Cr Carbides Research Articles

Mechanistic Understanding of the Dissolution Behavior of the Precipitates in 12Cr Martensitic Steel during Potentiodynamic Polarization in Strong Alkaline Solutions

Cr was reported to result in a selective dissolution of the Laves phase in 12Cr steel in strong alkaline solutions. However, the current study concludes that Cr does not cause the dissolution of the Laves phase, but plausibly is responsible for the dissolution of Cr carbide at a higher potential. Further, the shoulder of the Laves phase peak resulted from the change of magnetite to hematite on the surface, and the shoulder of the carbide peak resulted from the transpassive behavior of Cr as alloying elements in the matrix.

Different Cr Contents on the Microstructure and Tribomechanical Properties of Multi-Layered Diamond-Like Carbon Films Prepared by Unbalanced Magnetron Sputtering

To investigate the effects of Cr doping on the microstructure and tribological properties of multi-layered diamond-like carbon (DLC) films, Cr-DLC films with Cr contents ranging from 0 to 22 at.% were deposited on 0Cr19Ni10 stainless steel and Si wafer surfaces by unbalanced magnetron sputtering. The thickness of the transition layer is 180 nm and the Cr-DLC film ranging from 1.3 to 1.5 µm. The microstructure, mechanical and tribological properties of the films were systematically investigated at room temperature in atmospheric environment. Results show that increasing the Cr target current can effectively improve the incident particle density and reduce surface roughness. As a strong carbon metal, Cr has significant influence on the structure and properties of the film for bonding with carbon atoms during deposition. High-energy Cr particles are favorable for films to increase the sp3 hybrid bond ratio and reduce internal stress. The high-hardness sp3 hybrid phase, Cr carbide, oxide dispersion can effectively improve the mechanical properties of the film, but overdoping is detrimental for mechanical properties of the film. The internal stress shows a continuous trend of decreasing with the increasing Cr content and it reduced up to 80% compared with pure DLC films. The films prepared with Cr sputtering current of 0.4 A demonstrate the best tribological properties, and the friction coefficient and wear rate are 0.15 and 2.9 × 10−7 mm3/Nm, respectively.

Sintering Preparation of 15 wt% Cr Cast Iron as well as Its Mechanical Properties and Impact Abrasive Wear

15 wt% Cr sintered High Chromium Cast Iron (HCCI) with full density was successfully prepared by Super-solidus Liquid Phase Sintering (SPLS) technique, with water atomized 15 wt% Cr high chromium cast iron powder as initial materials. Its densification behavior and microstructure evolution in SPLS process and mechanical properties were investigated systematically. Additionally, the impact abrasive wear resistance under different impact energies were also analyzed and compared with another sintered HCCI with 20 wt% Cr. The results indicated that sintering temperature has a strong influence on the sintered alloy’s density, hardness, impact toughness and bending strength. The M7C3 type (M is Cr and Fe) carbides were obviously coarsened as temperature increased and their rod-shaped branches were fully developed at the same time, thereby resulting in carbide network formation in the matrix. The reasonable sintering temperature range was 1195–1205 °C, and the optimum mechanical properties had the hardness of 63.9 HRC, bending strength of 2112.65 MPa and impact toughness of 7.92 J/cm2. What is more important impact abrasive wear test results indicated 15 wt% Cr sintered HCCI’s wear resistance could be comparable to 20 wt% Cr sintered HCCI under impact energy 1~3 J/cm2, and it is more cost effective.

Microstructural and wear investigation of high chromium white cast iron hardfacing alloys deposited on carbon steel

The investigation of the microstructural development during solidification as well as wear performance of Nb and Mo added hypereutectic WCI hardface deposits with W and V as minor additives was aimed during the study. This would enable the development of the hardface deposits with superior abrasive performance for severe wear applications. The hardfacing alloys were deposited on carbon steel using self-shielded flux cored arc welding (FCAW) technique. Phase formation, microstructural and mechanical properties of hardface deposits were investigated in the as-deposited condition. The microstructural examination showed that the addition of alloying elements to the high-Cr WCI resulted in grain refinement of the primary proeutectic M7C3 (M = Cr and Fe) carbide phase. EDX analysis revealed that the addition of Nb and Mo resulted in the formation of MC (M = Mo and Nb) carbides which resulted in grain refinement and higher wear resistance. Phase investigation of the deposits using XRD analysis shows the existence of M7C3 for all alloys and MC carbides for alloy B, C and D along with the ferrite phase. The main wear mechanism observed for the base high-Cr WCI is abrasive wear, while hardface alloys with alloying addition showed surface delamination which was attributed to the presence of soft phase adjacent to the M7C3 carbides in the microstructure. Among all the alloys, hardface deposits prepared using a filler with 5.5 -Mo, 6 - Nb, 2 - W and 1 - V (wt%) addition showed highest wear resistance due to grain refinement, MC carbide formation and solid solution strengthening by W and V.

