A Kikuchimap for the 6H polytype of α-SiC has been constructed for the standard triangle Selected, indexed diffraction spot patterns have also been produced and are included as companion information for the map.

A Pd–U–Si metallic glass transforms upon annealing to a quasicrystalline phase of the same composition. Electron diffraction patterns of this material verify its icosahedral symmetry. Differential scanning calorimetry and transmission electron microscopy are used to obtain both the nucleation and growth kinetics of this glass-to-quasicrystal, first-order phase tranformation. The homogeneous nucleation rate of the quasicrystaUine phase in the metallic glass achieves a maximum at a temperture where its growth is still relatively slow.

Two currently proposed structural explanations for thermal embrittlement of Fe-based metallic glasses are discussed: embrittlement due to loss of excess free volume by annealing and embrittlement due to the formation of chemical heterogeneities due to phase separation in the amorphous alloy. It is shown that recent small-angle x-ray scattering results that were thought to be in disaccord with field-ion microscopy (FIM) atom-probe analyses indicating occurrence of phase separation are in fact in agreement with the latter. Then a new mechanism is presented, based on structural models and density measurements in Fe–B-type amorphous alloys, which results in loss of free volume during the occurrence of phase separation, thus integrating an important effect of phase separation in the free-volume models for plastic flow in amorphous alloys.

The passivation behavior of the P-implanted alloys in a Cl-containing electrolyte as a function of Cr concentration and P implantation has been investigated. At low Cr concentrations (6% Cr), P implantation sufficient to form an amorphous layer degrades the passive behavior of the base alloy and induces pitting, and at high-Cr levels (18%) P has little effect on passivation. However, at intermediate Cr levels (8%, 10%), P implantation significantly improves passivity, with the greatest improvement occurring at 10% Cr. When implanted to ∼25% P, the Fe–1OCr alloy exhibits a decrease in the passive current density by 4 orders of magnitude relative to the unimplanted alloy, and shows current decay characteristics that closely resemble those of the Fe–18Cr alloy.

The crystallization behavior of an arc-melted, splat-quenched amorphous Ta55–Ir45 alloy was investigated by differential thermal analysis (DTA) and transmission electron microscopy (TEM). The DTA experiments showed that the glass transition temperature (Tg) for this material was 485 °C and that the crystallization temperature (Tx) closely followed at 495 °C. This Tx is much lower than has been previously reported. In-situ TEM annealing experiments, in addition to confirming Tx, illustrated that crystallization proceeds as a two-step process. A fcc phase is the first to crystallize at 500 °C followed by the equilibrium phases, α and σ, and/or the bcc Ta phase near 600°–650 °C. Microhardness measurements were made as part of an initial mechanical properties investigation. Inconsistencies with the work of previous investigators of this system are discussed.

Measurements of pressure-concentration (p-c) isotherms of hydrogen in a wide variety of amorphous Ni—Zr alloys are presented. The measurements are complemented by an analysis of hydrogen sites in computer-generated amorphous clusters. The binding energy of these sites has been calculated using an effective medium theory. Filling these sites randomly in order of decreasing binding energy with a nearest-neighbor exclusion leads to a chemical potential in agreement with what is found from the (p-c) isotherms. In the pressure range required in a hydrogen-storage device (1–10 atm) the hydrogen occupies interstitial sites surrounded by 3Zr, 1Ni atoms or 2Zr, 2Ni atoms.

In an ultrahigh vacuum (UHV) environment, thin poly crystalline Ni films have been deposited on a Zr (112) single-crystal surface. In contrast to the case of poly crystalline Ni and Zr films, formation of amorphous Ni—Zr is not observed upon annealing at 300 °C for 11.5 h. The possible presence of an oxide or an amorphous phase diffusion barrier is ruled out and therefore the lack of a reaction must be due to a reaction barrier at the single-crystal Zr/ Ni interface. Either ion mixing of the interface with 400 keV, 5 × 1015 Xe+ /cm2, or deposition of a poly crystalline Zr layer in between the Zr single crystal and the Ni overlayer can overcome this reaction barrier. These results indicate that grain boundaries in polycrystalline Zr play an important role in amorphous Ni—Zr formation by a solid-state reaction.

Electron microscopic observations, electrical resistivity, and lattice parameter measurements of annealed Pd-12.5 at. % Y alloy indicate the presence of long-range order in the form of a Pt7Cu superlattice. This is similar to the order found in Pd7Ce, which is also isomorphous with Pt7Cu. The order-disorder transformation temperature was found to be Tc = 783 ± 5 K. Evidence was found from resistivity measurements for the existence of an ordered structure in the hypostoichiometric alloys: Pd-10.0 at. % Y and Pd-8.0 at. % Y. The order-disorder transformation temperatures were lower than that for the stoichiometric alloy Pd7Y.

