Search

The elastic and plastic deformations have significant effect on the tribological properties of the graphene-reinforced Ni3Al matrix self-lubricating composites. The primary purpose of this study is to investigate the tribological behavior and wear mechanisms of graphene-reinforced Ni3Al matrix self-lubricating composites by researching the effects of different loads and the corresponding friction heat on the elastic or plastic deformation. The dry sliding tribology tests of graphene-reinforced Ni3Al matrix self-lubricating composites are carried out at the loads of 7, 10, 13, and 16N, respectively. The elastic or plastic deformation is judged by comparing the yield stress with the contact stress analyzed by the numerical simulation method. It is found that graphene-reinforced Ni3Al matrix self-lubricating composites exhibit good tribological properties at 13 N due to the elastic deformation, leading to the formation of relatively stable wear resistant layer. Graphene-reinforced Ni3Al matrix self-lubricating composites show poor tribological performance at 16 N for the plastic deformation, resulting in the destruction of the wear resistant layer and the generation of surface cracks and material spalling. From the mechanical mechanism of wear, the plastic deformation and thermal stress are the important factors to lead to the material spalling. The results could be used to guide the selection of suitable working conditions for having good tribological performance of low wear and long service life. [ABSTRACT FROM AUTHOR]

The sliding friction and wear behaviors of TiAl-multilayer graphene (MLG)-silver composites (TMSCs) sliding against Si 3 N 4 balls from 0.10 to 0.30  m/s were studied in this paper. The tribological test results showed that friction coefficient and wear rate of TMSCs decreased with the increasing of sliding speed from 0.10 to 0.30  m/s. TMSCs exhibited the lower fiction coefficient and the less wear rate at 0.30  m/s, which was attributed to the formation of intact tribo-film containing MLG and Ag on the worn surface. In the formed tribo-film, Ag worked as the solid lubricant to provide good lubricating effect, while MLG with high strength played the active role in enhancing the anti-rupture ability of tribo-film. It indicated that TMSCs obtained the excellent tribological performance due to the remarkable synergistic effect of MLG and Ag. Moreover, the friction heat increased with the increase of sliding speed, which made contributions to the formation of tribo-film. [ABSTRACT FROM AUTHOR]

In order to study the effect of scanning velocity on the microstructure and tribological properties of Ni3Al matrix composites containing graphene nanoplatelets (NGs), a series of NG samples are successfully synthesized by laser melt deposition under the various scanning velocities from 300 to 500 mm s−1. The sliding friction tests of NG against GCr15 steel balls are carried out under 10 N and 0.2 m s−1 at room temperature. The microstructures, tribological properties and wear mechanisms of the NG samples are analyzed. The results show that the scanning velocity can be optimized to effectively control the surface hardness and relative density, as well as tribological performance of NG. The NG sample synthesized under scanning velocity of 450 mm s−1 has a dense and fine microstructure as well as excellent properties such as higher relative density (98.6%), lower friction coefficient (0.23) and wear rate (5.5 × 10−6 mm3 N−1 m−1). The lower substrate layer with dense and stable structure plays an important role in supporting the upper glaze layer with rich graphene and oxides, as well as nanocrystalline structure, which contributes to the excellent friction-reducing and wear resistance performances of NG. The research results could be used to guide the selection of suitable scanning velocity and study the wear mechanisms of NG for having excellent tribological performance. [ABSTRACT FROM AUTHOR]

In order to improve tribological performance of NiAl-based alloy, NiAl matrix composites containing 1.5 wt.% multilayer graphene (MLG) are prepared through additive manufacturing (AM) and spark plasma sintering (SPS), which are denoted as NMAM and NMSPS, respectively. Tribological behaviors of NMAM and NMSPS against SiN balls are researched under constant speed (0.2 m/s) and varied loads (from 4 to 16 N) for evaluating the tribological properties of NMAM and NMSPS. The results present that NMAM exhibits the excellent tribological properties [low friction coefficients (0.26-0.40) and considerable wear resistance (2.8-4.6 × 10 mm N m)] as compared to NMSPS, which attributes to the uniform enrichment of MLG with properties of high tensile strength and being easily sheared off on the worn surfaces. Owing to the use of spherical prealloyed powder containing multilayer graphene and the characteristics of layer by layer depositing in the AM process, NMAM has a more compact and uniform substrate, which persistently provides a source of the formation of continuous and stable frictional layer. Due to the characteristics of AM rapid solidification, NMAM has the small grain size and well-compacted microstructure, which can effectively reduce the probability of spalling wear and lead to the increase in wear resistance of materials. The research can offer the reference for self-lubricating materials prepared by AM technology. [ABSTRACT FROM AUTHOR]

