The stability of precipitated austenite and the toughness of 9Ni steel

A correlation was confirmed between the good low temperature Charpy toughness of 9Ni steel and the stability of its precipitated austenite against the martensitic transformation. Changes in the microstructure during isothermal tempering were studied in detail. The austenite/martensite interface is originally quite coherent over ∼100 A distances. With further tempering, however, the dislocation structure at the austenite/martensite interface changes, and this change may be related to the increased instability of the austenite particles. The reduction in austenite carbon concentration does not seem large enough to account for the large reduction in austenite stability with tempering time. The strains inherent to the transformation of austenite particles create dislocation structures in the tempered martensite. The large deterioration of the Charpy toughness of overtempered material is attributed, in part, to these dislocation structures.     

Phase equilibria of Co3 V

In situ neutron diffraction experiments were performed over a wide range of temperatures on the alloy Co₃V. These experiments showed that theL1₃ region of the phase diagram does not exist. The ob-served Ll₂ phase appears to be a metastable state that can be obtained in quenched alloys. The hP24-fcc phase boundary was estimated to be 1045 ?.     

Changes in vibrational entropy during the early stages of chemical unmixing in fcc Cu–6% Fe

A nanocrystalline face-centered cubic (fcc) solid solution of 6% Fe in Cu was prepared by high-energy ball milling, and annealed at temperatures from 200 to 360 °C to induce chemical unmixing. The chemical state of the material was characterized by three-dimensional atom probe microscopy, Mössbauer spectrometry and X-ray powder diffractometry. The unmixing was heterogeneous, with iron atoms forming iron-rich zones that thicken with further annealing. The phonon partial density of states (pDOS) of ⁵⁷Fe was measured by nuclear resonant inelastic X-ray scattering, showing the pDOS of the as-prepared material to be that of an fcc crystal. The features of this pDOS became broader in the early stages of unmixing, but only small changes in average phonon frequencies occurred until the body-centered cubic (bcc) phase began to form. The vibrational entropy calculated from the pDOS underwent little change during the early stage of annealing, but decreased rapidly when the bcc phase formed in the material.     

Human and nonhuman primate lymphocytes engrafted into SCID mice reside in unique mesenteric lymphoid structures

The present study compares the location and phenotype of B lineage lymphocytes in tissues from SCID mice engrafted with PBMC of human, chimpanzee, and pig-tailed macaque origin. In mice repopulated with both human and nonhuman primate lymphocytes, plasma cells were found in the peritoneal cavity in vascularized structures located in the mesentery near the pancreas, intestines, and spleen. The predominant isotype of the plasma cells was IgG; IgM and IgA cells were also present. Kappa and lambda light chains were expressed by 62% and 38% of the Ig-containing cells, respectively. J chain expression occurred in most cells irrespective of the Ig isotype. In the SCID mice engrafted with human lymphocytes, a few IgM-containing cells were found in the spleen; plasma cells were not found in other tissues, including the intestine. The aggregation of plasma cells did not appear to be a result of infection with EBV. T cells were rarely found in the lymphoid aggregates but were recovered from the spleen and peritoneal lavage. Human Ig levels in the serum of engrafted mice reflected the isotype distribution of the cells with IgG > IgM > or = IgA.     

Sonographic guidance of mediastinal biopsy: an effective alternative to CT guidance

OBJECTIVE: Our objective was to determine the diagnostic and cost efficacy of sonographically guided mediastinal biopsy as an alternative to CT-guided mediastinal biopsy and to review our biopsy triage experience in switching from CT to sonography. CONCLUSION: Sonography is as safe and accurate as CT and is 25% less costly than CT. Sonography proved particularly valuable for identifying vessels and perfused tissue and for permitting upright biopsy positions in dyspneic patients. When using our triage criteria, radiologists should find sonographically guided mediastinal biopsy to be an attractive alternative to CT-guided mediastinal biopsy in most patients.     

Incipient chemical instabilities of nanophase Fe-Cu alloys prepared by mechanical alloying

We used Mössbauer spectrometry, X-ray diffractometry, a novel imaging method of electron energy loss spectrometry, and small-angle neutron scattering (SANS) to study early stage thermal instabilities of nanophase Fe-Cu alloys prepared by mechanical attrition. Mössbauer spectrometry confirmed previous reports of an extended Cu solubility in the body-centered cubic (bcc) phase of the as-milled material. Mössbauer spectrometry also provided evidence that in the compositional range of bcc-face-centered-cubic (fcc) two-phase coexistence, the bcc phase had a Cu concentration nearly the same as the overall composition of the alloy. After the as-milled powders were annealed at temperatures as low as 200 °C, however, Mössbauer spectrometry showed significant chemical unmixing of the Cu and Fe atoms. In annealed bcc Fe-20 pet Cu alloys, SANS measurements indicated that Cu segregated to grain boundaries. This segregation of Cu atoms to bcc grain boundaries did not alter significantly the tendency for grain growth, however. X-ray diffractometry showed that grain growth during thermal annealing was similar for all alloys, although grain growth was small at temperatures below 300 °C. The two-phase (bcc plus fcc) alloy of Fe-30 pc Cu was more unstable against chemical segregation than were the single-phase (bcc or fcc) alloys. Energy-filtered imaging indicated that the Cu atoms segregated to regions around the bcc grains, perhaps to the adjacent fcc crystallites.     

Mechanical stability of retained austenite in tempered 9Ni steel

The behavior of the thermally stable austenite in the ductile fracture surface layer of a grain-refined and tempered 9Ni steel broken at 77 K was studied through use of Möss-bauer spectroscopy and transmission electron microscopy. Thin foils revealing the mi-crostructural profile of the fracture surface layer were prepared by electroplating a thick pure iron layer on the fresh fracture surface, then thinning a profile sample through a combination of conventional twin-jet electropolishing and ion milling techniques. The re-sults of both Mössbauer spectroscopy and TEM studies showed that the thermally stable austenite transforms to a dislocated martensite in the deformed zone adjacent to the duc-tile fracture surface. This result suggests that transformation of the retained austenite present in tempered 9Ni steel is compatible with low temperature toughness, at least when the transformation product is a ductile martensite.