Experimental Study on High-Speed Milling of SiCf/SiC Composites with PCD and CVD Diamond Tools

At a Glance

Metadata	Details
Publication Date	2021-06-22
Journal	Materials
Authors	Bin Zhang, Yanan Du, Hanliang Liu, Lianjia Xin, Yinfei Yang
Institutions	Nanjing University of Aeronautics and Astronautics, China Academy of Space Technology
Citations	31
Analysis	Full AI Review Included

Technical Documentation & Analysis: High-Speed Milling of SiCf/SiC Composites

This document analyzes the findings of the research paper “Experimental Study on High-Speed Milling of SiCf/SiC Composites with PCD and CVD Diamond Tools” to provide actionable technical specifications and material recommendations, leveraging the advanced capabilities of 6CCVD.

Executive Summary

This study provides critical validation for the selection of diamond materials in extreme machining environments, specifically high-speed milling of Silicon Carbide Fiber Reinforced Silicon Carbide (SiC_f/SiC) composites.

PCD Superiority Confirmed: Polycrystalline Diamond (PCD) tools demonstrated significantly better cutting performance, longer tool life (2x improvement under cryogenic conditions), and superior machined surface quality (Sa 3.8 µm) compared to Chemical Vapor Deposition (CVD) diamond tools.
Fracture Toughness is Key: The superior performance of PCD is directly attributed to its higher fracture toughness—a result of the metallic (Cobalt) binder—which allows it to withstand the high cyclic impact loads inherent in interrupted milling processes.
Cryogenic Cooling Efficacy: The use of cryogenic cooling (Liquid Nitrogen) dramatically reduced tool wear for both PCD and CVD tools (up to 4x life improvement for CVD) and improved the integrity of the machined surface by minimizing defects like fiber burr and edge chipping.
Application Validation: The research validates the use of high-toughness PCD for high-speed material removal in challenging aerospace and high-temperature ceramic matrix composite (CMC) applications.
6CCVD Value Proposition: 6CCVD specializes in synthesizing and processing high-toughness PCD plates and wafers, offering custom dimensions and internal metalization services necessary for fabricating robust, high-performance cutting tools required for this type of demanding machining.

Technical Specifications

The following hard data points were extracted from the experimental results, highlighting the performance metrics and processing conditions.

Parameter	Value	Unit	Context
Workpiece Material	SiC_f/SiC Composite	N/A	2.5 D braided structure, 30% fiber volume fraction
PCD Tool Hardness	Hv7000	N/A	Supplier specification
CVD Tool Hardness	Hv8000	N/A	Supplier specification
Spindle Speed (n)	10,000	rpm	High-speed milling parameter
Feed Speed (v_f)	3000	mm/min	High-speed milling parameter
Cutting Depth (a_p)	0.5	mm	Through-slot milling
Cryogenic Coolant Pressure	1.1	MPa	Liquid Nitrogen (LN₂)
Best Surface Roughness (PCD, Cryo)	3.8	µm (Sa)	3D surface evaluation parameter
Tool Life Improvement (PCD, Cryo vs. Dry)	2	Times Higher	Increased tool life due to cryogenic cooling
Tool Life Improvement (CVD, Cryo vs. Dry)	4	Times Higher	Increased tool life due to cryogenic cooling
Primary PCD Failure Mode (Dry)	Minute Spalling	N/A	Occurred around the tool nose
Primary CVD Failure Mode (Dry)	Severe Tool Nose Fracture	N/A	Large area spalling and edge chipping

Key Methodologies

The experimental procedure focused on comparing tool performance under high-speed, interrupted cutting conditions using two distinct cooling approaches.

Workpiece Material: SiC_f/SiC composite with a 2.5 D braided structure (30% SiC fiber volume fraction) was used. The material exhibits high hardness (up to 800 MPa bending strength) and high temperature resistance (>1500 °C).
Tool Selection and Geometry: Two straight-toothed end-mill cutters (6 mm diameter) were utilized. Blades (1 mm thickness) were fabricated from Polycrystalline Diamond (PCD) and Chemical Vapor Deposition (CVD) diamond and brazed onto cemented carbide shanks.
Milling Parameters: High-speed, through-slot milling was performed using a DMU 60 five-axis vertical machining center. Parameters were fixed at a spindle speed of 10,000 rpm and a feed speed of 3000 mm/min.
Cooling Conditions: Experiments were executed under two conditions:
- Dry Machining: Standard ambient conditions.
- Cryogenic Machining: Liquid Nitrogen (LN₂) was sprayed directly into the cutting area at a pressure of 1.1 MPa.
Evaluation: Tool wear was assessed using a camera-loaded microscope. Machined surface quality and defects (fiber burr, ladder fracture, edge chipping) were analyzed via Scanning Electron Microscopy (SEM) and quantified using the 3D surface roughness parameter Sa.

6CCVD Solutions & Capabilities

This research confirms that material selection—specifically prioritizing fracture toughness (PCD) over pure hardness (CVD)—is paramount for successful high-speed milling of advanced ceramic matrix composites. 6CCVD is uniquely positioned to supply the necessary diamond materials and engineering support to replicate and advance this research.

