A R C H I V E S O F M E T A L L U R G Y A N D M A T E R I A L S Volume Issue 2 DOI: /amm

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1 A R C H I V E S O F M E T A L L U R G Y A N D M A T E R I A L S Volume Issue 2 DOI: /amm GUANLIN ZHAO, YONG ZOU,, HUI ZHANG, ZENGDA ZOU EFFECT OF LOW-TEMPERATURE ANNEALING ON THE PROPERTIES OF NI-P AMORPHOUS ALLOYS DEPOSITED VIA ELECTROLESS PLATING WPŁYW OCENY MIKROSTRUKTURY NA ODPORNOŚĆ KOROZYJNĄ WYŻARZONEGO STOPU AMORFICZNEGO N-P Amorphous N-P alloys were prepared va electroless platng and annealng at 200 C at dfferent tmes to obtan dfferent mcrostructures. The effects of low-temperature annealng on the propertes of amorphous N-P alloys were studed. The local atomc structure of the annealed amorphous N-P alloys was analyzed by calculatng the atomc par dstrbuton functon from ther X-ray dffracton patterns. The results ndcate that the propertes of the annealed amorphous N-P alloys are closely related to the order atomc cluster sze. However, these annealed N-P alloys mantaned ther amorphous structure at dfferent annealng tmes. The varaton n mcrohardness s n agreement wth the change n cluster sze. By contrast, the corroson resstance of the annealed alloys n 3.5 wt% NaCl soluton ncreases wth the decrease n order cluster sze. Keywords: N-P amorphous, local atomc structure, corroson resstance, mcrohardness Amorfczne stopy N-P otrzymane metodą powlekana bezprądowego wyżarzano w temperaturze 200 C w różnych czasach, w celu otrzymana zróżncowanej mkrostruktur. Badano wpływ mkrostruktury wyżarzanych stopów amorfcznych N-P na ch odporność korozyjną w roztworze 3,5% wag. NaCl. Wynk wskazują, że welkość klastra w wyżarzanych stopach amorfcznych N-P najperw zmnejszyła sę, a następne zwększyła wraz z czasem wyżarzana. Odporność badanych stopów na korozję jest ścśle zwązana z welkoścą klastra, mmo, że stopy te po wyżarzanu w różnych czasach zachowują strukturę amorfczną. Odporność wyżarzanych stopów amorfcznych N-P w roztworze 3,5% wag. NaCl zwększa sę wraz ze zmnejszenem sę klastra. 1. Introducton N-P deposts have attracted consderable attenton of numerous researchers because of ther unque propertes, such as corroson resstance, wear resstance, paramagnetc characterstcs, hardness, and electrocatalytc actvty of hydrogen evoluton [1-13]. Among these propertes, the better corroson resstance of amorphous N-P alloys s nvestgated wdely. The prevous results ndcated that the corroson resstance of electroless N-P alloys depend upon the chemcal composton (P content), substrate structure, preparaton of substrate surface, depost thckness, and subsequent chemcal or heat treatment [14]. In generally, N-P alloys that contan hgh phosphorus (>12 wt.%) are consdered to be n an amorphous state [15]. However, as to other amorphous alloys, these hgh phosphorus N-P alloys are not fully dsordered. In other words, the amorphous matrx ncludes a specfc short-range order or medum-range order cluster. It had been reported that the mcrostructure affects the propertes of amorphous n other amorphous system [16-18]. Bozzn et al. had provded evdence of clusterng n amorphous N-P prepared va autocatalytc chemcal deposton [19], thereby ndcatng a possbly vared local atomc structure for amorphous N-P alloys. The cluster sze of N-P amorphous alloys not only depends on the phosphorus content or platng technology but s also relatve to the heat treatment condtons. When N-P alloys s heat treatment n dfferent temperature and tmes, the sze of the cluster should be dfferent. In prevous studes [12, 14, 20-22, 23, 24, 25], the effect of crystallzaton on the corroson of N-P alloys have been reported. However, nformaton about the effect of evaluaton of mcrostructure on corroson resstance of annealed N P amorphous alloys s lmted. Ths work ams to study the effect of evaluaton of mcrostructure on corroson resstance of annealed N-P amorphous alloys n 3.5wt% NaCl soluton As-plated N-P samples were heat-treated at 200 C at dfferent duratons to obtan annealed samples of amorphous state but wth dfferent ordered cluster szes. The local atomc structure was analyzed va X-ray dffracton. The correlaton between propertes and local atomc structure was dscussed. 2. Expermental procedure The substrates for electroless platng of N-P alloys, whch were szed 15 mm 15 mm 3 mm and composed of KEY LAB OF LIQUID STRUCTURE AND HEREDITY OF MATERIALS, MINISTRY OF EDUCATION, SHANDONG UNIVERSITY, JINAN , SHANDONG, CHINA Correspondng author: yzou@sdu.edu.cn