This study aimed to explore the possibility of improving the tribological performance of NiAl matrix composites by graphene addition. Friction and wear experiments of as-prepared specimens were conducted under different conditions using a pin-on-disk wear testing machine. NiAl matrix composites containing graphene showed satisfactory performance in friction coefficient and wear resistance compared to NiAl matrix composites without graphene. For the active effect of graphene, the friction coefficient and wear rate of NiAl matrix composites were maintained at relatively lower values. The beneficial antifriction and antiwear effects of graphene gradually failed when the applied load was above 8 N. Graphene in NiAl matrix composites played an active role in the formation of a friction layer, which was beneficial to the lower friction coefficient and wear rate. In light of this research, graphene plays an active role in reducing the friction coefficient and wear rate. Hence, graphene has great potential in applications as an effective solid lubricant to promote tribological behavior. [ABSTRACT FROM AUTHOR]

A favorable hardness ratio (Hdisk/Hpin = Hd/Hp) could lead to a transition to mild wear during sliding contact. To determine a more appropriate Hd/Hp value for the sliding wear, the dry sliding pin-on-disk wear tests of Ni3Al matrix composites (NMCs) with multilayer graphene (MLG) are undertaken at Hd/Hp values of 0.99, 0.83, 0.42, and 0.35 at sliding speeds of 0.1, 0.3, 0.5, and 0.7 m/s. It is found that the tribological properties of NMCs are strongly affected by the various hardness ratios. At 0.1 m/s, the friction coefficient decreases with a decrease in Hd/Hp value. The low friction coefficient is 0.14 and the wear rate is 0.9 × 10-5 mm3 N-1m-1 under the ceramic counterpart with Hd/Hp of 0.35. At 0.7 m/s, the tribological properties show the opposite trend with a decrease in Hd/Hp. At an Hd/Hp of 0.35, the smooth compact layer on the worn surface could decrease the friction at 0.1 m/s, and the improved hardness in the subsurface by strain hardening would play an important role in the improvement of wear resistance. Under the metal counterpart with Hd/Hp of 0.99, plastic deformation only occurs on the contact surface and the MLG could suppress further shear deformation in the subsurface, leading to a low wear rate (2.4 × 10-5 mm3 N-1m-1) and friction coefficient (0.15) at 0.7 m/s. [ABSTRACT FROM AUTHOR]

The dry sliding friction and wear behaviors of TiAl matrix self-lubricating composite (TMSC) containing multilayer graphene (MLG), silver (Ag) and MLG-Ag sliding against SiN balls from 25 to 750 °C were comparatively studied in this paper. The results suggested that TMSC containing MLG-Ag (TMA) showed better tribological properties over the wide temperature range, if compared to TMSC only containing MLG or Ag. Moreover, TMA exhibited the lower fiction coefficient and the less wear rate at 450 °C, which was attributed to the formation of intact lubricating films containing MLG and Ag on the worn surface. Furthermore, in the formed lubricating films, Ag worked as the solid lubricant to provide good lubricating effect, while MLG with high strength played the active role in enhancing the anti-rupture ability of lubricating films. The study indicated that TMA obtained the excellent tribological performance at 450 °C due to the remarkable synergistic effect of MLG and Ag. [ABSTRACT FROM AUTHOR]

In this study, the effect of friction layer thickness and subsurface nano-hardness of wear track on tribological behavior of γ-TiAl matrix composites is investigated. The results of dry sliding tribolocial tests of γ-TiAl matrix composites with 0-2.25 wt.% multilayer graphene (MLG) (0.25 wt.% in tolerance) under different applied loads are reported. The testing results show that the optimized addition amount of MLG is 1.75 wt.% at 12 N (friction layer thickness 3.23 µm, subsurface nano-hardness of wear track 9.03 GPa). It can be found that a continuous and thick friction layer is formed in γ-TiAl-1.75 wt.% MLG at 12 N, resulting in a lower friction coefficient of 0.31 and wear rate of 2.09 × 10 mm N m. During dry sliding process, the high subsurface nano-hardness of wear track leads to the increase in resisting plastic deformation capacity and reduces the material loss. Meanwhile, the thick friction layer contains MLG with high tensile strength which is easily sheared off. Hence, γ-TiAl matrix composites show excellent tribological performance of a friction-reducing and an increase in wear resistance. The investigation shows that γ-TiAl-1.75 wt.% MLG, due to its excellent tribological behavior at 12 N, can be chosen as a promising structural material for minimizing friction- and wear-related mechanical failures in sliding mechanical components. [ABSTRACT FROM AUTHOR]

