Pre-cementation treatment of glass-ceramics with vacuum impregnated resin coatings

OBJECTIVE

The study aimed to investigate the effectiveness of a vacuum impregnation process to eliminate the porosity at the ceramic-resin interface to optimize the reinforcement of a glass-ceramic by resin cementation.

METHODS

100 leucite glass-ceramic disks (1.0 ± 0.1 mm thickness) were air-abraded, etched with 9.6 % HF acid, and silanated. Specimens were randomly allocated to 5 groups (n = 20). Group A received no further treatment (uncoated control). Groups B and D were resin-coated under atmospheric pressure, whereas groups C and E were resin-coated using vacuum impregnation. The polymerized resin-coating surfaces of specimens in groups B and C were polished to achieve a resin thickness of 100 ± 10 µm, while in groups D and E no resin-coating modification was performed prior to bi-axial flexure strength (BFS) determination. Optical microscopy was undertaken on the fracture fragments to identify the failure mode and origin. Comparisons of BFS group means were made by a one-way analysis of variance (ANOVA) and post-hoc Tukey test at α = 0.05.

RESULTS

All resin-coated sample groups (B-E) showed a statistically significant increase in mean BFS compared with the uncoated control (p < 0.01). There was a significant difference in BFS between the ambient and vacuum impregnated unpolished groups (D and E) (p < 0.01), with the greatest strengthening achieved using a vacuum impregnation technique.

SIGNIFICANCE

Results highlight the opportunity to further develop processes to apply thin conformal resin coatings, applied as a pre-cementation step to strengthen dental glass-ceramics.

Comparing evolution of precipitates and strength upon aging of cast and laser-remelted Al-8Ce-0.2Sc-0.1Zr (wt.%)

The microstructural evolutions, upon solidification and subsequent aging, and associated hardening effects for both cast and laser-surface-remelted Al-8Ce-0.2Sc-0.1Zr (wt.%) hypo-eutectic alloy are investigated with focus on precipitation and coarsening behavior of their Al₁₁Ce₃ and L1₂-Al₃(Sc,Zr) precipitates. Laser surface remelting, which produces solidification conditions typical of additive manufacturing (AM) processes, suppresses formation of undesirable primary Al₁₁Ce₃ and Al₃(Sc,Zr) precipitates on solidification. It also greatly refines the interlamellar spacing of the eutectic Al₁₁Ce₃ phase, thus enhancing the Orowan strengthening effect as compared to the cast alloy, beyond the load-transfer effect from the Al₁₁Ce₃ phase. Subsequent aging at 325 °C leads to further hardening of both alloys due to secondary Al₃(Sc,Zr) nanoprecipitation, with much more pronounced hardness increases in the laser-remelted alloy, owing to a higher number density of finer Al₃(Sc,Zr) nano-precipitates, as compared to the cast alloy. This improvement is rationalized by an enhancement of Al₃(Sc,Zr) nucleation rate upon aging of laser-remelted alloy, as compared to the cast alloy, considering differences in elemental supersaturation within the α-Al regions of these alloys. Prolonged aging, up to 1000 h, at 325 °C causes the hardness of both alloys to decline relatively slowly, implying that this alloy is suitable for AM processes and subsequent applications where high strength and good heat resistance are needed.

Increasing strength of a biomedical Ti-Nb-Ta-Zr alloy by alloying with Fe, Si and O

Low-modulus biomedical beta titanium alloys often suffer from low strength which limits their use as load-bearing orthopaedic implants. In this study, twelve different Ti-Nb-Zr-Ta based alloys alloyed with Fe, Si and O additions were prepared by arc melting and hot forging. The lowest elastic modulus (65GPa) was achieved in the benchmark TNTZ alloy consisting only of pure β phase with low stability due to the 'proximity' to the β to α'' martensitic transformation. Alloying by Fe and O significantly increased elastic modulus, which correlates with the electrons per atom ratio (e/a). Sufficient amount of Fe/O leads to increased yield stress, increased elongation to fracture and also to work hardening during deformation. A 20% increase in strength and a 20% decrease in the elastic modulus when compared to the common Ti-6Al-4V alloy was achieved in TNTZ-Fe-Si-O alloys, which proved to be suitable for biomedical use due to their favorable mechanical properties.