2 866 low-carbon steel, were cleaned and polshed before platng. In ths case, nckel sulfate was used as the nckel source, and sodum hypophosphte was used as the reducng agent. Lactc acd and glycne were used as complexng agents. To determne the effect of local atomc structure on the propertes of the N-P coatng, the samples were subjected to annealng treatment at 200 C at dfferent tmes. The treatments were conducted usng an electrc furnace n a controlled Ar atmosphere. The mcrohardness measurements of annealed N-P alloys were carred out under a load of 100g. The structures of the samples were determned usng an X-ray dffractometer wth Cu Kα radaton operated at 40 kv/30 ma. The scannng rate and scannng step were fxed at 1 C/mn and 0.02, respectvely. The total structure factor S(Q) was calculated usng the equaton S(Q) = Icoh eu (Q) c f c f / c f 4π sn θ Q = (2) λ where 2θ s the dffracton angle, and λ s the X-ray wavelength. Ieu coh (Q) s the coherent X-ray scatterng ntensty n electron unts per atom, whch s drectly determned from the scatterng experments. f and c are the atomc scatterng factor and concentraton, respectvely, of the th element. The par densty functon (PDF), G(r), can be obtaned through a sne Fourer transform. 2 (1) annealed N-P coatngs, whch were heat-treated at 200 C for 2 h to 48 h. No sgnfcant changes n XRD patterns were observed for these samples, and only a sngle broad amorphous profle was observed. No crystallne peaks were detected, thereby ndcatng that no crystallne phase was formed at ths temperature. However, the shape of the amorphous profles changed slghtly, whch ndcates that specfc mcrostructural transtons occurred as a result of structural relaxaton. The PDFs of these alloys were calculated usng Eqs. (1) to (3) to analyze the local atomc structure of these annealed amorphous N-P alloys. Fgure 2 shows the calculated results of par dstrbuton functons of annealed N-P alloys, whch were heat-treated at 200 C for 2, 6, 12, 24, and 48 h. The calculated frst coordnaton radus, correlaton radus, and atomc number of the cluster are lsted n Table 1. The frst coordnaton radus, whch corresponds to the frst peak poston, was Å for all of the samples. Thus, the frst coordnaton radus was unaffected by annealng at 200 C. However, the correlaton radus ntally decreased and then ncreased. The correlaton radus s generally related to the order cluster sze, n whch a hgh order cluster sze corresponds to a larger correlaton radus. Meanwhle, the atomc cluster number also changed n the same trend,.e., the cluster number also ntally decreased and then ncreased. Ths result ndcates that the cluster sze of amorphous N P alloys decreased durng the annealng process when the heat treatment tme s less than 12 h. When the heat treatment tme exceeded 12 h, the cluster sze begns to ncrease. G(r) = 4πr [ ρ (r) ρ 0 ] = 2 π 0 Q[S(Q) 1] sn(qr)dq (3) where ρ(r) s the atomc densty functon, and ρ 0 s the average atomc densty. The PDF s a measure of the probablty of fndng an atom at a dstance r from another atom [26]. The surface morphology after polarzed was observed by a SUPRA TM 55 feld emsson scannng electron mcroscope (FE-SEM), and the chemcal composton of the N-P coatngs was determned va energy dspersve X-ray spectroscopy (EDS). Anodc potentodynamc polarzaton n 3.5wt% NaCl soluton was carred out usng an AUTOLABP GSTAT302N at a scan rate of 2 mvs 1 to nvestgate the corroson behavors of the annealed samples at ambent temperature. A classc three-electrode cell, wth the annealed N-P sample as the workng electrode, a platnum plate (Pt) as the counter electrode, and saturated calomel (SCE) as the reference electrode, was employed for the