In order to analyze the effects of friction layer thickness on the tribological performance of NiAl matrix self-lubricating composites containing Ag and MoO tabular crystals (NiAl-Ag-MoO), the dry sliding tribological tests of NiAl-Ag-MoO against SiN ball are undertaken under 4-16 N and 20-800 °C at 0.2 m/s. The results show that the friction layer thickness of NiAl-Ag-MoO is obviously affected by the applied loads and ambient temperatures. At 12 N-400 °C-0.2 m/s, NiAl-Ag-MoO exhibits excellent tribological performance, and the friction layer thickness obtained the maximum value of about 5 µm. Moreover, the simulation results, which based on the building of finite element models with different thickness of the friction layer, indicate that the decreased degree of the maximum equivalent stress in the substrate of NiAl-Ag-MoO with maximum thickness of friction layer is the larger one (about 39%), if compared to other thickness. It could avoid the generation of cracks and the spalling of subsurface materials during the dry sliding process, resulting in the excellent tribological performance. The results could be used to guide the selection of suitable working conditions and study the self-lubricating mechanisms of NiAl-Ag-MoO for having stable friction layer structure and excellent antifriction and antiwear performance. [ABSTRACT FROM AUTHOR]

Tribological behaviors of TiAl-multilayer graphene-microsphere composites (TMMC) are investigated at different loads in this paper. The tribological results show that TMMC exhibit excellent wear and friction performances from 4 to 20 N for the formation of the intact and smooth tribo-films containing multilayer graphene (MLG) and WS-SiO microsphere (WSM) on the worn surfaces. During the sliding process, MLG and WSM are ground out of TMMC to form the tribo-films on the worn surfaces, which is beneficial to the decreasing in friction coefficients and wear rates. MLG is easy to be sheared for the weak interlayer binding force, which can reduce the friction coefficients and wear rates. WSM can repair the tribo-film by filling its worn pits, resulting in the smooth worn surface and excellent tribological performance of TMMC. Moreover, the hardness of TMMC is increased for the addition of MLG and WSM, which makes contributions to the improvement of tribological behaviors of TMMC. [ABSTRACT FROM AUTHOR]

In order to improve the efficiency and durability of the kinematic pair systems, the research continues for novel materials and lubricants that can potentially reduce friction and wear. This article was dedicated to explore the combined lubrication of graphene nanoplatelets (GNPs) and MoS nanospheres (NSs) at different testing temperatures. Furthermore, the glaze layer with grain refinement could have a strong bearing capacity and resist the damage caused by high stress. At 450 °C, a integrated lubricating film containing GNPs and MoS NSs was continuously formed to provide the low-strength junctions at the interface, resulting in a lower friction coefficient of 0.15 and a smaller wear rate of 1.56 × 10 mm N m. Meanwhile, the GNPs played the role of reinforcement particles and improved loading carrying ability, while MoS NSs demonstrated the effect of repairing with being pressed into the microfurrows of the worn surface. [ABSTRACT FROM AUTHOR]

Microstructure and functional mechanism of friction layer need to be further researched. In the present work, the friction coefficients and wear rates are analyzed through response surface methodology to obtain an empirical model for the best response. Fitting results show that the tribological performance of NiAl matrix composites (NMCs) with graphene nanoplatelets (GNPs) is better than that of NMCs without GNPs, especially at high sliding velocities and high loads. Further research suggests that the formation of integrated friction layer, which consists of a soft microfilm on a hard coating, is the major reason to cause the differences. Of which, the wear debris layer (WDL) with a low shear strength can reduce the shear force. The ultrafine layer (UL), which is much harder and finer, can effectively avoid fracture and improve the load support capacity. Moreover, the GNPs in WDL and UL can be easily sheared and help to withstand the loads, trending to be parallel to the direction of shear force. [ABSTRACT FROM AUTHOR]

