How does a four-column hydraulic press improve TiBw/TA15? Master Microstructure with Precise Hot Extrusion

A four-column hydraulic press fundamentally improves the TiBw/TA15 microstructure by utilizing high extrusion force and constant velocity to induce severe plastic deformation. This intense deformation process is the physical catalyst that reorganizes the material's internal architecture, turning a raw composite into a high-performance structural component.

The press enhances the composite through three simultaneous mechanisms: forcing the directional alignment of TiB whiskers, triggering dynamic recrystallization to refine the matrix grain structure, and utilizing triaxial compressive stress to permanently close internal micro-voids.

The Mechanics of Microstructural Transformation

Directional Alignment of Reinforcements

The primary benefit of the four-column press is its ability to impose severe plastic deformation on the TA15 matrix.

As the material flows under this immense pressure, the rigid TiB whiskers (TiBw) are forced to rotate.

They align directionally along the extrusion axis, significantly boosting the material's strength in the direction of the load.

Grain Refinement via Dynamic Recrystallization

The high energy input and strain from the press trigger a phenomenon known as dynamic recrystallization (DRX) within the titanium alloy matrix.

Instead of retaining coarse, irregular grains, the matrix is forced to reorganize itself.

This results in a much finer, more uniform grain structure, which directly correlates to improved ductility and fatigue resistance.

Elimination of Internal Defects

The hydraulic press creates a state of triaxial compressive stress during the molding process.

Unlike simple compression, this forces material together from multiple directions, effectively crushing microscopic voids and closing unbonded regions.

This leads to a dense, seamless metallurgical interface free of the porosity that typically compromises structural integrity.

Critical Process Variables and Trade-offs

The Necessity of Constant Speed

The four-column hydraulic press is specifically valued for its ability to maintain a constant extrusion speed.

Fluctuations in speed can lead to uneven deformation rates, causing inconsistent grain sizes along the length of the component.

Stability in velocity ensures that the dynamic recrystallization process remains uniform throughout the entire part.

The Role of High Force Application

Achieving full density requires overcoming the material's natural resistance to flow.

If the extrusion force is insufficient, the triaxial stress may not be high enough to fully close the deepest micro-voids.

The press must be capable of delivering sustained, high-tonnage force to guarantee the elimination of density gradients and defects.

Making the Right Choice for Your Goal

To maximize the benefits of this process for your specific application:

• If your primary focus is anisotropic strength: Prioritize high deformation ratios to maximize the directional alignment of the TiB whiskers along the load-bearing axis.
• If your primary focus is fatigue resistance: Ensure strictly constant extrusion speeds to guarantee a uniform, fine-grained matrix via consistent dynamic recrystallization.

The combination of high force and controlled speed allows you to engineer the microstructure rather than simply accepting it.

Summary Table:

Mechanism	Action of Hydraulic Press	Impact on Microstructure
Reinforcement Alignment	High extrusion force & severe plastic deformation	TiB whiskers align along the extrusion axis for anisotropic strength
Grain Refinement	Induction of Dynamic Recrystallization (DRX)	Coarse grains transformed into a fine, uniform matrix for better ductility
Defect Elimination	Application of triaxial compressive stress	Closure of micro-voids and porosity to ensure full material density
Consistency Control	Maintenance of constant extrusion velocity	Prevents density gradients and ensures uniform grain size throughout the part

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