Steam oxidation of chromium corrosion barrier coatings for sic-based accident tolerant fuel cladding

SiC-based materials are currently being considered for accident tolerant fuel (ATF) cladding, however, there are concerns regarding hydrothermal corrosion rates and hermeticity. These issues may be addressed with the utilization of a Cr corrosion barrier coating (CBC) but the interaction of Cr with SiC under loss of coolant accident (LOCA) conditions needs to be investigated. In the present work, Cr coatings were deposited onto chemically vapor deposited (CVD) SiC with either high power impulse magnetron sputtering (HiPIMS), cathodic arc (CA), or a combination of both. Annealing and steam thermogravimetric analysis (TGA) was used to study reaction product formation with and without oxidation. After 1200 °C annealing, formation of a CrxCy carbide layer at the ambient interface and a CrxSiyCz silicide layer at the SiC interface was observed. After 1200 °C TGA exposure, similar carbide and silicide layers were observed but with a Cr2O3 outer reaction layer and a Si and O rich interfacial layer forming between the carbide and silicide layers. Initial mass gain of the coatings during the 1200 °C TGA exposure was parabolic and were similar to reported rates of chromia formation. Mass gain behavior and observed transitions in chromia microstructure indicate that metallic Cr may be consumed within the first ~1 h at 1200 °C and that subsequent chromia formation occurs at the expense of the underlying Cr carbide layer. Overall, the results show no detrimental impact of Cr coatings on the steam oxidation resistance of SiC up to 4 h at 1200 °C.

Change in Charpy impact toughness and carbide precipitation after ageing heat treatment of high Mn austenitic steel

ABSTRACT High-Mn austenitic steel is expected to be a next-generation structural material for cryogenic use by maintaining a stable fcc crystal structure even at cryogenic temperature by adding a large amount of C and Mn which are γ-stabilizing elements. In some cases, Cr is added together with C as a solid solution strengthening element to the high-Mn austenitic steel. Depending on the conditions of ageing heat treatment, the formation of Cr carbide may affect the mechanical properties. In this study, the formation behaviour of Cr carbide and the effect on cryogenic Charpy impact toughness in the ageing heat treatment at from 773 to 1273 K for 30 s to 18 ks of a high-Mn austenitic steel with 0.5%C-25%Mn-5%Cr. Regardless of the ageing heat treatment conditions, no cleaved but 100% ductile fracture surface was observed in all samples after the Charpy impact test at 77 K. On the other hand, M23C6 containing Cr was formed on the austenite grain boundaries in the sample aged for a long time at 1073 K, and the Charpy absorbed energy showed lower than those of the other ageing conditions. As the results of both detailed microstructure observation of M23C6 and adjacent austenite matrix and DICTRA simulation, it was clarified that M23C6 mainly act as a fracture initiation point but propagation to the matrix becomes ductile because no sharp alloy deficiency layer is formed at the M23C6/austenite matrix interface. As a result of calculation of stacking fault energy using a thermochemical model, it was confirmed that γ stability at cryogenic temperature could be sufficiently secured even in the alloy-deficient region near M23C6 as well as in the stable matrix.

