Densification behavior of mechanically milled Cu–8at% Cr alloy and its mechanical and electrical properties

AbstractSynthesis and consolidation behavior of Cu–8at% Cr alloy powders made by mechanical alloying with elemental Cu and Cr powders, and subsequently, compressive and electrical properties of the consolidated alloys were studied. Solid solubility of Cr in Cu during milling, and subsequent phase transformations during sintering and heat treatment of sintered components were analyzed using X-ray diffraction, scanning electron microscopy and transmission electron microscopy. The milled powders were compacted applying three different pressures (200MPa, 400MPa and 600MPa) and sintered in H2 atmosphere at 900°C for 30min and at 1000°C for 1h and 2h. The maximum densification (92.8%) was achieved for the sample compacted at 600MPa and sintered for 1000°C for 2h. Hardness and densification behavior further increased for the compacts sintered at 900°C for 30min after rolling and annealing process. TEM investigation of the sintered compacts revealed the bimodal distribution of Cu grains with nano-sized Cr and Cr2O3 precipitation along the grain boundary as well as in grain interior. Pinning of grain boundaries by the precipitates stabilized the fine grain structure in bimodal distribution

Structural integrity of ultrafine grain Al-3%Mg alloy under dynamic loading conditions

Utilization of various materials for constructing dynamic components and equipments has increased ever today. The high speed deformation mechanics was studied in various scale levels, especially in micro and nano scales. Understanding the micromechanics using shock waves led to development of armor plates in military technology. One dimensional elastic stress is applied using Split Hopkinson pressure bar for the ultra-fine grain aluminum samples and microstructural evolution was discussed in detail. The material characterization of equi channel pressing and its effect on stability of material after shock wave testing is provided. The grain size of material is steadily decreased to obtain ultra-fine grain structure during equi channel pressing and by application of shock waves on those pressed samples, the grain size again increases within the material. The recovery, re-crystallization and grain growth was observed in those shock tested samples due to induced temperature during such shock testing. The existing dislocation sub structure in pressed samples devoid after inertia effects. It is proposed further to understand the interaction between precipitate particle and dislocations

Behaviour and effect of Ti2Ni phase during processing of NiTi shape memory alloy wire from cast ingot

Binary NiTi alloy is one of the commercially successful shape memory alloys (SMAs). Generally, the NiTi alloy composition used for thermal actuator application is slightly Ti-rich. In the present study, vacuum arc melted alloy of 50.2Ti–Ni (at.%) composition was prepared and characterized using optical, scanning and transmission electron microcopy. Formation of second phase particles (SPPs) in the cast alloy and their influence on development of microstructure during processing of the alloy into wire form has been investigated. Results showed that the present alloy contained Ti2Ni type SPPs in the matrix. In the cast alloy, the Ti2Ni particles form in varying sizes (1–10 lm) and shapes. During subsequent thermo- mechanical processing, these SPPs get sheared/fragmented into smaller particles with low aspect ratio. The presence of SPPs plays a significant role in refinement of the microstructure during processing of the alloy. During deformation of the alloy, the matrix phase around the SPPs experiences conditions sim- ilar to that observed in severe plastic deformation of metallic materials, leading to localized amorphisa- tion of the matrix phase

Porous copper template from partially spark plasma-sintered Cu-Zn aggregate via dezincification

Present work deals with the preparation of spark plasma-sintered Cu-Zn aggregate (5, 10 and 20 wt% Zn) with interfacial bonding only starting from elemental powders of Cu and Zn (99.9% purity) and subsequently making of porous template of Cu by dezincification. Sintering is done so as to achieve only interfacial bonding with the aim to maintain maximum potential difference between the Cu and Zn particles during dezincification process in various solutions, viz. 1 N HCl and 3.5 wt% NaCl solutions. X-ray diffraction, optical microscopy and SEM-EDS are carried out to examine microstructural evolution and subsequent changes in hardness with sintering temperatures and different Zn percentages. Dezincification and pore formation are conducted on sintered 0.5 mm thick 12 mm diameter disc samples. The size, distribution and nature of pores in porous templates of Cu are then investigated using optical microscopy and SEM-EDS analysis

Ni24.7Ti50.3Pd25.0 high temperature shape memory alloy with narrow thermal hysteresis and high thermal stability

High temperature shape memory alloys with operating temperatures above 100 deg C are in demand for use as solid-state thermal actuators in aerospace, automobile and other engineering applications. The present study deals with transformation behaviour and thermal stability of Ni24.7Ti50.3Pd25.0 (at.%) high temperature shape memory alloy, in cast and homogenized condition. The martensite finish temperature and transformation hysteresis of the alloy were determined to be 181.0 deg C and ~8.5 deg C respectively. The alloy showed high stability upon stress-free thermal cycling, variation in transformation temperatures being ±1 deg C. The narrow thermal hysteresis and high thermal stability of the alloy upon transformation cycling has been discussed and correlated with its microstructural features, activation energy and elastic strain energy of thermoelastic martensitic transformation. The alloy exhibited modulus of ~82 GPa and hardness of ~4.7 GPa in martensite phase

Influence of stored elastic strain energy on fatigue behaviour of NiTi shape memory alloy thermal actuator wire

Influence of stored elastic strain energy, Eelse, on thermo-mechanical fatigue behaviour of NiTi shape memory alloy (SMA)thermal actuator wire was investigated. Two near equi-atomic NiTi SMA wires obtained from different sources were evaluated for quasi-static and functional fatigue properties. Study showed that the wires had similar chemical composition, transformation temperatures and static mechanical properties. However, the functional fatigue behaviour of the wires upon thermo-mechanical cycling (TMC) was found to be significantly different. Under avariable TMC stress in the range 150–450 MPa and 4% recovery strain, one of the wires showed better stability, and substantially higher fatigue life(~30000cycles)than the other (~3500 cycles). Thermodynamic and microstructural analyses indicated that the wide variation in fatigue response of the wires was due to difference in magnitude of Eelse in the material. It is observed that at a given temperature above austenite start temperature (As), the wire with higher stored Eelse, generated about 70–100MP a higher recovery stress than that of the wire with lower stored Eelse. As a consequence,the maximum temperature, Tmax, necessary for generation of preset peak stress during reverse(martensite-austenite)transformation, was always less in the former wire than that of the latter. This in turn was responsible for wide variations in thermo-mechanical fatigue behaviour of the two wires upon TMC