Crystallographic relations in the Fe-Zn system

Transcription

1 Crystllogrphic reltions in the Fe-Zn system Verplnke, J.C.; Bstin, G.F.; vn Loo, F.J.J. Published in: Kristll und Technik DOI: /crt Published: 01/01/1979 Document Version Publisher s PDF, lso known s Version of Record (includes finl pge, issue nd volume numbers) Plese check the document version of this publiction: A submitted mnuscript is the uthor's version of the rticle upon submission nd before peer-review. There cn be importnt differences between the submitted version nd the officil published version of record. People interested in the reserch re dvised to contct the uthor for the finl version of the publiction, or visit the DOI to the publisher's website. The finl uthor version nd the glley proof re versions of the publiction fter peer review. The finl published version fetures the finl lyout of the pper including the volume, issue nd pge numbers. Link to publiction Cittion for published version (APA): Verplnke, J. C., Bstin, G. F., & Loo, vn, F. J. J. (1979). Crystllogrphic reltions in the Fe-Zn system. Kristll und Technik, 14(4), DOI: /crt Generl rights Copyright nd morl rights for the publictions mde ccessible in the public portl re retined by the uthors nd/or other copyright owners nd it is condition of ccessing publictions tht users recognise nd bide by the legl requirements ssocited with these rights. Users my downlod nd print one copy of ny publiction from the public portl for the purpose of privte study or reserch. You my not further distribute the mteril or use it for ny profit-mking ctivity or commercil gin You my freely distribute the URL identifying the publiction in the public portl? Tke down policy If you believe tht this document breches copyright plese contct us providing detils, nd we will remove ccess to the work immeditely nd investigte your clim. Downlod dte: 10. Dec. 2018

2 1 Krietllund Technik I I I J. C. VERPLANKE, G. F. BASTIN, F. J. J. VAN Loo Lbortory of Physicl Chemistry, University of Technology, Eindhoven, Netherlnds Crystllogrphic Reltions in the Fe-Zn System The crystllogrphic reltions between the vrious Fe-Zn compounds hve been investigted by mens of single-crystl X-ry diffrction techniques. These techniques were pplied to primry single crystls of ech compound upon which fter cooling single crystlline lyer of the neighbouring compound richer in zinc ws grown. In this wy it hs been possible to determine reltionships in the sequence - r- r, -6 : [1101, II CllOlr II [11Olr, II [lo016 ; (111), II (1ll)r II (lll)r, II (OOOl), No crystllogrphic reltionship could be estblished for 6 -[ becuse it proved impossible to grow single crystlline lyer of t on S. The pprently bd comptibility of the two lttices ws reflected in the nucletion problems which were lwyys encountered during efforts to grow 5 on 6. The influence of the reltionships on the ctully observed textures in the 6 nd 5 lyers of hot dip glvnized specimens is discussed. Die kristllogrphischen Beziehungen zwischen den verschiedenen Fe-Zn Verbindungen sind mittels Einkristrtll-Rontgenmethoden untersucht worden. Zu diesem Zweck wurden primiire Einkristlle jeder Verbindung hergestellt, woruf durch Abkiihlen in mnchen Fllen eine einkristlline Schicht der niichsten, mehr Zink enthltenden, Phse geziichtet werden konnte. Auf diese Weise wr es moglich, kristllogrphische Beziehungen festzustellen in der Reihe -F-Fl-d: ClW, II [1101r I1 CllOlrl II C10016; (111)~ (111) Ill' (1ll)rL 11 (Ooo1)6 - Zwischen 6 und t konnte jedoch keine kristllogrphische Beziehung festgestellt werden, weil es sich ls unmoglich ergb eine einkristlline Schicht von 5 uf 6 zu ziichten. Die offensichtlich schlechte Pssung der Kristllgitter zeigt sich in Keimbildungsschwierigkeiten, mit denen ds Wchstum von 5 uf 6 verbunden ist. Der EinfluS der gefundenen Beziehungen uf die in der Prxis whrgenommenen Texturen in den 6 und t Schichten von feuerverzinkten Proben wird diskutiert. 1. Introduction During hot dip glvnizing of iron number of diffusion lyers re formed prllel to the originl ironlliquid Zn interfce. In the order of incresing Zn content these re the T, r,, 6 nd [ lyer. On withdrwl from the bth the whole ssembly is covered by lyer of dhering zinc. A lot of reserch hs been done on the kinetics of the lyer growth during hot dip glvnizing. It seems to be well estblished now tht up to 495 "C lyer growth follows prbolic kinetics which indictes tht the process is diffusion controlled. Between 495" nd 530 "C, however, liner time lw is obeyed. Above 530 "C, on the other hnd, lyer growth proceeds gin ccording to prbolic time lw. According to HORSTMANN the region of liner growth cn be explined by the premture (with respect to temperture) bsence of the lyer in the criticl tem-