Thermodynamic Investigation of New High-Strength Low-Alloy Steels with Heusler Phase Strengthening for Welding and Additive Manufacturing: High-Throughput CALPHAD Calculations and Key Experiments for Database Verification

High-strength low-alloy (HSLA) steels often comprise of Cu clusters and M2C (M: Mo, Cr) carbides as strengthening particles. In this work, three new HSLA steels with alternative strengthening phases, Fe2SiTi and Ni3Ti, are investigated by using HSLA-115 steel as the reference. To evaluate the weldability for potential fabrication using casting, welding, and additive manufacturing, freezing ranges are studied using differential thermal analysis (DTA), and CALPHAD (Calculation of Phase Diagrams) approach under equilibrium and nonequilibrium conditions. While the cooling signals in the DTA analysis are not pronounced enough for thermal analysis, the trend of freezing range change based on the nonequilibrium and equilibrium calculations are consistent with the heating signals. High-throughput calculations are performed to deduce the effect of variation of each alloying element on the freezing range. Moreover, the experimental and calculated phase fractions and compositions of the as-cast and heat-treated alloys were compared. Though CALPHAD model-prediction can provide valuable insights into the phase stability of these new alloys, there is a remarkable difference regarding phase fraction and composition of individual phases. Therefore, this study indicates that the application of the CALPHAD approach in new alloy discovery requires a careful model-validation and database calibration.

Influence of Thermal Processing Factors, Linked to the Destabilisation of Austenite, on the Microstructural Variation of a White Cast Iron Containing 25% Cr and 0.6% Mo

Hypoeutectic white cast irons containing 25% Cr are used in ore-processing industries due to their high resistance to erosive wear. Applying a Design of Experiments (DoE), the aim of this study is to analyse the influence of thermal processing factors on the microstructural variation of a white cast iron containing 25% Cr and 0.6% Mo. The carbides present in the as-cast state are of the M7C3, M2C, and M3C types. M2C carbides precipitate on the eutectic M7C3 carbides favoured by heterogeneous nucleation conditions. Two kinetics compete during the destabilisation of austenite. One dissolves those eutectic carbides precipitated as a result of non-equilibrium solidification (M7C3 and M2C), while the other enables the precipitation of secondary M7C3 and M23C6 carbides. The M7C3 carbides begin to precipitate first. Low destabilisation temperatures and short dwell times are insufficient to dissolve the precipitated eutectic carbides from non-equilibrium conditions, thus favouring the presence of M2C carbides, which are associated with Mo. The factor that has the greatest influence on hardness is the tempering temperature. The optimal tempering temperature is found to be 500 °C. Short tempering times maintain the distortion of the ferrite unit cell. The precipitation of Cr carbides during tempering requires a temperature of 500 °C and the prior dissolution of the carbon precipitated during the initial stages of said tempering. With short tempering times, the Cr atoms still remain dissolved in the ferrite, distorting its unit cell and increasing the hardness of the matrix constituent of the alloy.

Corrosion Resistance and Microstructure of Welded Duplex Stainless Steel Surface Layers on Gray Cast Iron

The degradation of pump components by corrosion and complex, simultaneous damage mechanisms, e.g., erosion–corrosion and cavitation–corrosion leads to high costs through replacement and maintenance of parts. To increase the lifetime of cost-efficient components with superior casting properties, surface welding of duplex stainless steel on gray cast iron parts was performed using inert shielding gas metal arc surface welding (GMA-SW) and plasma transferred arc surface welding (PTA-SW). The thermal conductivity of the used shielding gas and the preheating temperature influenced the dilution of the surface layers, which had a major impact on the corrosion resistance and the microstructure. Lower cooling rates enhanced diffusion and lead to precipitation of carbides. High heat input and prolonged cooling times during surface welding resulted in high dilution and a carbide network. The corrosion resistance in artificial seawater of those surface layers was substantially reduced compared to surface layers with lower heat input and higher cooling rates. The corrosion of the surface layers in the potentiodynamic polarization test was driven by selective corrosion of the phase boundary between Cr–carbides and Cr–depleted austenite. Passive behavior was observed for surface layers with low dilution, which had homogeneous chromium distribution and no carbide networks. In conclusion, the corrosion behavior of gray cast iron was improved by surface welding with duplex stainless steel. The corrosion resistance of the surface layers produced with PTA-SW with no preheating exceeded that of the surface layers produced with GMA-SW and came close to those of a commercially available duplex stainless steel used as reference material.

