THE FORMATION AND STABILITIES OF Fe-, Ni- AND Co-BASED METALLIC GLASSES

The inf luence of a l loy ing s u b s t i t u t i o n s from the 3d,4d and 5d t r a n s i t i o n s e r i e s on the thermal -s tab i l i t i es of Fe-, N i and Co-based m e t a l l i c g lasses containing 10 a t . % S i and 12 at.%B g l a s s formers has been systematical ly inves t iga ted . The changes a r e in te rpre ted i n terms of variat i o n s i n (s+d) e lec t ron concentrat ion and of the s i z e d i f fe rence between solvent and s o l u t e metals. The e f f e c t of changes i n metal loid r a t i o s on the s t a b i l i t i e s and formation of NiSiB a l l o y s is a l s o reported. Introduction.The ease of formation and the s tab i l i t y of m e t a l l i c g lasses a r e s t rongly inf luenced by the composition /1-6/. In t h i s paper we r e p o r t and discuss the r e s u l t s of a study of the e f f e c t s of a wide range of a l loy ing addi t ions from Periods 4, 5 and 6 on t h e thermal -s tab i l i ty of Fe-, N i and Co-based mate r ia l s containing S i and B. In addition, we d i scuss the e f f e c t of v a r i a t i o n s i n metal loid content and r a t i o on the glass-forming a b i l i t y and thermal -s tab i l i ty of Ni-based a l loys . Experimental.Alloy ingots of nominal compositions, N i [x+y)Si B and (Fe, N i , o r C O ) ~ ~ ~ M ~ S ~ ~ ~ B ~ ~ , x Y where M is a t r a n s i t i o n metal o r Cur were v i t r i f i e d a s t h i n ribbons ?. 20 pm th ick and 0.5-2.0 mm wide by chi l l -block melt-spinning i n a i r /7/. The amorphous s t r u c t u r e of t h e t apes was es tab l i shed by X-ray d i f f r a c t i o n . The thermal behaviour of t h e g lassy a l l o y s was es tab l i shed by DSC,scanning a t a heat ing r a t e of 80 ~min-1 . The high heat ing r a t e was employed i n an attempt t o resolve t h e g l a s s t r a n s i t i o n . In t h e absence of a well-defined g lass t rans i t ion , t h e c r y s t a l l i z a t i o n temperature, Tx, was taken a s a lower-limiting est imate of t h e g lass t rans i t ion temperature, T and hence of t h e 9 g l a s s s t a b i l i t y . I n a l l ins tances , T was defined X a s t h e temperature a t which t h e ca lor imet r ic t r a c e ( i . e . the s p e c i f i c hea t ) f i r s t depar t s from t h e base l i n e f o r the f i r s t exothermic peak i n a DSC scan. Alloy l iqu idus temperatures, T ~ ~ ~ , were determined by d i f f e r e n t i a l thermal ana lys i s (Stanton-Redcroft DTA 673-4) of powdered samples contained i n alumina o r fused s i l i c a c ruc ib les . Results.The glass-forming range and c r y s t a l l i zat ion temperature isotherms f o r NL-Si-B tapes of average thickness 17 f 3 Idn a r e shown i n f i g . 1 . Ternary a l l o y s were f u l l y v i t r i f i e d over a wide composition range from 17-49at.% metal loid, depending on the Si:B r a t i o . I n add i t ion , binary Ni-B a l l o y s were v i t r i f i e d i n t h e composition ranges 17-18.5at.%B and 31-41at.%B. Not a l l t h e amorphous compositions were f u l l y d u c t i l e . Alloys t o t h e r i g h t of t h e boundary 'A-B' shown i n f i g . 1 could no t be bent through 180°, i n t h e as -cas t s t a t e , without f rac tur ing . Compositions c lose t o t h e boundary exhib i ted some p l a s t i c deformation, although towards t h e high-metalloid extremity of t h e glass-forming range a l l o y s were completely b r i t t l e and exhibi ted no macroscopic p l a s t i c deformation.