HRTEM and TEM studies of amorphous structures in ZrNiTiCu base alloys obtained by rapid solidification or ball milling

Jan M. Dutkiewicz 1Lidia Lityńska-Dobrzyńska 1Wojciech Maziarz 1Robert Kocisko 2Maria Molnarova 2Jerzy Morgiel 1

1. Polish Academy of Sciences, Institute of Metallurgy and Materials Sciences (IMIM PAN), Reymonta 25, Kraków 30-059, Poland
2. Technical University Kosice Faculty of Metallurgy Department of Metal Forming, Letna 9, Kosice 04200, Slovakia (Slovak Rep.)

Abstract

Amorphous structure in melt spun or ball milled alloys was studied in ZrNiTiCu system with Mn, Nb and Ag additions. TEM studies of melt spun ribbons from alloys far from eutectic composition has shown usually presence of nanocrystals while that near eutectic only amorphous structure. The introduction of even small amount of 3 at. % of Al into high copper eutectic ZrTiNiCuMn alloys resulted in formation of additional coarse dendrite like primary crystallites. They were eliminated by decreasing the Al content down to 1,5 at%, i.e. from Ti15Zr15Ni25Cu39Mn3Al3 to to Ti15,5Zr14Ni27Cu39Mn3Al1,5 (in at. %). The glass transition range ΔTx ~26oC, Tx ~482oC and the reduced glass transition Tgr ~0,59 was determined in melt spun ribbons. The in-situ heating of thin foils within the crystallization range was applied to introduce controlled amount of nano-crystallites.

TEM studies of ball milled powders showed presence of nanocrystallites of size 2-5 nm and in consolidated compacts Cu50Ag10Zr30Ti10 amorphous matrix with nanocrystals of size close to 15 nm. The electron diffraction pattern showed amorphous hallow and a weak rings due to crystalline phases like Zr2(Cu,Al), Zr2Cu, Ti2Ni and a-Ti, β-(Ti,Zr). The diffused rings makes difficult identification of a crystal structure. The crystallites were imaged using HREM. Interplanar distances were measured in pictures obtained by IFFT (Inverse Fast Fourier Transform) of atomic planes to obtain better contrast. Following the HREM analysis of fringe spacing and angles CuZr2 phase was identified. Similar analysis was performed in the consolidated Zr36Cu29.5Ni19Ti10Nb5.5 alloy from ball milled powders. Analysis of the IFFT from high resolution micrographs allowed to identify Cu10Zr7 phase. Point analysis and elemental mapping performed using nondispersive X-ray energy spectroscopy showed uniform elements distribution indicating that chemical segregation to nanocrystals is within a measurement error.

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Presentation: Invited at E-MRS Fall Meeting 2007, Symposium J, by Jan M. Dutkiewicz
See On-line Journal of E-MRS Fall Meeting 2007

Submitted: 2007-05-14 16:41
Revised:   2009-06-07 00:44
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