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Search Results: 1 - 7 of 7 matches for " Kestenbach "
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Origen y endurecimiento por dispersión de carbonitruros en un acero comercial microaleado al niobio y laminado en caliente
Valencia, E.,Kestenbach, H. J.
Revista de Metalurgia , 1998,
Abstract: Throughout this work, a study on niobium carbonitrides formation and its hardening effect in a commercial hot strip microalloyed steel is presented. Optic and electron micrographs were obtained while mechanical tests and indirect models allow to predict samples yield strength, taking into account the steel composition and its structural characteristics. The results showed an extended precipitation on austenite boundary cells during the last thermomechanical processing stages, which probably achieved a considerable contribution to the hardening by dispersion in the material studied. Otherwise, no evidence of precipitation in ferrite by means of transmission electron microscopy (TEM) was observed. A poor interphase precipitation was detected in about 10 per cent of the total observed zones with no appreciated contribution to the steel hardness. Se presenta un estudio sobre el origen de los carbonitruros de niobio y su efecto en el endurecimiento de un acero comercial microaleado y laminado en caliente. Para tal fin se utilizaron micrografías ópticas y electrónicas; así como también ensayos mecánicos y modelos indirectos que permitieron predecir el límite elástico teniendo en cuenta la composición del acero y sus características estructurales. Los resultados mostraron una extensa precipitación en la austenita durante las últimas fases del proceso de laminación siendo ésta responsable del principal aporte al endurecimiento por dispersión en el material investigado. No hubo evidencias de precipitación en la ferrita por observaciones al microscopio electrónico de transmisión y sólo una escasa precipitación interfásica fue detectada en un 10 % de las zonas observadas sin una apreciable contribución al endurecimiento del acero.
Transcrystallization at the interface of polyethylene single-polymer composites
Kestenbach, H.-J.;Loos, J.;Petermann, J.;
Materials Research , 1999, DOI: 10.1590/S1516-14391999000400005
Abstract: the phenomenon of transcrystallization was studied at the interface of uhmwpe fibers embedded in an hdpe matrix. it was hoped that epitaxial crystallization in such model composites could eventually be used to improve adhesion between these high-strength fibers and the thermoplastic matrix material. matrix crystallization was induced and accompanied on a specially designed hot stage which made the crystallization front advance slowly along a thermal gradient. transcrystalline interfacial layers were observed without regard to temperature conditions, but with widely varying dimensions. lamellar resolution within these layers was achieved by low voltage scanning electron microscopy, and the very beginning of transcrystallization was observed in sample areas where uhmwpe fiber segments were only partially embedded into the hdpe matrix. lamellar alignment on the fiber surface indicated that transcrystallization in this system was associated with epitaxial nucleation.
Molecular orientation of individual LCP particles in injection-moulded PPS/LCP blends
Kestenbach, H.-J.;Rogausch, K.-D.;
Materials Research , 2003, DOI: 10.1590/S1516-14392003000100014
Abstract: polarized light microscopy was used to investigate the presence of preferred molecular orientation in the lcp phase of pps/lcp blends after injection moulding. normal birefringence effects appeared to be complicated by artifacts due to sample preparation and by the complex nature of polarized light transmission through a multicomponent sample. it was found, however, that, during low-temperature cutting of optically transparent thin sections on a standard microtome, individual lcp particles could be separated from the pps matrix, and their birefringence analyzed separately. preferred orientation was detected only in lcp fibrils which dominated in skin regions, but not in droplet-shaped particles which had formed in core regions. quantitative measurements indicated that the molecular orientation of the fibrils increased linearly with their length-to-diameter aspect ratios which ranged from 15 to 50. even for the highest aspect ratios, however, the degree of orientation was always less than that which could easily be introduced into pure lcp thin-film samples by manual shearing.
Molecular orientation of individual LCP particles in injection-moulded PPS/LCP blends
Kestenbach H.-J.,Rogausch K.-D.
