Trans.Nonferrous Met.Soc.China31(2021)1249−1261
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Influence of TiB2addition on friction and
wear behaviour of Al2024−TiB2ex-situ composites
Dipankar DEY,Abhijit BHOWMIK,Ajay BISWAS窈窕是什么意思
Mechanical Engineering Department,NIT Agartala,Tripura-799046,India
呃Received18May2020;accepted20October2020
Abstract:Prent work encapsulated the friction and wear behaviour of aluminium matrix composites reinforced with different mass fractions of titanium diboride(TiB2)particles,synthesized by stir casting.A pin on disc tribotester was employed for conducting the dry sliding wear tests of Al2024−TiB2composites.The tests were performed adopting various parameters like load,sliding distance and sliding velocity for investigating the effect of tribological parameters on the prepared composites.Microstructural characterization confirmed uniform dispersion of TiB2particles and good matrix−reinforcement bonding.Results of the experiments revealed that,low friction and wear rates were obrved in the developed composites compared to Al2024alloy,whereas wear rates of both Al2024alloy and fabricated composites incread with the increa in load,sliding velocity and sliding distance.However,friction coefficient of both Al2024alloy and fabricated composites reduced with the increa in applied load but ro with the increa in sliding velocity and sliding distance.SEM studies of the worn surfaces and debris depicted that enhancement in wear resistance can be ascribed to finer debris formation.
随机应变
Key words:Al2024alloy;TiB2;stir casting;friction;wear
1Introduction
Aluminium matrix composites(AMCs)are one of the most promising materials nowadays posssing remarkable properties such as good thermal conductivity,high strength,wear resistance, corrosion resistance and the properties make AMCs an appealing material for various automotive and aerospace applications[1−4].Properties of particulate reinforced AMCs are mainly influenced by type,size and quantity of reinforcements;and uniform dispersion of reinforcement results in enhancement of mechanical and tribological properties[5].Hard ceramic particles like Al2O3[6], TiC[7],SiC[8],TiB2[9]and B4C[10]are commonly employed as reinforcements for enhancing the mechanical and tribological properties of AMCs.Among the,TiB2emerged to be the most promising reinforcement as it posss high hardness,high stiffness and most importantly, it does not react with molten aluminium alloy to generate any detrimental by-product at the matrix−reinforcement interfaces[11].Further,TiB2 also contributes to the wear resistance of AMCs. Sound interfacial bonding between TiB2and Al enhances the hardness,which augments the wear resistance of Al−TiB2composites[12].Al2024 alloy is basically a wrought alloy consisting of copper as the primary alloying element,posssing excellent fatigue resistance,high strength,good machining properties and extensively ud in screw machine products,aircraft structures,automobile engines,orthopaedic
equipment and rivets. However,Al2024has some limitations in terms of tribological properties.Therefore,it is necessary to develop a composite posssing enhanced wear resistance without negotiating its strength[13,14].
Corresponding author:Dipankar DEY,E-mail:*******************
DOI:10.1016/S1003-6326(21)65575-9
1003-6326/©2021The Nonferrous Metals Society of China.Published by Elvier Ltd&Science Press
Dipankar DEY,et al/Trans.Nonferrous Met.Soc.China31(2021)1249−1261 1250
Adaptation of appropriate technique for AMC fabrication involves numerous challenges like matrix−reinforcement compatibility,uniformity in reinforcement distribution,grain refinement,clear interface and bonding characteristics[15].AMCs can be synthesized by many techniques like powder metallurgy,stir casting,centrifugal casting,vere plastic deformation,diffusion bonding,and friction stir processing[16−18].Among them,stir casting is an effective production technique as it provides a wide choice of materials and conditions for production and is comparatively cheap[19,20].
