The Study of corrosion behavior of aluminum, bronze and nickel alloys on different speeds rotated samples

Transcription

1 WALIA journal 30(1): , 2014 Avalable onlne at ISSN WALIA The Study of corroson behavor of alumnum, bronze and nckel alloys on dfferent speeds rotated samples Danal Nazeran *, Mazar Nazeran, Al Memar Young Researchers and Elte Club, Neyshabur Branch, Islamc Azad Unversty, Neyshabur, Iran Abstract: The purpose of ths paper s to nvestgate of the corroson behavor of alumnum, bronze and nckel alloys. In order to study the corroson behavor of C95700 alloy, Polarzaton experment was performed on the alloy on dfferent speed of rotaton sample n sodum chlorde soluton. The results show the corroson potental enhanced by ncreasng the rotaton speed from -416 mv to -330 mv. On the other hand, the densty of corroson rate ncreased from 12.6 A/cm2µ to 57.8 A/cm2µ by ncreasng rotaton speed. Key words: Corroson behavor; Speed of rotaton; Polarzaton experments; Alumnum, bronze; Nckel alloys 1. Introducton *Because of alumnum bronze propertes such as hgh strength and excellent corroson resstance, especally under condtons of turbulent flows, those are appled n ndustres lke chemcal and marne ndustry and also n makng peces such as bushes, pumps, valves, small gears, bearngs, and shp propellers (Tang et al, 2004). A proper selecton of materals and good desgn are effectve n reducng corroson cost. Now, corroson scence and ts mportance become clearer. In polluted envronments between sulfde nfluences of these ons to alloy surface ncrease corroson rate (Dehghan, 1392). Alumnum bronze s a group of copper-alumnum alloys, whch has good corroson resstance and stablty and s extensvely used n both states of casted and wrought. Alumnum bronzes has developed from a smple alloy of copper and alumnum to complex alloys wth the addton of elements such as ron, nckel, manganese, slcon and other elements (Powell, 2012). Alumnum- nckelmanganese bronze (C95700) s known CMA1 n Brtsh standard s alloys, whch wdely used for the manufacture of large marne propellers. For the frst tme n 1950, ths alloy developed n order to correctng common alloys whch were used n propeller manufacturng lke as elastc brass and alumnum-nckel bronze (Tang, 2004). C95700 alloy s formed of 75% (wt%) copper (Cu), 2% nckel (N), 3% ron (Fe), 8% alumnum (Al) and 12% manganese (Mn). Copper s one of the most mportant known useful metals for human and one of the frst metals whch have been used. Thermal conductvty of copper s very hgh and Due to made commercal product, there are about 400 dfferent copper alloys, (Bssey-Breton, 2014). * Correspondng Author. Ths alloy has better mechancal propertes than nckel bronze (NAB) and also ts densty s (7.45 gr/ cm 3 aganst 7.65gr / cm 3 ) lower. Its meltng pont s lower thus also ts weldng and castng propertes are better. In contrast of alumnum- nckel bronze, ths alloy doesn t have the brttleness problem n the temperature range C and therefore, Kargrm and ts fxng s easer; However, t has less resstance versus to types of corroson such as fatgue corroson, stress corroson and gap erosoncorroson (Tang, 2004). All of alumnum bronze has good resstance versus corroson; however the amount of resstance to corroson s dfferent due to ther metallurgcal structure that s dependent on the chemcal composton and producton hstory n partcular ther heat treatment has been done on them. These alloys on the surface have thn flms and adheson of copper oxdes and alumnum oxdes whch, f damaged or destroyed, spontaneously formed agan. These alloys also have consderable resstance versus eroson, abrason and fatgue corroson (Tang, 2004), smple alumnum bronzes, whch are only alloy of copper and alumnum to 8%, have sngle alpha phase structure. By ncreasng alumnum content to more than 8%, s formed betaphase and s produced alpha-beta structure alloy. If Alpha Beta alumnum bronze s cooled slowly rate from hgh temperatures about 600 C Beta phase s converted to the gamma2 phase at about temperature 565 C. As a result, f ths phase s formed contnuously, s caused decreasng of resstance corroson and ncreasng penetraton rate of corroson. Research performed on alumnum alloys wth 8.5 to 9.5% has shown that f the amount of alumnum n alumnum bronzes s less than 9.1 percent wll not be formed gamma2 phase contnuously. Alloys wth the hgher percentage of alumnum for lack of gamma phase must are cooled quckly e.g. by 172

