Structural changes accompanying the sintering of ultrafine aluminum nitride powders

Conclusions An electron-microscopical investigation has established that the sintering of compacts from an ultrafine plasma-chemical AlN powder is determined by the following processes: coagulation, with the formation of strong polycrystalline aggregates (1000–1400°C); coalescence, made possible by a geometric grain boundary match inside the aggregates, and formation of high-angle boundaries between aggregates (1200–1600°C); and collective recrystallization (above 1600°C). In an x-ray diffraction study annealing at temperatures above 1700°C was found to decrease the parameter c of AlN by 0.002 Å as a result of dissolution of oxygen in the lattice without affecting its parametera. The results of both electron-microscopical and x-ray diffraction studies show that annealing at temperatures above 1600°C increases the defectiveness of the wurtzite structure of AlN, brings about twinning and the formation of polytypal interlayers in recrystallized grains, and raises the concentration of other defects causing a broadening of lines in x-ray diffraction photographs. As a result of these phenomena the material experiences a strengthening at sintering temperatures of 1700–1800°C.Translated from Poroshkovaya Metallurgiya, No. 10(226), pp. 35–40, October, 1981.The authors wish to thank A. N. Pilyankevich for helpful discussion.     

Self-reinforced materials based on aluminum nitride

Powder Metallurgy and Metal Ceramics -     

Numerical simulation of die compaction and sintering

Abstract

A method to simulate die compaction and sintering is presented. By implementing user defined routines for both processes into the general purpose finite element program ABAQUS quantitative predictions of density distributions and shape distortions can be obtained as well as the stresses in the tool components. By computational optimisation of the individual production steps suggestions can be made to improve the final properties. As an example for both die pressing and sintering a complex three-dimensional part is simulated and suggestions to improve dimensional accuracy are made. Finally, stresses in the tools are calculated showing that the deflections are large enough to cause punch to punch contact so that tool wear must be expected.     

Features of skeletal composite compaction and sintering

Skeletal composites are prepared using highly porous cellular nickel as a volumetrically-bonded framework and features of their compaction and sintering are studied. The skeleton improves composite compactability and may slow down volumetric changes during low-temperature sintering, but it does not affect them during high-temperature sintering. In compacts of skeletal composites at skeleton-ceramic boundaries there is formation of pores that by growing during sintering form a volumetric network of microcracks. __________ Translated from Poroshkovaya Metallurgiya, Nos. 7–8(450), pp. 10–18, July–August, 2006.     

Activated sintering of polydisperse silicon nitride mixtures

Data on the granulometric composition of the initial components on prepared stock have been considered and summarized. The effect of additional mechanical processing (grinding in a planetary ball mill and roller mill) on the compaction of silicon nitride materials during activated sintering have been investigated. The composition of the initial stock as well as the preparation for the production of dense ceramic silicon nitride materials have been optimized.     

The oscillatory spectra of aluminum nitride

Translated from Poroshkovaya Metallurgiya, No. 2(326), pp. 80–82, February, 1990.     

压制方式和烧结工艺对置氢Ti6Al4V粉末烧结体组织和性能的影响

采用磁脉冲成形和模压成形2种方法对置氢Ti6Al4V粉末进行轴向压制,然后在保护气氛下烧结,研究压制方式和烧结工艺对烧结体真空退火后组织/性能的影响.结果表明:磁脉冲压实的不同氢含量粉末坯体烧结并真空退火后的相对密度、硬度和抗压强度分别比传统模压500 MPa下压制的高8%～13%、9～17 HRA和254～1033M...     

High-temperature tribotechnical characteristics of ceramics based on aluminum nitride

Studies have been made on the structure, phase composition, and strength parameters for ceramics based on AlN containing 5–15 mass % TiO₂. The tribotechnical characteristics of these ceramics have been determined under sliding friction conditions at 20–900°C in air. Quantitative characteristics are proposed for the friction surface as determined by metallographic, microdurometric, and sclerometric examination of the surfaces produced at various treatment temperatures. Materials Science Institute, Ukrainian Academy of Sciences, Kiev. Translated from Poroshkovaya Metallurgiya, Nos. 3-4(400), pp. 43–48, March–April, 1998.     

Sintering aluminum nitride at high pressure

Sintering kinetics have been examined for finely divided aluminum nitride powder at 5 GPa pressure and at 1920, 2020, 2120, and 2220 K. Sintering this material at high pressures is based on the mechanism of plastic strain combined with postdeformation annealing.Institute of Solid State Physics and Semiconductors, Belarus Academy of Sciences, Minsk. Institute of Problems in Materials Science, Ukrainian Academy of Sciences, Kiev. Translated from Poroshkovaya Metallurgiya, No. 8(368), pp. 62–65, August, 1993.     

Wettability of aluminum nitride by molten metals

The sessile drop method has been used with a vacuum of 2.10^–3 Pa to examine the wettability of aluminum nitride by fourteen molten pure metals as well as the effects of adding chromium, vanadium, niobium, tantalum, and titanium to the liquids on the wetting angle in systems containing aluminum nitride and liquid tin, copper, and germanium. Aluminum nitride is wetted only by molten silicon and aluminum. Out of the elements examined, titanium is the most adhesion-active for this ceramic. The results are examined from the viewpoint of thermodynamic wetting theory.Materials Science Institute, Ukrainian Academy of Sciences, Kiev. Translated from Poroshkovaya Metallurgiya, Nos. 5–6, pp. 74–78, May—June, 1996. Original article submitted June 29, 1994.