Dissolution of Copper Cylinder in Molten Tin under Dynamic Conditions

Transcription

1 Disslutin f Cpper Cylinder in Mlten Tin under Dynamic Cnditins Slutin rate cnstant K (in cm/s) exhibits a change pint at abut 415 C (779 F) in slutin rate cnstant/temperature curves, and the activatin energy fr the disslutin f cpper in mlten tin is 4 Kcal/ml BY Y. SHOJI, S. UCHIDA and T. ARIGA ABSTRACT. The present study was undertaken t evaluate the kinetics f the disslutin f slid cpper in mlten tin under isthermal cnditins. The cpper specimens were immersed in tin at varius temperatures in the range f 370 t 520 C (698 t 968 F), and rtated fr 3 t 25 min at speeds f 0 t 1000 rpm. Results were as fllws. The disslutin f cpper increases with increasing immersin time, rtatinal speed, and temperature. N effect f grain size f cpper n disslutin is bserved. The slutin rate cnstant exhibits characteristic change pint at abut 41S C (779 F) in slutin rate cnstant/temperature curves. The slutin rate cnstant depends n bth hydrdynamic cnditins and intermediate phases frmed at the disslving interface. The mass transfer is cnsidered, therefre, t be cntrlled by bth surface reactin and diffusin prcess. The activatin energy fr disslutin f cpper in mlten tin is 4 Kcal/ml. Intrductin The disslutin f slid metal in liquid metal is f cnsiderable fundamental and practical interest. This general prblem is f interest in brazing, 1 sldering, 2 extractive metallurgical prcesses, 3 and in the field f liquid metal crrsin. 4 It is cmmnly bserved that base metal will disslve in mlten filler metal even thugh the temperature is cnsiderably belw the melting pint f the slid. Base metal-filler metal interactins are mst imprtant in determining the behavir f brazed jints. The interactins may affect the physical and mechanical prperties f the jint. The disslutin reactin prducts are generally brittle and ffer preferred fracture prpagatin paths. The intermetallic cmpunds frmed may seriusly impair the strength at the slder-metal interface and prvide unreliable jints. 5 A number f investigatins have been undertaken t evaluate the kinetics f disslutin. Craighead, Cawthrne, and Jaffee 1 have made a detailed study f the slutin rate f slid aluminum in mlten aluminumsilicn ally, in which they reprt effects due t temperature, agitatin, and liquid- and slid-metal cmpsitin. Generally, the isthermal transfer frm slid t liquid in a cncentratin gradient can be brken up int tw cnsecutive prcesses. The first is the surface reactin in which atms g frm the slid slute int the liquid phase. The secnd is a diffusin prcess in which the slute atms diffuse frm the interface int the bulk liquid thrugh a bundary layer f cnstant thickness in the liquid. In mst f these studies, the slutin rate cnstant was determined n the basis f the Berthud equatin 46 r the relatin f Lmmel and Chalmers. 7 The slutin rate cnstant was analyzed n the basis f the Eisenberg crrelatin. 8 Generally, disslutin is Y. SHOjl is a Graduate Student, S. UCHIDA is Prfessr, and T ARIGA is Assciate Prfessr, Department f Mechanical Engineering, Faculty f Engineering, Tkai University, Tky, japan. cntrlled by mass transfer f the disslving species. The disslutin f lead in liquid Pb-Sn allys 7 is cntrlled by surface reactin at the slid-liquid interface, and that f zinc in liquid mercury 9 is mixed cntrlled. There has been nly a limited amunt f infrmatin abut the kinetics f the disslutin f slid cpper in mlten tin. 1 " Relatively few data are available n the effect f intermetallic cmpund n disslutin. It is clear that infrmatin f this type is essential t an understanding f the mechanism f base metal-filler metal interactin. The present study was undertaken as a fundamental study f the sldering. The purpse f the present paper is t describe the behavir f the disslutin f cpper in mlten tin under varius cnditins f temperature, agitatin, and grain size. Experimental Materials The cpper cylinders, machined frm pure cpper (99.9%), were 1.8 cm (0.71 in.) OD, 0.5 cm (0.2 in.) ID, and abut 2.0 cm (0.79 in.) lng. Befre each experiment, the specimens were annealed fr 3 hurs (h) at 500 C (932 F) in a vacuum f 10' mmhg r less. The specimens were degreased in acetne and cleaned in the chemical plishing bath; 2 ml HCI, 18 ml H,S0 4, 37 ml HNO ;i, and 43 ml H,0. Each cylindrical cpper specimen was weighed t ±0.001 g ( lb) and its length was measured t ±0.001 cm ( in.). As shwn in Fig. 1, the tp and WELDING RESEARCH SUPPLEMENT 19-s

