Discontinuous cracking of TiN films on a steel substrate induced by an adhesive interlayer

ABSTRACT

The basic mechanisms governing the process of cracking of single-layer brittle films have been extensively explored through both simulations and experiments. However, the role that an adhesive interlayer plays in the cracking of the overlying brittle film remains unclear. By performing three-point bending experiments, we observed that the insertion of a 100?nm thick Ti interlayer changed the cracking behaviour of TiN films from a continuous pattern to a discontinuous pattern. The slight change in the microstructure of the film and the increase in film thickness arising from the addition of the Ti interlayer are unlikely to cause the observed cracking morphology. The combination of the different interface between the Ti and the steel substrate and the fracture of the Ti interlayer are responsible for the transition in the TiN film cracking morphologies.     

Networking amorphous phase reinforced titanium composites which show tensile plasticity

Titanium matrix composites reinforced by an in situ formed networking amorphous phase have been prepared directly in the form of as-cast ingots. The composites show significant compressive and tensile plasticity. In contrast to the highly localized plasticity for most monolithic amorphous alloys, the tensile deformation of the current composites distributes uniformly over the entire specimen as a consequence of substantial work (strain) hardening. The formation mechanism of the networking structure, as a result of well-separated two-step solidification of the current alloy melts, have possible implications for composite synthesis in other alloy systems.     

In situ characterization of the martensitic transformation temperature of NiTi shape memory alloys via instrumented microindentation

A novel, instrumented microindentation technique was successfully used to measure the temperature associated with the martensitic transformation leading to the recovery of plastic strain in a Nickel–Titanium (NiTi) shape memory alloy. Following a standard indentation cycle, the indenter was partially unloaded such that a good contact was maintained between indenter and specimen surface. The onset and finish temperature of the martensitic transformation, the associated volume contraction, and the amount of the recovered plastic deformation were determined by quantifying the indenter displacement as a function of temperature. These experiments were compared to conventional measurements of the transformation temperature by differential scanning calorimetry and compression testing.     

HRTEM observation of misfit dislocations at non-faceted Al–Pb interfaces

Al–Pb samples containing 1?at.%?Pb were produced by high-energy ball milling and investigated by high-resolution transmission electron microscopy. The Pb inclusions embedded in an Al matrix exhibit a non-faceted, curved morphology. Dislocations have been found to accommodate the misfit of about 22% at the Al–Pb interfaces. Burgers circuits, drawn around these misfit dislocations, exhibit closing failures of the type a₀ /4〈211〉.     

Superelastic behavior of ultrafine-grain-structured Ti-35 wt%Nb alloy fabricated by equal-channel angular extrusion

The superelasticity of a Ti-35?wt%Nb alloy has been explored by fabricating an ultrafine-grain-structured specimen through equal-channel-angular-extrusion processing. A complete superelasticity of 3.5% was realized by refining the grain size down to about 0.25?µm and by inducing the precipitation of an ω-phase. The superelasticity was possible because the β-phase was largely stabilized at room temperature as a result of the severe grain refinement and Nb-enrichment in the matrix on account of the ω-precipitation.     

《易经》卦爻辞中之"惕"字质疑

帛书《易经》卦爻辞有大量与通行本相异的文字,需要考释。本文仅以通行本之"惕"字为例,论证帛书本异字"氵易"(即《小畜·六四》"血去惕出"的"惕"字,帛书写作"氵易"字)是""字之别写,而""通"",""的古体为"",故可校"惕"字为""字之误或原本相通。同时,帛书《乾·九三》"夕(残字)若厉"的"",讼卦卦辞"洫宁"的"洫",《·九二》"亻易号"的"亻易";通行本《师·九二》"王三锡命"的"锡",《涣·上九》"血去逖出"的"逖"字等,都得到相应的校释。     

Application of the Bons–Azuma method and determination of grain growth mechanism in rolled Ti–Zr alloys

Zr-containing Ti alloys have widely been developed owing to the infinite solid solubility of Zr in Ti and its avirulence, leading respectively to high strength and good biocompatibility. It is known that the Zr addition gives rise to grain refinement when rolled Ti–Zr alloys are annealed; nevertheless, the governing mechanism by which Zr addition in Ti can reduce grain size is not fully understood. In this study, the grain growth behaviour of rolled Zr-free and Zr-containing (Ti–10Zr, wt.%) alloys is analysed using analytical transmission electron microscopy and the classical and Bons–Azuma methods by evaluating the grain growth exponent. Irrespective of the evaluation technique and Zr content, the grain growth exponent is found to be close to ~0.3, indicating the occurrence of normal grain growth in the Zr-free alloy and solute drag mechanism in the Zr-containing alloy. It is found that the grain size and grain growth rate are significantly reduced by Zr segregation near grain boundaries, resulting from the solute drag mechanism.     

Microstructure and martensitic transformation behaviors of a Ti–Ni–Hf–Cu high-temperature shape memory alloy ribbon

The Ti₃₆Ni₄₁Hf₁₅Cu₈ melt-spun ribbon undergoes a B2 ? B19′ transformation upon cooling and heating. When the Ti₃₆Ni₄₁Hf₁₅Cu₈ melt-spun ribbon is annealed at 873 K for 1 h, the spherical (Ti, Hf)₂Ni particles with a diameter of 20–40 nm precipitate in the grain interior. The fine (Ti, Hf)₂Ni precipitates improve the stability of phase transformation temperatures and cause martensite domains, with (001) compound twins in three orientations dominant instead of (011) type I twins. {111}-, {113}- and (001)//{111}-type boundaries are observed among these martensite domains. When the (Ti,Hf)₂Ni precipitates coarsen, (011) type I twins become main martensite structures in the ribbon annealed at 973 K for 1 h.     

A novel lattice correspondence of B19 → B19′ transformation in Ti–Ni–Cu shape memory alloy thin film

In this study, we found a novel lattice correspondence of the B19–B19′ transformation in a Ti–Ni–Cu thin film: (1?1?1)_B19′//(0?0?1)_B19, [0, 1, 1]_B19′//[1?0?0]_B19. Near the coarse precipitate and the grain boundaries, the B19′ martensite forms with the novel lattice correspondence to product the (1?1?1) type I twinning instead of the usual (0?0?1) compound twinning. Crystallographic analyses show that the novel lattice correspondence results from the local stress concentration.     

Strain rate response of a Ni–Ti shape memory alloy after hydrogen charging

In this work, we investigate the susceptibility of Ni–Ti superelastic wires to the strain rates during tensile testing after hydrogen charging. Cathodic hydrogen charging is performed at a current density of 10?A/m² during 2–12?h in 0.9% NaCl solution and aged for 24?h at room temperature. Specimens underwent one cycle of loading-unloading reaching a stress value of 700 MPa. During loading, strain rates from 10^?6 to 5?×?10^?2?^?s^?1 have been achieved. After 8?h of hydrogen charging, an embrittlement has been detected in the tensile strain rate range of 10^?6 to 10^?4?s^?1. In contrast, no embrittlement has been detected for strain rates of 10^?3?s^?1 and higher. However, after 12?h of hydrogen charging and 24?h of annealing at room temperature, the embrittlement occurs in the beginning of the austenite-martensite transformation for all the studied strain rate values. These results show that for a range of critical amounts of diffused hydrogen, the embrittlement of the Ni–Ti superelastic alloy strongly depends on the strain rate during the tensile test. Moreover, it has been shown that this embrittlement occurs for low values of strain rates rather than the higher ones. This behaviour is attributed to the interaction between the diffused hydrogen and growth of the martensitic domain.