Comparative Analysis of Three Hot Extrusion Processes for Titanium Bars

Titanium and its alloys are widely utilized in aerospace, biomedical, and chemical industries due to their high strength, low density, excellent corrosion resistance, and biocompatibility. As a critical forming process, hot extrusion enables full densification of powders under elevated temperatures while precisely controlling material composition and internal microstructure. To prevent oxidation of reactive titanium powders, a "canning" method is typically employed: powders or compacts are sealed in a vacuumed jacket (often low-carbon or stainless steel) before extrusion. The cladding material must possess good thermoplasticity, remain non-reactive with the titanium, and be easily strippable post-extrusion. Currently, three primary hot extrusion processes are dominant:

Process 1: Integrated Forming, Sintering, and Thermal Processing

• Workflow:This process integrates three stages into one continuous flow. After initial forming, the powder undergoes sintering to bond particles through diffusion, followed by immediate hot extrusion to refine the internal structure and produce high-performance components.

• Advantages:Its primary strength lies in high production efficiency by reducing intermediate steps. The resulting products exhibit superior mechanical properties (strength and toughness) due to structural optimization during thermal processing.

• Disadvantages:It requires extremely rigorous parameter control. Minor fluctuations in pressure or temperature during forming can compromise subsequent stages, leading to defects like cracks or pores.

Process 2: Hot Extrusion of Pre-sintered Powder Compacts

• Workflow:Titanium powders are first pressed into compacts and then sintered to achieve specific density and strength. For instance, Ti-32Mo alloys are extruded at $1000\text{--}1100^{\circ}\text{C}$ after sintering. This method can achieve a theoretical density of $98.6\%\text{--}99.1\%$.

• Advantages:This is a mature, easily controlled process. Pre-sintering improves material flow during extrusion, resulting in a uniform microstructure. Density and mechanical properties can be adjusted by tuning the extrusion ratio.

• Disadvantages:The production cycle is longer, increasing time and costs. Non-uniform shrinkage during sintering may also affect dimensional accuracy, sometimes requiring additional machining.

Process 3: Canned Filling and Extrusion

• Workflow:Designed for complex cross-sections, this involves preparing a cladding cavity based on the final product size and extrusion ratio. The cavity is filled with powder via vibration, vacuumed, and sealed before extrusion. Finally, the cladding is stripped away.

• Advantages:Its standout feature is the ability to produce complex, non-standard cross-sections that other methods cannot achieve, while maintaining uniform internal structures.

• Disadvantages:The process is highly complex, demanding specialized equipment and precision. Variations in powder filling or cladding dimensions can lead to defects, and the stripping process may damage the product surface, requiring post-treatment.

Conclusion:

Each process has its trade-offs. Manufacturers must balance efficiency, complexity, and product requirements to select the optimal method, aiming to maximize quality while minimizing costs.