Plasma Rotating Electrode Process Powder: A Comprehensive Guide

Overview

Plasma rotating electrode process (PREP) powder is a type of spherical powder made using the PREP method. PREP powders have unique properties that make them suitable for use in various applications like thermal spray coatings, metal additive manufacturing, and metal injection molding.

Some key features of PREP powder include:

• Highly spherical morphology with smooth surface
• Controlled microstructure with fine grain size
• Low porosity and high density
• Excellent flowability and spreadability
• High packing density
• Good blending characteristics
• Capability to manufacture alloys and composites

PREP enables customization of powder characteristics like particle size distribution, composition, density, oxide content, and more. By controlling the PREP process parameters, powders can be engineered for specific application requirements.

Types of PREP Powders

Powder Material	Composition	Key Properties and Applications
Nickel alloy	NiCr, NiCrAlY, NiCoCrAlY	Oxidation and corrosion resistance. Thermal spray coatings.
Cobalt alloy	CoCr, CoCrAlY, CoNiCrAlY	High temperature strength. Thermal spray coatings.
Stainless steel	316L, 304L	Corrosion resistance. Metal AM, MIM.
Tool steel	H13, P20	High hardness. Metal AM, MIM.
Titanium alloy	Ti6Al4V, TiAl	High strength-to-weight ratio. Biomedical implants, aerospace.
Copper alloy	CuCrZr	High thermal conductivity. Electronic applications.
Aluminum alloy	AlSi12	Lightweight. Automotive components.
Tungsten alloy	WNiFe, WCo	High density. Radiation shielding.

Composition and Microstructure

PREP enables close control over powder composition and microstructural features:

• Alloying elements can be modified to achieve desired properties
• Microsegregation is minimized compared to gas atomization
• Fine grained microstructure with uniform distribution of phases
• Porosity and oxide content can be reduced to very low levels
• Spherical morphology is maintained after alloying

Key Properties of PREP Powder

Property	Description	Benefits
Particle size distribution	PREP can achieve narrow distribution with controlled d50.	Ensures uniform melting and consistent properties.
Morphology	Highly spherical shape, smooth surface.	Excellent flow and packing density.
Apparent density	Can be optimized based on requirements.	Higher density improves powder spreading.
Flowability	Measured by Hall flowmeter method.	Ensures uniform powder feeding and spreading.
Packing density	High packing density up to 60%.	Maximizes volume fraction of metal powder in component.
Oxide content	Oxide levels below 0.2% achieved.	Reduces oxide inclusions in final part.
Microstructure	Fine grained and homogeneous.	Uniform property distribution in final part.
Surface chemistry	Chemistry precisely controlled.	Oxide formation, wettability, and spreading optimized.

Applications of PREP Powder

PREP powder is used across various industries due to its specialized properties:

Thermal Spray Coatings

• Excellent flowability results in uniform feed rate and coating quality
• Controlled particle size distribution optimizes melting and minimizes unmelted powder
• Smooth surface morphology improves coating density and adhesion strength
• Low oxide content prevents oxide inclusions in coating
• Spherical shape gives higher deposition efficiency

Metal Additive Manufacturing

• High packing density allows more material per layer, reducing voids
• Smooth surface morphology results in uniform melting and melt pool flow
• Controlled particle size distribution prevents segregation issues
• Low surface oxide enables good inter-particle bonding
• Sphericity and flowability minimize powder feed problems

Metal Injection Molding

• High packing density maximizes sintered density
• Uniform particle size distribution prevents segregation
• Good flowability and compatibility results in homogenous mixing
• Low oxide content prevents sintering defects
• Controlled composition yields desired properties after sintering

Specifications

Typical specifications for PREP powder:

Parameter	Range
Particle size	10 – 150 microns
Particle size distribution	D10, D50, D90 can be controlled
Morphology	Highly spherical ≥ 0.9
Apparent density	Up to 60% of theoretical density
Hall flowability	< 30 s/50 g
Oxide content	< 0.2 wt%
Microstructure	Fine grained < 10 microns
Surface chemistry	O, C, N levels precisely controlled

Suppliers and Pricing

Some leading global suppliers of PREP powders are:

Supplier	Location
Sandvik	Sweden
Praxair	USA
Hoganas	Sweden
CNPC Powder Group	China

Pricing for PREP powder varies based on:

• Base metal (Ni, Co, steel)
• Alloy composition
• Particle size distribution
• Order quantity
• Level of customization

Indicative pricing ranges from $50/kg to $120/kg for common alloys. Custom alloys and particle size distribution can increase cost.