2 Electric mter T cunter system Stainless steel shaft The cpper cylinder munted in the center f the crucible was cnnected t a stainless steel shaft. The shaft was guided by ball bearings and rtated by a variable-speed mtr. The drive assembly culd be raised and lwered in rder t allw the cpper specimen t be quickly mved in and ut f the melt. Ball bearing Water in Thermcuple Electric furnace -«Specimen hlder Metal blck Refractry Fig. 1 Experimental apparatus ir dynamic cnditins Argn gas in T vacuum system Water ut Quartz crucible Mlten metal Slid specimen Prcedure T initiate an experiment, a quartz crucible was charged with tin and placed in the furnace. After evacuatin, argn gas was admitted t the crucible, and the furnace was heated t the desired temperature. The cpper specimen was preheated fr 40 min directly abve the melt, and then immersed in the melt and rtated fr 3 t 25 min at speeds f 0 t 1000 rpm. The temperature was cntrlled t within ±1 C and the rtatinal speed was maintained t ±1% f the set value. After the desired time interval the cpper specimen was withdrawn frm the melt and quenched in water. Any adherence t the specimen surface was remved by 30% nitric acid slutin, and the specimen was weighed. The specimen was sectined fr metallgraphic examinatin t bserve the shape f the slid-liquid interface. At least tw samples were tested fr each set f cnditins. bttm faces f the cylindrical cpper specimen were cvered with a steel hlder f identical diameter. In this way nly the sides f the cylinder were expsed t the mlten tin. The cpper specimens were annealed at 900 C (1652 F) fr times f frm 4 t 16 h in a vacuum t achieve a carse-grained structure. A tin sample was degreased in acetne. A fresh sample f tin (80.00 g) was used fr each experiment. 13 U < \ c > 37 r ] 48 rc.0 ORPM i }0 ORPM ^ \ Apparatus Figure 1 shws the apparatus used in determining the disslutin rates in the present study. The experimental apparatus cnsisted f a resistanceheated furnace, a specimen hldingstirring assembly, and a gas train. A cylindrical quartz crucible was 2.9 cm (1.14 in.) ID and 14.0 cm (5.5 in.) lng. ^^^D _ Time (sec) D v [ : q D Fig. 2 Relatin between the area f liquid-slid interface and immersin time Results and Discussin Disslutin f Cpper in Tin Slutin kinetic data fr the present study were btained fr seven different temperatures: 370, 400, 414, 420, 440, 480 and 520 C (698, 752, 777, 788, 824, 896 and 968 F). At each temperature, data were btained fr six different rtatins: 0, 200, 400, 600, 800 and 1000 rpm, a ttal f 42 cmbinatins f temperatures and rtatinal speeds. These rtatinal speeds crrespnd t surface velcities f 0, 18.9, 37.7, 56.6, 75.4 and 94.3 cm/sec (0, 446.5, 890.6, 1337, 1781, and ipm), respectively. At 370 and 480 C (698 and 896 F), data were btained fr six different immersin times: 3, 5, 10, 15, 20 and 25 min; at the ther temperatures, immersin time was 3 min. Changes in the area f the disslving surface were taken int accunt. "AW" was determined frm the weight change f the cpper befre and after disslutin. "A,," the area f liquid-slid interface at immersin time = t, was determined frm AW. It was assumed that the immersed slid cpper was a perfect cylinder. Figure 2 shws that the dependence f A t n the lgarithmic immersin time is represented by a straight line intersecting with the A, axis at the 20-s I JANUARY 1981

