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6CCVD Research

Influence of the atmosphere and temperature on the properties of the oxygen-affine bonding system titanium-diamond during sintering

At a Glance

Section titled “At a Glance”
MetadataDetails
Publication Date2022-04-21
JournalThe International Journal of Advanced Manufacturing Technology
AuthorsBerend Denkena, Benjamin Bergmann, Andreas Fromm, Christian Klose, Nils Hansen
InstitutionsLeibniz University Hannover
AnalysisFull AI Review Included

Executive Summary

Section titled “Executive Summary”

This research investigates the critical influence of sintering atmosphere and temperature on the properties of novel titanium-diamond abrasive layers designed for high-performance grinding tools.

  • Active Bonding Mechanism: Titanium (Ti) acts as an active bond material, chemically reacting with diamond (carbon) to form adhesive Titanium Carbide (TiC) at the interface, providing superior grain retention compared to conventional mechanical bronze bonds.
  • Atmosphere Dominance: The sintering atmosphere (oxygen partial pressure) was identified as the most significant factor influencing mechanical and thermal properties due to the high oxygen affinity of Ti.
  • Vacuum Optimization: A higher vacuum (Patm,1 ≈ 50 mbar) significantly reduced Ti oxidation during sintering, leading to stronger particle adhesion and improved layer properties.
  • Mechanical Improvement: Higher vacuum resulted in a 38% increase in critical bond stress (σ*) compared to lower vacuum conditions (Patm,2 ≈ 125 mbar) in pure Ti samples sintered at Ts=900 °C.
  • Thermal Improvement: Higher vacuum also yielded a 3.4% increase in thermal conductivity (λ) (18.8 W/(m·K) vs. 18.2 W/(m·K)) at room temperature (Ta=25 °C, Ts=1000 °C).
  • Temperature Effects: Increasing sintering temperature favored TiC formation (confirmed by XRD), which positively influenced bond stress when diamond grains were present, counteracting the general decrease in pure Ti bond strength observed at higher temperatures.
  • Commercial Impact: The resulting high critical bond stresses suggest that titanium-bonded tools will exhibit better macroscopic wear resistance and extended tool life compared to existing metal-bonded systems.

Technical Specifications

Section titled “Technical Specifications”
ParameterValueUnitContext
Bond MaterialPure Titanium (Ti)N/AOxygen-affine active bond
Abrasive MaterialDiamond (D251, blocky)N/AGrain concentration: 25 vol.-%
Sintering MethodFAST (Field Assisting Sintering Technology)N/ADr. Fritsch DSP 510 press
Sintering Temperature Range (Ts)900 to 1100°CRange investigated
High Vacuum Atmosphere (Patm,1)~50mbarLow oxygen content (Higher vacuum)
Low Vacuum Atmosphere (Patm,2)~125mbarHigher oxygen content (Lower vacuum)
Sintering Pressure (ps)3,500N/cm2Constant process parameter
Sintering Holding Time (ts)300sConstant process parameter
Max Critical Bond Stress Increase+38%Patm,1 vs Patm,2 (at Ts=900 °C, 0 vol.-% grain)
Max Thermal Conductivity (λ)18.8W/(m·K)Patm,1, Ta=25 °C, Ts=1000 °C (0 vol.-% grain)
Thermal Conductivity Increase+3.4%Patm,1 vs Patm,2 (at Ta=25 °C, Ts=1000 °C, 0 vol.-% grain)
Confirmed Carbide PhaseTitanium Carbide (TiC)N/AFm-3m structure, lattice parameter a = 432 pm
Ti Phase Transformation (α to ÎČ)882°CInfluences bond strength gradient
Measured Porosity (Patm,2)2.6%Lower porosity sample
Measured Porosity (Patm,1)5.7%Higher porosity sample

Key Methodologies

Section titled “Key Methodologies”

The titanium-diamond composite layers were characterized using a combination of manufacturing, mechanical, thermal, and microstructural analysis techniques:

