L.S. Cui

The ultrahigh mechanical energy-absorption capability evidenced in a high-strength NbTi/NiTi nanocomposite

A nanocomposite composed of NbTi nanowires uniformly embedded in NiTi matrices was fabricated, which exhibits an ultrahigh mechanical-damping capability. The absorption energy measured under an applied 8% strain is up to 54 MJ/m3, which is over three times higher than that (∼16 MJ/m3) found in the well-known Ni-Ti alloys. In-situ synchrotron x-ray diffraction reveals that a redistribution of stress between the nanowires and matrices was evidenced from an abrupt change in residual lattice strains. The ultrahigh mechanical-damping property is attributed to a combination of the strong interaction of nanowires and matrices and the plastic deformation occurring in NbTi nanowires during deformation causing large energy dissipation.

Grain size effect on the martensitic transformation temperatures of nanocrystalline NiTi alloy

The grain size effect on B19 martensitic transformation temperatures of a nanocrystalline Ti-50.2 at%Ni alloy was investigated by differential scanning calorimetry (DSC) analysis and (TEM) observation. It was found that the R → B19 transformation temperature decreases with decreasing grain size in the range of 50–150 nm, whilst the reverse B19 → R transformation temperature remains independent of grain size, leading to an increase of the hysteresis with decreasing grain size. The observed effects of grain size on the characteristics of the R ↔ B19 transformation are attributed to variations of both the elastic and the irreversible energies of the martensitic transformation in the nanograin regime.

In situ TEM observation of buffering the anode volume change by using NiTi alloy during electrochemical lithiation/delithiation.

A novel Ti3Sn/NiTi shape memory alloy anode with a sandwich structure was fabricated by arc melting. In order to characterize inxa0situ the Ti3Sn/NiTi anode microstructure changes and phase transformations during cycling, a nanoscale lithium battery was set up inside a transmission electron microscope, which consists of Li metal as the cathode, the native Li2O layer on the surface of Li metal as the solid electrolyte, and the Ti3Sn/NiTi as the anode. Only the Ti3Sn intermetallic compound experienced the electrochemical reaction, while the NiTi alloy (inactive with Li(+)) was applied for buffering the Ti3Sn volume change during cycling. An obvious reaction front of Ti3Sn migrated from one end to the other during lithiation, which can also return after delithiation. It provides direct evidence that the NiTi alloy can effectively accommodate the anode volume change during electrochemical lithiation and delithiation.

Fabrication and Property of W/Tininb Shape Memory Alloy Laminated Composite

W/TiNiNb shape memory alloy laminated composites were fabricated by vacuum hot press, forging and rolling. The microstructure, transformation behavior, mechanical behavior and damping capacity of the laminated composite were investigated by SEM, DSC, DMA and bending test, respectively. The results showed that the W layer and the TiNiNb shape memory alloy layer in the composite was about 15 μm and 5 μm, respectively. The TiNiNb alloy in the composite exhibited the reversible martensite transformation. The composite also had high damping capacity (tanδ=0.03). The three-point bending test showed various plateaus in the stress–strain curve due to delamination processes, which are suitable for enhancing the fracture toughness of the laminates. The flexure strength of the laminated composite was 1260 MPa.

Influence of Annealing and Pre-Straining on the Coupling Effect of a TiNi-Nb Nanowire Composite

The influences of different annealing temperatures and pre-strains on the coupling effect between TiNi matrix and the Nb nanowire were studied by means of synchrotron X-ray diffraction in form of variation in lattice strain of the nanowire upon temperature changing for four groups of samples. For every annealing temperature, variation in Nb (110) lattice strains initially increasing with increasing pre-strain and then decreased after 12% pre-strain. A maximum variation in Nb (110) lattice strain was observed approaching 2.4% within the sample 450°C-20min annealed and 12% pre-strained. Such variations in lattice strain of the embedded nanowires upon temperature changing provided the composite great potentials as structural-functional integrated two-way actuators.

Nanocrystalline NiTi shape memory alloys with huge superelasticity and high mechanical damping

Abstract Superelasticity and mechanical damping are important functional properties of nickel–titanium (NiTi) shape memory alloys (SMAs). Owing to the generation and accumulation of dislocation during loading, the recovery strain of commercial NiTi SMAs is usually smaller than 10%, which limits their ability to dissipate energy. In this paper, the superelasticity and mechanical damping of a nanocrystalline NiTi SMA was studied. The results show that the nanocrystalline NiTi SMA alloy possessed a large recovery strain of about 14%, greater than that of the commercial NiTi SMAs, and a high level of absorbed energy, or toughness, of 111 MJ m−3, which is higher than the highest value (about 81 MJ m−3) of all SMAs reported so far. The transmission electron microscopy (TEM) studies suggest that few full dislocations were generated in the nanocrystalline NiTi alloy during loading. Instead, the dominant deformation modes after stress induced martensitic transformation were elastic deformation and detwinning. The detwinning process decreased the twin boundary energy, which stabilised the martensitic phase.

Application Temperature Range of Temperature Memory Effect in Deformed TiNi Alloys

The application temperature range of temperature memory effect (TME) in deformed TiNi alloys was studied in this paper. The TME could be used in a wider temperature range when the specimen cold-rolled in a high deformation. And, the “highest” application temperature of TME could increase with the deformation, and finally rise to 573K with deformed 30%. This temperature no longer changes in higher deformations, while the characteristic of TME still increase with the deformation below 573K. This is due to the dislocation texture and deform-induced martensite structures restrain the reverse martensite transformation. And the restraint disappears when specimens are annealed more than 573K.

Novel Ti3Sn based high damping material with high strength

Abstract In this paper, ductile β-Ti was selected to toughen brittle high damping intermetallic compound Ti3Sn. An in situ Ti3Sn/β-Ti composite with a composition of Ti77Mo3Sn20 was prepared by arc melting. The composite simultaneously exhibited high yield strength (500 MPa), large plasticity (35%) and high damping capacity (tanu2009δ>0·06). In situ synchrotron high energy X-ray diffraction compression testing revealed that the β-Ti mainly accounts for the plasticity, while Ti3Sn provided the strength of the composite.