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Purpose: Bioabsorbable Mg-based implants were previously assessed due to their intrinsic advantages, but Mg-based cage related research is limited. The specific blood supply and stress of the intervertebral environment can affect the function of Mg-based implants. The objective of this study was to investigate the performance of a bioabsorbable Mg-Zn alloy cage in anterior cervical discectomy and fusion (ACDF) and evaluate the control of degradation of the Mg-Zn cage surface modified by microarc oxidation (MAO) technology containing Si under an intervertebral microenvironment., Methods: Twenty-four goats were divided into four groups according to the experimental period and all underwent ACDF at C2-3 and C4-5 with porous Mg-Zn cage covered with a MAO/Si-containing coating in one intervertebral space and with autologous iliac bone in another space. After 3, 6, 12, or 24 weeks after operation, the cervical spine specimens were harvested to evaluate the biocompatibility, fusion status, and degradation conditions using blood analysis, radiology, biomechanical testing, histology, and micro-CT., Results: The Mg-Zn cages showed ideal biocompatibility and biomechanical characterization; however, the fusion state, as evaluated with radiology and histology, was not acceptable. Modified by the MAO/Si-containing coating, the degradation rate of the Mg-Zn cages was controllable but slower than expected., Conclusion: MAO/Si-containing coating Mg-Zn alloy cages demonstrated excessive control of degradation and fusion failure after 24 weeks postoperatively. We conclude that further studies should be designed to improve the using of Mg-based materials at the intervertebral space.

Direct aging of water-quenched metastable β-titanium alloys usually follows the sequence: rapid growth of ωiso and then slow transformation into α. To inhibit ωiso growth and promote α nucleation, 6% pre-deformation was introduced in Ti-10V-6Cu alloy before 500°C/60s aging. An ultrafast α-formation and a few α-free kink-bands are observed, indicating the alteration of the precipitation sequence. For α-nucleation without ωiso as the sites, it shows that O' nanodomains induced by stress accumulation around slip bands mediate the ultrafast nucleation of hcp-α structure, while dislocation pipe diffusion accelerates the necessary phase separation. This provides new insights into regulating precipitation kinetics of age-hardenable β-titanium alloys. [ABSTRACT FROM AUTHOR]

The Ti-7Al-1Mo-0.5V-0.1C alloy exhibits low density and good mechanical properties, and has potential applications in aerospace industries. The microstructure features of titanium alloys, such as the morphology and volume fraction of the primary α phase (αp) and the precipitation of the secondary α phase (αs), are sensitive to heat treatment parameters, especially the cooling rate from the two-phase region. In this work, we have characterized the precipitation of the secondary α phase and ordered α2 phase in Ti-7Al-1Mo-0.5V-0.1C alloy under water quenching, air cooling, and furnace cooling, and have investigated their effects on the mechanical properties of the Ti-7Al-1Mo-0.5V-0.1C alloy. The results show that the secondary α phase is significantly coarsened in the air-cooled alloy and leads to an increase in the strength but decrease in the ductility of the alloy, while the equiaxed microstructure generated in the furnace-cooled alloy, with no precipitation of the secondary α phase and an increase in size of the ordered α2 precipitation phase within the primary α phase, contributes to a further increase in ductility. [ABSTRACT FROM AUTHOR]

The mechanisms associated with the interaction of {332} twins are investigated in metastable Ti 15Mo alloy. There are 12 possible twin-twin junctions (TTJs) induced by {332} twins that can be classified into 5 types according to the crystallographic relation. Twin-twin interactions are accompanied with the formation of twin-twin boundaries (TTBs) on the acute side and obtuse side. Experimental results based on transmission electron microscopy (TEM) and procession electron diffraction (PED) show that subsequent growth of the TTBs is asymmetric with the twin thickening preferred only on one side for each type. Besides, it is observed that the twin-twin interaction could stimulate sequential {332} twinning inside the primary twin with a specific twin variant promoted. To account for the subsequent growth of the TTBs and the preferred selection of the sequential twinning variant associated with twin-twin interactions, the elastic energy analysis of the resultant dislocations at TTBs indicates that the growth of the TTBs is energetically favorable only on one side. Displacement gradient based analysis shows that the active sequential twin variant could maximumly accommodate the accumulated strain induced by the twin-twin interaction. This work is useful for predicting the preferential growth of the interfaces and the associated accommodation mechanisms induced by the interactions of localized shear bands. [Display omitted] • The growth of the interacted {332} twins is preferred only on one side for each type. • Twin-twin interactions could stimulate sequential twinning with a specific variant promoted. • The general analysis method for interaction mechanisms of localized shear bands is proposed. [ABSTRACT FROM AUTHOR]

