Phase formation processes and densification kinetics of the β-Si3N4 based sialon charges during sintering

Conclusions We studied the densification and phase formation processes during reactive sintering of the -sialon charges based on the -modification of silicon nitride with an insignificant weight content of aluminum. Densification of the charge occurs according to the regularities of the liquid phase sintering process during which the liquid phase disappears. The kinetics of densification and phase formation and the degree of completion of these processes depend on the composition of the original charge and the degree of dispersion of the powders of the additives. Under the present sintering conditions, the process of -sialon formation from -Si₃N₄ occurs according to the mechanism of dissolution and redeposition through a liquid phase with a significant contribution from the processes of mass transport through a gaseous phase.Translated from Poroshkovaya Metallurgiya, No. 8(296), pp. 56–62, August, 1987.     

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.     

Influence of dispersed microadditives on the structure and properties of powder carbon and high-chromium steels

The influence of dispersed different nature microadditives on structure formation and volume changes during sintering, and strength of powder carbon and high-chromium steel is investigated. Mechanisms of the effect of additives on the formation of their structure are described. It is shown that the introduction of sodium bicarbonate provides the largest strengthening of carbon steel, while the introduction of boron nitride provides that of high-chromium steel. The level of increasing the strength depends on the sintering temperature and amount of additive.     

Effect of activated sintering factors and treatment schedules on the properties of refractory electroerosion and laser coatings

Fine powders and metal additives, steel base and applied material composition have been studied for their effect on mass transfer and properties of electroerosion and laser coatings. The results obtained make it possible to consider forming coatings under the action of concentrated energy flows as the total effect of sintering processes in surface microvolumes.     

Electric-discharge sintering of TiN-AlN nanocomposites

The structurization and properties of TiN-AlN and TiN-AlN-Y₂O₃ nanocomposites consolidated by electric-discharge sintering are examined. TiN-AlN composites with a relative density of about 98 to 99% are produced. Their structure is not homogenous and consists of TiN and AlN grains of about 200 nm in size. There are also large spherical grains of titanium nitride of 2 to 10 µm. This effect is probably caused by microdischarges between particles of the conducting phase and subsequent meltback of the interacting surfaces. The effect of yttrium oxide additives on the material structure and properties is investigated. It is shown that TiN-AlN composites consolidated by electric-discharge sintering have high hardness (HV ～ 25 GPa) and fracture toughness (K_1c ～ 6 MPa · m^1/2).     

Effect of Y2O3, CeO2 on Sintering Properties of Si3N4 Ceramics

The effect of rare earth oxides Y203 or Ce02 on sintering properties of Si3N4 ceramics was studied and the mechanism of assisting action during sintering was analyzed. The results in dicate that the best sintering properties appear in Si3N4 ceramics with 5% Y203 or 8% CeO2. Secondary crystallites are formed at grain boundaries after heat treatment,which decreases the amount of glass phase and contributes to the improvement of high-temperature mechanical properties of silicon nitride.     

Production of tungsten-based composite materials from mechanically activated powders

The effects of the composition and metal additives on the compressibility of mechanically activated tungsten-based powder mixtures, the volume changes upon sintering, and the structure and strength of high-temperature composite materials are studied.     

Formation of the structure and phase composition of titanium nitride—(Nickel—Molybdenum) materials

The features of structure and phase composition of sintered heterophase materials based on TiN with Ni—Mo binder have been studied. Molybdenum in the binder increases the material density in comparison with that of nickel binder. This seems to be due to less release of nitrogen from TiN. After sintering, the binder consists of intermetallics of titanium with nickel and molybdenum, as well as solid solution based on nickel and molybdenum. The effect of Al₂O₃ additives (20%) on the microstrucutre and phase composition of TiN—Ni—Mo was also studied. Sintering in argon ambient and in vacuum results in increase of microhardness and lattice parameter of TiN caused by dissolution of nickel, molybdenum, and oxygen in TiN. Institute for Problems of Materials Science, Ukraine National Academy of Sciences, Kiev. Translated from Poroshkovaya Metallurgiya, Nos. 7–8(402), pp. 82–89, July–August, 1998.     

