Fabrication of High Thermal Conductivity NARloy-Z-Diamond Composite Combustion Chamber Liner for Advanced Rocket Engines

At a Glance

Metadata	Details
Publication Date	2016-01-01
Journal	57th AIAA/ASCE/AHS/ASC Structures, Structural Dynamics, and Materials Conference
Authors	Biliyar N. Bhat, Sandra E. Greene, Jogender Singh
Institutions	Marshall Space Flight Center, Pennsylvania State University
Citations	2
Analysis	Full AI Review Included

Technical Documentation and Analysis: High Thermal Conductivity Diamond Composites

Reference: Fabrication of High Thermal Conductivity NARloy-Z-Diamond Composite Combustion Chamber Liner for Advanced Rocket Engines (NASA/MSFC, 2016)

Executive Summary

This NASA research demonstrates the successful synthesis and fabrication of a high thermal conductivity (HTC) copper alloy-diamond composite suitable for extreme environments, specifically targeting rocket engine combustion chamber liners.

Core Achievement: Successfully developed a NARloy-Z-Copper Diamond (NARloy-Z-CuD) composite exhibiting high thermal conductivity necessary for advanced propulsion systems.
Thermal Performance: The optimized 28 vol% Cu-coated diamond composite achieved a Thermal Conductivity (TC) of 462 W/mK, representing a 44% increase over the baseline NARloy-Z alloy (320 W/mK).
Fabrication Method: Used Field Assisted Sintering Technology (FAST) combined with diffusion bonding to create near net shape combustion chamber liner rings (2.75” OD, 8” long assembly).
Interface Solution: Metal coatings (Molybdenum Carbide and Copper) on the diamond powder were mandatory to prevent diamond segregation and drastically improve the critical diamond-matrix interfacial thermal conductance.
Material Optimization: Uncoated diamond composites suffered from severe ductility loss (<1% elongation) and inconsistent TC due to poor interfacial bonding; Cu-coated diamond solved the TC issue while retaining minimal, acceptable ductility (2-3% elongation).
Application Potential: This technology is explicitly positioned as a breakthrough for Metal Matrix Composites (MMCs) in high heat flux systems, including rocket nozzles, turbopump components, and thermal management systems (e.g., heat exchangers).

Technical Specifications

Parameter	Value	Unit	Context
Baseline Liner Material	NARloy-Z	Cu-3Ag-0.5Zr	Standard alloy used in RS-25, RS-68 engines
Baseline TC	320	W/mK	Measured at 300 °K
Optimized Composite	NARloy-Z-28%CuD	vol%	Highest performing material, utilizing Cu-MoC coated diamond
Optimized TC	462	W/mK	44% TC improvement over baseline, measured at 300 °K
TC Reduction (Ti-D Composite)	176	W/mK	Ti coating significantly lowered TC due to interfacial resistance
Prototype Ring OD	2.75	inches	Outer Diameter
Prototype Ring ID	2.5	inches	Inner Diameter
Finished Liner Length	8	inches	Total length of diffusion bonded rings
High Temp Tensile Strength (UTS)	5-7	ksi	Measured at 1000 °F, 250 psi He
Ductility (Baseline NARloy-Z)	33	%	Elongation at 75 °F
Ductility (Cu-MoC Composite)	2-3	%	Elongation at 70 °F (Acceptable loss for high heat flux application)
Processing Mold Material	TZM	N/A	Titanium-Zirconium-Molybdenum for elevated temperature strength

Key Methodologies

The composite fabrication process relied heavily on powder metallurgy and advanced sintering techniques to achieve high density and uniform dispersion of the diamond filler material.

Diamond Pre-Coating: Diamond powder was sequentially coated to improve bonding:
- Molybdenum Carbide (MoC) applied first for superior thermal contact conductance.
- Copper (Cu) overcoat applied for enhanced mixing behavior and improved sintering characteristics with the NARloy-Z matrix. (Note: Titanium (Ti) coating was tested but resulted in poor TC).
Powder Homogenization: NARloy-Z powder and the Cu-MoC coated diamond powder (28 vol%) were mixed using a Turbula mixer to ensure maximum homogeneity prior to consolidation.
FAST Sintering (Ring Formation): The homogenized powder was loaded into robust TZM molds (Titanium-Zirconium-Molybdenum) and sintered using Field Assisted Sintering Technology (FAST) at elevated temperature and pressure to form dense, individual composite rings.
Diffusion Bonding: Multiple individual rings (up to eight) were stacked inside a clean TZM mold, separated by thin interlayers of pure NARloy-Z, and subjected to a second high-temperature, high-pressure FAST cycle to create a unified, monolithic 8-inch long liner.
Post-Processing: The finished liner requires subsequent high-precision machining (using Electrical Discharge Machining/EDM and water jet grinding) to create internal cooling channels, followed by nickel electroplating to seal the channels and complete the combustion chamber assembly.

