amorphous Pd-40Ni-20P alloy:a compression study

Abstract Compressive deformation behavior of a cast Pd 40 Ni 40 P 20 bulk metallic glass in the supercooled liquid region (589–670 K) was investigated at strain rates ranging from 10 −4 to 10 −2 s −1 . The material exhibited excellent mechanical formability in the supercooled liquid region. However, in contrast to a Newtonian behavior generally observed in oxide glasses, the present alloy also showed a non-Newtonian behavior, depending upon the temperature and applied strain rate. Specifically, the alloy is like a Newtonian fluid at high temperatures, but becomes non-Newtonian at low temperatures and high strain rates. Structures of the amorphous material, both before and after deformation, were examined using X-ray diffraction and high-resolution transmission electron microscopy. The non-Newtonian behavior is proposed to be associated with the glass instability during deformation.

A 200nm thick glass-forming metallic film for fatigue-property enhancements

In this letter, we report the fatigue-property enhancement by a thin layer of glass-forming film. The fatigue life of a 316L stainless steel is considerably improved by at least 30 times, depending on the maximum applied stress when it is coated with a 200nm thick Zr47Cu31Al13Ni9 film. The application of the sputtered film yields an increase of the fatigue limit by 30%. The smooth surface, good adhesion, and compressive residual stress are found to play beneficial roles in achieving superior fatigue properties, revealing the glass-forming film as a potential material to enhance fatigue properties.

Characterization of vitrified slag from mixed medical waste surrogates treated by a thermal plasma system

Abstract Various mixed medical waste surrogates have been vitrified by a plasma system built at Institute of Nuclear Energy Research (INER) in Taiwan, Republic of China. Characterizations of vitrified slag were carried out in order to evaluate the effectiveness of an indirect plasma heating used in the INER system. After vitrification, a monolithic metal nugget was separated from the vitrified slag as a result of the gravity effect. The vitrified slag consisted of mostly amorphous state of SiO2, which in turn dissolved other minor constituents from waste feeds and crucible container. In the slag, dispersive metal-bearing second phases in different shapes were observed. Due to their insoluble nature, these phases were embedded in the slag matrix, and no macroscopic segregation was detected. This observation indicates the presence of mixing state during the vitrification treatment. The formation of second phases was closely related to the metallic waste treated, as evidenced by the increased slag densities for the high metallic feed samples. Leachability analysis results revealed that the encapsulation of these second phases by the slag matrix was very effective. Therefore, with optimal feed compositions, the indirect plasma heating condition used in this study has been shown to be satisfactory for the thermal vitrification of mixed medical wastes.

Deposition and characterization of TiNi-base thin films by sputtering

Abstract Chemical compositions, crystallography, microstructure and phase transformation behavior of TiNi-base alloy films grown by R.F. magnetron sputtering have been investigated. Effects of alloying elements such as Cu and Fe on film crystallography and properties are studied. Due to the non-equilibrium characteristic of sputter deposition, as-deposited TiNi-base films prepared are in a non-equilibrium, amorphous state. To yield crystalline structures and desirable phase transformation behaviors, post-deposition annealing in vacuum at 600°C for 1 h is needed. Phase transformation behavior is evaluated by a differential scanning calorimeter and results indicate a typical single-stage transformation in annealed binary films (Ti-48.9 at.%Ni and Ti-41.8Ni). For the Ti-36.6Ni-10.4Cu film, a two-stage transformation is revealed. The single-stage transformation takes place between the B2 parent phase and M (monoclinic) martensite or R (rhombohedral) phase, while the two-stage transformation occurs in a sequence of B2 phase to O (orthorhombic) phase to M phase on cooling and vice versa on heating. Yet, an imperfect phase transformation is found in the Ti-45.4Ni-6.3Fe film for the temperature range examined. Transformation temperatures as well as energies involved in the transformations are in general relatively lower than those of the target. Transformation peak-temperature hystereses of the film are also smaller than that of the target, implying a beneficial characteristic of fast response for shape memory effect.

Formation of a reacted layer at the barrierless Cu(WN)∕Si interface

This letter reports the formation of a reacted layer between Cu film and barrierless Si substrate during annealing. The Cu films with a minor WN phase are deposited by reactive cosputtering of Cu and W in an Ar∕N2 mixture gas. After annealing at 530 °C for 1 h, a ∼200-nm-thick reacted layer formed at the Cu(WN)∕Si interface acts as a barrier to protect the film from extensive interactions with Si. X-ray diffraction, focused ion beam, and transmission electron microscopy results confirm the presence of this layer and show this layer is mainly composed of Cu2WO4, Cu3Si, and Si2N2O. Leakage current and resistivity evaluations reveal the superior thermal reliability of Cu with a dilute amount of WN at the temperatures up to 530 °C, suggesting its potential application in the advanced barrierless metallization.

On annealing-induced amorphization and anisotropy in a ferromagnetic Fe-based film: A magnetic and property study

Magnetic and property characteristics of sputtered Fe65Ti13Co8Ni7B6Nb1 film in as-deposited and annealed conditions are examined. The film is transformed into various nanoscale and amorphous structures during annealing. Fully amorphous structure is obtained at 773–823K, whereas nanocrystalline γ-fcc FeNi, cubic Fe(Ni) and FeNi phases evolve sequentially at various temperatures. Amorphization and nanocrystallization yield alterations in electrical, hardness and magnetic properties with good soft magnetic properties obtained at 898K. Magnetic force images reveal stripe magnetic domain structures at 923–973K, indicating the presence of the strong stress-induced perpendicular magnetic anisotropy due to the combined effect of the positive magnetostriction and the compressive stress.

Thermal stability of sputtered copper films containing dilute insoluble tungsten: Thermal annealing study

This paper describes studies on the thermal annealing behavior of Cu films with 2.3 at.% W deposited on Si substrates. The magnetron cosputtered Cu films with insoluble W were vacuum annealed at temperatures ranging from 200 to 800 °C. Twins were observed in focused ion beam and transmission electron microscopy images of as-deposited and 400 °C annealed pure Cu film, and these twins were attributed to the intrinsic low stacking fault energy. Twins in pure Cu film may provide an additional diffusion path during annealing for copper silicide formation. The beneficial effect of W on the thermal stability of Cu film was supported by the following observations: (i) x-ray diffraction studies show that Cu 4 Si was formed at 530 °C in Cu-W film, whereas pure Cu film exhibited Cu 4 Si growth at 400 °C; (ii) shallow diffusion profiles for Cu into Si in Cu-W film through secondary ion mass spectroscopy analyses, and the high activation energy needed for the copper silicide formation from the differential scanning calorimetry study; (iii) addition of W in Cu film increases the stacking fault energy and results in a low twin density.

Liquid-phase sintering and chemical inhomogeneity in the BaTiO 3 –BaCO 3 –LiF system

An ongoing goal of multilayer capacitor research is to lower the firing temperature of the dielectric. This paper gives a detailed study of sintering BaTiO 3 with LiF flux, which lowers the firing temperature through liquid-phase sintering. A detailed set of experiments is discussed concerning microstructural evolution and corresponding dielectric properties under a number of processing variables, including amount of LiF, sintering temperature, and particle size. Different scales of chemical inhomogeneity were observed in this system, which reflect two underlying mechanisms: solution reprecipitation with limited grain growth at low temperatures, which resulted in distinct core–shell structures, and flux volatility, which gave rise to microscopic chemical inhomogeneity at higher sintering temperatures.