3 446 J. C. VERPLANKE et l. perture trject. As mtter of fct the phse should be stble up to 530 "C in the bulk; s diffusion lyer, however, it is lredy bsent from 495 "C on. As consequence, the 6 lyer is in contct with liquid zinc with which it cnnot be in equilibrium. According to HORSTMANN the reson for the bsence of the phse must be sought in nucletion difficulties of on 6 nd essentilly, this is crystllogrphic problem. Perhps even more importnt crystllogrphic fetures relted to the hot-dip glvnizing process re the textures in the 6 nd lyers. It hs been shown recently (BASTIN, VAN Loo, RIECK; BASTIN, VAN Loo) tht during hot dip glvnizing shrp fibre textures re produced in these lyers. About the origin of these textures nd those in diffusion grown lyers ingenerl little is known with certinty t the moment. In number of cses (e.g. HEUMANN, DITTRICH) it is suspected tht preferentil diffusion in certin crystllogrphic directions is responsible for the development of texture. In other cses one could suspect tht crystllogrphic reltionships between substrte nd/or djcent lyers ply n importnt role. With these thoughts in mind the present. investigtion into the orienttionreltionships between the vrious Fe-Zn phses hs becn crried out. 2. Generl pproch For the determintion of orienttion reltionships use hs been mde of single crystls of the vrious phses which were produced by, slowly cooling melt of suitble composition. On further cooling it hs been found possible in number of cses to grow thin lyer of the neighbouring phse, richer in zinc, on these primry crystls. Single crystl rottion nd Weissenberg techniques were subsequently used to estblish the nture of the reltionship between the two phses in question. Froru the rottion ptterns informtion ws obtined on which xes of rottion both phses hve in common. At the sme time the periodicities of both lttices long their coincident zone xes could be determined. The Weissenberg ptterns from the sme zones were used to gther the supplementry dt necessry to estblish the full orienttion reltionship. Not only will such pttern revel informtion bout crystllogrphic plnes being prllel; it will t the sme time show how prllel plnes of both phses fit with respect to their spcings. 3. The Fe-Zn system 3.1. Phse digrm The phse digrm (Fig. 1) of the Fe-Zn system is minly bsed on the work of SCHRAMM ( ). Since then number of ppers (BABLIK, GOTZL, HALLA; LIHL, DEMEL; LIHL; BUDUROV et l.; GHONIEM, LOHBERU) hve been published on this subject. Aprt from some ltertions in the 01- nd y-fe phse fields (BUDTJROV et l.), however, the min outlines of the digrm s given by Schrmm remined unchnged. Recently, dditionl investigtions hve yielded the incorportion of the previously unknown I'l phse (BASTIN, VAN Loo, RIECK, 1974) nd some modifictions of the 6 phse field (BASTIN, VAN Loo, RIECE, 1977) Crystllogrphic dt on the vrious Fe-Zn phses In Tble 1 the unit cell dt nd spce groups of the Fe-Zn phses re given. It will be noted tht the r, phse is closely relted to the r phse in tht both phses re cubic nd the unit cell prmeter of I', is exctly twice tht of r. The rphse, however, hs BCC lttice while tht of rl is FCC.

