Thermal Behavior of Single-Crystal Diamonds Catalyzed by Titanium Alloy at Elevated Temperature

At a Glance

Metadata	Details
Publication Date	2020-07-06
Journal	Applied Sciences
Authors	Pengyu Hou, Ming Zhou, Haijun Zhang
Institutions	Harbin Institute of Technology, China Academy of Engineering Physics
Citations	6
Analysis	Full AI Review Included

Technical Documentation & Analysis: SCD Wear in High-Temperature Ti Machining

Executive Summary

This analysis of the thermal behavior of single-crystal diamond (SCD) catalyzed by titanium alloy (Ti-6Al-4V) confirms that the primary limitation in ultra-precision machining of difficult-to-cut alloys is thermochemical wear, not mechanical abrasion.

Key Finding	Mechanism	6CCVD Value Proposition
Diffusion Wear (Anaerobic)	High temperature (up to 1473 K) causes diamond graphitization, followed by rapid carbon diffusion into the Ti-6Al-4V matrix, forming Titanium Carbide (TiC).	6CCVD SCD offers superior structural integrity, minimizing defect sites that initiate graphitization.
Oxidation Wear (Aerobic)	Carbon atoms shed from the diamond lattice react with oxygen to form CO and CO₂, leading to severe oxidative tool degradation.	Our SCD materials are optimized for high-temperature stability, crucial for applications where localized heat cannot be fully mitigated.
Quantified Reaction Rate	Carbon content on the Ti-6Al-4V surface increased significantly from 3.01% (initial) to 23.31% (after heating in Argon).	We provide SCD substrates with certified purity and low nitrogen content, ensuring maximum chemical inertness.
Thermodynamic Control	Diffusion wear is directly proportional to temperature, governed by the Gibbs free energy and carbon solubility in the titanium alloy.	6CCVD supports R&D into advanced tool coatings (via custom metalization) designed to suppress carbon diffusion barriers.

Technical Specifications

The following hard data points were extracted from the thermal analysis experiments simulating SCD tool wear:

Parameter	Value	Unit	Context
Heating Range	293 to 1473	K	Temperature sweep for thermal analysis
Heating Rate	10	K/min	Constant rate used in TGA1600
Gas Flow Rate (Argon/Air)	40	mL/min	Continuous flow rate during heating
Ti-6Al-4V Sample Dimensions	4 (Diameter) x 2 (Thickness)	mm	Dimensions of the workpiece sample
Initial Carbon Content (Ti-6Al-4V)	3.01	% (Wt%)	Before thermal analysis
Final Carbon Content (Argon)	23.31	% (Wt%)	After heating in Argon (Diffusion product: TiC)
Final Carbon Content (Air)	4.52	% (Wt%)	After heating in Air (Oxidation product: CO, CO₂)
Critical Bonding Temperature (Ti Alloy)	760, 740, 900	°C	Reported critical temperatures for tool/workpiece bonding [5]
Excess Free Energy of Carbon (920 °C)	39.727	kJ/mol	Used in Gibbs free energy calculation
Carbon Solubility in Ti Alloy (1500 K)	2.37 x 10^-2	N/A	Highest calculated solubility (Table 2)
Key Reaction Product (Argon)	TiC, C (Graphite), Ti₂O₃, TiO₂	N/A	Confirmed by XPS analysis
Key Reaction Product (Air)	TiO₂	N/A	Confirmed by XPS analysis (Oxidation dominant)

Key Methodologies

The research employed simultaneous thermal analysis (DTA/TG) coupled with advanced surface characterization techniques to isolate the thermochemical wear mechanisms.

Sample Preparation: Single-crystal diamond and Ti-6Al-4V samples (4 mm x 2 mm) were meticulously cleaned using ultrasonic acetone baths to ensure pristine contact surfaces.
Thermal Analysis Setup: A TGA1600 simultaneous thermal analyzer was used. The SCD crystallographic plane was placed in direct contact with the Ti-6Al-4V specimen within an aluminum oxide crucible.
Controlled Heating Profile: Samples were subjected to a linear temperature ramp from 293 K up to 1473 K (1200 °C) at a controlled rate of 10 K/min.
Atmosphere Control: Experiments were conducted under two distinct environments:
- Anaerobic: Continuous Argon gas flow (40 mL/min) to simulate diffusion wear conditions.
- Aerobic: Continuous Air flow (40 mL/min) to simulate oxidation wear conditions.
Post-Experiment Characterization:
- Scanning Electron Microscopy (SEM) and Energy Dispersive X-ray Spectroscopy (EDS) were used to analyze surface morphology and quantify elemental composition changes (specifically carbon diffusion).
- X-ray Photoelectron Spectroscopy (XPS) was utilized to determine the binding energy of carbon and titanium atoms, confirming the formation of reaction products like TiC and TiO₂.

