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This report consists of the following four parts: Field Ion Microscopy Studies of the Interaction of Hydrogen with Selected Metals and Alloys; The Role of Noncrystalline Films in Passivation and Breakdown of Passivation; Effect of Chromium Depletion on the Repassivation Kinetics 18-10 Austenitic Stainless Steel in Sodium Chloride Solutions; and Composition of Surface Films Formed During the Repassivation of Iron and Iron-Molybdenum Alloys. (Author)

?27This report consists of four parts as follows: (1) A study of the influence of Mo in Fe-Mo alloys on crevice corrosion. It was found that 5% Mo is needed to affect repassivation in a crevice. (2) The description of a new technique for measuring repassivation rates in a crevice. (3) A description of alloys prepared to simulate the composition of metal near grain boundaries of sensitized austenitic stainless steel. These alloys are used for studies of the effect of sensitization on repassivation kinetics. (4) A review of new approaches in the study of localized corrosion., See also report dated Oct 75, AD-A019 648.

Investigations on piezoelectricity and pyroelectricity in crystalline polymers have been carried out using a copolymer of vinylidene fluoride and tetrafluoroethylene which crystalliezes directly from the melt into a polar crystal form. The crystalline fraction is easily varied from 0.35 to 0.5. Alignment of the dipoles in an applied electric field appears to approach saturation electric fields of 250 kV/cm, independent of poling temperatures between 0 and 80 C. Piezoelectric responses from samples of varying crystallinity are consistent with increased polarization and lower compressibility as the degree of crystallinity is increased. Thermal pulse experiments reveal that when poled at room temperature, only a thin region near the positive electrode is poled but the thickness of this region increases with an increase in poling temperature. Copolymer films crystallized from the melt in the presense of a field show greatly improveed stability of piezoelectric activity when stored at elevated temperatures compared with samples poled only after crystallization. The room temperature poling of polyvinylidene fluoride using a corona discharge has been confirmed. Preliminary results are presented which imply that even the non-polar alpha phase of the polymer may be poled in this way but it is unstable--especially at elevated temperatures. (Author), Original contains color plates: All DDC reproductions will be in black and white.

To assure the reliability of silicon carbide and silicon nitride in turbine applications, their mechanical properties at high temperatures must be understood. Fracture properties are particularly important. Because the experimental techniques for the measurement of these properties had not yet been developed, at the start of this program, there existed little information on the fracture properties of silicon carbide and silicon nitride at high temperatures. This summary of work conducted at NBS over the past three years presents a considerable body of knowledge on these materials as a result of the improvement and development of new techniques of measurement.

Wear experiments have been conducted to determine the plastic strains that are introduced in the surface material near sliding wear tracks. Both oil lubricated and dry sliding experiments have been carried out at different sliding distances on surfaces of copper. The strain values were determined from selected area electron channeling patterns obtained using a scanning electron microscope from regions as small as 10 micrometers in size and 0.05 micrometer deep around the wear track. A deformed calibration specimen was used to relate electron channeling band contrast to deformation strain. Wear debris has been removed from a number of test systems and analyzed using different methods. Those methods produced specific information concerning the particulate size and composition. A magnetic debris recovery method was quantitatively evaluated using actual debris samples and also using collections of manufactured particulates having known sizes and compositions. A comparison between chemical analysis and particulate analysis findings is presented.

Three principal methods of failure prediction for brittle materials are analyzed statistically. Each method depends on fracture mechanics for its predictive value and hence, the variance of the failure time is found to depend on the scatter in the fracture mechanics data and the scatter in the estimate of the initial size of the strength limiting crack. The variance is used to calculate confidence limits for the prediction of failure for two materials, glass and silicon carbide. Procedures for the collection and analysis of data are discussed, and the implications of the analysis for lifetime prediction are evaluated.

A theory of strength loss for brittle surfaces in contact situations, developed in a previous paper for 'blunt' indenters, is here extended to the case of 'sharp' indenters. A prior fracture mechanics analysis of crack growth beneath ideal cone indenters serves as the basis for predetermining the prospective surface degradation of ceramic components in service. Compared to blunt indenters, severe degradation can occur at the lower contact loads. However, at high loads the extent of degradation becomes remarkably insensitive to indenter geometry. Essential theoretical predictions are verified by bend tests on glass slabs. The effect of indenter 'sharpness' and initial specimen surface flaw state are investigated systematically, along with some secondary rate effects in the contact process. The possibility of minimizing degradation via adjustment of material parameters (including hardness) or surface condition (e.g., residual stresses, frictional properties) is briefly discussed., See also report dated Feb 75, AD-A007 447.

