In this paper high-temperature shape memory alloys based on TiPd and TiPt are reviewed. The effect of the alloying elements in ternary TiPd and TiPt alloys on phase transformation and strain recovery is also discussed. Generally, the addition of alloying elements decreases the martensitic transformation temperature and improves the strength of the martensite and austenite phases. Additionally, it also decreases irrecoverable strain, but without perfect recovery due to plastic deformation. With the aim to improve the strength of high-temperature shape memory alloys, multi-component alloys, including medium- and high-entropy alloys, have been investigated and proposed as new structural materials. Notably, it was discovered that the martensitic transformation temperature could be controlled through a combination of the constituent elements and alloys with high austenite finish temperatures above 500 °C. The irrecoverable strain decreased in the multi-component alloys compared with the ternary alloys. The repeated thermal cyclic test was effective toward obtaining perfect strain recoveries in multi-component alloys, which could be good candidates for high-temperature shape memory alloys.

TiPd- and TiPt-Based High-Temperature Shape Memory Alloys: A Review on Recent Advances

First-principles calculations coupled with Monte Carlo simulations are used to probe the role of a surface CO monolayer formation on secondary electron emission (SEE) from Cu, Ag, and Au (110) materials. It is shown that formation of such a layer increases the secondary electron emission in all systems. Analysis of calculated total density of states (TDOS) in Cu, Ag, and Au, and partial density of states (PDOS) of C and O confirm the formation of a covalent type bonding between C and O atoms. It is shown that such a bond modifies the TDOS and extended it to lower energies, which is then responsible for an increase in the probability density of secondary electron generation. Furthermore, a reduction in inelastic mean free path is predicted for all systems. Our predicted results for the secondary electron yield (SEY) compare very favorably with experimental data in all three materials, and exhibit increases in SEY. This is seen to occur despite increases in the work function for Cu, Ag, and Au. The present analysis can be extended to other absorbates and gas atoms at the surface, and such analyses will be present elsewhere. 

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Carbon-oxygen surface formation enhances secondary electron yield in Cu, Ag and Au

Facilitation of detwinning through controlling crystal structure in Ti–Zr–Ni–Pd high temperature shape memory alloys

Since single solid solution tends to form in medium- or high-entropy alloys (MEAs or HEAs), it offers an opportunity to obtain shape-memory type bulk metallic glass (BMG) composites when the selected system belongs to not only BMG but also MEAs or HEAs. Herein, through phase prediction parameters used in MEAs and HEAs, the phase formations for the medium-entropy Ti40Cu36-xZr10Pd14Cox (x = 2, 4, and 6 at.%) glass-forming alloys were evaluated before experiments. According to prediction, both fully amorphous samples and BMG composites were fabricated by rapid solidification. To observe the phase formations and the transformation-induced-plasticity (TRIP) effect, fully crystalline MEAs were obtained by annealing. With increasing Co addition, B2 Ti(Pd,Cu) phase can be stabilized to room temperature. All the samples exhibit excellent mechanical properties mainly due to different contributions from the transformation strengthening, second phase strengthening, and dislocations strengthening effects. 

A bridge from metallic glasses to medium-entropy alloys in Ti-Cu-Zr-Pd-Co system: Design, microstructure, and deformation-induced-martensitic transformation

Self-cleaning stainless steel surfaces induced by laser processing and chemical engineering

Abstract Nanostructured surfaces exhibit remarkable chemical, physical and microbiological properties and have therefore various technical and industrial applications. The ultrashort laser pulse irradiation (wavelength λ = 355 nm, pulse duration Δt p = 12 ps, repetition rate f = 100 kHz) of copper samples with appropriate laser parameters results in the formation of a micro- and nanostructured surfaces. The influence of these hierarchically textured surfaces on the secondary electron yield (SEY) was studied especially with regard to their morphological and geometrical properties. Specific SEY changes are caused by both, the shape and the depth of the microstructures, as well as the morphology of the formed nanostructures; that can be either compact flower head-like nanostructures, non-compact filament-shaped nanostructures, molten and resolidified spherical structures, or minor modified surfaces. The measured SEY as a function of the primary electron energy is correlated with the surface topography that forms upon laser irradiation. The SEY decreases with increasing accumulated laser fluence and ablated volume, respectively. Especially flower-head-like nanostructures can be produced at high laser power (P ≥ 400 mW) and low scanning velocity (v ≤ 10 mm/s) and represent a surface with strongly reduced SEY maximum as low as 0.7. 