3 10 Time (min) Fig. 3 Effect f rtatinal speed n slutin rate curves at 370 C 10 Time (min) Fig. 4 Effect f rtatinal speed n slutin rate curves at 480 C b 520 C (time=180sec) A80 C 440 C 400 C 370 C E u S Grain Size N (JIS) A 3 2 < "q CO LO O time=180sec C1000RFIV ^ SI cn Oi 0.2 O' Rtatinal Speed (RPM) Fig. 5 Relatin between slutin rate and rtatinal speed Fig Grain Diameter (x10" 2 cm) 6 Effect f grain size f cpper n disslutin 2.5 initial area f A 0. In rder t determine the effective area f interface, the fllwing apprximate equatin was assumed: A- A 0 -((A 0 -A t )/lg t)lg(t/2) (1) where A = effective area f interface during the immersin; A 0 = area at time = 0; A t = area at time = t; and t = immersin time. Plts f weight lss f cpper cylinders AW/A against immersin time at 370 C (698 F) are shwn in Fig. 3. Figure 4 shws the same plts at 480 C (896 F). Figures 3 and 4 shw that disslutin f cpper increases with increasing immersin time, whereas the rate f disslutin decreases with time. The plts f weight lss against time indicate that the mlten tin becmes saturated with cpper in a cmparatively shrt time under stirred cnditins at any given temperature. The saturatin cncentratin in slutin at sme temperature is equivalent t the cncentratin f liquidus at the temperature. Apprximately 90% f the saturatin cncentratin was attained at 25 min. Figure 5 shws the influence f rtatinal speed f cpper cylinder n disslutin. The slutin rate f cpper increases with increasing rtatinal speed and temperature. It is assumed that the thickness f the effective cncentratin bundary layer in liquid decreases with increasing rtatinal speed. The type f attack f the allys is fund t depend n the grain size f the specimens. Fine-grained material is much mre prne t intergranular attack, whereas the carse-grained material is prne t intergranular attack nly at the highest velcities. 11 Figure 6 shws the effect f grain size n the disslutin f cpper in tin at temperatures f 370 and 480 C (698 and 896 F). N effect f grain size f cpper is bserved in the range f grain diameter frm 50 t 180 /wn. WELDING RESEARCH SUPPLEMENT I 21-s

4 370 C Rtatinal speed 400 RPM 480 C Rtatinal speed 400 RPM ^ 200 RPM - 0 RPM c (_> (A/V)-t (sec/cm) Fig. 7-Relatin between 1n(Cj(C, - Q) and (A/V)t at 370 C (698 E) (A/V)t (sec/cm) Fig. 8-Relatin between 1n(C B/(C, - Q) and (AIV)t at 480 C (896 F) Rtatinal speed (RPM) 1000 "s. E c IS ID Temperature ( C) 550 Fig. 9 Temperature dependence l slutin rate cnstant K tr each rtatinal speed /7 (x10~ 3 / K) Fig. 10 The Arrhenius plts fr disslutin f cpper in mlten tin Kinetics f Disslutin The isthermal transfer frm slid t liquid in a cncentratin gradient can be brken up int tw cnsecutive prcesses: surface reactin and diffusin prcess. The mst general slutin rate equatin, the Berthud equatin, 4-6 expresses the rate f apprach t saturatin as C = C 5(1 -exp(- K(A/V)t)) (2) r1n(q/(c 8-C)) = K(A/V)t (3) where K = (K SD/S)/(K S + D/S), C = bulk cncentratin (at-%), C s = saturatin cncentratin (at-%), K = slutin rate cnstant (cm/s), A = area f the interface (slid-liquid) (cm'-'), V = vlume f liquid (cm 3 ), t = time (s), K s = interface reactin cnstant, and D = diffusin cefficient f slute in the liquid (cmvs), S = the thickness f the effective cncentratin bundary layer (cm). The equatin is usually used in a limiting frm fr diffusin cntrl (D/ 5<<K S) r interface cntrl (D/ S > > K s). The slutin rate cnstant K reduces t D/8 fr cases f diffusin cntrl, and reduces t K s fr interface cntrl. The slutin rate cnstant K may be evaluated by pltting 1n(C s/ (Q - Q) vs. (A/V)t. It shuld be nted that this equatin neglects any diffu- 22-s I JANUARY 1981