4 ~ Crystllogrphic Reltions in the Fe-Zn System 447 Fig. 1. FeZn equilibrium digrm roo 4 fe zn f t. %) In Tble 1 Crystllogrphic dt on the Fe-Zn compounds Compound Formul Structure, Spce Group Unit cell prmeters References -Fe r r1 s 5 Zn Fe FesZn10 Fe,Zn, FeZn,,, FeZn, Zn Cubic, BCC 4-2 I-3- m m Cubic, RCC I43m Cubic, FCC F432, Fz3m or 4-2 F-3- m m Hexgonl P6,mc or P68/c Monoclinic 2 C- m, = A, = A, = A = b = A c = A = A b = A c = A = y = 90' B = = b = A c = A ASTM SCH~AMM (1938) BASTIN, VAN LOO, RIECE (1974), Present investigtion BASTIN, VAN LOO, RIECE (1977) BROWN ASTM 4. Experimentl As strting mterils for the preprtion of single crystls use ws mde of Zn rod (99.9 wt%; supplied by Merck) nd Fe sheet (99.5 wt%; supplied by Drijfhout, Amsterdm). The metls were weighed in in the proper weight rtio nd subsequently seled in

5 448 J. C. VERPLANKE et l. evcuted (0.05 Torr) silic cpsules. For sfety resons the cpsules were trnsferred into steel tubes. Next the specimens were heted t tempertures of "C during severl dys. For the zinc-rich compositions generlly chosen this implied tht the lloys were completely liquid. After homogeniztion of the melt the temperture ws lowered to vlue t which, for the given overll composition, the desired primry crystls could be brought into equilibrium with the liquid, iron-sturted, Zn phse. As it turned out sufficiently thick (10-20 pm) lyer of the secondry phse could be obtined in number of cses by merely quenching the lloy in wter. The mteril thus obtined ws next cut, embedded in synthetic resin nd ground nd polished. After etching with 4 vol% nitric cid in ethnol the specimen ws exmined under microscope. In order to check the composition nd homogeneity of the primry nd seondry crystls sometimes electron probe niicronlyses wore performed ccording to procedures reported before (BASTIN, VAN Loo, RIECR, 1974). Single crystls were extrcted from the Zn-rich mtrix by using dilute hydrochloric cid. As the mtrix dissolved much fster thn the crystls it ws esy to remove the ltter from time to time. Undcr stereo microscope number of suitble crystls were selected for the single crystl X-ry diffrction procedures. 5. Results 5.1. r-6 reltionship For the preprtion of r single crystls 2 different lloys were used. The overll compositions nd the therml tretment were s follows : Alloy number one: Overll coniposition 16.00t yo Fe, 5d 1000 "C, 2d 760 "C; 5d 720 "C; quenching in wter. Alloy number two : Overll composition 8.07 t yo Fe, 3d 898 "C, 3d 676 "C ; quenching in wter. The compositions of the r crystls s determined by electron probe micro-nlysis were: 27.3 t yo Fe for the first nd 22.0 t yo Fe for the second lloy. It will be noted tht these conipositions re in close greement with the results of SCHRAMM. In fct, the whole r/r + L boundry in the phse digrms hs been ccurtely redetermined in the present investigtion nd excellent greement with the results of SCHRAMM hs been obtined. The results hve been incorported in Figure 1. Fig. 2. Prt of r crystl coted with lyer of d Microscopic exmintion of the quenched lloys lerned tht the dimensions of the primry r crystls were bout mm. The 6 lyer which during quenching hs grown on top of the T crystls hd thickness vrying between 5 nd 15 pm. As Figure 2 shows the 6 lyer is bounded by number of sw-tooths with ngles of bout 120". Both the r nd the 6 phse give the impression of being single crystlline in the sense tht no grin boundries could be detected. This impression ws confirmed by

6 Crystllogrphic Reltions in the Fe-Zn System 449 oscilltion, rottion nd Weissenberg ptterns tken from vriety of r crystls. These ptterns which were obtined from the principl zone xes of r will now be discussed in detil [110] zone xis of r The rottion pttern of this zone xis showed no lyer lines of the 6 phse; only those of the r phse ppered to be present t first sight. The zero level Weissenberg photogrph (Fig. 3), however, clerly reveled diffrction pttern superimposed on Fig. 3. Zero level Weissenberg pttern of the [1101 zone of 8 coted r crystl; CoK rdition Fig. 4. Zero level Weissenberg pttern of the [lo01 (=10101) zone of 8 single crystl; CoK rdition Fig. 5. Zero level reciprocl lttice of r; xis of rottion [1101. The positions of the reciprocl xis of two 0 individuls rotted bout [OlO] hve been indicted tht of T. This extr diffrction pttern, which ws chrcterised by n extremely close rrngement of the diffrction spots, is typicl for zero level Weissenberg pttern tken bout [loo] (=[OlO]) of the 6 phse s Figure 4 shows. This implies tht [110] T nd [loo] 6 re prllel.

