Selective laser melting (SLM) is an additive manufacturing or 3D printing technique that uses a laser to fuse metallic powder into a solid part layer by layer. The properties of the final part are determined by the characteristics of the metallic powder used. This article provides a comprehensive overview of SLM powders covering composition, properties, applications, specifications, pricing, pros and cons, and more.
Overview of Selective Laser Melting Powder
Selective laser melting powder, also known as SLM powder, is the raw material used in the SLM additive manufacturing process. SLM uses a high power laser to melt and fuse powdered metal alloys into fully dense 3D parts.
SLM powders are fine metallic powders usually ranging from 15 to 45 microns in size. The most common SLM powders are alloys based on aluminum, titanium, nickel, cobalt, and stainless steel. The composition and particle size distribution of the powder determines the characteristics of parts printed by selective laser melting.
Choosing the right SLM powder is critical to producing high quality parts with the desired mechanical properties, precision, surface finish, and microstructure. This guide provides detailed information on different types of SLM powders, their applications, specifications, pricing, pros and cons, and leading global suppliers.
Main Features of SLM Powders
- Ultrafine powder size ranging from 15 to 45 microns for precise laser melting
- Spherical morphology for powder flowability
- Chemically pure composition to minimize flaws
- Controlled particle size distribution prevents segregation
- Inert gas atomized production method
- Alloying additions to enhance properties
- May include proprietary coatings to improve flow and melting
Table 1: Types of Selective Laser Melting Powder
| Powder Type | Common Alloys | Characteristics |
|---|---|---|
| Aluminum | AlSi10Mg, AlSi12, AlSi7Mg0.6 | Low density, good thermal conductivity |
| Titanium | Ti6Al4V, Ti6Al4V ELI, TiAl | High strength, biocompatible |
| Nickel | Inconel 718, Inconel 625 | Heat and corrosion resistance |
| Cobalt Chrome | CoCr, CoCrMo | Biocompatible, high hardness |
| Tool Steel | H13, Maraging Steel | High hardness, wear resistance |
| Stainless Steel | 316L, 17-4PH, 420 | Corrosion resistance, high strength |
Composition of SLM Powders
SLM powders are spherical metallic powders made from various alloys using gas atomization. The composition determines the material properties of printed parts.
Table 2: Composition of Common SLM Powder Alloys
| Alloy | Typical Composition |
|---|---|
| AlSi10Mg | 90% Al, 10% Si, 0.5% Mg |
| Ti6Al4V | 90% Ti, 6% Al, 4% V |
| Inconel 718 | 50% Ni, 19% Cr, 18% Fe, 5% Nb |
| CoCrMo | 60% Co, 30% Cr, 7% Mo |
| 316L Stainless Steel | 70% Fe, 17% Cr, 12% Ni, 2% Mo |
The major alloying elements in SLM powders include:
- Aluminum – Lowers melting point, increases thermal conductivity
- Silicon – Improves fluidity and weldability
- Magnesium – Strengthening agent
- Titanium – Biocompatible, high strength
- Aluminum – Alpha and beta stabilizer in titanium alloys
- Vanadium – Beta stabilizer in titanium alloys
- Nickel – Corrosion resistance, ductility
- Chromium – Oxidation and corrosion resistance
- Iron – Contributes to strength in superalloys
- Niobium – Strengthening element in superalloys
- Molybdenum – Solid solution strengthening in superalloys
- Cobalt – Enhances high temperature strength
Trace impurities are minimized to reduce defects in SLM printed components.
Properties of SLM Powders
The properties of SLM powders directly influence the characteristics of 3D printed parts. Desired properties include good flowability, high purity, and optimized particle size distribution.
Table 3: Key Properties of SLM Powders
| Property | Typical Range | Significance |
|---|---|---|
| Particle size | 15 – 45 microns | Precision of detail, resolution |
| Particle shape | Spherical | Improves flowability |
| Flowability | Excellent | Prevents powder agglomeration |
| Apparent density | Above 50% theoretical density | Improves laser absorption, densification |
| Tap density | Up to 65% theoretical density | Indication of flowability, packing density |
| Residual oxygen | <0.1 wt% | Prevents oxidation defects |
| Residual nitrogen | <0.04 wt% | Prevents nitride inclusions |
| Residual carbon | <0.03 wt% | Prevents carbide precipitates |
In addition, SLM powders feature optimized particle size distribution with a tight range to prevent segregation issues. Most powders for SLM have D10 and D90 values within 10 to 20 microns.
