Analysis of stress/strain distribution in dental mini-implants manufactured by additive manufacturing and machining.

The study aimed to analyze the stress/strain distribution of new designs of mini-implants manufactured by machining and additive manufacturing. Four designs were evaluated (Ø2.0 mm × 10 mm): Intra-lock, helical, threaded machined (MN threaded) and threaded by additive manufacturing (AM threaded). Analysis of stress was performed through photoelastic analysis (100 N axial/oblique loads) and analysis of strain by digital image correlation (DIC) (250 N axial/100 N oblique load). Data distribution was verified using the Shapiro-Wilk test and a significance level of 5% was adopted. Quantitative data were analyzed using the non-parametric Kruskal-Wallis test. In photoelastic analysis, the Intra-lock mini-implant showed the highest stresses in the cervical (104 kPa), middle (108 kPa), and apical (212 kPa) thirds. Higher stresses were observed in the oblique loading situation for all designs. For DIC analysis, axial loading, a significant difference was observed for the AM Threaded mini-implants about the other designs in the cervical third (p = .04), with the highest strain value 47 µÎµ [10; 76]. In oblique loading, a significant difference between the mini-implants was observed in the middle and apical thirds, with higher strains for the AM threaded design -185 µÎµ [-173; 162] (p = .009) and 242 µÎµ [87; 372] (p = .013), respectively. In general, the influence of different mini-implant designs and the additive manufacturing method on the stress/strain was observed, in the photoelastic and DIC analysis. The evaluated designs demonstrated a lower concentration of stress/strain in the cervical region compared to the apical region, and higher stress/strain in situations of oblique load compared with axial load.

Analysis of the mechanical and physicochemical properties of Ti-6Al-4 V discs obtained by selective laser melting and subtractive manufacturing method.

The surface properties of titanium and its alloys are commonly modified by different techniques, including additive manufacturing (AM), to improve the osseointegration of dental implants. The aim of this study was to evaluate and compare the wettability, topography, chemistry, and structure of titanium-aluminum-vanadium (Ti-6Al-4 V) discs fabricated by selective laser melting (SLM) and subtractive manufacturing (conventional machining). Three different groups were evaluated: selective laser melting (SLM); conventional machining with H3 PO4 + NaOH surface treatment (CM + ST); and conventional machining without surface treatment (CM), including analysis of wettability and roughness, morphological and chemical analyses by scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDX), and structural characterization analysis by computed tomography (micro-CT), and X-ray diffraction (XRD). The results showed that SLM surface had higher roughness (9.09 ± 1.94 Ra; 51.93 ± 11.59 Rz; 11.03 ± 1.95 Sa) and lower wettability (103.23° ± 13) than CM (0.06 ± 0.01 Ra; 0.42 ± 0.078 Rz; 0.07 ± 0.01 Sa) (76.95° ± 4.18) and CM + ST (0.17 ± 0.38 Ra; 0.88 ± 0.15 Rz; 0.18 ± 0.04 Sa) (18.55° ± 6.47) (p < 0.05). SEM images also proved the higher roughness of SLM surface, and CM + ST discs showed a topography resembling a sponge, characteristic of the nanometric treatment applied. EDX and XRD found no differences between the different surfaces, and micro-CT demonstrated the solid characteristic of the SLM disc. Compared with conventional machining, the SLM technique resulted in higher roughness and lower wettability. Meanwhile, the chemical properties and structure of the titanium alloy was not altered by the technique.

Amorphous martensite in ß-Ti alloys.

Martensitic transformations originate from a rigidity instability, which causes a crystal to change its lattice in a displacive manner. Here, we report that the martensitic transformation on cooling in Ti-Zr-Cu-Fe alloys yields an amorphous phase instead. Metastable ß-Ti partially transforms into an intragranular amorphous phase due to local lattice shear and distortion. The lenticular amorphous plates, which very much resemble α'/α″ martensite in conventional Ti alloys, have a well-defined orientation relationship with the surrounding ß-Ti crystal. The present solid-state amorphization process is reversible, largely cooling rate independent and constitutes a rare case of congruent inverse melting. The observed combination of elastic softening and local lattice shear, thus, is the unifying mechanism underlying both martensitic transformations and catastrophic (inverse) melting. Not only do we reveal an alternative mechanism for solid-state amorphization but also establish an explicit experimental link between martensitic transformations and catastrophic melting.

Correlation between structural heterogeneity and plastic deformation for phase separating FeCu metallic glasses.

Unlike crystalline metals, the plastic deformation of metallic glasses (MGs) involves a competition between disordering and structural relaxation ordering, which is not well understood, yet. Molecular dynamics (MD) simulations were performed to investigate the evolutions of strain localizations, short-range order (SRO) as well as the free volume in the glass during compressive deformation of Fe50Cu50 MGs with different degrees of phase separation. Our findings indicate that the free volume in the phase separating MGs decreases while the shear strain localizations increase with increasing degree of phase separation. Cu-centered clusters show higher potential energies and Voronoi volumes, and bear larger local shear strains. On the other hand, Fe-centered pentagon-rich clusters in Cu-rich regions seem to play an important role to resist the shear transformation. The dilatation or annihilation of Voronoi volumes is due to the competition between ordering via structural relaxation and shear stress-induced deformation. The present study could provide a better understanding of the relationship between the structural inhomogeneity and the deformation of MGs.

Towards the Better: Intrinsic Property Amelioration in Bulk Metallic Glasses.

Tailoring the intrinsic length-scale effects in bulk metallic glasses (BMGs) via post-heat treatment necessitates a systematic analyzing strategy. Although various achievements were made in the past years to structurally enhance the properties of different BMG alloys, the influence of short-term sub-glass transition annealing on the relaxation kinetics is still not fully covered. Here, we aim for unraveling the connection between the physical, (thermo)mechanical and structural changes as a function of selected pre-annealing temperatures and time scales with an in-house developed Cu46Zr44Al8Hf2 based BMG alloy. The controlled formation of nanocrystals below 50 nm with homogenous distribution inside the matrix phase via thermal treatment increase the material's resistance to strain softening by almost an order of magnitude. The present work determines the design aspects of metallic glasses with enhanced mechanical properties via nanostructural modifications, while postulating a counter-argument to the intrinsic property degradation accounted for long-term annealing.