Slurry wear characteristics of zinc-based alloys: Effects of sand content of slurry, silicon additio

Available online at www.sciencedirect.comTransactions of骂R。ScienceDirectNonferrous MetalsScienceSociety of ChinaEL SEVIER PressTrans. Nonferrous Met. Soc. China 19(2009) 277-286=一=www .nmsc.cnSlurry wear characteristics of zinc-based alloys: Effects of sand content ofslurry, silicon addition to alloy system and traversal distanceB.K. PRASAD, O.P. MODIAdvanced Materials and Processes Research Institute (CSIR), Bhopal-462026, IndiaReceived 16 April 2008; accepted 28 August 2008Abstract: This investigation deals with the observations pertaining to the efects of specimen and slurry compositions as well astraversal distance on the slurry wear response of a zinc-based aloy. The composition of the alloy was atered by adding 4% silicon toit. The slurry composition was varied through changing the concentration of the sand particles in the range of 0- 60% that weresuspended in the (liquid) electrolyte. The elctrolyte contained 4 g sodium chloride and 5 mL concentrated sulphuric acid dissolvedin 10 L of water. The slurry wear tests were conducted at a speed of 7.02 m/s over the traversal distance range of 15- -500 km. Thewear rate increased initially with traversal distance, attained a maximum and decreased thereafter irespective of the specimen andtest environment. However, the wear rate peaks were less prominent in the liquid plus sand environments than the liquid-onlymedium. Further, the wear rate peak in the liquid-only medium appeared at a shorter traversal distance than the one in the sandcontaining slurries. Addition of sand particles to the electrolyte reduced the wear rate of the samples to 5%- 15% depending on thesand concentration of the slurry. Morcover, intermediate (40%) sand content led to a maximum wear rate when compared with in theliquid plus sand media. However, this maximum was still less than in the liquid-only medium. The silicon containing alloy sufferedfrom higher wear rates than the silicon free alloy samples when tested in the liquid-only medium. On the contrary, the trend reversedin liquid plus 20% and 40% sand environments whereas a mixed response was noted in the slurry containing 60% sand. In the lttercase, the presence of silicon proved deleterious itallyl while an opposite trend was observed at longer traversal distances. The wearresponse of the samples was discussed in lerms of specific features of their microconstituents like silicon and the predominantmaterial removal mechanism in a given set of experimental conditions. The observed behaviour of the aloys was also substantiatedfurther through the characteristics of their afected surface and subsurface regions.Key words: zinc-based alloys; slurry wear behaviour, material removal mechanisms; erosion- corrosion-abrasion; microstructure-property corelationsagainst atmospheric corrosion also, wear takes place in1 Introductioncorrosive environments[4-8].Zinc-based aloys have been shown to be moreHigh strength zinc-basedalloys generallyeffective as protective coatings and sacrificial anodescomprising substantially large quantities of AI (> 8%)than pure zinc in more corrosive environments[9 1].and 1%- 3% Cu have been established as a potentialIt has been observed that the corrosion resistance ofmaterial system for use in a variety of engineeringzinc-based alloys increases with Al content[12] whileapplicationsencounteringwear[1-3].In manyaddition of Si to the alloy system has been proved to beapplications, corrosive environments with suspendedstill more beneficial in this context[9,11]. Studies suggestsolid particles are also encountered in practice inthat Zn-Al alloys behave in a manner similar to that ofaddition to wear by the (zinc-based) aloys. For example,bure Zn from corrosion resistance standpoint since Almining machinery components form an importantremains practically unaffected[13]. However, thecategory of applications wherein there exists thpresence of iron leads to higher chemical activity of thepossibility of the components coming in contact withalloy system[13]. Conflicting observations have beenmine water plus sand/soil particles during service.made中国煤化工ment particles inFurther, in applications of the zinc-based alloys ascontroFof the zinc-basedcoatings and sacrificial anodes to protect steel structuresalloysYHC N M H Ge presenece ofSiCCorresponding author: B. K. PRASAD; E-mail: brij-kprasad@aboo.o.ioDOI: 10.1016/51003-6326(08)60265-4278B. K. PRASAD, et al/Trans. Nonferrous Met. Soc. China 