Processing and Characterization of Cu-Al-Ni Shape Memory Alloy Strips Prepared from Prealloyed Powder by Hot Densification Rolling of Powder Preforms

The present work deals with the preparation of near-full density Cu-Al-Ni shape memory alloy (SMA) strips from argon-atomized prealloyed powder via a powder metallurgy (PM) route comprising cold die compaction to prepare powder preforms, sintering, and hot densification rolling of unsheathed sintered powder preforms under protective atmosphere at 1273 K (1000 °C). It has been shown that argon-atomized spherical Cu-Al-Ni SMA powder consisted of very fine equiaxed grains and no appreciable grain growth occurred during sintering at 1273 K (1000 °C). It also has been shown that no appreciable densification occurred during sintering, and densification was primarily achieved by hot rolling. The densification behavior of the sintered powder preforms during hot rolling was discussed. The hot-rolled Cu-Al-Ni strips were heat-treated at 1223 K (950 °C) for 60 minutes and water quenched. The heat-treated strips consisted of equiaxed grains with average size approximately 90 μm. The heat-treated Cu-Al-Ni SMA strips consisted of self-accommodated b₁^￠ \beta_{1}^{'} martensite primarily, and showed smooth b₁ T b₁^￠ \beta_{1} \Rightarrow \beta_{1}^{'} transformation behavior coupled with a very low hysteresis (≈25 K (25 °C)). The heat-treated strips exhibited an extremely good combination of mechanical properties with fracture strength of 530 MPa and 12.3 pct fracture strain. The mode of fracture in the finished strip was primarily void-coalescence-type ductile together with some brittle transgranular type. The shape memory tests showed almost 100 pct one-way shape recovery after 100 bending-unconstrained heating cycles at 4 pct applied prestrain, exhibiting good stability of Cu-Al-Ni strips under thermomechanical actuation cycling. The two-way shape memory strain was found approximately 0.45 pct after 15 training cycles at 4 pct training strain.     

Studies on the mechanism of the structural evolution in Cu–Al–Ni elemental powder mixture during high energy ball milling

The present work is focused on the understanding of the phase and microstructural evolution during mechanical alloying of 82Cu–14Al–4Ni powder mixture. Morphology and phase evolution in the milled powder at different stages of milling were studied and a physical modeling of the mechanical alloying has been proposed. It has been demonstrated that milling process mainly consisted of four stages, i.e., flattening and cold welding of powder particles to form a porous aggregate followed by its fragmentation, plastic deformation of small aggregates to form layered particles, severe plastic deformation of layered particles to form elongated flaky particles, and fragmentation of elongated particles into smaller size flaky powder particles. It was also found that the initial period of milling resulted in rapid grain refining, whereas alloying was accomplished during the later period of milling. TEM study of the 48 h milled powder revealed that the microstructure was equiaxed nanocrystalline in nature. It was found that the grains were either randomly distributed or arranged as banded type. A possible explanation for such a behavior has been presented.     

Preparation of Cu–Al–Ni shape memory alloy strips by spray deposition-hot rolling route

The present work describes the preparation of near-full density Cu–Al–Ni shape memory alloy (SMA) strips via a novel processing route consisting of ‘spray deposition’ of atomised liquid Cu–Al–Ni alloy with a jet of argon gas followed by hot-rolling densification of the deposited preform. The subsequent homogenisation of the hot rolled Cu–Al–Ni strips resulted in complete martensitic structure in the finished strip, consisting of self-accommodated plates of β₁′ and γ₁′ martensites. The characteristic transformation temperatures and shape memory effects of Cu–Al–Ni strips were studied. It has been demonstrated that the Cu–Al–Ni SMA strips, prepared in the present work, resulted in relatively finer grain size with better combination of strength and ductility compared to other techniques based on conventional casting method.     

Kinase in Motion: Insights into the Dynamic Nature of p38α by High‐Pressure NMR Spectroscopic Studies

Protein kinases are highly dynamic and complex molecules. Here we present high‐pressure and relaxation studies of the activated p38α mitogen‐activated protein kinase (MAPK). p38α plays a central role in inflammatory diseases such as rheumatoid arthritis and is therefore a highly attractive pharmaceutical target. The combination of high pressure and NMR spectroscopy allowed for a detailed per‐residue based assessment of the structural plasticity of p38α and the accessibility of low‐lying excited‐energy conformations throughout the kinase structure. Such information is uniquely accessible through the combination of liquid‐state NMR and high pressure and is of considerable value for the drug discovery process. The interactions of p38α and DFG‐in and DFG‐out ligands were studied under the application of high pressure, and we demonstrate how we can alter kinase dynamics by pressure in a similar way to what has previously only been observed by ligand binding. Pressure is shown to be a mild and efficient tool for manipulation of intermediate‐timescale dynamics.     

