Tool Steel Counterface Research Articles

Effect of Graphene Nanoplates Dispersed in Ethanol on Frictional Behaviour of Tool Steel Running Against Uncoated and DLC-Coated Tool Steel

Friction tests conducted between two tool steel surfaces sliding under boundary-lubricated condition in ethanol containing 5 × 10−4 wt% graphene nanoplates (GNP) under the boundary-lubricated condition showed a low coefficient of friction (COF) of 0.18, compared to 0.31 without the addition of GNP, and generated graphene incorporating tribolayers at the contact surfaces. Oxidation of the steel surfaces at high-sliding cycles increased the COF. When a diamond-like carbon (DLC)-coated counterface was used against the tool steel in GNP-containing ethanol a low steady-state COF (µS) of 0.06 was observed, and the wear rates of the DLC-coated steel were decreased by 70% compared to sliding against an uncoated tool steel counterface. Tribolayers that consisted of graphene flakes formed on top of and within the iron oxide layers that were generated on the steel surfaces. The graphene layers were deformed and damaged according to Raman spectroscopy. Cross-sectional high-resolution TEM revealed that sliding contact caused bending and occasional fragmentation of graphene layers. The graphene layers deposited on top of the tribololayers provided low friction.

Friction Behaviour of Multilayered Graphene against Steel

ABSTRACTFrictional behaviour of multilayered graphene was studied in air with different relative humidity (RH) levels (10–52% RH). Pin-on-disk type sliding tests were performed and the running-in and steady state coefficient of friction (COF) values were measured against M2 tool steel counterface. On increasing the RH, multilayered graphene showed a reduction in steady state COF from 0.11 at 10% RH to 0.08 at 52% RH. The low steady state COF values observed in graphene could be attributed to the transfer layer formed on the M2 tool steel counterface. A sliding-induced structural change was observed in graphene transfer layers which could have facilitated the graphitic transfer layer formation. The multilayered graphene showed a lower steady state COF values at all RH compared to non-hydrogenated diamond-like carbon (NH-DLC) which recorded a steady state COF of 0.47 at 10% RH and 0.25 at 52% RH.

Sliding wear behaviour of calcium containing AZ31B/Al 2O 3 nanocomposites

In the present study, the dry sliding wear characteristics of AZ31B/Al 2O 3 and AZ31B/Al 2O 3-(1–3) wt % Ca nanocomposite were investigated under different tribological conditions. Experiments were conducted using a pin-on-disc configuration against a hardened tool steel counterface over a range of sliding velocities of 1–10 m/s under a constant load of 10 N. The wear resistance of AZ31B improved due to the presence of Al 2O 3 as reinforcement and calcium (Ca), as alloying element and Al 2O 3 as reinforcement under both low and high sliding speeds. The better wear resistance of the nanocomposites was attributed to the improved hardness and strength due to the presence of calcium and nano alumina particulates in the matrix. Field emission scanning electron microscopy revealed abrasion and adhesion to be the dominant wear mechanism with transition to thermal softening only under highest sliding speed.

Microstructural evolution during high temperature sliding wear of Mg–3% Al–1% Zn (AZ31) alloy

Deformation microstructures generated during the high temperature sliding of a wrought Mg–3% Al–1% Zn alloy (AZ31) were investigated to delineate the micromechanisms of wear and material transfer to a tool steel counterface. Dry pin-on-disc type tests were conducted at 673 K. Optical profilometry and analytical microscopy revealed that material transferred to the counterface was heavily deformed and partially recrystallized. The subsurface grains beneath the contact surface were subjected to large plastic strains, and experienced dynamic recrystallization and growth as a result. Grain growth occurred in the subsurface zone beneath the recrystallized zone and followed a parabolic kinetic law with an activation energy of 35 kJ/mol. Surface damage and material transfer events proceeded in a cyclical manner, bringing the sliding process to a dynamic equilibrium, and leading to a constant wear rate.

