Investigating the Influence of Mechanical Loads on Built-Up Edge Formation Across Different Length Scales at Diamond–Transition Metal Interfaces

At a Glance

Metadata	Details
Publication Date	2025-05-28
Journal	Journal of Manufacturing and Materials Processing
Authors	Majed Al‐Ghamdi, Mohammed T. Alamoudi, Rami A. Almatani, M. Ravi Shankar
Institutions	King Abdulaziz City for Science and Technology, University of Pittsburgh
Citations	1
Analysis	Full AI Review Included

Executive Summary

This analysis investigates the fundamental failure mechanisms—specifically Built-Up Edge (BUE) formation—at the interface between single-crystal diamond tools and Niobium (Nb) transition metal during micromachining.

Core Mechanism Identified: BUE formation and subsequent rapid diamond tool wear are confirmed to be driven by tribochemical interactions resulting from high mechanical stress, even under strictly isothermal (low temperature) and vacuum conditions.
Experimental Setup: Plane Strain Machining (PSM) was conducted in situ inside a Scanning Electron Microscope (SEM) vacuum chamber at a low cutting speed (150 µm/s) and shallow depth of cut (3 µm) to isolate mechanical effects.
Key Finding (Chemical): High-resolution Transmission Electron Microscopy (TEM) and Energy-Dispersive X-ray Spectroscopy (EDS) confirmed the formation of an amorphous Niobium Carbide (NbC) diffusion layer at the interface.
Diffusion Layer Characteristics: The NbC layer thickness was measured at approximately 20 nm, exhibiting a strong concentration gradient of C and Nb, confirming inter-diffusion driven by mechanical energy.
Surface Degradation: The BUE formation severely degraded the tool surface integrity, increasing the diamond rake face roughness from an initial 6 nm to approximately 19 nm after machining.
Implications for Wear: The study confirms that Nb’s strong carbon affinity, combined with severe plastic deformation (SPD) in the secondary shear zone (SSZ), causes chemical bonding and rapid tool degradation, contrasting with non-carbide-forming metals like aluminum.

Technical Specifications

Parameter	Value	Unit	Context
Workpiece Material	Niobium (Nb)	N/A	Purity 99.8%
Tool Material	Single-Crystal Diamond	N/A	{110} Dodec orientation
Rake Angle (γ_o)	0	Degrees	Orthogonal cutting configuration
Machining Velocity (V)	150	µm/s	Constant cutting speed (quasistatic)
Depth of Cut (DOC, a_o)	3	µm	Preset cut depth
Workpiece Thickness (w)	≥100	µm	Ensured plane strain condition
Calculated Minimum Shear Strain (ε_min)	2	N/A	Achieved at shear angle (β_o) = 45°
Calculated Minimum Shear Velocity (V_s)	212	µm/s	Theoretical minimum
Estimated Temperature Rise (ΔT)	< 10	K	Confirmed isothermal deformation conditions
Initial Rake Face Roughness (R_a)	Approx. 6	nm	Measured via AFM before machining
Final Rake Face Roughness (R_a)	Approx. 19	nm	Measured via AFM after machining
NbC Diffusion Layer Thickness	Approx. 20	nm	Measured via EDS line scanning
Nb:C Ratio (Beginning Layer)	46:37	%	EDS point analysis
Nb:C Ratio (Middle Layer)	73:9	%	EDS point analysis

Key Methodologies

The investigation utilized a highly controlled, multi-scale approach combining in situ mechanical testing with advanced electron microscopy:

In Situ Plane Strain Machining (PSM):
- A custom-built two-axis deformation stage was installed inside an FEI SEM vacuum chamber.
- PSM was performed on Nb using a diamond tool at low speed (150 µm/s) and shallow DOC (3 µm).
- The environment was maintained under ultra-high vacuum (UHV) to eliminate atmospheric oxidation effects.
Thermal Control and Verification:
- Machining parameters were selected to ensure isothermal conditions, with theoretical calculations confirming a negligible temperature rise (less than 10 K) in the deformation zone.
Surface Integrity Assessment:
- Scanning Electron Microscopy (SEM) was used for real-time observation of BUE formation and material transfer on the diamond rake face.
- Atomic Force Microscopy (AFM) quantified the increase in rake face roughness (from 6 nm to 19 nm) due to the BUE.
Interface Sample Preparation:
- Focused Ion Beam (FIB) milling techniques were employed to extract site-specific cross-sectional lamellae directly from the diamond-Nb interaction zone (the BUE region).
Microstructural and Chemical Characterization:
- Transmission Electron Microscopy (TEM) provided high-resolution imaging of the interface structure.
- Energy-Dispersive X-ray Spectroscopy (EDS) line scanning and point mapping were used to determine elemental concentration profiles (C and Nb) across the interface, confirming the 20 nm thick amorphous NbC diffusion layer.

Commercial Applications

The findings are critical for industries relying on ultra-precision machining of high-performance metals, where tool wear and surface quality are paramount.

Aerospace and Defense: Machining refractory transition metals (Niobium, Titanium, Zirconium) used in high-temperature or high-stress components (e.g., turbine blades, rocket nozzles). Understanding BUE formation allows for optimized cutting strategies to maintain component integrity.
Biomedical Device Manufacturing: Ultra-precision turning of biocompatible metals (like Ti and Nb alloys) for implants, prosthetics, and surgical instruments, where nanoscale surface finish is mandatory.
Optical Manufacturing: Improving the reliability and lifespan of diamond tools used for single-point diamond turning (SPDT) of non-ferrous metals to produce mirror-finish optics.
Advanced Tool Design: Informing the development of next-generation cutting tools, including the use of inert atmospheres, specialized tool coatings, or interrupted cutting techniques to suppress the mechanically induced tribochemical formation of carbides.
Process Modeling and Simulation: Providing validated experimental data on diffusion kinetics under extreme mechanical strain, which is essential for refining predictive models of tool wear in manufacturing simulations.

View Original Abstract

Investigating failure mechanisms in cutting tools used in advanced industries like biomedical and aerospace, which operate under extreme mechanical and chemical conditions, is essential to prevent failures, optimize performance, and minimize financial losses. The diamond-turning process, operating at micrometer-length scales, forms a tightly bonded built-up edge (BUE). The tribochemical interactions between a single-crystal diamond and its deformed chip induce inter-diffusion and contact, rapidly degrading the cutting edge upon BUE fracture. These effects intensify at higher deformation speeds, contributing to the observed rapid wear of diamond tools during d-shell-rich metal machining in industrial settings. In this study, these interactions were studied with niobium (Nb) as the transition metal. Tribochemical effects were observed at low deformation speeds (quasistatic; <1 mm/s), where thermal effects were negligible under in situ conditions inside the FEI /SEM vacuum chamber room. The configuration of the interface region of diamond and transition metals was characterized and analyzed using focused ion beam (FIB) milling and subsequently characterized through transmission electron microscopy (TEM). The corresponding inter-diffusion was examined by elucidating the phase evolution, element concentration profiles, and microstructure evolution via high-resolution TEM/Images equipped with an TEM/EDS system for elemental characterization.

Tech Support

Original Source

DOI: https://doi.org/10.3390/jmmp9060176

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