2 quenchng n water from 600 C after castng or hot workng (Schossler, 1993). Obvously, the addton of other alloyng elements wll leads other changes n the metallurgcal structure alloys and exstng phases. The presence suffcent quantty of ron to prevent from formaton of gamma2 phase and thereby s refned the gran structure alloy and f s formed gamma-2, whch wll be dscontnuous. Nckel has the same effect wth ron and prevents the formaton of gamma 2 phase contnuously and destructve. However, wth ths goal cannot be added to alumnum bronze, because ron can have the same effect wth cheaper prce. To addng manganese also prevent the breakdown beta phase to gamma 2 and alpha phases. Beta phase of Alumnum bronzes contanng ten percent of alumnum wth ron and nckel produce alpha and kappa phase, n the temperature range C durng the coolng. Kappa phase contans all the components of alumnum, ron, nckel and manganese; f there s manganese. Usually, corroson resstance of alumnum bronze ncreases by ncreasng amounts of alumnum and other elements alloy (Powell, 2012) & (Schossler, 1993). Although more than one hundred years, the research s ongong better understand the actual mechansm of actve corroson and what happens n many corroson processes s understandable, but the nvestgaton sn t complete by no means; Many felds reman unexplored or are known lttle. In ths part we survey some of the smlar studes that assess dfferent clmate or envronmental on materals. Schussler and hs colleague experments showed n presence of sulfde contamnaton whch corroson rate ncreases due to changes n the structure of the passve layer caused by enterng copper sulfde nto structure. The amount of copper oxde and alumnum oxde are reduced n ths case, whch s corroson nhbtors. As such the corroson products are very porous and composed of copper sulfde. The sulfde accelerates the reacton of charge transfer for oxygen reducton that occurs on the surface of corroson layer dramatcally (Tang, 2006). Tang and hs colleagues seek to mprove the corroson resstance of these alloys n ther research. These researchers used a laser surface meltng (LSM) alumnum-nckel-manganese bronze and also laser surface alloyng (LSA) by usng of alumnum powder wth combned 75.6% Mn, 10.8 wt% Cu, 7.8 wt% Al, 3.6 Fe and 2.2 wt % nckel. In frst case, (LSM) was performed for surface meltng and creatng a resstant layer of depresson - gap corroson and the second case (LSA) wth the am of formng a new alloy layers. Resstance of erosongap corroson was mproved 5.8 tmes n soluton contan 3.5% sodum chlorde compared to the ntal alloy (Kwok, 2000). Results of Tang and hs colleagues survey showed an approxmate thckness of 1 mm alloy layer wthout cracks and pore s formed on the substrate usng laser surface alloyng method and alumnum powder. The sngle- beta phase layer wth 173 BCC structure has an alumnum amount greater than the substrate and also ts rgdty was measured two tmes than the substrate. Depresson - gap corroson resstance ths layer was about 30 tmes better than ntal alloy because of the formaton of sngle-phase layer wth hgh hardness. Also the samples due to hgher hardness and lower gran boundares were better than surface meltng samples by laser (Kwok, 2000). Kwak and hs colleagues were studed Smultaneous effects depresson and corroson of engneerng alloys n soluton wth 3.5% NaCl. 2. Materals and Methods The purpose of ths paper s to study the corroson behavor of base copper alloy, whch s C95700 standard number. The sample alloy prepared from engneerng company and study of the type and amount alloy elements of the chemcal composton and basement and ensure from ther range n the standard range was performed by quantmeter. After determnng test method (potental, flows and other varables) by computer, enter the control system nto t and test s performed. Rotatng dsk electrode rotates samples accordng to dfferent speed n a cell. To study the effects of rotaton speed of dsk was performed at dfferent perods of 0, 1500, 3000, 6000 and 9000 rpm. The effect of temperature was studed by examnng and testng on the ambent temperature and the temperature of 40 C. Way of ncreasng the tastng temperature at 40 C was performed as puttng the samples nto a beaker whch s connected to rotatng dsk electrode machne and s placed on hot plate and ts temperature s held statonary at 40 C by crculatng water. The corroson