Counter Material Research Articles

Improvement of Tribology in Sheet Metal Forming of High-Strength Steel Sheets by PVD-Coated Dies

During sheet metal formation, the high strength of sheet material leads to high contact stress between the die and blank material, which results in increased die wear. Moreover, the reduction in the use of lubricants because of environmental concerns has led to greater wear of sheet metal–forming dies. It is important to understand the tribological behavior of the blank die contact so that steps can be taken to reduce the die wear to an acceptable level. Die wear reduction is possible by using alternative die materials, modifying die geometry, or by creating a wear-resistant surface on sheet metal–forming dies using Physical Vapor Deposition (PVD) coatings. PVD coatings have a thickness in the micro range and greatly improve the tribological properties of the die material. In this work, three pins made of AISI D2 steel were coated with Titanium Nitride, Titanium Aluminum Nitride (TiAlN), and Aluminum Chromium Nitride using the PVD process. Friction and wear tests were conducted on the pin-on-disk testing machine as per ASTM G99, Standard Test Method for Wear Testing with a Pin-on-Disk Apparatus. The pins had diameters measuring 10 mm and lengths measuring 35 mm. They were heat treated until they reached 55 HRC and ground to a Ra value of 0.1 µm. A 5-mm-radius tip was provided on one end of the pin. D3 steel was used as counter material (disk). The normal load was 30 N, and the sliding speed was 0.3 m/s. The experiments were conducted in dry contact conditions. Based on the results, it was concluded that TiAlN coatings are an excellent choice to modify friction behavior and improve wear resistance of die material.

Investigation on Friction and Wear Properties of High-Temperature Bearing Steel 9Cr18Mo

This paper presented a study of friction and wear on 9Cr18Mo when rubbed against other materials (steel-304, steel-440C, steel-GCr15 or silicon nitride ceramic ball) at high temperature conditions. Friction and wear tests were carried out with universal a friction and wear testing machine. The wear morphology was analyzed by a Nanovea three-dimensional profilometer and trinocular positive Gang metallurgical microscope. The Vickers hardness of 9Cr18Mo at different temperatures was tested by means of a high temperature vacuum hardometer. Results showed that the friction and wear on the contact surface of the 9Cr18Mo sample are higher when the hardness of counter materials is higher than or similar to that of the sample. Under dry sliding conditions, the 9Cr18Mo sample surface presented various degrees of adhesion, plowing and pit, particularly if tested in the presence of a high temperature environment. During the worn stages, the counter materials on the worn surface successively produced cracks, crack growth, and wear debris under the action of load. Moreover, the frictional pair 9Cr18Mo-ceramic showed good anti-wear behavior at 400 °C that proved the anti high temperature performance of 9Cr18Mo.

Formation of commercially pure titanium with a bimodal nitrogen diffusion phase using plasma nitriding and spark plasma sintering

CP titanium with a bimodal microstructure consisting of a substrate surrounded by a network structure of nitrogen diffusion phase was fabricated by sintering nitrided powders, as a means of improving the mechanical and tribological properties. A nitrogen diffusion layer can be formed on CP titanium powder at temperatures above 873 K. The areal fraction of the nitrogen diffusion phase increased along with the sintering temperature. As results of ball-on-disk dry friction tests, CP titanium fabricated from powder nitrided at 873 K had a lower friction coefficient than compacts fabricated from as-received CP titanium powder. In contrast, adhesion of the counter material was observed over the worn surface of sintered compact fabricated from the powder nitrided at 973 K, which indicates a higher friction coefficient.

