Peng Lin

Aluminum volatilization during electron beam cold hearth melting (EBCHM) makes precise composition control of titanium alloys difficult. In this study, a thermodynamic–kinetic framework was established to describe Al evaporation, and a Global Prediction Model (GPM) and Stage-Dependent Prediction Model (SPM) were developed for composition prediction and process analysis. Under the reported comparison basis, the GPM predicted final Al content with a mean absolute percentage error (MAPE) of 4.51% and a maximum error of 8.47%; a first-order normalization of the 4.5 wt.% theoretical predictions to the 4.4 wt.% industrial charging basis reduced the concentration MAPE to approximately 2.10%, showing that part of the original offset arose from the charge-basis mismatch. The SPM showed a MAPE of 8.33% for final Al concentration. Both models systematically underestimated the measured Al loss, indicating a directional bias that remains to be resolved. The SPM predicted that the refining and melting hearths contributed approximately 44.4% and 32.5%, respectively, or 76.9% in total; these percentages are model-derived stage attributions and were not independently validated by stage-resolved measurements. The GPM is therefore most suitable for rapid overall composition prediction, whereas the SPM provides physically interpretable, stage-specific guidance for identifying candidate critical volatilization regions and optimizing EBCHM operating conditions.

The microstructure and mechanical properties of a hot-rolled Ti-22Al-25Nb (at%) alloy sheet after aging and solution-aging treatment were studied. A typical core-shell structure formed in the as-received specimens upon aging at 650 °C to 950 °C for 6 h. O phases precipitated around the grain boundaries or in the B2 matrix for the solution-treated specimens upon aging at 650 °C to 950 °C. The combined effect of the precipitation and solution strengthening led to a decrease in microhardness while aging from 650 °C to 900 °C and an increase in microhardness while aging from 900 °C to 1000 °C for both the as-received and solution-treated specimens after the aging treatment. Finer O phases contributed to the increase in yield strength and elongation and were more beneficial to the improvement of high temperature strength than of room temperature strength.

In order to thoroughly understand the quantitative relationships between the flow stress and deformation conditions for Ti₂AlNb-based alloys at elevated temperatures, the Arrhenius and Johnson–Cook constitutive models are analyzed and identified on the basis of the uniaxial tensile tests. The Johnson–Cook model is modified so that the referenced temperature range can be randomly adjusted. By experimental verification, the Arrhenius model (including the Backofen model) is suitable for the deformation at relatively low strain-rate deformation, such as the superplastic forming, and the modified J–C model is applicable for the deformation within a wide range of strain rates. For deformation at high temperatures, the constitutive model enables a more precise description of the effect of strain on the flow stress through introducing as train-softening factor exp(sε).

In this study, a Ti composite reinforced with 5 vol. % (TiB_w + TiC_p) was fabricated by an in situ casting route. Open die forging in (α + β) phase region was conducted on the composite casting. The microstructures of the as-forged composite pancake are inhomogeneous in terms of matrix microstructure and distribution of reinforcements. The matrix grains are gradually refined from the periphery to centre of the pancake. The reinforcements TiB_w and TiC_p tend to be uniformly distributed in the centre region. It is suggested that the microstructure difference can be mainly ascribed to the temperature variation from the periphery to the centre. The tensile testing results show that the centre region of the composite pancake exhibits higher strength than the peripheral region. The mechanical behaviour of the composite pancake with the temperature is discussed.