- Email: [email protected]
The crystal structure of a new triclinic ternary phase: τ3-Cr4(Al, Si)11
Intermetallics 14 (2006) 224–226 www.elsevier.com/locate/intermet
Short communication
The crystal structure of a new triclinic ternary phase: t3-Cr4(Al, Si)11 Franz Weitzera, Hailin Chena,b, Yong Dub, Julius C. Schustera,* a
Innovative Materials Group, Universitat Wien, A-1090 Wa¨hringer Street 42, Vienna, Austria b State Key Laboratory for Powder Metallurgy, Central South University, Changsha, 410083 Hunan, People’ Republic of China Received 3 February 2005; received in revised form 2 May 2005; accepted 11 May 2005 Available online 8 August 2005
Keywords: A. Intermetallics, miscellaneous (not otherwise listed, including model systems); B. Crystallography; F. Diffraction (electron, neutron and X-ray)
Of the ternary phases in the system Al–Cr–Si only the structure of Al13Cr4Si4 (labeled t1) can be found in the literature [1]. This short note reports on the ternary phase having an EDX determined composition of Al61Cr27Si12 when equilibrated at 800 8C with Cr5Si3 (s.s.Al) and CrSi2 (s.s.Al), but extending to lower Si contents such as Al65Cr27Si8 when coexisting with Cr5Si3 (s.s.Al) and g2Cr5Al8 (s.s.Si). Based on diffusion couple work combined with EDX analyses Gupta [2] assigned the label ‘Cr4Al9’ to a phase observed with very similar compositions (Al62Cr29Si9 at 1100 8C, Al60Cr29Si11 at 1000 8C, Al63Cr31Si6 at 800 8C; note: the composition given for the phase observed at 900 8C is more rich in Cr and within the accuracy of EDX identical to the composition assigned to ‘Cr5Al8’). Unnoticed by Gupta, however, the crystal structure of this phase is different from the crystal structure of either g4-Cr4Al9 (low temperature modification [3]) or g3-Cr4Al9 (high temperature modification [4]). Table 1 lists all XRD powder pattern peaks (Cu Ka1 radiation) having a relative intensity I(rel) O5% of the strongest peak observed for alloy Al63Cr27Si10 (nominal composition; arc melted using lumps of the pure (O4N) elements and annealed * Corresponding author. Tel.: C43 1 427752528; fax: C43 14277 9524. E-mail address: [email protected] (J.C. Schuster).
0966-9795/$ - see front matter q 2005 Elsevier Ltd. All rights reserved. doi:10.1016/j.intermet.2005.05.010
at 800 8C for w400 h in alumina crucibles sealed in evacuated quartz tubes). The pattern was indexed using the lattice parameters aZ0.51268(2) nm, bZ0.89810(4) nm, cZ0.50470(3) nm, aZ89.77(4)8, bZ100.711(4)8, gZ106.599(3)8, spacegroup P-1, and the atomic positions of the Mn4Al11-structure type [5]. With the exception of the (231) and (1-6-2) peaks having calculated I(rel) of 9.3 and 11.9%, respectively, all peaks are observed for which the relative intensity was calculated to be O5%. Thus, the match is considered good enough to assign to t3 without ambiguity Mn4Al11-type crystal structure, which does not occur in the Al–Cr binary. Hence, this new ternary phase is labeled t3-Cr4(Al, Si)11. Fig. 1 shows alloy Al62Cr28Si10 (composition by EDX analysis) in the as cast state (a) and after annealing for 2 weeks at 800 8C (b): as can be seen the heat treatment resulted in almost single phase material. The small (bright) crystallites are tentatively identified by EDX to be Cr5Si3, which would account for about half of the so far not indexed XRD peaks in Table 1. In order to obtain reliable information about XRD peaks with I(rel)!5%, full-profile Rietveld analysis is in progress. Such analysis will clarify, (a) whether the peaks so far unindexed in Table 1 belong to the pattern of t3 or are due to a so far not identified additional phase, and (b) whether the Al and Si atoms are statistically distributed over the six crystallographically different Al-sites, or if there is some preferential ordering [4].
