High temperature creep deformation of nanocrystalline diamond films
At a Glance
Section titled âAt a Glanceâ| Metadata | Details |
|---|---|
| Publication Date | 2022-01-01 |
| Journal | International Journal of Materials Research (formerly Zeitschrift fuer Metallkunde) |
| Authors | Markus Mohr, H.âJ. Fecht, K. A. Padmanabhan |
| Institutions | UniversitÀt Ulm, Anna University, Chennai |
| Analysis | Full AI Review Included |
High Temperature Creep Deformation of Nanocrystalline Diamond Films: 6CCVD Technical Analysis
Section titled âHigh Temperature Creep Deformation of Nanocrystalline Diamond Films: 6CCVD Technical AnalysisâThis document analyzes the findings of Mohr et al. (2022) regarding the high-temperature creep behavior of nanocrystalline diamond (NCD) films and outlines how 6CCVDâs advanced MPCVD capabilities can support and extend this critical research into high-performance material applications.
Executive Summary
Section titled âExecutive SummaryâThis research demonstrates that nanocrystalline diamond (NCD) films exhibit time-dependent inelastic deformation (creep) at temperatures and stresses significantly lower than those required for single-crystal diamond (SCD).
- Core Achievement: Observation of steady-state creep in NCD films at 1000 °C under low applied stresses (0.3-0.8 GPa).
- Mechanism Identification: Creep behavior is dominated by Grain-Boundary Sliding (GBS), evidenced by a low creep stress exponent (n â 1.7), rather than traditional crystal plasticity.
- Material Properties: The NCD films, synthesized via HFCVD, exhibited a fine grain size (7.9 nm), a high hardness (H = 36 ± 6 GPa), and a reduced elastic modulus (E = 403 ± 55 GPa).
- Density Reduction: The measured mass density (2.77 ± 0.13 g cm-3) is significantly lower than SCD (3.51 g cm-3), attributed to the high volume fraction of grain boundaries and porosity.
- Modeling Validation: The steady-state creep results are quantitatively consistent with a physics-based model for grain/interphase boundary sliding controlled flow.
- Application Relevance: These findings are crucial for designing robust diamond coatings and sensor devices operating under high thermal and mechanical loads, where long-term stability is paramount.
Technical Specifications
Section titled âTechnical SpecificationsâThe following hard data points were extracted from the experimental results on nanocrystalline diamond films:
| Parameter | Value | Unit | Context |
|---|---|---|---|
| Film Thickness (h) | 50 | ”m | Used for 3-point bending samples |
| Average Grain Size (L) | 7.9 | nm | Estimated via XRD (111) peak broadening |
| Creep Temperature (T) | 1000 | °C | Temperature where inelastic creep was observed |
| Elastic Limit Temperature | 700 | °C | Deformation was fully elastic below this point |
| Applied Stress Range (Ï) | 0.3 - 0.8 | GPa | Maximum stress applied during testing |
| Equivalent Steady State Stress (Ïss) | 0.08 - 0.13 | GPa | Calculated equivalent stress range |
| Steady State Strain Rate (Δss) | 10-7 - 5 x 10-7 | s-1 | Measured at 1000 °C |
| Creep Stress Exponent (n) | 1.69 - 1.79 | Dimensionless | Consistent with GBS (1 < n < 3) |
| Hardness (H) | 36 ± 6 | GPa | Measured via nanoindentation (Oliver-Pharr method) |
| Elastic Modulus (E) | 403 ± 55 | GPa | Measured via nanoindentation (as-grown) |
| Mass Density | 2.77 ± 0.13 | g cm-3 | Reduced density compared to bulk SCD (3.51 g cm-3) |
| Test Environment Pressure | 10-5 to 10-6 | mbar | Ultra-high vacuum (UHV) |
Key Methodologies
Section titled âKey MethodologiesâThe experimental procedure focused on synthesizing high-quality NCD films and performing precise three-point bending creep tests in a controlled high-temperature, ultra-high vacuum environment.
- Substrate Preparation: 4-inch (10.16 cm) silicon wafers were pretreated using ultrasonic seeding to achieve a high seeding density (â 1011 cm-2).
- NCD Synthesis: Nanocrystalline diamond films were grown via Hot Filament CVD (HFCVD) using a CH4/H2/NH3 gas mixture to a thickness of 50 ”m.
- Sample Structuring: Free-standing rectangular samples (4 mm x 13 mm x 50 ”m) were fabricated by structuring the film using a 1064 nm diode laser, followed by dissolution of the silicon substrate in potassium hydroxide (KOH) solution.
- Creep Test Setup: A simple three-point bending apparatus, constructed of molybdenum, was used. The setup was placed inside an evacuated tube furnace.