The dominant diffusing species in VA13, Co2Al9, CrAl7, and MoAl12 formation was determined. These are the initial phases to form in metal-Al reactions and the most Al-rich phases on the phase diagrams (except for VA13). It was found for the growth of VA13, Co2Al9, CrAl7, and MoAl12 that Al is the dominant moving species. This is very different from results with metal-Si marker experiments where either the metal or Si can be the dominant moving species in the initial phase. In aluminides the dominant moving species is related to the initial phase formed. For the growth of the Ni-rich phase, Ni3Al, Ni was the dominant moving species.

The effectiveness of oxidation-inhibiting nitride layers formed in silicon by ion implantation has been studied by in situ thermogravimetric analysis. The oxidation time delay and the oxidation rate after nitride breakdown were measured for various fluences of implanted nitrogen. The results generally confirm previous findings for the oxidation delay; however, a detailed analysis indicates that the onset of oxidation is not as abrupt as had been previously assumed. After the delay period, the oxidation of an implanted Si/SiO2 structure follows a linear time dependence at oxide thicknesses where unimplanted Si/SiO2 structures follow a parabolic dependence.

Using a material synthesis technique to optimize the coverage of metals on the surface of silicon, the iron-promoted nitridation of high-purity silicon was studied. The kinetic results indicated that conversions to silicon nitride were directly dependent upon the surface loading by iron up to the point of excess coverage where the rates dropped sharply. A further modification of the iron-promoted system by alkali and alkaline earth metals sharply increased the degree of conversion. The results suggested that the chief effect of the metal promotion was to reduce nitridation induction times and to disrupt the oxided silicon surface. Reaction rates were enhanced by the iron promoter to the extent that the silicon surface was covered and deoxidized by iron.

Galium phosphorus films grown on (211 )Si by molecular beam epitaxy have been investigated using a transmission electron microscope. The main defects observed in the alloy were of misfit dislocations, stacking faults, and microtwins. The misfit dislocations are of the 60° type with Burgers vectors of a/2 ‹110›, and the stacking faults are intrinsic in nature and bounded by Shockley partials and stair-rod partial dislocations. The habit planes of these defect structures were found to depend solely on the crystalline growth orientation with respect to the substrate orientation. A possible mechanism of the formation and growth of these misfit defects has been proposed for the present growth orientation.

Transmission electron microscopy (TEM) has proven to be an invaluable tool in a multifaceted research program at North Carolina State University, which centers on developing β-SiC as a useful semiconducting material. As such, techniques have been developed for fabricating both plan-view and cross-sectional TEM silicon carbide thin films grown by chemical vapor deposition. The results of the TEM observations are used to determine the effectiveness of specific processing parameters in terms of film quality and defect structure as well as oxidation, ion implantation, and annealing procedures.

Chemical reactions at the Au/InP interface were investigated in the temperature range 25°-510 °C by x-ray diffractometry, scanning electron microscopy (SEM), and energy dispersive x-ray analysis. The samples were prepared by depositing gold films onto clean InP (100) single-crystal substrates under 10∼9 Torr vacuum. Spots appeared in SEM micrographs of the deposited film of a sample annealed at room temperature for 35 days, indicating that a solid-state reaction had occurred. After the sample was heated to 330 °C under flowing N2 gas, £1 dendritic islands were observed in the film. A 365 °C anneal turned the color of the Au film from yellow to pink, and Au, £1 and Au2P3 were identified by x-ray diffractometry. In reacting with the InP substrate, £1 produced silver-colored γ and more Au2P3 at 450 ° C. With respect to InP, γ was relatively stable, and further reactions were minimal even when the sample was annealed at 510 °C for 40 min under atmospheric-pressure N2. The ternary phase diagram for the bulk Au-In-P system provides the basis for understanding the sequence of the above results and much of the information in the literature about Au/InP interfacial reactions.

