Metallurgical and Materials Transactions A最新文献

The structural and superconducting properties of a new niobium- and titanium-rich high-entropy alloy (NbTi)(_{text {0.67}})(MoHfV)(_{text {0.33}}) were determined. The alloy was synthesized by arc melting and its physical properties were characterized by means of X-ray powder diffraction, energy dispersive X-ray spectroscopy, magnetization, electrical resistivity and specific heat measurements. Experimental data revealed that the (NbTi)(_{text {0.67}})(MoHfV)(_{text {0.33}}) crystalizes in body-centered cubic structure and exhibits type-II superconductivity below about 5 K. In addition, electronic structure calculations were performed using the Density Functional Theory (DFT) method. Their results suggest that in case of HEAs, the influence of the local atomic configuration on their electronic structure in the energy region close to E(_{mathrm {text {F}}}) is rather small or even negligible.

The effects of different annealing times on the microstructure, mechanical and damping properties of a rolled state ZK60 alloy were investigated. The results show that with increasing annealing time, the degree of static recrystallization gradually increases, and the grains grow gradually. The grain orientation changes from the (0001) orientation to the (01-10) and (− 12-10) orientations, and the basal texture intensity of the alloy decreases gradually. The tensile and yield strengths decrease slightly, and the elongation increases gradually. Because of the gradual reduction in dislocation entanglement, the room temperature damping properties improve with annealing time, and the damping value Q⁻¹ at ε_0.01 increases from 0.008 to 0.013. After annealing, the ZK60 alloy becomes a high-damping alloy (Q⁻¹ > 0.01). The recrystallization damping peak is more intense than the background damping peak, and recrystallization damping peak P₁ becomes increasingly obvious. The peak value of damping peak P₂ gradually decreases in the temperature range of 270 °C < T < 290 °C, and the peak width slowly increases, which is characterized by grain boundary-type relaxation. These results indicate that annealing effectively maintains the high strength of the ZK60 alloy while improving its damping properties.

The biocorrosion of a new surgical wire (0.6, 0.8, and 1.0 mm in diameter) obtained from a ZnMg0.004 alloy by hot and cold drawing was characterized using in vitro tests in a bovine animal serum solution and in vivo tests – through placement in the muscles of a rabbit and a in cat's broken paw. Corrosion gravimetric tests were carried out in a corrosive environment refreshed every 3 days and also one which remained unchanged throughout the test period. Electrochemical tests were performed in the same solution of serum as in gravimetric tests. Depending on the initial diameter, complete dissolution of the wire was observed after 36-78 days of immersion in periodically changed serum solution. None of the wires completely dissolved over 120 days in the unreplaced serum solution. The corrosion rate values determined in electrochemical and gravimetric tests were similar. After 90 days of in vivo tests, both in the body of the rabbit and the cat, the degradation of the wire was similar to in vitro tests in the unreplaced serum solution. No harmful effects were observed in the animals.

Aluminum matrix composite have shown the great prospects in improving service performance and life of high-end equipment under harsh conditions due to lightweight and high specific strength. However, the presence of coarse Mg₂Si phase with undesired morphology in Mg₂Si/Al composites limits their engineering application. This study proposes a strategy of TiB₂ ceramic particles regulating the morphology and size of Mg₂Si to strengthen the aluminum matrix composites by incorporating dual-scale hybrid reinforcements of Mg₂Si and TiB₂. The TiB₂ particles were introduced into the Al-15 wt pct Mg₂Si composite by a master alloy method, and the influence of TiB₂ particles on the morphology and size of Mg₂Si, and Al grains of composites were investigated. The results demonstrate that 3 wt pct TiB₂ particles can refine the primary Mg₂Si from 14.6 to 10.4 μm, resulting in a more regular morphology. Additionally, the eutectic Mg₂Si transforms from a long and slender Chinese character shape to a short rod shape, reducing the aspect ratio by 65.9 pct from 10.9 to 3.7. During the solidification process, TiB₂ particles promote the heterogeneous nucleation of primary Mg₂Si phases and impede the growth, leading to significant refinement. However, the improved morphology of eutectic Mg₂Si is mainly attributed to the inhibited preferential growth due to the formation of a nanoparticle layer, with no observed heterogeneous nucleation of TiB₂. Moreover, TiB₂ particles significantly refine the grain size of Al from 212.7 to 70.8 μm. The addition of 3 wt pct TiB₂ greatly improves the strength of the composites from 302 to 373 MPa, without losing ductility. After T6 heat treatment, Al-15 wt pct Mg₂Si composites exhibit simultaneous improvement in the strength and ductility. Compared with composites without TiB₂ particles (361 MPa and 32 pct), Al-15Mg₂Si-3TiB₂ composites have more superior strength–ductility combination of 434 MPa and 35 pct due to the significant modification of Mg₂Si phase, grain refinement, and Orowan strengthening.

