The speed of the press plunger is the definitive control variable for the structural outcome of MgAl2O4-TiB2 composites during SHS-extrusion. By directly influencing the deformation rate, the plunger speed dictates whether the final product emerges as a solid, dense rod with a core-shell structure or as a hollow ceramic tube.
Core Takeaway: Plunger speed acts as a structural switch by manipulating the Barus effect (extrudate swell). Exceeding a specific velocity threshold shifts the manufacturing output from dense, segregated rods to hollow structures, allowing for geometric diversification without altering chemical composition.
The Mechanism of Structural Change
The physical shape of the composite is not determined solely by the die, but by how the material behaves under specific rates of deformation.
The Critical Threshold
The defining boundary for this process is a plunger speed of 65 mm/sec.
This velocity serves as a tipping point. The behavior of the ceramic paste changes fundamentally depending on whether the pressure is applied above or below this rate.
High-Speed Operation: Creating Hollow Rods
When the process requires lightweight or tubular components, high-speed extrusion is the effective strategy.
Triggering the Barus Effect
When the plunger speed exceeds 65 mm/sec, the material experiences a high deformation rate.
This rapid compression triggers the Barus effect, commonly known as extrudate swell.
Resulting Structure
Instead of retaining the exact dimensions of the die, the material expands immediately upon exiting.
This expansion phenomenon causes the extrudate to naturally form hollow ceramic rods.
Low-Speed Operation: Creating Dense Composites
Lower speeds are utilized when structural integrity and density are the priority.
Promoting Material Segregation
Operating the plunger below the 65 mm/sec threshold avoids the Barus effect.
This slower deformation rate allows the material to settle into a dense composite rod.
The Core-Shell Formation
Low-speed extrusion results in a specific internal architecture.
The finished product features a distinct TiB2 core surrounded by an MgAl2O4 shell.
Understanding the Trade-offs
While speed offers versatility, it introduces specific processing constraints that must be managed.
Sensitivity to Velocity
The primary trade-off is that the structural outcome is highly sensitive to the deformation rate.
You cannot achieve a "middle ground" structure easily; crossing the speed threshold drastically alters the geometry from solid to hollow.
Requirement for Precision
Because the speed determines the final form, the mechanical control of the press must be exact.
Precise regulation is mandatory to ensure the plunger velocity remains consistently on the desired side of the 65 mm/sec threshold to prevent structural defects.
Making the Right Choice for Your Goal
To select the correct plunger speed, you must define the required geometry and internal structure of your final application.
- If your primary focus is producing hollow components: Maintain a plunger speed above 65 mm/sec to leverage the Barus effect for natural tube formation.
- If your primary focus is high-density structural integrity: Maintain a plunger speed below 65 mm/sec to produce solid rods with a TiB2 core and MgAl2O4 shell.
By strictly controlling the deformation rate, you can produce two distinct ceramic products from a single material system.
Summary Table:
| Plunger Speed | Deformation Rate | Phenomenon | Final Structure | Core-Shell Result |
|---|---|---|---|---|
| < 65 mm/sec | Low | Material Segregation | Dense Solid Rod | TiB2 Core / MgAl2O4 Shell |
| > 65 mm/sec | High | Barus Effect (Swell) | Hollow Ceramic Tube | No Core-Shell Formation |
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References
- А. P. Chizhikov, М. С. Антипов. Influence of technological parameters on the process of SHS-extrusion of composite material MgAl2O4‑TiB2. DOI: 10.22226/2410-3535-2022-2-158-163
This article is also based on technical information from Kintek Press Knowledge Base .
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