Determinations of strains have been made on the surface and subsurface on specimens of high purity iron after different amounts of sliding wear have taken place. The method involved the measurement of loss of intensity (contrast) of particular electron channeling lines obtained from small selected areas near the wear track. Through the use of a calibration specimen deformed plastically to a range of strain values, the channeling line contrast loss was related to plastic strain. Strain maps lateral to the wear track and below the original surface were obtained for different total sliding distances by removing controlled thicknesses of iron using electropolishing. In all cases the maximum strain was found at the track center location at the surface and the strains decreased steadily with depth below the track. At 50 g load the strains vanished at about 40 micrometer depth. Significant strains were found to exist outside the wear track boundaries. The results are compared with other studies previously reported.

Contents: Piezoelectricity in polarized polyvinylidene fluoride; Piezoelectric polymer research in Japan; The melting temperature-composition curves of poly(vinylidene fluoride)-poly (vinyl fluoride) mixtures and vinylidene fluoride-vinyl fluoride copolymers; Texture and pyroelectricity in polyvinylidene fluoride; Dependence of the piezoelectric activity of polyvinylidene fluoride upon high speed uniaxial stretching and subsequent poling; Thermally stimulated currents and morphology in PVF2; Piezoelectricity and pyroelectricity in a poly(vinylidene fluoride-tetrafluoroethylene copolymer; Polyvinylidene fluoride as an active device element; Scanning for ferroelectricity in polycrystalline materials; Origins of persistent electrical polarization in polymer solids; Pyroelectric polymers applied to optical radiation measurements; Pyroelectricity in PVF2; Preliminary investigations of piezoelectric polymers; Piezoelectric polymer measuring instruments.

Using a subsecond-duration transient technique the specific heat, electrical resistivity, and hemispherical total emittance were simultaneously measured over the temperature range 1500-3000 K for some grades of graphite. Similar measurements were made on vanadium, and zirconium in the temperature range of 1500-2100 K. Melting points and radiance temperature (at 650 nm) are reported for zirconium and molybdenum. The temperature of the transition from the alpha-beta phase of zirconium and the energy difference of these phases has also been measured using the subsecond duration transient technique. The products of the reaction of Fe(g) and Ox have been investigated. A preliminary report on the study of the reaction of Ba(g) with vibrationally excited ozone is also presented. The dissociation energies of the scandium group and rare-earth gaseous monoxides are evaluated by reviewing the literature available on Knudsen effusion rates and mass-spectrometric data. A bibliography of the available literature on the spectroscopy of fluorides, oxides, and oxyfluorides belonging to the lanthanide series is given., See also report dated 1 Jul 73, AD-782 028.

A description is given of the mode of chipping fracture observed in highly brittle solids. It is pointed out that residual stresses about indentation deformation centers play a vital role. The implications of this mode in a number of mechanical phenomena are discussed. An explicit model for the wear of brittle surfaces under fixed abrasive conditions is presented in terms of indentation fracture concepts. The predicted wear rate for glass agrees with that observed experimentally to within an order of magnitude. Some implications concerning the parameters which influence the abrasion process, particularly the hardness, are discussed.

Indentation fracture mechanics is used to develop a theoretical basis for pre-determining the strength properties of brittle surfaces in prospective contact situations. Indenters are classified as 'blunt' or 'sharp,' of which only the first is considered in the present work. The classical Hertzian cone crack conveniently models the fracture damage incurred by the surface in this class of indentation event. Bend tests on abraded glass slabs confirm the essential features of the theoretical predictions. The role of controlling variables in the degradation process, notably starting flaw size and indenter radius, is systematically investigated. An indication is also given as to optimization of material parameters. The analysis leads to some novel suggestions concerning surface preparation procedures that might be followed in order to minimize strength losses.

Transmission electron microscopy was used to examine the nature of microcracking about small-scale indentations in two highly brittle solids, sapphire and carborundum. The observed crack geometry is discussed in terms of an earlier model of indentation fracture beneath a point force, in which both loading and unloading half-cycles contribute to the crack growth. The residual interfaces are characterized mainly by moire patterns, sometimes by dislocation networks. These observations are discussed in relation to spontaneous closure and healing mechanisms, and the 'lattice mismatch' necessary for their production estimated at about one part in a thousand. It is shown that cleavage steps comprise the main source of obstruction to lattice restoration across the interfaces. Mechanical and thermal treatments of the indented surfaces are found to influence the extent of the residual cracking. Some practical implications of the observations are discussed.