Materials Research , 2003,
Abstract: Polarized light microscopy was used to investigate the presence of preferred molecular orientation in the LCP phase of PPS/LCP blends after injection moulding. Normal birefringence effects appeared to be complicated by artifacts due to sample preparation and by the complex nature of polarized light transmission through a multicomponent sample. It was found, however, that, during low-temperature cutting of optically transparent thin sections on a standard microtome, individual LCP particles could be separated from the PPS matrix, and their birefringence analyzed separately. Preferred orientation was detected only in LCP fibrils which dominated in skin regions, but not in droplet-shaped particles which had formed in core regions. Quantitative measurements indicated that the molecular orientation of the fibrils increased linearly with their length-to-diameter aspect ratios which ranged from 15 to 50. Even for the highest aspect ratios, however, the degree of orientation was always less than that which could easily be introduced into pure LCP thin-film samples by manual shearing.
Transcrystallization at the interface of polyethylene single-polymer composites
Kestenbach H.-J.,Loos J.,Petermann J.
Materials Research , 1999,
Abstract: The phenomenon of transcrystallization was studied at the interface of UHMWPE fibers embedded in an HDPE matrix. It was hoped that epitaxial crystallization in such model composites could eventually be used to improve adhesion between these high-strength fibers and the thermoplastic matrix material. Matrix crystallization was induced and accompanied on a specially designed hot stage which made the crystallization front advance slowly along a thermal gradient. Transcrystalline interfacial layers were observed without regard to temperature conditions, but with widely varying dimensions. Lamellar resolution within these layers was achieved by low voltage scanning electron microscopy, and the very beginning of transcrystallization was observed in sample areas where UHMWPE fiber segments were only partially embedded into the HDPE matrix. Lamellar alignment on the fiber surface indicated that transcrystallization in this system was associated with epitaxial nucleation.
Influencia de los tratamientos de revenidos intercríticos en la concentración de níquel correspondiente, a partículas de austenita residual en un acero con 9% Ni
Casarin, S. J.,Kestenbach, H-J.,Valencia, E.
Revista de Metalurgia , 1999,
Abstract: Retained austenite particles with nanometric dimensions in 9 % nickel steels microstructures were observed after different intercritical tempering treatments ranged between 540 °C and 670 °C corresponding to the (α + γ) two-phase field of Fe-Ni diagram. The thermal stability of particles turned out to be strongly influenced by its nickel contents and gradients of this element. The gradients were dependent on time and temperature of tempering. En la estructura fina de aceros con 9% Ni, después de diferentes tratamientos térmicos de revenido a temperaturas entre 540-670°C correspondiente al campo bifásico (α + γ) del diagrama Fe-Ni se observaron partículas de dimensiones nanométricas de austenita residual. La estabilidad térmica de estas partículas resultó ser fuertemente influenciada por la concentración de níquel contenida en ellas. En este sentido fueron observados gradientes de concentración de níquel en las mismas dependiendo éstos del tiempo y la temperatura de revenido.
Resolu??o lamelar num novo microscópio eletr?nico de varredura
Kestenbach, Hans-Jürgen;Nocite, Nádia C. P. S.;Gregório F°, Rinaldo;Loos, Joachim;Petermann, Jürgen;
Polímeros , 1997, DOI: 10.1590/S0104-14281997000100010
Abstract: abstract: working with low energy electrons (in the range of 1kev), the new scanning electron microscope permits the lamellar (supermolecular) structure of semicrystalline polymers to be observed directly without the need of specimen coating or of any other sample preparation technique. microscope performance is demonstrated by several examples of high resolution micrographs which show spherulitic, lamellar and fibrilar morphologies developed by the a, b and g phases of pvdf as a function of processing conditions and crystallization temperature. another example reveals the early stages of transcrystalline layer formation in hdpe reinforced by uhmwpe fibers.
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