Synthesis of a single phase of high-entropy Laves intermetallics in the Ti–Zr–V–Cr–Ni equiatomic alloy

<p>The high-entropy Ti–Zr–V–Cr–Ni (20 at% each) alloy consisting of all five hydride-forming elements was successfully synthesised by the conventional melting and casting as well as by the melt-spinning technique. The as-cast alloy consists entirely of the micron size hexagonal Laves Phase of C14 type; whereas, the melt-spun ribbon exhibits the evolution of nanocrystalline Laves phase. There was no evidence of any amorphous or any other metastable phases in the present processing condition. This is the first report of synthesising a single phase of high-entropy complex intermetallic compound in the equiatomic quinary alloy system. The detailed characterisation by X-ray diffraction, scanning and transmission electron microscopy and energy-dispersive X-ray spectroscopy confirmed the existence of a single-phase multi-component hexagonal C14-type Laves phase in all the as-cast, melt-spun and annealed alloys. The lattice parameter <i>a</i> = 5.08 Å and <i>c</i> = 8.41 Å was determined from the annealed material (annealing at 1173 K). The thermodynamic calculations following the Miedema’s approach support the stability of the high-entropy multi-component Laves phase compared to that of the solid solution or glassy phases. The high hardness value (8.92 GPa at 25 g load) has been observed in nanocrystalline high-entropy alloy ribbon without any cracking. It implies that high-yield strength (~3.00 GPa) and the reasonable fracture toughness can be achieved in this high-entropy material.</p

Effect of Fe substitution by Co on off-stoichiometric Ni-Fe-Co-Mn-Sn Heusler alloy ribbons

We have synthesized Ni45Fe5-XCoXMn40Sn10 Heusler alloy with different Co doping and studied the effect on the structural and magnetic properties of Ni45Fe5-XCoXMn40Sn10 (at. X = 0,2.5,5) ribbons. X-ray diffraction, scanning and transmission electron microscopic characterization reveal the structural/microstructural features in melt-spun ribbons of different compositions. A significant transformation in the crystal structure has been observed in Fe substituted ribbons. The crystal structure changes from cubic L2(1) phase to bi-phasic 4O + L2(1) and 10M + L2(1) modulated phases for the partial and complete substitution of Fe by Co specimens respectively. Williamson-Hall analysis of x-ray diffraction data was used to compute the crystallite size and residual elastic strain. Magnetic properties and magnetic field-induced structural transformation of melt-spun alloy ribbons over a large temperature range of 10 K <= T <= 500 K were examined. Our results revealed that Fe substitution by Co causes a change in the magnetic behavior which could be ascribed to the increase in the lattice strain as well as a magnetic strain due to high antiferromagnetic fraction

Creep Behavior of Compact &gamma;&prime;-&gamma;&Prime; Coprecipitation Strengthened IN718-Variant Superalloy

The development of high-temperature heavy-duty turbine disk materials is critical for improving the overall efficiency of combined cycle power plants. An alloy development strategy to this end involves superalloys strengthened by &lsquo;compact&rsquo; &gamma;&prime;-&gamma;&Prime; coprecipitates. Compact morphology of coprecipitates consists of a cuboidal &gamma;&prime; precipitate such that &gamma;&Prime; discs coat its six {001} faces. The present work is an attempt to investigate the microstructure and creep behavior of a fully aged alloy exhibiting compact coprecipitates. We conducted heat treatments, detailed microstructural characterization, and creep testing at 1200 &deg;F (649 &deg;C) on an IN718-variant alloy. Our results indicate that aged IN718-27 samples exhibit a relatively uniform distribution of compact coprecipitates, irrespective of the cooling rate. However, the alloy ruptured at low strains during creep tests at 1200 &deg;F (649 &deg;C). At 100 ksi (689 MPa) load, the alloy fails around 0.1% strain, and 75 ksi (517 MPa) loading causes rupture at 0.3% strain. We also report extensive intergranular failure in all the tested samples, which is attributed to cracking along grain boundary precipitates. The results suggest that while the compact coprecipitates are indeed thermally stable during thermomechanical processing, the microstructure of the alloy needs to be optimized for better creep strength and rupture life

Creep Behavior of Compact <i>γ</i>′-<i>γ</i>″ Coprecipitation Strengthened IN718-Variant Superalloy

The development of high-temperature heavy-duty turbine disk materials is critical for improving the overall efficiency of combined cycle power plants. An alloy development strategy to this end involves superalloys strengthened by ‘compact’ γ′-γ″ coprecipitates. Compact morphology of coprecipitates consists of a cuboidal γ′ precipitate such that γ″ discs coat its six {001} faces. The present work is an attempt to investigate the microstructure and creep behavior of a fully aged alloy exhibiting compact coprecipitates. We conducted heat treatments, detailed microstructural characterization, and creep testing at 1200 °F (649 °C) on an IN718-variant alloy. Our results indicate that aged IN718-27 samples exhibit a relatively uniform distribution of compact coprecipitates, irrespective of the cooling rate. However, the alloy ruptured at low strains during creep tests at 1200 °F (649 °C). At 100 ksi (689 MPa) load, the alloy fails around 0.1% strain, and 75 ksi (517 MPa) loading causes rupture at 0.3% strain. We also report extensive intergranular failure in all the tested samples, which is attributed to cracking along grain boundary precipitates. The results suggest that while the compact coprecipitates are indeed thermally stable during thermomechanical processing, the microstructure of the alloy needs to be optimized for better creep strength and rupture life