Effects of Effective Dendrite Size on Dynamic Tensile Properties of Ti-Based Amorphous Matrix Composites

In this study, dynamic tensile properties of dendrite-containing Ti-based amorphous matrix composites were examined, and effects of dendrite size on dynamic deformation were investigated. The composites contained 73 to 76 vol pct of dendrites whose effective sizes were varied from 63 to 103 mu m. The dynamic tensile test results indicated that the ultimate tensile strength increased up to 1.25 GPa, whereas the elongation decreased to 1 pct, although the overall strength and elongation trends followed those of the quasi-static tensile test. According to the observation of dynamic tensile deformation behavior, very few deformation bands were observed beneath the fracture surface in the composite containing large dendrites. In the composite containing small dendrites, deformation bands initiated inside small dendrites propagated into adjacent dendrites through the amorphous matrix, and were crossly intersect perpendicularly in widely deformed areas, which beneficially worked for elongation as well as strength.open1131sciescopu

Interpretation of Fracture Toughness and R-Curve Behavior by Direct Observation of Microfracture Process in Ti-Based Dendrite-Containing Amorphous Alloys

Fracture properties of Ti-based amorphous alloys containing ductile beta dendrites were explained by directly observing microfracture processes. Three Ti-based amorphous alloys were fabricated by adding Ti, Zr, V, Ni, Al, and Be into a Ti-6Al-4V alloy by a vacuum arc melting method. The effective sizes of dendrites varied from 63 to 104 mu m, while their volume fractions were almost constant within the range from 74 to 76 pct. The observation of the microfracture of the alloy containing coarse dendrites revealed that a microcrack initiated at the amorphous matrix of the notch tip and propagated along the amorphous matrix. In the alloy containing fine dendrites, the crack propagation was frequently blocked by dendrites, and many deformation bands were formed near or in front of the propagating crack, thereby resulting in a zig-zag fracture path. Crack initiation toughness was almost the same at 35 to 36 MPaaem within error ranges in the three alloys because it was heavily affected by the stress applied to the specimen at the time of crack initiation at the crack tip as well as strength levels of the alloys. According to the R-curve behavior, however, the best overall fracture properties in the alloy containing fine dendrites were explained by mechanisms of blocking of the crack growth and crack blunting and deformation band formation at dendrites. (C) The Minerals, Metals & Materials Society and ASM International 2015ope

Ductile phase reinforced bulk metallic glass composites formed by chemical partitioning

NOTE: Text or symbols not renderable in plain ASCII are indicated by [...]. Abstract is included in .pdf document. A new class of ductile metal reinforced bulk metallic glass matrix composite material has been prepared that demonstrates improved mechanical properties. This newly designed material exhibits both improved toughness and large plastic strain to failure. Primary dendrite growth accompanied by solute partitioning in the molten state yields an equilibrium microstructure consisting of a ductile crystalline Ti-Zr-Nb [beta] phase, with the bcc-structure, in a Zr-Ti-Nb-Cu-Ni-Be bulk metallic glass matrix processed via in situ processing. Under mechanical loading, the microstructure imposes constraints on the glassy matrix that leads to the generation of highly organized shear band patterns throughout the sample. This results in a dramatic increase in the plastic strain to failure, impact resistance, and toughness of the metallic glass. This thesis shows how microstructural inhomogeneity can be used to control the initiation and propagation of localized shear bands in metallic glasses under a variety of unconstrained loading conditions. A series of mechanical property tests were conducted on composite materials. These include quasi-static tensile and compression tests, Charpy impact, and three point bend tests on specimens prepared according to ASTM standards. Also, in situ straining transmission electron microscopy (TEM) experiments were performed to study the propagation of the shear bands in the bulk metallic glass based composite

In-Situ Fracture Observation and Fracture Toughness Analysis of Zr-Based Amorphous Alloys Containing Ductile Dendrites

Effects of dendrite size on fracture properties of Zr-based amorphous alloys containing ductile beta dendrites were explained by directly observing microfracture processes using an in-situ loading stage installed inside a scanning electron microscope (SEM) chamber. Three amorphous alloy plates having different thicknesses were fabricated by varying cooling rates after vacuum arc melting. The effective size of beta dendrites was varied from 14.7 to 30.1 mu m in the alloy plates, while their volume fraction was almost constant. According to microfracture observation of the alloy containing fine beta dendrites, shear bands initiated at the amorphous matrix were connected with the notch tip as they were deepened through dendrites, which led to abrupt crack propagation. In the alloy containing coarser beta dendrites, shear bands were initiated at the amorphous matrix to form a crack near the notch tip region and were expanded over large matrix areas. The crack propagation was frequently blocked by beta dendrites, and many shear bands are formed near or in front of the propagating crack, thereby resulting in stable crack growth, which could be confirmed by the fracture resistance curve (R-curve) behavior. This increase in fracture resistance with increasing crack length could be explained by mechanisms of blocking of crack growth, multiple shear band formation, and crack blunting.open113sciescopu

Correlation of microstructure and tensile properties of Ti-based amorphous matrix composites modified from conventional titanium alloys

