Superhard pcBN materials with chromium compounds as a binder

Superhard cBN-based materials with Cr3C2, Cr2N and CrB2 binders were sintered in a high-pressure high-temperature (HPHT) toroidal apparatus under a pressure of 7.7 GPa and in the temperature range of 1600-2450°С. Initial mixtures of three compositions were chosen with 60 vol.% of cBN, 35 vol.% of binder phase and 5 vol.% of Al. Phase composition and microstructure of sintered samples were investigated by X-ray analysis and scanning electron microscopy, respectively. Elastic properties were measured using the ultrasonic pulse-echo technique. Composites with Cr3C2 and CrB2 binders sintered at 2000°C have the highest values of hardness

Investigation of the mechanical properties and cutting performance of cBN-based cutting tools with Cr3C2 binder phase.

In order to investigate new materials for metal cutting applications, cubic boron nitride, cutting tools with different amounts of binder phase were sintered in HPHT toroid type apparatus under 7.7 GPa and in temperature range of 1450-2450°C. Initial mixtures of three composition were chosen with 50, 60, 65 vol. % of cBN, 5 vol. % of Al was added to mixture to prevent oxidation. Phase composition, microstructure, elastic properties, hardness, fracture toughness and cutting performance were investigated. The highest value of the mechanical properties and tool life demonstrated samples sintered in temperature range 1850-2150 °C

Understanding wear and interaction between CVD α-Al2O3 coated tools, steel, and non-metallic inclusions in machining

The aluminum oxide-coating on cemented carbide tools used for metal cutting have been regarded as inert during cutting of steels. Because diffusional dissolution is not possible. Chemical degradation of aluminum oxide coatings is often overlooked, especially in the presence of ambient oxygen and non-metallic inclusions. High-pressure diffusion couples, advanced microscopy, and thermodynamics are used to investigate and predict the chemical degradation of aluminum oxide-coated tools. During interactions with steel and different combinations of inclusions with and without ambient oxygen. The results show that alumina is resistant to chemical degradation by steel in the absence of oxygen. However, this is not the case when oxygen and non-metallic inclusions are present. These experiments and microscopy together with the thermodynamic calculations allow for the creation of a method and guidelines for chemical wear modeling and steel inclusion engineering when machining with aluminum oxide-coated tools

Vickers Hardness of Diamond and cBN Single Crystals: AFM Approach

Atomic force microscopy in different operation modes (topography, derivative topography, and phase contrast) was used to obtain 3D images of Vickers indents on the surface of diamond and cBN single crystals with high spatial resolution. Confocal Raman spectroscopy and Kelvin probe force microscopy were used to study the structure of the material in the indents. It was found that Vickers indents in diamond has no sharp and clear borders. However, the phase contrast operation mode of the AFM reveals a new viscoelastic phase in the indent in diamond. Raman spectroscopy and Kelvin probe force microscopy revealed that the new phase in the indent is disordered graphite, which was formed due to the pressure-induced phase transformation in the diamond during the hardness test. The projected contact area of the graphite layer in the indent allows us to measure the Vickers hardness of type-Ib synthetic diamond. In contrast to diamond, very high plasticity was observed for 0.5 N load indents on the (001) cBN single crystal face. Radial and ring cracks were absent, the shape of the indents was close to a square, and there were linear details in the indent, which looked like slip lines. The Vickers hardness of the (111) synthetic diamond and (111) and (001) cBN single crystals were determined using the AFM images and with account for the elastic deformation of the diamond Vickers indenter during the tests

Performance and wear mechanisms of novel superhard diamond and boron nitride based tools in machining Al-SiCp metal matrix composite

