Experimental Investigation on Machinability of α/β Titanium Alloys with Different Microstructures

Area of Science:

• Materials Science
• Metallurgical Engineering

Background:

• Titanium alloys like Ti-6Al-4V (Ti64) and Ti-6Al-7Nb (Ti67) are crucial in aerospace and biomedical applications.
• Understanding their microstructure-property relationships is vital for optimizing performance and manufacturability.

Purpose of the Study:

• To investigate the effect of heat treatment on the microstructure and hardness of Ti64 and Ti67 alloys.
• To evaluate the machinability of these alloys, focusing on drilling performance, tool wear, and subsurface integrity.

Main Methods:

• Vacuum arc melting was used to prepare Ti64 and Ti67 alloy samples.
• Samples underwent various heat treatments, followed by microstructural analysis and hardness testing.
• Computerized drilling tests with TiAlN-coated tools assessed cutting forces, tool wear, and subsurface deformation.

Main Results:

• Water quenching from specific temperature ranges induced martensitic phase formation in both Ti64 and Ti67 alloys.
• Martensite formation increased alloy hardness, resulting in higher cutting forces and accelerated tool wear during drilling.
• Harder specimens exhibited thicker subsurface deformation layers (white layer) and increased burr heights; Ti64 showed higher surface roughness than Ti67.
• Drilling as-cast specimens led to partial tool coating attack, while martensitic formation exacerbated tool deterioration.

Conclusions:

• Heat treatment-induced martensite formation in Ti64 and Ti67 alloys significantly degrades machinability.
• Martensitic microstructure leads to increased cutting forces, tool wear, and compromised surface integrity.
• Ti67 generally offers better surface roughness compared to Ti64 under similar conditions.