液相烧结SiC陶瓷的微观结构

采用Al₂O₃、Y₂O₃为助烧剂,液相烧结获得了致密的α-SiC和β-SiC陶瓷,并研究了SiC了烧结体的物相组成和微观结构.实验结果表明,Al₂O₃,Y₂O₃原位形成了YAG,材料以液相烧结机制致密化,α-SiC通过溶解和再析出机制,促进晶体生长,并形成\     

Structuring and Mechanical Properties of Composite Ceramics SiC(C) ― Si3N4, Sintered under High Pressure

We have studied the kinetics of high-pressure sintering of a composite SiC(C) ― Si₃N₄ powder of a certain phase composition. We consider structuring and mechanical properties of the ceramics obtained on the basis of this powder.     

烧结温度对Mo_2FeB_2合金组织性能的影响

采用真空液相烧结法制备三元硼化物硬质合金,研究了烧结温度对三元硼化物硬质合金致密度、显微组织以及物相组成的影响.研究结果表明,三元硼化物硬质合金的密度和显微组织与烧结温度密切相关.当烧结温度较低时,合金中的硬质相晶粒发育不完全,且在粘结相中分布不均匀;烧结温度过高时,合金中的硬质相颗粒粗大,两者都会显著影响材料的性能.试样在1160～1210℃之间烧结时,随着烧结温度的不断增加,材料由固相烧结逐渐转化为液相烧结,试样的密度随着烧结温度的上升而逐渐增加,并确定试验最佳烧结温度为1210℃,此时材料的密度为8.23g/cm3,维氏硬度与洛氏硬度分别为8722.6N/mm2和75.3HRA,抗弯强度则达到1246.38MPa.通过对材料的显微组织与物相结构分析,阐述了该材料组织结构变化的原因.     

Novel technique for synthesis and consolidation of aluminium nitride nanopowders

Abstract

In this paper, the use of a microwave plasma method for the synthesis of aluminium nitride nanopowders is described. The powders were consolidated to near theoretical densities using the unique rapid consolidation technique, plasma pressure consolidation (P²C), developed by MMI. Rapid consolidation of nanopowders is an ideal requirement for better mechanical and thermal properties in the consolidated part, as it retains the fine microstructure preventing anomalous grain growth. Microwave plasma synthesis resulted in aluminium nitride nanopowders (85–200 nm), which were consolidated to near theoretical density using P²C in <5 min without sintering additives. The effect of yttria (3 wt-%) as a sintering additive on the thermal conductivity (TC) of aluminium nitride was also evaluated and compared with TC values obtained from additive free AlN consolidated samples.     

Structuring and Mechanical Properties of Composite Ceramics SiC(C) ― Si3N4, Sintered under High Pressure

We have studied the kinetics of high-pressure sintering of a composite SiC(C) ― Si₃N₄ powder of a certain phase composition. We consider structuring and mechanical properties of the ceramics obtained on the basis of this powder.

     

Dependence of the Structure of Sintered Boron Carbonitride on the Defect Level in the Starting BN Powder

We have carried out a comparative x-ray analysis of boron nitride powders with different degrees of ordering and sintered specimens of boron carbonitride based on such powders. We have established that an indicator of sintering activity for the boron carbonitride specimens is the rate of formation of the r-BN phase, the content of which depends on the degree of ordering of the starting BN powder. __________ Translated from Poroshkovaya Metallurgiya, Nos. 5–6(443), pp. 100–107, May–June, 2005.     