7 450 J. C. VERPLANEE et l. At the sme time this coincidence explins the bsence of extr lyer lines iu the rottion pttern becuse the periodicities long both directions re very much like : oi2 = A for rnd A.for 6. When Figures 3 nd 4 re compred in more detil it soon becomes cler tht in Figure 3 more thn one 6 individul is involved. In fct, the sequence of the c* nd * xes in the Weissenberg pttern of Figure 3 indictes the presence of two 6 individuls which mke n ngle of 70" (or 110"). This cn perhps best be illustrted with the id of Figure 5 in which the undistorted reciprocl lttice of P hs been constructed using the dt of Figure 3. The positions of the c* xes of the two 6 crystls indicte tht the hexgonl xes of these crystls re ligned long the <111) directions in the (110) plne of the r crystls. The ngle of bout 70" we found between the two 6 crystls rises simply from the fct tht this is the ngle between the two (111) directions in the (110) plne of cubic crystl. The reson for the presence of two 6 individuls is undoubtedly the fct tht both <111) directions in the cubic lttice hve n equl probbility of ccomodting the hexgonl xis of 6 crystl. The full orienttion reltionship which cn be estblished from the dt of Figure 3 is in generl terms : r 6 (110) 11 (llz0) (111) II {0001) (211) 11 (ioio} 5.3. [l 113 Zone xis of r The rottion pttern of this zone showed, contrry to tht of the [110] zone, lrge number of extr lyer lines which evidently belonged to the 8 phse. As could be predicted from the foregoing results [lll] r ws found to coincide with [OOl] 6. In Fig. 6. Observed superposition of the zero level reciprocl lttices of r (xis of rottion [llll) nd 8 (xis of rottion [OOl]). For resom of clrity the reciprocl lttioo point8 of d (t the intersections of the lines hd = constnt; k8 = constnt) hve not been depicted by symbols ddition to this the zero level Weissenberg photogrph of this zone demonstrted tht every diffrction spot of P nerly coincided with one of 6 which cn be tken s evidence tht the spcings of mny r nd 6 lttice plnes re lmost equl. This excellent mtching of both lttices is best demonstrted in Figure 6 in which the observed superposition of the reciprocl lttices hs been drwn. It is obvious tht the lttices mtch very well in directions perpendiculr to [lll] r. In the [lll] rdirection

