Tribochemical machining of polycrystalline diamond using ferrous tool materials

Abstract

This article studies the tribochemical machining of polycrystalline diamond (PCD) by utilizing ferrous tool material as the cutter. The influence of cutting parameters and different ferrous materials on the material removal rate of the PCD workpiece has been investigated. The material removal rate increases with the increase of the rpm of ferrous “cutter”, AISI 1020 steel is unable realize the tribochemical machining, and the material removal rate of using AISI 1045 steel was higher than that of using W2-21/2 steel, e.g. when rpm was 3000, the material removal rate of using AISI 1045 was 0.059?mm/min, and using W2-21/2 it was 0.020?mm/min. The surface roughness of the machined PCD workpiece using W2-21/2 (0.40?μm) was slightly improved in comparison to that produced using AISI 1045 (0.47?μm). The influence of hydrogen catalysis on tribochemical machining of PCD has been investigated. Compared with no use of steam, if a large amount of steam is continuously injected the material removal rate will significantly increase, e.g. when the rpm was 3000 (using AISI 1045) the material removal rate of no steam was 0.059?mm/min, while with steam it was 0.082?mm/min.     

Tribological Behavior of Si3N4-hBN Ceramic Materials without Lubrication under Different Test Modes

Unlubricated tribological behaviors of silicon nitride–boron nitride (Si ₃ N ₄ -hBN) composites were investigated with two test modes in air by using a pin-on-disc tribometer. Under upper-disc-on-bottom-pin test mode, the addition of hBN to Si ₃ N ₄ resulted in a significant decrease of the friction coefficient, from 0.54 for Si ₃ N ₄ against Si ₃ N ₄ to 0.19 for Si ₃ N ₄ -20% hBN against Si ₃ N ₄ . The surface analysis indicated that a tribochemical film consisting of SiO₂ and H ₃ BO ₃ was formed on the wear surfaces. The formation of tribochemical film might be attributed to the embedment of wear debris into the spalling pits on the wear surfaces of Si ₃ N ₄ -hBN specimen. The wear debris reacted with moisture in air, and the resultant tribochemical film lubricated the wear surfaces. Under upper-pin-on-bottom-disc test mode, the wear mechanism was dominated by abrasive wear, and no tribochemical products could be detected on the wear surfaces. A slight decrease of the friction coefficient, from 0.85 for Si ₃ N ₄ /Si ₃ N ₄ to 0.56 for Si ₃ N ₄ /Si ₃ N ₄ -30% hBN, was obtained, which might be attributed to the layered structure of hBN.     

Tribochemical Effects on Tribological Properties of Self-Mated Zirconia Ceramic in HFC-134a Gas

Tribochemical effects on the tribological properties of self-mated zirconia ceramic in CF₃CH₂F (HFC-134a) were investigated using a ball-on-disk type environmental tribometer. The friction chamber of the tribometer was attached to a micro-spot X-ray Photoelectron Spectrometer (XPS) for ensuring that surface analysis be conducted without exposuring the frictional surfaces to air. It was found that HFC-134a gas was an effective lubricant for zirconia ceramic, especially at a pressure higher than 10³ Pa. The products of tribochemical reactions between zirconia and HFC-134a molecules were detected. The amount and chemical state of the tribochemical products seemed to control the tribological behaviors. Thus, the role of tribochemical products on the tribological properties of zirconia in HFC-134a gas at 10⁴ Pa was studied in detail under applied loads of 0.6–5.0 N and sliding speed of 0.04–0.35 m/s. It was found that severe tribochemical reactions occurred at low speeds and high loads. The formation of ZrF₄ accelerated the chemical wear of zirconia, and raised the friction. Zirconia ceramic is suitable for use at moderate load and sliding speed under a reactive environment.     

Tribochemical Reactions and Lubricating Effects of Fluorinated Methanes for Al2O3 Ceramic

It has been found that CF₃CH₂F (HFC-134a) gas is an effective lubricant for several ceramics because of the formation of fluorine-containing tribochemical products. To understand the influence of the molecular structure of fluorine-containing gases on the lubricating characteristics, the lubricating effects and tribochemical reactions of some fluorinated methanes for Al₂O₃ ceramic were studied. X-ray Photoelectron Spectroscopy (XPS) and Time-of-Flight Secondary Ion Mass Spectroscopy (TOF-SIMS) were used to identify the chemical structure of tribochemical products. It was found that the friction and wear of Al₂O₃ ceramic were dependent on the molecular structure of the reacting fluorocarbon gases. The lowest friction was obtained in CH₂F₂. CHF₃ showed the best anti-wear effect. The results of surface analyses indicate that greater amounts of tribochemical products are produced when Al₂O₃ rubs in CH₂F₂ than in CF₄ and CHF₃ gases. C–C/C–H/carbon and AlF₃, which are mainly formed on the sliding surface in CH₂F₂, are responsible for the low friction. The mechanism of tribochemical reactions of the different environmental molecules on the nascent surface of Al₂O₃ was also discussed.     