Fabrication and tribological performances of Al−TiB2composites were extensively reported in Refs.[1
9−29].PORIA et al[19]investigated the hardness and wear behaviour of LM4−TiB2 composites by adopting various loads and sliding speeds and stated that,inclusion of TiB2particles into aluminium alloy increas the hardness as well as wear resistance capacity of LM4−TiB2 composites significantly.JOHNY JAMES et al[21] compared the mechanical and wear properties of aluminium matrix composites reinforced with SiC and TiB2particles and revealed that,TiB2-reinforced composites exhibit higher strength and wear resistance than SiC-reinforced composite. TJONG and LAU[22]fabricated Al−TiB2 composites by powder metallurgy and obrved that by the inclusion of20vol.%titanium diboride particles into Al−4Cu alloy,dry sliding wear resistance is improved noticeably.RADHIKA and RAGHU[23]fabricated Al−TiB2composites by centrifugal casting using LM13aluminium alloy as matrix and concluded that,applied load was the most important factor influencing wear behaviour. MAHAMANI et al[24]synthesized AA6061−TiB2/ ZrB2composites by flex-assisted synthesis process and obrved enhancement in mechanical and tribological properties of the fabricated composites compared to matrix alloy.The analysis of SURESH and MOORTHI[25]revealed that,incorporation of TiB2into AA6061alloy resulted in enhancement of mechanical and tribological properties.In another study by MANDAL et al[26],influence of TiB2 addition on wear behaviour of Al−4Cu alloy was analyzed and they concluded that,an increa in TiB2content results in an increa in wear resistance.KUMAR et al[27]produced in situ Al−7Si/TiB2c
预习琥珀
omposites by K2TiF6−KBF4reaction at800ºC and reported that,uniform dispersion of TiB2particles and good matrix−reinforcement interfacial bonding were achieved.Experimental results further revealed that the incorporation of TiB2particles resulted in significant improvement of mechanical properties and wear resistance followed by reduction in friction coefficient compared to the matrix alloy.RAMESH and AHAMED[28]conducted friction and wear analysis of in situ AA6063−TiB2composites by varying the load,sliding velocity and sliding distance.Outcome of the experiments revealed that, low friction and wear rates were obrved in the developed composites compared to unreinforced alloy,whereas wear resistance of both unreinforced alloy and composites reduced with the increa in applied load,sliding velocity as well as sliding distance.ZHAO et al[29]compared the wear resistance of TiB2P/Al and SiC P/Al composites synthesized by squeeze casting and stated that, TiB2P/Al composite exhibited an increa in wear resistance followed by the reduction in friction coefficient as compared to SiC P/Al composite. However,there are no literatures covering comprehensive studies of the impact of titanium diboride addition on friction and wear behaviour of Al2024alloy composites fabricated by stir casting.
Al2024alloy is one of the hardest aluminium alloy and TiB2also posss high hardness.The main aim of this work was to u the combined effect of hardness of both Al2024alloy and TiB2for improvi
ng the wear resistance capacity of Al2024 alloy for various tribological applications and to investigate the effect of various tribological parameters on dry sliding wear and friction behaviour of Al2024−TiB2composites.
2Experimental
Chemical composition of ba metal(Al2024 alloy)ud in the prent study is illustrated in Table1.TiB2powder having a purity of greater than99%and size of13−14μm was ud as reinforcement.The AMCs were made using0,3,6 and9wt.%of micro TiB2powders.Density of Al2024alloy was 2.78g/cm3and that of TiB2particles was4.52g/cm3.Composites were fabricated using an induction furnace equipped with a mechanical stirrer by means of stir casting method. At first,small pieces of measured quantity of Al2024alloy was heated to650°C in a graphite
Dipankar DEY,et al/Trans.Nonferrous Met.Soc.China31(2021)1249−12611251
crucible.TiB2powders were preheated at450°C for30min in a distinct muffle furnace to discard away the moisture and then added to the melt.2% magnesium was also introduced into the melt to increa the wettability.The mixture was then stirred at350r/min for10min to ensure even distribution of TiB2particles.Subquently,the mixture was poured into a preheated mould and allowed to cool at
ambient temperature.Then,the solidified metal was parated from the mould and machined correctly for conducting wear and friction analysis.
Table1Chemical composition of Al2024alloy(wt.%) Fe Si Mg Mn Cu Zn Ti Cr Al 0.50.5 1.50.8 4.10.250.150.1Bal.