8 Crystllogrphic Reltions in the Fe-Zn System 451 itself, however, this is pprently not the cse s comprison of the periodicities long some principl directions lerns : r 6 Direction Periodicity Direction Periodicity A 11 [21O] A [ A 11 [loo] A A 11 [ooi] A 5.4. [loo] Zone xis of r As cn be derived from the reltionship estblished so fr the (100) r plnes re not prllel to ny low-indices plne of the 6 phse. The rottion nd Weissenberg ptterns did not yield dditionl informtion on the reltionship (F-) rl-6 reltionship In order to be ble to estblish this reltionship single crystlline mteril of the rl phse hd to be prepred. For this purpose two different procedures were followed. In the first procedure number of 6 coted r crystls of lloy number one (see under r--6 reltionship) were heted t 400OC. As n inspection of the phse digrm (Fig. 1) lerns the r crystls of this prticulr composition (27.3 tyo Fe) cnnot be trnsformed into I', crystls upon cooling becuse the homogeneity regions of these phses do not overlp for this composition. Insted, only rection zone r F, cn be expected t the PIS interfce nd indeed this turned out to be the cse. These crystls were used to record the superimposed Weissenberg ptterns of the three compounds in one single exposure. In the second procedure the 6 coted r crystls of lloy number two were employed. The composition of these crystls (22.0 tyo Fe) ws more fvourble for trnsformtion into rl. A het tretment of 33d t 400 "C yielded fully trnsformed r, crystls still coted with single crystlline lyer of 6. These crystls were subsequently used to determine the rl/s reltionship. Furthermore, some of the crystls were used to collect more detiled crystllogrphic dt on the F, phse becuse up to now these dt hd only been obtined from polycrystlline specimens (BASTIN, VAN LOO, RIECK, 1974). To this end the 6 lyer ws etched wy. The remining pure I', single crystl ws ligned long the principl zone xes (OOl), (110) nd <111> nd Weissenberg photogrphs were tken from number of lyer lines (up to the third). The preliminry unit cell dt published in the literture were thereby confirmed nd lso the fct tht the lttice is FCC. Aprt from the systemtic extinction connected with the fce-centering trnsltions, however, no dditionl systemtic extinctions could be observed. In conjunction with the observed 4-fold symmetry this leves s possible spce groups for F, : F432, F43m or Fm3m. At the moment work is in progress to determine the crystl structure of the r, phse. As fr s the orienttion reltionships re concerned it ws found tht in the cse of the T/r,/S crystls the originl reltionship between the nd 6 phse ws fully mintined. The newly grown r, phse dpted itself perfectly to both the r nd the 6 lttice by simply extending the existing principl crystllogrphic directions from the rphse throughout the rl lyer to the Tl/6 interfce. Similr results were obtined with the rl/6 crystls : upon trnsformtion the r, crystls were found to mintin the originl orienttion of the T crystls. Thus the r,/s orienttion reltionship is identicl to tht of r/s. Undoubtedly, this similrity is cused by the very close reltionship between the r nd rl phses. 30 Kristll/Technik. Bd. 14, H. 4

9 452 J. C. VERPLANEE et l F reltionship For the investigtion of this reltionship two lloys with overll compositions of nd t yo Fe, respectively, were prepred. After homogenizing t 1000 OC for few dys the lloys were equilibrted t 820 "C during severl dys. The compositions of the -Fe crysbls were found to be 61.8 nd 61.3 t yo Fe, respectively, which is in excellent greement with the results of Budurov et l. During quenching the primry -Fe crystls (dimensions mm) were covered with thin (2-3 pm) lyer of r nd/or TI nd 6 lyer (bout 20 pm) which gin showed the fmilir sw-tooths. A number of -Fe crystls were used for single crystl rottion nd Weissenberg ptterns bout (1 10) nd (1 11) -Fe. The Weissenberg pttern tken bout <llo) -Fe hd, prt from the -Fe diffrction spots, the sme generl ppernce s tht shown in Figure 3, in prticulr the extremely close rrngement of the diffrction spots typicl for the zero level Weissenberg photogrph of 6 crystl rotted bout [loo]. Hence, between -Fe nd 6 the sme orienttion reltionship exists s the one lredy estblished for r-8 nd T-rl--6. This ws confirmed by the nture of the F reflections in the pttern which clerly showed tht r hd been rotted bout (110). The reltionship between -Fe nd r is thus, like the one between rnd rl, very strightforwrd: (110) -Fe 11 (110) T; (1ll)-Fe 11 (111) F. This reltionship ws substntited by the Weissenberg pttern bout (1 11) -Fe. Both Weissenberg ptterns, however, indicted tht the misfit betwwen the -Fe nd r lttices is somewht lrger thn tht between the r nd rl lttices which ws negligible. Clcultions showed tht in the present cse the misfit is bout 2%. Of course, this misfit is not correct for hot dip glvnizing tempertures (usully "C) t which tempertures the iron cn only dissolve 3.8% Zn insted of 38%. A rough estimte through liner interpoltion of the lttice prmeter of -Fe shows tht in this cse the misfit is doubled reltionship The experimentl technique so successfully pplied to obtin coted single crystls of the, I' nd rl phses proved unsuccessful to produce 5 coted 6 crystls. It ws observed tht on the 6 crystls, grown during equilibrtion within the 6 + L phse field, no 5 lyer would nuclete on cooling, not even fter cooling very slowly. Insted, the 5 phse preferred to nuclete between the 6 crystls in the zinc-rich mtrix. Efforts to obtin 5 lyer on the 6 crystls by keeping the ltter in supercooled zinc-rich liquid lso filed; the only result of this procedure ws tht the 6 crystls were bdly ttcked by the liquid Zn. This ttck proceeded preferbly in directions perpendiculr to the hexgonl xis of 8. The 6 crystl disintegrted thereby grdully into segments perpendiculr to the hexgonl xis. Exctly the sme observtions were mde during etching of 6 crystls in dilute hydrochloric cid nd during ttck by zinc vpour. This cn be tken s evidence tht Zn (nd lso cid) hs esier ccess to the S crystls in directions perpendiculr to the hexgonl xis thn long this xis. Most probbly this points to lyer structure of the 6 phse. Another effort to produce 5 coted 6 crystls consisted of heting the 6 crystls in solidified zinc-rich mtrix t 375 "C. Through the solid stte diffusion process which hs to tke plce in this cse the 5 phse hs no choice thn to grow on 6. Even so the growth of 5' proved very lborious: fter 0.5 h t 375 "C no sign of 5 ws visible yet. Only fter bout 1 h the first nuclei of 5 were observed nd these were then found to grow rpidly until fter bout 2 h resonble lyer of 8 hd been trnsformed into ('Fig. 7). Apprently the 5 phse needs n incubtion time to form the first nuclei.

