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14. On liesegang bands in internally oxidized AgCd-based ternary alloys
xxxiii
ABSTRACTS
OF ARTICLES
TO APPEAR
Fully ordered and disordered Cu3Au single crystals were cycled to fracture in tensioncompression under strain control over a wide range of fatigue life. The fully ordered crystals exhibited an initial rapid fatigue hardening followed by softening. The disordered crystals showed continuous fatigue hardening until fracture. Fatigue hardening is interpreted by the unidirectional hardening concepts and softening by disordering. For both fully ordered and disordered crystals, defomnation bands developed during fatigue hardening for all strain amplitudes investigated. Fatigue cracks were observed to initiate at the intersection of slip bands and deformation bands and then propagate along the deformation band boundaries. Order had little effect on the fracture mode and both fully ordered and disordered crystals showed ductile fracture features. 12.
INTERPRETATIONS FOR THEP~IGRATION RESULTS IN ALUMINUMANDALUMINUMALLOYS R.A. McKEE * & J.P. STARK + • Institute for Materials Research, Metallurgy Division, National Bureau of Standards, Washington, D.C. + Materials Science Laboratory, University of Texas at Austin, Austin, Texas. Received January 23, 1975
Recent anomalies have been reported for thermomigration r e s u l t s i n al~ninum and alu~nin~n a l l o y s . A s i g n r e v e r s a l for the measured heat of t r a n s p o r t and consequently a mass flux r e v e r s a l i n the thermomigration experiment was reported for s e l f - t h e r m o m i g r a t i o n i n pure a l omin~n and for thermomigration of copper i n a l ~nin~n. These events occurred as a r e s u l t of varying the g r a i n or c r y s t a l s i z e i n the experiment. A g r a i n size e f f e c t on the measured heat of t r a n s p o r t ~ r s i l v e r i n al~nin~n has a l so been reported. Experim~p~al data for nonisothermal d i f f u s i o n of Ag**v i n al~ninum has e s t a b l i s h e d the e x i s t e n c e of s t a b l e p o i n t def e c t c o n c e n t r a t i o n s i n excess of those p r e d i c t ed for thermal e q u i l i b r i u m , and the e x p l a n a t i o n for the anomalies i n al~ninum thermomigration experiments i s now p o s s i b l e . 13.
THEORY OF SURFACEE N R I ~ AND SURFACE DISORDER EFFECTS IN BINARY ALLOYS K. BINDER, D. STAUFFER & V. WILDPANER* Fachrichtung Theoretische Physik, Universit~t des Saarlandes, 66 Saarbr~Jcken, W. Germany. * A t o m i n s t i t u t der (Jsterreichischen Hochschulen, 1020 Wien, Sch~Ittelstr. l l S , Austria. Received January 31, 197S Revised March 27, 1975
IN ACTA MET
Vol.
9, No.
7
Cooperative effects at binary (AB) surfaces are investigated. In general, the concentration of B-atoms at the surface will differ from the bulk ("surface enrichment"). But it may also occur that phase separation occurs at the surface of alloys which are miscible in the bulk ("surface segregation"). These effects are possible even if the bulk displays order-disorder phenomena. On the other hand, surface order-disorder phenomena may occur rather than surface segregation effects. We study these effects by phenomenological theories (using the concept of "extrapolation lengths"), microscopic (Ising-) models and Monte Carlo computations, similar to previous studies of magnetic surfaces by Binder and Hohenberg. We obtain the concentration "profiles" near the surface of bulk samples, thin films and small grains in several of these cases, and find that these "profiles" are quite smooth and monotonic. Attention is paid to treat the effects of concentration fluctuations, particularly near the respective criticai points of ordering or phase separation. It is shown that the phenomenological theory cannot account for the correct scaling properties in the general case, even if one allows for an arbitrary temperature dependence of the extrapolation length. But from the computer simulation detailed nr~nerical results are obtained for the surface enrichment as a function of temperature and bulk concentration. The typical order of magnitude of this surface enrichment is 0.i. A simple model including the effects of surface roughness is also treated. Possible experimental applications (catalysis phenomena etc.) are briefly mentioned. 14.
ON LIESEGANGBANDS IN INTERNALLYOXIDIZED AgCd-BASED TERNARYALLOYS V.A.vanROOIJEN, E.W.vanROYEN, J.VRIJEN & S. RADELAAR Laboratori~n voor Fysische Metaalkunde, Materials Science Center, Universiteitscomplex Paddepoel, Groningen, The Netherlands. Received February 3, 1975
The o r i g i n of the occurrence of Liesegang band formation (periodic p r e c i p i t a t i o n ) during internal oxidation of AgCd-alloys containing low concentrations of Be, Mg, A1 or Y has been investigated both experimentally and theoretically. A simple model of internal oxidation of ternary alloys is presented. The theory pred i c t s band spa~ing as a f u n c t i o n of temperature, Cd-concentration and c o n c e n t r a t i o n of the t h i r d element i n good agreement with e x p e r i m e n t a l results.