tests carred out on samples ncluded of electrochemcal mpedance spectroscopy, potentodynamc polarzaton and lnear polarzaton. To perform the corroson test s prepared soluton wth a known concentraton of commercal sodum chlorde (3.5%) and dstlled water whch t s dstlled one tme. Cell preparaton process for the test s as follows: Frst step: Preparaton of sodum chlorde soluton wth the specfed concentraton of at least 30 mnutes, before the start of each test, ths was performed n order to create same aeraton n all the experments. The electrolyte s replaced by fresh and clean soluton after each test. Second step: washng test chamber by dstlled water. Thrd step: the sample was attached to the rotatng dsk electrode and was placed nto the cell contanng brne. Fourth step: manner of connectng the sample between the rotatng dsk electrode and Potentostat s performed by the connectng cable. Ffth step: The tme and manner puttng the reference and auxlary electrode before turnng machne on and wthn the cell contanng brne around the sample that each of the electrodes s connected to the machne by cables. For the

3 preparaton of the samples s polshed the sample before performng each test at each speed of rotaton. The polshng was performed by slcon carbde sandpaper wth numbers 600, 1000 and 2000 respectvely. Water was used as a lubrcant durng the polshng process. The samples were rotated 90 degrees between successve steps to be removed scrape the prevous steps. Next step was polshed by an electrc polsher. After polshng, ol, grease and probable polluton are releved on the surface of sample by alcohol and then were dred n Dryer, and samples have been kept n the desccator untl tests to ensure remanng wthout polluton and contact wth other materals or components. To evaluate the results of corroson tests and plottng the necessary dagrams and data extracton were used Ivum soft and Excel software. Cross secton area exposed to corroson was a crcle wth a dameter of 5 mm. 3. Corroson test results at room temperature and at 40 C wth changng speed of rotaton of the sample 3.1. Study of C95700 alloy behavor for lnear polarzaton test In order to study the corroson behavor of C95700 alloy, lnear polarzaton tests were performed at dfferent speeds of sample rotaton t nto sodum chlorde soluton. Fg. 1 show curves obtaned from the lnear polarzaton tests. Based on ths Fg., a lne has been transferred to up by ncreasng the speed of sample rotaton of the lnear polarzaton whch t represents the surface alloy has became more decent. Accurate analyses of these curves were performed by the Ivumstat software. In order to calculate the polarzaton resstance tests based on lnear polarzaton s needed to equvalent weght and sample densty. In order to calculate the equvalent weght of studed alloy samples were used ASTM-G 102 standard. Based on ths standard, weght of alloy sample s calculated as follows: (1) EW = 1 n f W In ths equaton) f : weght percentage of element, W: atomc weght of element, n: number of valence electron of element. Due to ths equaton and quantmeter analyss of the tastng sample, equvalent weght of studyng sample was obtaned 9.25 gr. Furthermore, sample densty was obtaned accordng to the ASTM-G102 standard and the followng formula: D = 1 f D (2) 174 Fg. 1: the curves obtaned from lnear polarzaton tests C95700 alloy for dfferent speeds of rotaton samples n 3.5% sodum chlorde soluton at room temperature. Fg. 2: the changes polarzaton resstance of the C95700 sample n sodum chlorde soluton or dfferent speeds of rotaton samples n 3.5% sodum chlorde soluton based on lnear polarzaton testng at room temperature. Fg. 2 shows the changes polarzaton resstance of the C95700 sample at dfferent speeds of rotaton samples n 3.5% sodum chlorde soluton on the bass of lnear polarzaton testng at room temperature. As t s seen n ths Fg., polarzaton resstance was 6263 Ωcm 2 n statc soluton t and has been reduced to 4618Ωcm 2 by ncreasng rotaton speeds to 1500 rpm;. By further ncreasng the rotaton speed, polarzaton resstance reduced more, and t s reduced to 2446 Ωcm 2 n the 9000 rpm Study of C95700 alloy behavor n potentodynamc polarzaton tests Polarzaton curves were nvestgated n order to study anodc behavors of the samples and comparng them wth each other. Fg. 3 shows the electrochemcal polarzaton curves of C95700 sample n sodum chlorde soluton at dfferent speed of the sample rotaton.

