This paper reviews some fundamental aspects of the rapid solidification of iron-based alloys and commercial steels, concentrating on heat flow during cooling, the thermodynamics and kinetics of solidification, post-solidification solid state phase transformations, and the effect of these processes on the resulting steel microstructures.

Silicon-iron alloy ribbons containing around 6 wt% silicon and Sendust alloy ribbons in the crystalline state were prepared by a rapidly quenching roll method. In the as-prepared ribbons columnar grains about 1Oμm in diameter wer observed to grow from the surface to the middle part of the ribbon thickness. For the high silicon-iron ribbons annealed at 1200°C for 30 minutes the grain size was more than 1 mm and the texture was highly oriented to (100)[0kl] cube-on-face. The coercive force was 55 mOe for the 6.6Si 93.4Fe ribbons annealed at 1180°C for 60 minutes in vacuum, and the average magnetic iron loss W15/50 and W10/50 of the ribbons having the coercive force of 80 mOe was 0.7 Watt/kg and 0. 25 Watt/kg, respectively. For Sendust ribbons, the lowest coercive force was 8mOe when the ribbons was annealed at 1040°C for 30 minutes and then cooled at the rate of 60 deg/hour down to 550°C in vacuum. The recording heads made of laminated Sendust ribbons exhibit much better recording characteristics than ferrite heads, while frequency response remains flat.

Rapid 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.

The 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.

Control of alloy composition and processing to achieve grain coarsening resistance in rapidly solidified alloys is examined via the theory of grain boundary pinning and particle coarsening. The principles are illustrated for the case of manganese sulfides in steels. A thermodynamic survey of potential stable dispersed phases identifies TiN and rare-earth sulfides as particularly promising for alloy development via rapid solidification.

High purity, splat-quenched metal ribbons, produced by the melt spinning technique, were examined for preferred orientation using x-ray diffraction. Of the materials tested (Zn, Cd, Ag, Bi, Pb, Sb, Mg, Sn) all except Sn exhibited some degree of preferred orientation in the plane of the metal ribbon. the hcp metals Zn and Cd showed an extreme degree of preferred orientation with the 002 plane being closely parallel to the ribbon plane. The Zn ribbon was analysed more closely with a view to its use as a crystal monochromator for x-ray diffraction. The high purity Zn was found to have some instability of preferred orientation with increase in time and temperature. The orientation was found to be effectively stabilized by the intentional addition of impurities, or by the use of lower purity (99.99%) Zn. In this form, the Zn ribbon could be used as a crystal analyser for x-ray diffraction with both intensity and resolution comparable to that of the 1011 plane in Quartz.

Observations made on different consolidated and wrought microstructures suggested that in addition to the simple variations in size and size distributions there were also differences in shape. Furthermore, clusters of oriented precipitates were often observed. The different particle morphologies were related to solidification rate effects. This paper describes the changes in microstructure which occur during the heating of rapidly solidified AI-3.3Fe-4.6Co-2.3Ni splat.

The influence of rapid solidification processing on the microstructure of long-range-ordered alloys in the (Fe,Co,Ni)3 V system has been studied by transmission electron microscopy. The main microstructural feature of the asquenched alloys was a fine cell structure (∼300 nm diameter) decorated with carbide particles. This structure was maintained after annealing treatments which develop the ordered crystal structure. Other features of the microstructures both before and after annealing are presented and discussed.

Nb75−xGa25+xtapes (1≤ x ≤ 6) were prepared by liquid quenching technique in an argon atmosphere. The transition temperature Tc, upper critical field Hc2 and critical current density Jc were measured in both as-quenched and annealed samples. The values of Tc (onset) ranged from 16.5 to 18.0K in the asquenched samples and increased upon annealing up to 20.0 K. Similar increase was also observed in the values of Hc2 (4.2 K) from ∼190 kOe to values higher than the attainable field of 220 kOe. For annealed samples near stoichiometric composition, Hc2 was estimated to be higher than 300 kOe. The critical current densities of these tapes are relatively low [Jc (4.2 K) ≤ 2 × 104A/cm2] compared to other melt-quenched A-15 compounds. Flux pinning force, FP, does not obey a single scaling law. The existence of two peaks in FP at low temperatures and of only one peak at 13.4 K for 1 ≤ x ≤ 4 is discussed in terms of the microstructural characteristics of the samples.

Dilute Sn-Ge alloys were prepared as ribbons by meltspinning using a 4" copper drum. They were then transformed into grey tin at 242 K in the as-cast-condition, and after annealing. It is shown that germanium: (1) when in solid solution impedes β → α transformation; (2) when in solid solution cannot effect nucleation; and (3) has a solubility in α-Sn in excess of 1 wt. % Ge.

In addition it is proposed that β → α transformation is restricted because the presence of germanium strengthens the β-Sn matrix.

The synthesis and catalytic properties of hydrogenation catalysts of the RaneyR type derived from aluminum-nickel and aluminum-molybdenum-nickel RSR alloy powders have been evaluated. Two binary aluminum-nickel alloys, RSR 588, with 50 w/o Ni corresponding to currently available RaneyR commercial alloys, and RSR 587, with 28.5 w/o Ni corresponding to the proeutectic composition which produces exclusively Al3Ni as the precursor phase, were synthesized. One ternary, RSR 589, aluminum-molybdenum-nickel alloy with a nickel and molybdenum content to correspond to a commercial promoted RaneyR alloy was prepared.