A study of the effect of alloying chromium and molybdenum in ferritic stainless steels has been made using techniques to study repassivation kinetics (tribo-ellipsometry) and depassivation kinetics (a recently developed ellipsometry technique for studying optical changes occurring within a crevice). Constant strain rate studies were performed using AISI 304 stainless steel exposed to acidified 1.ON NaCl solution (pH=3.0). In this particular environment, repassivation kinetics measurements using the tribo-ellipsometric technique had shown that the metal dissolution rates were rather large due to reduced film repair kinetics, indicating the possibility of susceptibility to stress corrosion cracking (SCC). Reduced time to failure and maximum sustained load at a one strain rate suggest a relationship between SCC, repassivation kinetics, and rate of pure metal production. A review of current approaches to the study of stress corrosion and a discussion of how these approaches can lead to new failure prediction tools is given.

Normal alcohols were used as lubricants in a study of friction and wear of soda lime silicate glass against silicon carbide. Abrasion surfaces were 600 grit silicon carbide paper and a roughened plate of hot-pressed silicon carbide. Generally, as the abrasion time or the alcohol chain length increased, the coefficient of friction decreased. This result was attributed to better lubrication of the abrading surfaces by the long chain length alcohols. The wear rate and the coefficient of friction were strongly dependent on pullout of carbide grains from the silicon carbide paper. Wear on fresh abrasive paper was independent of alcohol chain length. As the paper becomes used, long chain length alcohols were more effective cutting fluids. For all conditions, the highest wear rate and coefficient of friction were obtained in water. Data are explained in terms of classical theories of friction and wear.

The report covers a feasibility study on the potential use of mercurous chloride crystals for construction of prism polarizers, primarily for the infrared region of the spectrum. In particular, the research has consisted of crystal growth from the vapor phase and optical characterization of the absorption, dichroism, and birefringence. Conditions for growth have not yet been optimized, but reasonably good growing conditions have been delineated. Single crystal samples have been oriented by Laue back-reflection techniques and measurements made of optical absorption, dichroism, and birefringence. Proper sample handling procedures have been determined to minimize thermal shock and thermal etching. The index of refraction has been measured at selected wavelengths, and calorimetric absorption studies have been performed at AFML on some of the samples produced. (Modified author abstract)

This report (covering July 1974 through June 1975) gives summaries (a) for high-speed thermophysical measurements on hafnium, iron, tantalum, and molybdenum and (b) for an interpretation of the Raman Spectra of PF5, AsF5, and VF5. Details of these activities have been or are in the publishing process. In addition, this report includes two articles which are current and have not started the publication process. One is a study on the chemiluminescence of the Pb(g) + 03(g) reaction, and the other is a review of the literature for dissociation energies of diatomic oxides and fluorides relevant to chemical kinetics are indicated.

High temperature slow crack growth processes in several ceramic materials are examined under static and cyclic loading conditions. Data obtained at temperatures up to 1400C are used for purposes of failure prediction and for analysis of the slow crack growth phenomena. It is shown that purity plays a major role in slow crack growth resistance, particularly in the hot pressed materials, and that cycling in the low frequency regime does not significantly increase the rate of slow crack growth. The slow crack growth mechanisms appear to be primarily plasticity related. Two semi-quantitative mechanisms are presented, one due to dislocation motion and the other due to grain boundary sliding. (Author), Previously announced as COM-74-10476.

This report covers results from density and chemical durability measurements on a borosilicate glass widely used commercially for chemical glassware while the glass undergoes liquid-liquid immiscibility. A net decrease in density is observed during an isothermal heat-treatment below the transition temperature. This density or molar volume change is related to the effect of pressure on the phase transition temperature by means of equations derived herein. The chemical durability of the material is measured following the ASTM titration technique and shows a large degradation of chemical resistance to attack by water as a result of sub-immiscibility structure development. The effect is analyzed in terms of the change in composition of the phases associated with the immiscibility transition. (Author)

The enthalpy of high-purity molybdenum was accurately measured 273-1173K, and joined smoothly to lower-temperature (German) and higher-temperature (NBS) results to give thermodynamic functions 273-2100K. The heat capacity of a grade of Poco graphite was measured by a subsecond-duration pulse-heating technique 1500-3000K (estimated inaccuracy, 3% or less). Based largely on earlier NBS IR and Raman spectroscopy, ideal-gas thermodynamic functions for MoF5 were generated and are tabulated for 0=6000K. Three alternative classical-thermodynamic or quasi-chemical treatments are developed for deriving thermodynamic properties from vaporization data on partially associated vapors, with calculations to illustrate experimental-error propagation for one treatment. A subsecond-duration pulse-heating technique was applied to niobium metal to measure its change in normal spectral emittance and radiance temperature at and near its melting point (wavelength, 650 nm), studying dependence on solid-state roughness (0.1 to 0.95 micrometers)., See also AD-782 028.