19(2009) 277-286reinforcement in the alloy matrix has been noted tovalues of the paramcters[42,.50.58- 60]. Also, increasingimprove the corrosion resistance of the alloy systemradial distance, angle of inclination/attack and interfacial[14- -16], as evinced by reduced open circuit potentialattack accelcrates the severity of damage[42- -58]. Further,[14]. Better response of the composite has beenthe addition of suspended solid mass to the electrolyteattributed to the passive/inert nature of the SiC particles has been found to deteriorate the response of materialsthat replace some fraction of the more active metallic[45,47] while opposite efects have also been observedmaterial surface exposed to the corrosive environment[42.50,58- 60]. Changing severity of surface damage has[14]. On the contrary, a reversal in the trend has alsobeen attributed to the predominance of one damagebeen noted in view of severe dispersoid/matrix interfacialmechanism over the other[42,50,58- 60]. The complexattack[17-l9]. From microstructure point of view,nature of the influence of controlling parameters on thecorrosion resistance improves with increasing secondarywear behaviour of materials is in view of the fact that indendritic arm spacing in hypereutectic Zn-AI alloys addition to the wear process, chemical effects also come[20- -21] while the trend reverses in the case of into picture and have a synergistic influence on thehypoeutectic alloys[20]. The corrosion process in Zn-Aloverall wear response of the samplesl11,55-57,61-65].alloys has been shown to initiate in the Al rich region in For example, both erosion and corrosion have beenthe interdendritic area[9] while the Zn rich phase is morenoticed to accelerate each other 's negative influence[66].susceptible to corrosion[ 14].Corrosion accelerates erosion[6I- 63] through surfaceHigh strength zinc-based alloys in general sufferroughening[11,63] since the severity of erosion isfrom shortcomings like dimensional instability ansensitive to the angle of attack[60]. Also, removal of theinferior elevated temperature mechanical properties thatwork hardened layer (produced by the impact of erodinglimit their use to slow moving applications operatingparticles) due to corrosion further enhances erosionbelow 120 C[1- -3]. Recently, a few modified versions[11,63-65]. On the contrary, erosion .enhances corrosionof zinc-based alloys have been developed through the through the removal of the surface deposits, surfaceaddition of silicon, showing potential to reduce throughening and increase of local turbulence[11] whilementioncd shortcoming of the high strength alloysthe work hardened layer produces a reverse effect.[22-41]. Si in this case imparts improved physical,Entrapped erosive particles decrease the wear rate. Themechanical and wear properties to the alloy system underseverity of further material loss may increase due tospecific conditions[9-11,22- -31,41].preferential interfacial attack or decrease as a result ofWear being a surface phenomenon is a complexreduced efective area of the corroding metallic surfacc.process of material removal. This is evident from aAn appraisal of the available information indicatesvariety of material and test parameters which greatlythat some studies have been carried out pertaining to thecontrol the wear behaviour of materials[29-31,42-58].corrosion characteristics of zinc-based alloys in differentThe degree of complexity increases further in the media[4- 16.20- -21.55,61 -64.66-74] while very limitedpresence of a chemical (corrosive) environment, more soinvcstigations deal with the response of the zinc-basedin the presence of suspended solid mass. As far as slurryalloys in sluris[42,58- -60]. The highly sensitive naturewear response of materials is concemned, material relatedof the wear response of materials in corrosivecontrotling factors include nature, type, size, shape,environments and synergistic effects of parameterscontenl, chemical reactivity to the test environment andinvolved therein[11,55 -57,61 -65] suggest the need tohardness of their various microconstituents; the nature ofassess the corrosive wear characteristics of zinc-basedphase/matrix interfacial regions; work hardeningalloys in order to widen the range of their applications.capability; cracking tendency, compactness and stabilityThe influence of silicon on the wear behaviour of theof the reaction products on the affected surface etcalloy system in corrosive environments adds to the[42,44- 46,48-49,53- -56,58]. Experimental parameterssignificance of the studies further in view of itsaffecting the slurry wear characteristics include thapplication potential.nature (pH) of the electrolyte, the characteristics anIn view of the above, an attempt has been made infeatures of the suspended solid (erosive) particles in thethis study to analyze the response of a (high strengh)electrolyte, traversal distance, radial distance, speed,zinc-based alloy in various test environments over aangle of attack etc.