10 Crystllogrphic Reltions in the Fe-Zn-System 453 On microscopic exmintion the 5 phse eventully grown gve the impression of being polycrystlline. This ws confirmed by rottion ptterns which gve continuous Debye-Scherrer rings superimposed on the single crystl pttern of 6. For the lst method which ws tried in order to obtin single crystlline 5' lyer on top of 6 crystl use ws mde of zinc trnsfer through the vpour phse. In this experiment two 6 single crystls together with grin of Zn (crefully kept seprted from the 6 crystls) were brought into silic cpsule which ws then evcuted nd seled. The cpsule ws subsequently held t 450 "C during 47 h. One of the crystls ws fterwrds used for rottion ptterns. These ptterns clerly showed Debye- Schemer rings thus indicting the polycrystlline nture of the [ phse grown on the Fig. 7. Microgrph of d crystls heted in Zn-rich mtrix for 2 h t 375 "C, showing the trmformtion of d into 5 Fig. 8. Microgrph of d crystl heted in Zn vpour for 47 h t 450 "C. Notc the preferentil ttck perpendiculr to the hexgonl xis nd the polycrystlline nture of the 5 pheeventullyformed 6 crystl. Next the crystl ws embedded nd ground prllel to the hexgonl xis. Figure 8 shows microgrph of this section. Apprently under the ttck of gseous zinc the 6 crystls hs been split up into lmelle perpendiculr to the hexgonl xis, similr s during the ttck of 6 by liquid zinc mentioned before. Furthermore, it is obvious from Figure 8 tht nucletion of 5 hs tken plce only loclly nd tht the [ phse which eventully forms is polycrystlline. Summrizing the results on the6-5 reltionship it would seem tht ll the observtions mde so fr on the growth of 5 on 6 point to certin incomptibility of the crystl lttices of the 6 nd 5 phses. The reluctnt growth of 5 on 6 is pprently symptom of this incomptibility. 6. Discussion The crystllogrphic reltionship observed between the cubic Fe-Zn compounds, r nd r, my not be surprising t first sight in tht the indices of prllel plnes nd directions re simply the sme in ll cses. It is remrkble, though, tht this reltionship pplies in spite of the fst growing complexity of the structures: -Fey 2 t/cell; r (Fe,Zn,,), 52 t/cell; r, (Fe5Z%l), probbly 416 t/cell. This is even more so if one tkes into considertion tht number of these reltionships re estblished under circumstnces which cn hrdly be considered idel, i.e. during quenching. Nevertheless unique reltionships were observed nd this cn be tken s evidence tht there re lrge similrities between the structures of e.g. the r nd r, phses. 30

11 454 J. C. VERPLANKE et l. The unique reltionship found between r nd 6 (nd through the reltionships between the cubic phses between nd 6) my be of immedite prcticl importnce becuse here the reltionship between the iron substrte nd one of the mjor constituents of the coting formed during hot dip glvnizing, is involved. Whether this reltionship hs mjor influence on the nture of the texture formed in the 6 lyer or tht other fctors ply role hs to be determined yet. A most striking observtion in this respect is the fct tht the 8 crystls hve been found to be so much more vulnerble in directions perpendiculr to the hexgonl xis thn long this xis. The esy ccess which Zn toms pprently hve in the former directions corresponds very well with the texture observed in the 8 lyer: in ll cses the hexgonl xes of the 6 crystllites were found to be perpendiculr to.the direction of diffusion (BASTIN, VAN LOO, RIECK, 1976). Undoubtedly, hot dip 'glvnizing experiments crried out which iron single crystls of vrious orienttions 'cn decide in fvour of one of the possibilities; work to this effect will be crried out 'in the future. Chrcteristic for the r-6 (oror-6) reltionship is the stonishing ese with which it is estblished : during quenching fully dpted single crystlline lyers of 6 with thicknesses of up to 20 pm were obtined. Evidently this points to similrities between the r(rj nd 6 phses. Quite contrry to the ese with which the reltionships discussed sofr seem to be estblished re the troubles which pprently ccompny the nucletion of 5 on 6. The fct tht under none of the pplied prcticl circumstnces single crystlline lyer of 5 on 6 could be obtined must be tken s evidence for bd comptibility of the two crystl lttices. In prticulr the delyed nucletion with incubtion times of pprox. 0.5 h points in tht direction. Although these results re in full greement with those of HORSTMANN it is hrd to see why these nucletion problems re respon- sible for the premture bsence of 5 in the criticl temperture rnge of hot dip glvnizing. MACKOWIAK) tht lso in specimens, in which It hs nmely been shown (ALLEN, fully coherent 5 lyer is produced by glvnizing below the criticl temperture rnge, this 5 lyer nevertheless disppers during subsequent further glvnizing in the criticl temperture rnge. This mens tht lthough 5 nuclei were originlly present these cnnot prevent the disppernce of the 5 lyer. Concerning the origin of the texture found in the 5 lyer of hot dip glvnized specimens it must be stted tht this texture is obviously not cused by crystllogrphic reltionship between the 8 nd 5 lyers s pprently such reltionship does not exist. In this cse it is most probbly pproprite to ssume preferentil diffusion of Zn toms in certin crystllogrphic direction s hs been pointed out before (BASTIN, VAN Loo 1978). References ALLEN, C., MACKOWIAK, J.: Corr. Sci. 3, 87 (1963) ASTM: X-ry Powder Dt File (inorgnic volume) (1967) no for -Fe; no for Zn BABLIK, H., GOTZL, F., HALLA, I?.: Z. Metllkde. 30, 249 (1938) BASTIN, G., VAN Loo, F.: Z. Metllkde. 69, 540 (1978) BASTIN, G., VAN Loo, F., RIECK, G.: Z. Metllkde. 66, 656 (1974) BASTIN, G., VAN Loo, F., RIECK, G.: Z. Metllkde. 67, 694 (1976) BASTIN, G., VAN Loo, F., RIECK, G.: Z. Metllkde. 68, 359 (1977) BROWN, P.: Act? Cryst. 16, 608 (1962) BUDIJROV, F., KOVATCHEV, P., STOJEEV, N., KAMENOVA, Z.: Z. Metllkde. 63, 348 (1972) GHONIEM, M., LOHBERC, K.: Metl1 26, 1026 (1972)

12 Crystllogrphic Reltions in the Fe-Zn System 455 HEUMANN, T., DITTRICH, S.: Z. Metllkde. 60, 10 (1959) HORSTMANN, D. : Proc. Seminr on Glvnizing of Silicon Contining Steels, LiBge, Belgium 1975, p. 86 LIHL, F.: Z. Metllkde. 46, 434 (1955) LIHL, F., DEMEL, A.: Z. Metllkde. 48, 307 (1952) SCHRAMM, J.: Z. Metllkde. 28, 203 (1936) SCHRAMM, J.: Z. Metllkde. 29, 222 (1937) SCHRAMM, J.: Z. Metllkde. 30, 122 (1938) (Received October 31, 1978) Authors' ddress : Dr. Ir. G. F. BASTIN, J. C. VERPLANEE, F. J. J. VAN LOO University of Technology Dept. of Physicl Chemistry P. 0. Box 513 Eindhoven/Netherlnds