Metal matrix composites are the desired materials in aerospace and automotive industries since they possess high specific strength. However addition of reinforcement to the matrix material brings the adverse effects of high wear rate of tool materials used in their machining. The current study addresses the issues of wear and performance of superhard tools when high speed machining cast Al-Si alloy reinforced with particulate SiC (20% vol.). A wide range of developed superhard materials was compared to the commercial PCD tools. Nano grain sized wBN-cBN, binderless cBN; B6O-cBN, nano-diamond with WC binder; diamond/MAX-phase; and diamond/SiC tool materials were employed. Use of nano-diamond/WC and diamond/MAX-phase composites resulted in their rapid deterioration due to primarily adhesive pluck-out of diamond and binder phase. Diamond/SiC material exhibited slightly lower performance than the PCD, with the primary wear being the abrasive on the SiC binder phase. Machining with cBN-based tooling at lower speed lead to formation of stable build-up layer, frequently accompanied by severe seizure of tool and workpiece material. However at speed of 400 m/min the absence of such build-up layer caused rapid tool wear. Presence of chemical and diffusional wear mechanisms for diamond tooling has been confirmed through scanning and transmission electron microscopy. Archard-type model of abrasive tool wear was developed for modelling of tool deterioration for all studied tool materials

Multicomponent binders for PcBN performance enhancement in cutting tool applications

This study proposes a novel design of binders for polycrystalline cubic boron nitride (PcBN) cutting tool materials. Well-known binder phases TiC and TiN were combined with transitional metal nitrides ZrN, VN, and HfN. Performance screenings of longitudinal turning Inconel 718 and AISI 316 L highlighted the superior performance of PcBN materials with mixed TiC-ZrN and TiC-VN binders. These two systems were further sintered in a wider range of temperatures. XRD and STEM-XEDS analysis confirmed mutual dissolution of both TiC and ZrN, and TiC and VN, thus forming two types of solid solutions (Ti,Zr)(C,N) and (Ti,V)(C,N). Extended performance tests showed that tools with TiC-ZrN binder outperform reference PcBN with TiC binder by up to 20% when machining Inconel 718. When machining hardened Caldie tool steel, the performance of tools with TiC-ZrN and TiC-VN binders were 80–90% higher than the reference tools

Extreme Hardness Achievements in Binderless Cubic Boron Nitride Tools

Binderless cubic boron nitride tools are available in two forms: single phase cBN and dual phase wBN/cBN (w is wurtzite phase). In this work, a novel heat treatment process involving surface heating using a continuous wave CO2 laser followed by tandem waterjet quenching of the laser beam path was applied to increase the hardness of both forms of boron nitride. Stress-induced phase transitions and nanometric grain sizes accompanying the rapid quench heat treatment enabled a hardness increase of 20% in single phase cBN (nominal 60 GPa) and 100% in dual phase wBN/cBN (nominal 75 GPa) that attest the ability of cBN to reach the hardness of polycrystalline diamond (65-80 GPa). The effects of laser heat treatment are identified by an examination of the changes in phase and microstructure by Raman spectroscopy, high resolution scanning electron microscopy and X-ray diffraction

Ultrahard boron nitride material through a hybrid laser/waterjet based surface treatment

We report a dual phase boron nitride (BN) material composed of 50% cubic and 50% wurtzite phases that has the same level of hardness as polycrystalline diamond. The dual phase BN material was initially synthesized from high pressure and high temperature consolidation of powder materials and subsequently, a laser/waterjet heat treatment (LWH) was applied to the material surface. The LWH process consisted of heating the sample surface using a continuous wave CO2 laser beam followed by tandem waterjet quenching of the laser irradiated material. The indentation hardness of the as-synthesized material was measured to be nominally 37 GPa. After the heat treatment the indentation hardness increased to nominal values of 75 GPa reaching the hardness of polycrystalline diamond 65-80 GPa. Dispersive Raman spectroscopy, high-resolution scanning electron microscope (HRSEM) and surface grazing XRD were used to characterize the BN phase signatures, grain size changes and phase transitions in both as-synthesized and heat treated material. Comparison of the as-synthesized and heat treated material microstructure revealed that heat treatment resulted in microstructure that consists of large grains; surrounded with regions of nano-grains between larger grains and; formation of solid interlayer along the grain boundaries. The increase in hardness was observed for LWH processing at laser fluence below 35 J/mm(2), and LWH processing above this value resulted in spallation of BN material from the surface. Raman spectrums of the material processed below the laser fluence of 35 J/mm(2) indicated that there are minimal phase transitions in the material; however, above that fluence, BN transformed into hexagonal phase resulting in surface damage through spallation. A combination of amorphous phase formation at the grain boundaries and grain size refinement are suggested as the mechanisms responsible for the LWH processing induced hardness increase. (C) 2015 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved