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Ti‐reinforced AZ61 magnesium matrix composites, demonstrating enhanced strength and plasticity, are synthesized via powder metallurgy method, including mechanical milling and spark plasma sintering. This study investigates the evolution of microstructure and compressive mechanical properties of Ti/AZ61 composites across various Ti weight percentages: 0%, 5%, 10%, 15%, and 20%. The composites at 5, 10, 15, and 20 wt% Ti concentrations are effectively compacted, achieving relative densities of 99.1%, 99.4%, 98.7%, and 98.6%, respectively. The integration of Ti particles facilitates a refinement of the Mg grain size. The average Mg grain size in the AZ61 alloy is refined from 8.7 ± 3.6 to 7.2 ± 4.5 μm and 4.4 ± 2.2 μm upon the addition of 5 and 10 wt% Ti particles. Conversely, incremental Ti concentrations of 15 and 20 wt% result in minor increases in the average Mg grain size to 5.3 ± 2.6 and 5.7 ± 3.2 μm, respectively. Interfacial compounds, notably Al3Ti, are identified. Compressive mechanical properties, including compressive yield stress (CYS), ultimate compressive stress (UCS), and compressive failure strain (CFS), are synergistically enhanced with Ti particle incorporation. Optimal mechanical properties, specifically CYS at 250 MPa, UCS at 502 MPa, and CFS at 13%, are observed in the 10 wt% Ti/AZ61 composite. The enhanced compressive behavior is attributed to strong interfacial bonding between deformable Ti and Mg, effective load transfer, and grain refinement. Additional contributing factors include variations in the elastic modulus and thermal expansion coefficients between Ti and Mg. The fracture mechanisms observed in the Ti/AZ61 composites involve both ductile and brittle modes of failure. [ABSTRACT FROM AUTHOR]

Isothermal rolling is conducted at 1050 °C (α2 + B2 phase region) and 1100 °C (B2 phase region) for a spark plasma sintering (SPS)‐processed Ti‐22Al‐25Nb alloy. The effects of rolling temperature, pass, reduction per pass, and solution and aging on microstructure evolution, phase transformation, and tensile property at ambient temperature are systematically investigated. The results show that as the alloy is rolled at 1050 °C for 1 pass (P), the optimal tensile strength (TS) and the yield strength (YS) are 964.78 and 935.16 MPa, respectively, and the elongation (δ) reaches 23.65%. Then, followed by a subsequent solution and aging at 940 °C/30 min/water quenching (WQ) + 760 °C/24 h/air cooling (AC), it exhibits a decrease in mechanical properties. Moreover, a mixed fracture mechanism dominated by ductile fracture is shown for the as‐rolled alloy. However, after a solution and aging, it is transformed to a mixed fracture mechanism dominated by brittle fracture, which attributes to the void aggregation and the development of the discontinuous brittle α2 precipitates along B2 matrix grains during the solution and aging treatment. Finally, fracture models of the as‐rolled alloy and the solution and aging‐treated alloy are established. [ABSTRACT FROM AUTHOR]

A powder metallurgy (P/M) Ti-22Al-25Nb (at%) alloy was prepared by spark plasma sintering of pre-alloyed powders at 1000 °C/80 MPa/10 min. The solution treatments of the P/M Ti-22Al-25Nb alloy were conducted at a temperature range of 940–1030 °C at 30 °C intervals and holding times of 10 min, 30 min, 60 min, and 120 min. The effects of the solution temperature and the holding time on the microstructure evolution, B2 grain growth behavior, phase transition, tensile mechanical properties, and fracture behavior of the P/M Ti-22Al-25Nb alloy were systematically evaluated using optical microscopy (OM), scanning electron microscopy (SEM), X-ray diffraction, and tensile tests. The results indicated that the microstructure and mechanical properties were closely linked to the solution temperature and the holding time. The effect of the holding time and the solution temperature on the B2 grain growth is well described by Beck's equation and Hillert's equation, respectively. The tensile tests showed that the tensile properties of the solution-treated P/M Ti-22Al-25Nb alloy were mainly affected by the number of O phases in the interior of the B2 grains and the phase transition degree of the α 2 phase at the grain boundary. The P/M Ti-22Al-25Nb alloy solution-treated at 940 °C/10 min exhibited the best mechanical properties at room temperature with a yield strength, tensile strength, and elongation of 867.8 MPa, 949.5 MPa, and 7.4%, respectively. A phase transition model of the α 2 phase was established. In addition, a tensile fracture model of the P/M Ti-22Al-25Nb alloy solution-treated under different conditions was established. • A powder metallurgy Ti-22Al-25Nb alloy was fabricated by spark plasma sintering. • Microstructure evolution and phase transition during solution treatment were studied. • B2 grain growth behavior of the solution-treated alloys was investigated. • A phase transition model of α 2 phase at the grain boundary was established. • Fracture mechanisms were analyzed and a fracture model was established. [ABSTRACT FROM AUTHOR]

Grain growth behavior of a powder metallurgy (P/M) Ti-22Al-25Nb alloy was investigated by applying a series of isothermal treatment tests over a wide range of temperatures and holding times. An isothermal treatment scheme was conducted in the B2 phase region (1070-1110 °C) and α2 + B2 phase region (1010-1050 °C) at holding times of 10, 30 min, 1, 2, and 3 h, respectively. The effects of temperature and holding time on the microstructure evolution and microhardness of the P/M Ti-22Al-25Nb alloy at elevated temperatures were evaluated using optical microscope, scanning electron microscope, x-ray diffraction, and Vickers hardness test techniques. The results revealed that the alloy’s treated microstructure was closely linked to temperature and holding time, respectively. The change law of B2 grain growth with holding time and temperature can be well interpreted by the Beck equation and Hillert equation, respectively. The B2 grain growth exponent n and activation energy Q were acquired based on experimental data in the α2 + B2 and B2 phase regions. In addition, the grain growth contour map for the P/M Ti-22Al-25Nb alloy was constructed to depict variations in B2 grain size based on holding time and temperature. [ABSTRACT FROM AUTHOR]

The flow behavior of a powder metallurgy (P/M) Ti-22Al-25Nb alloy during hot compression tests has been investigated at a strain rate of 0.01 s − 1 and a temperature range of 980–1100 °C up to various true strains from 0.1 to 0.9. The effects of deformation temperature and strain on microstructure characterization and nucleation mechanisms of dynamic recrystallization (DRX) were assessed by means of Optical microscope (OM), electron backscatter diffraction (EBSD) and transmission electron microscope (TEM) techniques, respectively. The results indicated that the process of DRX was promoted by increasing deformation temperature and strain. By regression analysis, a power exponent relationship between peak stresses and sizes of stable DRX grains was developed. In addition, it is suggested that the discontinuous dynamic recrystallization (DDRX) and continuous dynamic recrystallization (CDRX) controlled nucleation mechanisms for DRX grains operated simultaneously during the whole hot process, and which played the leading role varied with hot process parameters of temperature and strain. It was further demonstrated that the CDRX featured by progressive subgrain rotation was weakened by elevating deformation temperatures. [ABSTRACT FROM AUTHOR]

The flow behavior of a powder metallurgy (P/M) Ti–22Al–25Nb alloy was evaluated during hot compression at temperature range of 950–1070 °C and strain rate range of 0.001–1 s −1 . The dynamic globularization kinetics at elevated temperature was quantitatively characterized and investigated. The results showed that the dynamic globularization kinetics and kinetics rate were sensitive to deformation conditions. The variation of globularization fraction with strain approximately followed an Avrami type equation. It can be found that the process of dynamic globularization was promoted by decreasing strain rate and increasing deformation temperature. Moreover, the critical strain ( ε c ) for the onset of dynamic globularization and the completed strain ( ε f ) for the full dynamic globularization were predicted to be 0.094–0.198 and 1.082–2.113, respectively. The kinetics rate of dynamic globularization firstly increased severely to a peak value at a strain corresponded to 12.7–26.7% globularization fraction, and then decreased sharply with increasing strain. It was revealed that the peak value of kinetics rate increased with increasing temperature and decreasing strain rate. Furthermore, the microstructure examination was conducted by applying optical microscope (OM), scanning electron microscope (SEM) and electron backscattered diffraction (EBSD) techniques. The results exhibited a good agreement with the predicted dynamic globularization kinetics model. [ABSTRACT FROM AUTHOR]