Tribochemical Reactions between Methylated Diamond (111) Surfaces: A Theoretical Study

The possibility of tribochemical reactions between methylated diamond surfaces was studied by quantum chemical Hartree–Fock and B3LYP methods. Lateral sliding of two diamond surfaces cleaved from the diamond crystal lattice and substituted with methyl groups was performed at planar distances of 400 and 350 pm for two models, C₂₈H₄₈ and C₄₆H₇₂. In each case, the calculations suggest that tribochemical reaction is possible. At planar distance of 400 pm, the reaction occurs within a diamond plane, whereas the shorter planar distance allows the reaction to occur between two planes.     

Tribochemical synthesis of zinc ferrite

A comparative tribochemical study of zinc ferrite synthesis from -FeOOH + 2ZnCO₃·3Zn(OH)₂ and -FeOOH + 2ZnCO₃·3Zn(OH)₂ was carried out. It was found that the end product of tribochemical activation is thermally unstable, partially inverse, zinc ferrite, (Zn_0.74Fe_0.26)_tetra[Fe_1.74Zn_0.26]_octaO₄. The synthesis kinetics is rate-limited by the tribochemical dehydration of the two polymorphous forms of Fe(III) oxyhydroxides and is considerably higher for the -FeOOH + 2ZnCU₃ · 3Zn(OH)₂ system.     

Tribochemical effects on the friction and wear behaviors of diamond-like carbon film under high relative humidity condition

Friction and wear behaviors of diamond-like carbon (DLC) film in humid N₂ (RH-100%) sliding against different counterpart ball (Si₃N₄ ball, Al₂O₃ ball and steel ball) were investigated. It was found that the friction and wear behaviors of DLC film were dependent on the friction-induced tribochemical interactions in the presence of the DLC film, water molecules and counterpart balls. When sliding against Si₃N₄ ball, a tribochemical film that mainly consisted of silica gel was formed on the worn surface due to the oxidation and hydrolysis of the Si₃N₄ ball, and resulted in the lowest friction coefficient and wear rate of the DLC film. The degradation of the DLC film catalyzed by Al₂O₃ ball caused the highest wear rate of DLC film when sliding against Al₂O₃ ball, while the tribochemical reactions between DLC film and steel ball led to the highest friction coefficient when sliding against steel ball.     

Sliding friction and wear performance of Ti6Al4V in the presence of surface-capped copper nanoclusters lubricant

The friction and wear properties of Ti₆Al₄V sliding against AISI52100 steel ball under different lubricative media of surface-capped copper nanoclusters lubricant—Cu nanoparticles capped with O,O′-di-n-octyldithiophosphate (Cu-DTP), rapeseed oil and rapeseed oil containing 1 wt% Cu-DTP was evaluated using an Optimol SRV oscillating friction and wear tester. The wear mechanism was examined using scanning electron microscopy (SEM) and X-ray photoelectron spectrosmeter (XPS). Results indicate that Cu-DTP can act as the best lubricant for Ti₆Al₄V as compared with rapeseed oil and rapeseed oil containing 1 wt% Cu-DTP. The applied load and sliding frequency obviously affected the friction and wear behavior of Ti₆Al₄V under Cu-DTP lubricating. The frictional experiment of the Ti₆Al₄V sliding against AISI52100 cannot continue under the lubricating condition of rapeseed oil or rapeseed oil containing 1 wt% Cu-DTP when the applied load are over 100 N. Surprisingly, the frictional experiment of Ti₆Al₄V sliding against AISI52100 steel can continue at the applied load of 450 N under Cu-DTP lubricating. The tribochemical reaction film containing S and P is responsible for the good wear resistance and friction reduction of Ti₆Al₄V under Cu-DTP at the low applied load. However, a conjunct effect of Cu nanoparticle deposited film and tribochemical reaction film containing S and P contributes to the good tribological properties of Ti₆Al₄V under Cu-DTP at the high-applied load.     

