Mechanical behavior under nanoindentation of a new Ni-based glassy alloy produced by melt-spinning and copper mold casting

Abstract

An investigation was made into the thermal stability and mechanical behavior under nanoindentation of a new glassy alloy with composition Ni 50 Nb 28 Zr 22 , produced in the form of melt-spun ribbons and copper mold-cast wedges. The alloy composition was designed based on the lambda criterion combined with the electronegativity difference among the elements. X-ray diffraction and scanning electron microscopy confirmed that the ribbons and wedges (up to 200 μm in thickness) are amorphous. The thermal properties of these samples were evaluated by differential scanning calorimetry (DSC). Nanoindentation revealed that the hardness of this alloy, around 10 GPa, is among the highest reported for metallic glasses. Remarkably, the cast wedge exhibits greater hardness and higher elastic modulus than the ribbon. This correlates with the larger amount of frozen-in free volume in the ribbons than in the cast wedges, as evidenced by DSC. In addition, finite element simulations of nanoindentation curves were performed. The Mohr-Coulomb yield criterion allows for better adjustment of the experimental data than the pressure-independent Tresca yield criterion. The simulations also reveal that the cohesive stress in the ribbons is lower than in the wedges, which explains the difference in hardness and Young's modulus between the two samples.

Microstructure and Air Trace Defects of the Rapidly Solidified ZK60 Magnesium Alloy Ribbon

“…A profilometer measured the ribbon contact surface’s gas trace. The mechanical properties of the ribbon were evaluated through nanoindentation using a Berkovich pyramid-shaped diamond tip [ 27 ]. Before indentation, the samples were polished to a mirror-like appearance using a diamond spray down to 0.5 μm diamond particles.…”

Electrochemically synthesized amorphous and crystalline nanowires: dissimilar nanomechanical behavior in comparison with homologous flat films

“…Remarkably, yielding in metallic glasses cannot be simply described by the usual von Mises or Tresca criteria, as for crystalline metals, since normal stress components acting on the shear plane play a key role at the onset of plasticity. 5,[28][29][30] This effect, which needs to be taken into account in the simulations, is captured by the Mohr-Coulomb yield criterion, which is expressed as τ y = c − β M-C × σ n , where τ y is the shear stress on the slip plane at yielding, c is the shear strength in pure shear (also termed cohesive stress), σ n is the normal stress acting on the shear plane and β M-C denotes the internal friction coefficient. The simulations on the amorphous continuous film reveal that this alloy exhibits E = 151 GPa, a friction angle of 11°(β M-C = 0.194) and a cohesive stress of 2 GPa (Fig.…”

Investigation of the free volume change of Fe41Co7Cr15Mo14C15B6Y2 bulk metallic glass using the cyclic thermal dilatation test

“…The cooling rates during fabrication of the samples with diameters of 1, 3, and 5 mm were estimated to be 4.0 × 10 3 , 4.4 × 10 2 , and 1.6 × 10 2 K/s, respectively, based on the approximate method proposed by Johnson et al [34]. A faster cooling rate creates a greater free volume of liquid frozen into the amorphous solid [9,10,35], and hence a larger free volume is released in the cyclic heating process. The Δ δV=V 0 ð Þvalues of the samples with diameters of 1, 3, and 5 mm were 3.31 × 10 −3 , 2.65 × 10 −3 and 2.36 × 10 −3 , respectively.…”

“…In the rapid cooling process, some of the excess free volume is frozen into an amorphous solid [5,6]. The free volume is an important structural feature of BMGs, and has a great effect on their properties and behaviors, such as the invar effect [7], Young's modulus [8], plasticity [9][10][11], and glass-forming ability [12][13][14]. Although the free volume is not a tangible physical entity that can be directly determined [15], its change during the heating process can be investigated based on changes in enthalpy [16,17], positron lifetime [18,19], density [20][21][22][23], and thermal expansion [11][12][13][23][24][25][26][27][28][29].…”