18ni300 Alloy Powder Stainless Steel Nickel

Author：Enrique J. Lavernia

Enrique J. Lavernia is a renowned materials scientist and Professor at Texas A&M University, recognized for his pioneering contributions to additive manufacturing. His research focuses on metallic powders, including their atomization, characteristics, and impact on part quality, as well as the microstructural evolution and mechanical performance of advanced alloys during additive processes.

He has advanced the understanding and application of complex materials such as aluminum alloys and high-entropy alloys in AM, and co-authored authoritative works on metallic powders for additive manufacturing, significantly influencing both scientific research and industrial practice.

Depth Analysis Of 18ni300 Alloy Powder

Basic composition and classification of materials:

The name “18Ni300” is actually very intuitive. It tells us two key messages: 18% nickel content and the 300 ksi (about 2070 MPa) tensile strength it can finally achieve.

An important point must be emphasized here: the 18Ni300 it is not stainless steel, it is the 1 maraging steel (Maraging Steel). In terms of strict material classification, it belongs to the category of high-strength nickel-based alloys. Stainless steel mainly depends on chromium to form a passive film to resist corrosion, while maraging steel is completely another 1.

What makes it such a good performance? Mainly these alloying elements:

• Nickel (Ni), about 18%, is a core element that forms a martensitic matrix and provides excellent toughness.
• Cobalt (Co) is usually between 8-12%. Its main function is to increase the martensite transformation temperature and promote the precipitation of intermetallic compounds during the aging process.
• Molybdenum (Mo), usually between 3-5%, contributes to solid solution strengthening and promotes age hardening together with nickel and cobalt.
• Titanium (Ti) and aluminum (Al) are usually present in lower amounts, but are essential. They form fine intermetallic compounds (such as Ni3Ti, Ni3Al) during aging treatment, and it is these nanoscale precipitates that give 18Ni300 ultra-high strength.

Unique Performance Benefits: Why Is It So Important?

In my opinion, the reason why 18Ni300 can be favored in the field of additive manufacturing is mainly due to its combination of properties.

• Ultra-high strength combined with toughness: this is its most dazzling label. Consider that after additive manufacturing (such as SLM or EBM) is completed, the tensile strength of the material can soar to nearly 2000 MPa through a simple heat treatment- aging treatment -usually held at 480-500°C for several hours-while maintaining excellent fracture toughness. This perfect combination of strength and toughness is extremely rare in traditional materials. For us doing 3D printing, this means being able to design parts that are both lightweight and extremely strong.
• Excellent dimensional stability: The deformation of 18Ni300 is very small during heat treatment, especially aging treatment. This is simply a boon for the manufacture of precision parts. We all know that many materials will undergo considerable shrinkage or expansion after heat treatment, resulting in difficult to control dimensional accuracy, but 18Ni300 is very stable in this regard.
• Good workability: Although we mainly focus on the performance after 3D printing, it is also necessary to mention the 1 sentence. In the annealed state (that is, when not aged), its hardness is relatively low, very easy to mechanical processing, such as turning, milling. This is undoubtedly a plus for some complex parts that require post-processing.
• Corrosion resistance: I have to say realistically that the corrosion resistance of 18Ni300 is not its main advantage, after all, it is not stainless steel. In some specific environments, it will perform well, but if your application has high requirements for corrosion resistance, you may need to combine surface treatment or consider other more professional corrosion resistant alloys. Don’t expect it to be “leather” like 316L stainless steel “.

Material Properties Issues and Opportunities:

• Question:
  • Crack sensitivity: This is the 1 big problem we encounter when doing 3D printing. 18Ni300 is sensitive to thermal stress in the printing process, especially for thick cross-sections or complex geometric structures, where internal stress accumulation can easily lead to cracks. This requires our engineers to make a lot of exploration and adjustment in printing parameter optimization and preheating strategy.
  • Internal stress control: Due to rapid melting and solidification, residual stress will be generated inside the printed part, which not only affects the mechanical properties of the part, but may also cause deformation or even cracking. Therefore, the heat treatment after printing is very important.
  • Print parameter optimization: Finding the best combination of print parameters is a long and costly process. Each device, each batch of powder, and even the ambient temperature can affect the final result, which requires us to invest a lot of energy to carry out experimental verification.
• Opportunity:
  • Complex geometry and lightweight design: this is the biggest advantage of additive manufacturing. The ultra-high strength of the 18Ni300 means that we can design thinner and lighter structures that are still strong enough, such as grid structures and bionic structures in the aerospace field. This is beyond the reach of traditional manufacturing processes.
  • High-performance customized parts: For some special parts that require extremely high performance and do not require too much output, such as mold inserts, high-performance mechanical parts, and even some key components of rocket engines, 18Ni300 can be quickly and efficiently manufactured through 3D printing, and its performance far exceeds that of traditional processes.

Application Scenarios And Cases Of 18ni300 In Additive Manufacturing

Aerospace field:

This is definitely the home of the 18Ni300. Satellite components, jet engine turbine blades, various complex brackets and structural parts, all of which have strict requirements on the strength, toughness and lightweight of materials. Additive manufacturing, combined with 18Ni300, enables lightweight designs and high strength/weight ratios that are unimaginable with conventional processes.

More importantly, it can also print parts with complex internal cooling channels, which is simply revolutionary in engine parts. The manufacturing cycle can also be greatly shortened, which is undoubtedly a great boon for the aerospace industry with fast iteration speed.