In this study, three Ti-based amorphous matrix composites containing ductile dendrites were fabricated by adding alloying elements of Zr, Ni, and Be in conventional titanium alloys such as the Ti-6Al-4V alloy in order to develop new cost-effective Ti-based amorphous matrix composites having improved tensile ductility. Deformation mechanisms related with improvement of strength and ductility were investigated by focusing on how ductile dendrites affected the initiation and propagation of deformation bands or shear bands. The composites contained similar to 61-76 vol% of large dendrites sized similar to 37-81 mu m, and had excellent tensile properties of yield strength over 1 GPa and elongation over 5%. In the composite containing increased amounts of V and Al, which were effectively working to control dendritic beta phases, many deformation bands were formed inside dendrites in directions different from previously formed deformation band directions because the dendrites were relatively small. As the deformation proceeded further, deformation bands crossed each other, and the deformation occurred homogeneously in wide areas, while multiple shear bands were well developed in the amorphous matrix. This wide and homogeneous deformation in both dendrites and amorphous matrix beneficially worked for the tensile ductility, thereby showing high strength and elongation simultaneously. (C) 2012 Elsevier B.V. All rights reserved.X1116sciescopu

Dendrite Size and Tensile Ductility in Ti-Based Amorphous Alloys Containing Ductile Dendrites

Three Ti-based amorphous alloy sheets containing ductile dendrites were fabricated by varying cooling rate, and deformation mechanisms related with improvement of tensile ductility were investigated by observing initiation and propagation processes of deformation bands at dendrites. The alloy sheets contained many dendrites (volume fraction; 64 similar to 68%, size: 2.1-9.4 mu m), and showed the yield strength of 1.5 GPa and the elongation up to 5%. According to the observation of tensile deformation behavior of the 3-mm-thick alloy sheet, many deformation bands were formed inside dendrites in several directions, and deformation bands met crossly each other to form widely deformed areas. Since the wide and homogeneous deformation in this alloy sheet beneficially worked for the tensile strength and ductility simultaneously, the optimum size of dendrites and thickness of the alloy sheets were about 3.1 mu m and 3 mm, respectively. (C) 2013 Elsevier B.V. All rights reserved.X1144sciescopu

Tensile Deformation Behavior of Two Ti-based Amorphous Matrix Composites Containing Ductile beta Dendrites

In this study, two Ti-based amorphous matrix composites containing Nb and Ta contents were fabricated by a vacuum arc melting method, and deformation mechanisms related to improvement of strength and ductility were investigated by observing the initiation and propagation of deformation bands, shear bands, or twins occurring at ductile dendrites and hard amorphous matrix. The two composites contained 60-66 vol.% of coarse dendrites sized by 42-73 mu m had excellent tensile properties of yield strength over 1 GPa and elongation over 5%. In the composite having higher Ta content, shear bands were formed first at the amorphous matrix, while dendrites were hardly deformed. With further deformation, dendrites were deformed in a band shape as a considerable number of twins were formed inside some dendrites. According to the EBSD analysis result of this composite, parts of beta phases were transformed to alpha phases during the tensile deformation, and twins were formed at phase-transformed a phases. In this composite mixed with a and beta phases, beta phases could play a role in interrupting the twin formation at alpha phases, which resulted in the increase in stress required for the twin formation and consequently the increase in yield and tensile strengths. (c) 2012 Elsevier B.V. All rights reserved.X112120sciescopu

Quasi-static and Dynamic Compressive Properties of Ti-Based Amorphous Alloys Modified from Conventional Ti-6Al-4V Titanium Alloy

Quasi-static and dynamic compressive properties of three Ti-based amorphous alloys modified from a conventional Ti-6Al-4V alloy were examined, and deformation mechanisms related with improvement of strength and ductility were investigated. The alloys contained 73-76 vol% of dendrites whose effective sizes ranged from 63 mu m to 103 pm, and showed excellent compressive properties of the maximum strength over 1.7 GPa and the total strain over 18% under the quasi-static loading. Under dynamic compressive loading, the compressive strength increased up to 1.9 GPa, whereas the total strain decreased to 4-6%. In the alloy containing considerably large dendrites, the dynamic deformation was mainly concentrated on a maximum shear stress plane, and only a few deformation bands were observed beneath the fracture surface. In the alloy having sufficiently small effective dendrites for developing deformation bands, deformation bands and shear bands were initiated simultaneously at dendrites and the amorphous matrix, respectively, as the applied stress could be effectively dispersed. These findings provided the optimum effective dendrite size (63 for improving compressive properties by understanding the quasi-static and dynamic compressive deformation behavior. (C) 2014 Elsevier B.V. All rights reserved.X1144sciescopu

Microstructure and tensile properties of high-strength high-ductility Ti-based amorphous matrix composites containing ductile dendrites

In the present study, two Ti-based amorphous matrix composites containing ductile dendrites dispersed in an amorphous matrix were fabricated by a vacuum arc melting method, and deformation mechanisms related to the improvement of strength and ductility were investigated by focusing on how ductile dendrites affected the initiation and propagation of deformation bands, shear bands or twins. Ti-based amorphous matrix composites contained 70-73 vol.% coarse dendrites of size 90-180 mu m, and had excellent tensile properties of the yield strength (1.2-1.3 GPa) and elongation (8-9%). The Ta-containing composite showed strain hardening after yielding, and reached fracture without showing necking, whereas necking occurred straight after yielding without strain hardening in the Nb-containing composite. The improved tensile elongation and strain hardening behavior was explained by the homogeneous distribution of dendrites large enough to form deformation bands or twins, the role of beta phases surrounding alpha phases to prevent the formation of twins, and deformation mechanisms such as strain-induced beta to alpha transformation. (C) 2011 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.X117566sciescopu