F. Weitzer et al. / Intermetallics 14 (2006) 224–226
225
Table 1 XRD pattern of t3-Cr4(Al, Si)11 as observed in alloy Al63Cr27Si10 equilibrated at 800 8C obs. sin2 q (!10,000)
(HKL) for t3
calc. sin2 q (!10,000)
calc. rel. Int.(%)
17.7 19.7 6.1 27.6 36.0 9.1 18.1 12.5 6.7 23.3
0242 0253 0308 0401 0410 0413 0418 0534 0576 0592
001 1 K1 0
0242 0253
15.2 18.1
23.9 6.7 7.9 5.6 15.6 11.8 18.4 53.0 12.1 100.0
1008 1020 1057 1089 1165 1208 1226 1230 1239 1245
1 1 1 1 0 1 0 1 0 0 1 2 1 1 1 0
0 K1 K2 0 K1 K1 10 2 K1 K1 1 21 01 31 1 K2 K1 K2 K2 K1 1 K2 K4 0 30 2 K2
0401 0411 0413 0419 0534 0576 0592 0593 1008 1019 1058 1090 1166 1208 1227 1231
28.4 29.7 9.7 14.6 16.7 5.6 20.5 7.5 16.0 4.0 6.9 3.8 13.9 13.5 18.8 52.9
1 K2 K2 2 K3 0
1245 1246
49.6 50.4
8.1 39.2 67.2 7.9 53.8 37.4 33.8 50.0 5.9 34.6 9.3 7.9 22.5 15.1 12.8 9.8 17.0 6.2 14.5 8.8 3.8 5.0 4.2 6.1 6.6
1264 1268 1284 1298 1304 1340 1347 1355 1377 1383 1397 1414 1460 1468 1487 1543 1550 1603 1609 1642 1960 2254 2272 2474 2559
210 040
1268 1285
40.9 63.9
2 2 0 2
1303 1340 1347 1354
55.6 38.1 36.8 52.2
1 K1 2
1383
34.6
1 1 0 1
02 2 K2 4 K1 K4 1
1415 1461 1469 1488
8.7 25.1 14.6 13.6
2 K1 K2
1549
23.1
5.8 6.0 6.9 11.4 12.1 15.4
2828 2930 3060 3405 3489 3601
18.2 12.3 6.7 14.8 8.7 11.7
3633 3682 3718 3743 3793 3839
131 2 K4 0 122 2 K1 2 3 K3 K1 132 2 K5 1 231 301 113 1 K3 3 2 K5 2 3 K1 K3 3 K5 K2 1 K6 K2 4K2 K1 0 6 K2 2 3 K3 1 0 K4 2 K7 0 2 5 K1
1609 1642 1960 2257 2271 2474 2559 2719 2827 2927 3063 3404 3487 3598 3599 3629 3685 3714 3743 3794 3837
15.6 8.5 4.7 5.2 4.9 7.9 6.7 9.3 6.2 8.5 4.2 8.9 13.0 5.7 11.9 15.2 9.3 5.6 14.3 9.0 11.7
obs. rel. Int. (%)
1 K1 K3 K1 22 K1 1
Fig. 1. (a): SEM micrograph of as cast alloy Al62Cr28Si10 (EDX analyzed): the bright primary phase has a composition of Al54Cr37Si9 in the core and Al58Cr32Si10 on the ‘outskirts’. The grey phase surrounding it is t3 (Al61Cr28Si11). The major dark phase is 3Al4Cr (Al72Cr21Si7). (b): SEM micrograph of alloy Al62Cr28S10 (EDX analyzed) annealed for 2 weeks at 800 8C showing t3 as the dominant grey phase (composition almost identical to the composition of the alloy) and some tiny white crystals presumed to be Cr5Si3 (tentative EDX: Al5Cr61Si34). The black spots are holes.
Acknowledgements This work is supported by the Austrian Science Foundation through FWF grant # P16422, and the Austrian–Chinese cooperation through OEAD project VII.B.9.
226
F. Weitzer et al. / Intermetallics 14 (2006) 224–226
References [1] Robinson K. Acta Crystallogr 1953;6:854–9. [2] Gupta SP. Mater Character 2004;52:355–70. [3] Lindahl T, Pilotti A, Westman S. Acta Chem Scand 1968;22:748–52.
[4] Chen H, Thesis, Central South University, Changsha, Hunan, PR China, to be presented. [5] Kontio A, Stevens ED, Coppens P, Brown RD, Dwight AE, Williams JM. Acta Crystallogr 1980;B36:435–6.