Deposition rate, phosphorus content, hardness, appearance, and metal distribution are reported for deposits from two acid, hypophosphite type electroless nickel baths, one proprietary and one non-proprietary. The baths were operated under a variety of conditions with variations of composition. Extensive data is given on the relation of deposit hardness to phosphorus content and to heat treatment at 100, 200, and 400C. (Author)

A model for a polymer electret, based on an elastically isotropic solid with orientationally frozen molecular dipoles, was developed and tested experimentally. This electret is shown to be both piezoelectric and pyroelectric. The polarization is shown to change with mechanically and thermally induced strains in the polarization direction. The currents generated by the electret will be proportional to the strain rate and, for thin contact electrodes and uniform strains, unaffected by the presence of real charges. Poly(vinyl chloride) films were poled at 80C, just above their glass transition temperature. The pressure- and temperature-induced short-circuit currents in the polarization direction equalled 0.15(pA/sq cm)/(bar/min) and 2.2(pA/sq cm)/(K/min) respectively for a specimen poled at 320 kV/cm. These currents were reversible and proportional to the rate of temperature or pressure change, proportional to poling voltage up to 320 kV/cm, in the direction corresponding to increasing polarization with increasing pressure and decreasing temperature, about 1.6 times as great for temperature induced strains as for equivalent pressure induced strains, and about 2-4 times as great in magnitude as expected from dielectric constant measurements. (Author Modified Abstract)

Research is summarized which was involved with high pressure polymerization of fluorocarbon olefins.

Crack velocity studies were conducted in various acids, bases and neutral solutions using the double cantilever beam techniques. Results are explained in terms of crack tip pH, which is controlled by the electrolyte at low crack velocities and by the glass composition at high crack velocities. The crack velocity data are consistent with the known dependence of strength on pH for soda-lime silicate glass. Results also suggest that the slope of the universal fatigue curve should depend on surface pH. (Author)

The report presents the results of two studies on the fracture behavior of glass at elevated pressures. One was conducted in an inert environment at pressures up to 20 kbar. The other was conducted in water at pressures up to 7 kbar. Fracture mechanics techniques were used in both studies. In inert environment the fracture surface energy of three glass compositions was found to be independent of pressure suggesting that no change in the fracture mechanism occurs as a result of pressure. The brittle behavior of glass thus differs from plastics and metals which are observed to become stronger and more ductile with increasing pressure. The fracture behavior of glass in water was also observed to be insensitive to pressure. It is suggested that the reason for this null effect results from compensating mechanisms, in which the increase in fracture resistance arising from a positive activation volume for stress corrosion cracking process is balanced by a decrease in fracture resistance due to increased hydroxyl ion concentration at the crack tip. (Author), See also Technical rept. no. 1, AD-700 332.

The report summarizes work conducted during the past eight years on the fracture and deformation of ceramic materials. Accomplishments discussed in this report include: an elucidation of fracture process of aluminum oxide and sodium chloride; the development of techniques to study the deformation of aluminum oxide during abrasion; and the development of techniques for measuring fracture mechanics parameters on ceramic materials. (Author)

Topics include the optical constants of titanium, diffusion of oxygen in oxides, growth of Al2O3, bicrystals by chemical vapor deposition, high temperature creep in copper, fracture in glass, the electronic structure of transition metal borides and related compounds, the enthalpy of pyrolytic graphite at high temperatures, the mechanism of volatilization of polymers, and the interaction between mechanical relaxation and annealing in polymers. (Author), Paper copy also available from Superintendant of Documents, GPO, Washington, D. C. 20402. $0.35.

The early stages of crevice corrosion of AISI 304 stainless steel in 1.ON NaCl solution have been detected using the ellipsometer to measure changes in optical properties occurring within the crevice between a polished metal surface and a glass plate. Changes in the ellipsometer parameters begin almost immediately upon creation of the crevice and can be interpreted as resulting from a build-up of soluble species within the crevice solution, followed by an overall thinning of the protective film and general corrosion attack. Such optical changes could not be reproduced by deoxygenation of the bulk solution without the presence of a crevice nor were they observed during experiments using a Ti-8Al-1Mo-1V alloy, which is not susceptible to crevice corrosion in the 1.ON NaCl at room temperature. (Author)