Microstructure and mechanical properties at room and elevated temperature of crack-free Hastelloy X fabricated by laser powder bed fusion

In this study, dense and crack-free specimens were fabricated from the solid-solution strengthened nickel-based superalloy Hastelloy X (HX) through laser powder bed fusion (LPBF) in both horizontal and vertical build orientations. Samples were subjected to one of three conditions: as-built (AB), hot isostatic pressing treatment (HIP), and conventional heat treatment (HT). Tensile testing was carried out for every orientation and condition at room temperature (RT) and an elevated temperature of 750 °C (ET). AB samples showed columnar grains and a partial fiber texture aligned with the build direction, which is reduced after HIP and HT, where partial recrystallization occurred. Mo and Cr carbides, as well as Al–O enriched precipitates were found in the RT microstructures, and were seen to increase in size after ET exposure. AB samples displayed high strength (up to 924 ± 10 MPa ultimate tensile strength), while HIP and HT samples maintained strength values close to a reference HX wrought alloy. Although lower ductility was observed for the AB samples when testing at ET, the elongation was improved after HIP and HT. Strength and elongation comparable to that of the wrought alloy at RT can be obtained by performing just HT, without the need of HIPing.

Experimental investigation on Ytterbium fiber laser butt welding of Inconel 625 and Duplex stainless steel 2205 thin sheets

In this study, welding of Superalloy Inconel 625 and duplex stainless steel 2205 (DSS 2205) has been successfully performed through Ytterbium fiber laser at different heat inputs. With decreasing energy input, width of the weld bead narrowed and the mechanical properties of the joint improved. Characterization of the weld joint was carried out using Scanning Electron Microscopy (SEM), Energy Dispersive Spectroscopy (EDS), X-Ray Diffraction (XRD), and micro-hardness testing. No solidification cracks or porosity was observed in the microstructure of the weld metal (WM). Cellular dendritic and columnar dendritic grains were main grain types observed in the weld metal. At heat input of 43 J/mm, inter-dendritic arms of the weld metal witnessed more segregation of Molybdenum and Niobium in comparison of welded samples at heat input of 21.5 J/mm. Carbides of Cr, Mo and Ni are formed in the weld joint interface as revealed by the XRD analysis. Tensile strength study reveals the maximum strength of 890 MPa when the heat supplied is low i.e. 21.5 J/mm. This strength value is more than that of the base metal (DSS 2205). The result obtained in terms of comprehensive structure-property correlation, recommends the effectiveness of laser beam welding for joining of the said dissimilar alloys.

Comparative Study of High-Chromium Cast Iron Coatings Modified with WС-W2C/Co+B4С+Ni/Al Complexes and Cr3C2/PG-US25 Ceramet

The article describes the preparation and comparative wear resistance testing Fe-Cr-C- (B) coating materials, intended to harden the working bodies of agricultural machines, using high-performance method of inductive surfacing, and contains the results of microstructure analysis of such coatings. These coatings are made of powder compositions, based on PG-US25 high-chromium cast iron, and borate flux for inductive surfacing of P-0.66 grade, modified with W, B, Cr carbides in amounts from 2...5 to 25...30 wt.%, which can be applied to machine’s elements without significant technology changes. Modifying agents were commercial products (WC-W2C / Co spherical cast tungsten carbide, B4C abraser). The article demonstrates that the injection of these complexes into the fusion mixture for inductive surfacing can increase their hardness (up to 1000...1200 HV100) and wear resistance of the surfacing metal 3.1...4.5 times, compared to the base metal (65G steel), and 1.3...1.8 times, compared to the base material. The observed changes in coatings characteristics are explained by Charpy effect, dispersion hardening and the formation of new phases in the coatings (boride eutectics).

Study of corrosion mechanism of cast iron in molten aluminum

The corrosion mechanism of three aluminum ingot mold materials used by Chinese aluminum electrolytic enterprises in molten aluminum was studied: The three materials are pearlite cast iron(PCI) contains vermicular graphite, lamellar graphite, and spherical graphite respectively. After 800 °C molten aluminum corrosion for 4 h, the intermetallic compound (IMC) layers of Fe2Al5 and FeAl3 is formed at the interface. It was found that the volume of spherical graphite in IMC was reduced to 20%, and lamellar graphite aggregated in the IMC layer. The average thickness of the Fe2Al5 layer in PCI1, PCI2 and PCI3 is about 180 μm, 100 μm and 101 μm, respectively. The weight loss rate of PCI1 is 2.57 (mg cm−2)min−1, PCI2 is 2.20 (mg cm−2)min−1, and PCI3 is 2.24(mg cm−2)min−1. There are dispersed Cr and Mo carbides in the IMC layer. Si-rich ribbon-shaped region was found at the interface between cast iron and IMC. The needle-like precipitates (Al4C3) were observed only at the only at the boundary between cast iron and IMC in PCI1.