Tribological studies comparison between UHMWPE and PEEK for prosthesis application

This work reports on the tribological and surface hardness modifications of ultrahigh molecular weight polyethylene (UHMWPE) and polyether ether ketone (PEEK) after plasma immersion dual ion implantation of nitrogen, oxygen and helium ions at constant energy and fluence. The results show that the hardness and wear rate can be improved in both polymers by an appropriate combination of the bombarding ions. Wear tests were carried out on modified UHMWPE and PEEK against CoCrMo and Al2O3 counter materials, in an adult bovine serum (ABS) medium at 37°C. In particular, the dual bombardment with nitrogen and oxygen in a 3:1 ion fluence ratio provides the highest wear rate reduction on both polymers when sliding against CoCrMo. In the case of the test against Al2O3, the averaged low wear rates were obtained using He/N ion fluencies of 3:1. More specifically, the wear performance of plasma treated PEEK is superior to this shown by UHMWPE.

Structure and Function of Transfer Film Formed from PTFE/PEEK Polymer Blend

Improving the tribological performance of polytetrafluoroethylene (PTFE) resin is important for industrial use of PTFE. An effective way to do this is to blend pure PTFE with another resin material to improve the quality of the transfer film, i.e., adhesion to a counter metallic surface. It is well-known that PTFE/polyetheretherketone (PEEK) polymer blends show significantly less wear than pure PTFE and PEEK. However, the structure and function of the transfer film formed from the blend, which is the key process for reducing friction and wear, have not yet been understood well. Accordingly, the tribological properties and the structure of transfer film of PTFE/PEEK polymer blends were investigated. The blends were prepared by compression and calcination of mixed powders, and a conventional pin-on-disk friction test was performed using pure aluminum as a counter material. Both the friction coefficient and wear rate of the polymer blends were lower than those of pure PTFE and PEEK, respectively. This is con...

Quantification of cartilage wear morphologies in unidirectional sliding experiments: Influence of different macromolecular lubricants

Quantifying surface damage on articular cartilage after exposure of the tissue to extreme or prolonged mechanical stress is not only relevant for evaluating clinically relevant alterations, e.g. when the physiological lubrication mechanisms fail, but also useful for assessing the suitability of artificial cartilage replacement materials, implants or synovia-mimetic lubricants. Here, we establish a systematic quantification method for cartilage wear formation which is based on optical profilometry – a variant of confocal microscopy. With this approach, we compare three different macromolecular lubricants, i.e. solutions containing either hyaluronic acid, lubricin or porcine gastric mucin. Depending on the counter material used for tribological testing and the macromolecule used for lubrication, we detect different types of tissue damage which we quantify with suitable topographical parameters. In our setup, mucin solutions outperform the other two lubricants: when using mucin solutions for lubrication, we do not find any signs of topographical alterations on the cartilage surface. Our results underscore the supreme protective abilities of mucin solutions - even on biological surfaces where they do not occur physiologically.

Wear performance of different nitride-based coatings on plasma nitrided AISI M2 tool steel in dry and lubricated conditions

AISI M2 high speed tool steel is one of the widely used materials in the machining industry. The most common problems of this material are wearing of the cutting edge and adhesion of the work materials to the tool during the machining operations. To overcome these disadvantages, single and duplex surface treatments combining a diffusion process and a thin film ceramic coating are performed. In this study, various nitride-based coatings (TiN, TiCN, AlTiN and CrN) were deposited on untreated and plasma nitrided AISI M2 high speed tool steel specimens using cathodic arc physical vapour deposition (CAPVD) technique. The plasma nitriding treatment was performed in 50%N2−50%H2 gas mixture at 500°C for 2h. The influences of different surface treatments on structural properties of AISI M2 steel were investigated by means of field emission scanning electron microscope, X-ray diffractometer, focused ion beam milling system, microhardness tester and optical profilometer. The tribological properties of specimens were examined in dry and cutting fluid conditions by using reciprocating sliding wear test with Al2O3 ball as a counter material. According to tribological test results, the solely coating treatment was more effective in improvement of the wear resistance of AISI M2 high-speed tool steel rather than duplex treatment. The lowest worn volume was obtained from the solely CrN coated surface. Whereas under cutting fluid condition, solely TiN and TiCN coated surfaces showed higher wear resistance. It was also observed that the friction coefficients of all specimens tested in boron-containing cutting fluid were lower and quite stable compared with dry sliding condition.