[42- -56,58]. It has been observed that range of traversal distances. The influence of adding 4%no direct relation exists between the parameters and thesilicon to the alloy system on its wear characteristics hasresponse of materials, and even mixed infuence has beenalso t中国煤化工litions. The wearobserved in many instances. For example, thbchavin various testperformance of materials deteriorates initially withconditiYCNMHGbasisofseeceincreasing speed, traversal distance and solid content in roles played by the silicon particles and the predominantthe medium but the trend becomes opposite at still highernature of different operating mechanisms of matcrialB. K. PRASAD, et al/Trans. Nonferrous Met. Soc. China 19(2009) 277-286279removal in view of the changing nature of the test sufaces and subsurface regions were studied with theenvironment. Analyses of the features of affectedhelp of a scanning electron microscope (SEM). Thesurfaces and subsurface regions further substantiated thespecimens were mounted on brass studs and sputteredobserved response of the samples.with gold prior to their SEM examination.2 Experimental2.3 Slurry wear testslurrywear testswereconducted on2.1 Alloy preparation and determination of propertiesmetallographically polished (15 mm in diameter, 10 mmThe experimental zinc-based alloys (Table l) werein thickness) samples by sample rotation technique. Aprepared by liquid metallurgy route. The alloy meltsschematic representation of the test apparatus is shown inwere solidified in the form of 20 mm diameter, 150 mm Fig.1. Samples fixed on a non-conducting disc werelong ecylindrical castings using permanent moulds.rotated at a speed of 7.02 m/s for various traversalHardness and density measurements Iwere carried out ondistances (15- -500 km) in a container having the slurry.15 mm diameter and 15 mm thick samples that were cutThe composition of the test environment was changed byfrom the castings and machined well. The samples wereadding sand particles (212- -300 μm) in varying quantitiesthen polished as per standard metallographic techniques(0 -60%) to an electrolyte. The clectrolyte was preparedfor the determination of their hardness and densityby dissolving 4 g sodium chloride and 5 mL concentratedproperties. Density of the samples was determined bysulphuric acid in 10 L of water, a compositionwater displacement technique. A Mettler microbalanceconforming to mine water. The specimens were cleanedwith a precision level of 0.01 mg was used for weighingwell with acetone prior to and after testing and weighedthe samples in air and water for computing the density.using a Mettler microbalance with a precision level ofHardness measurements were made using a Vickers'0.01 mg. Wear rate was computed by mass losshardness tester at an applied load of 294 N. The reportedmeasurement. An average of three observations wasvalues of density and hardness represent an average of reported in this study.five observations, the range of variation being土3%.Tensile tests were conducted on round samples having 4nm gauge diameter and 20 mm gauge length. Theapparatus used for conducting the tensile tests was anInstron make universal testing machine while the strainrate employed for the purpose was4.6X10-s-'.,Table 1 Chemical compositions of experimental zinc-basedalloySampleSpecimenw/%o.Zn ACu Mg__ SiSilicon-Bal.37.5 2.5 0.2free alloyFig.1 Schematic representation of slurry wear tester: 1- -Disc;Siliconcontaining aloyal. 37.5 2.5 0.5 4.02- -Sample holder; 3- -Sample; 4- Sury medium; 5- -Doublewall container, 6- - Spindle; 7- -Driving motor;, 8- Column;9 -Machine base2.2 Specimen preparation and microscopySpecimens (15 mm in diamcter, 10 mm in thickness)or microstructural observations were prepared by3 Resultspolishing them metallographically and etching withdiluted aqua regia. For conducting slurry wear tests, the3.1 Microstructural observations and propertiessamples (15 mm in diameter, 10 mm in thickness) wereFig.2 shows the microstructure of the alloys. Themetallographically polished. Affected surfaces after thesample without silicon reveals dendritic structurewear tests were cleaned thoroughly with acetone for theircomprising primary a, eutectoid a+n and 8 (Fig.2(a),analysis. Transverse sections were cut from the aectedregions marked bv A. B and arrow respectively).surfaces, mounted in polyester resin, polishedAlloy中国煤化工nation of discretemetallographically and etched with diluted aqua regia forparticlCNMHarked by C). Tableanalyzing the subsurface regions.