1. Raw Material Preparation
Billet selection: choose the grade by the forging's service requirements. Ti-6Al-4V (UNS R56400) is the most common α+β alloy - an excellent balance of strength, toughness and weldability, used across aerospace and medical components. For maximum corrosion and formability, commercially pure grades (Grade 1–4) are used; for higher-temperature service, near-α and β alloys are selected.
Billet pretreatment: the surface is cleaned of oxide scale, oil and contaminants by mechanical methods (sandblasting, machining) or chemical methods (pickling) so surface defects are not forged into the part and oxygen-enriched α-case is removed before hot working.
2. Heating
Temperature control: the forging window is defined by the alloy's beta transus temperature (Tβ). For α+β alloys such as Ti-6Al-4V, forging is performed in the α+β field, typically 900–980 °C - about 30–60 °C below Tβ - to develop a fine, equiaxed structure. Heating too close to or above Tβ produces coarse Widmanstätten grains with poor ductility; heating too low makes deformation difficult and risks cracking. β alloys are deliberately forged above Tβ in specialized practice, but that requires controlled process design.
Heating equipment and atmosphere: electric or gas-fired furnaces with uniform temperature distribution and modern control systems hold the billet in the optimum window. Because titanium absorbs oxygen, nitrogen and hydrogen aggressively above about 500 °C, heating is done under inert gas (argon) protection, or with allowance for the oxygen-enriched α-case layer to be removed in subsequent machining.
3. Forging Operations
- Open-die (free) forging: suitable for large, simple shapes; the billet is deformed by hammer or press between flat dies. Flexible and low-investment, but dimensional precision is limited.
- Closed-die forging: the billet is formed in a die cavity, giving high dimensional accuracy, good surface quality and suitability for volume production of complex parts.
- Isothermal forging: die and workpiece are held at the same temperature, enabling complex geometries with low deformation force, minimal internal stress and superior material properties - usually in dedicated equipment with precise temperature and strain-rate control.
4. Cooling and Heat Treatment
Cooling: after forging, cooling rate is controlled because it directly sets the microstructure. Air cooling is typical for α+β alloys; water quenching is used only where a solution-treated microstructure is required and distortion can be managed.
Heat treatment: annealing relieves residual stress and restores ductility; solution treatment and aging (e.g., 955 °C solution + 720 °C/8 h aging for Ti-6Al-4V in many aerospace specs) raise strength and toughness to the specified level. Heat treatment atmosphere and time must be controlled to limit surface contamination.
5. Surface Treatment and Finishing
Surface treatment improves corrosion and wear resistance. Note that conventional electroplating does not work well on titanium - its dense oxide film gives poor plating adhesion - so industrial practice uses anodizing, micro-arc oxidation, thermal spraying, chemical conversion coatings or ion implantation instead. Finishing (turning, milling, grinding) achieves final dimensions, and pickling or acid milling removes any α-case from hot working.
6. Quality Assurance
Aero-grade titanium forgings are verified by ultrasonic inspection for internal defects (with reference-block standards), liquid penetrant testing for surface defects, dimensional and hardness checks, and tensile testing from sacrificial prolongations. Heat number and process records are retained for full traceability.
7.Applications and Outlook
Titanium forgings serve aerospace structures and engine parts, medical implants, and high-performance automotive and energy components - anywhere strength-to-weight and corrosion resistance justify the cost. As near-net-shape forging, isothermal and closed-die routes mature, titanium forgings will increasingly replace machined-from-bar parts in demanding applications.