Effect of magnesium on the morphology of carbides and on M7C3→M23C6 carbides transformation in the 21-4N heat-resistant steel

ABSTRACTThis paper presents the effect of magnesium on the morphology of carbides and on M7C3 → M23C6 (M = Cr and/or Fe) carbides transformation in the 21-4N heat-resistant steel. 21-4N heat-resistant steel was calculated by using the FactSage. The equilibrium carbide phase is M23C6 and is stable up to 1492 K in Mg-added 21-4N heat-resistant steel. The studies involve a wide range of experimental techniques to characterize the investigated steels in the as-cast and hot-rolled state, including X-ray diffractometer, confocal scanning laser microscope (CSLM), scanning electron microscope, transmission electron microscopes (TEM) and microhardness testers. In the as-cast and hot-rolled samples with different magnesium contents, M7C3 was detected due to nonequilibrium solidification, while the carbide types are M23C6 in the prediction from equilibrium phase diagram. Lamellar structure in the as-cast sample is composed of FCC austenite and M23C6. And blocky shape carbide M7C3 is wrapped by the lamellar structure M23C6.

Characterization of internal and intergranular oxidation in Alloy 690 exposed to simulated PWR primary water and its implications with regard to stress corrosion cracking

Oxidation testing of Ni-base Alloy 690 was conducted in simulated PWR primary water, and the internal and intergranular (IG) oxidation layers were systematically characterized by analytical transmission electron microscopy to obtain insight into its IG stress corrosion cracking (IGSCC) resistance and behavior. The internal oxidation layer consisted of upper NixFe1-xCr2O4 and innermost Cr2O3. Each internal oxidation layer had a crystallographic orientation relationship with the Alloy 690 matrix, indicating that the layers formed through solid-state reactions between inward diffusing oxygen and the alloying elements. Strong evidence that the Cr2O3 layer formed through the outward grain boundary diffusion of Cr was found, leaving severe Cr depletion along the grain boundary with a steep composition gradient toward the surface. The innermost Cr2O3 layer had a continuous and compact band-shaped morphology around the surface grain boundary. This Cr2O3 layer was revealed to be protective of the inward grain boundary diffusion of oxygen from the surface and therefore responsible for the prevention of grain boundaries from IG oxidation. IG Cr carbides suppressed the internal and IG oxidation further. The key findings obtained in this work may present the main reason for the high resistance of Alloy 690 to IGSCC under PWR normal operating conditions.

Effect of Co on the phase stability of CrMnFeCoxNi high entropy alloys following long-duration exposures at intermediate temperatures

The effect of Co on the phase stability of the CrMnFeCoxNi family of alloys, where the atomic ratio x = 0, 0.5, 1.5, has been experimentally established following 1000 h heat treatments at 900 and 700 °C and up to 5000 h at 500 °C. All the alloys were single phase fcc in the homogenised condition, except for CrMnFeNi which also contained bcc precipitates that remained present following exposures at 900 °C and 700 °C. The exposures at 900 °C and 700 °C also resulted in the formation of σ phase precipitates in the CrMnFeNi and CrMnFeCo0.5Ni alloys but not in the CrMnFeCo1.5Ni alloy. These data, in conjunction with results previously published in the literature, conclusively establish that Co stabilises the fcc matrix at elevated temperatures. However, at 500 °C, further bulk decomposition in the CrMnFeNi alloy was observed, consisting of a fine-scale intergrowth of a NiMn L10 phase and CrFe σ phase. Grain boundary precipitates were also observed following exposure at 500 °C in the CrMnFeCo0.5Ni and CrMnFeCo1.5Ni alloys. Four different phases were observed on the grain boundaries of the CrMnFeCo0.5Ni alloy (Cr carbide, σ, FeCo B2 and NiMn L10), whilst only two phases were found on the grain boundaries of the CrMnFeCo1.5Ni alloy (Cr carbide and NiMn L10). The experimental observations facilitated an assessment of the fidelity of current thermodynamic predictions of phase equilibria. All the phases predicted were observed experimentally and the σ stability fitted the experimental observations well. However, at lower temperatures, thermodynamic predictions were less consistent with experimental observations, underpredicting the extent of the B2 phase field and failing to predict the formation of the L10 phase.