The microstructural characterization of the prepared composites was accomplished using SEM with EDS.A pin on disc tribotester(Model:Ducom TR20LE-M5)was employed for carrying out the wear tests of Al2024−TiB2composites,for analyzing the friction and wear behaviour.All the tests were performed at room temperature (20−25°C).Cylindrical pins(from both matrix and fabricated composites)of6mm in diameter and 40mm in length were ud for conducting the tests. For attainment of uniformity in surface roughness of all the pins,sliding faces of the pins were polished with emery paper of200,400and600grit, respectively.The pins were made to slide against a hardened steel disc(EN31material)with hardness of62HRC.For all the tests,a track diameter of 8cm was ud.Before starting of every experiment, the counter disc and pin sliding faces were washed with acetone to eliminate the footprint of foreign materials.The tests were carried out in three ts, combining different loads(10,20and30N),sliding distances(900,1800and2700m)and sliding velocities(0.5,1.0and1.5m/s).After every test, the volume loss was determined using Eq.(1):
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外铄论的代表人物V=πr2(l i−l f)(1)
where V is the volume loss,r is the pin radius,l i is the pin length before testing and l f is the pin length after testing.In order to establish confidence in the experimental results,all the tests were repeated three times.During all the experiments,the frictional force was recorded by means of a data acquisition system attached to the tribotester for determining the friction coefficient.After the tests, wear tracks and debris were analyzed using SEM. 3Results and discussion
3.1Microstructure
Figure1reprents the SEM images and EDS spectrum of the developed Al2024−TiB2 composites.Figure1(a)displays the SEM micro-graph of unreinforced material(Al2024alloy). Figures1(b−d)show that the developed composites are compact and also confirm uniform dispersion of TiB2particles,thus establishing good matrix−reinforcement bonding.Figure1(d)also depicts that the shape of TiB2particles is either hexagonal or spherical.All the SEM micrographs demonstrate unavailability of casting defects like micro cracks, porosity,slag inclusion and shrinkage,thus confirming the accomplishment of excellent quality of casting.All the properties together help to enhance the tribological behaviour of the prepared composites.The EDS spectrum of Al2024−9%TiB
2 composite is prented in Fig.1(e).Peaks of B and Ti were spotted in the spectrum which endors the existence of TiB2in Al2024−9%TiB2 composite.
Figure2displays the EDS mapping of Al2024−6%TiB2composite.It clearly shows the existence of Ti and B in the fabricated composite, which are were uniformly distributed within the matrix.
3.2Wear behavior
3.2.1Impact of load
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Wear tests were performed at three different loads(10,20and30N),keeping the sliding velocity and sliding distance constant at1.5m/s and 1800m,respectively.Figure3shows the influence of load on volume loss of Al2024−TiB2composites. From Fig.3,it can be obrved that,with the increa in load,volume loss of Al2024−TiB2 composites increas and the behaviour is approximately concave except for Al2024−6%TiB2 composite.The increa in load leads to high contact pressure and generation of high frictional heat between the pin sliding face and disc,resulting in plastic deformation.A higher degree of plastic deformation may cau sub-surface cracking of pin, leading to higher material removal[5,24].The ri in wear rate at higher loads can be attributed to
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Fig.1SEM images of Al2024−0%TiB2(a),Al2024−3%TiB2(b),Al2024−6%TiB2(c),Al2024−9%TiB2(d)(at higher magnification)composites,and EDS spectrum of Al2024−9%TiB2composite(e)
delamination,abrasion and chipping out of TiB2 particles from the matrix.At a higher load of30N, abrasion occurs in which hard asperities of reinforcement particles lying between the sliding faces,cut and plough the pin,resulting in higher wear rates.Delamination consists of propagation and nucleation of cracks,and the ri in load accelerates the phenomena and increas wear[30].Figure3further depicts that volume loss of Al2024alloy is more than that of the fabricated composites under all load conditions.The increa in TiB2mass fraction increas the hardness,which boosts up the load-bearing capacity,as this emergence of adhesive process is delayed by increasing the mating metal hardness[28].Uniform distribution of TiB2particles resists the plastic deformation of asperities.This results in oxide formation on newly expod surface.Wear loss of matrix material is significantly quicker until the contact of oxide film comes into play.In the ca of unreinforced material,the plastic deformation of asperities is very high so that the newly expod surface does not have enough time for oxide film growth,resulting in the increa in wear rate of unreinforced material.Another important phenomenon for decread wear resistance in the ca of u
nreinforced materials is adhesion of debris to sliding surfaces of the steel disc and pin and with prolonged sliding action,and the small asperities take the shape of bigger asperities,penetrate the pin surfaces,resulting in greater wear.But for Al2024−TiB2composites,reinforcement particles resist the
Dipankar DEY,et al/Trans.Nonferrous Met.Soc.China31(2021)1249−12611253 Fig.2EDS mapping results of Al2024−6%TiB2composite
Fig.3Influence of load on volume loss of Al2024−TiB2 composites penetration of asperities,which accelerates the formation of metallic oxide,leading to smaller debris formation.Further increa in reinforcement content increas the intensity to resist the penetration of asperities,resulting in increa of wear resistance[31].From Fig.3,it can also be obrved that volume loss of Al2024−3%TiB2and Al2024−6%TiB2composites at load20N are almost same,due to the adhesion of debris into the valley of the disc,resulting in higher material removal in the ca of Al2024−6%TiB2composite at a load of20N.
Figure4displays the SEM images and EDS spectra of wear tracks of Al2024−TiB2composites at10N load,0.5m/s sliding velocity and1800m
