水基硅氧烷聚合物润滑剂在铝合金热冲压工况下的润滑可行性

铝合金热冲压是实现汽车轻量化目标的重要制造手段,生产过程中的摩擦磨损造成的板料擦伤和开裂是批量生产的主要阻碍。为了研究热冲压过程中润滑剂的适用性和润滑机理。基于此,基于销-盘摩擦实验设备,通过合理的实验设计模拟了热冲压的实验工况,选用了一种使用工况接近的水基脱模剂进行摩擦实验,并评价其在热冲压工况下的润滑性能,探究其润滑机理。通过实验发现,水基硅氧烷润滑剂能够通过隔绝模具与工件直接接触,获得较长时间的低摩擦因数状态。利用水基润滑剂实现铝合金热冲压过程中的稳定低摩擦因数状态是可行的。

A review of recent advances in tribology

The reach of tribology has expanded in diverse fields and tribology related research activities have seen immense growth during the last decade.This review takes stock of the recent advances in research pertaining to different aspects of tribology within the last 2 to 3 years.Different aspects of tribology that have been reviewed including lubrication,wear and surface engineering,biotribology,high tem perature tribology,and computational tribology.This review attempts to highlight recent research and also presents future outlook pertaining to these aspects.It may however be noted that there are limitations of this review.One of the most important of these is that tribology being a highly multidisciplinary field,the research results are widely spread across various disciplines and there can be omissions because of this.Secondly,the topics dealt with in the field of tribology include only some of the salient topics(such as lubrication,wear,surface engineering,biotribology,high tem perature tribology,and computational tribology)but there are many more aspects of tribology that have not been covered in this review.Despite these limitations it is hoped that such a review will bring the most recent salient research in focus and will be beneficial for the growing community of tribology researchers.

A review of advances in tribology in 2020–2021

Around 1,000 peer-reviewed papers were selected from 3,450 articles published during 2020–2021,and reviewed as the representative advances in tribology research worldwide.The survey highlights the development in lubrication,wear and surface engineering,biotribology,high temperature tribology,and computational tribology,providing a show window of the achievements of recent fundamental and application researches in the field of tribology.

High temperature tribological behaviour of PVD coated tool steel and aluminium under dry and lubricated conditions

Aluminium alloys are commonly used as lightweight materials in the automotive industry.This non-ferrous family of metallic alloys offers a high versatility of properties and designs.To reduce weight and improve safety,high strength-to-weight ratio alloys(e.g.6XXX and 7XXX),are increasingly implemented in vehicles.However,these alloys exhibit low formability and experience considerable springback during cold forming,and are therefore hot formed.During forming,severe adhesion(i.e.galling)of aluminium onto the die surface takes place.This phenomenon has a detrimental effect on the surface properties,geometrical tolerances of the formed parts and maintenance of the dies.The effect of surface engineering as well as lubricant chemistry on galling has not been sufficiently investigated.Diamond-like carbon(DLC)and CrN physical vapour deposition(PVD)coated steel have been studied to reduce aluminium transfer.However,the interaction between lubricants and PVD coatings during hot forming of aluminium alloys is not yet fully understood.The present study thus aims to characterise the high temperature tribological behaviour of selected PVD coatings and lubricants during sliding against aluminium alloy.The objectives are to first select promising lubricant-coating combinations and then to study their tribological response in a high-temperature reciprocating friction and wear tester.Dry and lubricated tests were carried out at 300℃ using a commercial polymer lubricant.Tests using DLC,CrN,CrTiN,and CrAIN coated tool steel were compared to uncoated tool steel reference tests.The initial and worn test specimen surfaces were analysed with a 3-dimensional(3D)optical profiler,scanning electron microscope(SEM)and energy dispersive X-ray spectroscope(EDS)as to understand the wear mechanisms.The results showed formation of tribolayers in the contact zone,reducing both friction and wear.The stability of these layers highly depends on both the coatings'roughness and chemical affinity towards aluminium.The DLC and CrN coatings combined with the polymer lubricant were the most effective in reducing aluminium transfer.

Mechanical and tribological properties of nanocomposites incorporated with two-dimensional materials

In recent years, attempts to improve the mechanical properties of composites have increased remarkably owing to the inadequate utilization of matrices in demanding technological systems where efficiency, durability, and environmental compatibility are the key requirements. The search for novel materials that can potentially have enhanced mechanical properties continues. Recent studies have demonstrated that two-dimensional (2D) nanomaterials can act as excellent reinforcements because they possess high modulus of elasticity, high strength, and ultralow friction. By incorporating 2D nanomaterials in a composite, 2D nanomaterial-based composites (2DNBCs) have been developed. In view of this, a critical review of recent mechanical and tribological studies based on 2DNBCs has been undertaken. Matrices such as polymers, ceramics, and metals, as well as most of the representative 2D nanomaterial reinforcements such as graphene, boron nitride (BN), molybdenum disulfide (MoS2), and transition metal carbides and nitrides (MXenes) have been included in this review. Their preparation strategies, intrinsic mechanical properties, friction and lubrication performances, strengthening mechanisms, influencing factors, and potential applications have been comprehensively discussed. A brief summary and prospects are given in the final part, which would be useful in designing and fabricating advanced 2D nanocomposites in the future.

