C-Therm Blog

Characterizing the CTE (Coefficient of Thermal Expansion) of a Medical-Grade Titanium Alloy

Ti 6Al-4V ELI is a high-purity (“Extra Low Interstitial” or ELI) alloy of titanium with 6 wt% aluminum and 4 wt% vanadium. It is used primarily for applications where a combination of high strength, light weight, corrosion resistance, and high toughness are required. Owing to its excellent biocompatibility, good fatigue strength, and low Young’s modulus, it is particularly suited for applications as a biomedical implant. As it contains alloying elements which stabilize both the α crystal phase and the β crystal phase, it is an α + β alloy, which allows its thermal properties to be tailored by careful control of heating and machining processes. As with all titanium alloys, the thermal expansion behavior of Ti 6Al-4V ELI is a key performance metric of the material.

The C-Therm Dilatometer was employed to run the test. The sample was a piece of a proximal humeral rod medical implant, made with a Ti 6Al-4V ELI titanium alloy. The sample’s coefficient of thermal expansion (CTE) was measured from room temperature to 1200°C at a heating rate of 5°C/min. The data was collected on heating of the sample. The data are plotted below using CALISTO Thermal Analysis Software:

The titanium sample exhibits fairly consistent thermal expansion until the beta transus, the temperature at which the allotropic transformation from the hexagonal close-packed α phase to the body-centered cubic β phase occurs, at 847°C. Average coefficient of thermal expansion at various temperature ranges of interest, compared with reference values, are listed in the table below:

Temperature range

Average CTE (106/°C)

30°C – 100°C

7.808

30°C – 300°C

8.985

30°C – 315°C

9.030

30°C – 538°C

9.191

30°C – 650°C

8.930

30°C – 815°C

8.398

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