Microstructural modifications and mechanical property improvements on chill-block melt spinning of austenitic manganese steels containing molybdenum and high carbon concentrations are described and discussed.
The electronic density of states of clusters composed from Ti and Cu was calculated in the local coherent potential approximation (LCPA). Using real space representations and the muffin-tin approximation calculations were carried out for different composition rates and for different structures simulating the possible short range order of the amorphous alloys. By comparing the numerical results with experimental data one can collect arguments for the geometrical structure of these alloys.
The dynamic structure factor S(Q, ω) of the metallic glass Ni 24 Zr 76 was investigated for momentum transfers Q between 0.8 ≤ Q ≤ 2.5 A −1 and energy transfers hM below 20 meV using neutron inelastic scattering techniques. The experiments were done at the time focussing time-of-flight (t-o-f) spectrometer IN6 at the HFR of the Institut Laue-Langevin in Grenoble. The metallic glass and the same glass after crystallization were measured at 380K.
On discussing electron transport properties of metallic glasses, we have proposed to classify them into groups in terms of their magnetic states; (1) ferromagnetism with T c > 300 K, (2) weak ferromagnetism, (3) spin glass or Kondo state, (4) temperature independent strong paramagnetism and (5) weak para- or diamagnetism. Attention is focused on the temperature dependence of the electrical resistivity in non-magnetic group (4) and (5) metallic glasses. The results for group (5) metallic glasses can be consistently interpreted in the framework of the generalised Faber-Ziman model. On the contrary, unique temperature dependences in group (4) metallic glasses, being different from that of group (5) alloys, lead us to conclude the presence of different scattering mechanism. The role of d-electrons is emphasised.
The Gibbs free energy change λGC on crystallization of an amorphous (Fel-xNix)80P14B6 alloy. 0–10 ≤ x ≤ 0.90, is calculated by a method, previously proposed by the present authors, using the thermal analysis data of the amorphous alloy and the thermodynamic data of the components. An anomalous behavior in x = 0.20 − 0.50 seen in the |λGC| versus × relation is explained on the assumption that the structure of crystallized products transfers from bcc to fee phase in such a composition range as in case of amorphous (Fel-xNix)83B17 alloys indicated in the literature. It is also shown that the |λGC| versus × relation with two minima near x = 0.15 and 0.50–0.60, substantially agrees with the composition dependence of the glass-formability and the thermal stability in amorphous state of the present alloy.
Controlling crystallization is necessary for potential applications of glassy alloys. This chapter explores the early stages of crystallization of various iron and nickel based glasses. It describes a differential thermal analysis (DTA) carried out on these alloys. To elucidate the nature of the crystallizing phase corresponding to the first stage, heat treatments of 40 K were chosen below the onset of the first peak. Because the crystallization kinetics varies with composition, DTA was also carried out after heat treatment to check whether the amplitude of the first peak was substantially reduced. The crystallization products were identified by X-ray diffraction. The microstructure and morphology were determined using electron microscopy, generally on ion-beam thinned specimens. The initial crystallization products can be separated into two classes: (1) single-phased products and (2) two-phased products. The first stage of crystallization corresponds to clear primary crystallization for TA 772, 2605 CO, 2826 MB, and YH 498. For the first two, the structure of the crystallizing phase was b.c.c. and perfect single crystals with dendritic morphology were observed. The two other glasses produced primary crystals with an f.c.c. structure. The morphology of these crystals was completely different. The crystals were oblong and contain twins. The long direction is parallel to the projection of the twin plane. There was no evidence for dendritic growth despite the fact that similar amounts of metalloids are necessarily rejected into the glassy matrix and the super cooling is similar.
The distribution in sign of the principal component of the electric field gradient tensor and the average value of the asymmetry parameter are determined using the magnetic perturbation method of quadrupolar 57 Fe Mossbauer spectra. The local order of the Fe structural environment is compared in amorphous, metastable and crystalline phases of composition FeZr 3 .
Photoemission spectra of the UPS-region of quench condensed Ag/Sn and Cu/Sn films in both the amorphous and the crystalline state are reported and compared with data measured on Au/Sn alloys 1 . It is found that the amorphous state has a structure-induced minimum in the density of states near E F which disappears during crystallization. The structure-induced minimum in the density of states is dependent upon the noble-metal content. The minimum will be discussed in connection with structure data as well as the stability against crystallization and electronic transport properties.
Glass melts of the system Pd-Ni-P were saturated with He gas during the melt-spinning process. After extraction of the He from the glasses in a specially designed apparatus the amount of gas was quantitatively measured by means of a mass spectrometer. The He solubilities of the melts and those obtained after extrapolation to T g are related to the free volume in the structure.
The structure of type 308 stainless steel was evaluated following rapid quenching using the hammer-arc process. A large degree of variation was found from a fully austenitic structure to the duplex ferrite plus austenite structure commonly found in welded material. The lack of large-scale segregation, as determined by electron microprobe analysis, indicates the structural variations are due to cooling rate changes rather than compositional fluctuations. The results also show that this material is very sensitive to cooling rate in the range prevalent in the hammer-arc process.