The accumulated dislocations are widely reported to be easily transmitted at low angle grain boundaries (GBs), while the associated mechanism at high angle GB needs further investigation. In this paper, the mechanisms associated with the interaction between GBs and 〈111〉 dislocations are investigated in Ti-5553 alloy with body-centered cubic structure. Slip traces transmitted into the neighboring grain or blocked by GBs are observed on the surface of the sample via secondary electron imaging. The corresponding slip system is determined with the combined use of EBSD-detected grain orientation and slip traces. The experimental results indicate that most slips can transfer at low angle GBs, while some slips can also transmit into the neighbor at high angle GBs. The misorientation angle of GBs is invalid to evaluate the mechanism induced by the interaction of dislocations with GBs. Crystallographic alignment-based analysis shows that slip transfer happens at GBs with favorable parameters of high geometric alignment (m ′) and low residual Burgers vector magnitude (|∆ b |). The general relation of GB misorientation angle with m ′ and |∆ b | is established. The results indicate that low angle GBs always possess high m ′ and low ∆ b , while only some high angle GBs meet the requirement of large alignment parameters. This difference contributes to their preference of slip transfer. Finally, the orientations of best neighboring grains that are favorable for slip transfer are calculated, which is in agreement with the experimentally detected examples. [Display omitted] • Dislocations can transmit at some high-angle grain boundaries with special orientations. • General effect of grain boundary misorientation angle on slip transmission is studied. • The best orientations of neighboring grains favorable for slip transmission are established for low- and high-angle GBs. [ABSTRACT FROM AUTHOR]

The resistance to dislocation glide associated with slip systems {110}<111> and {112}<111> in single phase FeCrAl alloy is measured via micromechanical testing in a scanning electronic microscopy at room temperature. Two important factors, the shape and orientation of a pillar, are discussed with respect to the glide resistance and stress-strain response. Maximizing Schmid factor of one specific slip system while minimizing others is recommended in order to diminish obvious dislocations-induced hardening during in-situ testing. Apparent Schmid factor analysis is conducted to select grains with preferred orientations. Two types of pillars with conventional cylindrical shape or dog-bone shape are tested under compression to estimate the resistance to dislocation glide and evaluate the effect of pillar shape on the compression stress-strain response. One dog-bone pillar is tested under tension to check the tension-compression isotropy of dislocation slip. We find that the shape of a pillar to a smaller extent affects the measured resistance but strongly influences the stress strain response. Cylindrical pillars exhibit apparent hardening associated with early yielding due to stress or strain concentration at contact region, while dog-bone pillars show an obvious yielding and continuous shearing without hardening. The resistance is 220 MPa for slip system {110}<111> and 230 MPa for slip system {112}<111>. Finite element analysis is performed to account for the influence of pillar shape and contact condition on mechanical response. Image 1 • The resistance to dislocation glide in FeCrAl alloy is measured via micromechanical testing in a SEM. • The shape and orientation of a pillar are discussed with respect to the glide resistance and stress-strain response. • Cylindrical pillars exhibit apparent hardening associated with early yielding due to stress or strain concentration. • Dog-bone pillars show an obvious yielding and continuous shearing without hardening. • Finite element analysis accounts for the influence of pillar shape and contact condition on mechanical response. [ABSTRACT FROM AUTHOR]

