Volume 100, Issue 5

Events are described that precede the announcement of the high performance permanent magnets based on the neodymium-iron boride Nd 2 Fe 14 B. When accounts of innovations stem from the principals initiating them, they can be distorted in the interest of establishing a patent position of high commercial value. The problems of finding objective criteria to assess inventiveness in this technological breakthrough are discussed.

The continuum theory of micromagnetism has been found to be a rather effective tool to describe magnetic states and magnetization processes. In this paper some rigorous micromagnetic results obtained for characteristic magnetic properties of nanocrystalline hard magnetic materials will be outlined and their application to the development of outstanding magnetic materials will be discussed. In particular the role of exchange coupled composite systems will be considered and the effects of the microstructure will be investigated. Furthermore, the deteriorating effects of magnetically softened surface regions, the depinning and pinning of domain walls at phase boundaries, the remanence exchange enhancing effects and the depinning fields of domain walls of composite particles in the case of high-density recording systems will be discussed.

The continuous increase in magnetic recording density has so far been achieved by scaling the geometrical dimensions. However, it is now obvious that conventional magnetic recording is reaching its scaling limit. To realize ultrahigh recording densities of 1 Tbit/in 2 and beyond in the future one of the most straightforward concepts is bit-patterned composite media with a regular arrangement of magnetic nanodots, where each nanodot is composed of a hard magnetic and a soft magnetic part and represents one bit. The hard magnetic component guarantees thermal stability for smallest dot sizes whereas the soft magnetic component reduces the coercivity and thus enables writeability with conventional heads. In this review the requirements for ultrahigh density magnetic recording are presented which seem to be optimally fulfilled by L1 0 -FePt (hard magnetic)/Fe (soft magnetic) nanocomposites.

The Al x Mg (1 – x ) B 2 solid solution was studied at temperatures of 900, 1000, 1200 and 1400 °C using X-ray diffraction. From the obtained data, isothermal sections at 1000, 1200 and 1400 °C have been proposed for the Al – Mg – B ternary system. Based on these results there exists an equilibrium between Al and AlMgB 14 at temperatures above 1000 °C.

In this paper, the effects of lanthanum on the deposition rate, composition, structure, hardness, magnetic and anti-corrosion behaviors of electroless Ni – Fe – P deposits prepared from sulphate bath were investigated. In order to characterize the deposits, gravimetric and electrochemical measurement, scanning electron microscopy, X-ray diffraction, and magnetic measurement were applied. The results show that the deposition rate decreases with increasing LaCl 3 · 7 H 2 O concentration in the bath due to the competition adsorptions between rare earth lanthanum, metal ions, and hypophosphite on the surface of the substrate. The magnetic behavior of the deposit is strongly dependent on the LaCl 3 · 7 H 2 O concentration in the bath. The coercive force of the deposit increases, while its saturation magnetization decreases with LaCl 3 · 7 H 2 O concentration increase. When the LaCl 3 · 7 H 2 O concentration reaches 1.50 g l – 1 , the deposit shows a rectangular hysteresis loop with high coercivity. The moderate addition of lanthanum in the bath will increase the hardness of the deposits as a result of the change of composition and structure of deposits. However, the addition of lanthanum has little effect on the corrosion resistance of the deposits.

Interfacial reactions between Sn, Sn-3.0 wt.% Ag-0.5 wt.% Cu (SAC) and an Au/Ni/SUS304 stainless steel (SUS304) substrate were conducted using the reaction couple technique at 240, 255 and 270 °C for 1 – 5 h. In the earliest stage of the reaction, only the Ni 3 Sn 4 phase was formed on the Sn/Au/Ni/SUS304 interface. As the reaction time increased to 4 h, the Ni layer was gradually consumed and the Ni 3 Sn 4 phase detached from the interface. Meanwhile, the Sn reacted with the SUS304 to form the FeSn 2 phase. In the SAC/Au/Ni/SUS304 reaction couple, both Ni 3 Sn 4 and Cu 6 Sn 5 phases were formed on the interface. When the reaction time exceeded 4 h, the Ni 3 Sn 4 phase disappeared; the Cu 6 Sn 5 phase was spread over the SUS304 surface and the FeSn 2 phase was formed on the SUS304 surface. The growth of intermetallic compounds can be described by the parabolic law and the reactions were diffusion-controlled.

The melting behavior of Sn – Bi alloy powder compacts was observed using optical dilatometry. The change in standard deviation of compact width with temperature obtained by dilatometry was used to evaluate the melting behavior by considering the factors in the shape change of the compact under heating. The effects on melting behavior of alloy composition, particle size and pressing load at compacting are discussed in this study. The difference in composition affected the melting behavior in accordance with the phase diagram. Smaller particle size showed a lower degree of melting. The effects of these two parameters, viz. composition and particle size, however, are highly dependent on surface oxidation of powders. The influence of surface oxidation, on the other hand, was reduced by producing the compacts with a higher pressing load.

The paper presents a novel porous, ductile, V particles reinforced, Mg-based metallic glass composite, exhibiting superior mechanical performance with up to 10 % compressive strain and 1100 MPa stress at room temperature. Indentation tests show that the addition of V particles can improve significantly the plastic deformation ability of the glass composites in local regions around the particles. Furthermore, during deformation process, the highly localized shear-banding of the infiltrated glassy matrix within the porous V particles induces an increase in temperature in local regions, where the dilating and softening behavior happen. The heated V particle regions become more effective “sites” for the initiation and arrest of shear bands in the surrounding amorphous matrix. We suggest that porous ductile particles might therefore preferably be used to toughen amorphous materials with stubborn brittleness.