SLM powder characteristics like powder bed density, flowability, spreading, and recyclability determine the quality of printed parts. Powders are engineered to balance these factors.
Applications of SLM Powders
SLM powders are used to print functional metal parts across a variety of industries:
Table 4: Applications of Selective Laser Melting Powders
| Industry | Common Applications | Typical Materials Used |
|---|---|---|
| Aerospace | Turbine blades, rocket nozzles | Inconel, titanium |
| Automotive | Lightweighting parts, custom geometries | Aluminum, tool steel |
| Medical | Dental copings, implants, surgical tools | Titanium, cobalt chrome |
| General Engineering | Rapid prototypes, tooling, end use parts | Stainless steel, tool steel |
The main advantages of SLM for part production include:
- Ability to create complex geometries not possible with casting or machining
- Customized parts on demand with no hard tooling
- Reduced weight by optimizing designs for function
- Consolidation of assemblies into single parts
- Rapid turnaround time from design to part
SLM is suitable for low to medium volume production of end use metal components across industries.
Specifications of SLM Powders
SLM powders must meet strict specifications in terms of composition, particle size distribution, morphology, flow characteristics, apparent density, contamination levels, and microstructure.
Table 5: Typical Specifications for Selective Laser Melting Powders
| Parameter | Typical Specification | Test Method |
|---|---|---|
| Powder composition | Within alloy specification limits | ICP-OES chemical analysis |
| Particle size | D10: 10-25 μm <br> D50: 20-35 μm <br> D90: 30-45 μm | Laser diffraction |
| Particle shape | >80% spherical, minimal satellites | SEM imaging |
| Apparent density | >50% of alloy theoretical density | Hall flowmeter |
| Tap density | Up to 65% theoretical density | Tap density tester |
| Flowability | Angle of repose <30° | Hall flowmeter |
| Residual oxygen | <0.1 wt% | Inert gas fusion analysis |
| Residual nitrogen | <0.04 wt% | Inert gas fusion analysis |
| Residual carbon | <0.03 wt% | Combustion infrared detection |
Leading SLM powder suppliers have in-house powder characterization facilities to ensure these parameters are met for each powder batch before delivery to customers.
Pricing of Selective Laser Melting Powders
The cost of SLM powders depends on the alloy composition, quality, supplier, purchase quantity, and geographical region. Some typical powder pricing is shown below:
Table 6: Indicative Pricing Ranges for Popular SLM Powder Alloys
| Alloy | Price per kg |
|---|---|
| AlSi10Mg aluminum alloy | $50 – $120 |
| Ti6Al4V titanium alloy | $350 – $600 |
| Inconel 718 | $150 – $250 |
| Stainless steel 316L | $50 – $100 |
| Cobalt chrome | $110 – $250 |
Prices are highest for reactive alloys like titanium and lowest for commodity alloys like aluminum and stainless steel. Aerospace grades cost more than conventional alloys. Bulk purchase discounts are available from SLM powder suppliers.
Overall, material cost constitutes 15-30% of total part cost for metals AM. The powder itself accounts for a major share of this materials cost. Optimizing reuse of unfused powder helps lower average part cost.
Leading Suppliers of SLM Powders
Many companies offer gas-atomized metallic powders specifically engineered for SLM additive manufacturing. Some leading global suppliers include:
Table 7: Major Suppliers of Selective Laser Melting Powders
| Company | Headquarters | Key Alloys |
|---|---|---|
| AP&C | Canada | Ti, Al, Co alloys |
| Carpenter Additive | USA | Ti, Al, Co, Cu alloys |
| EOS | Germany | Ti, Al, Ni alloys |
| Sandvik Osprey | UK | Ti, Al, Ni, stainless, tool steel |
| SLM Solutions | Germany | Ti, Al, Ni, Co alloys |
| Linde | Germany | Ti, Al, stainless, tool steel |
| Praxair | USA | Ti, Co, Ni alloys |
| LPW Technology | UK | Ti, Al, CoCr, Inconel |
These companies have invested in atomization technology and advanced characterization to ensure SLM powders meet strict requirements for 3D printing high quality parts. They offer a wide range material options tailored for SLM.
Pros and Cons of SLM Powders
Table 8: Advantages and Limitations of Selective Laser Melting Powders
| Pros | Cons |
|---|---|
| Very fine size for high resolution | Limited alloy options compared to casting/machining |
| Good flow characteristics | Reactive alloys like Ti prone to contamination |
| Spherical morphology with few satellites | Moisture sensitivity requires careful handling |
| Chemically pure to minimize defects | Metallic powders pose health hazards |
| Controlled particle size distribution | Higher cost than standard powders |
| Custom alloys designed for SLM | Limited suppliers and availability of some alloys |
| Inert gas atomization avoids oxidation | Unused powder must be reused instead of disposed |
Pros
- The fine 15-45 micron size of SLM powders allows very high resolution and small features to be printed.