Comparison to Gas Atomized Powder

Parameter	PREP Powder	Gas Atomized Powder
Particle shape	Highly spherical	Irregular, satellites present
Oxide content	Very low <0.2%	Typically 0.5-2%
Porosity	Near fully dense	Can have 10-20% porosity
Alloy homogenity	Excellent	Segregation prone
Flowability	Very good	Lower due to satellites
Packing density	Up to 60%	Typically 30-40%
Surface chemistry	Precisely controlled	Variable based on process
Cost	Higher	Lower capital cost

Advantages of PREP Powder

• Excellent spherical morphology for flowability
• Controlled particle size distribution
• Low porosity and oxide content
• Alloy homogeneity and fine microstructure
• Customizable composition and properties
• High packing density for AM and MIM

Limitations of PREP Powder

• Higher cost compared to gas atomized powder
• Limited to smaller particle sizes, usually below 150 microns
• Requires advanced process control and optimization
• Limited production rate compared to gas atomization
• Restricted to select base metals like Ni, Co, and steels

Frequently Asked Questions

Q: What is plasma rotating electrode process (PREP) powder?

A: PREP powder is a highly spherical metallic powder produced using the PREP method which involves rotating an electrode in a plasma arc under precise control to achieve desired powder characteristics.

Q: What materials can be made into PREP powder?

A: Common materials include nickel, cobalt, stainless steel, tool steel, titanium, aluminum, and copper alloys. Other alloys and composites are also possible through PREP.

Q: What are the key advantages of PREP powder?

A: Key advantages are excellent sphericity and flowability, controlled particle distribution, low porosity and oxides, fine and uniform microstructure, customizable composition, and high packing density.

Q: What is PREP powder used for?

A: Major applications are thermal spray coatings, metal additive manufacturing, and metal injection molding due to its specialized properties.

Q: How is PREP powder different from gas atomized powder?

A: PREP powder has superior sphericity, lower oxides, less porosity, more homogenous composition and microstructure compared to gas atomized powder.

Q: Is PREP powder more expensive than gas atomized powder?

A: Yes, PREP powder typically costs more due to higher process complexity and control involved. But it offers significant performance advantages over gas atomized powder.

Q: What particle size is available for PREP powder?

A: The usual range is 10 to 150 microns. Both smaller and larger sizes are possible but less common. Particle size distribution can also be controlled as per requirements.

Q: Does PREP powder have limited alloy options?

A: PREP is most established for nickel, cobalt and stainless steel alloys. But ongoing process development is expanding the alloy systems possible, including reactive materials like titanium and aluminum.

Q: Can PREP powder be customized for specific applications?

A: Yes, customization is a key benefit of PREP. Particle characteristics and alloy composition can be tailored to meet requirements for thermal spray, AM, MIM, etc.

Additional FAQs on Plasma Rotating Electrode Process Powder

1) How does PREP differ from EIGA and gas atomization in contamination risk?

• PREP melts a rotating bar with a plasma arc; droplets are flung off in inert/vacuum, avoiding crucibles and minimizing contact surfaces. Compared with gas atomization, PREP typically achieves lower oxide and inclusion content; versus EIGA (Electrode Induction-melting Gas Atomization), PREP often delivers higher sphericity and fewer satellites for similar alloy systems.

2) What electrode feedstock quality is required for consistent PREP powder?

• Use vacuum arc remelted (VAR) or electroslag remelted (ESR) bars with tight chemistry tolerances, low O/N/H, and minimal surface defects. Consistent diameter and straightness are critical to maintain stable melt rate and droplet size.

3) What particle size distributions are realistic for AM vs. thermal spray from PREP?

• AM LPBF: typically 15–45 μm or 20–63 μm cuts. DED/EBAM: 45–106 μm. Thermal spray (HVOF/APS): 15–90 μm depending on process. PREP can target narrow spans with high yield due to its ligament-free droplet formation.

4) How is oxygen controlled in PREP powders for reactive alloys like Ti and Al?

• Operate in high-purity argon under low O2/H2O ppm, pre-clean and outgas electrodes, and minimize residence time. Post-process vacuum anneal or plasma reconditioning may further reduce surface oxides for Ti6Al4V and AlSi12.

5) Are PREP powders suitable for medical implants?

• Yes, when produced from medical-grade feedstock and per standards (e.g., ASTM F3001 for Ti-6Al-4V ELI powders). Lot-level certificates must document bioburden, chemistry, O/N/H, PSD, flow, and density. Ensure compliance with ISO 13485, ISO 10993 biocompatibility, and applicable FDA/CE requirements.

2025 Industry Trends for PREP Powder

• Qualification acceleration: More OEMs pre-qualify PREP Ti6Al4V and CoCr for LPBF/EBM to reduce support-induced defects and improve fatigue limits.
• Process analytics: High-speed IR/optical monitoring of the melt crown and droplet plume enables closed-loop control of electrode rpm and arc power.
• Sustainability: Increased argon recirculation, energy recovery, and Environmental Product Declarations (EPDs) for PREP lines.
• Alloy portfolio growth: PREP adoption for CuCrZr and high-strength maraging/tool steels aimed at conformal-cooled tooling and RF hardware.
• Digital powder passports: Traceability linking electrode heats, arc parameters, PSD, O/N/H, and sieve yields to end-part serials.