Wear of Mg-5%Al-5%Nd Alloy with Nanocrystalline Grain Size

This paper explores the wear characteristics of nanocrystalline Mg-5%Al-5%Nd, synthesized by mechanical alloying. Pin-on-disc unlubricated sliding wear tests were conducted against a hardened tool-steel counterface under loads of 10 and 30 N, and within a velocity range of 0.2-5.0 m/s. Despite its appreciably superior mechanical properties, the nanostructured alloy did not exhibit the expected improvement in wear resistance when compared to its conventional microngrain- sized counterpart; in fact, the former performed worse when testing conditions became more severe. Scanning electron microscopy (SEM) suggested that extensive delamination in the nanocrystalline alloy was the primary reason for its high wear rates. This wear mechanism was promoted by the presence of MgxNd dispersiods, which were found only within the nanocrystalline material. These compounds likely resulted from the long duration (20 hrs) of ball-milling, which was the mechanical alloying technique employed to reduce the grain size of the final alloy.

Wear behaviour of SiC p-reinforced magnesium matrix composites

This paper investigates the wear behaviour of magnesium (Mg)-based metal–matrix composites (MMCs) reinforced with silicon carbide particulates (SiC p) during dry sliding. Experiments were conducted using a pin-on-disc configuration against a hardened tool-steel counterface under loads of 10 and 30 N, and within a sliding velocity range of 0.2–5.0 m/s. The composites exhibit slightly superior wear resistance under the lower load, but the effects of the SiC particulate reinforcements on wear resistance are not as conclusive under the higher load. Scanning electron microscopic (SEM) examinations of the worn composites identified the following wear mechanisms: abrasion, oxidation, delamination, adhesion, thermal softening and melting. The useful range of Mg/SiC p composites appears to be limited to loads and speeds below 30 N and 5.0 m/s, respectively. Under this sliding condition, melt wear becomes the dominant wear mechanism, causing gross deformation of the magnesium matrix at the contacting interface, thus rendering any component useless.

The rolling sliding wear response of conventionally processed and spray formed high speed steel at ambient and elevated temperature

The effect of spray forming on the wear properties of a 1.2C–3.4W–8.9Cr–4.3V–2.7Mo high speed steel is described. The microstructure, fracture behaviour and wear response of the spray cast materials are compared with those of conventionally cast material of the same composition. Spray forming resulted in a substantial reduction in microstructural scale for both grain size and carbide size. In addition, large primary and interconnected eutectic carbides observed in the conventionally cast material were replaced by a more uniform distribution of discrete globular carbides in the spray cast material. This refinement is shown to give rise to an increase in the resistance to fracture. Wear testing was undertaken in the rolling/sliding configuration (8% slippage) at 300 N against an M2 tool steel counterface in the temperature range 20–650 °C. The wear rate of the conventional material was significantly higher than that of the spray cast material at all temperatures. Both adhesive and oxidative wear mechanisms were observed, with the latter becoming more prominent as the test temperature increased. Surface degradation occurred preferentially at the carbide/matrix interface for both materials, but was particularly prominent in the Fe/M 2C–M 6C eutectic regions and at large primary VC carbides in the conventionally cast material, resulting in higher rates of material loss in these regions. The improvement in wear resistance observed for the spray formed material can be directly attributed to the refinement of both primary and eutectic carbide phases and the elimination of microsegregation. The laboratory observations are compared to a worn surface of a spun cast hot mill work roll of nominally the same composition following a normal campaign in the roughing stands of a hot rolling mill. This showed that the wear mechanisms in the field were reproduced in the laboratory. The relationship between process parameters microstructure and wear mechanisms is discussed.

Wear behaviour of tool steels with added (WTi)C particles

The volume fraction of hard second phase particles in tool steels is limited by the formation of large interconnected carbides on solidification that embrittle the alloy. In this work, a novel carbide master alloy, FeWTiC, which contains (WTi)C particles, was used to increase the volume fraction of carbide in an H21 hot work die steel (0.3%C, 9%W, 3%Cr). Additions of up to 5 vol.% (WTi)C were successfully made to the vacuum melted steel, producing a homogeneous distribution of (WTi)C throughout the microstructure. TEM and fracture testing confirmed that a good bond existed between the (WTi)C and martensitic matrix. Wear testing was undertaken using pure sliding against an M2 tool steel counterface, in a block on ring configuration, in the load range of 54–254 N and a sliding speed of 0.98 m/s. At 54 N, an increase in volume fraction of (WTi)C gave a reduction in wear coefficient, associated with predominantly oxidational wear, with associated ploughing of the tool steel surface by oxide particles. At higher loads the addition of (WTi)C did not result in reduced wear rates. In addition to oxidational wear, delamination occurred, frequently initiated at the matrix/M 6C particle interface. Fracture of the (WTi)C became more common as the load increased. A 1% (WTi)C marginally reduced the depth of deformation compared to the H21, but further additions had little additional effect. Detailed TEM indicated the complex interaction between oxide formation and surface deformation of the tool steel. The relationship between wear mechanism and microstructure is discussed.

