Densities of liquid Fe-Ni and Fe-Cr alloys

Formerly Graduate Student, Department of Materials Science and Engineering, Carnegie Mellon University.     

Substructure of ausformed martensite in Fe-Ni and Fe-Ni-C alloys

The martensite substructure after ausforming has been studied for two different martensite morphologies: partially twinned, lenticular martensite (Fe-33 pct Ni, M_s =-105‡C) and completely twinned “thin plate” martensite (Fe-31 pct Ni-0.23 pct C, M_s = -170‡C), and in both cases ausforming produces a dislocation cell structure in the austenite which is inherited, without modification, by the martensite. In the Fe-Ni alloy, the dislocation cell structure is found in both the twinned (near the midrib) and untwinned (near the interface) regions, the latter also containing a regular dislocation network generated by the transformation itself and which is unaltered by the austenite dislocation cell structure. Similarly, in the Fe-Ni-C alloy, the transformation twins are unimpeded by the prior cell structure. These observations show that carbide precipitation during ausforming is not necessarily required to pin the austenite cell structure and that the martensite-austenite interface, backed by either twins or dislocations, does not exhibit a ”sweeping” effect. Although the martensite transformation twins are not inhibited by the ausforming cell structure, they do undergo a refinement with increased ausforming, and it is indicated that the transformation twin width in martensite depends on the austenite hardness. However, the relative twin widths remain unchanged, as expected from the crystallographic theory. T. MAKI, Formerly with the University of Illinois     

Substructure of ausformed martensite in Fe-Ni and Fe-Ni-C alloys

The martensite substructure after ausforming has been studied for two different martensite morphologies: partially twinned, lenticular martensite (Fe-33 pct Ni, M_s =-105?C) and completely twinned “thin plate” martensite (Fe-31 pct Ni-0.23 pct C, M_s = -170?C), and in both cases ausforming produces a dislocation cell structure in the austenite which is inherited, without modification, by the martensite. In the Fe-Ni alloy, the dislocation cell structure is found in both the twinned (near the midrib) and untwinned (near the interface) regions, the latter also containing a regular dislocation network generated by the transformation itself and which is unaltered by the austenite dislocation cell structure. Similarly, in the Fe-Ni-C alloy, the transformation twins are unimpeded by the prior cell structure. These observations show that carbide precipitation during ausforming is not necessarily required to pin the austenite cell structure and that the martensite-austenite interface, backed by either twins or dislocations, does not exhibit a ”sweeping” effect. Although the martensite transformation twins are not inhibited by the ausforming cell structure, they do undergo a refinement with increased ausforming, and it is indicated that the transformation twin width in martensite depends on the austenite hardness. However, the relative twin widths remain unchanged, as expected from the crystallographic theory.     

Supercooling and structure of levitation melted Fe-Ni alloys

The effect of processing variables, such as supercooling, quenching rate, and/or growth inhibitors on the structure of levitation melted Fe-25 pct Ni alloys was investigated. The subgrain microstructure of samples solidified in water, molten lead, or ceramic mold was found to fall into three categories of dendritic, spherical, or mixed dendritic plus spherical morphologies. All three morphologies were observed when the samples had solidified with a superheat or a supercooling less than 175 K. At larger supercoolings, however, only the spherical morphology was observed. The structure fineness was shown to depend on the supercooling as well as on the solidification medium. The grain size and shape, on the other hand, was found to depend on the morphology of the microstructure, but not on the supercooling. The cooling rates during solidification and the heat transfer coefficient at the metal-quenching medium boundary were calculated. The coefficient for the samples solidified in water, molten lead, and ceramic mold was calculated to be 0.41, 0.52, and 0.15 w/cm2 K, respectively.     

Thermal and irradiation-induced phase separation in Fe-Ni based invar-type alloys

