Pendant Drop Melt Extraction Research Articles

Microstructures of Rapidly Solidified Fe-Al-Zr Alloys

ABSTRACTRapidly quenched short fibers of Fe–8Al and Fe– 8Al–XZr (X = 0.1, 0.2, 0.4, and 1) alloys were produced by the Pendant Drop Melt Extraction Process, (PDME) to explore the feasibility of producing intermediate temperature, oxidation resistant iron base alloys. The fibers had a diameter of 20 to 50 μm and ranged in length from 2–5 mm. The cooling rate was insufficient to retain zirconium in solution in the Zr-containing alloys, resulting in precipitates of the type Fex(Zr,Al) having differing compositions at the grain boundaries and within the matrix. No precipitates were observed in the FeAl alloys. The precipitates were uniform in distribution and size (nominally 0.1 to 0.3 μm diameter). Grain boundary precipitation and precipitate size both decreased with decreasing Zr contents.

Rapidly solidified nickel-base superalloys

The structures of rapidly solidified APK1, In 100 and low-carbon In 792 are described and compared with that of Nimonic 80A. Under identical processing conditions, cellular, dendritic and homogeneous equiaxed structures can be obtained. This is not due to either the influence of cooling conditions or to any single alloying addition, but depends on the combined effects of the Ti, Cr and C contents. The spinodal-type formation of γ′, proposed for Nimonic 80A, cannot be suppressed in these alloys by pendant drop melt extraction or melt spinning techniques. However, detailed atom-probe field-ion microscopy suggests that the γ′ formation in APK1 does develop by a similar mechanism. Although not directly attributable to a modulated microstructure or to the presence of disordered particles, the extremely high strength levels observed in this alloy after heat treatment are due to the subsequent development of small, ordered, γ′ precipitates in a fine-grained matrix, together with the absence of deleterious grain boundary carbide precipitation.

Structure and initial precipitation in a rapidly solidified nickel superalloy

A nickel base superalloy (Nimonic 80A) has been rapidly solidified at cooling rates of between 105 to 106 K.S-1 by pendant drop melt extraction and by chill block melt spinning in an evacuated chamber backfilled with helium or argon. The internal structure is described in terms of process variables pertaining to rotating chill block quenching techniques. Both transmission electron microscopy and atom-probe field-ion microscopy have been employed to give structural and constitutional data on quenched and aged specimens. The as-quenched structure is homogeneous apart from fluctuations in titanium concentration which upon aging undergoes a spinodal phase decomposition to form disordered Ni3(Ti,Al,Cr) precipitates in the matrix, which after prolonged aging produces ordered γ (Ni3(Ti,Al)). inin6 particles form readily on grain boundaries and also appear in conjunction with ordered γ, via a discontinuous reaction, after short aging times.

Production of dental alloy by the melt extraction technique

Filaments of a commercial dental alloy (Ag3Sn) have been produced using the technique of pendant drop melt extraction. The filaments are 50 μm in diameter with a mean grain size of 5μm. Both the mechanical and structural properties of these wires have been determined to show that the results are consistent with those predicted in a previous study on small flakes made by the “gun” splat quenching technique. The ultimate tensile strength and ductility of these wires are significantly superior to samples made by chill block casting. Simple amalgamation experiments have been undertaken to confirm that alloys made in this way would be acceptable in practical situations.

Casting of metallic filament and fiber

The production of metallic fiber and filament directly from the melt has been practiced for some years. However, the application of these techniques has been limited due to materials-compatibility problems. Two new fiber-casting methods have been developed: Crucible Melt Extraction and Pendant Drop Melt Extraction. Both methods involve bringing the edge of a rotating disk into contact with a source of molten metal. Molten metal solidifies on the periphery of the disk, adheres there for a short time as it is removed from the melt source, and is then spontaneously released from the disk in the form of solid fiber. Both methods significantly reduce the technical difficulties heretofore associated with fiber casting and are amenable to operation in air, inert atmosphere, or vacuum. Metals as diverse as tin and niobium have been fiberized successfully.