Optimized Hot Pressing of High-Speed Steel–Bronze Composites for Diamond-Reinforced Tool Applications

At a Glance

Metadata	Details
Publication Date	2025-08-26
Journal	Materials
Authors	Filip Průša, A. Romański, M. Książek, Hana Thürlová, Dorota Tyrała
Institutions	University of Chemistry and Technology, Prague, AGH University of Krakow
Analysis	Full AI Review Included

Executive Summary

This study successfully optimized the hot-pressing parameters for ASP60 high-speed steel (HSS) composites using CuSn20 bronze alloy as a densification aid for diamond-reinforced tools.

Optimal Processing Conditions: The best results were achieved at a compaction temperature of 1050 °C with 9.8 wt.% CuSn20 addition, yielding minimal residual porosity and maximum mechanical strength.
Densification Mechanism: CuSn20 significantly reduced porosity (down to ~3.7%) by partially melting (onset ~778 °C) during compaction, acting as a transient liquid binder that facilitates particle rearrangement and void filling.
Mechanical Performance: The optimized matrix exhibited a maximum bending strength of 374.51 ± 36.73 MPa. Hardness measurements (HV30 and HRC) confirmed high strength, significantly exceeding low-alloy steel matrices hot-pressed at lower temperatures.
Tribological Enhancement: The incorporation of CuSn20 consistently lowered the coefficient of friction across all tested temperatures (up to 800 °C) due to its self-lubricating properties and localized melting near 800 °C.
Extreme Wear Resistance: The ASP60 matrix demonstrated zero measurable wear under test conditions, attributed to the deformation-induced transformation of retained austenite into highly wear-resistant martensite.
Tool Potential: The resulting composite material (ASP60 + CuSn20 + TiC/Diamond) shows strong potential for aggressive wire sawing and stone-cutting applications, offering superior thermal stability compared to commercial matrices (potentially operating above 750 °C).

Technical Specifications

Parameter	Value	Unit	Context
Optimal Compaction Temperature	1050	°C	ASP60 + 9.8 wt.% CuSn20
Maximum Compaction Pressure	35	MPa	Applied at final temperature
Optimal Residual Porosity (Archimedes)	3.70 ± 0.01	%	ASP60 + CuSn20 at 1050 °C
Maximum Bending Strength (σ_bending)	374.51 ± 36.73	MPa	ASP60 + CuSn20 matrix at 1050 °C
Diamond Composite Strength (σ_bending)	359.1 ± 26.5	MPa	ASP60 + CuSn20 + 20C at 1050 °C
ASP60 Median Particle Size (D₅₀)	62.0	µm	Water-atomized powder
CuSn20 Median Particle Size (D₅₀)	22.8	µm	Gas-atomized powder
CuSn20 Partial Melting (Peritectic)	~778	°C	Second endothermic peak (DSC)
ASP60 Hardness (Crack Site, 1050 °C)	906.0	HV30	ASP60 + CuSn20 composite
ASP60 Hardness (Crack Site, 1050 °C)	64.8	HRC	ASP60 + CuSn20 composite
ASP60 Oxygen Content Reduction	0.285 to 0.120	wt.%	Confirms carbothermal reduction during DSC
Diamond Reinforcement	60/80 mesh, c = 20	mesh, carat cm^-3	TiC-coated synthetic diamond grits

Key Methodologies

I. Powder Characterization and Preparation

Base Materials: ASP60 HSS (water-atomized) and CuSn20 bronze (gas-atomized).
Composition Analysis: XRF confirmed ASP60 contained high V (8.250 wt.%) and W (7.270 wt.%). CuSn20 composition was 80.587 wt.% Cu and 19.314 wt.% Sn.
Phase Identification (XRD): ASP60 showed α-Fe, retained γ-Fe, Vanadium Carbide (VC), and Cobalt Carbide (Co₂C). CuSn20 showed metastable intermetallic phases (δ-phase Cu₄₁Sn₁₁ and ε-phase Cu₃Sn).
Thermal Analysis (DSC):
- ASP60: Irreversible exothermic peaks (650 °C, 900 °C, 1100 °C) confirmed surface oxide reduction by carbon. Endothermic peaks identified martensite-to-austenite transformation (700-860 °C) and carbide dissolution (>1200 °C).
- CuSn20: Endothermic peaks confirmed partial melting (peritectic reaction) at ~778 °C and complete melting above 930 °C.
Diamond Preparation: Synthetic diamond grits (60/80 mesh) were used, commercially pre-coated with a thick TiC layer.