4 Accordng to ths Fg., the polarzaton curve of the statc soluton s on the left sde than the other curves. It means; ts corroson rate densty s lower than the other curves. By ncreasng rotaton speed, electrochemcal polarzaton curves are transferred to the rght. Furthermore by ncreasng the soluton speed, electrochemcal polarzaton curves have been shfted upwards, more postve potentals. Ths may s related to makng an oxde flm on the surface of copper oxde. In order to evaluate more accurate of electrochemcal polarzaton curves, these curves analyses by Ivum soft. Table 1 shows the analyss results of the polarzaton curves. Table 1: The results of electrochemcal polarzaton curves of C95700 alloy at dfferent rotaton speeds of samples n soluton of 3.5% sodum chlorde at room temperature Rotatng Rate(rpm) Ecorr (mv) (µa/cm 2 ) a(mv/dec)β c(mv/dec)β Fg. 3: The electrochemcal polarzaton curves at dfferent rotaton speeds of C95700 alloy sample n a soluton of 3.5% sodum chlorde at room temperature Accordng to Table 1, the corroson potental enhanced wth ncreasng the rotaton speed from mv to about-.330 mv. Ths potental enhance s justfed by formng passve flm on the surface. On the other hand, the corroson rate densty enhanced from 12.6 μ A / cm 2 to 57.8 μ A / cm 2 by ncreasng the rotaton speed. Ths corroson rate enhancement represents that formed flm on the surface s not protectve and does not make a barrer versus corrosve ons. When corroson potental s more postve and when corroson rate densty decreases, corroson resstance ncreases. Excellent corroson resstance of alumnum bronze s because of formng an nherent and thn flm connectng or adhesve s stronger than alumnum oxde. The flm has selfhealng capabltes, and as soon as t forms, t prevents the further oxdaton and thus prevents to flake, whch usually occurs n ferrous alloys. After ths layer s formed, n order to contnue corroson, oxygen should penetrate through ths layer to reach the surface of the substrate alloy. Oxde flm on the copper surface s a mxture of Cu 2 O and CuO oxde. When alumnum also s present n the alloy composton, the formed flm s a mxture of copper and alumnum oxde. Vsble lght extremely reduces the formaton rate of copper oxdes. Ths flm s easly extermnated n the turbulent water easly and dssolves n carbonc acd or organc acds whch are present n fresh water or sol, and dssolvng ncreases the rate of corroson. Wth ncreasng rotaton speed of sample s done varous processes. Wth ncreasng the rotaton speed, because of enhanced turbulence of soluton, oxygen and corrosve ons reach to surface easer. Easer access of oxygen to surface causes passve flm s formed on the surface, and potental becomes more postve. On the other hand, wth ncreasng the rotaton speed, stress s created on the surface. Ths shear stress can separate lnked layer to surface whch don t have hgh adhesve to surface. So by ncreasng the rotaton speed, the access of oxygen and corrosve ons to the surface ncreases and the corroson products and formed layer on surface separate from the surface more easly Study of C95700 alloy behavor n electrochemcal mpedance test Impedance test (3.5 wt% sodum chlorde soluton) was performed on the samples n the same envronment. Nyqust curves obtaned from expermental data are plotted n Fg. 4. Nyqust dagrams (magnary part of the mpedance on the Y- axs and real part of the mpedance on-axs X) by usng dfferent equvalent crcut models are descrbed and nterpreted. It s seen that the curves are not perfect semcrcle. Quas-semcrcle dameter s related to chargng transfer resstance; ths value s equal to the polarzaton resstance f there sn t quasnduced behavor. The dstance between the source and the semcrcle represents soluton resstance, whch there s between the reference electrode and the workng electrode. 175