electrochemcal nvestgatons. To prevent the effect of the oxde flm, the specmens were polshed before beng sealed to remove the possble oxde flm. The polarzaton curves were recorded by scannng the electrode potental from -1 V to 1 V. Parameters such as corroson potental (E corr ) and corroson current densty ( corr ) were deduced va the Tafel extrapolaton method on the recorded data. 3. Results and dscusson As tested by EDS, the phosphorus content was 12.8 wt% of the as-plated N-P coatng, whch belongs to hgh phosphorus N-P alloys. Fgure 1 shows the XRD patters of the Fg. 1. XRD patterns of the N-P alloys annealed at 200 C for dfferent tmes TABLE 1 Calculated frst coordnaton radus, correlaton radus, and atomc cluster number for N-P alloys annealed at 200 C at dfferent tmes Calculate the frst coordnaton radus Calculate the correlaton radus calculate atomc number of cluster 200-2h 200-6h h h h

3 867 Fg. 2. Par dstrbuton functons of the N-P alloys annealed at 200 C for dfferent tmes exceeded 12 h, the corroson potental contnued to shft toward the hgh potental drecton, but the corroson current densty ncreased and polarzaton resstance decreased. These results ndcate that the corroson resstance begns to decrease at 12 h annealng tme. The sample annealed at 200 C for 12 h showed the lowest corroson rate n 3.5 wt% NaCl soluton. As shown n Fg. 4, a broad anode passvaton zone s found n the samples annealed at 200 C for 2 h to 12 h. Ths result ndcates that the corroson mechansm of the amorphous N-P alloys can be attrbuted to protecton by a passvaton flm. For the samples annealed more than 12 h, the anode passvaton zone becomes relatvely narrow. When the potental s beyond 0.2 V, the corroson current densty shows an evdent ncrease and then decrease, formng anodc peaks, whch are marked by an arrow n Fg. 3. Ths phenomenon corresponds to the collapse of the passvaton flm. Fgure 3 shows the dependence of the Vckers hardness of the annealed N-P alloys on the dfferent annealng duratons at 200 C. The mcrohardness values exhbt the same trend as the correlaton radus. That s, the mcrohardness of the annealed N-P alloys ntally decreased and then ncreased. When the annealng tme s 12 h, the N-P alloys exhbt the lowest hardness. Thus, these annealed samples possess dfferent mcrostructures, even though they possess smlar amorphous structures. The change n mcrohardness corresponds well wth that of cluster sze. When the heat treatment exceeded 48 h, the mcrohardness dd not ncrease further. Fg. 4. Polarzaton curves of the annealed N-P alloys annealed at 200 C for dfferent tmes TABLE 2 Corroson parameters obtaned from the polarzaton curves of the annealed N-P samples Fg. 3. Varatons n Vckers hardness of the amorphous N-P alloys annealed at 200 C for dfferent tmes Fgure 4 shows the respectve anodc potentodynamc polarzaton curves of the annealed N-P deposts n 3.5 wt% NaCl soluton. The corroson potental E corr and corroson current densty corr were calculated from the potentodynamc polarzaton curves va Tafel extrapolaton method. The values of polarzaton resstance R p were calculated from the lnear polarzaton curves; the results are summarzed n Table 2. The corroson resstance ntally ncreased and then decreased f corroson current densty corr was used to determne the corroson resstance. The corroson potental shfted toward the hgh potental drecton, and the corroson current densty decreased wth ncreasng annealng tme for the samples that were annealed for less than 12 h. When the annealng tmes I corr (Acm 2 ) E corr (V) R p (.Ωcm 2 ) Corroson Rate (mm/a) 2h E h E h E h E h E Fgure 5 shows the EIS data acqured n 3.5% NaCl soluton for the annealed N-P samples as Nyqust plots. Shapes of the Nyqust plots for all the samples were smlar, whch comprsed only one semcrcle; the dameters of the semcrcles were qute dfferent. The dameter of the Nyqust plot, whch determned the corroson resstance of a materal, ntally ncreased and then decreased. The result mpled that the corroson resstance was changed n ths order, consstent wth that obtaned from the polarzaton test.