Fatigue of 0.55C-1.72Si Steel with Tempered Martensitic and Carbide-Free Bainitic Microstructures

High-Si spring steel was heat treated in three different ways： Quenching and tempering at 460 ℃ to obtain a tempered martensite microstructure, and austempering at 300 and 350 ℃, respectively, to obtain two different carbide-free bainitic microstructures. In the steel austempered at 350 ℃, both the bainite lath thickness and retained austenite content were higher than those of the steel austempered at 300 ℃. Rotating-bending fatigue tests were done in order to evaluate the effect of each heat treatment on the high-cycle fatigue behavior of the steel. When the austempering temperature was 300 ℃, the endurance limit was increased by 25% despite a 5% reduction in tensile strength when compared with that of the quenched and tempered steel. The relationship between endurance limit [Rfat （50~）] and ultimate tensile strength （Rm） was higher for the austempered samples in comparison with that of the quenched and tempered material. Therefore, it is believed that the presence of retained austenite affects the relationship between endurance limit and tensile strength.

Static/dynamic friction and wear of some selected polymeric materials for conformal tribo-pairs under boundary lubrication conditions

This work is aimed at investigating the friction and wear performance of different polymeric materials having potential for hydraulic system components under lubricated sliding conditions against a steel counter face.A pin-on-disc test configuration was used for the experimental study.The different polymeric materials selected for these studies were commercial polyimides(PI),polyether ether ketone(PEEK),and flouropolymers.Some of these materials were bulk materials whereas others were used as coatings applied on to the cast iron substrate.The tribological characteristics of the polymers were compared with a reference grey cast iron.The frictional characteristics were evaluated in both static and dynamic conditions.The results have shown that by using polymeric materials it is possible to reduce breakaway friction by an order of magnitude compared to grey cast iron.However,the breakaway friction increased significantly after the wear tests.The polymeric materials having lowest breakaway friction have shown the highest wear with the exception of the PEEK-PTFE coating which showed low wear.PI with graphite fillers also showed low wear but it resulted in relatively high friction.The carbon fibre reinforced materials resulted in unstable friction as well as higher wear compared to the PI materials with graphite fillers.

Tribological performance of iron- and nickel-base self-lubricating claddings containing metal sulfides at high temperature

Iron-based coatings with the incorporation of solid lubricants have been prepared by means of laser cladding,in an effort to control friction and decrease tool wear at high temperatures during metal forming applications.The choice of a Fe-based powder has been considered advantageous,as it can lead to decreased costs compared to nickel-based claddings previously studied by the authors,in addition to having a lower environmental impact.In particular,the incorporation of transition metal dichalcogenides such as MoS_(2) as precursors leads to the encapsulation of silver in Fe-based self-lubricating claddings,resulting in a uniform distribution of the soft metal across the thickness of the coating.Subsequent tribological evaluation of the claddings at high temperatures shows that the addition of lubricious compounds leads to lower friction at room temperature and significantly decreased wear up to 600℃ compared to the unmodified iron-based reference alloy,although higher than similar self-lubricating Ni-based claddings.In order to cast light into these observed differences,the corresponding microstructures,phase composition,and self-lubricating mechanisms have been studied and compared for Fe-and Ni-based claddings having both of them the addition of silver and MoS_(2).The results suggest a key role of the formation of protective tribolayers on the counter body during high temperature sliding contact.Additional simulation of the phase evolution during solidification reveals that the formation of different chromium-and nickel-based metal sulfides in Fe-and Ni-claddings during laser cladding by the decomposition of MoS_(2) plays a key role in determining their tribological behaviour at high temperatures.

Influence of lubrication,tool steel composition,and topography on the high temperature tribological behaviour of aluminium

The use of high strength aluminium alloys,such as 6 XXX and 7 XXX series,is continuously increasing for automotive applications in view of their good strength-to-weight ratio.Their formability at room temperature is limited and they are thus often formed at high temperatures to enable production of complex geometries.Critical challenges during hot forming of aluminium are the occurrence of severe adhesion and material transfer onto the forming tools.This negatively affects the tool life and the quality of the produced parts.In general,the main mechanisms involved in the occurrence of material transfer of aluminium alloys at high temperature are still not clearly understood.Therefore,this study is focussed on understanding of the friction and wear behaviour during interaction of Al6016 alloy and three different tool steels in as-received and polished state.The tribotests were carried out under dry and lubricated conditions,with two distinct lubricants,using a reciprocating friction and wear tester.The worn surfaces were analysed using scanning electron microscopy(SEM)and energy dispersive X-ray spectroscopy(EDS).The results showed a high dependence of friction and wear behaviour on the tool steel roughness as well as on the stability of the lubricant films.Tribolayers were found to develop in the contact zone and their capacity to improve the tribological behaviour is seen to be drastically impacted by the surface roughness of the tool steel.When the tribolayers failed,severe adhesion took place and led to high and unstable friction as well as material transfer to the tool steel.