An investigation is conducted on the unexplored synergistic effects of multilayer graphene (MLG) and Ti3SiC2 in self-lubricating composites for use in high-temperature friction and wear applications. The tribological properties of TiAl matrix self-lubricating composites with different solid lubricant additions (Ti3SiC2-MLG, MLG) are investigated from room temperature to 800°C using a rotating ball-on-disk configuration. Tribological results suggest the evolution of lubrication properties of MLG and the excellent synergistic lubricating effect of MLG and Ti3SiC2 as the testing temperature changes. It can be deduced that MLG has great potential applications as a promising high-temperature solid lubricant within 400°C, and a combination of MLG and Ti3SiC2 is an effective way to achieve and maintain desired tribological properties over a wide temperature range. [ABSTRACT FROM AUTHOR]

In this study, the tribological properties of NiAl matrix composites with 1.5 wt% graphene nanoplatelets (NAG) at elevated temperatures were simulated and tested. NAG exhibits excellent characteristics at 100 and 200°C due to the formation of metal oxides and graphene nanoplatelets lubrication film. Furthermore, the removed layer thickness, the stress distributions, and the high stresses of the affected layer have been estimated theoretically. At 400°C, the friction coefficient increased due to the absence of the lubrication layer. In addition, the wear rate increased due to the excessive stresses, the increased layer thickness removal, and the propagation of subsurface cracks. [ABSTRACT FROM PUBLISHER]

This research was carried out on the beneficial effect of graphene additive in self-lubricating composites for use at different loads of tribological application. The dry friction and wear behaviors of NiAl self-lubricating matrix composite with graphene (NSMG) were investigated at different loads at room temperature. Finite element method served as aided method to analyze the stress condition of contact pair, which would provide another perspective to comprehend the relationship between tribological behaviors and different degrees of load-induced deformation. In the load range of 2-16 N, the results indicated that NSMG showed excellent tribological performance at load of 16 N due to the formation of anti-friction tribo-film on the worn surface. Moreover, suitable load would lead to the contact situation transfer from multi-point contact to area contact, which could contribute to the beneficial effect on friction behavior of NSMG. [ABSTRACT FROM AUTHOR]

The friction layer structure has been proved to be formed during severe plastic deformation and markedly improves the tribological properties of material. The dry friction and wear performance of graphene-reinforced TiAl matrix self-lubricating composites (GTMSC) at different sliding velocities are systematically researched. GTMSC show the best tribological properties and special friction layer structure containing a wear-induced layer and a grain refinement layer with a nanocrystalline (NC) structure under surface after sliding at a sliding speed of 1.1 m/s. Nanoindentation results show that the grain refinement layer has a higher hardness and elastic modulus than the wear-induced layer. This special microstructure of friction layers beneath the surface after sliding leads to a low coefficient of friction and high wear resistance of GTMSC. Moreover, it is deduced that the appearance of an NC structure results in hardening of the material. The formation mechanisms of friction layers are researched in detail. It can be concluded that the formation of a wear-induced layer results from frictional heat and fracture of the counterpart. The formation of a grain refinement layer is due to severe plastic deformation and dynamic recrystallization. Severe plastic deformation results in the formation of an NC structure and dynamic recrystallization leads to grain refinement. [ABSTRACT FROM PUBLISHER]

To better understand respective lubrication effects and mechanisms of graphite, multi-walled carbon nanotubes (MWNTs), and multilayer graphene (MLG), comparison of tribological properties of NiAl matrix composites (NAMC) containing graphite, MWNTs, or MLG is investigated. Tribological results clearly indicate that the incorporation of solid lubricant remarkably improves the tribological properties of NAMC. NAMC containing MWNTs have better tribological properties than that containing graphite. NAMC containing MLG have the best tribological properties. EPMA, AFM, and FESEM analyses of worn surfaces suggest that the discontinuous island-like solid lubricant-rich films with different compacting extent forms on the worn surfaces of NAMC containing solid lubricant. The worn surface of NAM shows the slighter delamination and comparatively more compact films than that of NAC; in contrast, the worn surface of NAG presents the slightest delamination and the most compact films. It is concluded that graphite, MWNTs, and MLG indeed possess different lubrication effects and mechanisms. [ABSTRACT FROM AUTHOR]

Multilayer graphene (MLG) shows an attractive prospect for the demanding engineering applications. This paper reports the mechanical and tribological properties of MLG reinforced Ni 3 Al matrix composites (NMCs) under dry sliding at varying sliding speed. The hardness and elastic modulus of the NMCs are significantly influenced with MLG content. It is found that the hardness and elastic modulus of the NMCs are found to be increased by increasing MLG content up to 1.0 wt.%, while decreased when MLG content is above 1.0 wt.%. Tribological experiments suggest that MLG can dramatically improve the wear resistance and decrease the friction coefficient of the NMCs. Such marked improvement of wear resistance is attributed to the reinforcing mechanisms of MLG, such as crack deflection and pull-out, and reduction of friction coefficient is related to the formation of a tribofilm on the sliding contact surface. [ABSTRACT FROM AUTHOR]