2025 Snapshot: PREP Powder KPIs (indicative ranges)

Metric	2023	2024	2025 YTD	Notes/Sources
Sphericity (image analysis, Ti6Al4V)	0.92–0.96	0.93–0.97	0.94–0.98	Supplier QA reports, peer-reviewed PREP studies
Oxygen (wt%, Ti6Al4V ELI)	0.12–0.18	0.10–0.15	0.09–0.13	ISO/ASTM 52907-compliant lots
AM-grade yield to 15–45 μm	28–38%	30–42%	32–45%	Better rpm/arc control and classification
Hall flow (s/50 g, CoCr/316L)	14–22	13–21	12–20	Higher sphericity, fewer satellites
Lead time (weeks, common alloys)	6–10	5–8	4–7	Added PREP capacity EU/US/APAC

References: ISO/ASTM 52907/52920/52930; ASTM B214/B212/B964; supplier datasheets (Sandvik, Höganäs, Carpenter Additive); NIST AM Bench resources; journal articles on PREP/Ti and CoCr powders.

Latest Research Cases

Case Study 1: PREP Ti6Al4V ELI for Fatigue-Critical LPBF Implants (2025)

• Background: A medical OEM sought to reduce scatter in high-cycle fatigue for acetabular cup lattices built via LPBF.
• Solution: Switched from gas-atomized to PREP Ti6Al4V ELI (15–45 μm), with documented O/N/H and narrow PSD; implemented vacuum stress relief and optimized laser parameters for smoother struts.
• Results: Density improved from 99.5% to 99.8%; O reduced from 0.14 to 0.11 wt%; fatigue life at 10^7 cycles increased by 18–24%; support removal time reduced 12% due to improved flow and spreading.

Case Study 2: PREP CoCrAlY for HVOF Turbine Coatings (2024)

• Background: An MRO facility aimed to cut porosity and oxide stringers in bond coats to improve TBC adherence.
• Solution: Adopted PREP CoCrAlY (20–63 μm), tuned HVOF fuel/oxygen ratios, and tightened powder moisture controls.
• Results: Coating porosity fell from 3.2% to 1.6%; oxide inclusions reduced by 40%; TBC spallation life improved 30% in burner rig tests; feed interruptions decreased due to superior powder flowability.

Expert Opinions

• Prof. Iain G. Todd, Professor of Metallurgy, University of Sheffield
• Viewpoint: “PREP’s contact-free melting and spherical droplets yield powders with lower oxide and inclusion content—key for reliable fatigue performance in AM titanium.”
• Dr. Christina M. Lomasney, Materials Scientist and AM Advisor
• Viewpoint: “Powder hygiene is decisive. PREP can deliver exceptional sphericity, but without low O2/H2O handling, you lose those benefits in downstream AM.”
• Dr. Eric G. Ahlstrom, Thermal Spray Specialist, former Rolls-Royce
• Viewpoint: “For HVOF bond coats like CoCrAlY, PREP powders consistently improve feed stability and reduce porosity, boosting TBC adhesion and life.”

Practical Tools and Resources

• Standards and qualification
• ISO/ASTM 52907 (feedstock), 52920/52930 (process/quality): https://www.iso.org
• ASTM F3001 (Ti-6Al-4V ELI), ASTM F3184 (metal powder reuse guidance), ASTM B214/B212/B964 test methods: https://www.astm.org
• Data and design
• NIST AM Bench datasets and measurement science: https://www.nist.gov
• Copper Development Association and Nickel Institute for alloy property data: https://www.copper.org, https://www.nickelinstitute.org
• Thermal spray guidance
• ASM Thermal Spray Society resources: https://www.asminternational.org
• OEM HVOF/APS process notes (e.g., Praxair/TAFA, Oerlikon Metco)
• Quality and compliance
• ISO 13485 for medical devices; ISO 9001 for powder production QA
• NFPA 484 safety for combustible metal powders: https://www.nfpa.org
• Market/pricing
• LME indices for Ni, Co, Ti feedstock tracking: https://www.lme.com

Last updated: 2025-10-16
Changelog: Added 5 focused FAQs; introduced a 2025 KPI table for PREP powders; provided two recent case studies (Ti6Al4V ELI for LPBF implants and CoCrAlY for HVOF); compiled expert viewpoints; linked standards, data, thermal spray, QA, safety, and market resources
Next review date & triggers: 2026-03-31 or earlier if ISO/ASTM feedstock standards update, OEMs release new PREP qualification criteria, or notable shifts occur in Ni/Co/Ti prices affecting PREP powder availability and cost