Investigation of the transfer film characteristics and tribochemical changes of Kevlar fiber reinforced polyphenylene sulfide composites in sliding against a tool steel counterface

Composites of polyphenylene sulfide reinforced with Kevlar 29 fiber were prepared by compression molding. The friction and wear behavior of the composites was examined with a pin-on-disc test rig. The morphologies and elemental composition of the transfer films on the counterface were analyzed with a scanning electron microscope equipped with an energy dispersive spectrometer. The tribochemical changes of polyphenylene sulfide composites during friction were examined by means of X-ray photoelectron spectroscopy. It has been found that the inclusion of Kevlar fiber increases the wear resistance of polyphenylene sulfide considerably. A discontinuous and thick transfer film forms on the counterface against unfilled polyphenylene sulfide, while a thin and uniform transfer film is generated on the counterface against the composite with 30% Kevlar fiber. The Kevlar fiber as a reinforcing agent promotes the decomposition and oxidation of the polymer matrix by way of increasing the frictional heating and the wear face temperature. This helps to increase the bonding strength of the transfer film on the counterface, and subsequently increases the wear resistance of the composites.

Wear mechanisms of monolithic and multicomponent nitride coatings grown by combined arc etching and unbalanced magnetron sputtering

Polycrystalline nitride coatings TiAlCrN and TiAlCrYN have been grown by combined steered arc etching and unbalanced magnetron sputtering. The multicomponent coatings were found to exhibit superior wear resistance compared with commercial TiN and CrN coatings in dry-sliding conditions at low load, but similar wear rates at higher loads. An understanding of the wear mechanism was obtained by analytical transmission electron microscopy and scanning electron microscopy of the worn surfaces. The sliding wear was dominated by a surface film of Fe-based oxides, formed through material transfer from the tool steel counterface. For the TiN, this layer contained a significant contribution from the coating, while for the TiAlCrYN there was only a minimal content. Below this, a thin layer of plastically deformed material was observed. Pre-existing peaks on the surface, arising from deposition defects, were preferentially removed during the early stages of wear, resulting in locally more severe surface deformation and consequent delamination. At higher load or low speed, more severe wear modes were observed associated with (a) cracks due to friction traction; (b) delamination sheets resulting from coalescence of cracks perpendicular and parallel to the worn surface; (c) cohesive cracking and detachment of the film due to substrate deformation; and (d) more severe tribo-oxidation than found in the mild wear regime.

Tribological investigation of TiAlCrN and TiAlN/CrN coatings grown by combined steered-arc/unbalanced magnetron deposition

The dry sliding wear of monolayer TiAlCrN and multilayer TiAlN/CrN coatings has been investigated against a BM2 tool steel counterface. The coatings were deposited on a BM2 tool steel substrate by combined steered-arc/unbalanced-magnetron deposition. Increasing either contact load or sliding speed led to a reduction in friction coefficient, typically from 1.1 to 0.2. Increasing load resulted in an increase in wear rate for both TiAlCrN and TiAlN/CrN (e.g. from 7×10 -6 mm 3/m at 22 N to 4×10 -5 mm 3/m at 189 N for the TiAlCrN monolayer coating, and from 7×10 -6 mm 3/m at 22 N to 2.5×10 -5 mm 3/m at 189 N for TiAlN/CrN multilayer). The wear rate for all coatings was at least an order of magnitude lower than the uncoated BM2 steel. The wear rate of the TiAlCrN coating tended to decrease with an increase in sliding speed (from 7.4×10 -5 mm 3/m at 0.2 m/s to 1.3×10 -5 mm 3/m at 1.1m/s) while the wear rate of the TiAlN/CrN was approximately constant as a function of sliding speed (∼1.5×10 -5 mm 3/m).