， uCoity, 1101UI100 HisUnsile strength andMicrostructural characterization was carried ouelongation of the samples. The silicon containing alloyusing a Leitz optical microscope whereas the affectedattains less density but higher hardness as compared with280B. K. PRASAD, ct al/Trans. Nonferrous Met. Soc. China 19(2009) 277-286Open symbols一Base alloy+SiClose symbols- Base alloy0% sand20% sand40% sande61- 60% sandb)100 20030040500Sliding distance/kmFig3 Wear rate plotted as function of travel distance forsilicon-free alloy in various test environments and itscomparison with silicon containing alloy in liquid-only medium50 m2.0Fig.2 Microstructural features of silicon-ftee (a) and silicona◆- 20% sandcontaining alloysb) (A: Primary a; B: atn; Arow: E; C:. 1.6口1- 40% sand "Silicon particles)41- 60% sandTable 2 Properies of experimental zinc-based alaysPropertiesSample Specimcn" Density Hardness UTS/ Elongaion/No.. (gmL)__ (HV) MPa___ %Silicon-三0.4-free alloy4.41140 3807.Open symbols- Base alloy+SiCiose symbols一Basc alloySilicon100200300 4002containing4.38150 3005.alloyFig.4 Wear rate plotted as function of travel distance for alyswith and without silicon tested in liquid plus sand environmentsthat of the silicon-fee alloy samples. Further, thpresence of Si in the samples also decreases theistrength and elongation.●一Base aloy+Si3.0▲一Base aloy.3.2 Slurry wear responseE 2.5Wear rate of the samples was plotted as a functionof traversal distance (Figs.3 and 4) and sand content for aF 2.0-typical traversal distance of 500 km (Fig.5). The1.5influence of adding 4% Si to the alloy system on thewear rate of the samples is evident in the figures. Theowear rate increases with lraversal distance, attains themaximum and decreases thereafter at longer traversaldistances (Figs.3 and 4). The rate of initial increase inwear rate with distance is substantially larger; the wear200一60rate peak becomes sharper and higher; and the peak isSand content%observed at shorter distances in the liquid-only mediumFig.5 Wear rate of silicon containing and silicon freas compared with that in liquid plus sand environmentszinc-ba中国煤化工nd content of sury(Figs.3 and 4). Addition of silicon to the alloy systemfor typ:YHCNMHGincreases the wear rate when tests are conducted in theliquid-only medium (Fig.3). A reverse trend is observeda mixed response is noted in the medium containing 60%in the liquid plus 20%-40% sand environments whereassand (Fig.4). In the latter case, the silicon containingB. K. PRASAD, et alTrans. Nonferrous Met. Soc. China 19(2009) 277-28628alloy performed better than the silicon-free alloy samplesinitiated in the form of fine pits in different locations ofat longer distances whereas an opposite trend is followedthe specimen surface (Fig.7(a), region marked by singleinitially. Presence of' the sand particles in the testarrow). The severity of atack of the medium increasesenvironment decreases the wear rate of the samples towith increasing travel distance (Fig.7(b)). Silicon5%-15% depending on the sand content as comparedparticle/matrix interfacial attack on the specimen surfacewith that in the liquid- only medium (Figs.3, 4 and 5).by the medium is also noted (Fig.7(c), region marked byMoreover, a comparison of the wear response of thedouble arrow). The severity of attack by the testsamples in the liquid plus sand slurries suggests theenvironment reduces in the presence of the (40%)intermediate (40%) sand content to cause higher wearsuspended sand particles (Figs.7(d) vs (C)) whilerate than the remaining (20% and 60%) sand contents inabrasion grooves are observed in the case of testing thealloy in liquid plus 60% sand slurry (Fig.7(e), regionthe medium.marked by triple arrow). .3.3 Affcted surfacesFig.6 shows afected surfaces of the alloy without3.4 Subsurface characteristicsFeatures of subsurface regions of the samples aresilicon in various test environments. Corrosive attack ofshown in Fig.8. The regions marked by A and singlethe liquid-only medium causing the formation of pits onthe specimen surface is evident in Fig.6(a) (regionarrow in Fig.8(a) represent an indentation mark andmarked