Effects of Changes in Chemistry on Flex Bending Fatigue Behavior of Al-Based Amorphous Alloy Ribbons

  • PDF / 694,138 Bytes
  • 10 Pages / 593.972 x 792 pts Page_size
  • 6 Downloads / 249 Views

DOWNLOAD

REPORT


INTRODUCTION

A combination of good strength and low density (i.e., specific strength) is a necessary requirement for structural materials, whereas damage tolerance and fatigue resistance are also critical. Amorphous and nanocrystalline aluminum alloys have attracted significant interest in recent years because of their high strength and low density.[1] Among the most studied Al-based amorphous alloys are the aluminum-rare earth-transition (Al-RETM) metal systems because of their good glass-forming ability and mechanical properties.[2–4] These alloys have been shown to exhibit strengths nearly twice that of conventional Al alloys (7075-T6:ry  500 MPa) with similar densities.[1] Recent work showed positive effects of Fe, Co, and Fe/Co additions to Tg, Tx, strength at different temperatures, and activation energy for crystallization for Al-Gd-Ni-X amorphous alloy ribbons.[5] However, essentially no fatigue data exist for these amorphous materials, although both high cycle fatigue (HCF) and fracture toughness data exist for nanocrystalline composites produced via devitrification.[6] The mechanical properties of amorphous alloys have continued to receive great attention, with significant opportunities to improve fatigue performance. Some reports show that the fatigue limit of Zr-based metallic glasses is less than 10 pct of their ultimate tensile strength.[7,8] On the other hand, several studies including a recent review reveal that the fatigue limits of Pd-based and Zr-based metallic glasses are as high as crystalline metallic materials, 30 to 50 pct of their ultimate tensile CHUN-KUO HUANG, Graduate Student, and JOHN J. LEWANDOWSKI, Professor, are with the Department of Materials Science and Engineering, Case Western Reserve University, Cleveland, OH 44106-7204. Contact e-mail: [email protected] Manuscript submitted February 24, 2011. Article published online August 30, 2011 METALLURGICAL AND MATERIALS TRANSACTIONS A

strength (UTS).[9–14] Such differences in the fatigue limits of amorphous alloys have been proposed as a result of different loading conditions,[14] as well as because of the presence/absence of defects (e.g., inclusions, crystalline regions, pores, etc).[11] Although the high elastic limit/strength of such systems might imply good fatigue resistance in the HCF regime, mixed results have been obtained.[7–15] Early work on amorphous wire ribbons revealed generally good HCF behavior,[16] whereas the behavior of bulk metallic glasses has been much more variable.[7–15] In this article, fatigue tests on a series of Al-RE-TM amorphous alloy ribbons were performed under fully reversed flex bending fatigue conditions via cyclic bending over mandrels of different diameter. The wide range of mandrel sizes enables examination in both the low cycle fatigue and high cycle fatigue regimes. The fatigue performance is presented by cyclic stress/strain vs fatigue life curves (S-N curves) to examine the effects of systematic changes in chemical composition on fatigue performance.

II.

EXPERIMENTAL PROCEDURES

The Al-based amorphous all

Data Loading...