The rolling/sliding wear response of conventionally processed and spray formed high chromium content cast iron at ambient and elevated temperature

The effect of spray forming on the wear properties of a 17% Cr 2.5% C white cast iron is described and compared with conventionally cast material of the same composition. Spray forming resulted in a substantial reduction in microstructural scale (eutectic (Cr,Fe) 7C 3 fields of up to 500 μm in conventionally cast material were replaced by discrete carbides of typically 2–8 μm diameter in the spray cast deposit). Wear testing was undertaken in the rolling/sliding configuration (8% slippage) at 300 N against a tool steel counterface in the temperature range 20–700°C. The wear rate of the conventional material was significantly higher than the spray cast material when tested at 20–500°C. At 600 and 700°C, the wear rate was similar, but gross microstructural changes had occurred in the matrix of both materials induced by the high temperatures. At all test temperatures, carbide cracking extended to much greater depths below the worn surface of the conventionally cast (e.g., 150 μm at 700°C) compared with the spray cast (∼55 μm at 700°C). Similarly, the depth of deformation was greater in the conventionally cast iron compared with the spray cast material. The relationship between microstructure and wear mechanisms is discussed.

TEM observations of wear mechanisms of TiAlCrN and TiAlN/CrN coatings grown by combined steered-arc/unbalanced magnetron deposition

The dry sliding wear of monolayer TiAlCrN and TiAlCrYN and multilayer TiAlN/CrN coatings has been investigated against a BM2 tool steel counterface using a ring on block configuration at 91 N, 0.42 m/s. The coatings were deposited on a BM2 tool steel substrate by combined steered-arc/unbalanced-magnetron deposition. The wear rate of the multilayer was superior to the monolayer, although both provide a substantial improvement compared with the wear behaviour of the base BM2 tool steel (e.g., wear rate=6.1×10 −4 mm 3/m for the BM2 tool steel; 3.98×10 −5 mm 3/m for the TiAlCrN monolayer and 2.58×10 −5 mm 3/m for the TiAlN/CrN multilayer). Wear of the coatings occurred by several mechanisms, fine scale (<200 nm) detachment in the early stages and micron scale detachment associated with cracking in the coating in the later stages. Detailed transmission electron microscopy of cross-sections of the worn surface indicated that two dominant types of cracking were present within the coating: (1) cracking perpendicular to the coating surface, often along columnar grain boundaries, typically running through the entire coating; (2) cracking approximately parallel to the worn surface, extending across several columnar grains. For the multilayers, there was no evidence that the spalling was induced by decohesion along the interface of the multilayers. Limited surface deformation was detected at the worn surface of the TiAlCrYN and TiAlCrN, but not at the worn surface of the TiAlN/CrN, tested under identical conditions. In contrast, the uncoated BM2 tool steel worn surface exhibited extensive plastic deformation. The relationship between wear mechanism and coating structure is discussed.

An investigation of the friction and wear behaviors of ceramic particle filled polyphenylene sulfide composites

The composites of polyphenylene sulfide (PPS) filled with 1–3 μm size ceramic particles of Al 2O 3, SiC, Si 3N 4, and Cr 3C 2 were prepared by compression molding. The hardness and the friction and wear behaviors of these composites were studied. For the latter a pin-on-disc friction and wear tester was used and sliding was performed between 5 mm × 6 mm pins and AISI 02 tool steel counterface at a speed of 1.0 m s −1 and a normal load of 19.6 N. The worn composite pin surfaces and the transfer films formed on the couterface were examined by scanning electron microscopy. An X-ray photoelectron specrometer (XPS) was used to characterize the chemical states of the elements in the transfer film for the possible tribochemical changes which occurred during sliding. It was found that SiC, Si 3N 4, and Cr 3C 2 as the fillers increased the wear resistance of PPS considerably while Al 2O 4 decreased it. The fillers promoted the decomposition of PPS and generated compounds which accounted for the changes in wear resistance of the composite. The fillers also caused abrasion and thereby disrupted the transfer film in some cases. XPS and SEM observations have been used to develop understanding for the changes in wear resistance of the composites with the use of fillers.

