THIN MICROSTRUCTURE OF AMORPHOUS Ti-Ni-Cu ALLOY SUBJECTED TO HIGH PRESSURE TORSION
Recent studies have shown that severe plastic deformation (SPD) processing can be used not only for grain refinement in metals, but also to produce the amorphous or amorphous-nanocrystalline states, for example, in the case of Nd-Fe-B and Ti-Ni alloys. However, there remains a fundamental question: are there any differences in the atomic structure of amorphous alloys produced by SPD as compared with amorphous alloys from melt spinning, which allows to obtain thin ribbons by cooling the melt with a high cooling rate (up to 10 6 K/s). Recently a new kind of amorphous materials, called “nanoglasses”, was introducedADDIN CSL_CITATION { "citationItems" : [ { "id" : "ITEM-1", "itemData" : { "DOI" : "10.3762/bjnano.4.61", "ISSN" : "2190-4286", "PMID" : "24062978", "abstract" : "Nanoglasses are a new class of noncrystalline solids. They differ from today's glasses due to their microstructure that resembles the microstructure of polycrystals. They consist of regions with a melt-quenched glassy structure connected by interfacial regions, the structure of which is characterized (in comparison to the corresponding melt-quenched glass) by (1) a reduced (up to about 10%) density, (2) a reduced (up to about 20%) number of nearest-neighbor atoms and (3) a different electronic structure. Due to their new kind of atomic and electronic structure, the properties of nanoglasses may be modified by (1) controlling the size of the glassy regions (i.e., the volume fraction of the interfacial regions) and/or (2) by varying their chemical composition. Nanoglasses exhibit new properties, e.g., a Fe90Sc10 nanoglass is (at 300 K) a strong ferromagnet whereas the corresponding melt-quenched glass is paramagnetic. Moreover, nanoglasses were noted to be more ductile, more biocompatible, and catalytically more active than the corresponding melt-quenched glasses. Hence, this new class of noncrystalline materials may open the way to technologies utilizing the new properties.", "author" : [ { "dropping-particle" : "", "family" : "Gleiter", "given" : "Herbert", "non-dropping-particle" : "", "parse-names" : false, "suffix" : "" } ], "container-title" : "Beilstein journal of nanotechnology", "id" : "ITEM-1", "issued" : { "date-parts" : [ [ "2013", "1" ] ] }, "page" : "517-533", "title" : "Nanoglasses: a new kind of noncrystalline materials.", "type" : "article-journal", "volume" : "4" }, "uris" : [ "http://www.mendeley.com/documents/?uuid=2eca162f-3370-44e8-90f0-8d21906def2d" ] } ], "mendeley" : { "previouslyFormattedCitation" : "[7]" }, "properties" : { "noteIndex" : 0 }, "schema" : "https://github.com/citation-style-language/schema/raw/master/csl-citation.json" }. Nanoglasses consist of amorphous nanoclusters (about 5 nm in size), separated by amorphous interfaces with a different topology. The first nanoglasses were produced by inert-gas condensation and further consolidation, but this technique can be used only for obtaining very small samples and may have problems with residual porosity. Since deformation leads to a redistribution of the free volume in the amorphous phase, due to shear banding one may assume that severe plastic deformation of initially - amorphous alloys can lead to the formation of a state similar to nanoglasses. The amorphous melt-spun (MS) Ti 50Ni 25Cu 25 alloy is subjected by high-pressure torsion (HPT) at temperatures of 20-150 °C. The bright-field TEM image (BF) changes as a result of HPT processing: after HPT at T = 20ºC in the BF there can be seen amorphous clusters with a size of »25 nm separated by darker interfaces. The alloy subjected to HPT at T = 150 °C remains predominantly amorphous, although the fraction of nanocrystals somewhat grows as a result of some activation of nanocrystallization. In the case of HPT at T = 150 °C, in the BF there can be seen clusters with a size of »40 nm separated by brighter interfaces. These changes in the microstructure may be connected with the evolution