Guide to Metal 3D Printing: Choosing the Right Material

Additive manufacturing, also known as 3D metal printing, is a technology that builds complex metal parts by layering either metal powders or metal wires. There is a significant advantage over conventional subtractive manufacturing techniques, like turning and milling, since one may go directly from a CAD model to a part without molds and extra tooling. This capability is of particular value when there is a need to manufacture complicated, special-shaped, and small-lot parts.

Metal 3D Printing Processes

Direct metal 3D printing processes can be divided into two main categories, but there are also some indirect or alternative methods.

● Powder Bed Fusion (PBF): This technology uses a laser or electron beam to melt metal powder. Common PBF techniques include Selective Laser Melting (SLM) and Electron Beam Melting (EBM). This process is ideal for producing complex metal parts with high precision and detail.

● Directed Energy Deposition (DED): DED uses a laser or electron beam to melt metal powder or wire on the workpiece while depositing material layer by layer to form the final 3D shape. Generally, DED is suitable for repairing and additively manufacturing large parts.

● Binder Jetting: Binder jetting uses inkjet technology to spray a binder onto a metal powder bed, binding layers to form parts. The green parts then need to be sintered or melted to achieve final strength. This process is fast and suitable for producing large quantities of parts.

● Material Jetting: This technique is similar to an inkjet printer, where liquid metal is jetted onto a substrate to build up the 3D object layer by layer. Material jetting is highly precise and suitable for manufacturing small, high-precision parts.

● Metal Extrusion: Similar to Fused Deposition Modeling (FDM), this technology uses metal wire that is extruded through a heated nozzle to build parts. It is suitable for low-cost production and prototyping.

Fig 1. Selective Laser Melting (SLM)

Advantages of Metal Powders for 3D Printing

3D printing material is available in several forms, including plastic, metal, ceramic, and resin. Of all these, the advantages of metal powder cannot be beaten for "critical component" applications.

1. Excellent Mechanical Properties

The mechanical properties of metal powders are excellent; it has high strength, high hardness, and is highly tough. In sharp contrast, plastic and resin materials normally have a low strength value and have possibilities to get deformed easily; hence, those materials cannot be used in high-stress conditions. Ceramic materials, though hard, are rather brittle and fracture easily.

2. High Resistance to Heat and Corrosion

Most of the metal powders have great resistance to high temperature and corrosion. Plastic and resin usually have a melting or decomposition problem in high temperatures, so they are not suitable for use in high-temperature conditions. Although ceramics are resistant to high temperatures, they can easily result in thermal shock fracture during a rapid temperature change.

3. Good Electrical and Thermal Conductivity

Metal materials ensure good electrical and thermal conductivity, making metal 3D printing well-advantaged in fabricating electronic components, heat sinks, and conductive structures. Generally speaking, plastics, resins, and most ceramics are insulators and do not possess these functions.

4. Superior Wear and Fatigue Resistance

In particular, functional parts with high demands on wear resistance and good fatigue performance should first be made from metal materials, such as gears, bearings, and friction pairs. While in general, plastics and resins are very poorly resistant to wear, being easily worn; the wear-resistant ceramics, being a kind of brittle material, will fracture under cyclic load.

5. Fabrication of Functional Parts

The most significant advantage of 3D printing in metal is creating parts with internal channels and features that could not be manufactured by any other process.

6. Low Recycling Costs

This is because the unused metal powder in the process can be recycled, hence minimizing wastage and cost. In contrast, plastic and resin materials generate much waste, which is difficult to recycle, and so is the case with ceramics.

Top 7 Metal Powders for 3D Printing

The choice of metal powder is critical to achieving the properties and performance required for a specific application.

1. Titanium-Based Powder

Titanium has exceptional characteristics: lightweight, strong, and high corrosion resistance; hence, its large adoption in additive manufacturing.

The general 3D printing titanium powders are titanium alloy Ti6Al4V (Grade 5 or Ti64), and Ti6Al4V ELI (Grade 23 or Ti64ELI). Grade 5 titanium powder is the most in use because of its versatile nature. It is weldable, heat treatable, withstands temperatures over 300°C, and has very high specific strength and corrosion resistance. Due to such a combination of properties, Grade 5 powder titanium finds wide applications in industries with high performance: aerospace, medical, marine, and chemical.

In turn, Grade 23 titanium powder (Ti6Al4V ELI) provides higher purity and biological suitability. This material maintains specific strength, corrosion resistance, and toughness for biomedical applications in surgical instruments and implants.

