Analysis of Metal Powder Sintering Technology

Powder metallurgy is a technology that uses metal powder as a raw material to produce metal materials, composite materials, and various types of products after molding and sintering

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01 Analysis of powder sintering process

Powder sintering is a process of reducing the free energy of the system, which is manifested in the flattening of the sintering neck and particle surface, the reduction of the total surface area and surface energy of the system, the reduction of the total void volume and total surface area, and the elimination of lattice distortion in the grain

The sintering of powder particles is divided into three stages: (1) Particle bonding (initial): The particles change from point or surface contact to crystal bonding, forming a certain strength sintering neck, resulting in increased strength and conductivity; (2) ) Sintering neck growth stage (middle stage): The sintering neck grows up through atomic diffusion between particles, forming a connected network structure, the distance between the particles is reduced, and the overall porosity is reduced; (3) closed-cell spheroidization and Shrinking stage (late stage): The pores are mostly closed cells, and the number increases, and the sintered body shrinks slowly, mainly due to the reduction and shrinkage of closed cells

02 Influencing factors of powder metallurgy sintering quality

There are many factors that affect the performance of the sintered body, including the characteristics of the powder, molding and sintering conditions

The sintering atmosphere commonly used in powder metallurgy is reduced atmosphere, vacuum, hydrogen atmosphere, etc.

03 Analysis of metal powder sintering technology

3.

Selective laser sintering (SLS) is the use of laser to selectively sinter solid powder in layers, and superimpose the sintered solidified layers to produce parts with the desired shape

Figure 1 The working principle of the rapid prototyping system of SLS technology (picture source: Metallurgical Series)

The use of metal powder for rapid prototyping is the trend of laser rapid prototyping from prototype manufacturing to rapid direct manufacturing.
It can greatly accelerate the development of new products and has broad application prospects
.
In the selective sintering method of metal powder, there are three commonly used metal powders:

(1) Mixture of metal powder and organic binder

The two powders are mixed uniformly in a certain proportion, and then the mixed powder is selectively sintered with a laser beam
.

(2) Mixture of two metal powders

One of them has a lower melting point and acts as a binder
.
The sintering molding is similar to liquid phase sintering.
The laser energy melts the low melting point components in the composite component, and the formed liquid phase infiltrates the solid phase.
After cooling, the low melting point liquid phase solidifies to bond the high melting point components together
.

(3) Single metal powder

For unit system sintering, especially for metals with high melting points, the melting temperature needs to be reached in a relatively short period of time, and a very powerful laser is required
.
The biggest problem is the low density and poor mechanical properties of the parts due to the porous structure
.

3.
2 Selective laser melting technology (SLM)

SLM is a rapid prototyping technology for metal powders that was born in recent years.
With it, metal parts that are nearly completely dense can be directly formed
.
SLM technology overcomes the complexity of the process of manufacturing metal parts with SLS technology
.

SLM technology uses a high-energy laser beam with a spot diameter of less than 100μm to directly melt metal powder, layer by layer selected areas are melted and accumulated, and finally form metallurgical bonding and densely organized metal parts.
The schematic diagram of the SLM technology principle is shown in the figure
.

Figure 2 Schematic diagram of the forming principle of SLM technology

SLM is an important research direction of metal 3D printing technology, which can directly form complex and lightweight structural parts such as hollow lattice, hollow interlayer, and integration
.
At present, SLM technology molding has begun to be used in aviation, aerospace, automotive, mold, medical and other fields
.

3.
3 Microwave sintering technology

Microwave sintering is a high-efficiency, energy-saving, clean and environmentally friendly sintering method, which can make sintered products obtain finer microstructure and mechanical properties.
It has been recognized by the world and is called a new generation of sintering technology
.
After nearly ten years of development, domestic and foreign scholars have made certain progress in the research of microwave sintering mechanism of metal powder
.

Microwave heating uses the interaction of molecules or atoms with electromagnetic fields to generate heat energy on the material itself.
During the sintering process, changes in quality and quantity occur on the bonding surface of the particles, as well as the spheroidization and reduction of pores in the sintered body.
These processes are all based on the migration of substances.
The basis is that the material migration is the root cause of the growth of the sintering neck, so it is very important to clarify the material migration mode to study the sintering behavior of metal powder in the microwave field
.

Figure 3 Schematic diagram of microwave penetrating metal powder (picture source: powder metallurgy technology)

The theory of microwave heating technology for metal powders is still in the exploratory research stage.
There is still a lack of in-depth research and understanding of some special phenomena observed in microwave sintering and the mechanism of physical and chemical changes; research methods are relatively lacking, and direct evidence for some microwave effects cannot be obtained.
, Staying in the speculation stage
.

04 Summary

In recent years, with the gradual development and maturity of materials, equipment, molds, processes, and automation technology, the application of powder metallurgy has become wider and wider, and it has become a new industrial technology that has attracted much attention in consumer electronics, automotive and other industries
.
More and more attention has been paid to metal powder sintering technology
.
We believe that as people master the forming mechanism of laser sintering metal powder, obtain the best sintering parameters of various metal materials, and the emergence of special rapid prototyping materials, the research and reference of metal sintering technology will surely enter a new Realm
.

Reference source:

[1] Shi Lei.
Research on Molybdenum Copper Alloy Activation Sintering Technology.
2020.

[2] Shao Juan, et al.
Analysis of rapid prototyping technology for selective laser sintering of metal powders.
Metallurgical Series.
2007.

[3] Zhuang Tianya, et al.
Research progress in the mechanism of microwave sintering of metal powders.
Powder metallurgy technology.
2019.

[4] Zhou Song.
SLM-based metal 3D printing lightweight technology and its application research.

[5] Admin.
Influencing factors and sintering methods of powder metallurgy sintering quality.