6CCVD Solutions & Capabilities

The findings underscore the critical need for high-purity, structurally perfect SCD materials to resist the high-temperature chemical attack encountered when machining reactive alloys like Ti-6Al-4V. 6CCVD is uniquely positioned to supply the necessary materials and customization for both fundamental research and industrial tool development.

Applicable Materials

To replicate or extend this research, engineers require diamond materials optimized for thermal and chemical stability:

Optical Grade Single Crystal Diamond (SCD): Recommended for ultra-precision tool applications. Our SCD is grown via MPCVD, offering exceptional purity and low defect density, which minimizes the initiation sites for graphitization and subsequent carbon diffusion.
- Relevance: High-purity SCD ensures that the observed wear is due solely to the Ti-C reaction, not impurities or structural defects in the tool material.
Electronic Grade Single Crystal Diamond (SCD): For extreme high-temperature or high-power density applications, this grade offers the highest thermal conductivity and structural perfection, crucial for dissipating the concentrated heat identified as the primary wear driver.
Polycrystalline Diamond (PCD) Plates: For large-scale tool inserts or substrates up to 125 mm in diameter, 6CCVD can supply PCD plates with controlled grain size and thickness (0.1 µm to 500 µm), polished to Ra < 5 nm.

Customization Potential

The study highlights the interface reaction as the key failure point. 6CCVD offers specialized services to engineer this interface:

Requirement from Research	6CCVD Customization Capability	Technical Advantage
Interfacial Reaction Control	Custom Metalization Services: We apply diffusion barrier layers (e.g., Ti, W, Pt, Au) directly onto SCD or PCD substrates.	A Tungsten (W) or Titanium (Ti) layer can be engineered to react preferentially or act as a sacrificial barrier, suppressing the direct diffusion of carbon from the diamond tool into the workpiece.
Precise Sample Geometry	Custom Dimensions & Laser Cutting: We provide SCD plates up to 500 µm thick and substrates up to 10 mm thick, cut to precise geometries (e.g., the 4 mm diameter samples used in this study) for thermal analysis or tool insert fabrication.	Ensures consistency and accuracy in R&D experiments and final tool integration.
Surface Finish	Ultra-Precision Polishing: SCD surfaces can be polished to an atomic-level finish (Ra < 1 nm), minimizing friction and localized heating at the tool-workpiece interface.	Directly addresses the paper’s conclusion that reducing cutting temperature is the fundamental measure to suppress wear.

Engineering Support

6CCVD’s in-house PhD team specializes in the material science of CVD diamond and can assist researchers and tool manufacturers in selecting the optimal diamond grade and interface engineering strategy for similar High-Temperature Machining and Thermochemical Wear projects. We provide consultation on:

Optimizing diamond crystallographic orientation for specific cutting applications.
Designing multi-layer metalization schemes for diffusion suppression.
Material selection for high-power density thermal management applications.

For custom specifications or material consultation, visit 6ccvd.com or contact our engineering team directly. We offer global shipping (DDU default, DDP available) to ensure rapid delivery of specialized diamond materials worldwide.

View Original Abstract

Single-crystal diamonds are considered as the best tool material for ultra-precision machining. However, due to its low thermal conductivity, small elastic modulus and strong chemical activity, titanium alloy has poor machinability and is a typically difficult-to-machine material. Excessive tool wear prevents diamonds from cutting titanium alloy. This study conducts a series of thermal analytic experiments under conditions of different gas atmospheres in order to research the details of thermochemical wear of diamonds catalyzed by titanium alloy at elevated temperatures. Raman scattering analysis was performed to identify the transformation of the diamond crystal structure. The change in chemical composition of the work material was detected be means of energy dispersive X-ray analysis. X-ray photoelectron spectroscopy was used to confirm the resultant interfacial thermochemical reactions. The results of the study reveal the diffusion law of the single-crystal diamond under the action of titanium in the argon and air environment. From the experimental results, the product of the chemical reaction corresponding to the interface between the diamond and the titanium alloy sheet could be found. The research results provide a theoretical basis for elucidating the wear mechanism of diamond tools in the titanium alloy cutting process and for exploring the measures to suppress tool wear.

Tech Support

Original Source

DOI: https://doi.org/10.3390/app10134651

References

2019 - An investigation of cutting forces and tool wear in turning of Haynes 282 [Crossref]
2001 - Wear mechanisms of ultra-hard cutting tools materials [Crossref]
1996 - Chemical aspects of tool wear in single point diamond turning [Crossref]
2003 - An overview of the machinability of aeroengine alloys [Crossref]
2012 - Tool wear mechanisms and tool life enhancement in ultra-precision machining of titanium [Crossref]
2003 - Wear mechanisms of new tool materials for Ti-6Al-4V high performance machining [Crossref]
2013 - Tool life and wear mechanisms in high speed machining of Ti-6Al-4V alloy with PCD tools under various coolant pressures [Crossref]