The present study demonstrates the feasibility to fabricate a multiscale bioactive surface structure onto a biomedical grade Ti-6Al-4V alloy substrate using a multi-material blown powder laser Direct Energy Deposition process (DED). The multiscale surface structure consisted of two layers: a Ti-6Al-4V transition layer with a customised structure, deposited onto a Ti-6Al-4V alloy substrate, followed by a layer of customised bioactive glass cladded on top. It is possible to create a transition layer with physical interlocking features that are fully bonded with the bioactive glass for enhancement of the metal-glass adhesion. The metal|glass interface was characterised in terms of metallurgical reactions and mechanical properties. Indentation tests confirmed excellent cohesion of the metal-glass interface. The microhardness of the bioactive glass near the interface varied from 5.44 to 7.78 GPa. Fracture toughness of the cladded glass was estimated in the range of 1.40-3.91 MPa m1|2.
Phosphate glasses can dissolve high concentrations of rare earths and have excellent spectroscopic properties making them useful solid-state laser materials. Solid-state lasers doped with different rare-earth ions find applications in a wide range of LIDAR (Light Detection and Ranging) and sensing applications; phosphate glasses are useful host materials for many applications in the visible and near-infrared spectral regions. For example, trivalent erbium (Er3+) doped phosphate glasses operate at the eye-safe wavelength of 1.54 μm and are used for range finding and sensing applications. Tm3+ doped solid-state lasers operating at ~ 2 μm can be used for wind-shear and turbulence monitoring. Similarly, Nd-doped metaphosphate glasses are the preferred gain medium for high-peak-power lasers used for fusion energy research because they can store optical energy at greater densities than other glass-types and can be fabricated in large sizes with high rare-earth ion concentration. This paper discusses issues affecting glass quality, with particular focus on defect formation, especially crystallisation. Avoiding crystallisation during processing is essential to form high quality laser cavities. The work presented explores some of the factors controlling these defects including contamination during melting. The crystallisation behaviour of the glass was investigated for several different phosphate glass compositions and different melting conditions, including melting duration, temperature and crucible material.
Comparing the crystallization mechanism of stoichiometric and B 2 O 3 and P 2 O 5 containing glass reveals that the additives extend the gap between the glass transition and crystallization temperatures and suppress formation of μ, cordierite while promoting direct crystallization of α cordierite. Detailed TEM analysis of nucleation and growth of crystals in hot‐pressed pellets of B 2 O 3 /P 2 O 5 ‐containing glass particles shows that nucleation occurs on unidentified heterogeneous nuclei at the sites of the previous particle surfaces. Growth of α cordierite with a cellular morphology or μ cordierite with a dendritic morphology is most likely controlled by the glass composition directly ahead of the growth front.
This study presents a comprehensive analysis of the effect of tempering and wall thickness on the fracture of tempered drinking glasses typically used in bars and pubs in the United Kingdom. The fracture patterns are related to the manufacturing process, the glass geometry, and the level of residual stress. The bulk of experimentation was split into two categories: Firstly, an assessment of the residual stress was conducted, followed by an assessment of the fracture response of the glass in practical applications. Drinking glasses have a variable wall thickness as a consequence of their design and manufacture. This has a direct effect on the level of residual stress in the article, which in turn produces glasses that break to give fragments of variable sizes, with large sharp‐edged fragments nearer the glass rim. It is also shown that tempered glasses broken by impact have a characteristic fracture pattern. The results show that to control the fracture of glasses to produce small fragments similar to those in tempered flat glass, the wall thickness and resulting level of residual stress need to be optimized.
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