Tribological Behavior of 1-Methyl-3-Hexadecylimidazolium Tetrafluoroborate Ionic Liquid Crystal as a Neat Lubricant and as an Additive of Liquid Paraffin

Ionic liquid crystal (ILC), 1-methyl-3-hexadecylimidazolium tetrafluroborate, was synthesized. The tribological behavior of ILC was evaluated using a four-ball machine at 80 °C. X-ray photoelectron spectroscopic analysis shows that ILC takes part in tribochemical reactions to generate tribochemical products such as B₂O₃, FeF₂, and/or FeF₃, and amine which form a protective film on sliding steel surface, resulting in reduced friction and wear. Besides, ILC 1-methyl-3-hexadecylimidazolium tetrafluoroborate is completely transformed from solid state to liquid crystalline phase at 80 °C, which facilitates the ordered arrangement of its long alkyl chain on sliding steel surface and helps to improve the tribological properties. When the ILC is used as an additive of liquid paraffin (LP), it contributes to reduce friction and wear and increase the load-carrying capacity of the base stock both at room temperature and 80 °C. The reason might lie in that a small amount of F from ILC takes part in tribochemical reactions to generate tribochemical products that form a protective film on sliding steel surface, and friction-induced heat accelerates the transition of as-synthesized ILC to a mesophase and the ordered arrangement of its long alkyl chain on sliding steel surface, both resulting in improved load-carrying capacity and anti-wear ability of the ILC.     

Quantum mechanochemistry understanding of tribochemical reactions

Abstract

The conceptual framework of quantum mechanochemistry for tribochemical and mechanochemical systems has been developed that is constructed from density functional theory, Lewis acid-base theory (particularly Lewis acid-base reaction chemistry theory), minimisation of energy gaps of solids (metals and non-metals) and frontier molecular orbitals of chemical systems (atoms, radicals, ions, molecules and macromolecular assemblies) under shearing stress, and exoelectron emission in sliding contacts. Quantum mechanochemistry is oriented to understand fundamental issues in tribochemistry and lubrication chemistry, and to formulate tribochemical design principles for lubrication excellence of tribochemical systems. Quantum mechanochemistry concepts and principles are also expected to shed light on the interaction chemistry of additive components and packages in lubricants for tribometric addition and synergism.     

Improved wear resistance of Si3N4 tool inserts by addition of Al2O3 platelets

In the present work, Si₃N₄ matrix composites reinforced with different amounts of Al₂O₃ platelets (0, 30 and 50vol%) were produced with the aim of increasing the tribochemical resistance in the machining of steels. Tool wear was related to the linear increase of the main cutting force (F_c) with time (dF_c/dt); a real-time parameter that can be used to assess the cutting edge damage and to stop machining before the tool fails. For all machined steels, tool wear resistance increased with increasing Al₂O₃ platelet content.     

Tribological Behaviors of 52100 Steel in Carbon Dioxide Atmosphere

The tribological behavior of 52100 steel in a carbon dioxide (CO₂) atmosphere was investigated using a reciprocating ball-on-disk tribometer. X-ray photoelectron spectroscopy (XPS) was used to identify the adsorbed surface layers and tribochemical products. We found that CO₂can substantially reduce friction and wear of the steel. Adsorbed and reacted surface layers containing iron carbonate and/or bicarbonate play an important role in reducing friction. A disk, exposed once to CO₂atmosphere, also shows a low friction for a long time even in a vacuum environment. An optimum CO₂pressure exists for effectively reducing friction and wear. A low-pressure CO₂atmosphere is insufficient to produce iron carbonate. In contrast, high pressure engenders serious chemical wear.     

Tribological Characteristics and Tribochemical Reactions of Various Ceramics Lubricated with HFC-134a Gas

The role of tribochemical products in the friction and wear reduction of ceramics with different fractional ionic character in CF₃CH₂F (HFC-134a) gas was investigated using a ball-on-disk type tribometer. Without exposure to air, the wear tracks on the disks were characterized with the aid of a micro-spot X-ray Photoelectron Spectroscope (XPS) whose analytical chamber was connected to the friction chamber of the tribometer. Further, the adsorption and desorption behaviors of HFC-134a molecules on the nascent surfaces of the ceramics were studied using an adsorption test apparatus in high vacuum. It was found that the lubricating effect of HFC-134a gas was closely related to the fractional ionic or covalent characters of the ceramics. HFC-134a gas was more effective in lubricating ionic ceramics than the covalent ceramics. XPS analysis revealed that metal fluorides were mainly formed on the frictional surfaces of the ionic ceramics, whereas the composition of the tribochemical products on the frictional surfaces of the other ceramics was complicated. The adsorption tests proved that HFC-134a was decomposed to an olefin CF₂=CHF on the nascent surfaces of the ionic ceramic Al₂O₃ and the covalent ceramics. However, the formation of organic fluorine-containing compounds was not detected on the frictional surfaces of the ionic ceramics by XPS. This result implies that the mechanism of tribochemical reactions is strongly dependent on the bond type of ceramics. It is concluded that the low friction and wear of the ionic ceramics in HFC-134a gas result from the metal fluorides formed with high surface concentration on the sliding surfaces.     

