3D Printing Titanium Ti6Al4V Grade 5 (Ti64-G5)

Ti64-G5 is an alpha-beta titanium alloy that accounts for over half of the titanium used worldwide. It is commonly referred to as Grade 5 Titanium or Ti6Al4V Grade 5. Thanks to its excellent mechanical, thermal, and corrosion properties, Grade 5 Titanium has become a common material in demanding application areas, such as the medical, aerospace, automotive, power generation, and marine industries.

Just like in these markets, Ti6Al4V is a sought-after material in metal 3D printing due to its excellent mechanical strength, corrosion resistance, biocompatibility, and low density. One of the most common uses of 3D-printed Ti6Al4V is spare parts, which helps minimize the need for large warehousing of spare parts. Other uses include functional prototypes, medical devices, and end-use products.

In this article, we will explore the world of Grade 5 Titanium, discuss its properties, and find out how it is used in additive manufacturing.

What is Ti6Al4V Grade 5?

Ti6Al4V is an alloy made of about 6% Aluminum, 4% Vanadium, and a balance of Titanium. It also contains traces of iron and oxygen. Ti6Al4V Grade 5 is one of the three commercialized grades of Ti6Al4V alongside TC4 (according to Chinese standard GB/T 3620.1-2017) and Ti6Al4V Grade 23 (according to American standard ASTM B348-13).

Ti6Al4V is a heat-treatable alloy, which is where the alpha and beta phases become points of interest. A phase is an area within a material that exhibits homogenous physical and chemical properties.

• The alpha phase represents the presence of alpha-stabilizing elements (such as Al and O), which render the alloy relatively low in its mechanical properties but high in corrosion resistance.
• The beta phase contains beta stabilizers (such as Fe, V, and Mo), which help strengthen the alloy and improve its mechanical properties. These stabilizers lower the beta transition temperature to enable the beta phase at room temperature.

Ti6Al4V contains both alpha and beta phases. This allows it to be processed and have a comprehensive range of properties. The processing takes the form of heat treatment, in which properties like strength, weldability, ductility, fatigue strength, fracture toughness, and corrosion resistance are optimized. These properties, in turn, enable the alloy’s use in a wider range of applications. In fact, about 56% of the total titanium market is held by Ti6Al4V.

The table below displays the different properties of Ti6Al4V Grade 5.

How is Ti6Al4V G5 used in 3D printing?

Titanium alloys like Ti64-G5 are commonly low in elastic modulus and thermal conductivity, which makes them difficult to machine. In fact, titanium alloys have approximately a 50% lower elastic modulus and an 80% lower thermal conductivity than those of steel.

Those properties, alongside their high chemical reactivity, dynamic shear strength, and high hot hardness, make titanium alloys difficult to work with using traditional manufacturing methods. Challenges such as springback, high heat stress, chip thickness variation, high pressure loads, and residual stress are issues traditional manufacturing has to deal with when machining titanium alloys. As a result, wear in manufacturing tools increases, and the machined surface integrity of the part worsens, not to mention the chemical reactivity that can take place between various cutting tool materials and titanium alloys.

That is why additive manufacturing (AM) of titanium alloys has emerged as a robust and reliable solution to circumvent such challenges and minimize the subtractive steps of traditional manufacturing to create parts with near-net-shapes. Furthermore, AM allows for designing complex geometries and reducing material waste.

It all starts with having Ti6Al4V alloy in powder form. This can be achieved using gas atomization or plasma atomization. Both procedures result in spherical particles of Ti6Al4V that are ready to be 3D printed. But it is important to know which procedure is used as it defines the particle size and characteristics of the powder, which eventually determines the printed part’s properties.

3D printing methods for manufacturing Ti6Al4V Grade 5

Ti6Al4V Grade 5 can be 3D printed using DMLS, SLM, LMD, or EBM techniques. DMLS and SLM are two methods referred to as powder bed fusion (PBF) methods.

A PBF method typically applies a high-energy laser onto a metal powder bed to selectively fuse the particles and create a predesigned 3D shape. PBF is commonly used in manufacturing titanium-based parts. Its inert chamber environment enables fabrication without the risk of oxidation, a common issue in titanium manufacturing due to its titanium’s affinity to oxygen.

Nonetheless, one limitation of PBF is the relatively small part dimensions compared to other laser-based AM methods. Still, it is quite suitable for manufacturing small pieces, such as spare parts or medical devices. Furthermore, the particle size has to be specifically small and uniform (< 40 µm), increasing the manufacturing costs. And since the laser selectively hits specific areas of the powder bed, the remaining portion of the powder goes unused to be recycled and reused in future manufacturing trials.

LMD, on the other hand, is usually used when working on parts of larger sizes, especially for cases of repairing, surface coating, or adding new part features. LMD also makes use of a laser source but not in a similar way to PBF. Here, the laser source hits the surface of a base material to create a melt pool on that metal surface. Then, titanium alloy powder is deposited into the melt pool using a gas stream – thus the name laser metal deposition.

This method minimizes the amount of powder used and allows for larger particle sizes (40 – 150 µm). However, the environment here is not inert, subjecting the material to potential oxidation. That is why inert gas is introduced to the processing area using a nozzle. That being said, other challenges can arise here, including heat evacuation, surface temperature control, and geometric obstructions. Since the supply of inert gas moves as the processing area moves, considerations should be taken to avoid those challenges.

EBM is quite similar to SLM (a PBF method) in its working principle. The main difference, though, is the high-energy source used to fuse the metal powder. Instead of a laser, EBM uses a high-energy electron beam. This beam is supported by two magnetic fields that narrow down the beam’s diameter and navigate it towards the desired target points on the powder bed. The electron bombardment converts the kinetic energy into thermal energy, raising the powder’s temperature beyond its melting point, where selective fusion begins to take place. A distinct characteristic of EBM is its high manufacturing speed; however, it usually has lower accuracy and finish quality than SLM.

What is Ti6Al4V used for?

Ti6Al4V has been found very useful in multiple industries and application areas, most prominently the aerospace, medical, and automotive sectors. Its high strength-to-weight ratio, outstanding corrosion resistance, high-temperature resistance, and biocompatibility enable its diverse applications.

3D-printed Ti6Al4V is in no way less than traditionally manufactured titanium alloys. A 2019 study comparing 3D-printed Ti6Al4V with metallurgically produced Ti6Al4V found that titanium parts made via SLM showed higher strength and yield points than those made conventionally. So, 3D printing Ti6Al4V can even expand the material’s range of applications, especially with the additional benefits of local manufacturing, minimized supply chain steps, and reduced warehousing that AM can help achieve.

Some of the most common Ti6Al4V Grade 5 uses include:

• Compressor blades and discs
• Airframe components
• Jet engine rings
• Components for space capsules
• Spare parts
• Medical implants
• Surgical instruments