FCC and BCC Solidification Products in a Rapidly Solidified Austenitic Steel.

1981 ◽  
Vol 8 ◽  
Author(s):  
Thomas F. Kelly ◽  
John B. Vander Sande ◽  
Morris Cohen
Keyword(s):  
Austenitic Steel ◽  
Cell Walls ◽  
Steel Powder ◽  
Wetting Angle ◽  
Local Composition ◽  
Bcc Structure ◽  
Powder Particles ◽  
Micron Diameter ◽  
20 Nm ◽  
Rapidly Solidified

ABSTRACTThe microstructures and local composition variations in centrifugally atomized high-sulfur stainless steel powder are investigated. Both fcc and bcc are found to be primary solidification phases in the as-solidified powder of this nominally austenitic steel where the smaller powder particles (≲ 70 micron diameter) tend to be bcc.Cellular solidification structures, with sulfide precipitates (100 to 200 nm diameter in size) at the cell walls, are observed in both fcc and bcc particles. The bcc structure, however, has many small sulfide precipitates (10 to 20 nm diameter) in the cell interior with few larger sulfide precipitates at the cell walls. The small precipitates, observed only in the bcc structures, form on cooling from a supersaturated solid solution that results from reduced solute partitioning during solidification. Partitioning of chromium and nickel is minimal in these cellular structures. A non-cellular bcc structure is also observed with small sulfide precipitates throughoutthe entire structure. This non-cellular bcc structure results from smooth-front massive solidification. Analysis of the nucleation process for solidification indicates that a transition from fcc nucleation to bcc nucleation occurs with increasing wetting angle in heterogeneous nucleation. Thus bcc should nucleate in the smaller droplets of a liquid dispersion where catalytic surfaces of low potentcy (large wetting angle) tend to be the only heterogeneous nucleants available.

Analysis of a Rapidly Solidified High-Phosphorus Austenitic Steel Containing an Amorphous Phase

1981 ◽  
Vol 8 ◽  
Author(s):  
T. F. Kelly ◽  
G. B. Olson ◽  
J. B. Vander Sande
Keyword(s):  
Austenitic Steel ◽  
Rapid Solidification ◽  
Amorphous Phase ◽  
Cell Walls ◽  
Solidification Structure ◽  
Metastable Austenite ◽  
Glass Forming ◽  
High Phosphorus ◽  
Rapidly Solidified

ABSTRACTRapid solidification of a high-phosphorus austenitic steel produces a fine cellular solidification structure containing an amorphous phase at the cell walls. The amorphous phase, which is stable to ∼500°C, is enriched in phosphorus and chromium, but contains significantly less phosphorus than conventional glass-forming alloys. Hot consolidation of powders produces a chemically-uniform metastable austenite which can be effectively precipitation hardened by phospho-carbides.

On the Origin of the Microscystalline Structure in Rapidly Solidified IN-100 Powder

1977 ◽  
Vol 35 ◽  
pp. 260-261
Author(s):  
J. M. Walsh ◽  
K. P. Gumz ◽  
J. C. Whittles ◽  
B. H. Kear
Keyword(s):  
The Other ◽  
Coarse Grained ◽  
Microcrystalline Structure ◽  
Routine Examination ◽  
Atomization Process ◽  
Centrifugal Atomization ◽  
Splat Quenching ◽  
Powder Particles ◽  
Dendritic Microstructures ◽  
Rapidly Solidified

During a routine examination of the microstructure of rapidly solidified IN-100 powder, produced by a newly-developed centrifugal atomization process1, essentially two distinct types of microstructure were identified. When a high melt superheat is maintained during atomization, the powder particles are predominantly coarse-grained, equiaxed or columnar, with distinctly dendritic microstructures, Figs, la and 4a. On the other hand, when the melt superheat is reduced by increasing the heat flow to the disc of the rotary atomizer, the powder particles are predominantly microcrystalline in character, with typically one dendrite per grain, Figs, lb and 4b. In what follows, evidence is presented that strongly supports the view that the unusual microcrystalline structure has its origin in dendrite erosion occurring in a 'mushy zone' of dynamic solidification on the disc of the rotary atomizer.The critical observations were made on atomized material that had undergone 'splat-quenching' on previously solidified, chilled substrate particles.

