John T. Krause

Elastic constants, hardness and their implications to flow properties of metallic glasses

The longitudinal and transverse sound velocities and Vickers hardness of metallic glasses (Pd1 − xNix)0.80P0.20, (Pd1 − xFex)0.80P0.20 and (Pt1 − xNix)0.75P0.25 have been measured. The elastic constants at room temperature exhibit a positive deviation with composition χ from linearity whereas the hardness shows a negative deviation. The increase in elastic constants has been attributed to a denser packing of the alloys on mixing. The reduced hardness HrH/μ versus χ exhibits a remarkable similarity to a Tg versus χ relationship. This seems to indicate that flow mechanisms involved in metallic glasses above and below the glass-transition temperature are of similar origins. It is the excess entropy of disorder associated with alloying which lowers the hardness as well as the viscosity of metallic glasses. The metallic glasses possess in general a relatively high Poissons ratio ν ≈ 0.40 and a shear modulus approaching that of the noble metals Cu, Ag and Au. Among the metallic glasses observed, the PtP glasses exhibit the highest ν = 0.42, whereas the glasses containing Fe tend to have lower values. The phenomenon that the conduction electrons in the glassy alloys behave as in the noble metals may be partly attributed to the filling of d shell orbitals of the transition metals in the PtP, PdP and NiP alloys. The high ν of metallic glasses is believed to be responsible for the ductile behavior of these glasses. Poissons ratio ν of metallic glasses was observed to decrease with decreasing temperature. It is suggested that the decreasing ν with falling temperature causes the rapid increase in the fracture strength of Fe-based glasses.

Strength and fatigue of silica optical fibers

After a brief review of early lightguide work, the authors assess advances since the mid-1970s. They note important work on strength distributions and procedures for improving strength. This is followed by a discussion of long-length strength, prooftesting and splicing. Flaw character is studied along with strength degradation, fatigue limits, aging and fatigue, and hermetic coatings. >

Thermal expansion and density of glassy PdNiP and PtNiP alloys

Abstract Thermal expansion and density of (Pd1−xNix)0.80P0.20 and (Pt1−yNiy)0.75P0.25 alloys in their various states have been measured from room temperature to the glass transition temperature Tg. The thermal expansion of the glassy alloys at room temperature varies linearly with x and y and is 10 to 20% higher than that of corresponding pure metals. The thermal expansion of the undercooled alloy liquids near Tg as well as the molar volume v deduced from the density of glasses in contrast exhibits a negative deviation with composition x and y. This behavior is in line with the previously reported negative deviation of the glass transition temperature of these glassy alloys with metal content and may be explained in terms of excess volume associated with a mixture of hard spheres.

Young's modulus of Fe-, Co-, Pd- and Pt-based amorphous wires produced by the in-rotating-water spinning method

This paper presents the Youngs modulus of Fe100−x−ySixBy, Fe100−x−yPxCy, Co100−x−ySixBy, Pd77.5Cu6Si16.5, Pd48Ni32P20 and Pt60Ni15P25 amorphous wires determined from the Youngs modulus sound velocity measurement. With increasing metalloid content, the Youngs modulus increases from 1.58×1011 to 1.87×1011 N m−2 for Fe-Si-B, from 1.40×1011 to 1.52×1011 N m−2 for Fe-P-C and from 1.73×1011 to 1.75×1011 N m−2 for Co-Si-B systems. The increase in Youngs modulus with the amount of metalloid elements is the largest for B, followed by Si, C and then P. The Youngs modulus of Fe- and Co-Si-B amorphous wires increases significantly with the replacement of iron or cobalt by IV–VII group transition metals. It was recognized that there existed a strong correlation between Youngs modulus (E) and tensile fracture strength (σf); the ratio of σf to E is approximated to be 0.02 for all the amorphous wires investigated. These results imply that the Youngs modulus is dominated mainly by the structural and compositional short-range orderings due to the strong interaction between metal and metalloid atoms which hinders the internal displacements. The existence of a constant ratio for σf/E was interpreted to originate from a common mechanism for plastic flow of the amorphous wires. Further, it was noted that the Youngs modulus of the Fe- and Co-based amorphous wires with diameters of ≃ 100 to 120 Μm was slightly lower than that of the amorphous ribbons with thicknesses of ≃ 20 to 25 Μm. This difference was attributed to the difference in structural ordering due to the differences in the solidification processes.

