Magnetic and vibrational properties of high-entropy alloys

The magnetic properties of high-entropy alloys based on equimolar FeCoCrNi were investigated using vibrating sample magnetometry to determine their usefulness in high-temperature magnetic applications. Nuclear resonant inelastic x-ray scattering measurements were performed to evaluate the vibrational entropy of the ^(57)Fe atoms and to infer chemical order. The configurational and vibrational entropy of alloying are discussed as they apply to these high-entropy alloys

Absence of long-range chemical ordering in equimolar FeCoCrNi

Equimolar FeCoCrNi alloys have been the topic of recent research as "high-entropy alloys," where the name is derived from the high configurational entropy of mixing for a random solid solution. Despite their name, no systematic study of ordering in this alloy system has been performed to date. Here, we present results from anomalous x-ray scattering and neutron scattering on quenched and annealed samples. An alloy of FeNi_3 was prepared in the same manner to act as a control. Evidence of long-range chemical ordering is clearly observed in the annealed FeNi_3 sample from both experimental techniques. The FeCoCrNi sample given the same heat treatment lacks long-range chemical order

The unusual character of microstructure evolution during "abc" deformation of commercial-purity titanium

Microstructure evolution during "abc" deformation of commercial-purity titanium was investigated. Continuous dynamic recrystallization (CDRX) played a dominant role in the microstructural changes, although mechanical twinning also contributed to some extent. It was found that CDRX developed preferentially at the original grain boundaries, thus resulting in a necklace-type microstructur

Microstructure evolution and mechanical behavior of ultrafine Tie6Ale4V during low-temperature superplastic deformation

The influence of microstructure evolution on the low-temperature superplasticity of ultrafine Tie6Ale4V was established. For this purpose, the static and dynamic coarsening response and plastic-flow behavior of the alloy with a mean size of a (sub)grains and b particles of 0.1-0.4 μm were determined via a series of tension tests at temperatures between 450 and 700°

Microstructure response of cryogenically-rolled Cu-30Zn brass to electric-current pulsing

The effect of transient electric-current pulses (ECP) on the evolution of microstructure and texture of cryogenically-rolled Cu-30Zn brass was determined. The pulsing was shown to lead to recrystallization followed by grain growth. The mean grain size in the recrystallized material was 0.5 μm, thus indicating that cryogenic rolling coupled with ECP is suitable for the production of an ultrafine-grain microstructure in Cu-30Zn brass. The differences in the recrystallization texture in pulsed versus statically-annealed conditions suggested a distinct recrystallization mechanism during ECP

Microstructure evolution during warm working of Ti-5Al-5Mo-5V-1Cr-1Fe at 600 and 800°C

Microstructure evolution during compression to the true height strain 0.29, 0.69, or 1.2 at 600 and 800. °C of the Β-rich titanium alloy Ti-5Al-5Mo-5V-1Cr-1Fe (VT22) with an initial lamellar microstructure was established using scanning and transmission electron microscopy. It was found that microstructure evolution at both temperatures was controlled primarily by substructure evolution within the Β phase. At 800. °C, extensive recovery within the Β phase resulted in the formation of a stable structure comprising subgrains ~1.5. μm in diameter. During deformation at this temperature, lamellae of the α phase fragmented via a boundary-grooving mechanism. Due to the sluggish diffusion kinetics, however, spheroidization at 800. °C was incomplete. At the lower processing temperature, recovery processes within the Β phase were much slower, leading to greater refinement of the Β matrix. The decomposition of the metastable Β phase during warm working, gave rise to very fine α-lath precipitates, which resulted in the formation of an ultrafine microstructure with a grain size of 0.5. μm. © 2012 Elsevier B.V

The effect of β stabilizers on the structure and energy of α/β interfaces in titanium alloys

The structure and energy associated with interfaces between the BCC and HCP lattices (β and α phase, respectively) in titanium alloys with commonly used β stabilizers were analyzed. For this purpose, the crystallographic structure of the matching facets of broad, side and end faces was described using misfit dislocations and structural ledges which compensate the mismatch in atomic spacing of the α and β phases. The effect of the β/α transformation temperature due to various concentration of b stabilizers on periodicity of misfit dislocations and structural ledges was estimate

Phonon densities of states of face-centered-cubic Ni-Fe alloys

Inelastic neutron scattering and nuclear resonant inelastic x-ray scattering were used to determine the phonon densities of states of face-centered-cubic Ni-Fe alloys. Increasing Fe concentration results in an average softening of the phonon modes. Chemical ordering of the Ni_(0.72)Fe_(0.28) alloy results in a reduction of the partial vibrational entropy of the Fe atoms but does not significantly change the partial vibrational entropy of the Ni atoms. Changes in the phonon densities of states with composition and chemical ordering are discussed and analyzed with a cluster expansion method

Electronic structure and vibrational entropies of fcc Au-Fe alloys

Phonon density of states (DOS) curves were measured on alloys of face-centered-cubic (fcc) Au-Fe using nuclear resonant inelastic x-ray scattering (NRIXS) and inelastic neutron scattering (INS). The NRIXS and INS results were combined to obtain the total phonon DOS and the partial phonon DOS curves of Au and Fe atoms from which vibrational entropies were calculated. The main effect on the vibrational entropy of alloying comes from a stiffening of the Au partial phonon DOS with Fe concentration. Force constants were calculated from first principles for several compositions and show a local stiffening of Au-Au bonds close to Fe atoms. The calculated phonon DOS curves reproduce the experimental trend. The stiffening is attributed to two main effects comparable in magnitude: (i) an increase in electron density in the free-electron-like states and (ii) stronger sd hybridization

Formation of Minor Phases in a Nickel-Based Disk Superalloy

The minor phases of powder metallurgy disk superalloy LSHR were studied. Samples were consistently heat treated at three different temperatures for long times to approximate equilibrium. Additional heat treatments were also performed for shorter times, to then assess non-equilibrium conditions. Minor phases including MC carbides, M23C6 carbides, M3B2 borides, and sigma were identified. Their transformation temperatures, lattice parameters, compositions, average sizes and total area fractions were determined, and compared to estimates of an existing phase prediction software package. Parameters measured at equilibrium sometimes agreed reasonably well with software model estimates, with potential for further improvements. Results for shorter times representing non-equilibrium indicated significant potential for further extension of the software to such conditions, which are more commonly observed during heat treatments and service at high temperatures for disk applications