Short communication
The crystal structure of a new triclinic ternary phase: t3-Cr4(Al, Si)11 Franz Weitzera, Hailin Chena,b, Yong Dub, Julius C. Schustera,* a
Innovative Materials Group, Universitat Wien, A-1090 Wa¨hringer Street 42, Vienna, Austria b State Key Laboratory for Powder Metallurgy, Central South University, Changsha, 410083 Hunan, People’ Republic of China Received 3 February 2005; received in revised form 2 May 2005; accepted 11 May 2005 Available online 8 August 2005
Keywords: A. Intermetallics, miscellaneous (not otherwise listed, including model systems); B. Crystallography; F. Diffraction (electron, neutron and X-ray)
Of the ternary phases in the system Al–Cr–Si only the structure of Al13Cr4Si4 (labeled t1) can be found in the literature [1]. This short note reports on the ternary phase having an EDX determined composition of Al61Cr27Si12 when equilibrated at 800 8C with Cr5Si3 (s.s.Al) and CrSi2 (s.s.Al), but extending to lower Si contents such as Al65Cr27Si8 when coexisting with Cr5Si3 (s.s.Al) and g2Cr5Al8 (s.s.Si). Based on diffusion couple work combined with EDX analyses Gupta [2] assigned the label ‘Cr4Al9’ to a phase observed with very similar compositions (Al62Cr29Si9 at 1100 8C, Al60Cr29Si11 at 1000 8C, Al63Cr31Si6 at 800 8C; note: the composition given for the phase observed at 900 8C is more rich in Cr and within the accuracy of EDX identical to the composition assigned to ‘Cr5Al8’). Unnoticed by Gupta, however, the crystal structure of this phase is different from the crystal structure of either g4-Cr4Al9 (low temperature modification [3]) or g3-Cr4Al9 (high temperature modification [4]). Table 1 lists all XRD powder pattern peaks (Cu Ka1 radiation) having a relative intensity I(rel) O5% of the strongest peak observed for alloy Al63Cr27Si10 (nominal composition; arc melted using lumps of the pure (O4N) elements and annealed * Corresponding author. Tel.: C43 1 427752528; fax: C43 14277 9524. E-mail address: [email protected] (J.C. Schuster).
0966-9795/$ - see front matter q 2005 Elsevier Ltd. All rights reserved. doi:10.1016/j.intermet.2005.05.010
at 800 8C for w400 h in alumina crucibles sealed in evacuated quartz tubes). The pattern was indexed using the lattice parameters aZ0.51268(2) nm, bZ0.89810(4) nm, cZ0.50470(3) nm, aZ89.77(4)8, bZ100.711(4)8, gZ106.599(3)8, spacegroup P-1, and the atomic positions of the Mn4Al11-structure type [5]. With the exception of the (231) and (1-6-2) peaks having calculated I(rel) of 9.3 and 11.9%, respectively, all peaks are observed for which the relative intensity was calculated to be O5%. Thus, the match is considered good enough to assign to t3 without ambiguity Mn4Al11-type crystal structure, which does not occur in the Al–Cr binary. Hence, this new ternary phase is labeled t3-Cr4(Al, Si)11. Fig. 1 shows alloy Al62Cr28Si10 (composition by EDX analysis) in the as cast state (a) and after annealing for 2 weeks at 800 8C (b): as can be seen the heat treatment resulted in almost single phase material. The small (bright) crystallites are tentatively identified by EDX to be Cr5Si3, which would account for about half of the so far not indexed XRD peaks in Table 1. In order to obtain reliable information about XRD peaks with I(rel)!5%, full-profile Rietveld analysis is in progress. Such analysis will clarify, (a) whether the peaks so far unindexed in Table 1 belong to the pattern of t3 or are due to a so far not identified additional phase, and (b) whether the Al and Si atoms are statistically distributed over the six crystallographically different Al-sites, or if there is some preferential ordering [4].