by single arrow). The severity of attack reducesmicrocracking around the indented region, respectively.considerably when tests are carried out in liquid plusA typical sand particle entrapped in such an indented40% sand slurry (Fig.6(b)) over that in the liquid-onlyregion is shown in Fig.8(b) (region marked by B).medium (Fig.6(a)). A typical indentation mark on theMicrocracking of the sand particles was also observedspecimen surface in this case is evident in Fig.6(b)(Fig.8(b), region marked by double arrow). Silicon(region marked by A). A magnified view clearly revealsparticle/matrix interfacial attack below the affectedthe pits and indentation marks (Fig.6(c), regions markedsurface (top portion) is evident in Fig.8(c) (regionby single arrow and A, respectively). Abrasion groovesmarked by triple arTow).are observed on the affected surfaces of the samplestested in the slurry containing 60% sand (Fig.6(d), region4 Discussionmarked by double arrow).Fig.7 represents affected surfaces of the alloyFrom microstructural considerations, the Al rich acontaining silicon. The influence of test environment andand zinc rich η phases are essentially solid solutions oftravel distance on the nature of surface damage is evidentZn and Al in each other and basically soft in naturein the figure. The attack of the liquid-only environment[23-25,31,34,36, 76]. Further, the ε phase is somewhat中国煤化工fYHCNMHGmFig.6 Afected surfaccs of silicon-free aly ater testing for 500 km in liquid-only medium (a), 40% sand slury (b, c), and 60% sandslury (d) (Single arrow: Pis; A: indentation mark; Double arrow: Abrasion grooves)282B. K. PRASAD, et alTrans. Nonferrous Met. Soc. China 19(2009) 277 -28620 umI 20umFig.7 Affcted surfaces of silicon containingalloy after testing in liquid-only medium (a)-(C), 40% sand suy (d), 60% sand slurry for(a) 15 km, and 500 km (b)-(e) (Single arrow:is; Double arrow: Silicon particle/matrixinterfacial attack; Triple arrow: AbrasionL 20mgrooves)harder than the a and 1 phases and offers wear resistanceelongation of the alloy system in the presence of Si[23-25,30,33,35,75]. As far as Si particles are concerned,(Table 2) could be attributed to the enhanced crackthey are the hardest amongst all the four phases. Fromsensitivity[23- 25,30,33,35,75]. It has been suggestedhardness, strength and wear resistance points of view, thethat Si has negligibly small solid solubility both in Alfour phases could be graded as Si > c> a> nη and Zn[77]. This leads to the generation of discrete[23- -25,30,33,35,75]. The same gradation is also validparicles of Si in the alloy matrix (Fig.2(b), regionfor the phases from corrosion resistance point of view.marked by C). In such cases, interfacial regions becomeThis could be conceived keeping in mind the place of thepreferential sites for the nucleation followed bymajor constituents, i.e. Si, Cu, Al and Zn in Si, e, a andηpropagation of cracks in the material system[78-79]respectively, in the electrochemical series that suggests during tensile testing that utimately leads to inferiorSi> Cu> Al> Zn in terms of the degrce oftensile strength and ductility in the Si containingelectrochemical passivation[76]. Accordingly, the overallzinc-based alloy as compared with the samples withoutresponse of the specimens is controlled by the propertiesSi (Table 2).like hardness, strength and corrosion and wear resistancelurry wear testing by sample rotation techniqueoffered by the various microconstituents of the samplesinvolves the rotation of specimens fixed on a disc in theand the predominance of one set of characteristics of thetest environment. In the event of rotation in liquid alone,constituent phases over the other producing a reversesurface damage to the specimen is caused by theffect[12,23-40.42.58.75]. The nature of the testchemical attack and impinging action of the droplets ofenvironment is expected to play an important role in thisthe medium. Droplets are formed due to the turbulencecontext[42,58- 60.75]. Higher hardness and less densityreat中国煤化工e medium. In ceaseof the Si containing zinc-based alloy than that of the Sithe nparticles. damagefree alloy samples could be atributed to the light massduc tYHCNMHGonthespecimenand high hardness characteristics of Si [23- 25,30.33,35,surface. The damage occurs in the form of impingement75]. On the contrary, a reduction in the strength andof the solid paricles on the exposed surface, i.e. erosionB. K. PRASAD, et al/Trans. Nonferrous Met. Soc. China 19(2009) 277 -286283mass/thickness exceeds a limit allowing the