4 868 Fg. 5. EIS data acqured n 3.5% NaCl soluton for the annealed N-P samples as Nyqust plots Fgure 6 shows the SEM mage of the annealng 48 h N-P alloys after mmersng 3.5wt% NaCl soluton for 3 weeks. The mage shows typcal pttng corroson morphology, whch ndcates that the annealed N-P alloys exhbt mcronhomogenety, whch can be attrbuted to the short-range order clusters. Accordng to the results n Table 1, the cluster sze of amorphous N-P alloys ntally decreased and then ncreased durng the annealng process. The results ndcate that mcrohardness and corroson resstance are assocated wth the cluster sze. Fg. 6. SEM mage of the annealng 48 h N-P alloys after mmersng 3.5wt% NaCl soluton for 3 weeks The decrease n cluster sze of the alloy durng the annealng process can ntally be attrbuted to structural relaxaton. The as-plated N-P coatng was subjected to specfc vacancy and resdual stresses durng the electroless process. Certan vacances may have been flled by nckel or phosphorus atoms va dffuson caused by annealng. Therefore, the homogenety of the elements was mproved, and depost defects were elmnated through stress relef and porosty agglomeraton. As shown n Table 1, the correlaton radus that corresponds to the order cluster sze gradually decreased when the annealng tme s less than 12 h, as well as to the mprovement n corroson resstance. When annealng tme s beyond 12 h, the order cluster sze began to ncrease, the corroson resstance decreased. These phenomena were observed because the atoms n the amorphous N-P alloys aggregate n order and form the precursor phase of N-P ntermetallc compounds, such as N 3 P, n whch the dstrbuton of the elements wll not be unform. A large order cluster sze translates to a consderable composton dfference between the cluster and matrx. The pttng corroson morphology presents a good evdence of the mcronhomogenety of the annealed N-P alloy. However, the cluster sze cannot nfntely ncrease to form ntermetallc compounds. Gven that the formaton of ntermetallc compounds requres actve energy, when the annealng temperature s too low to provde the necessary actve energy, no crystallzaton compounds were formed because the annealng temperature (200 C) s far from the crystallzaton temperature. The results ndcate that the corroson resstance of amorphous N-P alloys s affected by the order atomc cluster sze. The ncrease n the order cluster sze ncreases the composton dfference between the cluster and matrx, whch negatvely affects the corroson resstance of the amorphous N-P alloys by formng sgnfcantly more mcro-electrochemcal cells between the cluster and the matrx. The potentodynamc polarzaton testng ndcates that anode passvaton zone becomes relatvely narrow when the annealng tme s beyond 12h, whch corresponds to the ncreasng of order cluster. 4. Conclusons The effects of low-temperature annealng on the propertes of amorphous N-P alloys were studed. The order cluster sze of the N-P amorphous alloys affects the mcrohardness and corroson resstance. The mcrohardness ntally decreased and then ncreased wth the ncrease n annealng tme, as well as wth the ncrease n the order cluster sze. The corroson resstance n 3.5 wt% NaCl soluton shows the opposte trend to the varaton of hardness, that s, an ntal decrease and then ncrease are observed. The ncrease n the order cluster sze ncreases the composton dfference between the cluster and the matrx, whch negatvely affects the corroson resstance of the amorphous N-P alloys by formng more mcro-electrochemcal cells between the cluster and the matrx. The corroson morphology of the annealed N-P alloys after mmersng 3.5wt% NaCl soluton for 3 weeks shows the typcal pttng corroson. Acknowledgements Ths project s supported by Natonal Natural Scence Foundaton of Chna (No ). REFERENCES [1] R.L. Zeller, III, Corroson 47, 692 (1991). [2] L. Hao, M.-h. Mu, T. Y, R. L, Z.-l. Chen, A. Ln, F.-x. Gan, Corros. Sc. Prot. Technol. 20, 381 (2008). [3] J. Mskuf, K. Csach, V. Ocelk, E.D. Tabachnkova, V.Z. Bengus, P.S. Popel, V.E. Sdorov, Czech. J. Phys. 54, D133 (2004). [4] A. Krolkowsk, B. Karbowncka, O. Jaklewcz, Electrochmca Acta 51, 6120 (2006). [5] Y. Gao, Z.J. Zheng, M.Q. Zeng, C.P. Luo, M. Zhu, J. Mater. Res. 23, 1343 (2008).