Live spectroscopy to observe electrochromism in viologen based solid state device

In-situ Raman and UV–vis spectroscopies have been carried out from viologen based electrochromic device fabricated in two simple geometries. Ethyl viologen diperchlorate in polyethylene oxide matrix was used as the active layer in the device without any counter material to understand the effect of bias on viologen. The device, which is transparent otherwise, changes its color to navy blue when a bias of 2V is applied. Reduction of viologen to its free radical state as revealed from Raman spectroscopy recorded in-situ in both the geometries appears to be the mechanism for this color switching. It is also observed that absorbance of the device is perturbed when bias is applied with maximum change in absorbance corresponding to green wavelength which is giving the blue tint of the device in on state. We establish that UV–vis and Raman spectroscopies prove to be the best method for understanding the mechanism of color switching in viologen based electrochromic device because it gives the advantage to see a device ‘live’ while operating.

Reciprocating sliding wear behavior of high-strength nanocrystalline Al84Ni7Gd6Co3 alloys

Nanocrystalline Al-Ni-Gd-Co alloys with exceptionally high hardness have been recently developed from amorphous precursors. In the present work, the reciprocating sliding wear in the gross slip regime of these novel nanocrystalline Al-based alloys has been investigated under small amplitude oscillatory sliding motion using a martensitic chrome steel as the counter material. When compared to pure Al or Al-12Si alloy, these nanocrystalline alloys exhibit excellent wear resistance and a lower coefficient of friction when sliding against steel. The enhanced wear resistance of the novel nanocrystaline Al alloys is related to their ultra-high hardness and the hybrid nanostructure that mainly consists of nanometric intermetallic phases embedded in a nanocrystalline fcc-Al matrix. Three body abrasive conditions were created at the initial stages of the wear tests due to the formation of micro- and nano-particulate debris from the worn surface of the Al alloys; the debris was compacted under the subsequent sliding cycles forming layers that are protective to the extensive wear of the Al alloys.

Effect of mechanical properties of substrate and coating on wear performance of TiN- or DLC-coated 316LVM stainless steel

In order to improve the tribological properties of 316LVM medical grade stainless steel, TiN and DLC coatings were deposited. The TiN coating was prepared by CAE-PVD (Cathodic Arc Evaporation), whereas DLC was deposited by the PACVD (Plasma-Assisted Chemical Vapor Deposition) technique. Surface roughness, nanohardness, and anti-wear performance for both coated and unmodified specimens, as well as adhesion of the coatings were evaluated. The results show that the HCOATING/ECOATING and ECOATING/ESUBSTRATE ratios significantly affect the anti-wear and scratch performance of the thin coatings. As a result, remarkably different wear and cracking patterns are observed for the two thin films. In wear tests, the prevalent wear mechanisms of TiN coating are tribochemical wear, oxidation of wear debris and counter material transfer. However, the DLC coating undergoes wear by ploughing induced by small patches of the film detached from the substrate. What is more, in scratch tests, for the DLC coating a deformation regime of six stages was found to operate on the basis of OM and SEM observations, whereas for TiN coating four main cracking stages were registered. Nevertheless, despite its unsatisfactory performance in wear tests, in scratch tests, TiN provides better adhesion to the substrate than DLC.

Electronic properties of electron-doped [6,6]-phenyl-C61-butyric acid methyl ester and silylmethylfullerene

Electronic properties of electron-doped chemically decorated C60 fullerenes, [6,6]-phenyl-C61-butyric acid methyl ester (PCBM) and silylmethylfullerene (SIMEF), by a planar electrode were studied using density functional theory combined with the effective screening medium method to simulate the heterointerface between the chemically decorated C60 and cationic counter materials. We find that the distribution of accumulated electrons and induced electric field depend on the molecular arrangement with respect to the external electric field of the electrode. We also show that the quantum capacitance of the molecule is sensitive to molecular arrangement owing to the asymmetric distribution of the accumulated electrons.