Graphical Abstract

The development of the microstructure during severe plastic deformation of an aluminum single crystal by complex shearing of the extruded tube (CSET) was studied in this paper. The research has demonstrated that even in a single crystal, an ultrafine-grained microstructure can be obtained during this one-step process. The size of the grains gradually changes and reaches the minimum size on the level of 1 μm at the inner surface of the resulting tube. Simultaneously, preferential orientations in individual parts of the deformed sample change in a complex way. The main mechanism affecting the final microstructure is continuous dynamic recrystallization. The microhardness also exhibits a gradient character with higher values at the inner surface of the tube compared to its center.

Graphical Abstract

The medium-entropy alloy (NbTa)(_{0.67})(HfZr)(_{0.33}) and the high-entropy alloy (NbTa)(_{0.67})(HfZrTi)(_{0.33}) were prepared by mechanical alloying using high-energy planetary ball mill. The results of X-ray diffraction, scanning electron microscopy, and positron annihilation lifetime spectroscopy measurements suggest that both as-prepared powders are multicomponent alloys in amorphous (or highly disordered) state. The magnetic and thermodynamic results obtained for these powders undoubtedly prove that bulk superconductivity is not observed at temperatures exceeding 2 K. Thermal treatment of both studied materials leads to decomposition of the amorphous phase and precipitation of several crystalline phases. In both annealed samples, the structure of the main crystalline phase was identified as body-centered cubic (bcc), and in this phase, bulk superconductivity was observed below 6.5 K.

Al–5Ti–1B master alloy has been used to refine the microstructure of a commercial high-strength aluminum alloy (B206). The effects of grain refinement and mold preheat on the semi-solid contraction behavior were investigated. A coupled thermal-stress model combined with displacements measured during solidification was utilized to determine the semi-solid contraction coefficients (SSCC). The simulation results show that Al5TiB additions and preheating the mold significantly reduced SSCC values and limited the semi-solid contraction of B206 alloy.

This study presents a comprehensive and innovative approach to tailoring the microstructure of AISI 9254 steel using a quenching and partitioning (Q&P) process, demonstrating significant improvements in mechanical and wear properties. The initial pearlitic microstructure was first heated to the fully austenitizing region before undergoing phase transformation into a multi-phase matrix using the novel Q&P process, resulting in the formation of ferrite, bainite, martensite, and retained austenite. Investigation revealed the central role of retained austenite in enhancing the mechanical properties through the Transformation Induced Plasticity (TRIP) effect. In particular, heat-treated specimens exhibited a mechanical resistance of up to 1.9 GPa and an elongation of approximately 12 pct. Furthermore, this study highlights remarkable enhancements in wear resistance of the treated AISI 9254 steel. A decreased wear rate, reduced volume loss, and improved contact area stability were achieved, attributed to debris aggregation, contact area changes, and the work hardening of the wear track. Consequently, the Q&P process can considerably enhance the in-service performance and life span of AISI 9254 steel components. The insights provided by this work into the potential benefits of a tailored Q&P process in AISI 9254 steel set forth a promising pathway towards reduced maintenance costs and heightened reliability across various applications. Exploring this process showcases the transformative potential of materials engineering for industrial applications.

A novel galvanic-polishing-assisted near net shape forming was proposed to improve the heat dissipation capacity of the liquid-cooled plates. The coarsest upper surface roughness of channels was reduced from 74 to 37 μm. The coolant flow rate and heat dissipation capacity of the liquid-cooled plates with the polished channels were increased by 35.2 and 51.0 pct compared with those of untreated liquid-cooled plates, respectively.

Graphical Abstract

Prediction of texture changes during cold rolling is important because they affect the recrystallization and anisotropy of an aluminum sheet during successive forming steps. During cold rolling of aluminum alloys, the through-thickness textural change in the subsurface layer depends heavily on the shear stresses exerted on the material. The intensity of this shear stress is determined by the value of and change in the coefficient of friction as the contact length between the rolls and metallic sheet changes. The quality of the texture prediction under constant and variable coefficients of friction are assessed for three established texture models: the grain interaction (GIA) model, the viscoplastic self-consistent (VPSC) approach, and the full-field crystal plasticity Düsseldorf Advanced Material Simulation Kit (DAMASK) code. The simulation results are compared with subsurface layer textures obtained from conducting experimental cold-rolling trials on an aluminum alloy, which are designed to maximize shear in a single rolling pass. The formulation of a variable coefficient of friction is crucial for ensuring both the reasonable prediction of rolling forces and changes in texture. GIA and DAMASK yield the best texture prediction results for a variable coefficient of friction model.