5 869 [6] B. Allen, C. Po-Yao, H. Ch-Chang, Mater. Chem. Phys. 82, 93 (2003). [7] C. YanHa, Z. Yong, C. Ln, L. Wen, Mater. Lett. 62, 4283 (2008). [8] Y.H. Cheng, Y. Zou, L. Cheng, W. Lu, Mater. Sc. Technol. 24, 457 (2008). [9] R. Taher, I.N.A. Oguocha, S. Yannacopoulos, Mater. Sc. Technol. 17, 278 (2001). [10] Y.D. He, H.F. Fu, X.G. L, W. Gao, Scr. Mater. 58, 504 (2008). [11] L.-K. Yang, Y.-F. Jang, F.-Z. Yang, D.-Y. Wu, Z.-Q. Tan, Surf. Coat. Technol. 235, 277 (2013). [12] T. Rabzadeh, S.R. Allahkaram, A. Zarebdak, Mater. Des. 31, 3174 (2010). [13] H.-C. Huang, S.-T. Chung, S.-J. Pan, W.-T. Tsa, C.-S. Ln, Surf. Coat. Technol. 205, 2097 (2010). [14] C. Leon, E. Garca-Ochoa, J. Garca-Guerra, J. Gonzalez- Sanchez, Surf. Coat. Technol. 205, 2425 (2010). [15] M. Crobu, A. Scorcapno, B. Elsener, A. Ross, Electrochmca Acta 53, 3364 (2008). [16] M. Nabaek, P. Petrusewcz, M. Szota, A. Dobrzanska- Dankewcz, S. Lesz, M. Dospa, K. Boch, K. Ozga, Archves of Metallurgy and Materals 59, 259 (2014). [17] P. Petrusewcz, M. Nabaek, M. Szota, M. Dospa, K. Boch, J. Gondro, K. Gruszka, Archves of Metallurgy and Materals 59, 663 (2014). [18] S. Petrzyk, P. Palmaka, W. Gebarowsk, Archves of Metallurgy and Materals 59, 545 (2014). [19] B. Bozzn, P.L. Cavallott, Scr. Mater. 36, 1245 (1997). [20] Y. Lu, D. Beckett, D. Hawthorne, Appl. Surf. Sc. 257, 4486 (2011). [21] J.N. Balaraju, T.S.N.S. Narayanan, S.K. Seshadr, Mater. Res. Bull. 41, 847 (2006). [22] H. Ashass-Sorkhab, S.H. Rafzadeh, Surf. Coat. Technol. 176, 318 (2004). [23] T. Mman, S.M. Mayanna, Surf. Coat. Technol. 79, 246 (1996). [24] Y. Gao, Z.J. Zheng, M. Zhu, C.P. Luo, Mater. Sc. Eng. A, Struct. Mater., Prop. Mcrostruct. Process. A381, 98 (2004). [25] K.G. Keong, W. Sha, S. Malnov, J. Alloys Compd. 334, 192 (2002). [26] M. Satou, Y. Okudara, W. Oshkawa, J. Electrochem. Soc. 150, C140 (2003). Receved: 20 February 2014.