The Importance of Powder

Importance of feedstock

Powder is the foundational feedstock to revolutionary advanced manufacturing  technologies such as additive and cold spray.

Traditional atomized powder is inconsistent, and negatively impacts the manufacturing process resulting in parts with defects and inconsistent mechanical properties.  Furthermore, flawed powder limits the number and types of applications that can be adopted.

Equispheres’ premium powder enables the manufacture/repair of superior quality parts and reduces the costs associated with part rejection.  Importantly, the unique features of the powder expands the number of additive manufacturing and cold spray applications that can be achieved.

The Solution
Additive Manufacturing

A few important attributes of powder feedstock have a direct impact on the additive manufacturing process and final product quality.

Table AM
Comparison for Mono-size – Equispheres vs. Competitor

Equispheres

Traditional Atomized Powder

Spherical, Agglomerate and FineFree with Superior Flowability

Round and smooth particles move more freely than irregular shaped particles with bumps, lumps, bulges and unwanted small ‘fines’ in the way. Said differently, “Particles’ size and size distribution drive powder flowability” [1], and unwanted “fine particles (ø: 0.1-5µm) tend to form clusters and prevent uniform recoating during SLM.” [2]. However, Equispheres’ powder is virtually spherical, agglomerate, fine-free and rolls smoothly under the PBF blade/roller without clumping. Furthermore, research has shown that the “processing of aluminium powders with spherically shaped particles results in the formation of a homogeneous and dense layer” [3]. The result for our customers is a superior surface finish with better mechanical properties in their final product.

Size Distribution

Mono-sized (narrow size distribution)

Smooth round particles that are the same size, naturally arrange themselves consistently for a given volume. Equispheres’ virtually spherical, agglomerate-free powder particles significantly improve the repeatability of the additive manufacturing process because the amount of material for a given volume is uniform and the quantity of material to be heated by the incoming energy pulse is consistent. Thus, the temperature, the melting, and the solidification speed in the affected volume is constant which results in a chemically homogenous deposition layer. Ultimately, this provides superior and consistent mechanical properties in the final product.

Consistent Microstructure

Equispheres novel atomization process is highly controlled and brings a very consistent thermal history during solidification. Because the particles are spherical and mono-sized, the cooling and solidification process is consistent across all particles. This is in stark contrast to traditional processes involving particles of various sizes whereby the smaller particles cool faster and produce a much finer microstructure than the neighboring larger particles. The consistent microstructure of the Equispheres’ powder melts and solidifies uniformly and predictably. The result for our customers is a final product with consistent and superior mechanical properties.

Competitor's Micro-Structure
Equispheres Micro-Structure

Cross section of traditionally atomized aluminium – with visible entrapped gas

Cross section of Equispheres’ aluminium – consistent microstructure with no entrapped gas

Packing Density

Unwanted agglomerates, ‘potato-shape’ particles and meddlesome ‘fines’ get in the way when powder particles settle in a powder-bed. This has a significant and negative impact on packing density. Because Equispheres’ powder is virtually spherical, mono-sized, agglomerate and fine-free, the powder packs much better than leading competitors. In fact, using the ASTMB 212-99 Apparent Density assessment, the powder packs 30% better. Packing density is important in that “a higher powder packing density produces dense(r) parts with smoother as-built surfaces.” [4, 5]

Competitor's packing density vs. Equispheres' packing density

Traditionally Atomized      Equispheres

Equispheres is presently working with leading academic and research organizations to verify and quantify the impact of the key powder features discussed above.

[1] – Inside Metal Manufacturing – The role of (super) powder in SLM 04/10/2014

[2] – R. K. Mcgeary, “Mechanical Packing,” J. Am. Ceram. Soc., vol. 58, no. 1931, 1955.

[3] E. O. Olakanmi, “Selective laser sintering/melting (SLS/SLM) of pure Al, Al–Mg, and Al–Si powders: Effect of processing conditions and powder properties,” J. Mater. Process. Technol., vol. 213, no. 8, pp. 1387–1405, Aug. 2013.

[4] Korner C, Bauereiss A, Attar E (2013) Fundamental consolidation mechanisms during selective beam melting of powders. Model Simul Mater Sci Eng 21(8):085011

[5]  Spierings A, Herres N, Levy G (2011) Influence of the particle size distribution on surface quality and mechanical properties in am steel parts. Rapid Prototyping J 17(3):195-202

The Importance of Powder to Cold Spray

A few important attributes of powder feedstock have a direct impact on the cold spray process and final product quality.