The multi layers structure made of Ti-Al intermetallic are meet the request both light weight and resistant to elevated temperatures in the aerospace vehicle. Powder metallurgy (P/M) Ti-22Al-25Nb alloy was prepared by hot pressed sintering at 1050 ˚C for 1 h under a pressure of 35 MPa. The flow behavior of a P/M Ti-22Al-25Nb alloy was evaluated by applying a series of compression tests with height reduction of 50% performed in a temperature range of 940-1070 ˚C and a strain rate range of 0.001-1s -1 . The hot deformation behavior of the P/M Ti-22Al-25Nb alloy was investigated by using the true stress-true strain behavior analysis, processing maps and the standard kinetic analysis. Processing maps at the strain of 0.4 and 0.6 were constructed on the basis of dynamic material model theory by applying the flow stress data obtained from isothermal compression tests. The Ti-22Al-25Nb sintered alloy was applied to manufacture three-layer structure part. The forming process was divided into hot bending and diffusion bonding. The hot bending of core sheet was performed at 1100 ˚C in a vacuum furnace. The diffusion bonding of three layers sheets was carried out at 1200 ˚C for 120 min and 10 MPa. The microstructures of the core sheet bending forming and bonding joint of three layers sheets was analyzed by SEM. [ABSTRACT FROM AUTHOR]

A study has been undertaken to verify the feasibility of using a powder metallurgy (P/M) approach to fabricate Ti–22Al–25Nb alloys. Pre-alloyed powders with a nominal composition of Ti–22Al–25Nb (at%) obtained by argon atomization were sieved to the spherical size less than 180 μm and used for the fabrication of P/M Ti–22Al–25Nb alloys via hot pressing in vacuum. Vacuum hot pressing sintering was carried out in a temperature range of 950–1200 °C with a pressure of 35 MPa for 1 h followed by furnace cooling. Microstructure and phase composition examinations of the as-atomized powders and hot pressed (HP׳ed) samples were conducted by applying optical microscopy, back-scatter electron imaging and X-ray diffraction analysis. Tensile tests were studied at room temperature and 650 °C, respectively. The results showed that all HP׳ed samples were composed of coarse equiaxed B2 grains, fine lamellar O phase inside the B2 grains, and some α 2 along B2 grain boundaries. The elongations of HP׳ed samples were less than 3.95%, indicating the bad ductility at room temperature. However, the elongations were improved as the tensile temperature increased to 650 °C. The sample sintered at 1050 °C exhibited a better ductility with the elongation of 7.97% at 650 °C than that of other samples. [ABSTRACT FROM AUTHOR]

Abstract: The flow behavior of a P/M Ti–22Al–25Nb alloy was evaluated by applying a series of compression tests to a height reduction of 50% performed within the temperature range of 950–1070°C using strain rate range of 0.001–1s−1. The dynamic recrystallization (DRX) behavior at elevated temperature was evaluated by the modified Avrami type equation based on stress–strain data. By means of conventional hyperbolic sine function, the activation energies for DRX were estimated to be 1053.06kJ/mol in the (α2+β/B2+O) phase region and 734.77kJ/mol in the (α2+B2) phase region, respectively. The critical strain (ε c) for the onset of DRX, the strain for peak stress (ε p) and the strain for maximum softening rate (ε ⁎) under different deformation conditions were identified according to the strain hardening rate curves. The DRX kinetics model was proposed to characterize the evolution of DRX volume fraction, which revealed that the DRX exhibited the ‘slow-rapid-slow’ evolution with the increasing strain. It was also found that the process of DRX was promoted by decreasing strain rate and increasing deformation temperature. Moreover, the microstructure examination results indicated that the theoretical prediction results were shown to be in good agreement with the statistical results. Finally, the continuous dynamic recrystallization (CDRX) was identified to be the DRX mechanism by referring to a transmission electron microscope (TEM) observation. [Copyright &y& Elsevier]