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One-dimensional glide of loops during ion irradiation at 773 K in a series of Ni-containing concentrated solid solution alloys has been observed directly during experiments conducted inside a transmission electron microscope. It was found that the frequency of the oscillatory motion of the loop, the loop glide velocity as well as the loop jump distance were dependent on the composition of the alloy and the size of the loop. Loop glide was most common for small loops and occurred more frequently in the less complex alloys, being highest in Ni, then NiCo, NiFe and NiCoFeCr. No measurable loop glide occurred in the NiCoCr, NiCoFeCrMn and NiCoFeCrPd alloys. [ABSTRACT FROM AUTHOR]

Nanoindentation is a critical technique to probe mechanical properties at the micrometer and sub-micrometer scales, accompanied by challenges from indentation size effect, pile-up/sink-in effect, and strain rate sensitivity. In this study, different nanoindentation techniques have been employed to explore Ni-based concentrated solid solution alloys (CSAs) with the addition of 3 d transition metal elements including Co, Cr, Mn, and Fe, including unique single-crystal Ni, NiCo, NiFe, Ni 80 Cr 20 , and NiCoFeCr samples with (100) surfaces. A procedure of nanoindentation tests and data analysis/correction have been developed, and a data set of hardness, elastic modulus, strain rate sensitivity, and activation volume for Ni-based CSAs are provided, including the less explored binary alloys such as Ni 80 Cr 20 and Ni 80 Mn 20. The results show that the type of alloying elements is more critical than the number of elements in strengthening: Co does not provide strengthening in NiCo, while Cr, Mn, and Fe are effective strengthening elements. Cr is the most effective among all the 3 d transition metal elements. Furthermore, atomic-level lattice distortion is responsible for the strengthening and the role of stacking fault energy is insignificant in Ni-based CSAs at room temperature. In summary, nanoindentation shows increasing promise as a reliable and fast tool to provide comprehensive mechanical information for new alloy design and development. [ABSTRACT FROM AUTHOR]

Abstract: In this paper, the creep behaviors of two Al2O3 particle reinforced copper composites were investigated using nanoindentation creep testing method. It has been shown that stress exponent determined by nanoindentation creep is much larger than that determined by traditional uniaxial tensile/compressive creep. A low externally applied loading results in a large scattering of the stress exponent due to limited grains joining the creep deformation and thus the different strain rates resulted from different grain orientations to the applied stress. The stress exponent of the composites increases with the externally applied loading for both composites, and the composite with higher reinforcement concentration shows larger stress exponents. [Copyright &y& Elsevier]

Unlike many Mg alloys that exhibit limited ductility, duplex Mg–Li alloys possess enhanced ductility but the underlying mechanisms are unclear. Using real-time in situ neutron diffraction measurements, we show that the underlying deformation modes in this duplex microstructure include an early yield of body-centered-cubic (BCC) β-Li phase and the later elevated hardening in this phase at large macroscopic plastic strain, and the sequential activation of basal and pyramidal < a > slip systems in hexagonal-close-packed (HCP) α-Mg phase. The latter relieves the Mises constraint for deformation compatibility, and the successive yielding sequence promotes the overall work hardening rate, both of which are beneficial for ductility enhancement. No obvious twinning activities were found and correspondingly the hysteresis loops were symmetric upon a full loading cycle within ±1% applied strain. [ABSTRACT FROM AUTHOR]

In contrast to the catastrophic failure arising from the unconstrained shear band propagation in monolithic bulk metallic glasses (BMGs), the introduction of second phases in BMG composites (BMGCs) provides an extrinsic way of reducing the magnitude of strain localization, and thus may significantly improve the ductility. For this mechanism to be effective, a multitude of experiments have found that the volume fraction should reach a rather high threshold of about 30–40%, corresponding to the percolation limit with variations depending on the second phase morphology. However, we demonstrate here that an enhanced ductility can be realized in a BMGC made from crystalline Ni foam (completely percolated even with a volume fraction of about 11%), suggesting the resistance in the second phase to the impinging shear-force dipole from neighboring shear bands be the dominant factor for such a ductility improvement. The shortcomings of percolation approach, as well as the synergistic effects of microstructure and mismatches in mechanical properties, are investigated here in a thermo-mechanical finite element method based on the free volume model and plasticity-induced heating. The effectiveness of ductility improvement will be demonstrated by calculating the probability distributions of the shear-band effective strain. [ABSTRACT FROM AUTHOR]

The deformation behavior and mechanism of Ti–36Nb–2Ta–3Zr-0.35O alloy at room and cryogenic temperatures (77 and 200K) were investigated. The microstructure near the fracture was observed with electron backscattered diffraction analysis (EBSD) and transmission electron microscopy (TEM). The results show that the plastic deformation behavior of the alloy is sensitive to test temperature and cold deformation history of the alloy. For the alloy without cold deformation, both tensile strength and ductility have a significant enhancement at cryogenic temperatures, mainly due to the occurrence of mechanical twinning. Moreover, with the decrease of the temperature, the density of mechanical twinning increases. For the alloy cold swaged by 85%, an increase in strength accompanied by a decrease in uniform elongation was found at cryogenic temperatures. The unique temperature dependence of the deformation behavior was due to the low stability of β phase. At 200K, ω phase precipitated in β phase; while at 77K, an interesting transformation (β phase to β′ phase) was observed. [ABSTRACT FROM AUTHOR]