The main objective of this work has been the characterization of wear behavior of the graphene nanoplates (GNPs) in Ni3Al matrix composites (NMC). The friction and wear behaviors of NMC with the addition of 1 wt.% GNPs against Si3N4 ball are tested under different loads using a constant speed of 0.2 m/s. Tribological test results have revealed that small amounts of GNPs are able to drastically improve the antifriction and antiwear properties of NMC. A possible explanation for these results is that, the GNPs not only provide an enhanced effect for NMC to produce better wear resistance, but also form a local protective layer on the contact surfaces to reduce the friction. The investigation shows that GNPs hold great potential applications as an effective solid lubricant for Ni3Al matrix composites and possibly other alloys. [ABSTRACT FROM AUTHOR]

In recent years, reducing friction and wear-related adverse impacts on efficiency and durability in moving mechanical systems has gained increased attention. Herein, the search continues for novel materials and lubricants that can potentially reduce friction and wear. As one of the emerging self-lubricating materials, the tribological potential of graphene has been researched deeply. This article was dedicated to explore the combined lubrication of multilayer graphene (MLG) and WS. The as-prepared sample of NiAl-1.5 wt% MLG-5 wt% WS (NB) exhibited excellent tribological properties. During the sliding process, a continuous lubricating film was formed to provide the low-strength junctions at the interface, reducing the friction coefficient and wear rate. Moreover, the MLG played the role of reinforcement particles and improved loading carrying ability. [ABSTRACT FROM AUTHOR]

Research on the friction layer is needed to minimize friction- and wear-related mechanical failures in moving mechanical assemblies. Dry sliding tribological tests of NiAl matrix composites (NMCs) with 1.5 wt% graphene nanoplatelets (GNPs) sliding against different counterface balls are undertaken at the condition of 10 N-0.234 m s in this study. When sliding against GCr15 steel, a uniform and thick friction layer is formed, resulting in a lower friction coefficient (0.29-0.31) and wear rate (2.0-3.1 × 10mmNm). While sliding against AlO and SiN, the formation and stability of the friction layers are restricted in the severe wear regime, and the NMCs exhibit higher friction coefficients and wear rates. Therefore, various counterface balls have a great effect on the stability and thickness of the friction layer, thus affecting the tribology performance of NMCs. The result also shows that GNPs exhibit enrichment and self-organized microstructures in the friction layer. In addition, the friction layer is also found to be divided into two layers, protecting the subsurface from further damage and reducing shear. [ABSTRACT FROM AUTHOR]

Abstract: Investigations in graphene of controlling friction and wear of Ni3Al matrix self-lubricating composites (NMSC) are needed for moving mechanical assemblies. The friction and wear behaviors of NMSC with graphene nanoplatelets (GNPs) against Si3N4 ball are tested using a constant load of 10N and a constant speed of 0.2m/s from room temperature (RT) to 600°C. Tribological test results have revealed that small amounts of GNPs in the NMSC are able to drastically reduce the friction coefficients and wear rates over the effective operating range (RT-400°C). A possible explanation for these results is that the refinement of grains accompanying the slippage of laminated sheets between GNPs could provide a source of the stress dissipation and form the GNP protective layer during sliding process, leading to the reduction of wear rates as well as the friction coefficients. It is concluded that GNPs hold great potential applications as an effective solid lubricant for moderate loads and stress, and can be easily used for the preparation of the self-lubricating composites in the future. [Copyright &y& Elsevier]

Abstract: This paper reports on preparation technique and tribological properties of multilayer graphene (MLG) reinforced TiAl matrix composites (GTMC). GTMC are successfully prepared by spark plasma sintering (SPS). Structural characterization of starting MLG and the sintered GTMC are performed using Raman spectroscopy and field emission scanning electron microscopy, which indicates that MLG homogeneously distributes in GTMC. Tribological studies suggest that MLG plays an important role in decreasing friction coefficients by a factor of 4 and wear by almost 4–9 times of magnitude. Such marked reductions are attributed to the fact that MLG easily shears and forms a conformal anti-wear protective layer on the sliding contact interfaces, thus drastically reduces the friction coefficients and wear rates of GTMC. MLG can actually act as an effective reinforcement and lubricant phase in GTMC. [Copyright &y& Elsevier]