The primary purpose is to induce plastic deformation and densification. By applying extreme pressure, such as 700 MPa, to the material after the initial sintering phase, the press forces the metallic particles to rearrange. This process significantly reduces the material's porosity and reinforces the internal matrix.
Core Takeaway Secondary pressing is not merely about shaping; it is a structural enhancement method. By mechanically closing internal voids and interlocking the metallic matrix, this step converts a porous sintered compact into a high-density composite with superior tensile strength and scuffing resistance.
The Mechanism of Densification
Inducing Plastic Deformation
The process targets the material after it has been sintered (heated to bond particles). The laboratory press applies a massive load—specifically around 700 MPa—to the sintered compact.
This extreme pressure exceeds the yield strength of the metal matrix, causing plastic deformation. Unlike elastic deformation, which is reversible, this permanently alters the shape and structure of the metallic particles.
Particle Rearrangement
As the pressure is applied, the metallic particles are forced to move and slide past one another. This rearrangement allows the particles to fill the interstitial voids (gaps) that naturally occur during the initial sintering process.
Impact on Material Properties
Significant Reduction in Porosity
The most immediate physical change is the reduction of void space within the material. The re-pressing process can reduce porosity by 25% to 32%.
This reduction is critical for high-performance applications, as excess porosity can act as stress concentration points where cracks initiate under load.
Structural Support for Lubricants
These iron-based materials are "self-lubricating," meaning they contain solid lubricant particles embedded within the metal. The densification ensures the metal matrix provides robust mechanical support for these solid lubricants.
Without this tight structure, solid lubricants might dislodge or fail to function effectively under stress.
Performance Enhancement
The cumulative effect of reduced porosity and better support is a measurable increase in mechanical performance. Specifically, this treatment enhances:
- Ultimate Tensile Strength: The material can withstand higher pulling forces before breaking.
- Scuffing Resistance: The surface becomes more resistant to damage caused by sliding contact and friction.
Understanding the Trade-offs
Process Complexity vs. Performance
While secondary pressing is a "critical method" for achieving high performance, it introduces an additional step in the manufacturing workflow. It requires specialized high-pressure equipment capable of delivering 700 MPa safely and consistently.
Density vs. Permeability
It is important to note that this process is designed to reduce porosity. If the application requires a highly porous structure (for example, to hold large amounts of liquid oil in a bushing), this aggressive re-pressing might be counterproductive. It is specifically optimized for applications requiring high strength and solid lubrication support rather than maximum fluid permeability.
Making the Right Choice for Your Goal
When developing high-performance iron-based composites, consider how secondary pressing aligns with your specific mechanical requirements.
- If your primary focus is mechanical durability: Utilize re-pressing at pressures near 700 MPa to maximize tensile strength and minimize the risk of structural failure.
- If your primary focus is wear life: Implement this step to improve scuffing resistance by ensuring the solid lubricant is firmly locked into a dense metallic matrix.
The laboratory press transforms the material from a porous sintered part into a dense, high-strength component capable of surviving demanding tribological environments.
Summary Table:
| Feature | Impact of Secondary Pressing |
|---|---|
| Primary Mechanism | Plastic deformation and particle rearrangement |
| Applied Pressure | Approximately 700 MPa |
| Porosity Reduction | 25% to 32% decrease |
| Mechanical Gains | Higher tensile strength & improved scuffing resistance |
| Key Outcome | Enhanced structural support for solid lubricants |
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Precision and power are critical for achieving the 700 MPa pressures required for high-performance material densification. KINTEK specializes in comprehensive laboratory pressing solutions tailored for battery research and advanced materials science.
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References
- José Daniel Biasoli de Mello, Aloı́sio Nelmo Klein. Tribological behaviour of sintered iron based self-lubricating composites. DOI: 10.1007/s40544-017-0186-2
This article is also based on technical information from Kintek Press Knowledge Base .
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