Zero stress strength reduction and transitions in static fatigue of fused silica fiber lightguides

Abstract This study shows that the transition in slope of static fatigue (log fracture stress vs. log time to failure) of fused silica fibers, is an intrinsic property of the glass which is modified by the presence of coating materials. The transition for fibers in water at 90°C occurs in the 300–400 Ksi range and is characterized by a change in slope and intercept. The slopes and intercepts preceding the transitions are dependent upon zero stress soak time in water at 90°C, however in the transition region they are unchanged by this treatment. At a stress level of about 160 Ksi the transition region appears to terminate in a more normal fatigue dependence. This may possibly be a fatigue limit. These observations suggest that changes will be required in the theories correlating static fatigue with crack growth parameters as determined from macro-crack experiments. Long-term extrapolations of fatigue data will accordingly have to incorporate modifications based on such changes.

Splice loss of single-mode fiber as related to fusion time, temperature, and index profile alteration

The lower bound in loss for fusion splices is ∼ 0.01 dB due principally to lateral offset of the cores and alteration of the index profile. This paper investigates the effects on loss of viscous flow and diffusion of the glass constituents during fusion, defining their time-temperature dependencies, and changes in index profile.

The effects of quench rate and cold drawing on the structural relaxation and young's modulus of an amorphous Pd77.5Cu6Si16.5 wire

Abstract The effects of quench rate and cold drawing on the structural relaxation and Youngs modulus have been investigated for an amorphous Pd 77.5 Cu 6 Si 16.5 wire. With increasing quench rate (decreasing wire diameter) and with increasing cold-drawn reduction in area, the heat of structural relaxation increased and the Youngs modulus decreased. It was concluded from these results that (1) the amorphous wires produced at the faster quench rates and the more heavily cold-drawn wires possess a higher degree of disorder, and (2) the Youngs modulus is higher in the more relaxed state where a short-range ordering among constituent atoms developed.

Factors affecting arc fusion splice strengths

The principle factors affecting arc fusion splice strength are discussed, which collectively lead to splices having greatly improved strengths.

On the anomalies in density, Young's modulus and glass temperature of PdSi glasses

Abstract The densities, Youngs moduli and glass transition temperatures have been measured for binary PdSi glassy alloys. These glassy alloys exhibit a negative deviation from Vegards law an enhancement in Youngs modulus and a tendency to lower the glass transition temperature in the region of the eutectic composition. The observed nonlinearity in these physical properties is shown to be better agreement with an alloy mixing effect rather than the structural ordering model.

Ultrasonic measurement technique to study thermometric effects in glass

Abstract Ultrasonic measurements of shear wave propagation in alkali containing glasses reveal temporal instabilities and thermal after-effects which parallel thermometric effects, the secular rise and zero point depression in the ice point of glass thermometers. The ultrasonic method of observing these effects has advantages over the thermometric technique. Sound velocity is a dynamic quantity proportional to the elastic moduli and density which can be measured on an absolute basis and over a frequency range if desired. Thus in measuring instabilities in the elastic properties of glass the ultrasonic method provides additional information over the use of the thermometric technique whose measured changes relate only to density changes in the glass and only on a relative basis. In addition sound velocity can be measured over as wide a temperature range as desired extending from cryogenic to above glass transition range temperatures. Also no fixed reference points are required as with thermometers. Sample preparation is relatively simple and the availability of ‘packaged’ ultrasonic measurement facilities makes this method of measuring very small changes (ppm) in elastic properties very attractive. Data as a function of time and temperature are presented for a series of alkali-lead-silicates incorporating separately Li, Na, K, Rb, Cs, and for a lead silicate containing the alkaline earth Ba. The results indicate the reversible nature of the instabilities and after-effects and express their magnitudes and sensitivities to the temperature and temperature interval of measurement. They are also related to the thermal history of the glass, and the concentration and species of the incorporated alkali.