Mechanical Properties, Biodegradation, and Biocompatibility of Ultrafine Grained Magnesium Alloy WE43.

In this work, the effect of an ultrafine-grained (UFG) structure obtained by multiaxial deformation (MAD) on the mechanical properties, fatigue strength, biodegradation, and biocompatibility in vivo of the magnesium alloy WE43 was studied. The grain refinement down to 0.93 ± 0.29 µm and the formation of Mg41Nd5 phase particles with an average size of 0.34 ± 0.21 µm were shown to raise the ultimate tensile strength to 300 MPa. Besides, MAD improved the ductility of the alloy, boosting the total elongation from 9% to 17.2%. An additional positive effect of MAD was an increase in the fatigue strength of the alloy from 90 to 165 MPa. The formation of the UFG structure also reduced the biodegradation rate of the alloy under both in vitro and in vivo conditions. The relative mass loss after six weeks of experiment was 83% and 19% in vitro and 46% and 7% in vivo for the initial and the deformed alloy, respectively. Accumulation of hydrogen and the formation of necrotic masses were observed after implantation of alloy specimens in both conditions. Despite these detrimental phenomena, the desired replacement of the implant and the surrounding cavity with new connective tissue was observed in the areas of implantation.

Oxidation Behavior of Refractory AlNbTiVZr0.25 High-Entropy Alloy.

Oxidation behavior of a refractory AlNbTiVZr0.25 high-entropy alloy at 600⁻900 °C was investigated. At 600⁻700 °C, two-stage oxidation kinetics was found: Nearly parabolic oxidation (n = 0.46⁻0.48) at the first stage, transitioned to breakaway oxidation (n = 0.75⁻0.72) at the second stage. At 800 °C, the oxidation kinetics was nearly linear (n = 0.92) throughout the entire duration of testing. At 900 °C, the specimen disintegrated after 50 h of testing. The specific mass gains were estimated to be 7.2, 38.1, and 107.5, and 225.5 mg/cm² at 600, 700, and 800 °C for 100 h, and 900 °C for 50 h, respectively. Phase compositions and morphology of the oxide scales were analyzed using X-ray diffraction (XRD) and scanning electron microscopy (SEM). It was shown that the surface layer at 600 °C consisted of the V2O5, VO2, TiO2, Nb2O5, and TiNb2O7 oxides. Meanwhile, the scale at 900 °C comprised of complex TiNb2O7, AlNbO4, and Nb2Zr6O17 oxides. The oxidation mechanisms operating at different temperatures were discussed and a comparison of oxidation characteristics with the other alloys was conducted.

Microstructure and Mechanical Properties Evolution of the Al, C-Containing CoCrFeNiMn-Type High-Entropy Alloy during Cold Rolling.

The effect of cold rolling on the microstructure and mechanical properties of an Al- and C-containing CoCrFeNiMn-type high-entropy alloy was reported. The alloy with a chemical composition (at %) of (20-23) Co, Cr, Fe, and Ni; 8.82 Mn; 3.37 Al; and 0.69 C was produced by self-propagating high-temperature synthesis with subsequent induction. In the initial as-cast condition the alloy had an face centered cubic single-phase coarse-grained structure. Microstructure evolution was mostly associated with either planar dislocation glide at relatively low deformation during rolling (up to 20%) or deformation twinning and shear banding at higher strain. After 80% reduction, a heavily deformed twinned/subgrained structure was observed. A comparison with the equiatomic CoCrFeNiMn alloy revealed higher dislocation density at all stages of cold rolling and later onset of deformation twinning that was attributed to a stacking fault energy increase in the program alloy; this assumption was confirmed by calculations. In the initial as-cast condition the alloy had low yield strength of 210 MPa with yet very high uniform elongation of 74%. After 80% rolling, yield strength approached 1310 MPa while uniform elongation decreased to 1.3%. Substructure strengthening was found to be dominated at low rolling reductions (<40%), while grain (twin) boundary strengthening prevailed at higher strains.