F. Weitzer et al. / Intermetallics 14 (2006) 224–226
225
Table 1 XRD pattern of t3-Cr4(Al, Si)11 as observed in alloy Al63Cr27Si10 equilibrated at 800 8C obs. sin2 q (!10,000)
(HKL) for t3
calc. sin2 q (!10,000)
calc. rel. Int.(%)
17.7 19.7 6.1 27.6 36.0 9.1 18.1 12.5 6.7 23.3
0242 0253 0308 0401 0410 0413 0418 0534 0576 0592
001 1 K1 0
0242 0253
15.2 18.1
23.9 6.7 7.9 5.6 15.6 11.8 18.4 53.0 12.1 100.0
1008 1020 1057 1089 1165 1208 1226 1230 1239 1245
1 1 1 1 0 1 0 1 0 0 1 2 1 1 1 0
0 K1 K2 0 K1 K1 10 2 K1 K1 1 21 01 31 1 K2 K1 K2 K2 K1 1 K2 K4 0 30 2 K2
0401 0411 0413 0419 0534 0576 0592 0593 1008 1019 1058 1090 1166 1208 1227 1231
28.4 29.7 9.7 14.6 16.7 5.6 20.5 7.5 16.0 4.0 6.9 3.8 13.9 13.5 18.8 52.9
1 K2 K2 2 K3 0
1245 1246
49.6 50.4
8.1 39.2 67.2 7.9 53.8 37.4 33.8 50.0 5.9 34.6 9.3 7.9 22.5 15.1 12.8 9.8 17.0 6.2 14.5 8.8 3.8 5.0 4.2 6.1 6.6
1264 1268 1284 1298 1304 1340 1347 1355 1377 1383 1397 1414 1460 1468 1487 1543 1550 1603 1609 1642 1960 2254 2272 2474 2559
210 040
1268 1285
40.9 63.9
2 2 0 2
1303 1340 1347 1354
55.6 38.1 36.8 52.2
1 K1 2
1383
34.6
1 1 0 1
02 2 K2 4 K1 K4 1
1415 1461 1469 1488
8.7 25.1 14.6 13.6
2 K1 K2
1549
23.1
5.8 6.0 6.9 11.4 12.1 15.4
2828 2930 3060 3405 3489 3601
18.2 12.3 6.7 14.8 8.7 11.7
3633 3682 3718 3743 3793 3839
131 2 K4 0 122 2 K1 2 3 K3 K1 132 2 K5 1 231 301 113 1 K3 3 2 K5 2 3 K1 K3 3 K5 K2 1 K6 K2 4K2 K1 0 6 K2 2 3 K3 1 0 K4 2 K7 0 2 5 K1
1609 1642 1960 2257 2271 2474 2559 2719 2827 2927 3063 3404 3487 3598 3599 3629 3685 3714 3743 3794 3837
15.6 8.5 4.7 5.2 4.9 7.9 6.7 9.3 6.2 8.5 4.2 8.9 13.0 5.7 11.9 15.2 9.3 5.6 14.3 9.0 11.7
obs. rel. Int. (%)
1 K1 K3 K1 22 K1 1
Fig. 1. (a): SEM micrograph of as cast alloy Al62Cr28Si10 (EDX analyzed): the bright primary phase has a composition of Al54Cr37Si9 in the core and Al58Cr32Si10 on the ‘outskirts’. The grey phase surrounding it is t3 (Al61Cr28Si11). The major dark phase is 3Al4Cr (Al72Cr21Si7). (b): SEM micrograph of alloy Al62Cr28S10 (EDX analyzed) annealed for 2 weeks at 800 8C showing t3 as the dominant grey phase (composition almost identical to the composition of the alloy) and some tiny white crystals presumed to be Cr5Si3 (tentative EDX: Al5Cr61Si34). The black spots are holes.
Acknowledgements This work is supported by the Austrian Science Foundation through FWF grant # P16422, and the Austrian–Chinese cooperation through OEAD project VII.B.9.
226
F. Weitzer et al. / Intermetallics 14 (2006) 224–226
References [1] Robinson K. Acta Crystallogr 1953;6:854–9. [2] Gupta SP. Mater Character 2004;52:355–70. [3] Lindahl T, Pilotti A, Westman S. Acta Chem Scand 1968;22:748–52.
[4] Chen H, Thesis, Central South University, Changsha, Hunan, PR China, to be presented. [5] Kontio A, Stevens ED, Coppens P, Brown RD, Dwight AE, Williams JM. Acta Crystallogr 1980;B36:435–6.