Hierarchical microstructure (HM) shows excellent comprehensive properties, but the relationship between mechanical properties and HM characteristics is not clear. In this work, seven HMs of Ti20C were tailored by aging treatments, containing equiaxed α (α ep), lamellar α of micron and submicron scale (α lp-i , α lp-ii) and transformed β t (with nano-scale precipitated phases ω/α s in β). Different combinations of strength and plasticity were achieved. It was found that, the different phase interfaces hindered dislocation transferring, and ω/α s phase restricted dislocation movements in β t , which resulted in strength improvement. Moreover, HM was quantitatively characterized, then the relationship between HM characteristics and yield strength (R p0.2), elongation after fracture (A) was precisely deciphered by referring to Hall-Petch formula and mixing law. It was found that the influence of β t , α lp-ii , α ep and α lp-i on R p0.2 decreased orderly. The decrease in the thickness of α lp-ii and increase in the volume fraction (VF) of β t , α lp-ii , were the most effective methods to improve R p0.2. For A, the VF of β t was negatively correlated with it, but the equivalent circle diameter (ECD) of α ep and the thickness of α lp-i , α lp-ii were positively correlated with it. Specifically, α ep and α lp-ii had a higher contribution to plasticity than α lp-i , and the increase in the ECD (or thickness) and VF of α ep and α lp-ii was most beneficial to improve plasticity. • Hierarchical microstructures containing α ep , α lp-i , α lp-ii and β t (β + ω/α s) phases by aging were induced. • Wide range of strength and plasticity was achieved by tailoring microstructures. • Quantitative relationship between microstructure and tensile properties (R p0.2 , A) was precisely deciphered. • The influence of β t , α lp-ii , α ep and α lp-i on yield strength was found to decrease orderly. • Size and content of α ep , α lp-i and α lp-ii was beneficial for the elongation, while β t was adverse. [ABSTRACT FROM AUTHOR]

In this paper, Mg-Al-Ca-Mn-Cu magnesium alloys by Cu alloying were studied with the aim of developing Mg alloys with higher heat conduction. As a result, the mechanical properties and thermal conductivity of the alloys was evaluated simultaneously, owing to the addition of Cu, which meets the requirements of the project to develop high-strength and high-conductivity magnesium alloy. Compared with the commercial AZ31 magnesium alloy, the strength and plasticity are improved by means of fine grain strengthening. Meanwhile, the amount of solid solution atoms in the alloy decreases, and the content of the second phase particles increases, which reduces the degree of lattice distortion. On the other hand, the Cu element provides a large amount of free electron for heat transfer, which makes the alloys have a high thermal conductivity. • The microstructure and morphology characteristics of the Mg-Al-Ca-Mn magnesium alloy by Cu alloying were investigated. • Cu addition improved the mechanical properties and thermal conductivity of the Mg-Al-Ca-Mn alloy. • The microstructure evaluation during the extrusion processing effected by the addition of Cu content was investigated. [ABSTRACT FROM AUTHOR]

The stress-induced α" phase transformation in titanium alloys has received extensive attention due to its significant effect on mechanical properties. In this work, by adjusting the heat treatment process, the stress-induced α" phase transformation is activated in Ti-5Al-2.5Cr-5Mo-1Sn. The quasi-static tensile mechanical properties of the alloy under air-cooled and as-quenched states have been compared. Further, the morphology and orientation of the stress-induced α" phase and its interaction with dislocations are investigated by X-ray diffraction (XRD), optical microscope (OM), electron backscattered diffraction (EBSD) and transmission electron microscope (TEM) experiments. The value of average misorientation at the stress-induced α" bands region is larger than that in the β matrix, which indicates that the degree of plastic deformation in the stress-induced phase transformation region is higher. Therefore, the stress-induced α" phase exhibits a strong strain partitioning effect during the stretching process and improves the ductility of the material. The β/α" interface has a weak effect to hinder the dislocations, which results in low tensile strength of the alloy. This work can provide insight into the influence of stress-induced α" phase transformation on the mechanical properties of transformation induced plasticity (TRIP) type titanium alloys. • The Ti-5Al-2.5Cr-5Mo-1Sn alloy is elaborately regulated to produce TRIP effect. • Average misorientation of α" band region is generally larger than that of β matrix. • α" phase exhibits a strong strain partitioning effect to increase alloy ductility. • The β/α" interface is semi-coherent and has a weak effect to hinder dislocations. [ABSTRACT FROM AUTHOR]