exposure of(a)fresh metallic surface to the medium. Thus, theformation and removal of reaction products take placealmost continuously in quite succession during the tests.The role of a reaction/corrosion product in controllingthe wear behaviour of materials in slurry depends on itscompactness (inverse of permeability) and adhesivenesswith the substrate surface. The degree of compactness ofa corrosion product in turm has been found to be20 um|dependent on the nature, shape, size and orientation ofthe particles therein[7]. Further, the higher thecompactness and adhesiveness of the reaction productare, the less the severity of further corrosion would bedue to the reaction product. Thus, removal of a corrosionproduct/passive layer due to erosive and/or corrosiveaction could be detrimental or beneficial depending onthe degree of its cormpactness.Coming to the composition of the test environment,[100 umit may be noted that the liquid comprises of sulphate andchloride ions which are quite corrosive in nature.Adition of sand particles to the liquid (maintaining theame volume fraction of the slurry) decreases theeffective volume fraction of the (corrosive) liquid,thereby reducing the severity of its corrosive action.Increasing pH of the environment from 1.93 for theliquid-only medium to 3.64, 6.85 and 7.12 for theenvironments containing 20%，40% and 60% sand,respectively, further substantiates the reducingFig.8 Subsurface regions of silicon-free (a, b) and siliconcorrosivity of the medium in the presence of the sandcontaining alloys (c) (A: Indentation mark; Single arrow:particles. However, the presence of the (sand) particlesMicrocracks around indented region; B: Typical sand particleproduces impinging action, causing erosive damage inentrapped in indented region; Double artow: Microcracks inview of their mobility in the rotating liquid[42- 48,58].sand particle; Triple arrow: Silicon particle/matrix interfacialThe severity of erosion increases with the content of theattack)suspended solid mass up to a critical value in the liquid.Beyond the critical content, the suspended solid particleswhen their concentration in the medium is relatively lowenjoy only a limited freedom in the medium and rather[45,50,58]. Another form of surface damage takes placeexperience sliding action against the specimen surfacethrough the sliding action of the suspended particles, i.ecausing abrasion[42,50,58 -59,75].abrasion in view of their restricted mobility due to highInitial increase in wear rate with distance (Figs.3concentration in the medium[50,58]. Entrapment of theand 4) could be attributed to the increasing severity ofimpinging particles in the indented regions also occurs.attack by the environment (Figs.7(b) vs (a)). Wear rateDamage to the rotating specimen surface by thepeak corresponds to the formation of deep craters[42- -48,medium initiates in the form of fine pits[42- -48,58].58- -59,75]. A decrease in wear rate beyond the wear rateGrowth of the pits takes place, leading to the formationpeak is due to the deposition of reaction productsof deep craters as the test progresses. By this time,in/aroundtheaffectedregions[42,50,58- -59,75].reaction products are deposited inside/around theEntrapment of suspended sand particles in the indentedpits[42- -48,58]. Accordingly, the deposited massregions (Fig.8(b), region marked by B) may be partiallydecreases the severity of attack by the medium by way ofresponsible for the decrease in wear rate in liquid plusreducing the extent of penetration of the environment tosand中国煤化工uid only mediumthe mtallic surface. Evolution of hydrogen in the(Figs.crevices/pits also produces a similar efect[42 -48,58].YHC N M H Gontaining aloy asThe reaction products are removed due to the impingingcompared with the silicon-free alloy samples in theaction of the medium especially when theirliquid-only medium (Fig.3) in spite of less corroding284B. K. PRASAD, et al/Trans. Nonferrous Met. Soc. China 19(2009) 277-286nature of the silicon particles present therein could beslurries. However, this maximum is less than that in theowing to the predominant silicon particle/matrixliquid-only medium. The predominant operating wearinterfacial attack[14] by the environment (Fig.7(c),mechanism also changes with the sand concentration ofregion marked by double arrow, and Fig.8(C), regionthe medium from corrosion in the liquid-onlymarked by triple arrow). On the contrary, better wearenvironment to corrosion-assisted-erosion in the sluryperformance of the samples alloyed with silicon than