Papers by Keyword: Liquid Phase Sintering (LPS)

Abstract: Tungsten heavy alloy of two different compositions (93W-4.0Ni-2.0Co-1.0Fe and 90W-6.1Ni-3.0Fe-0.5Co-0.4Mo in wt%) was synthesized in conventional powder metallurgy route through the liquid phase sintering. Studies have been carried out on the effect of alloying elements, tungsten particle size, and amount of matrix on mechanical properties. The alloy with 93% W had shown the higher tensile strength value and lower elongation along with double the value of impact energy than that of 90% W due to lower tungsten particle size and weight fraction in addition to an increase in cobalt and increase in ratio of iron to nickel. Relatively higher porosity could also have resulted in reduced properties.

Abstract: Lead-free Li_0.06(Na,K)_0.94NbO₃ (LNKN) piezoelectric ceramics were sintered by a new process, “two-step mixing process”, in which a part of alkali source powders (R_A) was initially preserved and mixed with the rest matrix powders after the calcinations step, in order to improve bulk density. Sintering of the LNKN ceramics was improved by this process, and the sample with R_A = 5% had the highest bulk density of 4.34 g/cm³ (ca. 95%TD). The pore shape and the fracture morphology of the samples suggested the formation of a liquid phase. The present results indicated that the two-step mixing process was an universal approach for improvement in the densification of alkali niobate ststem.

Abstract: In this work, one stage and two stages compaction technique were used to fabricate the tungsten-copper composite powder. Liquid infiltration technique was used to consolidate the W-Cu green compact and a low concentration iron powder was added as activation material to enhance the sintering behavior. In addition, two-steps compaction process was developed for improving mechanical properties of W-Cu composite as well as segregation of Fe around W grain. The green compact was directly infiltrated at 1250 °C for about 2 hours under vacuum conditions. The microstructure, inter-boundary layer and the contamination levels of the infiltrated compacts were characterized using the scanning electron microscope (SEM) and the energy dispersive X-ray analysis (EDX). Relative sintering density varied in the range of 97.1 to 99.3 % of theoretical density, and it was highly depended on Fe concentration and method of compaction. In contrast to one stage compaction, the experimental results showed that the composites fabricated by the two stages of compact ion had better homogeneous structure, high densification and a clear segregation of inter-boundary layer of Fe-W around W grains.

Abstract: The effect of V₂O₅ addition on the microstructures and the microwave dielectric properties of 0.9CaWO₄-0.1Mg₂SiO₄(9CWMS) ceramics prepared by conventional solid-state routes have been investigated. The V₂O₅ were selected as liquid phase sintering aids to lower the sintering temperature of 9CWMS ceramics. A small amount of V₂O₅ (0.25~1 wt%) were used for sintering aid and led to high densification at 1050°C. The dielectric properties of 9CWMS ceramics with V₂O₅ additions are strongly dependent on the densification, the microstructure. As the amount of V₂O₅ additives increased from 0.25 to 1.0 wt%, the dielectric constantsεrdecreased following the trend with density. The quality values Qdecreased with the increase of V₂O₅ amount for all sintering temperatures. The 0.25 wt% V₂O₅-doped 0.9CaWO₄-0.1Mg₂SiO₄ ceramicssintered at 1080°C for 2 h had the optimum dielectric properties: εr= 5.7; Q×f= 73000 (at 14 GHz).

Abstract: Low fracture toughness of SiC ceramics limits their applications for the low reliability. Inclusion of second ceramic phase improves the toughness of SiC ceramics. In this presentation, SiC ceramics with 5wt% TiC was pressureless liquid phase sintered (LPS) with the additives of Al₂O₃ and Y₂O₃ to ~98% theoretical density at the temperature of 1920 °C for 1 hour. The TiC grains were well distributed and good for the uniform distribution of the liquid phase YAG in the SiC matrix, which resulted in the homogeneous microstructure with fine SiC grains. The existence of TiC benefited the formation of elongated α-SiC, which favored the bridging and deflection of cracks so that the fracture toughness was improved to some extent. Because the amount of TiC was so small that the inherent properties of SiC was not degraded. The flexural strength and Vickers hardness maintained similar with the LPS SiC without TiC. The phase compositions detected in the sample were SiC, YAG and TiC. And no solid-solution of SiC and TiC was revealed by the mapping of EDS.

Abstract: In this study, the effect of sintering temperature on the properties of tungsten-copper (W-Cu) composite produced by liquid phase sintering (LPS) process has been investigated. W-20 wt.% Cu composite powders with particle size less than 1 μm was prepared by cold compaction and followed by cold isostatic pressing. The green specimens were then sintered under nitrogen based atmosphere in the temperature range of 1100°C to 1300°C. The sintering studies were conducted to determine the extent of densification and corresponding to microstructure changes. In addition, the properties of the sintered specimens such as physical appearance, microstructure evolution, mechanical and electrical properties were presented and discussed.

Abstract: The present study aims to investigate the oxidation behavioue of pressuerless sintered SiC ceramic with the AlN-Y₂O₃ as sintering additives. Two main aspects are considered: The evaluation of oxidation kinetics in the temperature rang 1200°C-1400°C for short term test (30hr) and the degradation of the flexural strength after oxidation at temperature 1400°C for 100hr. The microstructure of surface oxidation layer of silicon carbide at high temperature is studied, and the effect of reactive product s on the high temperature oxidation resistance is also analyzed. The results showed that the oxidation began at temperature more than 1200°C, and the oxidation kinetics is obeyed parabolic rule. After long term oxidation, the fracture strength decreased greatly.Key words: oxidation behavior, liquid phase sintering, silicon carbide

Abstract: High purity aluminium powder was sintered in a dilatometer in flowing high purity nitrogen. The distinct shrinkage segments observed on the dilatometry curves were the basis of experiments consisting of interrupted sintering. In this way compacts with microstructure frozen at different steps of sintering cycle were produced. Optical microstructure examinations and LECO analysis of nitrogen content showed the development of aluminium nitriding. Additionally, X-ray diffraction was used to examine phases appearing in the system investigated. Microstructure analysis of structural components revealed evidence that isothermal sintering proceeds in the presence of a liquid phase, despite taking place below the melting point of aluminium. It seems that aluminium nitrogen interactions are responsible for the appearance of this phase, which is accompanied by extensive shrinkage.

Abstract: The technology is introduced about mechanical ball milling and liquid phase sintering of machining crumbs of steel based carbide alloy in this article. The materials obtained from machining crumbs of steel-bonded cemented carbide are qualified compared with the conventional steel-bonded cemented carbide materials in the aspects of hardness, wear resistance by using the technology and the process is reasonable and practicable, according to experimental results. It can be extremely important when considering the recycling and make full use of tungsten resources.

Abstract: In this article, studies were conducted to evaluate the densification of W-Cu sintered compacts produced using two methods; liquid phase sintering (LPS) and combination of liquid phase sintering and liquid infiltration technique (LPS+LI) named Cu-melt infiltration (Cu-MI). Low concentration of nickel (1wt.%) was used to activate the sintering process in both methods. Isothermal sintering was carried out in alumina tube furnace at temperatures of 1150°C for 2 hr. under H₂/Ar. as protective gas. The infiltration (Cu-MI) method proved to be effective in the densification, microstructure and hardness enhancement of the 80W-Cu compact as opposed to the other conventionally liquid phase sintered compacts. The relative densities of 80W-Cu-1Ni composites prepared by using insert method (Cu-melt infiltration) achieved 96.22% of theoretical density.