5 All curves have the same shape of the semcrcle but wth dfferent szes. Ths ndcates that the man reacton s the same for all the electrode rotaton speeds but for each of them to be, effectve coverng area s dfferent versus corroson. As t s observed n the Nyqust graphs, the graphs have a crush whch represents are not deal capactve loop. Thus for analyss of curves, capactor has been smulated by usng a constant phase element (CPE) as mathematcally. CPE values were calculated usng the followng equaton: CPE = Y 0 ( ω ) n-1 (3) Where Yo s constant ω, CPE s angular frequency n maxmum magnary mpedance condton and n s power of CPE whch f the value of n s close to 1, t represents more capactve behavor of CPE element. Fg..4. the electrochemcal Nyqust curves of C95700 alloy at dfferent rotaton speeds of sample n 3.5% sodum chlorde soluton at room temperature. As t s evdent n ths the Fg., electrochemcal mpedance curve formed from a semcrcle, whch represent the corroson process s nfluenced by charge transfer. By ncreasng rotaton speed does not make any dfference n the appearance of curves, and curves reman n a semcrcle. Fxng shape curves shows by ncreasng rotaton speed, corroson processes and ts rulng mechansms are fxed and not changed. Accordng to these curves, clearly by ncreasng rotaton speed of the sample, electrochemcal Nyqust curves dameter has been reduced. For the electrochemcal mpedance curves, analyzng s used crcut equal Sel Randles crcut. These curves were analyzed by usng the Ivumsoft software. Table 2 shows the results of the analyss of these curves. Table 2: The results of the analyss of electrochemcal mpedance curve at room temperature Rpm Rp(Ωcm 2 ) CPE(µF/cm 2 ) N Accordng to ths table, polarzaton resstance of samples s 6416 ohm/cm 2 n resdng soluton. Whle by ncreasng rotaton speed of sample to 1500 rpm, the polarzaton resstance decrease strongly and s reached to 3853 ohm/ cm 2. By ncreasng soluton speed, polarzaton resstance decreased less and n rotaton speed 9000 rpm, polarzaton resstance has been reduced to Corroson test results by varyng the speed rotaton of the sample at 40 C shows the varaton of polarzaton resstance obtaned from analyzed lnear polarzaton tests at dfferent rotaton speed of the samples. It can be sad that almost the temperature ncreases the rate of all chemcal reactons. Sometmes temperature ncreasng has Akspvnansyly and strong effect from the begnnng and another tme hasn t been sgnfcant effect and then became strong. Temperature ncreasng n acdc envronment enhances oxdaton power. In order to study more accurate corroson mechansm and the effect of smultaneously temperature and rotaton on the corroson process of the C95700alloy n 3.5 wt% NaCl soluton, all of tests were performed at room temperature (Lnear polarzaton, potentodynamc polarzaton and electrochemcal mpedance) and 40 C at dfferent rotaton speeds of the alloy samples. Fg. 5 shows the lnear polarzaton curves at 40 C on C95700alloy. Based on ths Fg., by ncreasng the rotaton speed of the sample, potental slope s reduced due to rate and thereby resstance s reduced to corroson. Accurate analyss of these curves was performed based on the Ivumstat curve software. Values of equvalent weght and alloy densty were consdered accordng to prevous calculatons. Fg. 6 Fg. 5: The curves obtaned from lnear polarzaton tests of C95700 alloy at dfferent rotaton speed of the sample n 3.5% sodum chlorde soluton at 40 C As you can see n ths Fg., the polarzaton resstance s greatly reduced by ncreasng rotaton speed of the sample. As prevously mentoned, ths s related to easer achevg corrosve partcles to surface. 176

6 Fg. 6: The varaton polarzaton resstance of C95700 alloy at the dfferent rotaton speed at 40 C For Contnung work (or after that), electrochemcal polarzaton tests were performed at dfferent rotaton speeds of samples at 40 C. Fg. 7 shows the curves obtaned from these experments. Accordng to ths electrochemcal polarzaton, curves were shfted to the rght and above by ncreasng the rotaton speed of the sample. Shftng curves to the rght represents an ncreasng n the corroson rate. Table 3 shows the analyss of the polarzaton curves. Table 3: The results of electrochemcal polarzaton curve analyzng at 40 C at dfferent rotaton speeds. Rotatng Rate(rpm) Ecorr (mv) (µa/cm 2 ) a(mv/dec)β c(mv/dec)β Based on the results obtaned, values of corroson rate densty enhanced by ncreasng the rotaton speed and ncreased from 13.1 μa / cm 2 to 716 μa / cm 2. Corroson rate