Zhe Cheng

Ti48Al2Cr2Nb alloys containing 0–2.0 wt% C were prepared by vacuum arc melting to investigate the effects of carbon on microstructure and mechanical properties. The results indicate that, carbon initially dissolves in the α ₂ -Ti ₃ Al and γ -TiAl matrices, causing lattice distortion; when C content exceeds its solubility limit (approximately 0.4 wt%), Ti ₂ AlC precipitates. The average α ₂ / γ lamellar colony size and average Ti ₂ AlC aspect ratio decrease with increasing C content, while the volume fraction of Ti ₂ AlC and its average grain size increases. Many mechanisms, such as solid-solution strengthening by C, grain refinement strengthening, and precipitation strengthening via Ti ₂ AlC, influence the mechanical properties of Ti48Al2Cr2Nb-xC(wt%) alloys. Ti48Al2Cr2Nb-0.8C shows the best overall performance, with the highest hardness (452.4 HV), elevated tensile strength (342 MPa) and compressive strength (2091.8 MPa) at room temperature, and improved compressive strength at 800 °C (927 MPa).

In this paper, the microstructure and mechanical properties of a high Nb-TiAl alloy with different carbon contents were characterized and measured, and the influence mechanisms of carbon addition were discussed. The results indicate that, the added carbon was first dissolved in alloy matrix and caused lattice distortion in α₂-Ti₃Al and γ-TiAl. Exceeding its solid solubility, which was proved to be about 0.6 at%, the extra carbon was precipitated in the form of Ti₂AlC. In addition, with the increasing of carbon content, the volume fractions of the α₂ phase and Ti₂AlC enhancement phase increased, while the relative contents of γ phase and B2 phase decreased. Under the synergistic effects of phase composition, C solid solution strengthening, Ti₂AlC precipitation strengthening and fine crystal strengthening, the high Nb-TiAl-0.6 C alloy exhibits the best overall performance, especially the high temperature compression performance. Compared with the original alloy without carbon addition, at 800 °C, its compressive stress increases from 900 MPa to 1074 MPa and compressive strain corresponding to the maximum compressive stress increases from 11.3 to 12.5% respectively.

To solve the problem of inadequate plasticity of traditional processing routes in improving the plasticity of novel Co-saving 18Ni (300) maraging steel, a cold deformation-cycle solution treatment process was developed. Through systematic characterization and tensile property testing, the study focuses on elucidating the impact of the number of solution treatments on the microstructure and mechanical behavior. The results showed that with a 30% cold deformation, three times of solution treatment at 860 °C for 10 min refined the original austenite grains (equivalent circle radius: 3.3 μm) and martensite structure (length and width: 7 μm and 1.3 μm, respectively) to the utmost extent. The grains became uniformly equiaxed, and the texture was eliminated, and a moderate content (4.5%) of retained austenite was formed. At this time, the material achieves the best match between strength (tensile strength of 1240 MPa) and plasticity (elongation of 9.93%), which are increased by 15.3% and 94.3%, respectively, compared with the traditional process. Mechanistic analysis revealed that grain refinement and uniform equiaxialization were the primary drivers for enhancing strength and plasticity. This study has demonstrated that the cold deformation-cyclic solution treatment process is an effective methodology for tailoring the microstructure and mechanical properties of maraging steel.

Combining a comparative experimental study and theoretical analysis, the feasibility and corresponding action mechanisms of the pre-hardened hot forming (PHF) process applied to 6082-0.2Zr-0.3Er alloy were discussed. The results indicate that unlike a traditional process, after PHF treatment, both the grains and the precipitates at the grain boundaries show a certain directional arrangement, and the texture coefficients of (220) and (200) are enhanced. Although the average size of the second phase is almost the same, the proportion of the fine second phase in the PHF-treated sample is larger. In addition to shortening the processing time and improving the production efficiency, the PHF process was proven to be beneficial for the improvement in the comprehensive mechanical properties of this 6082-0.2Zr-0.3Er alloy, with the product of strength and elongation increased by about 12.1% under the given conditions. Furthermore, with the optimization of process parameters, the improvement effect is expected to be further enhanced.