Production of Bulk Metallic Glasses by Severe Plastic Deformation

Krämer, Lisa; Kormout, Karoline; Setman, Daria; Champion, Yannick; Pippan, Reinhard

doi:10.3390/met5020720

Cited by 25 publications

(15 citation statements)

References 35 publications

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“…In the present study, we investigate the influence of pressure on the formation of the ductile β-phase in γ-based TiAl alloys, which is not only of fundamental interest, but is also most relevant to modelling high-pressure deformation techniques, such as high-pressure torsion, in order to achieve severe plastic deformation [11][12][13][14][15] and high-pressure near-net-shape forging [16][17][18][19]. These deformation processes operate at pressures up to 7 GPa and forces exceeding 1 GN, respectively.…”

Section: Introductionmentioning

confidence: 99%

Hydrostatic Compression Behavior and High-Pressure Stabilized β-Phase in γ-Based Titanium Aluminide Intermetallics

Liss

Funakoshi

Dippenaar

et al. 2016

Metals

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Titanium aluminides find application in modern light-weight, high-temperature turbines, such as aircraft engines, but suffer from poor plasticity during manufacturing and processing. Huge forging presses enable materials processing in the 10-GPa range, and hence, it is necessary to investigate the phase diagrams of candidate materials under these extreme conditions. Here, we report on an in situ synchrotron X-ray diffraction study in a large-volume press of a modern (α 2 + γ) two-phase material, Ti-45Al-7.5Nb-0.25C, under pressures up to 9.6 GPa and temperatures up to 1686 K. At room temperature, the volume response to pressure is accommodated by the transformation γ → α 2 , rather than volumetric strain, expressed by the apparently high bulk moduli of both constituent phases. Crystallographic aspects, specifically lattice strain and atomic order, are discussed in detail. It is interesting to note that this transformation takes place despite an increase in atomic volume, which is due to the high ordering energy of γ. Upon heating under high pressure, both the eutectoid and γ-solvus transition temperatures are elevated, and a third, cubic β-phase is stabilized above 1350 K. Earlier research has shown that this β-phase is very ductile during plastic deformation, essential in near-conventional forging processes. Here, we were able to identify an ideal processing window for near-conventional forging, while the presence of the detrimental β-phase is not present under operating conditions. Novel processing routes can be defined from these findings.

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Section: Introductionmentioning

confidence: 99%

Hydrostatic Compression Behavior and High-Pressure Stabilized β-Phase in γ-Based Titanium Aluminide Intermetallics

Liss

Funakoshi

Dippenaar

et al. 2016

Metals

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“…To discern the origins of this variability in properties, significant experimental and theoretical efforts are currently underway to improve our understanding of the links between processing, structure and properties in BMGs [5,6,11,[26][27][28][29][30][31][32][33][34][35][36][37][38][39][40]. Aside from these structure-property relationships, which invariably dictate the characteristics and hence performance of a material, there also appears to be a strong influence of testing conditions on the mechanical behavior of (certain) metallic glasses.…”

Section: Introductionmentioning

confidence: 99%

On the understanding of the effects of sample size on the variability in fracture toughness of bulk metallic glasses

et al. 2017

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High strength in combination with improvements in failure characteristics and associated gains in fracture toughness have placed bulk-metallic glasses (BMGs) among the most damage-tolerant materials to date. Recent studies show, however, that there can be large variabilities in the mechanical performance of these alloys, particularly in their toughness, which are likely associated with sample-size effects or structural variations from differences in processing. Here, we examine the variation in fracture toughness of the Pdbased metallic glass Pd77.5Cu6Si16.5, using single-edge notched bend specimens but in two different sizes. Although all toughness results on this glass were "valid" in terms of the nonlinear-elastic fracture mechanics J-standard, i.e., one would expect a single value of the fracture toughness for this alloy, marked differences were apparent in the toughness values and failure characteristics of the differently-sized samples. Specifically, significantly larger variations in toughness values were measured in larger-sized samples, which all essentially failed catastrophically, whereas, none of the smaller-sized samples failed catastrophically yet displayed far less scatter in their measured toughness. Additional in-situ tests on the smaller-sized samples in a scanning electron microscope revealed stable crack growth and progressive resistance to crack extension, i.e. rising crack-resistance (R-curve) behavior. Overall, this marked transition from brittle catastrophic failure in large samples where a sizeindependent fracture toughness can be measured, to non-catastrophic, more

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“…Zr-MG powder was compacted and deformed via HPT beforehand. It could be shown that fully dense and amorphous specimens without cracks and pores can be fabricated with sufficient applied strains and no crystallization occurred during the HPT process 45 .…”

Section: Introductionmentioning

confidence: 99%

From powders to bulk metallic glass composites

Krämer

Champion

Pippan

2017

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One way to adjust the properties of materials is by changing its microstructure. This concept is not easily applicable on bulk metallic glasses (BMGs), because they do not consist of grains or different phases and so their microstructure is very homogeneous. One obvious way to integrate inhomogeneities is to produce bulk metallic glass composites (BMGCs). Here we show how to generate BMGCs via high-pressure torsion (HPT) starting from powders (amorphous Zr-MG and crystalline Cu). Using this approach, the composition can be varied and by changing the applied shear strains, the refinement of the microstructure is adjustable. This process permits to produce amorphous/crystalline composites where the scale of the phases can be varied from the micro- to the nanometer regime. Even mixing of the two phases and the generation of new metallic glasses can be achieved. The refinement of microstructure increases the hardness and a hardness higher than the initial BMG can be obtained.

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Production of Bulk Metallic Glasses by Severe Plastic Deformation

Cited by 25 publications

References 35 publications

Hydrostatic Compression Behavior and High-Pressure Stabilized β-Phase in γ-Based Titanium Aluminide Intermetallics

Hydrostatic Compression Behavior and High-Pressure Stabilized β-Phase in γ-Based Titanium Aluminide Intermetallics

On the understanding of the effects of sample size on the variability in fracture toughness of bulk metallic glasses

From powders to bulk metallic glass composites

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