We summarize and review critically the existing experimental and theoretical evidence concerning both thermal and irradiation-induced high-temperature miscibility gaps in Fe-Ni based Invar-type alloys. Independent data regarding phase separation are obtained from studies on magnetic, low-expansion Invar-type alloys and model austenitic Fe-Ni based alloys studied for potential nuclear applications. The response of these alloys to long-term thermal aging is found to be inconsistent with that of single-phase alloys predicted by most accepted or proposed phase diagrams. These alloys show anomalies in numerous properties which suggest compositional or magnetic heterogeneities or both. We herein model the kinetics and thermodynamics of spinodal decomposition and nucleation in these alloys under thermal conditions. The absence of models for surface energy and gradient energy in systems with negative departure from ideality severely limits our analysis of the kinetics of both nucleation and spinodal decomposition. We can combine our calculations with those of others and also with experimental studies of decomposition to reach a conclusion that suggests a high-temperature miscibility gap for Fe-Ni alloys in the Invar regime. The gap is found to be very narrow at high temperatures but to be broadened at low temperatures by magnetic effects. Alloys in the Invar composition range have been subjected to a variety of high fluence irradiation treatments in the 725 to 1000 K temperature range. The result in most cases was large-scale decomposition into approximately 25 and 50 pet Ni phases. The apparent miscibility gap under irradiation is much wider than that observed thermally. We discuss these observations in the light of existing theories of irradiation-induced or irradiation-altered alloy decomposition. We conclude that although irradiation-enhanced diffusion speeds up phase separation, other processes must be operating to produce the greatly widened miscibility gap. This paper is based on a presentation made in the “G. Marshall Pound Memorial Symposium on the Kinetics of Phase Transformations” presented as part of the 1990 fall meeting of TMS, October 8–12, 1990, in Detroit, MI, under the auspices of the ASM/MSD Phase Transformations Committee.     

Behavior of model Fe-Ni-Cr alloys during stress-rupture in sulfidizing and oxidizing environments

Stress-rupture tests of model Fe-Ni-Cr alloys have been performed at 815 °C in gaseous environments containing multiple oxidants (O, S, C). The decrease in stress-rupture lifetime, when present, was the result of an accelerated onset of tertiary creep brought about by environment related surface cracking. Secondary creep rates were not significantly affected. The applied stress was found to increase the depth of environmental attack but it did not alter the morphology of attack. Penetration depths were modeled using a diffusion analysis which included both bulk and grain boundary diffusion.     

Effect of a catalyst on heterogeneous nucleation in pure and Fe-Ni alloys

In order to elucidate the nature of the heterogeneous nucleation, a differential scanning calorimetry (DSC) thermal analysis of pure Fe and Fe-Ni alloys (Ni content: 1.0 to 29.3 mass pct) containing TiN, Al₂O₃, and Ti₂O₃ was conducted. Then, special attention was paid to the difference in the phase of the primary crystal nucleated by the triggering effect of a catalyst (nucleating agent). The solidification and transformation mode appearing during cooling in these alloys is classified into three cases: F mode, FA mode, and A mode. The change of modes and the critical undercooling (ΔT) depend on the kind of catalyst used as well as the chemical composition (Ni content). In addition, in spite of the kind of primary crystal, the value of ΔT is always small in the order of TiN, Al₂O₃, and Ti₂O₃. As a matter of fact, only TiN has a practical effect as a catalyst on the triggered nucleation of the primary crystal of the δ phase. None of them has a practical effect on the nucleation of the primary crystal of the γ phase. This article is based on a presentation given in the Mills Symposium entitled “Metals, Slags, Glasses: High Temperature Properties & Phenomena,” which took place at The Institute of Materials in London, England, on August 22–23, 2002.     

Effect of oxide scale on carbon deposition on Fe-Ni alloys in carburizing gas

The behavior of carbon deposition on preoxidized Fe-Ni alloys containing 0 to 57.0 mass pct Ni in 10 pct CH₄-H₂ mixture at 1203 K was studied by metallography and thermogravimetry. Nickel retarded carburization and carbon deposition by lowering the solubility limit of graphite in austenite and by reducing catalytic activity for the pyrolytic reaction of CH₄. On oxidation in air, the addition of nickel to iron depressed the development of FeO and, thereby, caused a significant decrease in the thickness of the scale. The exposure of the alloys to 10 pct CH₄-H₂ mixture after the oxidation in air led to a sudden mass loss in the early stage and then a rapid mass gain. This mass change is primarily ascribed to mass loss by reduction of iron oxides and to mass gain by carbon deposition. The rapid mass gain by carbon deposition is probably due to the formation of active iron by reduction of iron oxides and to the increase in the reaction area by spallation of the scale; the active iron formed may promote filamentous carbon deposition through Fe₃C formation and decomposition. Carbon deposition on the alloys containing 27.2 mass pct Ni or more was considerably retarded because of the formation of a thin oxide scale which consists of α-Fe₂O₃ and spinel (Ni_xFe_3−xO₄) and the reduction of catalysis by enrichment of nickel in the subscale. However, the amounts of carbon deposition increased compared with those on the as-polished alloys, owing to the presence of reducible iron oxides.     