Results are reported of (00l) x-ray studies of the α(Ic = 10.65 Å) and β(Ic = 11.49 Å) phases of stage 1 graphite-CsBix ternary intercalation compounds that are air stable. The integrated intensities of the (OOl) x-ray lines are analyzed in terms of a centrosymmetric sandwich model that consists of two laycrs each of Cs, Bi, and C. The results of these analyses indicate that the Bi layers are nearly centered in the cell as Suggested by Lagrange et al. [Synth. Met. 12, 201 (1985)]. Furthermore, stoichiometries of the α and β phases are found to be Cs0.99 Bi0.43C4 and Cs0.83Bi0.81C4, respectively. The β phase is found to contain nearly twice as many Bi atoms'. The sample mass change upon intercalation is in good agreement with the x-ray analyses. The substantial difference in the Bi concentration in the α and β phases would be expected to have strong influence on the superconducting properties of these graphite intercalation compounds (GIC's).

The kinetics of changes in void size during annealing of glass-like carbons in the temperature range 1000°−2800 °C for times up to 150 h were studied using small-angle x-ray scattering determinations of the radius of gyration Rg. The results show that Rg ranged from 9 Å at 1000°C to about 24 Å at 2800 °C. A pore coarsening analysis and a superimposition kinetic analysis applied to Rg gave activation energies of 76 ± 4 kcal/mole and 74 ± 9 kcal/mole, respectively, which are associated with migration of vacancies within graphitic layers in the matrix material.

The microstructure of three different types of γ-Fe2O3 particles were examined using transmission electron microscopy. These included pure γ-Fe2O3, γ-Fe2O3 that had been surface modified using Co, and γ-Fe2O3 that had been doped with Co. The major internal microstructural defects found in the particles in all of the samples were pores and antiphase boundaries. Some particles also had a very high density of dislocations and low-angle boundaries. In general, the particles could be described as single crystals with symmetric cross section. The structure is based on a tetragonal unit cell, and each particle is divided into antiphase domains in which the c axis is oriented at 90°with respect to adjoining domains. The particles often exhibited very irregular shapes. No effect of Co modification was seen on the internal or surface structure of the particles. The Co-doped particles were found to be smaller in size and contained a lower density of internal defects. The effect of the microstructural defects and morphological irregularities in these particles on magnetic behavior is discussed.

Substrate curvature and submicron indentation measurements have been used recently to study plastic deformation in thin films on substrates. In the present work both of these techniques have been employed to study the strength of aluminum and tungsten thin films on silicon substrates. In the case of aluminum films on silicon substrates, the film strength is found to increase with decreasing thickness. Grain size variations with film thickness do not account for the variations in strength. Wafer curvature measurements give strengths higher than those predicted from hardness measurements suggesting the substrate plays a role in strengthening the film. The observed strengthening effect with decreased thickness may be due to image forces on dislocations in the film due to the elastically stiffer silicon substrate. For sputtered tungsten films, where the substrate is less stiff than the film, the film strength decreases with decreasing film thickness.

Crack propagation thresholds in brittle materials are explained by consideration of the work done by the applied loading and that needed to create new surfaces as a crack propagates. The threshold mechanical energy release rate is shown to be a measure of the equilibrium surface energy of the material, dependent on the chemical environment. For applied loadings greater than those needed to maintain equilibrium the surface energy term introduces nonlinearities into the crack propagation characteristics. Any surface force or lattice trapping behavior at the crack tip will not influence the observed threshold provided the crack tip remains invariant on crack extension. A simple indentation/strength technique is demonstrated that permits the surface energy in the equilibrium state to be estimated. The technique is applied to the propagation of cracks in sapphire and the surface energy in water estimated as 1.42 J m−2, suggesting that the surfaces in water are stabilized by interactions stronger than van der Waals forces or hydrogen bonding alone.

Dried gel films of poly (vinyl alcohol) were drawn at high temperature using zone heating devices. Hot air zones 5 and 10 mm wide were used to draw the gels to draw ratios up to λ = 23 × at 200 °C. A 3.2 mm wide heated bar in direct contact with the specimen enabled use of drawing temperatures up to 235°C and resulted in draw ratios of 25-38 ×. Drawn films had a highly fibrous nature, were well oriented, and contained crystals about 10 nm long. Gel permeation chromatography studies of the material before and after drawing showed that drawing at high temperatures caused some changes in molecular weight and dispersity. Storage moduli of the fibers increased with draw ratio, reaching a high of 59 GPa at 31× but, in general, leveled off at high A. Low draw ratio (10-15 ×) fibers drawn in the 5 mm air zone had moduli comparable to high draw ratio (25-38 ×) fibers drawn with the high-temperature contact heater (20-60 GPa). Retraction studies showed that low modulus fibers, even those highly drawn, had low effective molecular extension. Drying the fibers increased both their room temperature modulus and glass transition temperature.