6CCVD Solutions & Capabilities

6CCVD provides the specialized CVD diamond materials and customization services essential for replicating and advancing the high thermal conductivity composites developed by NASA/MSFC. Our high-purity MPCVD diamond plates offer the superior thermal properties required for next-generation thermal management and propulsion systems.

Applicable Materials

To replicate or extend this research, 6CCVD recommends materials optimized for metal matrix composite integration:

Polycrystalline Diamond (PCD): 6CCVD supplies high-purity PCD wafers and plates up to 125mm in diameter. These materials are ideal for large-scale composite fabrication, offering high intrinsic thermal conductivity and mechanical robustness required for FAST processing. We can supply PCD precursor wafers up to 500 µm thick, which can be processed into powder or used as structural inserts.
Heavy Boron-Doped Diamond (BDD): For applications where the thermal conductivity requirements are balanced with electrical demands (e.g., integrated heating or sensing within the liner structure), our BDD materials offer customized resistivity across a wide range (p-type).
Optical Grade Single Crystal Diamond (SCD): While this paper used powder, substituting powder for high-purity Isotopically Pure SCD precursors can provide a pathway to composites exhibiting the absolute highest potential thermal conductivity (>2000 W/mK) for ultimate heat rejection performance.

Customization Potential

The success of the NARloy-Z-CuD composite hinges on optimizing the diamond-matrix interface through custom metal coatings—a core capability of 6CCVD.

Required Service	6CCVD Capability	Research Connection
Custom Metalization	We offer internal deposition services including Au, Pt, Pd, Ti, W, and Cu.	Critical for enhancing interfacial thermal conductance and preventing diamond segregation (as validated by the superior performance of the Cu-coated composite).
Large Area Substrates	Plates/wafers up to 125mm (PCD) and substrates up to 10mm thickness.	Allows for the scaling of FAST composite fabrication, accommodating the 2.75” OD liner rings demonstrated in the research.
Precision Machining	Laser cutting services allow diamond materials to be supplied in custom geometries (rings, discs, or specialty shapes).	Essential for supplying pre-shaped diamond inserts or precise dimensions required for complex TZM molds and diffusion bonding alignment.
Surface Finish	High-precision polishing (Ra < 5nm for inch-size PCD).	Crucial for ensuring high-quality subsequent coating adhesion and optimal interfaces for reliable thermal transfer performance in MMCs.

Engineering Support

6CCVD’s in-house PhD material science team specializes in developing CVD diamond solutions for extreme environments. We can assist clients replicating this process by focusing on:

Diamond Selection: Guidance on optimizing diamond particle size, purity, and volume fraction to maximize TC while managing mechanical properties (e.g., minimizing elongation loss).
Interface Engineering: Consulting on appropriate metal stacks (e.g., Cr/Cu or MoC/Cu substitutes) to maximize wettability and minimize phonon scattering at the diamond-metal boundary for similar High Heat Flux (HHF) projects.
Thermal Modeling: Support in correlating CVD material properties with expected composite performance in high-temperature, high-pressure processing regimes like FAST sintering.

For custom specifications or material consultation, visit 6ccvd.com or contact our engineering team directly.

View Original Abstract

This paper describes the process development for fabricating a high thermal conductivity NARloy-Z-Diamond composite (NARloy-Z-D) combustion chamber liner for application in advanced rocket engines. The fabrication process is challenging and this paper presents some details of these challenges and approaches used to address them. Prior research conducted at NASA-MSFC and Penn State had shown that NARloy-Z-40%D composite material has significantly higher thermal conductivity than the state of the art NARloy-Z alloy. Furthermore, NARloy-Z-40 %D is much lighter than NARloy-Z. These attributes help to improve the performance of the advanced rocket engines. Increased thermal conductivity will directly translate into increased turbopump power, increased chamber pressure for improved thrust and specific impulse. Early work on NARloy-Z-D composites used the Field Assisted Sintering Technology (FAST, Ref. 1, 2) for fabricating discs. NARloy-Z-D composites containing 10, 20 and 40vol% of high thermal conductivity diamond powder were investigated. Thermal conductivity (TC) data. TC increased with increasing diamond content and showed 50% improvement over pure copper at 40vol% diamond. This composition was selected for fabricating the combustion chamber liner using the FAST technique.

Tech Support

Original Source

DOI: https://doi.org/10.2514/6.2016-1416

References

2013 - JANNAF Liquid Propulsion Meeting
2014 - NASA-MSFC, Materials and Processes Laboratory, Material Test Branch (EM10) Memorandum dated