Sintering liquid phase

Another possible source of flaws can be introduced during the cold pressing of agglomerated powders as a result of density differences between the agglomerates and the matrix. When the pressure is removed, the elastic dilation of the agglomerates and the matrix may be sufficiently different to cause cracks to form i.e., the springback of the agglomerates will be different from the matrix as a result of differences in their density. 

Liquid-phase sintering offers two significant advantages over solid-state sintering. First, it is much more rapid second, it results in uniform densifica-tion. As discussed below, the presence of a liquid reduces the friction between 

During liquid-phase sintering, the compositions of the starting solids are such as to result in the formation of a liquid phase upon heating. The liquid formed has to have an appreciable solubility of the solid phase and wet the solid. In the next sections, the reasons these two requirements should be met and the origin of the forces at play during liquid-phase sintering are elucidated. 

When a liquid is placed on a solid surface, either it will spread and wet that surface (Fig. 10.22fl) or it will bead up (Fig. 10.22ft). The degree of wetting and whether a system is wetting or nonwetting are quantified by the equilibrium contact angle 9 that forms between the liquid and the solid and is defined in Fig. Q.22a and ft. A simple balance of forces indicates that at equilibrium 

The complete penetration of grain boundaries with a liquid is also important for microstructural development (e.g., it could lead to the breakup of agglomerates). It can be shown (Prob. 10.116) that a necessary condition for the penetration and separation of the grains with a thick liquid film is 7gb 27is. This implies that the equilibrium dihedral angle shown in Fig. 10.36, and defined as 

Sintered products include cutting tools, bearings, contact points, and other irregularly shaped parts where it is desirable to combine extreme hardness with the toughness and thermal or electrical conduction of the metal matrix. 

The second stage further depends upon many other factors, such as the composition of the glass. This composition may vary within the compact, and this is why dissolution and reprecipitation take place. Another factor is the viscosity of the glass. Viscosity changes with temperature. As temperature increases, viscosity decreases. Viscosity also depends on the composition. 

In the third stage, the grains coarsen. This is a time-dependent phenomenon, and the rate is low. It is similar to the grain growth that takes place in 

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Liquid-phase sintering is significantly more complex tlian solid-state sintering in tliat tliere are more phases, interfaces, and material transport mechanisms to consider. In general, densification will occur as long as it is... 

Densification during liquid-phase sintering occurs in tliree stages. Initially, liquid fonns at particle intersections and redistributes tliroughout the particulate mass under the influence of the capillary action. Shear stresses due to the... 

In liquid-phase sintering, densification and microstmcture development can be assessed on the basis of the liquid contact or wetting angle, ( ), fonned as a result of the interfacial energy balance at the solid-liquid-vapour intersection as defined by the Young equation ... 

German R M 1985 Liquid Phase Sintering (New York Pienum)... 

Figure 10.3 The model for liquid phase sintering of high-melting solids with liquid metals as a sintering aid...

R.M. German. Liquid Phase Sintering. Plenum Piess New York (1985) TN695. G469. 

Fig. 19.5. Liquid phase sintering a small amount of additive forms a liquid which accelerates sintering and gives fully dense products but with some loss of high-temperature strength.

Chick LA, Kiu J, Stevenson JW, Armstrong TA, McCready DE, Maupin GD, Coffey GW, and Coyle CA. Phase transitions and transient liquid-phase sintering in calcium-substituted lanthanum chromite. J. Am. Ceram. Soc. 1997 80 2109-2120. 

Liquid-phase reactions photocatalytic, 19 85 of titanium nitride, 25 10 Liquid-phase sedimentation, 18 142 Liquid-phase sintering, 5 661 Liquid phosgene assay, 18 808 Liquid phosphate esters, 19 51, 68... 

Reactive liquid-phase sintering, 5 661 Reactive molecules, oliigonucleotides conjugated to, 17 636-637 Reactive organic phosphorus compounds, 11 496-497... 

Liquid Phase Sintering of High-Speed M2 Steels 360... 

Chandrasekaran, L. and Miodownik, A. P. (1989) Phase equilibria relevant to liquid phase sintering in Fe-base alloys . Report to SERC under contract GR/D 99935 (University of Surrey, Guildford, January). 

R.B. Heady and J.W. Cahn. An analysis of capillary force in liquid-phase sintering of spherical particles. Metall. Trans., 1(1) 185—189, 1970. 

Cemented carbides and nitrides are manufactured by a powder metallurgy process using liquid phase sintering (Figure 2.1). The cobalt or nickel binder metal, in the form of fine powder, is blended with the carbide or nitride powders in ball mills or attritor mills lined with carbide sleeves. 

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