Exploiting Adiabatic Softening for Defect-Free Hot Forging of Ti-6Al-4V Femoral Stems

Area of Science:

• Materials Science and Engineering
• Manufacturing Processes
• Biomedical Engineering

Background:

• Hot forging of Ti-6Al-4V is crucial for orthopedic implants like femoral stems.
• Quantifying strain rate and temperature effects on ductile damage during forging is essential but challenging.

Purpose of the Study:

• To develop a finite element framework for analyzing and optimizing the hot forging of Ti-6Al-4V femoral stems.
• To investigate the coupled influence of strain rate and temperature on ductile damage evolution.

Main Methods:

• Implemented a finite element model with strain rate- and temperature-dependent plasticity and the Johnson-Cook damage criterion.
• Utilized a full factorial design varying ram velocity (0.1-0.5 m/s) and billet temperature (850-950 °C).
• Validated the damage criterion to identify safe operating windows.

Main Results:

• Process kinetics, particularly ram velocity, significantly impact mechanical response and damage.
• Increased ram velocity enhances strain-rate hardening, leading to higher forging loads but reduced stress triaxiality and ductile damage.
• Temperature had a secondary influence within the studied range; low-velocity forging poses a high risk for defects.

Conclusions:

• Strain rate is a critical parameter for controlling ductile damage during Ti-6Al-4V femoral stem forging.
• Established practical guidelines for optimizing thermomechanical processing parameters based on strain rate.
• Identified low-velocity forging as a condition prone to localized defect formation, necessitating careful process control.