11 MODIFICATION OF AMORPHOUS Co-BASED METAL ALLOY BY SHOCK-WAVE LOADING A.Z.Bogunov, R.S.Iskhakov, V.I.Kirko, A.A.Kuzovnikov JSC « Pulse technologies » , Krasnoyarsk, Russia, POB 26780, L.V. Kirenskiy Institute of physics SB RAS, , Krasnoyarsk, Siberian federal university, , Krasnoyarsk, st. Svobodny, 62

2 Research Objectives Obtaining a Co-based massive metallic glass samples by dynamic compaction of powder Annealing the compacts in order to study them in three structural states: amorphous, metastable nanocrystalline; stable crystalline; Measurement of the shock adiabat of amorphous and stable crystalline samples; Measurement of the pressure profile in the shock wave front for the amorphous and stable crystalline material; Measurement of changes in the electric resistance of some amorphous ribbon during the shock loading Study of recovered samples after shock loading by X-ray diffraction, DTA; magnetic structure analysis, microhardness; The possibilities of practical application of the results.

Preparation of samples Grinding ribbon to powderExplosive compaction Massive amorphous sample: Density 7,4 g/cm 3 Porosity  0,2% Diameter 20 mm Thickness 3 mm Quenching from the melt Detonator HE Powder Base Shell Pressure of compaction 5 GPa Container

Manufacture metastable nanocrystalline and equilibrium crystalline samples Annealing temperature based on DTA Metastable nanocrystalline Amorphous alloy Crystalline samples Annealing С+Grinding Compaction Ribbon Co 58 Ni 10 Fe 5 Si 11 B 16 → Powder Co 58 Ni 10 Fe 5 Si 11 B 16 → Compact Co 58 Ni 10 Fe 5 Si 11 B 16 Annealing С metastable Compact Co 58 Ni 10 Fe 5 Si 11 B 16 → fcc Со + Со 3 (BSi) Annealing С crystalline Compact Co 58 Ni 10 Fe 5 Si 11 B 16 → fcc Co + Co 2 B+Co 2 Si Shock loading up to 40 GPa

5 Experimental assembly Sample HE Copper plate 3 mm Two layer Cu barrier 3mm+1mm Steel collar Manganin gauge Р t Pressure profile P  14 GPa P  16 GPa Reflected shock wave Reflected unloading wave ( impedance matching method)

6 Hugoniot compression curve of the amorphous alloy CoNiFeSiB New phase Р = 13 GPa Curve kink: Elasto-plastic transition Phase transition Initial phase There is no inflection on the shock adiabat of the stable crystalline samples V/V 0 P, GPa T.Mashimo,H.Togo,Y.Zhang,Y.Kawamura. Material science and Engineering A (2007) Similar results for Zr- based alloy

7 Pressure history on the front of the shock wave Experimental assembly Two-wave profile of a shock wave in the amorphous sample Manganin gauge in the samples Р t Stable crystalline Amorphous alloy 1  s Р 1 = 13 GPA Р 2 =18 GPa HE Cooper plate Barrier Steel collar

8 Electric resistance measure during shock loading The ribbon of amorphous alloy Co 70 Fe 5 Si 10 B 15 Исходная фаза Р, GPa  R/R о,% Р R t RR

9 X – ray diffraction of recovered samples Amorphous alloy Metastable nanocrystalline No measurable changing 20 GPa 5 GPa МоК  - radiation

Microhardness of the recovered samples Amorphous alloy Metastable nanocrystalline Stable crystalline Р, GPa H V x10 2, GPa DTA of amorphous material has no change after shock loading ( P = 30 GPa)

11 Magnetic structure analysis М(Т) = М s (1 - ВТ 3/2 ), Bloch law М s В B = const M s 1/2 A -3/2 Bloch constant Exchange interaction А fcc-Co  2A hpc-Со  4 А Со 3 (B,Si) Structure characteristic M s – phase composition A – close order (inter distance and number of magnetoactive atoms) М, Gs Т 3/2, 10 3 К 3/2

12 Magnetic saturation – pressure dependence No measurable changing Amorphous alloy Metastable nanocrystalline Stable crystalline М s, Gs Р, GPa

13 Constant Bloch - pressure dependence Disordering (phase transition) fcc-Со  hcp-Со: Т  С; High pressure; Plastic deformation Bx10 5, К -3/2 Metastable nanocrystalline Amorphous alloy Ordering P, GPa Stable crystalline

Discussion 1.Elasto-plastic transition This transition was observed experimentally in shock wave loading amorphous alloys Amorphous alloys exhibit high values of HEL with subsequent loss of strength Changing the nature of deformation (shear band) could lead to disordering of the short-range order 2. fcc-Co  hcp-Co transition This transition was observed during the crystallization of the Co-based alloy under high pressure The irreversible transition can be quantitatively explained by changes of the magnetic characteristics for the amorphous and metastable (crystalline analogue) alloys, but the transition is not confirmed by structural method (X- Ray, DTA) Large volume changes on the shock adiabat - 12% There are no features at the Hugoniot of crystalline alloy like amorphous alloy

15 Сonclusion 1. A kink on the Hugoniot compression curve and two-wave profile of the shock wave, which may indicate a phase transition, were found at the Co-based metallic glass compacts. 2.The electrical resistance - pressure dependence of the amorphous Co-based ribbon shows a sharp decrease, which may be caused by phase transition. 3.The features of the basic magnetic characteristics indicate possible transition of the fcc-Co close order to the hcp-Co close order at the amorphous and nanocrystalline states under shock loading. 4.Amorphous alloys, which have reversible transformation with a large relative volume change, may be used as a medium for creating and maintaining the pressure after unloading (the method of dynamic- static compression)