- Environmental Control: Experiments were conducted in ultra-high vacuum (10-5 to 10-6 mbar) to prevent the strong reaction of diamond with oxygen at elevated temperatures.
- Load Application: Constant loads (F = 0.414 N, 0.443 N, 0.666 N) were applied by placing corresponding masses on top of the punch.
- Displacement Measurement: Downward displacement at the load point was measured remotely using optical photographs taken by a camera mounted in a fixed position relative to the bending setup.
- Characterization: X-ray diffraction (XRD) was used to confirm the lack of grain growth after annealing (90 min at 1000 °C). Nanoindentation was used to determine elastic modulus (E) and hardness (H).
6CCVD Solutions & Capabilities
Section titled â6CCVD Solutions & Capabilitiesâ6CCVD is uniquely positioned to support researchers replicating or extending this high-temperature mechanical study. While the paper utilized HFCVD, 6CCVD specializes in MPCVD (Microwave Plasma CVD), offering superior purity, control, and scalability essential for advanced materials research.
Applicable Materials for Replication and Extension
Section titled âApplicable Materials for Replication and ExtensionâTo replicate the nanocrystalline structure and investigate the GBS mechanism, 6CCVD recommends the following materials, tailored for mechanical and high-temperature stability:
| 6CCVD Material | Specification | Relevance to Research |
|---|---|---|
| Mechanical Grade PCD | Polycrystalline Diamond (PCD) with controlled grain size (L < 10 nm). | Direct replacement for the NCD film used. MPCVD offers higher purity and better control over sp2 content in grain boundaries, crucial for GBS studies. |
| High-Purity SCD | Single Crystal Diamond (SCD) plates (0.1 ”m - 500 ”m thickness). | Ideal for comparative studies to quantify the difference in creep behavior between GBS-dominated NCD and dislocation-mediated SCD plasticity. |
| Boron-Doped Diamond (BDD) | PCD or SCD doped with Boron. | Allows researchers to investigate the influence of dopants on grain boundary structure and creep kinetics, potentially altering the GBS threshold stress (Ï0). |
Customization Potential for Advanced Mechanical Testing
Section titled âCustomization Potential for Advanced Mechanical TestingâThe success of this research relies heavily on precise sample geometry and environmental control. 6CCVDâs capabilities directly address the experimental requirements:
- Custom Dimensions and Thickness: The paper used 50 ”m thick films structured into 4 mm x 13 mm rectangles. 6CCVD routinely supplies PCD plates up to 125 mm in diameter and offers custom thicknesses ranging from 0.1 ”m to 500 ”m, allowing for optimization of the three-point bending geometry.
- Precision Structuring: We provide advanced laser cutting services to fabricate the exact rectangular or complex geometries required for three-point bending, tensile, or compression creep tests, ensuring high dimensional accuracy.
- Surface Finish: While the NCD films were relatively rough, 6CCVD offers ultra-smooth polishing (Ra < 5 nm for inch-size PCD). A smoother surface finish can minimize surface defects that might act as stress concentrators, ensuring more reliable mechanical data.
- Metalization Services: For future studies requiring integrated strain gauges or heating elements for in situ testing, 6CCVD offers custom metalization (Au, Pt, Pd, Ti, W, Cu) capabilities, which can be applied directly to the diamond surface.
Engineering Support
Section titled âEngineering SupportâThe authors noted the need for future investigation using advanced techniques like FIB preparation and low-voltage TEM to confirm GBS mechanisms. 6CCVDâs in-house PhD team specializes in diamond material science and can provide expert consultation on:
- Material Selection: Optimizing PCD grain size and purity to isolate specific deformation mechanisms (e.g., maximizing GBS contribution).
- Interface Engineering: Assisting with the design of diamond films for high-temperature applications, such as robust sensor devices or wear-resistant coatings, where creep resistance is critical.
- Sample Preparation: Advising on optimal material handling and preparation techniques for subsequent high-resolution structural analysis (e.g., TEM/FIB).
For custom specifications or material consultation, visit 6ccvd.com or contact our engineering team directly.
View Original Abstract
Abstract Diamond displays a combination of unique properties, including the highest hardness among materials, chemical inertness and high thermal conductivity. Therefore, nanocrystalline diamond films offer a huge potential for industrial applications. In fine-grained ceramics as well as metallic materials, high temperature creep deformation is dominated by grain-boundary-deformation mechanisms that become increasingly important with decreasing grain size. In this work we demonstrate that it is possible to inelastically deform nanocrystalline diamond films at elevated temperatures and stresses that are significantly lower than those reported for single-crystal diamond. The initial, isothermal, transient creep flow exhibits a logarithmic character, typical of creep in general. The isothermal steady state creep deformation, which follows transient creep, is analyzed using a physics-based model for grain boundary sliding rate controlled flow.