For example, I once came into contact with a project, which is to manufacture a certain type of spacecraft bracket through 3D printing 18Ni300. The final result is encouraging, not only about 30% less weight than the traditional manufacturing stent, but also better performance in key performance indicators. At that moment, I really felt the huge value of this technology.

Mold manufacturing and tools in the field:

The mold industry’s demand for high hardness, wear resistance and cooling efficiency makes 18Ni300 useful in additive manufacturing. Injection mold inserts, die-casting molds, and even some tooling fixtures can benefit from this material and process. The most prominent advantage is the ability to design and print out conformal cooling channels. This is no joke, which means that you can make the coolant as close to the mold cavity as possible, thereby greatly improving the cooling efficiency and shortening the injection molding cycle. At the same time, high hardness and wear resistance also ensure the service life of the mold.

I remember that there was an injection mold manufacturer who tried to use 3D printing 18Ni300 mold inserts, and the cooling time was reduced by 15%. This 15% is a real efficiency improvement and cost savings for their mass production. This intuitive improvement gives me confidence in the future of additive manufacturing.

Medical device field:

Although titanium alloys are more common in orthopedic implants, the high strength characteristics of 18Ni300 make it have great potential in certain specific medical device fields, especially in parts with high load-bearing requirements.

Personalized customization is the strength of 3 D printing, which is especially important in the medical field, and can be accurately printed according to the patient’s anatomy. Of course, biocompatibility requires further surface treatment to optimize, but its potential as a high-strength substrate is beyond doubt.

Other high-performance applications:

In addition to the above fields, 18Ni300 also has broad application prospects in the automotive industry, military field, high-end sports equipment, etc. These areas all pursue extreme performance and lightweight, and the combination of 18Ni300 and additive manufacturing just happens to meet these needs.

Process Flow And Key Considerations For Additive Manufacturing 18ni300

3D printing process selection:

When we talk about 3 D printing for 18Ni300, the first thing to do is to pick the right printing process. At the moment, laser powder bed melting (L-PBF/SLM) and electron beam melting (EBM) are the two processes we use most.

L-PBF (SLM): It is currently the most widely used technology. It melts metal powder layer by layer through a laser beam of high energy density. L-PBF performs very well in terms of density.

The printed parts have high precision and relatively good surface quality. But the problem is that when L-PBF prints an 18Ni300, residual stress is a big nuisance because it cools quickly and can easily cause parts to deform or even crack. We usually take some warm-up measures or adjust the scanning strategy to mitigate them, but their complete elimination is almost impossible.

EBM: In contrast, EBM uses an electron beam as a heat source, operates in a vacuum environment, and has a higher preheating temperature. This makes the residual stress problem much better when EBM handles 18Ni300, and the risk of deformation is greatly reduced. In addition, the forming efficiency of EBM is usually a bit higher. However, EBMs tend to have worse surface roughness than L-PBFs, and the equipment costs and operational complexity are relatively high.

Powder Characteristics and Management:

For 18Ni300, a high-performance alloy, the quality of the powder is key to making or breaking a print.

The importance of powder quality: our focus is on particle size distribution —— too coarse and too fine will not work, uniform particle size can ensure the flatness of the powder; sphericity, this directly affects the fluidity of the powder, the better the sphericity, the better the fluidity of the powder, the more uniform the powder layer, and the density is easier to ensure; and oxygen content, This is a very critical indicator, and too high an oxygen content can lead to oxide inclusions inside the print, seriously affecting the mechanical properties of the material, especially fatigue properties.

Powder handling and storage: The powder should be managed very carefully. 18Ni300 This alloy is sensitive to oxidation, so preventing oxidation and contamination is a top priority. Usually, we carry out the sieving and recovery of the powder under inert gas protection, and it must also be a sealed, dry container when storing. Once the powder gets damp or contaminated, it can affect the quality of the print at least, and at worst cause the batch to be scrapped, which is not worth the gain.

Printing parameter optimization:

 Key parameters:

• Laser power: too small for insufficient melting, too large for overburning.
• Scanning speed: affects energy density and molten pool behavior.
• Layer thickness: directly affects printing efficiency and surface roughness.
• Scanning strategies: like “checkerboard” scanning, which helps disperse residual stress.
• Preheating temperature: In L-PBF, proper raising of the platform preheating temperature can be very helpful in reducing residual stress.

What I found is that none of these parameters exists on their own, and they influence each other to form a complex network. We need to fumble through a lot of experiments to find that optimal equilibrium point to achieve the highest density, the best mechanical properties and the lowest residual stress.

Post-processing:

• Heat treatment: Aging Heat Treatment is central to achieving its ultra-high intensity. The printed 18Ni300 is usually in a solid solution and not very strong. We need to induce the precipitation of nanoscale intermetallic compounds inside the material through precise aging temperature and time control, thereby significantly increasing its hardness and strength. I usually do a solution treatment to eliminate tissue inhomogeneities during printing, followed by multi-stage aging. The principle in this is to allow the microstructure inside the material to undergo a phase change through heat treatment, so that its hardness and strength can be greatly improved.
• Finish: The surface of the print tends to be rough, and there may be some minor defects inside.
• Polishing and sandblasting: can effectively improve the surface roughness and is very important for parts that require fine fit.
• Thermal isostatic pressure (HIP): This is a very powerful tool, especially for additive manufactured parts. It can effectively eliminate internal pores and micro-cracks under high temperature and pressure, greatly improving the density and fatigue performance of parts.