Applicable Materials

Research Requirement	6CCVD Material Recommendation	Technical Rationale
High Fracture Toughness for Interrupted Cutting	High-Grade Polycrystalline Diamond (PCD) Plates.	PCD’s metallic binder (Co) provides the necessary toughness to resist cyclic impact loads and brittle fracture, minimizing tool failure (spalling, chipping) observed in the study.
Extreme Hardness for SiC/SiC Composites	Chemical Vapor Deposition (CVD) Diamond Wafers.	While less suitable for interrupted milling, our SCD/PCD materials offer extreme hardness (Hv > 8000) ideal for continuous cutting or specialized finishing passes where fracture risk is lower.
Potential for Electrochemistry	Boron-Doped Diamond (BDD) Substrates.	For future research extending into electrochemical machining or sensor applications related to SiC/SiC processing, 6CCVD offers custom BDD materials.

Customization Potential

The success of the tools in this study relied on precise geometry (1 mm blade thickness, brazing). 6CCVD offers comprehensive customization capabilities to meet these exact engineering requirements:

Custom Dimensions: We supply PCD plates and wafers up to 125 mm in diameter, allowing for the fabrication of multiple tool inserts from a single high-quality source.
Thickness Control: We offer precise thickness control for both SCD and PCD materials, ranging from 0.1 µm up to 500 µm for wafers, and substrates up to 10 mm, ensuring optimal blade geometry.
Advanced Metalization: The study required brazing the diamond blades onto carbide shanks. 6CCVD provides internal metalization services (including Ti, W, Cu, Pt, Au, Pd) essential for creating robust, high-strength bonds necessary for high-speed (10,000 rpm) and cryogenic machining environments.
Precision Polishing: While the study focused on material removal, 6CCVD offers ultra-fine polishing services (Ra < 5 nm for inch-size PCD) to enhance the surface quality of the diamond tool itself, reducing friction and improving the final surface finish of the SiC_f/SiC composite.

Engineering Support

6CCVD’s in-house PhD team can assist researchers and engineers with material selection and optimization for similar Ceramic Matrix Composite (CMC) Milling projects. We provide consultation on selecting the optimal diamond grade (balancing hardness vs. fracture toughness) and designing the necessary metalization layers for specific brazing or bonding requirements.

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

View Original Abstract

Silicon carbide fiber reinforced silicon carbide ceramic matrix composite (SiCf/SiC composite) is characterized by a high strength-to-density ratio, high hardness, and high temperature resistance. However, due to the brittleness of the matrix material and the anisotropy of the reinforcing phase, it is a huge challenge for machining of the material. The milling method has advantages of a high material removal rate and applicability to complex surface geometry. However, no published literature on milling of SiCf/SiC composite has been found up to now. In this paper, high-speed milling of SiCf/SiC composites was carried out under dry conditions and cryogenic cooling using liquid nitrogen, respectively. Polycrystalline diamond (PCD) and chemical vapor deposition (CVD) diamond cutting tools were used for the milling work. The cutting performance of the two kinds of tools in high-speed milling of SiCf/SiC composites was studied. Tool failure modes and mechanisms were analyzed. The effects of the cooling approach on tool wear and machined surface quality were also investigated. The experimental results showed that under identical cutting parameters and cooling approaches, the PCD tool yielded better cutting performance in terms of a longer tool life and better surface quality than that of the CVD diamond tool. In dry machining, the failure modes of the CVD diamond tool were a large area of spalling on the rake face, edge chipping and severe tool nose fracture, whereas for the PCD tool, only a small area of spalling around the tool nose took place. Compared to the dry machining, the wear magnitudes of both PCD and CVD diamond tools were decreased in cryogenic machining. Additionally, the surface quality also showed significant improvements. This study indicates that the PCD tool is highly suitable for machining of SiCf/SiC composite, and that the cryogenic method can improve machining efficiency and surface quality.

Tech Support

Original Source

DOI: https://doi.org/10.3390/ma14133470

References

2020 - Fabrication of Silicon Carbide Fiber-Reinforced Silicon Carbide Matrix Composites Using Binder Jetting Additive Manufacturing from Irregularly-Shaped and Spherical Powders [Crossref]
2018 - Characteristics of silicon carbide fiber-reinforced composite for microwave absorbing structures [Crossref]
2017 - Processing-temperature dependent micro- and macro-mechanical properties of SiC fiber reinforced SiC matrix composites [Crossref]
2017 - Effect of oxidation treatment on KD-II SiC fiber-reinforced SiC composites [Crossref]
2020 - Tensile properties of two-dimensional carbon fiber reinforced silicon carbide composites at temperatures up to 2300 °C [Crossref]
2018 - Fixed abrasive machining of non-metallic materials [Crossref]
2021 - Machining of SiC ceramic matrix composites: A review [Crossref]
2020 - Feasibility study on cryogenic milling of carbon fiber reinforced silicon carbide composites
2018 - Effect of machining parameter on femtosecond laser drilling processing on SiC/SiC composites [Crossref]
2016 - Effect of different parameters on machining of SiC/SiC composites via pico-second laser [Crossref]