Composition-dependent tunability of thermoelectric properties at low temperature for Pr-doped LPFCO double perovskite

The current research focuses on the synthesis, characterization, and low temperature thermoelectric characteristics along with optical bandgap analysis of La_2?xPr_xFeCoO₆ (x?=?0, 0.25, 0.50, 0.75, and 1) double perovskite. The sintered sample’s crystal structure, microstructural features, electrical properties, and thermal transport parameters were examined. The nanocrystalline single-phase material was confirmed after 6 h of sintering, and the crystallite size increases with increasing Pr concentration along with the occurrences of various oxidation states of La, Pr, Fe, Co, and O. The conductivity analysis confirms the presence of a closest neighbor hopping charge carrier conduction mechanism due to decreased bandgap in entire samples. For all the compositions (x), conductivity, power factor, and figure of merit were increased with increasing temperature and Pr-content, confirming the presence of larger charge carrier concentration along with decreased bandgap. Positive S values indicate the presence of p-type charge carriers in LPFCO double perovskite and intrinsic behavior was conserved with increasing Pr-doping concentration (x). The highest Figure of Merit (ZT?=??~?0.007) was observed for the LaPrFeCoO₆ compound at 300 K. The observed results of ZT and their narrow optical bandgap suggested that, at ambient temperature, the LaPrFeCoO₆ compound can be also a good choice for solar cells, sensors, bolometers, and other optoelectronic devices as well.

     

Processing and Characterization of Cu-Al-Ni Shape Memory Alloy Strips Prepared from Elemental Powders <Emphasis Type="Italic">via</Emphasis> a Novel Powder Metallurgy Route

In the present work, Cu-Al-Ni shape memory alloy strips were prepared successfully from premixed elemental Cu, Al, and Ni powders in the ratio 82:14:4 (wt pct) by a novel processing route consisting of preparing powder preforms, sintering, and unsheathed hot rolling of the sintered preforms. Subsequently, the hot rolled strips were homogenized. The as-rolled strips consisted of two phases—α and β′. A postconsolidation homogenization of the hot rolled strips was carried out at 1173 K (900 °C) for different time periods. It has been shown that a homogenization period of 4 hours was sufficient to achieve a single-phase material consisting of only martensitic phase. It also has been shown that the 4-hour homogenized and quenched Cu-Al-Ni shape memory alloy strips primarily consisted of self-accommodated β′ martensite plates, which are necessary for realizing shape memory effect (SME). The finished hot rolled Cu-Al-Ni strips had a fracture strength of 476 MPa, coupled with 2.5 pct elongation. The shape memory tests showed almost 100 pct recovery after 10 thermomechanical cycles in the hot rolled strips at 1 pct and 2 pct prestrain level.     

Preparation of nanocrystalline Ni–Fe strip via mechanical alloying–compaction–sintering–hot rolling route

Nanocrystalline structures offer opportunity for the development of soft magnetic materials, such as 80 wt% Ni–20 wt% Fe, with superior properties. In recent years, nanocrystalline 80Ni–20Fe (wt%) alloy has been prepared by mechanical alloying of elemental powders. However, retention of nanocrystallinity during consolidation of powder is the key issue to take advantage of improved magnetic properties. In the present work, it has been shown that near-full density bulk nanocrystalline 80Ni–20Fe strip can be prepared via a route consisting of mechanical alloying, cold compaction, sintering, and multi-step unsheathed hot rolling. A crack-free strip of nanocrystalline 80Ni–20Fe, having 99% theoretical density and a grain size of approximately 55 nm, was successfully prepared by sintering and hot rolling of mechanically alloyed powder preforms at 1140 °C. The bulk nanocrystalline 80Ni–20Fe material resulted in a very narrow hysteresis loop indicating a very small hysteresis loss. The present study shows that mechanical alloying–sintering–hot rolling route can be a promising method for producing bulk nanocrystalline materials.