Spherulite Structures in a Melt Spun Fe-Ni Austenitic Steel

1985 ◽  
Vol 43 ◽  
pp. 52-53
Author(s):  
G. M. Michal ◽  
T. K. Glasgow ◽  
T. J. Moore
Keyword(s):  
Austenitic Steel ◽  
Room Temperature ◽  
Elevated Temperatures ◽  
Large Range ◽  
Amorphous Structure ◽  
Nucleation And Growth ◽  
Ni Alloys ◽  
Melt Spun ◽  
Crystal Fibers ◽  
Rapidly Solidified

Large additions of B to Fe-Ni alloys can lead to the formation of an amorphous structure, if the alloy is rapidly cooled from the liquid state to room temperature. Isothermal aging of such structures at elevated temperatures causes crystallization to occur. Commonly such crystallization pro ceeds by the nucleation and growth of spherulites which are spherical crystalline bodies of radiating crystal fibers. Spherulite features were found in the present study in a rapidly solidified alloy that was fully crysstalline as-cast. This alloy was part of a program to develop an austenitic steel for elevated temperature applications by strengthening it with TiB2. The alloy contained a relatively large percentage of B, not to induce an amorphous structure, but only as a consequence of trying to obtain a large volume fracture of TiB2 in the completely processed alloy. The observation of spherulitic features in this alloy is described herein. Utilization of the large range of useful magnifications obtainable in a modern TEM, when a suitably thinned foil is available, was a key element in this analysis.

Shock consolidation of Ni-Ti alloy powder

1986 ◽  
Vol 44 ◽  
pp. 430-431
Author(s):  
Naresh N. Thadhani ◽  
Thad Vreeland ◽  
Thomas J. Ahrens
Keyword(s):  
Alloy Powder ◽  
Amorphous Material ◽  
Ti Alloy ◽  
Two Phase ◽  
Near Surface ◽  
Optical Micrograph ◽  
Shock Compaction ◽  
Powder Particles ◽  
Ti Powder ◽  
Rapidly Solidified

A spherically-shaped, microcrystalline Ni-Ti alloy powder having fairly nonhomogeneous particle size distribution and chemical composition was consolidated with shock input energy of 316 kJ/kg. In the process of consolidation, shock energy is preferentially input at particle surfaces, resulting in melting of near-surface material and interparticle welding. The Ni-Ti powder particles were 2-60 μm in diameter (Fig. 1). About 30-40% of the powder particles were Ni-65wt% and balance were Ni-45wt%Ti (estimated by EMPA).Upon shock compaction, the two phase Ni-Ti powder particles were bonded together by the interparticle melt which rapidly solidified, usually to amorphous material. Fig. 2 is an optical micrograph (in plane of shock) of the consolidated Ni-Ti alloy powder, showing the particles with different etching contrast.

Vacuum reduction of oxide films on Kh18N15 steel powder particles

1973 ◽  
Vol 12 (8) ◽  
pp. 605-607 ◽  
Author(s):  
A. K. Petrov ◽  
I. Ya. Kondratov ◽  
I. M. Pecherskii ◽  
G. N. Sergeev
Keyword(s):  
Oxide Films ◽  
Steel Powder ◽  
Powder Particles ◽  
Kh18n15 Steel

Sintering and Dielectric Properties of Ba(Mg1/3Ta2/3)O3 Particle Prepared by Spray Pyrolysis

2008 ◽  
Vol 388 ◽  
pp. 245-248 ◽  
Author(s):  
Hiroki Yamada ◽  
Takashi Okawa ◽  
Takashi Ogihara
Keyword(s):  
Electron Microscopy ◽  
Spray Pyrolysis ◽  
Ultrasonic Spray Pyrolysis ◽  
Nano Particles ◽  
Ultrasonic Spray ◽  
Transmission Electron ◽  
Powder Particles ◽  
Average Size ◽  
Micrometer Size ◽  
20 Nm

Ba(Mg1/3Ta2/3)O3 (BMT) powders were successfully prepared by ultrasonic spray pyrolysis from an aqueous solution of Ba, Mg and Ta. The particles characteristics of BMT nano-sized powders were studied by scanning electron microscopy (SEM) and X-ray diffraction (XRD). As-prepared powder particles had a sub-micrometer size with a narrow distribution. Transmission electron microscopy (TEM) observation revealed that the average size of the BMT nano-particles was around 20 nm, and that these particles were aggregated. The dielectric constant (r) of 23.2 and the Q・f of 98,300 were obtained at 1550°C by a spray pyrolysis.

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