Narrow Results

Ti–6Al–2Sn–4Zr–2Mo (Ti-6242), a near-$\alpha$ titanium alloy explicitly designed for high-temperature applications, consists of a martensitic structure after selective laser melting (SLM). However, martensite is thermally unstable and thus adverse to the long-term service at high temperatures. Hence, understanding martensite decomposition is a high priority for seeking post-heat treatment for SLMed Ti-6242. Besides, compared to the room-temperature titanium alloys like Ti–6Al–4V, aging treatment is indispensable to high-temperature near-$\alpha$ titanium alloys so that their microstructures and mechanical properties are pre-stabilized before working at elevated temperatures. Therefore, the aging response of the material is another concern of this study. To elaborate the two concerns, SLMed Ti-6242 was first isothermally annealed at 650${}^{\circ }\mathrm{\text{C}}\le T\le 1025^{\circ }$C and then water-quenched to room temperature, followed by standard aging at 595${}^{\circ }$C. The microstructure analysis revealed a temperature-dependent martensite decomposition, which proceeded sluggishly at $T\le 700^{\circ }$C despite a long duration but rapidly transformed into lamellar $\alpha +\beta$ above the martensite transition zone (770${}^{\circ }\mathrm{\text{C}}\le T\le 800^{\circ }$C). As heating to $T>\beta -\mathrm{\text{transus}}(993^{\circ }$C), it produced a coarse microstructure containing new martensites formed in water quenching. The subsequent mechanical testing indicated that SLM-built Ti-6242 is excellent in terms of both room- and high-temperature tensile properties, with around 1400 MPa (UTS)$+$5% elongation and 1150 MPa (UTS)$+$10% elongation, respectively. However, the combination of water quenching and aging embrittled the as-built material severely.

At the onset of post-implantation embryonic development, the specification of human primordial germ cells (hPGCs) marks the preparation to attain the totipotent state through the extraordinary features of extensive epigenetic reprogramming (in terms of DNA demethylation and chromatin reorganization), a mitochondrial bottleneck, and a characteristic gene regulatory network, which are in stark contrast with those of the somatic lineage. Together, they provide for the attribute of immortality to the germ cell lineage, reflecting their significance in transgenerational inheritance. Interestingly, these features are the antithesis of the several hallmark phenotypes of aging, which gradually accumulate in the somatic lineage over time. In this chapter, we discuss the salient features of hPGC development, the hallmarks of aging, the application of cellular reprogramming as a therapeutic route to rejuvenation, and the intriguing translational potential of the lessons learned from the immortal human germline lineage in the field of anti-aging research.

The accelerated aging test of SBR-based absorption materials in heat seawater were carried in laboratory. The elongation at break of the materials in aging time was investigated. Two methods were adopted to forecast the life expectancy of the materials. Mathematical model was applied through MATLAB software programming to gain the forecasted life expectancy is 10.98y in seawater at 25 ℃. The time-temperature superposition method was applied to gain the life expectancy, which is 12.08y in seawater at 25 ℃.