5 O trlcu) 9.1, i> 15.8) la. OJ 400 l_ 0) a 300 dl \ j I r -350 /6.2 / (11.0) J l R a-c 640 ^43.1 ( T r 9" 44 8(60.31 (59.0) U5.5 (60.9) i-v 415" 227 \86 7(92.4) (99.3) Sn (at%) Fig. 11 Binary Cu-Sn phase diagram" sin in the slid, which is a reasnable assumptin in view f the high rate f disslutin f the slid metal. The bulk cncentratin was calculated frm the weight change f the cpper AW. The bulk liquid is maintained at a unifrm cncentratin by cnvectin under static cnditin. The saturatin cncentratin C s fr the cpper-tin system was taken frm a published diagram. 12 Figures 7 and 8 shw plts f 1 n(c B / (C s -C)) vs. (A/V)t, accrding t equatin (3), fr a few typical experiments f the present study. In evaluating the quantity (A/V)t, crrectins were made fr any changes in A r V due t disslutin. Figures 7 and 8 shw that the slpes are nnlinear fr each case; in agreement with the literature.' 111 This behavir culd be explained by variatins in D, S, r cpper cncentratin with time. The bundary layer thickness is a functin f the rtatinal speeds and the kinematic viscsity f the liquid. In the dilute cncentratin range, a linear relatinship exists between 1n(C s / (C s -C)) and (A/V)t. Therefre, the values f slutin rate cnstant K were taken frm the data at 3 min fr each cnditin. Figure 9 shws a characteristic change pint at abut 415 C (779 F) in slutin rate cnstant/temperature curves. The disslutin rate cnstant f cpper in tin at 420 C (788 F) is lwer than that btained at 415 C (779 F). It wuld appear that the change pint indicates sme change f state in the slid- r in the liquid. It is well knwn that temperature dependence f slutin rate cnstant can be expressed apprximately by an Arrhenius-type equatin: K = cnst. exp( - Q/RT) (4) where K = slutin rate cnstant (cm/s), Q = activatin energy fr disslutin (cal/ml), R = gas cnstant (cal/deg ml), and T = abslute temperature (K). Figure 10 shws the Arrhenius plts in the present study. The activatin energy Q fr disslutin f cpper in mlten tin, which can be btained frm plts f In K vs. 1/T, are 4 Kcal/ml fr mst cnditins, whereas Q is 5 Kcal/ml at temperatures greater than 415 C (779 F) under static cnditin. If S is cnstant fr ne system at different temperatures, K is directly prprtinal t D, and Ihe activatin energies fr disslutin shuld be similar t that fr diffusin f the slute in the liquid metal. The activatin energy fr diffusin f cpper in liquid tin is 4.2 Kcal/ ml. 13 The higher activatin energy fr disslutin in the higher temperature range under static cnditin is due t strnger cnvectin effects. If cnvectin, due t density variatins in the liquid bath, is cmplicating the disslutin prcess, then these effects wuld be much mre prnunced in the higher temperatures wing t the greater increase in cpper cncentratin with temperature rise. The cpper-tin phase diagram 12 in Fig. 11 shws a peritectic reactin at 415 C (779 F) resulting in the frmatin f an intermediate n-phase. Since Cu 6 Sn 5, n-phase, decmpses peritectically at 415 C (779 F), the change in disslutin rates in Fig. 9 prbably reflects the change in intermediate phases that are frmed at the disslving interface. Figure 12 shws the variatin in appearance f the intermediate phases that are frmed at the disslving interface at 370 and 480 C (698 and 896 F). Frm the binary diagram fr the Cu-Sn system 12 and experimental results f ther investigatrs, the intermediate phases frmed at 370 C (698 F) are believed t be n- and e-phases, whereas at 480 C (896 F) are believed t be e- and S-phases. Figure 12 reveals the marked change in micrstructures at the interface fr different temperatures. The cpper specimen surface was relatively smth after disslutin under static cnditin, but cncentric grves were frmed n the surfaces under dynamic cnditins. The grves became spiral and irregular as the rtatinal speed was increased. The frmatin f the grves was caused by the vrtices develped in the liquid arund the cylindrical specimen. ^'wyyy m mm «; P " $ ' % i d Cu Fig. 12-Phtmicrgraphs t liquid-slid interface tr disslutin f cpper in tin. A-370 C (698"F), 1000 rpm, 25 min; B-480 C (896 E), 1000 rpm, 25 min. X420 WELDING RESEARCH SUPPLEMENT I 23-s