  1. Powder Mixing: Pure Ti powder and D251 diamond grains (25 vol.-% concentration) were weighed and mixed using a WAB Turbula 3D shaker mixer.
  2. Sintering (FAST): Samples (22 mm diameter, 5 mm height) were hot-pressed in graphite molds using a Dr. Fritsch DSP 510 sintering press. Critical parameters were systematically varied:
    • Sintering Temperature (Ts): 900 °C, 1000 °C, 1100 °C.
    • Sintering Atmosphere (Patm): ~50 mbar (high vacuum) and ~125 mbar (low vacuum).
  3. Mechanical Testing: Critical bond stress (σ*) was determined by performing three-point-flexural tests on the cylindrical specimens until fracture, using a Kistler 9255C dynamometer. Results were adjusted for residual pore volume content (porosity Ί).
  4. Thermal Testing: Thermal diffusivity (α) was measured using a NETZSCH LFA 447 xenon-flash instrument across ambient temperatures (Ta) from 25 °C to 300 °C. Thermal conductivity (λ) was calculated using measured density (Archimedes’ principle) and a temperature-dependent model for specific heat capacity (cp).
  5. Crystallographic Analysis (XRD): X-ray diffraction (XRD) was performed on specimen cross-sections (Seifert XRD 3003 TT, Cobalt target) to identify crystalline phases, specifically confirming the formation of Titanium Carbide (TiC) at the interface.
  6. Microstructural Analysis (SEM/EDS): Scanning Electron Microscopy (SEM) with a backscattered electron detector (BSE) was used to visualize grain retention, fracture behavior, and grain damage (graphitization). Energy-Dispersive X-ray Spectroscopy (EDS) mapping was used to analyze the elemental distribution of Ti, C, and O, quantifying oxidation effects based on sintering atmosphere.

Commercial Applications

Section titled “Commercial Applications”

The development of titanium-diamond abrasive layers with superior adhesive bonding is highly relevant for industries requiring high-performance, long-lasting grinding tools:

  • Advanced Tool Manufacturing: Production of premium metal-bonded grinding wheels, segments, and cutting tools used for demanding material removal applications.
  • Hard Material Processing: Grinding and finishing of extremely hard, wear-resistant materials such as cemented carbides, technical ceramics, and specialized alloys (e.g., nickel-based superalloys).
  • Precision Engineering: Applications where high thermal stability is crucial. The improved thermal conductivity of the Ti bond minimizes heat buildup at the grinding interface, reducing thermal damage to both the tool and the workpiece.
  • Aerospace and Defense: Machining of critical components where tool life and reliability must be maximized, leveraging the high grain retention forces provided by the TiC adhesive bond.
  • Sintering Technology: The findings provide critical process control knowledge for manufacturing any oxygen-affine metal composite, emphasizing the necessity of high vacuum environments (low oxygen partial pressure) during FAST/hot pressing to ensure optimal material properties.
View Original Abstract

Abstract Grinding tools can be manufactured from metal, vitrified, and resin bond materials. In combination with superabrasives like diamond grains, metal-bonded tools are used in a wide range of applications. The main advantages of metal over vitrified and resin bonds are high grain retention forces and high thermal conductivity. This paper investigates the influence of the atmosphere and manufacturing parameters such as sintering temperature on the properties of titanium-bonded grinding layers. Titanium is an active bond material, which can increase the retention of diamond grains in metal-bonded grinding layers. This can lead to higher bond stress and, consequently, decreased wear of grinding tools in use when compared to other commonly used bond materials like bronze. The reason for this is the adhesive bond between titanium and diamond due to the formation of carbides in the interface, whereas bronze can only form a mechanical cohesion with diamond grains. However, when using oxygen-affine metals such as titanium, oxidizing effects could limit the strength of the bond due to insufficient adhesion between Ti-powder particles and the prevention of carbide formation. The purpose of this paper is to show the influence of the sintering atmosphere and temperature on the properties of titanium-bonded diamond grinding layers using the mechanical and thermal characterization of specimens. A higher vacuum ( Δp atm = − 75 mbar) reduces the oxidation of titanium particles during sintering, which leads to higher critical bond stress (+ 38% @ T s = 900 °C) and higher thermal conductivity (+ 3.4% @ T s = 1000 °C, T a = 25 °C). X-ray diffraction measurements could show the formation of carbides in the cross-section of specimens, which also has a positive effect on the critical bond stress due to an adhesive bond between titanium and diamond.

Tech Support

Section titled “Tech Support”

Original Source

Section titled “Original Source”

References

Section titled “References”
  1. 2009 - Manufacturing processes 2 [Crossref]
  2. 2016 - Life cycle and sustainability of abrasive tools [Crossref]
  3. 2007 - Pulvermetallurgie: Technologien und Werkstoffe [Crossref]
  4. 2001 - Inorganic chemistry

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