Study On The Microstructure And Tribological Properties Of Boride Al_0.1CoCrFeNi High-entropy Alloy

High-entropy alloys generally refer to alloys that contain five or more main elements,and each main element is composed of equal or near-equal atomic ratios.High-entropy alloys have received extensive attention due to their unique structure and excellent properties.Among them,the study of tribological behavior of high-entropy alloys has always been a hot topic.However,the current studies on the tribological behavior of high-entropy alloys are mostly limited to normal temperature and dry environments,and there are relatively few studies on their tribological properties under other conditions,such as liquids and high-temperature environments.It is well known that high-entropy alloys with a single-phase face-centered cubic(FCC)structure have good plasticity.However,due to its limited strength and hardness at room temperature,its wear resistance is poor,which hinders its application in tribology and engineering.Therefore,this article attempts to use a traditional solid boronizing treatment to improve its hardness and wear resistance.In this study,the Al_0.1Co Cr Fe Ni high-entropy alloy with FCC structure was selected as the research object,and mainly explores the microstructure and tribological behavior of Al_0.1Co Cr Fe Ni high-entropy alloy before and after boronizing under different conditions.The high-entropy alloy used in this experiment was smelted in a WK-type tungsten electrode non-consumable vacuum arc furnace,and the surface of the high-entropy alloy was treated by solid pack-boronizing.The MFT-R4000 type reciprocating friction and wear tester was used to study the tribological behavior of the alloy in dry and deionized water at different times of boronizing.The high-temperature tribological behavior of high-entropy alloy boronizing at different temperatures(room temperature,100?,200?,300?,400?,500?and 600?)was tested by the HT-4001 ball-disk high temperature friction and wear tester.In addition,this experiment uses OM,XRD,SEM,EDS,XPS,AFM and Vickers hardness to study the structure and properties of the high-entropy alloy boride layer.The results of the study are as follows:(1)The annealed Al_0.1Co Cr Fe Ni high-entropy alloy is composed of a single-phase FCC structure with an equiaxed crystal structure.The thickness of the alloy boronized layer increased from 17.3?m for 2h of boronizing to 57.9?m for 8h of boronizing.The boronized layer has an obvious layered structure.The surface boride layer is mainly composed of(Co,Fe)B,Cr B,and Ni B phases,and the internal diffusion layer is mainly composed of(Co,Fe,Ni)₂B,Cr B,Cr₂B and other phases.The hardness of the alloy is increased from 201HV in the annealed state to 1398HV in the 8h boronized alloy,which is about 7 times higher.(2)The wear rate of high-entropy alloys in deionized water is lower than that in dry environments.With the extension of boronizing time,the wear rate gradually decreases with the increase of surface hardness.In addition,the friction coefficient of the alloy in deionized water is lower than that in air.The main wear mechanisms of annealed alloys in a dry environment are adhesive wear and plastic furrow wear.The wear mechanism in deionized water is mainly abrasive wear and delamination wear,accompanied by slight adhesive wear.With the increase of boronizing time under dry conditions,the main wear mechanism is gradually changed from the delamination wear and abrasive wear of the boronizing 2h alloy to the polishing wear of the boronizing 8h alloy.In deionized water,the wear mechanism has gradually changed from the two-body sliding abrasive wear of the boronizing 2h alloy to the three-body rolling abrasive wear of the boronizing 8h alloy.(3)In the air,as the boronizing time increases,the wear mechanism of Si3N4 balls gradually changes from adhesion and furrow wear to abrasive wear.In deionized water,as the boronizing time increases,the wear mechanism of Si₃N₄balls gradually changes from two-body sliding abrasive wear to three-body rolling abrasive wear.(4)Compared with annealed alloys,boronized alloys have lower friction coefficient and wear rate at high temperatures.As the temperature increases,the overall trend of the friction coefficient of the annealed alloy increases first and then decreases,while the friction coefficient of the boronized alloy decreases gradually with the increase of temperature.The wear rates of the annealed and boronized alloys both increased first and then decreased.The wear rates of both increased to the maximum at 400°C.(5)The main wear mechanism of annealed alloys at room temperature is abrasive wear.As the temperature increases,the wear mechanism transforms into plastic furrow and delamination wear,and finally transitions to oxidative wear.The wear mechanism of boronized alloy is mainly from polishing wear at room temperature,to abrasive wear and layered wear,and finally to oxidation wear.The main components of the oxide film on the wear surface of annealed alloy at high temperature are metal oxides and Si O₂,while the main components of the oxide film on the wear surface of boronized alloy at high temperature include some metal oxides,B₂O₃,Si O₂and Si₃N₄,which further promotes the lubrication effect of sliding interface.