The Sn – Ti – Zr system is an important subsystem for Cu based active brazing filler metals. Experimental results on this system, however, are rather scarce. The diagram is rather uncertain regarding most of the liquidus, especially on the Sn rich side. In this work, the atomic structure and temperature dependence of structure-sensitive physical properties (dynamic viscosity and electrical conductivity) of liquid Sn – Ti – Zr alloys in the Sn-rich corner were investigated in a wide temperature range with special attention to the melting – solidification region. The results allowed the liquidus line position to be specified.

Super-high angular speed polishing of diamond films is a new polishing method. During the polishing process, the rotational velocity of the cast iron polishing plate is higher than that of conventional polishing methods, and friction between the polishing plate and the diamond film during rotary motion generates heat that creates a diffusion condition for carbon atoms. The temperature and strain energy density distributions of the polished surface directly affect the polishing quality of diamond films. In this paper, a three-dimensional thermo-mechanical coupled finite element analysis was employed to analyze the temperature and strain energy due to the friction between the polishing plate and the thick diamond film while the polishing plate rotates at super-high angular speed. The results indicate that when the diamond film and polishing plate rotate in the same direction, the differences of temperature and strain energy evidently decrease, and the temperature and strain energy in the diamond film become more uniform. The removal rate by super-high speed polishing has been quantitatively described by the diffusion mechanism, and it agrees well with the experiment data. This work will provide theoretical guidance to the design and operation of the super-high speed polishing of diamond films.

Thin films typically exhibit variations in modulus and hardness with increasing indentation depth during depth-sensing indentation experiments at ultramicroscopic contacts (“nanoindentation”) because the measured stiffness response is affected by the substrate. There are three techniques commonly used to sample this variation in properties with depth: multiple indentations with increasing peak load, a single indentation with multiple-partial-unload cycles, and continuous stiffness measurement during a single indentation event. Experiments using the first two options were performed on a series of thin film systems and the method of multiple-partial-unloading found to have significant drawbacks when used at the sub-micron length scale that lead to erroneous conclusions.

Undoped and Mn doped ZnO ceramics, sintered at 1200 °C, were produced from sol-gel derived nanocrystalline powders calcined at 750 °C. Mn doped powders showed trace amounts of spinel (ZnMn 2 O 4 ) phase in addition to a dominant zincite phase, while Mn doped ceramics were comprised solely of zincite structure. X-ray mapping of the powders did not reveal any Mn concentrated areas, indicating that the ZnMn 2 O 4 phase was homogeneously distributed with a very small grain size. The grain size of the undoped powders was around 50 nm, and there was a minor increase in the grain size when powders were doped with Mn. Undoped ceramics exhibited grain sizes distributed in the range 2 – 10 μm while Mn doped ceramics displayed slightly smaller grains. Relative densities of the undoped and Mn doped ceramics were measured as 0.695 and 0.950, respectively.

A comprehensive study of 18 % Ni maraging steel welds is done in order to determine the suitability of repair welding of aluminum die-casting dies and to prolong the in-service tool life. This study emphasizes the influence of welding parameters and post-welding precipitation annealing heat treatment on the welds' mechanical and metallurgical properties. A series of U-grooved specimens of 1.2344 tool steel is prepared. These grooves are filled with 1.6356 maraging steel as filler wire using multi-pass Gas Tungsten Arc welding. The metallurgical properties of the filler welds, in the as-welded condition and after precipitation annealing with a series of different parameters, are studied. The influence of preheat temperature, heat input during welding, and hot working of maraging steel welds is evaluated regarding mechanical and metallurgical properties. The response surface models for the prediction of mechanical properties (i. e. hardness, toughness, tensile strength, and yield stress after post-welding heat treatment) are developed. The results show that metallurgical and mechanical properties significantly depend on welding technology and post-welding heat treatment parameters. Gas Tungsten Arc welding with low heat input permits the omission of solution heat treatment after welding, while hot working of welds during welding increases the mechanical properties. Developed models for the prediction of mechanical properties enable selection of precipitation annealing parameters for a particular application based on desired mechanical properties.

The paper aims to present the processing and development of functionally graded Cu – Cr materials, widely used as a monolithic contact material in vacuum circuit breakers. Simple and novel processing routes, used in this study, in addition to being cost-effective and energy efficient, generate higher density and electrical conductivity of the Cu – Cr compacts. It is shown that the use of mechanically alloyed Cu – Cr powders enhances the properties of the compacts, as compared to those prepared from as-received powders. Furthermore, explosive compaction and application of coated powder were found to result in still better properties. Scanning electron microscopy and atomic force microscopy were used to explain the scientific significance of this development.

As promising candidates for new high-temperature structural materials, Ti – Si eutectic alloys are required for the next generation of advanced aircraft engines. In this paper, microstructures of the Ti – Si eutectic alloys with various Cr contents were investigated by means of X-ray diffraction, scanning electron microscopy and light optical microscopy. The results show that with the increase of Cr content up to 9 wt.%, β-Ti (Si, Cr)ss matrix and Ti 5 Si 3 form in the as cast alloy, however, the α-Ti (Si, Cr)ss phase disappears. Cr element solute in β-Ti and Ti 5 Si 3 can significantly change the morphology and distribution of Ti 5 Si 3 intermetallic phase. This greatly affects the fracture behavior and mechanical properties of as-cast Ti – Si eutectic alloys.