The hydrogenation catalytic activity for six organic compounds representing diverse functionalities was measured in a bench scale batch liquid slurry catalytic reaction. Each catalyst was suspended in an agitated solution of the reaction (0.8 to 5M) at 22°C under a constant hydrogen over pressure of 0.86 atmospheres. A declining pressure technique was also used as a measure of catalytic activity where the catalyst was suspended in an agitated solution of the three reactants at 80°C at an initial hydrogen pressure of four atmospheres. The reactants selected consisted of acetone, nitrobenzene, itaconic acid, butyronitrile, toluene, and dextrose. The organic functionalities hydrogenated consisted of the conversion of:

(1) Carbonyl to alcohol

(2) Nitro group to amine group

(3) Double carbon bond to a single carbon bond

(4) Nitrile group to an amine group

(5) Aromatic to a hydroaromatic ring

(6) Aldehyde to an alcohol.

RSR 587 catalyst, containing 28.5 w/o nickel, provides superior hydrogenation rates over bulk cast RaneyR nickel catalysts by factors ranging from 2 to 20 for selected reactions. Rapid solidification followed by heat treatmen0t at 850°C of Al ∼42 w/o Ni powders yielded the greatest specific catalytic activity and provides a unique enrichment path for the formation of the peritectic phase, A13Ni, and subsequently the most active skeletal nickel pore structure with the least amount of waste aluminum.

During the last five years Pratt & Whitney Aircraft has developed rapid solidification powder metallurgy and consolidation techniques to produce advanced aluminum alloys. A centrifugal rotary atomization device with forced high velocity helium convective cooling has been developed to pilot-plant stage, to produce aluminum alloys of novel compositions for advanced gas turbine engine applications. Rapidly solidified aluminum alloys solidify as spherical droplets up to 100 μm diameter with cooling rates of 105 — 106 K/sec, and demonstrate new microstructural features which have been exploited to develop elevated temperature mechanical properties. Alloys have been developed for 400 — 500°F fan and compressor applications that have traditionally used titanium alloys, and this paper reviews the microstructural evolution of rapidly solidified structures during thermomechanical processing.

Rapidly quenched tapes of Fe-C-X alloys (X=Cr, Mn,Ni, Co, Al, Si) were produced by melt spinning. The hardness, ductility, grain size and micro and lattice structure were determined. The system Fe 2.1C 13 Cr was chosen for further study. The transformation (isothermal and continious) characteristics were determined for the as quenched and reaustinitized states. The results can be presented in the form of TTT diagrams and hardness measurements

Ribbons of pure tin (99.9999%) and dilute Sn-Ge alloys, prepared by melt spinning using a 4′ diameter copper cylinder, were strained in tension. Reversible strains of a few percent were recorded in the dilute alloys but not in the pure tin. X-ray diffraction examination suggests that this pseudoelasticity is due to twinning rather than a martensitic transformation.

Iron, nickel and/or cobalt base metallic glasses with low contents of metalloids, predominantly boron, upon heat treatment at temperatures well above crystallization temperature of the glassy phase transform into ultra-finegrained (microcrystalline) alloys containing finely dispersed boride phases.

Microcrystalline alloys devitrified from glassy phase are characterised by high strength, excellent thermal stability and superior corrosion/oxidation resistance. Mechanical properties of bulk microcrystalline alloys hot consolidated-devitrified from selected low metalloid metallic glass alloys are reported.

The crystallization phenomena of certain ternary glass Ni-Mo-B alloys and their consolidated bulk properties, including age hardening effects after proper heat treatment, are investigated. Within the composition range studied, the glassy alloys crystallize by a two-stage process - first by forming a metastable microcrystalline structure of Ni solid solution at temperature around 490–530°C followed by boride precipitation at temperatures around 700–770°C. The boride, which is identified by x-ray diffraction as Mo2NiB2 , grows to submicron size after the alloys have been thermally treated at 1000°C and above for certain periods of time. Microstructural analysis shows borides isolated and well dispersed in Ni-Mo alloy matrix. Age hardening is achieved by precipitating the Ni/Mo intermetallic compound(s) in Ni-Mo matrix at an intermediate temperature of previously solutionized samples. Another characteristic of this group of alloys is the relatively high eutectic temperature, i.e. 1230°C and above. This will allow the alloys to be hot consolidated to full density by certain commercially available processes, such as hot isostatic pressing (HIP), while still maintaining the unique microstructure inherited from rapid solidification process. Hardness, hot hardness and hot tensile properties of some consolidated alloys are discussed.

Several amorphous alloys were subjected to thermal processing subsequent to their rapid solidification. These alloys have been characterized utilizing metallographic (optical, TEM, and SEM) and x-ray methods. Also, mechanical property evaluations have been made. The alloys exhibit extremely fine grain size; some have a high degree of preferred orientation and second-phase precipitates in the submicron size range. Most have good modulus, high yield and ultimate strength, high reduction in area but limited percent elongation.

Depending on the Zr-concentration crystallization of (Fe-,Co,Ni)-Zr glasses has been found by TEM studies to occur by primary and polymorphic crystallization, however, not by eutectic crystallization reactions. Nucleation and growth rates of these ractions have been analyzed systematically. Thermal stability as indicated by orowth as well as nucleation rates decreases with increasing Zr-content and atomic number of the late transition metal. Using this knowledge on nucleation and orowth rates conditions for designing particular microstructures by crystallization reactions can be predicted.

The surface heat treatment of iron alloys using high power lasers is reported. The essential features e.g. epitaxial growth, homogeneity etc. are discussed. The results are tabulated for the technically important alloys. The possibilities of laser hardening are demonstrated by four examples.

The major effects of laser and electron beam glazing on solidification microstructure and melt zone geometry are described. It is shown that under comparable processing conditions, i.e. absorbed power density and interaction time, the glazed microstructures are similar. Some variations in microstructure of laser and electron beam glazed M2 steel have been noted, which seem to be related to fluid flow effects in the melt zone and possible interactions with the environment.