Isothermal martensitic transformation in Fe-Ni and Fe-Ni-C alloys at subzero temperatures

A survey of experimental work on the isothermal martensitic transformation in the presence of prior martensite is given in Fe-Ni and Fe-Ni-C alloys having subzero Ms (Mb) temperatures. Low temperature dilatometric measurements are correlated with internal friction measurements in the 5 to 200 K temperature range. This study will show that this transformation can be discussed in terms ofC-curve behavior as in Fe-Ni-Mn alloys. Nevertheless, in Fe-Ni and Fe-Ni-C alloys internal stresses created by the austenite-to-martensite transformation during cooling play an important part in the development of the isothermal transformation. Furthermore, internal friction is shown to be proportional to expansivity thus indicating that the internal friction technique can be applied successfully for the study of phase transformations.     

Diffusivity and solubility of hydrogen as a function of composition in Fe-Ni alloys

An electrochemical method has been used to determine the permeability,P, diffusion coefficient,D, and solubility,c, of hydrogen in alloys of the Fe-Ni system. The heats of activation for diffusion and the heats of solution have been derived.D falls from ≃10⁻⁴ sq cm per sec for pure iron to ≃10⁻¹⁰ sq cm per sec for 40 wt pct of Ni in the alloy. Thereafter it rises slightly to that for pure nickel,c rises by about 10³ between pure iron and 40 wt pct Ni, then remains constant up to pure nickel. The resultantP doubles at 5 wt pct Ni and then falls by 10³ times up to 40 wt pct Ni, afterwards rising slightly to that for pure nickel. Between 0 and 40 wt pct Ni the dominant factor in controlling the value ofP is the fall of the mole fraction of the α phase in the alloy. This hypothesis gives a reasonable quantitative calculation of theP-composition relation. Between 40 and 100 wt pct, the crystallographic phase is allγ and the major effect is the bonding of hydrogen in the alloy, the small changes noted being reasonably calculable. The negligible change of solubility in this region reflects the negligible change ind character of the alloy from 40 to 100 wt pct Ni. The hydrogen permeability of Fe-Ni (5 wt pct) is greater than that of palladium atT > 200°C. The corrosion rate and hydrogen permeability (hence, susceptibility to hydrogen embrittlement) pass through a minimum at about 50 wt pct Ni. A remarkable parallelism exists between corrosion rate and hydrogen permeation in Fe-Ni alloys. An interpretation is suggested. Formerly with the University of Pennsylvania Formerly with the University of Pennsylvania Work carried out by P. K. SUBRAMANYAN in partial fulfillment of the requirements for the degree of Doctor of Philosophy, University of Pennsylvania, 1970.     

Ce对Fe-Ni膨胀合金凝固组织的影响

Ce对Fe-Ni膨胀合金凝固组织的影响研究结果表明:经Ce处理后,Fe-Ni膨胀合金中形成了大量的高熔点Ce₂O₃包芯Al₂O₃复合物,尺寸约为2μm.错配度理论计算表明,Ce₂O₃的某些低指数面与Fe-Ni膨胀合金的低指数面具有7.1%的较低错配度,因此Ce₂O₃作为非均匀形核核心使膨胀合金凝固组织由完全的柱状晶变为完全的等轴晶组织.Ce在凝固组织的等轴晶晶界上以Ce₂O₃、Ce₂O₂S和CeS形式存在,具有阻止晶粒长大的作用.     

A prospective study of changes in morphology and dimensions of abdominal aortic aneurysms following endoluminal repair: a preliminary report

Rhabdomyosarcoma (RMS), a high-grade, malignant, skeletal muscle tumor, represents approximately 5% of neoplasms in children. The poorly differentiated forms of RMS are often not easily diagnosed and classified. Among the four histologic variants, alveolar RMS is the least frequently reported subtype. A poorly differentiated solid variant of alveolar RMS occurred on the right hand of a 16-year-old girl. Because of the tumor size, local invasiveness, and occurrence of cutaneous and breast metastases at presentation, the clinical staging was group IV (T2/NO/M1). Surgical excisions of the primary and metastatic locations were performed and chemotherapy with vincristine, dactinomycin, cyclophosphamide, and doxorubicin was administered. Light and electron microscopy studies revealed a solid proliferation with a focal alveolar pattern of monomorphous, small, round neoplastic cells without easily detectable muscular morphologic features. The skeletal muscle origin was revealed by the positive immunostaining for desmin, alpha-sarcomeric actin, muscle-specific actins, and enolase, and confirmed by immunoblotting for desmin. Despite the age of our patient, which is considered by some authors an independent predictor of outcome, all prognostic variables were unfavorable. However, a disease-free interval during three years of follow-up underlines the importance of multidisciplinary regimens for the treatment of this rare solid tumor of childhood and adolescence.