Tribochemical Behavior of Ashless Dialkyl Dithiophosphate Ester as an EP/AW Additive in Mineral Oil for Steel–Aluminum Contact

Dialkyl dithiophosphate ester (DDPE) used as an extreme pressure/antiwear (EP/AW) additive in mineral base oil (BO) was introduced to a steel–aluminum contact in this study. The tribological performance of DDPE was explored by means of a universal tribotester under different loads and durations. The worn aluminum surface topographies were observed and photographed via laser scanning confocal microscopy (LSCM) and scanning electron microscopy (SEM). Tribochemical interactions between the additive and aluminum surface were investigated using energy-dispersive spectroscopy (EDS) and X-ray photoelectron spectroscopy (XPS). The distinction of chemical structure between lubricant untapped and the counterpart retrieved after a 3-h sliding process was detected by Fourier transform infrared spectroscopy (FTIR). The friction coefficient of a BO + DDPE-lubricated friction pair under 300 N shows the lowest value. LSCM and SEM images show that the aluminum surface lubricated with BO + DDPE was well protected under a high loading condition of 300 N, and the 3-h sliding process deteriorated the surface topography. However, DDPE was not able to offer an effective lubricating film under a mild condition of 50 N. EDS results of S and P elements on the worn surface indicate that a tribochemical film was generated under 300 N in the sliding process. XPS results further show that the chemical compounds in the tribochemical film included Al₂S₃, Al₂(SO₄)₃, AlPO₄, and Al₂O₃. The P-containing compound in the tribofilm acted as a sacrificial layer, whereas the S-containing compounds were more durable. FTIR analyses demonstrate that the phosphorus–sulfur double bond was broken up due to the tribochemical interactions.     

Influence of Sliding Speed on the Tribological Characteristics of Si3N4-hBN Ceramic Materials

The influence of sliding speed on the unlubricated tribological behaviors of silicon nitride–boron nitride (Si₃N₄-hBN) composites was investigated with two modes in air by a pin-on-disc tribometer. Using the upper disc–on–bottom pin test mode, as the sliding speed increased, the friction coefficient of the sliding pairs showed an upward trend; for example, from 0.18 at the sliding speed of 0.40 m/s to 0.54 at the sliding speed of 1.31 m/s for the Si₃N₄/Si₃N₄–20% hBN pair. The surface analysis indicated that a tribochemical film consisting of SiO₂ and H₃BO₃ formed on the wear surfaces of the Si3N4/Si3N4–20% hBN sliding pair at sliding speeds of 0.40 and 0.66 m/s. Moreover, the formation of this film lubricated the wear surfaces. At the sliding speed of 1.31 m/s, no tribochemical film formed on the wear surfaces, most likely due to the increase in surface temperature. In the upper pin–on–bottom disc test mode, the wear mechanism was dominated by abrasive wear, and no tribochemical products could be detected on the wear surfaces. The increase in sliding speed weakened the degree of abrasive wear, leading to a decrease in the friction coefficients.     

Friction and Wear Properties of Cyanex 302-Modified MoS2 Micro-Sized Spheres as Additive in Liquid Paraffin

The friction and wear properties of MoS ₂ micro-sized spheres (MS-MoS₂) modified by Cyanex 302 (bis(2,4,4-trimethylpentyl) monothiophosphinic acid) as additive in liquid paraffin (LP) were studied and compared with those of commercial colloidal MoS ₂ (CC-MoS ₂ ) on a four-ball tester and an Optimol SRV oscillating friction and wear tester in a ball-on-disc contact configuration. The worn surfaces were examined with SEM and XPS, respectively. The results showed that the Cyanex 302-modified MS-MoS ₂ was a better extreme-pressure and antiwear and friction-reducing additive in LP than CC-MoS ₂ . The boundary lubrication mechanism could be deduced as the effective chemical adsorption film formed by the alkyl and active elements (S, O, and P) in Cyanex 302 and tribochemical reaction and deposition film containing MoS ₂ , Fe ₂ O ₃ , and FePO ₄ . Moreover, the coexistence of sliding and rolling frictions in the lubricant of MS-MoS ₂ /LP also contributed to the enhanced tribological properties.     