Filter paper derived nanofibrous silica–carbon composite as anodic material with enhanced lithium storage performance

A filter-paper-derived nanofibrous silica–carbon composite composed of thin silica layer conformally coated on carbon nanofibers is synthesized by employing natural cellulose substance (ordinary laboratory filter paper) as both scaffold and carbon source. When the nanocomposite is employed as an anode material for lithium-ion batteries, it displays improved lithium-ion storage performance compared with the bare silica and carbon counter materials, due to the unique three-dimensional porous network structures of the carbon fiber scaffold and the thin silica layer. For the silica–carbon nanocomposite with 31.2wt% of silica content and the silica layer with a thickness of ca. 60nm, it delivers a stable discharge capacity of ca. 400mAhg−1 after 200 discharge/charge cycles at a current density of 100mAg−1. Moreover, improved electrochemical performances are achieved by coverage of an additional carbon layer or deposition of silver nanoparticles onto the silica–carbon nanofibers, which exhibits specific capacities of 488.7 and 477.5mAhg−1 after 100 discharge/charge cycles, respectively. The current synthetic method provides a facile and low-cost strategy for the large-scale production of nanofibrous silica–carbon based composites as anodic materials for lithium-ion batteries.

Plasma Polishing and Finishing of CVD-Diamond Coated WC (Co) Dies for Dry Stamping

Abstract The CVD-diamond coated WC (Co) dies have been high-lighted as a tool to make dry stamping of stainless sheets, aluminium alloys and cold-rolled steel sheets. The bare CVD-diamond film had higher roughness with steep asperities than 1.5 Rz so that the friction coefficient became 0.3 to 0.5. These asperities of rough diamond crystals ploughed and worn the counter material surface. Manual and mechanical polishing processes by using the diamond powders and oxidizers required for long, tedious time; in addition, the curved surfaces of diamond coated die shoulders are difficult to be homogeneously polished and finished. On the other hand, the nano-optical polishing was only effective to remove the nano-sized residuals on the polished surfaces. In the present paper, the plasma oxidation polishing and finishing process was proposed as a non-traditional method to reduce the original maximum surface roughness down to 0.1 µm in Rz or less than. The plasma-density intensifying device was designed and used to control the plasma sheath on the diamond films toward the homogeneous polishing in large surface area. Two types of test-pieces were prepared for polishing experiments; e.g., the diamond-coated flat and curved WC (Co). The former specimen was employed to prove the low friction and wearing state should be preserved in the tribo-testing. The latter one was used to demonstrate that the diamond film on the deep-drawing dies should be homogeneously polished and finished.

Corrosion and Tribocorrosion Behavior of Ti-Alumina Composites

This work focuses in the corrosion and wear properties of titanium reinforced with 1% wt. alumina particles, produced by a combination of colloidal techniques and powder metallurgy. The alumina particles were added to control the grain growth of titanium during sintering, and simultaneously to increase hardness and wear resistance. Colloidal techniques permitted a homogeneous dispersion of alumina particles on the surface of fine Ti particles by the formulation of stable aqueous suspensions that were further processed by spray-dry to obtain spherical granules with improved compressibility. Ti-alumina samples were produced by uniaxial pressing of granules and vacuum sintering leading to materials with homogeneous microstructure, a reduction of grain size higher than 50 % with respect to pure titanium, and a sensible increase in hardness. But the addition of ceramic particles can also have an influence on the corrosion behavior that is one of the most interesting properties of titanium alloys, and on wear resistance, that is one of the drawbacks of Ti. Moreover, the study of simultaneous action of wear and corrosion (tribocorrosion) is an area of highest interest in applications like biomedical or automotive. The corrosion behavior was evaluated by Electrochemical Impedance Spectroscopy (EIS) and Potentiodynamic Polarization (PP) in NaCl at two concentrations (0.9 % and 3.5 %) and temperatures (37 oC, and room temperature). Tribocorrosion tests were performed using a reciprocating ball-on-plate tribometer where a 10 mm diameter alumina ball was used as counter material, and 10 N normal load was applied during 30 min in the same concentrations and temperatures of NaCl as in the static corrosion tests. The results showed a clear improvement of wear resistance on the composite without reducing the corrosion behavior in both conditions.

