Titanium alloys are widely used in the engineering field, because of their high specific strength and exceptional corrosion resistance. However, the machinability of titanium alloys is difficult due to their low thermal conductivity and elastic modulus, high hardness at elevated temperature, and high chemical reactivity.
Titanium is an expensive and challenging material to machine. Although not as popular in machine shops as steel or aluminum, due to the high material and manufacturing cost, it’s an important material to master. The machinability ranges from 15% to 45%.

What Is a Titanium Alloy?

Titanium is a chemical element with the symbol Ti. Titanium alloy is usually made from: about 88% of Ti with alloying elements, mostly vanadium (V) and aluminum (Al).

Titanium alloys have good features such as:
  • High specific strength
  • Good high temperature mechanical properties
  • It has an excellent strength-to-weight ratio.
  • Excellent corrosion resistance
  • On the one hand, it is almost as light as aluminum, and on the other hand, it has a higher strength than most steel alloys. On top of that, it has superb corrosion resistance. This combination makes it popular in aerospace components and transportation, power generation and chemical industries.

    Titanium Machinability

    Titanium alloys still suffer from a poor machinability compared to other metals owing to several inherent mechanical and material properties. The main reasons of relative low machinability of titanium alloys are due to their:

  • Low thermal conductivity → (This causes heat generating from the cut to transfer mainly to the cutting tool, instead of flowing to the chips and the workpiece).
  • High chemical reactivity
  • Low elasticity modulus.
  • Titanium alloys are characterized by a high cutting temperature, a short tool life and a high level of tool vibration.

    Titanium has high flexibility, thus bending easily by the cutting forces.
    Some of the popular titanium alloys have high hardness. For example, the popular Ti-6Al-4V alloy is 32 HRC, and other alloys can reach 40 HRC.

    Pure Titanium alloys is the easiest to machine, they are made from 99.5%-99.8% of titanium with a small addition of Iron (Fe) and carbon (C) so they are not exactly pure. They are classified according to the titanium content as grade 1 through grade 4. (The most popular being grade 2).

    Machinability of Pure Titanium

    Material Hardness Machinability SAE DIN
    Ti-99.5(Grade 1) 100 HRB 46% Grade 1 B381F4 Ti-99.5
    Ti-99.6(Grade 2) 90 HRB 40% Grade 2 B381F3 Ti-99.6
    Ti-99.7(Grade 3) 80 HRB 35% Grade 3 B381F2 Ti-99.7
    Ti-99.8(grade 4) 70 HRB 28% Grade 4 B381F1 Ti-99.8

    The Excellent mechanical properties: the combination between alloys that contain alloying elements up to 15% weight content, on top of that, most of the alloys are heat-treated to a hardness of 30-40 HRC. Also makes them much tougher to machine compared with pure titanium.

    Machinability of Titanium Alloys

    Material Hardness Machinability SAE DIN
    Ti-10.2.3 35 HRC 18%
    Ti-13V-11Cr-3Al 40 HRC 15% 4917 TiV13Cr11Al3
    Ti-15-333 32 HRC 20%
    Ti-15Mo (Alpha + Beta) 38 HRC 16%
    Ti-15Mo (Beta) 24 HRC 28%
    Ti-3Al-2.5V 24 HRC 28% 4943, 4944
    Ti-3Al-8V-6Cr-4Mo-4Zr 32 HRC 20%
    Ti-425 36 HRC 17%
    Ti-425 MIL 36 HRC 17%
    Ti-48Al-2Cr-2Nb 22 HRC 31%
    Ti-4Al-4Mo-2Sn-0.5Si 35 HRC 18% TiAl4Mo4Sn2Si0.5
    Ti-5Al-2Sn-2Zr-4Cr-4Mo 38 HRC 16% 4995 Ti5Al2Sn2Zr4Cr4Mo
    Ti-5Al-5Mo-5V-1Cr-1Fe 40 HRC 15%
    Ti-5Al-5V-5Mo-3Cr 40 HRC 15%
    Ti-6-2-4-6 36 HRC 17% 4981
    Ti-6-7 32 HRC 20%
    Ti-6Al-4V (Grade 5) 32 HRC 20% 4906, 4920, 4928, TiAl6V4
    Ti-6Al-4V ELI 32 HRC 20% 4907, 4930, 4931
    Ti-6Al-4V MIL 37 HRC 17% 4906, 4920, 4928, TiAl6V4
    Ti-6Al-4Zr-2Mo-2Sn 28 HRC 24%
    Ti-6Al-4Zr-2Mo-2Sn 28 HRC 24% 4919 TiAl6Zr4Mo2Sn2
    0.2Si  4975, 4976
    Ti-6Al-6V-2Sn 35 HRC 18% 4971 TiAl16V6Sn2
    Ti-8Al-1Mo-1V 35 HRC 18% 4915, 4933, 4972 TiAl8Mo1V1