Interdendritic Areas Research Articles

Microsegregation and eutectic ferrite-to-austenite transformation in primary austenite solidified CF-8M weld metals

Solidification and microsegregation studies were performed on alloy CF-8M weld metal which solidified via the primary austenite/eutectic ferrite mode. All of the major alloying elements (chromium, nickel, molybdenum) were observed to segregate to interdendritic areas upon solidification. Electron microprobe analysis revealed a substantial chromium and molybdenum enrichment of the eutectic ferrite relative to the austenite dendrites even in structures water-quenched from the solidus temperature. Scanning transmission electron microscopy/energy dispersive spectrometry (STEM/EDS) profiles taken within the eutectic ferrite phase revealed a similar pattern of major element distribution as has been observed by other investigators in residual primary delta ferrite dendrites. Within the eutectic ferrite, the highest chromium and molybdenum content and the lowest nickel content was found at the eutectic ferrite/austenite boundary. STEM/EDS analyses of in situ water-quenched weld microstructures revealed that compositional modification of the eutectic ferrite had occurred upon cooling from the solidus. In particular, the chromium concentration of the eutectic-ferrite was observed to increase by approximately 3 wt% in the temperature range ∼ 1300 to ∼ 750°C. In the same temperature range, the nickel content of the eutectic-ferrite decreased by approximately 4 wt % and the molybdenum content increased within the same phase by approximately 1 wt%. The transformation of eutectic ferrite to austenite as the weld metal cools to room temperature is consistent with a volume diffusion-control mechanism.

On the mechanism of pore formation in metals

The formation of different types of gas pores has been investigated by directional solidification experiments. A mathematical model of pore growth has been derived and the calculated pore growth has been compared with experimental data and a good correlation was found. The nucleation process of pores has also been treated. It was shown that micropores can be homogeneously nucleated in an interdendritic area according to the pressure drop caused by the solidification shrinkage.

Anodization of Lead and Lead Alloys in Sulfuric Acid

The anodic lead dioxide coatings formed on lead and selected alloys in sulfuric acid were examined by electron and x‐ray diffraction and by electron and light microscopy; the self‐discharge of the dioxide films on the metals was followed by time‐potential curves; the relation between anodic attack, self‐discharge characteristics, and the microstructures of the metals are reported.Anodically formed dioxide coatings on lead and the alloys comprise a mixture of two polymorphic forms of at the metal‐coating interface, and common tetragonal lead dioxide at the solution‐coating interface. Discharge of these dioxide coatings indicates that discharges more rapidly than . The potential of a discharging surface is determined by these relative rates as well as by the physical structure of the dioxide layers. This in turn is determined to some extent by the microstructure of the metal.The metals were shown to be preferentially attacked at grain boundaries and in interdendritic areas depending on the nature of the segregated material and structural discontinuities. A discussion of some of the crystal chemistry of the lead compounds, potential‐pH diagram, and the lead acid cell is included.