Corrosion behaviour of 316H stainless steel in molten FLiNaK eutectic salt containing graphite particles

The effect of various concentrations of graphite particles in molten FLiNaK eutectic salt (LiF-NaF-KF: 46.5-11.5–42.0 mol.%) on the corrosion behaviour of 316H stainless steel was investigated using a static immersion corrosion technique. Higher graphite particle concentration caused severer corrosion. Weight loss, Cr depletion distance, and surface Cr carbide concentration were positively correlated with graphite particle concentration in molten FLiNaK eutectic salt. Carbon from the graphite particles in the molten FLiNaK salt diffused into the 316H stainless steel and formed Cr carbides. The rate of carbide formation on the 316H stainless steel surface was much lower than the Cr corrosion rate.

Microstructure and mechanical properties of inertia friction welded joints between alloy steel 42CrMo and cast Ni-based superalloy K418

The alloy steel 42CrMo and the cast Ni-based superalloy K418 were successfully joined by inertia friction welding. The effects of the initial flywheel kinetic energy on the microstructure and mechanical properties of the joints were investigated. The results showed that inertia friction welding is a rapid and efficient way to achieve metallurgical bonding between 42CrMo and K418. Intermetallic compounds Fe0.64Ni0.36, Ni–Fe–Cr, Ni3 (Al, Ti) and MC-type carbides like NbC and TiC were observed at the interface containing a diffusion layer because of element diffusion. Elemental distribution analysis indicated that Fe and Ni were intermixed at the interface. The maximum tensile strength of the dissimilar 42CrMo/K418 joint was 772.19 MPa. Tensile fracture was identified to have occurred on the K418 side with brittle fracture features at an initial flywheel kinetic energy of 50.6 kJ. The origin and expansion of the cracks were mainly attributed to the MC carbides.

Metallurgical, impact and fatigue performance of electron beam welded duplex stainless steel joints

Fusion zones of electron beam welded (EBW) 2205 duplex stainless steel (DSS) joints pertaining to two different levels of heat input, exhibited variable microstructural morphology as well as ferrite-to-austenite (α/γ) ratio. Both the weld zones showed phase imbalance with ferrite being the dominating phase over austenite. However, as governed by the associated thermal cycles experienced by these welds, low heat input weld metal exhibited a relatively higher proportion of austenite as compared to the high heat input weld. Thermal aging at 850 °C/0.5 h promoted the formation of Cr and Mo-rich intermetallic σ-phase and carbides in the welds, whereas welding resulted into Cr2N precipitation, which consequentially influenced their impact toughness and fatigue crack growth behavior. The aged joints showed a severe degradation in their impact toughness, the extent of which was more in the base metal than in the weld metal. The role played by the prevalence of secondary phases, unlike impact toughness degradation, was not detrimental but rather beneficial, as aged weld metals exhibited significantly superior fatigue crack growth resistance as compared to their unaged counterparts, which probably could be attributed to dispersion strengthening that occurred due to intermetallic precipitation.

Role of deposition temperature on the mechanical and tribological properties of Cu and Cr co-doped diamond-like carbon films

In this study, Cu and Cr co-doped diamond-like carbon (Cu/Cr-DLC) films were synthesized using a hybrid ion beam deposition system. The effects of deposition temperature on the metal content, hardness and wear behavior of Cu/Cr-DLC films were investigated. Particularly, an optical emission spectroscopy was applied to characterize the plasma at different deposition temperatures. Results showed that the intensities of Cu and Cr spectral lines decreased dramatically as the temperature increased from 60 to 250 °C. The concentrations of Cu and Cr decreased from 18.1 to 2.7 at.% and 10.5 to 2.2 at.%, respectively. Meanwhile, high temperature promoted the formation of the Cr carbide phase, which was beneficial to achieve high hardness of the film. Although the residual stress increased with the rise of deposition temperature, the Cu/Cr-DLC film showed a better adhesive strength in comparison with pure amorphous carbon film. The wear resistance was also significantly improved at high deposition temperature, and only faint wear was observed when the temperature was above 150 °C. The excellent tribological performance of Cu/Cr-DLC film was mainly attributed to good mechanical properties and the formation of continuously compacted graphitized transfer film under dry sliding conditions.