Ultra-low friction properties of carbon nitride tantalum coatings in the atmosphere

In this research, a tantalum (Ta) addition to the Carbon Nitride (CNx) coating was focused on to obtain its high hardness and a low-friction coefficient by varying the graphite-like structure at the topmost surface. A CNx:Ta coating was synthesized by a co-sputtering technique with tantalum set on a carbon target, and then XPS analysis was conducted for a better understanding of chemical bonding. The friction test was conducted in the atmosphere, and basic mechanical property of hardness was measured by Nanoindentation hardness tester. The XPS analysis revealed that TaC and TaNx in the coating bonded with some sort of oxygen and also TaC and TaNx did not strongly interact with the carbon structure. The friction coefficient of CN0.22:Ta was observed to be 0.01–0.02 with a built-up transfer layer on the counter material′s surface.

Bio-Inspired Hierarchical Nanofibrous Fe3O4-TiO2-Carbon Composite as a High-Performance Anode Material for Lithium-Ion Batteries.

A bioinspired hierarchical nanofibrous Fe3O4-TiO2-carbon composite was fabricated by employing natural cellulose substance (e.g., filter paper) as both the scaffold and the carbon source and showed improved electrochemical performances when it is employed as an anode material for lithium-ion batteries. FeOOH nanoparticles were first grown uniformly onto the surface of the titania thin-layer precoated cellulose nanofibers, and thereafter, the as-prepared FeOOH-TiO2-cellulose composite was calcined and carbonized in argon atmosphere at 500 °C for 6 h to produce the Fe3O4-TiO2-carbon composite. The resultant composite possesses a hierarchical structure that was faithfully inherited from the initial cellulose substance, which was composed of titania-coated carbon fibers with corncob-like shaped Fe3O4 nanoparticles immobilized on the surfaces. The diameter of the composite nanofiber is ca. 100-200 nm, and the diameter of the Fe3O4 nanoparticle is about 30 nm, which is coated with an ultrathin carbon layer with a thickness about 3 nm. This composite displayed superior lithium-ion storage performance. It showed a first-cycle discharge capacity of 1340 mAh/g, delivering a stable reversible capacity of ca. 525 mAh/g after 100 charge-discharge cycles at a current density of 100 mA/g, and the efficiency is as high as ca. 95% of the theoretical value. This is much higher than those of the commercial Fe3O4 powder (160 mAh/g) and the Fe3O4-carbon counter material (310 mAh/g). It was demonstrated that the thin titania precoating layer (thickness ca. 3-5 nm) is necessary for the high content loading of the Fe3O4 nanoparticles onto the carbon nanofibers. Owing to the unique three-dimensional porous network structure of the carbon-fiber scaffold, together with the ultrathin outer carbon-coating layer, the composite showed significantly improved cycling stability and rate capability.

Influence of roughness on in-vivo properties of titanium implant surface and their electrochemical behavior

Abstract This study proposed an electrochemical etching method to modify and control the surface roughness of G2 titanium, and the roughness effects on electrochemical behaviors were further verified by electrochemical impedance spectroscopy (EIS). Through electrochemical etching process within an electrolyte of 3.5 wt.% NaCl, the rough surface, big pits and cavities on titanium surface are suitable for the growth and fixity of bone cells and tissues. When the etched G2 titanium immersed in Hank's solution, bone-like compositions, including calcium and phosphorus of hydroxyl apatite, likely precipitate on such rough surface. For EIS study, the equivalent circuit for molding the rough G2 titanium immersed in the Hank's solution can be express as: (R0) + (C1//R1) + {C2//[R2 + (C3//R3)]}. The internal resistances of electrodes or load wire were simulated by a resistance, the characterizations of electron and charge transportation or diffusion between interfaces was simulated by a RC parallel circuit. It was found that the resistances of G2 titanium, transport wire and counter material appeared as ohmic impedance (R0). The other resistances of oxide film resistance (R1), hydroxyl apatite/electrolyte (R2), and hydroxyl apatite (R3) as the internal resistances. The interface capacitances include contact capacitance (C1), chemical capacitance (C2), and double-layer capacitance (C3).