ABSTRACTS
OF ARTICLES
TO APPEAR
Fully ordered and disordered Cu3Au single crystals were cycled to fracture in tensioncompression under strain control over a wide range of fatigue life. The fully ordered crystals exhibited an initial rapid fatigue hardening followed by softening. The disordered crystals showed continuous fatigue hardening until fracture. Fatigue hardening is interpreted by the unidirectional hardening concepts and softening by disordering. For both fully ordered and disordered crystals, defomnation bands developed during fatigue hardening for all strain amplitudes investigated. Fatigue cracks were observed to initiate at the intersection of slip bands and deformation bands and then propagate along the deformation band boundaries. Order had little effect on the fracture mode and both fully ordered and disordered crystals showed ductile fracture features. 12.
INTERPRETATIONS FOR THEP~IGRATION RESULTS IN ALUMINUMANDALUMINUMALLOYS R.A. McKEE * & J.P. STARK + • Institute for Materials Research, Metallurgy Division, National Bureau of Standards, Washington, D.C. + Materials Science Laboratory, University of Texas at Austin, Austin, Texas. Received January 23, 1975
Recent anomalies have been reported for thermomigration r e s u l t s i n al~ninum and alu~nin~n a l l o y s . A s i g n r e v e r s a l for the measured heat of t r a n s p o r t and consequently a mass flux r e v e r s a l i n the thermomigration experiment was reported for s e l f - t h e r m o m i g r a t i o n i n pure a l omin~n and for thermomigration of copper i n a l ~nin~n. These events occurred as a r e s u l t of varying the g r a i n or c r y s t a l s i z e i n the experiment. A g r a i n size e f f e c t on the measured heat of t r a n s p o r t ~ r s i l v e r i n al~nin~n has a l so been reported. Experim~p~al data for nonisothermal d i f f u s i o n of Ag**v i n al~ninum has e s t a b l i s h e d the e x i s t e n c e of s t a b l e p o i n t def e c t c o n c e n t r a t i o n s i n excess of those p r e d i c t ed for thermal e q u i l i b r i u m , and the e x p l a n a t i o n for the anomalies i n al~ninum thermomigration experiments i s now p o s s i b l e . 13.
THEORY OF SURFACEE N R I ~ AND SURFACE DISORDER EFFECTS IN BINARY ALLOYS K. BINDER, D. STAUFFER & V. WILDPANER* Fachrichtung Theoretische Physik, Universit~t des Saarlandes, 66 Saarbr~Jcken, W. Germany. * A t o m i n s t i t u t der (Jsterreichischen Hochschulen, 1020 Wien, Sch~Ittelstr. l l S , Austria. Received January 31, 197S Revised March 27, 1975
IN ACTA MET
Vol.
9, No.
7
Cooperative effects at binary (AB) surfaces are investigated. In general, the concentration of B-atoms at the surface will differ from the bulk ("surface enrichment"). But it may also occur that phase separation occurs at the surface of alloys which are miscible in the bulk ("surface segregation"). These effects are possible even if the bulk displays order-disorder phenomena. On the other hand, surface order-disorder phenomena may occur rather than surface segregation effects. We study these effects by phenomenological theories (using the concept of "extrapolation lengths"), microscopic (Ising-) models and Monte Carlo computations, similar to previous studies of magnetic surfaces by Binder and Hohenberg. We obtain the concentration "profiles" near the surface of bulk samples, thin films and small grains in several of these cases, and find that these "profiles" are quite smooth and monotonic. Attention is paid to treat the effects of concentration fluctuations, particularly near the respective criticai points of ordering or phase separation. It is shown that the phenomenological theory cannot account for the correct scaling properties in the general case, even if one allows for an arbitrary temperature dependence of the extrapolation length. But from the computer simulation detailed nr~nerical results are obtained for the surface enrichment as a function of temperature and bulk concentration. The typical order of magnitude of this surface enrichment is 0.i. A simple model including the effects of surface roughness is also treated. Possible experimental applications (catalysis phenomena etc.) are briefly mentioned. 14.
ON LIESEGANGBANDS IN INTERNALLYOXIDIZED AgCd-BASED TERNARYALLOYS V.A.vanROOIJEN, E.W.vanROYEN, J.VRIJEN & S. RADELAAR Laboratori~n voor Fysische Metaalkunde, Materials Science Center, Universiteitscomplex Paddepoel, Groningen, The Netherlands. Received February 3, 1975
The o r i g i n of the occurrence of Liesegang band formation (periodic p r e c i p i t a t i o n ) during internal oxidation of AgCd-alloys containing low concentrations of Be, Mg, A1 or Y has been investigated both experimentally and theoretically. A simple model of internal oxidation of ternary alloys is presented. The theory pred i c t s band spa~ing as a f u n c t i o n of temperature, Cd-concentration and c o n c e n t r a t i o n of the t h i r d element i n good agreement with e x p e r i m e n t a l results.