Fig 2. Titanium-Based Powder for 3D printing

2. Aluminum Alloy Powder

The properties that make aluminum alloy powder very attractive include excellent chemical resistance, very lightweight, and one of the best strength-to-weight ratios among metals. Currently, the two most commonly used aluminum alloy powders for 3D printing are AlSi12 and AlSi10Mg.

AlSi12 and AlSi10Mg are alloys for casting and are weldable, while their mechanical properties are not very strong or resistant to high temperatures. However, they are good enough in a wide range of applications and guarantee no crack appearance during 3D printing.

The AlSi7Mg0 alloyed powders represent the right combination of aluminum, silicon, and a small amount of magnesium to ensure the production of parts that are strong but lightweight.

3. Stainless Steel Powder

Resistant and powerful, it is a metal that can be subjected to corrosion. Due to the versatility of this material, when it comes to additive manufacturing, it happens to be one of the common materials. The usual stainless steel powders in 3D printing include types 304L and 316L.

304L stainless steel powder has very good corrosion resistance, is tough enough, and also demonstrates excellent weldability; hence, these powders have a wide scope of use in the manufacturing of industrial equipment and consumer product components. In addition, it exhibits good performance at low to high temperatures making it suitable for general manufacturing, food processing equipment, and construction.

316L stainless steel powder has higher corrosion resistance, especially in chloride environments. Low carbon content ensures good mechanical properties at high temperatures. In this respect, 316L SS powder is suitable for usage in applications with higher environmental requirements, such as medical devices, chemical equipment, marine engineering, and aerospace parts.

Fig 3. 3D printed bicycle steel frame

4. Cobalt Alloy Powder

The complex shape and high precision of the parts can be realized by additive techniques such as SLM and EBM. Among all the 3D printing cobalt alloy powders, the most usually applied is the cobalt-chromium alloy powders such as CoCrMo and CoCrW.

CoCrMo alloy powder has a broad range of applications in the medical field, especially because they exhibit excellent mechanical properties and biocompatibility. The corrosion and wear resistance of the alloy makes it suitable for implants of hips and knees, as well as restoration materials, inside the human body.

CoCrW alloy powder represents an excellent combination of wear resistance and high-temperature properties. Thus, their application includes aerospace and industrial equipment, among others. These materials retain strength and hardness at extremely high temperatures; hence, the material finds application in gas turbine engines, combustion chambers, and other such high-temperature applications.

Fig 4. Spherical Cobalt-Based Powder (CoCrW)

5. Nickel-Based Powder

These alloy powders are relatively dense but are suited for internal engine applications because of their excellent heat resistance. Among the most common 3D printing nickel-based alloy powders are Inconel 718, Inconel 625, and HX, all made up of two main elements: nickel and chromium. These materials can resist high temperatures, oxidation, and corrosion, keeping strength up to 1,200°C.

In high-temperature environments, even though the corrosion resistance and stability of Inconel 625 is superior to 718, its strength and conductivity are twice as high. Of these three materials, Hastelloy has the best weldability.

6. Copper-Based Powder

The most common 3D printing copper-based powders are pure copper powder and copper alloy powders, such as CuCrZr. Pure copper powder boasts extremely high electrical and thermal conductivity, suitable for manufacturing electrical components and heat sinks that require high thermal and electrical conductivity.

CuCrZr alloy powder is a type of copper-chromium-zirconium alloy that maintains high electrical and thermal conductivity while offering better mechanical strength and wear resistance.

7. Refractory Metal Powder

Refractory metals are a group of metals that are predominantly resistant to heat, such as niobium, molybdenum, tantalum, tungsten, and rhenium. Properties include high melting points above 2000°C, resistance to corrosion, high density, and hardness.

Tantalum powder is highly resistant to corrosion and has great conductivity; for this reason, it finds great application in the electronics industry. Pure tungsten boasts the highest melting temperature among all elements, up to 3422°C. This metal is quite dense and far from easy to work with, but due to its stability, it finds its application in the production of wear-resistant items such as knives, drills, grinders, and saws. Tungsten powder also has good resistance to oxidation and resistance to acids and bases; therefore, it finds its application in radiation shielding.

Conclusion

3D printing with metal powders has several unique advantages. Whether it's titanium, aluminum, stainless steel, cobalt, nickel, copper, or refractory metals, the choice of metal powder is critical in achieving the desired properties and performances for a particular application. As technology continues to evolve, so will the available materials and their uses, further expanding capabilities and the effect of metal additive manufacturing into more and more industries.

Stanford Advanced Materials (SAM) is committed to driving research and innovation in the field of spherical powder technology. We offer a variety of 3D printing metal powders, including refractory metal powders, titanium, aluminum, stainless steel, cobalt chromium, nickel, copper, etc. If you are interested, please Get A Quote.