densty ehanced at room temperature by ncreasng rotaton speed, but t has ncreased sharply at 40 C. Ths ndcates that the effect of sample rotaton was greater at hgher temperatures and has ncreased corroson rate more. The values of anodc tafel slope enhanced greatly by ncreasng rotaton speed. On the one hand, ths ncreasng s related to ncreasng envronment temperature and the other hand, to easer dstrbuton of anons at soluton. Fg.8: The electrochemcal Nyqust curves of C95700alloy at dfferent rotaton speeds of the sample n 3.5% sodum chlorde soluton at room temperature. Fg. 7: The electrochemcal polarzaton curves at dfferent rotaton speeds of the samples n 3.5% sodum chlorde soluton at 40 C 177 Fg.9: The changng polarzaton resstance at dfferent rotaton speed at 40 C For contnung work (after that), Electrochemcal mpedance tests were performed at dfferent

7 rotaton speeds of sample at 40 C that s shown n Fg. 8. Based on ths Fg., the dameter of electrochemcal Nyqust, s curves has been reduced by ncreasng rotaton speed so that, by further ncreasng rotaton speed of the sample, percentage changng of polarzaton resstance has been reduced. These curves analyzed by approprate equvalent crcut and Fg. 9 shows the polarzaton resstance changes at dfferent rotaton speeds at 40 C. As you can see n ths Fg., polarzaton resstance was decreased by ncreasng rotaton speed. Notable thng n ths Fg. compared wth the results n table 3 s, n addton to polarzaton resstance changng to rotaton speed, polarzaton resstance changng to temperature. Polarzaton resstance values were decreased by ncreasng temperature. Ths was observed n values of obtaned from corroson speed and ts ncreasng. In general, corroson rate s related to temperature accordng to Arrhenus equaton and s enhanced by ncreasng temperature. 4. Concluson In ths paper, from all of tests performed on C95700 alloy have been receved the followng results generally. Surface of alloy becomes nobler by ncreasng rotaton speed of the sample at room temperature. Corroson enhanced from -416 mv to about - 330mV by ncreasng rotaton speed. Ths ncreasng potental s justfed wth formed passve flm on the surface. On the other hand, corroson rate densty s enhanced from 12.6μA/cm 2 to 57.8μA/cm 2 by ncreasng rotaton speed. Ths corroson rate ncreasng represents the formed flm on the surface sn t protectve and does not create a barrer versus corrosve ons. By ncreasng rotaton speed, values of corroson rate densty enhanced greatly and ncreased from 13.1µA/cm 2 to 716µA/cm 2. Corroson rate densty ncreased by ncreasng rotaton speed at room temperature, but ncreased sharply at 40 C. Ths ndcates that the effect of sample rotaton was greater at hgher temperatures and was ncreased corroson rate more. Powell. C., Webster. P. (2012), Copper alloys for marne envronments, copper development assocaton publcaton. Tang. C. H., Cheng. F. T., Man. H. C. (2004), Improvement n cavtaton eroson resstance of a copper-based propeller alloy by laser surface meltng, Surface and Coatngs Technology 182, Stéphane Bssey-Breton, Vncent Vgnal (2014), "Influence of post-machnng thermal treatment on the corroson behavour of copper"proceda CIRP 13, Schossler. A., Exner. H. E. (1993), The Corroson of nckel-alumnem bronzes n seawater-part I. protectve layer formaton and the passvaton mechansm, Corroson Scence, Vol. 34, No. ll, pp Tang. C. H., Cheng F. T., H. C. Man (2006), Laser surface alloyng of a marne propeller bronze usng alumnum powder, Part II: Corroson and eroson corroson synergsm, Surface & Coatngs Technology 200, Kwok. C. T., Cheng. F. T., Man. H. C. (2000), Synergstc effect of cavtaton eroson and corroson of varous engneerng alloys n 3.5% NaCl soluton, Materals Scence and Engneerng A290, References C.H. Tang et al (2004). "Effect of Laser Surface Meltng on the Corroson and Cavtaton Eroson Behavors of a Manganese-Nckel- Alumnum Bronze", Materal Scence & Engneerng A, Vol. 373, pp Dehghan. A., Ehteshamzade. Sorushyan. S. (1392), "Study of the Effect of sulfde on contamnaton on the corroson behavor of alumnum bronze alloy nckel." Thrd Natonal Conference of Appled Chemcal n new technologes. 178