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[en] Use of isostatic pressing at high temperature for ceramics is recent. The pros and cons for various materials concerned by this process. Different applications are briefly given to show importance of this process for the elaboration of high technology materials. One of them concerns radioactive waste storage
[fr]L'usage du pressage isostatique a chaud (HIP) dans le domaine des ceramiques est recent. On decrit ses avantages et ses inconvenients pour les diverses varietes de materiaux concernes par ce procede. Une enumeration des diverses applications du pressage HIP montre son importance pour l'elaboration des materiaux de haute technologie. Une des applications citees concerne le stockage des dechets radioactifs
[en] An original hot pressing method which may be applied to ceramics, metals, and refractory powders is described. The products obtained are fine grained polycristalline materials, with homogeneous structure, very high density, unstrained and of very large dimensions (several square meters). This process equally applies to composite materials including powders, fibers, etc..
[fr]Le procede original presente s'applique a la densification des poudres a faible plasticite ceramiques, metalliques ou refractaires par frittage a retrait accompagne en vue d'obtenir des materiaux polycristallins a grains fins, de structure homogene, de tres haute densite, sans contraintes, pouvant atteindre plusieurs metres carres. Procede egalement applicable a la mise en oeuvre de materiaux composites a partir de poudres, fibres, etc..
[en] Microstructure and low-cycle fatigue (LCF) behavior of A319 cast alloy were investigated in this work. Microstructure analysis indicated that both degassing and hot isostatic pressing (HIPing) process could help to reduce and eliminate porosity. The strain-controlled low-cycle fatigue tests were conducted at total strain amplitude ranging from 0.2% to 0.4%. The stress-strain hysteresis loops were acquired and the effect of HIPing and degassing on cyclic deformation behavior was analyzed combining the cyclic stress response curves. Moreover, the effect of HIPing and degassing on LCF life was analyzed, and a fatigue life model based on the area fraction of defects was proposed which was found to be suitable to predict life. Finally, the fatigue fractography observation showed that the presence of porosity could accelerate the initiation and propagation of cracks and the fatigue failure of materials. (paper)
[en] A method has been developed for fabricating long, cylindrical rubber-mill rolls of boron carbide for use with abrasive materials. The technique consisted of initially hot pressing the boron carbide (to 90% of the theoretical density) to short, hollow cylinders having a length-to-diameter ratio of about one. This initial hot-press operation was followed by a second hot press to join or bond, and further densify, the short sections into a final compact having a length-to-diameter ratio of three. Flexural-strength data show that the integrity of the bond is comparable to that of the base material
[en] A new technique based on hot isostatic pressing (HIP) has been developed to produce dense nanosized WC-Co hardmetals without the addition of grain growth inhibitors. The glass encapsulation process is the key for the effective application of isostatic pressure at temperatures well below those usually required for reaching the closed porosity state in the WC-Co system. Fully dense WC-Co samples with cobalt contents ranging from 10 to 12 wt. % have been obtained by this technique at temperatures between 1000 oC and 1200 oC with 150 MPa of applied isostatic pressure for 30 minutes. The role of isostatic pressure on the activation of densification mechanisms is discussed. (author)
[en] Piezoelectric ceramics (PZT4, PZT5, PZT7 and SPN) were investigated for development of high frequency (30-100 MHz) normal and focussed transducers. Hot pressed piezoelectric materials with a controlled grain size of ∼ 2 μm and approaching theoretical density can be lapped down to 30 μm thickness without structural damage whereas conventional sintered piezoelectric material with gram sizes ranging from 2-15 μm and at least 3% porosity can only be lapped down to 100 μm. Hot pressed piezoelectric ceramics when compared with conventional piezoelectric ceramics, show higher values of coupling coefficient (10-20%), elastic compliance ∼ 12% and moderate increases in mechanical quality factor (Qm) and dielectric constant. The compressional sound velocity measured along the poling direction is very sensitive to the switching of dipoles other than 180o ones. The velocity increases as the polarization increases and this constitutes a useful method for quality control of the piezoelectric ceramic as it gives the correct thickness resonant frequency. By accurately measuring the change by a comparison method, the dipole behaviour can be better understood and the degree of polarization and depolarization can be established. Temperature dependent polarization and depolarization is also discussed in the light of dipole switching. Hot pressed SPN and PZT5 are sufficiently transparent to be considered for use in opto-ultrasonic applications such as in medicine. Because of the high value of the thickness-frequency constant and low Qm, SPN seems a better choice as a high frequency transducer material. The signal spectra of a high frequency transducer constructed from these materials is presented
[en] The propertis of hot-pressed ceramics are influenced by those of the employed powders, additives and body and by the process mode at the time of hot pressing. On the basis of a data-analysis concept for the compaction curve and all process parameters relevant to uniaxial hot pressing and a pertinent program system, various examples are used to demonstrate the effects of additive content, powder processing and temperature-dependent load-application point on the compaction behavior of silicon nitride during hot pressing. The compaction curves show significant differences in post-load-point isothermic and isobaric holding phase of the hot-pressing process, thereby indicating the modified effect of various sintering mechanisms. (orig.)
[de]Die Eigenschaften heissgepresster Keramikwerkstoffe werden von den Pulvereigenschaften, den Additiven, den Versatzeigenschaften sowie von der Prozessfuehrung beim Heisspressen beeinflusst. Ausgehend von einem Konzept fuer die Datenanalyse der Verdichtungskurve sowie aller relevanter Prozessparameter beim uniaxialen Heisspressen und einem darauf aufbauenden Programmsystem wird an Beispielen demonstriert, welchen Einfluss unterschiedlicher Additivgehalt, unterschiedliches Pulverprocessing und der Lasteinsatzpunkt bezogen auf die Temperatur, auf das Verdichtungsverhalten beim Heisspressen von Siliciumnitrid haben kann. Die Verdichtungskurven zeigen in Abhaengigkeit vom Lasteinsatzpunkt signifikante Unterschiede in der darauffolgenden isothermen und isobaren Haltephase des Heisspressprozesses, was auf die veraenderte Wirkung unterschiedlicher Sintermechanismen hinweist. (orig.)