thecontaining up to 40% sand and to corrosion-assisted-ones without the element in liquid plus sandabrasion in the 60% sand slurry.environments(Fig.4) is due to the resistance offered bythe silicon particles to the softer matrix against the5 Conclusionsdestructive action of the environments[14,17-19]. Lowerwear rate of the silicon-free alloy in the 60% sand1) Wear rate increases illy with traversalenvironment at shorter travel distances (Fig.4) can bedistance, attains the (wear rate) peak and decreasesattributed to more firmly sticking of the reactionthereafter at still longer traversal distances. The wear rateproducts on the affected surfaces{7] in view of betterpeak is quite prominent when the tests are conducted inductility and less hardness of the (ilicon-free alythe liquid-only medium; the peaks are rather shallow in(Table 2). The sticking mass appears to offer resistancethe sand slury and less defined in some cases. Further,against the (abrasive) action of the medium causingthe peaks are observed to reach at shorter distances in theimproved wear response of the silicon-free alloy asliquid-only medium than those in the sand slurries.compared to that of the one with silicon (Fig.4).2) The presence of Si in the alloy system provesMaximum wear rate in the liquid-only mediumbeneficial by offering decreased wear rate in general(Figs.3 and 4) suggests that the dominant wearwhen the tests are conducted in the liquid plus sandmechanism causing material loss is corrosion (Figs.6(a),surries. On the contrary, the Si containing alloy exhibits7(a)-(c) and 8()), A reduction in the wear rate in spite ofhigher wear rates as compared to that of the silicon freethe additional (erosive and/or abrasive) damagealloy in the liquid-only medium.(Figs.6(b)-(d), 7(d) and (e), and 8(a) and ()) by the3) Maximum wear rate of the samples is noted insuspended solid mass in the medium indicates that thethe liquid-only medium. The presence of suspended sandadditional (abrasive and/or erosive) damage by theparicles in the test environment leads to a reduced wear(suspended) solid particles is less detrimental than therate irespective of the alloy composition, the degree ofreduction in the (corrosive) attack of the medium in viewreduction in the wear rate being to the extent of 5%- 15%of its decreasing volume fraction in the test environment.depending on the sand content of the slury. AIncreasing wear rate of samples due to the increasingcomparison of the wear behaviour of the samples in thesolid content from 20% to 40% can be due to a greatersand slurries shows that the intermediate (40%) sandseverity of the impinging action of the solid masscontent leads to a maximum wear rate. However, thiscausing erosion of the specimen surface (Figs.6(C) andmaximum wear rate is less than that in the liquid -only8(a), regions marked by A). On the contrary, a reductionmedium.in wear rate in the liquid plus 60% sand medium over the4) Corrosion is the dominant mechanism of materialone in 40% sand slurry (Fig.5) can be owing to theremoval in this investigation, erosion and abrasiondominating abrasive action of the sand particles on theplaying a secondary role. The predominance of one wearspecimen surface. It may be noted that abrasive action ofmechanism over the other is responsible for the changingthe environment leading to the generation of groovesbehaviour of the samples with the composition of the test(Fig.6(d), region marked by double arrow, and Fig.7(e),environment in terms of sand content. Also, the dominantregion marked by triple arrow) is less detrimental itand opposite effects of factors like silicon particle/matrixtermns of material loss than their impinging actioninterfacial attack and (corrosion/erosion/abrasion)wherein large craters are formed (Fig.6(b), regionresistance offered by the silicon particles to the alloymarked by A, and Figs.8(a) and (b), regions marked by Asystem over each other are responsible for the varyingand B).wear response of the aloys in various test environments.An appraisal of the observations made in thisinvestigation suggests significant effects of the presenceReferencesof silicon in the alloy system on slury wear response.Further, the nature and severity of the influence are[川]中国煤化工re in mining cquipent1983. 36: 727-728.dependent on the sand content of the test environments.Addition of sand particles to the test medium causes the[2YHCNMHGIntermational Materialswear rate to decrease. Intermediate sand content leads to3] KUBEL E J. 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