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	China Academy of Space Technology, Nanjing University of Aeronautics and Astronautics
Citations	31
Analysis	Full AI Review Included

Executive Summary

This study investigated the high-speed milling performance of SiC_f/SiC ceramic matrix composites using Polycrystalline Diamond (PCD) and Chemical Vapor Deposition (CVD) diamond tools under dry and cryogenic conditions.

Tool Performance Superiority: The PCD tool demonstrated significantly better cutting performance than the CVD diamond tool, exhibiting longer tool life and achieving superior machined surface quality under identical parameters.
Cryogenic Impact on Tool Life: Cryogenic cooling using liquid nitrogen drastically improved tool life. PCD tool life increased by a factor of two, while CVD diamond tool life increased by a factor of four compared to dry machining.
Tool Failure Mechanisms: The CVD diamond tool failed primarily due to brittle fracture (large area spalling on the rake face, edge chipping, and severe tool nose fracture), attributed to its inherently lower fracture toughness compared to PCD.
Surface Quality Improvement: Cryogenic machining resulted in significant improvements in surface integrity, reducing defects such as fiber burr, fiber stripping, and edge chipping compared to dry machining.
Optimal Machining Strategy: The combination of PCD tools and cryogenic cooling is highly recommended for milling SiC_f/SiC composites to maximize machining efficiency and surface quality.
Material Removal Mechanisms: Primary material removal included fiber breakage, interface debonding, and brittle fracture of the SiC matrix.

Technical Specifications

Parameter	Value	Unit	Context
Workpiece Material	SiC_f/SiC Composite	N/A	2.5 D braided structure, 30% fiber volume fraction
Spindle Speed	10,000	rpm	High-speed milling parameter
Feed Speed (v_f)	3000	mm/min	High-speed milling parameter
Cutting Width (a_e)	6	mm	Straight slot geometry
Cutting Depth (a_p)	0.5	mm	Straight slot geometry
PCD Tool Hardness	7000	Hv	Tool material property
CVD Tool Hardness	8000	Hv	Tool material property
SiC_f/SiC Density	2.2-2.5	g/cm³	Material property
SiC_f/SiC Tensile Strength	280-330	MPa	Material property
SiC_f/SiC Young’s Modulus	190-210	GPa	Material property
S_a (PCD, Cryogenic)	3.8	µm	Best surface roughness achieved
S_a (CVD, Dry)	5.4	µm	Worst surface roughness achieved
Tool Life Improvement (CVD)	4	times higher	Cryogenic vs. Dry machining
Tool Life Improvement (PCD)	2	times higher	Cryogenic vs. Dry machining
Cryogenic Pressure	1.1	MPa	Liquid nitrogen jet pressure

Key Methodologies

The experimental investigation utilized high-speed milling under two cooling conditions to evaluate PCD and CVD diamond tool performance on SiC_f/SiC composites.

Workpiece Preparation: SiC_f/SiC composite blanks (200 x 20 x 5 mm³) with a 2.5 D braided structure were surface ground to ensure flatness prior to milling.
Tooling: Two straight-toothed end-mill cutters (6 mm diameter) were used: a Polycrystalline Diamond (PCD) tool and a Chemical Vapor Deposition (CVD) diamond tool, both brazed onto cemented carbide shanks.
Milling Parameters: All tests were conducted at a fixed high-speed setting: Spindle speed of 10,000 rpm, Feed speed of 3000 mm/min, Cutting width (a_e) of 6 mm, and Cutting depth (a_p) of 0.5 mm.
Cooling Methods:
- Dry Machining: Standard ambient conditions.
- Cryogenic Machining: Liquid nitrogen (LN₂) was sprayed directly into the cutting zone at 1.1 MPa pressure. Workpieces were pre-cooled for 5 minutes before cutting.
Tool Wear Analysis: Tool wear (flank wear, VB) and failure modes (spalling, chipping, fracture) were observed using a camera-loaded microscope.
Surface Quality Assessment: Machined surface morphology and defects (fiber ladder fracture, burr, stripping) were analyzed using Scanning Electron Microscopy (SEM). Surface roughness (S_a) was quantified using a 3D optical profiler.

Commercial Applications

The findings regarding optimized high-speed milling of SiC_f/SiC composites are critical for industries requiring precision manufacturing of high-performance ceramic components.

Aerospace and Hypersonics: Manufacturing of lightweight, high-temperature resistant components for jet engines, rocket nozzles, and thermal protection systems, where SiC_f/SiC is used due to its stability above 1500 °C.
Defense and Military: Production of specialized armor and structural components requiring high specific strength and hardness.
High-Performance Automotive: Fabrication of brake rotors, engine components, and structural parts where high stiffness and low density are essential.
Advanced Materials Processing: Establishing efficient, high-quality subtractive manufacturing protocols for complex ceramic matrix composites, reducing waste and improving throughput in specialized machine shops.

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

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