The early relaxation in amorphous Pd77.5Cu6Si16.5 is followed by measuring the internal friction using a torsion pendulum. The sample was 'an almost 1 mm diameter wire. Two relaxation contributions are considered a chemical and a topological one. The latter one is the slowest of the two and is, attributed to a decrease in free volume. A typical relaxation time measured at 420 K is 3.103 min. The former contribution is attributed to the interchange of atoms of different kind. It is a reversible process as long as the amount of free volume is kept constant. An activation energy measured between 400 and 500 K is 2.75 eV.
The three partial structure factors of NiZr alloy glass were derived by pulsed neutron total scattering experiment using isotope substitution method. As the weighting factors for Ni-Zr unlike atom pairs were adjusted to have same contribution in experimental total structures, separation of partial structures was made with little uncertainties. The chemical short-range structure in NiZr alloy glass is quite similar with that in NiZr crystalline compound.
EXAFS (Extended X-ray Absorption Fine Structure) and, to a lesser extent XANES (X-ray Absorption Near Edge Structure) studies are now routinely used to determine local atomic coordinations in amorphous materials. The great advantage of these techniques is that they give the structure relative to a known atomic type, that whose absorption edge is measured, and that the type of the surrounding atoms can be determined from the energy dependence of their electron scattering factors. Thus partial R.D.F.s may readily be obtained and interatomic distances and the degree of chemical ordering determined.
The atomic scale structure of metallic glass wires produced by the in-rotating-water spinning method has been studied by x-ray diffraction and was compared to those of the metallic glass ribbon of the same composition prepared by a conventional single roller method. The present results on metallic glass wires are strikingly similar to those on metallic glass ribbons, although there are small variations in the magnitude of structural functions among the metallic glass samples produced by the different quenching techniques.
Publisher Summary This chapter discusses the atomic structure of the metallic glass Ni 80 P 20 . It describes experiments that were performed to follow the structural changes in a metal–metalloid type glass if the atomic size of the metalloid atom is increased. The total structure factors in this experiment were calculated from coherent scattering cross sections. The Faber–Ziman-, and the Bhatia Thornton- partial structure factors of amorphous Ni 80 P 20 have been determined by the isotopic substitution neutron diffraction technique. The difference of the Ni-and the P-coordination and the pronounced size effect show that the Ni 80 P 20 glass, like the Ni 81 P 19 glass, is no substitutional alloy at all.
The use of rapid solidification processing (RSP) to produce supersaturated solutions of Er and O in Ti is discussed. Subsequent heat treatment of such solutions has been found to result in precipitation of ultrafine dispersions of rare earth oxides which are partially coherent with the matrix. The thermal stability of these particles has been examined as a function of temperature and specimen composition.
A series of 11 metallic glasses has been irradiated with 360-MeV Xe ions at various irradiation temperatures. All glasses show large radiation growth, i.e. during ion bombardment large anisotropic changes occur in sample dimensions. The influence of irradiation temperature as well as alloy composition is investigated and some implications in the radiation-growth mechanism are outlined. No radiation stability of metallic glasses can be expected if anisotropic irradiation conditions are applied.
High Resolution Electron Microscopy (HREM) has been performed on ‘amorphous’ Fe-B-alloys of different compositions in order to investigate the short range order. One finds ordered regions of various sizes for different compositions, as one expects from the pair distribution functions of these samples. A model which describes these experimental findings is introduced. Multislice image calculations from this model show qualitatively the same images as found in the microscope.
A complete re-examination of the thermal and structural characteristics of Ti-Zr-Be metallic glasses has been undertaken in order to investigate the existence of amorphous phase separation. Thermograms from differential scanning calorimetry show reproducible multiple glass transitions from the as-quenched ribbons. However, transmission electron microscopy images and diffraction patterns were unable to detect distinct, separated regions. Considering limitations in detection, we suggest that domains are less than 50 nm in size.
This chapter provides an overview of the modeling of the nucleation temperature for alloys in the Cu–Ti system under laser irradiation conditions. Alloys of composition in the vicinity of a deep eutectic are expected to crystallize from the melt in the form of a multiphase structure, particularly if the TO curves of the phases involved do not cross in the eutectic region. In such a case, even during very rapid cooling, the crystallization process is likely to be difficult because of the required mandatory partitioning of the solute, and glass formation may become the alternative mode of solidification. Glass-forming ability is a feature associated with eutectic regions of the phase diagram. After application of very rapid cooling rates preponderance of the amorphous phase was greatest in alloys in the middle of the Cu–Ti phase diagram, gradually diminishing as the binary sides were approached. This behavior with composition is related to three major factors associated with the FCC structure as it competes with glass formation: (1) the driving force for composition-invariant crystallization (Gv), (2) the nucleation temperature (Tn), (3) and the cooling rate (T).