II. Hot Pressing (HP) Compaction Cycle

Equipment: UNIDIAMOND DC HP uniaxial hot press using a graphite mold.
Compaction Temperatures Tested: 950 °C, 1000 °C, and 1050 °C.
CuSn20 Content Tested: 14 wt.% (for 950 °C and 1000 °C) and 9.8 wt.% (for 1050 °C, based on ASP60 porosity results).
Staged Pressure Application (3 min dwell time):
1. Up to 750 °C: 15 MPa.
2. Above 750 °C: Increased to 20 MPa.
3. At Final Temperature (950/1000/1050 °C): Increased to 35 MPa.

III. Post-Processing and Testing

Porosity Measurement: Determined using both Archimedes method (paraffin wax sealed) and dimensional analysis.
Mechanical Testing: Three-point bending tests (flexural strength) and Vickers (HV30) / Rockwell (HRC) hardness tests on both tensile (porous) and compressive (crack) sides.
Microstructural Analysis: SEM and EDS were used for fractographic analysis of fracture surfaces and elemental mapping.
Tribological Testing: Ball-on-disc setup (Al₂O₃ ball, 5 N load, 0.5 mm/s) to measure the coefficient of friction at 25 °C, 300 °C, 500 °C, and 800 °C.

Commercial Applications

The optimized ASP60-CuSn20 composite material is highly suitable for demanding applications in abrasive environments, particularly where high wear resistance and thermal stability are critical.

Stone Processing and Quarrying:
- Aggressive wire sawing tools.
- Segments for cutting hard abrasive stones (e.g., granite and basalt).
- Low-speed sawing operations in quarry environments.
Advanced Cutting Tools:
- Diamond-reinforced tools requiring matrices that maintain integrity and strength at elevated operational temperatures (potentially exceeding 750 °C).
High-Performance Powder Metallurgy (P/M):
- Manufacturing of near-full-density HSS components where liquid phase sintering (enabled by CuSn20) is used to minimize residual porosity.
Extreme Wear Components:
- Industrial parts requiring exceptional resistance to abrasive wear, leveraging the ASP60 matrix’s ability to form martensite under deformation.

View Original Abstract

This study investigates the optimization of hot-pressing parameters for ASP60 high-speed steel composites incorporating CuSn20 bronze alloy for use in diamond-reinforced tool applications. ASP60 and CuSn20 powders were characterized using XRD, XRF, DSC, SEM, and laser diffraction. The effects of CuSn20 addition at varying concentrations and compaction temperatures (950-1050 °C) on porosity, mechanical properties, and tribological performance were evaluated. Results showed that adding CuSn20 significantly reduced residual porosity due to its partial melting during compaction, which facilitated particle rearrangement and densification. Optimal conditions were identified at 1050 °C with 9.8 wt.% CuSn20, yielding minimal porosity (~3.7%) and the highest bending strength (374.51 ± 36.73 MPa). The optimized matrix was further reinforced with TiC-coated diamond particles at concentration c = 20, producing a composite material with excellent wear resistance, despite minor defects in the TiC coating observed on fracture surfaces. Tribological testing demonstrated that CuSn20 consistently lowered friction coefficients across all tested temperatures due to its self-lubricating properties and partial melting at elevated temperatures. Furthermore, ASP60 exhibited no measurable wear, making it a promising candidate for highly demanding applications. Overall, the study demonstrates that CuSn20 alloy enhances densification, mechanical performance, and tribological behavior of ASP60-based composites, indicating their strong potential for aggressive wire sawing and stone-cutting tool applications.

Tech Support

Original Source

DOI: https://doi.org/10.3390/ma18173999

References

2020 - The manufacturing and the application of polycrystalline diamond tools—A comprehensive review [Crossref]
2001 - Consolidation of diamond tools using Cu-Co-Fe based alloys as metallic binders [Crossref]
2018 - Investigating the effect of brazing parameters on joint quality in DIN 2391 steel material and natural stone cutting core sockets joined by using induction brazing method [Crossref]
2024 - Improving wear resistance and machining performance of diamond tools in ferrous metals cutting: A review [Crossref]
2025 - Wear mechanisms of diamond tools and their material basis in machining iron-based materials [Crossref]
2018 - New Diamond-Based Superhard Materials. Production and Properties. Review [Crossref]
2020 - A critical review on the chemical wear and wear suppression of diamond tools in diamond cutting of ferrous metals [Crossref]
2025 - Comparative study of brazing granite/marble diamond segments for applications in decorative stone cutting machines: Microstructural and microhardness characterization with Cu/Ag-based filler metals [Crossref]