Scratch test induced shear banding in high power laser remelted metallic glass layers
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Laser remelted surface layers of a Cu-based metallic glass forming alloy have been produced with fully amorphous depths up to 350 m for single track widths of around 1.3 mm and have been checked by transmission of synchrotron radiation. They have been subjected to indentation hardness and scratch testing, and the development of shear bands in both situations has been addressed. During the cross-sectional hardness indentation tests, Vickers values of over 735 HV2 have been found through the depth of the treated layer, and the scratch testing has revealed extremely low friction coefficient values (250 m) surface layers,5 and the glass forming composition chosen was Cu 47 Ti 33 Zr 11 Ni 6 Sn 2 Si 1 . 6 The scratch test has long been used to analyze thin coatings and surfaces in terms of coating–substrate adhesion, friction properties, and even as a model test for abrasive wear.7 The methodology of the test itself is straightforward, and by varying load (contact stress), pass number, a)
Address all correspondence to this author. e-mail: [email protected] DOI: 10.1557/JMR.2007.0056 460 J. Mater. Res., Vol. 22, No. 2, Feb 2007 http://journals.cambridge.org Downloaded: 09 Mar 2016
pass direction, and scratch speed (strain rate), it is proposed that it will be possible to determine shear band characteristics associated with those variables. During scratch testing, one of the outputs is sliding friction,8 which itself is a more complex phenomenon than the classic Coulomb laws of friction may suggest. This states that, first, friction is proportional to the applied load (this proportionality is known as the friction coefficient); second, friction is not dependant upon the (apparent) applied area; and third, kinetic friction is not dependant upon the sliding velocity. In multipass scratch testing, the ploughing component has been shown to decrease in passes subsequent to the first,9 thus leading to a reduction in friction on these passes also. Published data on multi-pass scratch testing concentrate on the failure of deposited thin films. In this paper, we address the multipass scratch test for (bulk) metallic glass investigations and investigate the development of shear bands during repetitive cycling. II. EXPERIMENTAL PROCEDURE
Alloys were prepared by weighing the component elements and then producing an approximately 1 cm3 “button” by arc melting. The materials are of at least 99.99% purity and in sheet, plate, pellet, or powder form prior to fabrication. The melting process is conducted in a Tigettered, high-purity argon (500 mbar) atmosphere. To ensure chemical and microstrucural homogeneity, the buttons are turned and remelted 3–5 times within the furnace. The buttons are then prepared for laser remelting © 2007 Materials Research Society IP address: 128.122.230.132
D.T.A. Matthews et al.: Scratch test induced shear banding in high power laser remelted metallic glass layers
microscopy [(HR)TEM; FEG JEOL 2010, Tokyo, Japan] with in situ heating and electron energy loss spectroscopy (EELS) capability, and x-ra
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