Hierarchical SnO2 /Carbon Nanofibrous Composite Derived from Cellulose Substance as Anode Material for Lithium-Ion Batteries.

A hierarchical fibrous SnO2 /carbon nanocomposite composed of fine SnO2 nanocrystallites immobilized as a thin layer on a carbon nanofiber surface was synthesized employing natural cellulose substance as both scaffold and carbon source. It was achieved by calcination/carbonization of the as-deposited SnO2 -gel/cellulose hybrid in an argon atmosphere. As being employed as an anode material for lithium-ion batteries, the porous structures, small SnO2 crystallite sizes, and the carbon buffering matrix possessed by the nanocomposite facilitate the electrode-electrolyte contact, promote the electron transfer and Li(+) diffusion, and relieve the severe volume change and aggregation of the active particles during the charge/discharge cycles. Hence, the nanocomposite showed high reversible capacity, significant cycling stability, and rate capability that are superior to the nanotubular SnO2 and SnO2 sol-gel powder counter materials. For such a composite with 27.8 wt % SnO2 content and 346.4 m(2) g(-1) specific surface area, a capacity of 623 mAh g(-1) was delivered after 120 cycles at 0.2 C. Further coating of the SnO2 /carbon nanofibers with an additional carbon layer resulted in an improved cycling stability and rate performance.

Adhesive wear performance of tungsten carbide based solid lubricant material

In this work, adhesive wear performance of the developed tungsten carbide based solid lubricant material is presented. In-house developed materials were evaluated for the sliding wear performance against the commercial tungsten carbide disc. Removal of cobalt binder in the sintered material is identified as the major surface failure mechanism under adhesive wear condition. The formation of the transfer layer on the counter material during adhesive wear is confirmed with the aid of non-contact profiler. Soft phase calcium fluoride formed a bulky transfer layer on the counter disc which resulted in the reduction of friction and wear. In spite of similar frictional force, wear loss was found to be less when compared to that of abrasive condition. The measured net surface temperature of the test specimen also confirmed that tungsten carbide with calcium fluoride exhibited less friction. Wear tracks obtained after scratch resistance test confirmed that WC with 5% CaF2 material exhibited shallow and wide wear track. However, tungsten carbide without calcium fluoride material exhibited deep and narrow wear track.

Tribological and thermal stability study of nanoporous amorphous boron carbide films prepared by pulsed plasma chemical vapor deposition

In this work, the thermal stability and the oxidation and tribological behavior of nanoporous a-BC:H films are studied and compared with those in conventional diamond-like carbon (DLC) films. a-BC:H films were deposited by pulsed plasma chemical vapor deposition using B(CH3)3 gas as the boron source. A DLC interlayer was used to prevent the a-BC:H film delamination produced by oxidation. Thermal stability of a-BC:H films, with no delamination signs after annealing at 500 °C for 1 h, is better than that of the DLC films, which completely disappeared under the same conditions. Tribological test results indicate that the a-BC:H films, even with lower nanoindentation hardness than the DLC films, show an excellent boundary oil lubricated behavior, with lower friction coefficient and reduce the wear rate of counter materials than those on the DLC film. The good materials properties such as low modulus of elasticity and the formation of micropores from the original nanopores during boundary regimes explain this better performance. Results show that porous a-BC:H films may be an alternative for segmented DLC films in applications where severe tribological conditions and complex shapes exist, so surface patterning is unfeasible.