Electrical conductivity of sintered heterophase materials TiN-Cr,TiN-Ni

Conclusions We investigated the nature of change of electrical resistivity of the quasibinary systems TiN-Cr and TiN-Ni at normal and elevated temperatures.It was established that the experimental concentrational dependences of electrical resistivity in both systems lie higher than the corresponding theoretical curves; this is due to the dissociation of titanium nitride on specimens obtained at temperatures at which interaction is slight, and after high-temperature sintering this is due, as a rule, to formation of complex solid solutions based on TiN, and also of nitrogen and titanium in chromium (in the case of TiN-Cr) and of solid solutions and intermetallic phases (in the case of TiN-Ni).The thermal coefficient of electrical resistance of specimens of the system TiN-Cr is positive but it decreases with rising temperature as a result of the change of the phase composition of the material in the process of sintering.Translated from Poroshkovaya Metallurgiya, No. 3(303), pp. 80–85, March, 1988.     

Conditions for preparing large blanks of hexanite-R and their properties

Sintering of pure wurzitic boron nitride [99% (wt.) BN_w] was performed under high static pressure at high temperature (P=8–9 GPa, T=1700–2000 K). The “double toroid” equipment is used at high pressure. Compact single- and two-layer plates 14–15 mm in diameter are fabricated. It is shown that sintering of BN_w is accompanied by the phase transformation BN_w→BN_sp (cubic boron nitride). The phase composition, microstructure, density, Young’s modulus, and wear resistance during cutting are also studied. It is found that sintered materials have the same physical and chemical properties as the well-known superhard material Hexanite-R but due to the larger blank dimensions there are greater cutting possibilities. Materials Science Institute, Ukrainian Academy of Sciences, Kiev. Translated from Poroshkovaya Metallurgiya, Nos. 1-2, pp. 55–63, January–February, 1998.     

Use of aluminum nitride in melting a V-Al-N master alloy

The possibility to use aluminum nitride as a nitriding agent for out-of-furnace aluminothermic melting of V-Al-N master alloys is studied and tested. It has been found that the replacement of nitrided vanadium by aluminum nitride in a charge for melting does not change the phase composition of the master alloy and the uniformity of the distribution of nitride inclusions in the ingot volume. The nitrogen-containing phase of the V-Al-N master alloy is represented by aluminum nitride. The mean values of the structural parameters of the master alloys melted from charges containing nitrided vanadium or aluminum nitride are identical.     

Effect of current pulse frequency on the structure and properties of electric-spark alloyed coatings of the Ti - Al - N system

The mass transfer kinetics, composition, structure, and properties of coatings, formed by high-frequency electric-spark alloying of 45 and 40X steels with the Ti - Al (3:1, 1:1, 1:3) intermetallics and TiN - AIN (1:1) nitride were studied as a function of the current pulse frequency(ν = 1200 and 1600 Hz). A decrease in ν was found to lead to a higher mass transfer coefficient and higher microhardness and Young’s modulus of the coating as well. This is due to the decrease in the Ti/Al ratio on the surface. The phase composition of intermetallic and nitride coatings differed only insignificantly and did not depend on the value of ν. The main phases of the coatings were Fe - Ti - O and Al - Ti - O solid solutions. The nitride and intermetallic coatings had similar friction coefficients f and wear rates I (f = 0.26 and 0.28, I = 5.4 and 5.9 µm/km), despite the difference in their structure. We can assume that the coating phase composition which defines the composition of the secondary structure under dry friction, is the main factor controlling tribological behavior.     

稀土夹杂物对D6AC超高强度钢力学性能的影响

本文研究了稀土夹杂物含量对Ｄ６ＡＣ钢强度和塑性的影响，得出了夹杂物的体积百分率与断面收缩率的定量关系式。从夹杂物尺寸和数量方面探讨了对Ｄ６ＡＣ钢韧性的影响。并提出了改善性能的途径。     

高炉炮泥中氮化物的组成与结构分析

为了改善高炉炮泥的烧结性能,提高其抗侵蚀能力,在炮泥配料中加入了氮化硅或氮化硅铁。对加人氮化物的炮泥组成与结构以及氮化物的作用机理进行了分析。结果表明：氮化硅存在由氮氧化物转化为氧化物的反应过程,而氮化硅铁则氧化为硅铁的氧化物。氮化物的氧化过程伴随着结构致密化反应,能减缓碳的氧化,从而改善炮泥的耐用性能。