Study on the tribological properties of surfactant-modified MoS2 micrometer spheres as an additive in liquid paraffin

Tribological properties of MoS₂ micrometer spheres modified by self-prepared surfactant as an additive in liquid paraffin (LP) are studied and compared with those of the commercial colloidal MoS₂ on a four-ball tester and an Optimol SRV oscillating friction and wear tester. The worn surfaces are examined with SEM and XPS, respectively. Results show that MoS₂ micrometer sphere is a much better extreme-pressure additive and anti-wear and friction-reducing additive in LP than the commercial colloidal MoS₂. The boundary lubrication mechanism can be deduced as an effective chemical adsorption protective film formed by the long chain alkyl and active elements (S and N) in the prepared surfactant and tribochemical reaction film composed of the tribochemical reaction products of the additive. Moreover, sliding and rolling frictions exist simultaneously in the MoS₂ micrometer spheres /LP lubricating system, which also do more contributions to the good tribological properties.     

The tribological properties and action mechanism of non-active organic molybdate ester and its combination with ZDDP

A non-active molybdate ester (ME) was synthesized in a batch process. Its tribological performance and its synergistic effect with ZDDP in 5CST were evaluated using a four-ball machine, and the chemistry of tribofilms was analyzed with XANES. The results indicate that ME possesses excellent anti-wear and friction-reducing properties, not load-carrying capacity. Both ME and ZDDP show excellent synergistic tribological behavior in 5CST. According to the XANES results, the tribochemical films generated from ME alone are mainly composed of MoO₃, and the tribochemical films generated from the oil blends containing ME and ZDDP consist mainly of MoS₂, sulphate and polyphosphate.     

Friction and wear properties of CN<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>/SiC in water lubrication

Amorphous carbon nitride coatings (a-CN_x) were deposited on SiC disk by ion beam assisted deposition (IBAD). The tribological behavior of a-CN_x coating sliding against SiC ball in water was investigated and compared with that of SiC/SiC system at room temperature. The influences of testing conditions on friction coefficient and specific wear rate of both kinds of tribopairs were studied. The worn surfaces on disks were observed by scanning electron microscope (SEM). The results indicate that the running-in period of a-CN_x/SiC was shorter than that of SiC/SiC system in water. At a sliding velocity of 120 mm/s, the mean steady-state friction coefficients of SiC/SiC (0.096) was higher than that of a-CN_x/SiC (0.05), while at 160 mm/s, lower friction coefficient (0.01) was obtained for SiC/SiC in water. With an increment of normal load, the mean steady-state friction coefficients after running-in first decreased, reaching a minimum value, and then increased. For self-mated SiC, the specific wear rate of SiC ball was a little higher than that of SiC disk, while for a-CN_x/SiC, the specific wear rate of SiC ball were 10 times smaller than that of a-CN_x coating. Furthermore, the specific wear rate of SiC ball sliding against a-CN_x coating was reduced by a factor up to 100~1000 in comparison to that against SiC in water. The wear mechanism of SiC/SiC system in water is related to micro-fracture of ceramic and instability of tribochemical reaction layer. Conversely, wear mechanism for a-CN_x/SiC is related to formation and transfer of easy-shear friction layer.     

Combined in situ (ATR FT-IR) and ex situ (XPS) Study of the ZnDTP-Iron Surface Interaction

Attenuated total reflection infrared (ATR FT-IR) and X-ray photoelectron spectroscopy (XPS) have been used for the in situ and ex situ characterization of thermal and tribological films formed on iron from a commercial zinc dialkyldithiophosphate (ZnDTP). From in situ ATR FT-IR analysis, information on the chemical changes occurring at the iron/lubricant additive interface was obtained during heating and sliding at high temperatures. Different mechanisms and chemical compositions have been found for the thermal and tribochemical reactions between the ZnDTP and the iron surface under the experimental conditions used in this work. Both the ATR FT-IR and the XPS results show the decomposition of ZnDTP with the formation of polyphosphates following thermal testing at 150°C. However, after tribological testing at the same temperature an inorganic phosphate film has been detected on the iron surface instead.