6 A D O 520 C A80 C 4A0 C A00 C 370 C at the disslving interface. 5. The mass transfer is cnsidered therefre, t be cntrlled by bth surface reactin and diffusin prcess. 6. The activatin energy fr disslutin f cpper in mlten tin is 4 Kcal/ ml where K = slutin rate cnstant (cm/s). Acknwledgments 5.0 The authrs are particularly indebted t Prfessr S. Kda, Tkai University, fr his useful discussins fr this paper, and als are grateful t Japan Slder MFG.C.,LTD. fr a gift f tin n U Fig. 13 Relatin between In K and In U at varius temperatures. Influence f Hydrdynamic Cnditins Interface cntrlled slutin rate shuld be independent f hydrdynamic cnditins, whereas a diffusin r mixed cntrl slutin prcess shuld depend n hydrdynamic cnditins. The relative mtin f the fluid and slid influences the thickness f the bundary layer S. In cmplex prcesses such as fluid flw, heat transfer, and mass transfer, useful phenmenlgical relatins have been develped using dimensinless grups f variables. The relevant relatin fr the present investigatin is given as fllws: 9 dk/v = a(du/v)^(v/d)t- 1 = a(re)/ 5 (Sc)T- 1 (5) where a, j3, y = dimensinless numbers, d = diameter f rtating cylinder (cm), U = peripheral velcity f rtating cylinder (cm/s), v = kinematic viscsity (cmvs), Re = Reynlds number, Sc = Schmidt number. When velcity is the nly variable at cnstant temperature, K = cnst. U" (6) and the expnent f the Reynlds grup can be determined by pltting lg K vs. lg U. Frdiffusin cntrlled prcesses, the expnent n the Reynlds number varies between 0.6 and 0.8. The expnent n the Reynlds number wuld be 0.00 fr interface cntrl, and sme value between 0.0 and 0.6 fr mixed cntrl." Figure 13 shws plts f lg K vs. lg U fr each temperature; U is the average peripheral velcity f rtating cylinders. The expnent fi, determined frm the slpes in Fig. 13, is abut 0.4 fr each temperature. The expnent f 0.4 Re shws that slutin rate cnstant K in the present study is less dependent n Re than a nrmal diffusin cntrlled prcess, indicating that the disslutin f cpper in mlten tin is mixed cntrlled. Cnclusins 1. The disslutin f cpper increases with increasing immersin time, rtatinal speed, and temperature. 2. N effect f grain size f cpper n disslutin is bserved. 3. The slutin rate cnstant exhibits a characteristic change pint at abut 415 C (779 F) in slutin rate cnstant/temperature curves. 4. The slutin rate cnstant depends n bth hydrdynamic cnditins and intermediate phases frmed References 1. Craighead, C. M., Cawthrne, E. W., and ]affee, R. I., "Slutin Rate f Slid Aluminum in Mlten Al-Si Ally," Trans. AIME, 215 (1), 1955, pp. 81 t Bader, W. C, "Disslutin f Au, Ag, Pd, Pt, Cu and Ni in a Mlten Tin-Lead Slder," Welding lurnal, 48 (12), Dec. 1969, Research Suppl., pp. 551-s t 557-s. 3. Kim, Y., and Pehlke, R. D., "Mass Transfer During Disslutin f a Slid int Liquid in the Irn-Carbn System," Met. Trans., 5 (12), 1974, pp t Weeks,. R., and Gurinsky, D. H., "Liquid Metals and Slidificatin," A.S.M., Ohi, 1958, pp. 106 t Saperstein, Z. P., and Hwes, M. H., "Mechanical Prperties f Sldered jints in Cpper Allys," Welding jurnal, 48 (8), Aug. 1969, Research Suppl., pp. 317-s t 327-s. 6. Melwyn-Hughes, E. A., The Kinetics f Reactins in Slutin, 2nd ed., Clarendn Press, Oxfrd, 1947, pp. 374 t Lmmel,. M., and Chalmers, B., "The Isthermal Transfer frm Slid t Liquid in Metal Systems," Trans. Met. Sc. AIME, 215 (6), 1959, pp. 499 t Eisenberg, M., Tbias, C. W7, and Wilke, C R., "Mass Transfer at Rtating Cylinders," Chem. Eng. Prgr., Symp. Ser., 51, 1955, N. 16, pp. 1 t Hinzner, F. W., and Stevensn, D. A., "Kinetics f Slutin in Liquid Metals. Slutin Rate f Zinc, Silver, and Tin int Liquid Mercury," /. Phys. Chem., 67 (11), 1963, pp t Kawakatsu, I., and Yamaguchi, H., "On the Disslutin f Cpper in Liquid Tin," Nippn Kinzkugakkaishi, 31 (12), 1967, pp t Stevensn, D. A., and Wulff, )., "The Slutin Rate f Cpper, Nickel, and Their Allys in Lead," Trans. Met. Sc. AIME, 211 (4), 1961, pp. 279 t Hansen, M., Cnstitutin f Binary Allys, McGraw-Hill, Inc., New Yrk, 1958, pp. 633 t Ma, C. H., and Swalin, R. A., "A Study f Slute Diffusin in Liquid Tin," Acta Met., 8 (6), 1960, pp. 388 t s I JANUARY 1981