Similarities and differences between solid phase sintering and liquid phase sintering, what is solid

The main mass transfer modes of solid-phase sintering are evaporation-condensation mass transfer and diffusion mass transfer, and the main mass transfer modes of liquid-phase sintering are dissolution-precipitation mass transfer and flow mass transfer.

The common denominator between solid-phase sintering and liquid-phase sintering is that the driving force of sintering is surface energy; The sintering process consists of stages such as particle rearrangement, material transport and porosity filling, and grain growth.

The differences are: because the flow mass transfer is faster than the diffusion mass transfer, the densification rate is high; Solid-phase sintering is mainly related to the particle size and activity of raw materials, sintering temperature, atmosphere forming pressure and other factors, and liquid-phase sintering is related to the quantity of liquid phase, the properties of liquid phase, liquid-solid wetting, and the solubility of solid phase in liquid phase.

Similarities: the driving force (energy difference) is all surface, and the sintering process is also composed of stages such as particle rearrangement, pore filling, and grain growth;

Differences. The flow mass transfer rate is faster than the diffusion mass transfer, so the densification rate of dense liquid phase sintering is high, so that the liquid phase sinter can obtain a dense sinter body at a much lower temperature than solid sintering.

Types of liquid phase sintering and their characteristics:

Viscous flow, when the liquid phase is large, Newton occurs due to high-temperature fluids.

type of mass transfer due to flow.

Plastic flow, when the liquid phase content in the embryo body is very small, the flow at high temperature cannot be regarded as pure Newtonian flow.

Sintering, which refers to the transformation of powdered materials into dense bodies, is a traditional process. People have long used this process to produce ceramics and powder metallurgy.

Refractory materials, ultra-high temperature materials, etc. Generally speaking, after the powder is formed, the dense body obtained by sintering is a polycrystalline material, and its microstructure is composed of crystals and glass.

and stomata composition. The sintering process directly affects the grain size, pore size and grain boundaries in the microstructure.

shape and distribution, which in turn affects the properties of the material.

1. The influencing factors of the two are different:

1. Influencing factors of solid-phase sintering:

1) Properties of the material: such as the surface energy, diffusion coefficient, viscosity coefficient, critical shear stress, vapor pressure and evaporation rate of the material, these factors will affect the sintering driving force and the growth rate of the sintering neck.

2) Powder properties: including powder particle size, surface activity (surface activity is related to the presence of oxide film on the surface and the structural perfection of the surface, and its activity is high when there are a large number of dislocations and vacancies on the crystal surface), lattice activity (lattice defects and lattice distortion) and foreign substances (impurities, oxides, adsorption gases and sintering atmosphere).

2. Influencing factors of liquid-phase sintering:

1) The wettability of the slippery reed cover on the surface of liquid phase and solid phase particles, usually the wetting angle is less than 90 degrees, and it is best to be close to zero degrees. Improving the relative solid-phase wettability of the liquid can improve the liquid-phase sintering effect.

2) The solid phase has a certain solubility in the liquid phase, while the liquid phase has little solubility in the solid phase, or it is insoluble.

3) The number of liquid phases is limited. Generally, it is limited to be able to fill the gap between the solid particles during cooling. Generally, 20% to 50% (volume fraction) is appropriate.

Second, the overview of the two is different:

1. Overview of solid-phase sintering: solid-phase sintering can be divided into two categories: unit-based solid-phase sintering and multi-system solid-phase sintering according to the number of its components. Powder sintering is carried out by the unit solid-phase sintering of pure metals, fixed composition compounds or loose powders or pressed blanks of homogeneous solid solutions at temperatures below the melting point (generally 2 3 4 5 of the absolute melting point temperature).

2. Overview of liquid-phase sintering: Liquid-phase sintering refers to the sintering process of powder or pressed blank with at least two components in the state of forming a liquid phase.

Third, the use of the two is different:

1. The use of solid-phase sintering: the recovery of metals, the volatilization of adsorption gas and water, and the decomposition and removal of forming agents in the blank. Due to the elimination of the elastic stress during compression, the contact area between the powder particles is relatively reduced, and the sinter shrinks not obviously, or even slightly expands due to the exclusion of volatiles.

During this phase, the density of the sintered body remained basically unchanged.

2. The use of liquid-phase sintering: The liquid-phase sintering process has been widely used to manufacture various sintered gold parts, electrical contact materials, cemented carbide and cermets.

Powders or pressed blanks with at least two components are sintered in a state that forms a liquid phase.

The sintering process with liquid phase generation can be divided into two categories:

First, there is a liquid phase in the whole sintering process.

Second, the liquid phase disappears in the late stage of sintering.

The liquid-phase sintering process can be divided into four stages: preparatory sintering stage, shrinkage stage, liquid-phase sintering, and cooling stage. Sintering in which a small part of the raw material becomes liquid.

In the alloy powder to be sintered (base phase alloy powder), the appropriate alloy powder with a lower melting point (liquid alloy powder) is evenly mixed, and at the sintering temperature, the liquid phase alloy vertical powder becomes a liquid state, which can increase the densification rate of sintering and the density of the final product.

Compare with liquid-phase sintering.

Liquid-phase sintering is that at a certain temperature, the main component has not been liquefied, but the impurity component has been liquefied, and the main component is sintered and crystallized in the liquid phase formed by impurities, which is called liquid-phase sintering.

Solid-phase sintering means that the main components are sintered without a liquid phase environment.

Comparatively, liquid phase sintering requires a lower temperature, but solid phase sintering is stable and has good high temperature performance.