Cold Spray table

Spherical, Agglomerate-free with Superior Flowability

Perfectly round particles roll more freely than ‘potato’ shaped particles with bumps, lumps, and bulges and unwanted small ‘fines’ in the way.  Said differently, “Particles’ size and size distribution drive powder flowability” [1].  Flowability is of primary importance to cold spray processes in that it directly impacts feeding rates, feeding stability and pulsing.  This has a direct impact on coating thickness and surface finish.

Equispheres’ powder has exceptional flowability characteristics that can be readily observed when handling the product or empirically measured using Hall Flow testing standards.

Spherical Mono-size powder

Mono-sized

With cold spray technology, powder particles are accelerated in a supersonic gas jet and impinge a substrate to form a coating.  The impact speed and the mechanism of plastic deformation are the primary drivers in achieving good bond strength. Large particles accelerate more slowly than small particles and when using a powder that contains a wide range of particle sizes, a variety of impact velocities are achieved. Particles that impact too slowly form a poor bond, while those that impact too quickly erode the substrate. Furthermore, irregular shaped particles will deform inconsistently depending on their orientation at the time of impact, while spherical particles deform repeatably as the orientation of a sphere is always the same.

Equispheres’ mono-sized and spherical powder provides consistent adhesion to the substrate and more reliable mechanical properties in the final product.

Virtually Fine-Free

Traditional atomization processes produce powders that have an abundance of very small particles known as ‘fines’. These particles are a nuisance to cold spray operators and negatively impact the spraying process, foul the machines and cause unexpected, unnecessary, and costly downtime. Research has identified that copper powder with more that 1% of particles by volume between 1 µm and 5 µm in diameter tends to cause clogging [2]. Equispheres’ novel atomization process is precise and highly controlled and produces a minimal quantity of fines as compared to other vendors. This allows our customers to improve productivity and reduce costs by minimizing unscheduled down-time.

Importantly, because the small particles are so lightweight, the magnitude of the ‘fines’ can be easily overlooked when characterizing a powder distribution based on volume as “particle size distribution displayed in volume tend to ‘hide’ the fines.” [2]

Particles per Gram Chart
Competitor's powder

Traditional Atomized Powder

Equispheres Powder

Equispheres

Consistent Microstructure

Aluminium alloy – A357.0

Consistent microstructure

The microstructure of cold spray powder establishes the general deformability and therefore the sprayability and deposition efficiency that can be achieved. The Equispheres’ controlled and precise atomization process ensures that the microstructure of the powder is consistent (i.e. phases, grain size, minimal voids). This provides highly predictable deformation dynamics when a particle impacts the substrate and enables customers to obtain improved and reliable mechanical properties with minimal cracks and other defects.

Oxide/hydroxide Surface State

The surface state of the powder in terms of composition, thickness and structure influences the velocity and the deformation mechanics of the particle and has a direct impact on the coating cohesive strength and adhesion to the substrate.  Equispheres’ powder has a consistent surface state and produces coatings with reliable and repeatable results.

Equispheres is presently working with leading academic and research organizations to verify and quantify the impact of the key powder features discussed above.

[1] – Inside Metal Manufacturing – The role of (super) powder in SLM 04/10/2014

[2] – Powder Development and Qualification for Nuclear Waster Canister Application

Dominique Poirier, Jean-Gabriel Legoux, Phuong Vo, Jason D. Giallonardo,

Peter G. Keech, National Research Council, Boucherville QC, Canada, Nuclear Waste Management Organization, Toronto, Ontario, Canada

Nov 30th, 2016

Custom Solutions

Additive manufacturing and cold spray are revolutionary technologies that use metal alloys differently than traditional ‘subtractive’ manufacturing and repair processes. Currently, the alloys that are being used by these new advanced processes are simply the existing chemical compositions of traditional ‘subtractive’ manufacturing techniques. The alloys have not been engineered or optimized to support the new technology.

Equispheres’ researchers have a deep understanding of metallurgy and the dynamics of cold spray and additive manufacturing processes. We work closely with our customers to develop unique chemical compositions that are designed to optimize results for a specific application.

Chemistry