Influence of matrix hardness on the dry sliding behaviour of 20 vol.% Al 2O 3-particulate-reinforced 6061 Al metal matrix composite

In the present investigation the wear behaviour of the 6061 Al alloy reinforced with 20 vol. % Al 2O 3 particles dry sliding against a tool steel counterface was studied as a function of load and with reference to different values of the matrix hardness, obtained by submitting the extruded composite to thermal and forging treatments. The obtained wear rates were interpreted on the basis of the analysis of the surface and subsurface damage to the composite due to sliding. If the hardness of the materials is increased by a treatment, their wear rate also increases, because of the occurrence of subsurface softening and the formation of surface mixed scales prone to leaving the tribological system. On the other hand, the as-extruded composite is characterized by a lower matrix hardness (and thus a higher ductility) which prevents the conditions for subsurface softening and formation of the mixed scale from being reached. In this case a transfer layer mainly consisting of iron oxides then forms and protects the composite, thus reducing its wear rate.

Effect of quench temperature on mechanical behaviour of hot work tool steels: N.Tsujii et al. (Sanyo Special Steel Co, Himeji, Japan.) J. Jpn. Soc. Powder Powder Metall., Vol 42, No 12, 1995, 1446–1451. (In English.)

The volume fraction of hard second phase particles in tool steels is limited by the formation of large interconnected carbides on solidification that embrittle the alloy. In this work, a novel carbide master alloy, FeWTiC, which contains (WTi)C particles, was used to increase the volume fraction of carbide in an H21 hot work die steel (0.3%C, 9%W, 3%Cr). Additions of up to 5 vol.% (WTi)C were successfully made to the vacuum melted steel, producing a homogeneous distribution of (WTi)C throughout the microstructure. TEM and fracture testing confirmed that a good bond existed between the (WTi)C and martensitic matrix. Wear testing was undertaken using pure sliding against an M2 tool steel counterface, in a block on ring configuration, in the load range of 54–254 N and a sliding speed of 0.98 m/s. At 54 N, an increase in volume fraction of (WTi)C gave a reduction in wear coefficient, associated with predominantly oxidational wear, with associated ploughing of the tool steel surface by oxide particles. At higher loads the addition of (WTi)C did not result in reduced wear rates. In addition to oxidational wear, delamination occurred, frequently initiated at the matrix/M6C particle interface. Fracture of the (WTi)C became more common as the load increased. A 1% (WTi)C marginally reduced the depth of deformation compared to the H21, but further additions had little additional effect. Detailed TEM indicated the complex interaction between oxide formation and surface deformation of the tool steel. The relationship between wear mechanism and microstructure is discussed.

The effect of reinforcement and the synergism between CuS and carbon fiber on the wear of nylon

The polymer composite specimens were prepared with nylon 11 as the matrix material, CuS as the filler, and short fibers of carbon as the reinforcement. This was done because CuS filler has shown an unusual ability in reducing the wear of a number of polymers including nylon. It was expected that the synergistic action of filler and fiber would produce a highly wear-resistant material. The friction and wear behaviors of the composite materials were investigated in a pin-on-disk system where sliding occurred under ambient conditions between the composite pin and a tool steel counterface. The sliding conditions used were 1 m s −1 speed and 0.65 MPa contact pressure. When nylon was reinforced with carbon fiber, wear and the coefficient of friction were reduced considerably. Wear rate was the lowest for 20 vol.% fiber content and it was higher for both the lower and higher percentages of fiber. Wear reduction was still more significant when carbon fiber was used for reinforcement along with CuS as the filler. These differences in wear behavior have been investigated in terms of the synergism between fiber and CuS. This synergistic action occurred because of the role of fiber in enhancing the decomposition of CuS which increased the adhesion between the transfer film of the composite and the steel substrate.

Etched-pocket, dry-bearing materials

Novel, dry-bearing materials have been fabricated by photo-etching an array of very small, blind holes in metal surfaces and filling them with solid lubricant formulations. Friction and wear were assessed against a tool-steel counterface in reciprocating line-contact conditions. Preliminary experiments demonstrated feasibility with a range of substrates (bronze, steel, cobalt alloy) and lubricants (PTFE + Pb, MoS 2 + polyimide). Detailed studies were made with different copper alloys to examine the effects of substrate hardness and the distribution, size, spacing and depth of the etched pockets. BeCu containing PTFE + Pb exhibits wear lives over a range of stresses (Hertzian) to 375 MPa which are appreciably longer than those of a porous bronze composite containing the same lubricant. Wear rates of etched Be-Cu are also much lower than those of a typical, woven PTFE fibre-type of dry-bearing composite. Wear life is not, in general, limited by the depth of the etched pockets and several failure mechanisms have been identified.