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Secondary electron yield reduction of copper after 355 nm ultrashort pulse laser ablation

https://link.springer.com/content/pdf/10.1007/s40516-022-00167-5.pdf

Secondary electron yield reduction of copper after 355 nm ultrashort pulse laser ablation

Effect of single and simultaneous addition of Ni and Co to Ti45Zr5Pdx on the phase transformation and strain recovery of the alloys was investigated to understand multi-component effect on high-temperature shape memory alloys. The martensitic transformation from B2 to B19 structures occurred in Ti45Zr5Pd40Ni10, Ti45Zr5Pd40Co10, Ti45Zr5Pd40Ni8Co2, and Ti45Zr5Pd40Ni2Co8. In contrast, at room temperature, martensitic transformation did not occur and the B2 structure was stable in Ti45Zr5Pd30Ni20 and Ti45Zr5Pd40Ni5Co5. This is due to the effect of Ni for Ti45Zr5Pd30Ni20 and the effect of multi-component for Ti45Zr5Pd40Ni5Co5. The shape memory effect was investigated using a thermal cyclic test. The perfect shape recovery was obtained after the repeated thermal cyclic test, indicating the potential of TiZrPd (Ni, Co) alloys as shape memory alloys.

/pdf/effects-of-ni-and-co-on-phase-transformation-and-shape-uwnv5a0vvg.pdf

Effects of Ni and Co on Phase Transformation and Shape Memory Effect of Ti–Pd–Zr Alloys

The texturing of copper surfaces with ultrashort laser pulses leads to microscopic groove formation but results also in nanostructure development at the surface. Both structure types, micro- and nanostructures, are influenced by the laser processing parameters such as the laser power, the scanning speed, the repetition rate, and the line spacing. The generated nanostructures determine mainly the macroscopic properties of the laser-modified copper surface such as the optical reflectivity as well as the secondary electron yield (SEY). To study these effects, polycrystalline copper surfaces were irradiated with infrared picosecond laser radiation (wavelength of 1064 nm, pulse duration of 12 ps, repetition rate of 100 kHz and 1 MHz, respectively) and the secondary electron yield, as well as morphology and shape of the formed nanostructures were analyzed by scanning electron microscopy. The impact of the laser processing parameters on morphology and SEY show the effect of the nanostructures. From these correlations, the reduction of the SEY with increasing accumulated laser fluence and decreasing scanning speed has been identified as a general trend. Especially at high laser power (< 1.9 W) and low scanning speed (< 20 mm/s), the irradiation leads to the formation of compact nanostructures that results in surfaces with a SEY maximum as low as 0.7. SEY values lower than unity are interesting for practical applications of SEY reduction in particle accelerators. Fast processing is necessary to fulfil the technical and technological demands of the deployment and the fabrication of advanced accelerator components. Based on the results, a productivity of ~ 110 s/cm² for SEY ≤ 1 can be estimated at a laser power of 15 W.

Karolina Bogdanowicz

Papers

Secondary electron yield reduction of copper after 355 nm ultrashort pulse laser ablation

Secondary electron yield reduction of copper after 355 nm ultrashort pulse laser ablation

Effects of Ni and Co on Phase Transformation and Shape Memory Effect of Ti–Pd–Zr Alloys

Secondary electron yield engineering of copper surfaces using ultra short infrared laser pulses