- Spherical particle shape and good flowability prevents powder aggregation and feed issues during printing.
- High chemical purity minimizes defects like inclusions and voids in printed parts.
- The particle size distribution is optimized to prevent segregation and ensure homogeneous melting.
- Specialist suppliers engineer custom alloys with compositions tailored for SLM applications.
- Inert gas atomization avoids powder oxidation.
Cons
- There are fewer established alloys for SLM compared to traditional manufacturing methods.
- Reactive alloys like titanium require special handling to prevent contamination which increases cost.
- As fine powders, SLM materials are sensitive to moisture absorption during storage and handling.
- Metal powders pose risks like dust explosions and health hazards which require safety precautions.
- SLM alloys cost substantially more than standard powder grades due to the specialized production process.
- Some alloys have very few suppliers limiting availability and material quality.
- Unfused powder cannot simply be discarded and must be reused due to sustainability and cost factors.
How to Choose SLM Powder
Selecting the optimum SLM powder for an application requires considering factors like:
- Part function – Mechanical requirements, stresses, operating conditions
- Alloy properties – Strength, hardness, ductility, heat resistance
- Post processing needs – Heat treatment response, machinability
- Process factors – Powder bed density, laser absorption, flowability
- Cost considerations – Material price, equipment implications
Part function primarily guides alloy selection. Critical highly stressed parts demand powders that can achieve maximum density and mechanical properties. Less critical prototyping applications allow more flexibility.
Process factors like print speed, achievable accuracy, and surface finish also depend on the powder. Benchmarking candidate materials on actual printers identifies the best match.
Cost plays a key role. Higher performance alloys for aerospace applications are far more expensive than conventional grades. Unique alloys may only be available from a single supplier.
Thoroughly evaluating application requirements against material capabilities and costs leads to the optimum SLM powder choice.
How to Store and Handle SLM Powder
Careful handling and storage of SLM powders is essential to preventing material degradation and ensuring high quality printed parts:
- Store unopened containers in a cool, dry location away from sunlight and moisture. Avoid excess heat.
- Open powder containers only in an inert glovebox with oxygen levels below 10 ppm to prevent oxidation.
- Transfer powders in a glovebox using proper grounding to avoid static buildup. Wear nitrile gloves.
- Seal containers tightly during storage. Use only original containers, not plastic bags.
- For large volumes, store powder in machines with integrated inert gas systems.
- Before reuse, sieve powder through recommended mesh sizes to break up agglomerates and remove contaminants.
- Use powder drying ovens and vacuum thermal degassers to lower moisture levels if needed.
- When discarding used powder, wet it with water to prevent airborne dust hazards and dispose as hazardous waste.
- Follow all safety precautions for handling fine metallic powders including PPE and explosion prevention.
Proper powder management maintains consistency between print runs and allows reuse of up to 80-90% of unfused powder. This maximizes yield while minimizing raw material costs.
Selective Laser Melting Powder FAQ
Q: What is the typical particle size range for SLM powders?
A: Most SLM powders fall between 15-45 microns in size, with the majority of particles in the 20-35 micron range. Finer powders improve resolution while larger sizes hurt detail and accuracy.
Q: How are SLM powders produced?
A: SLM powders are made by inert gas atomization where the molten alloy stream is broken into droplets which solidify into spherical particles. This avoids oxidation of the powder.
Q: What is meant by “apparent density” and “tap density” of powder?
A: Apparent density is the bulk density measured under normal conditions. Tap density is the increased density achieved after mechanically tapping a powder sample to compact it. Higher densities improve powder bed characteristics.
Q: Why are flow characteristics important for SLM powders?
A: Good powder flow and spreadability ensures uniform layers for consistent melting and prevents aggregation issues. Spherical particles enhance flow compared to irregular shapes.
Q: How are SLM powders reused after printing?
A: Unfused powder is sieved to break up agglomerates, vacuum dried to lower moisture, and blended with fresh powder before reuse. This allows recycling rates over 80%.
Q: What safety precautions are required when handling SLM powders?
A: Metallic powders pose explosion, fire, and health hazards. Use appropriate PPE, adequate ventilation, proper grounding, and inert gas gloveboxes. Never pour powder in open air.