Coating and fiber effects on SiC-reinforced titanium

This article reviews the state of the art of continuous silicon carbide fibers for reinforcing titanium matrices, including fibers produced in the United States, the United Kingdom, and Ukraine. A new coating system has been developed, based on compliant layer and thermodynamic considerations, which significantly enhances the behavior of SiC/Ti metal-matrix composites.     

Orientation domains and texture in hot-dipped galvanized coatings

The crystallographic orientation of galvanized coatings (Zn-0.2Al-0.15Sb in wt pct) has been characterized by Electron-Backscattered Diffraction (EBSD) and optical microscopy. While 80 pct of the nucleation spots in the coating give rise to single-crystal Zn grains, it has been found that about 20 pct of them give rise to two or more orientation domains, each having a specific crystallographic orientation. For such “polycrystalline Zn grains,” the orientations of the domains are crystallographically related: they have a dense crystallographic direction (〈1010〉, 〈1120〉, or 〈0001〉) in common. Moreover, the crystallographic relationships are similar to those observed in snowflakes and can be partially explained by the concept of a coincidence-site lattice (CSL). The EBSD measurements were also used in order to measure quantitatively the crystallographic texture. In particular, it has been evidenced that the (0001) texture of galvanized coatings is the result of two contributions: (1) the nuclei are preferentially oriented with the basal plane parallel to the coating plane (33 pct of the grains have an angle between the basal plane and the coating plane smaller than 22.5 deg), and (2) the grains having the basal plane parallel to the coating plane grow faster (these grains represent 43 pct of the coating surface). This reinforcement of the texture during growth is in agreement with that predicted by growth models, which take into account the effect of the interfaces.     

Mikrobielle Werkstoffzerstörung – Biofilm und Biofouling: Anforderungen an biokorrosionsfeste Pumpen

Microbial deterioration of materials – biofilm and biofouling: Requisition to biocorrosion resistant pumps     

Dielectric study of hollow microsphere composites

Composites of epoxy resins filled with hollow microspheres of ceramics, glass and polymer were studied in an attempt to produce a material of low dielectric constant. The accumulation of interfacial water was tested for exposures to 85% humidity at 85° C for periods of up to 1000 h. Water absorption was monitored by gravimetry and dielectric measurements. With all but one type of microsphere, a dramatic increase of the dielectric constant developed after durations of exposure which were of the order of the Fickian diffusion time of samples of unfilled resin. Unfilled samples, on the other hand, did not exhibit this behaviour. Impedance spectroscopy carried out at frequencies of up to 1 GHz gave evidence for two distinct modes of ionic conduction: about the spheres and across the bulk of the sample. Microspheres of acrylonitrile-vinylidene chloride copolymer in amine-cured epoxy resins did, however, remain stable and therefore yielded a reliably low dielectric constant.     

The history of permanent-magnet materials

From lodestones and carbon steels to today’s rare-earth magnets, a steady improvement in magnetic properties has expanded the technological importance of permanent-magnet materials. These materials have progressed through several major developmental stages, with a bit of serendipity contributing to the discovery process.     

The sensitivity of lab-measured friction coefficients

Friction plays an important role in the production of stamped or drawn parts. Because of the interest in quantifying frictional behavior, measured coefficients of friction are often determined using laboratory tests. This article addresses the sensitivity or experimental error in the coefficients of friction reported using such tests.