Significant achievements have been made in preparing Ti2AlNb/Ti-48Al-2Cr-2Nb composites using an EBM-forming method. The current Ti-48Al-2Cr-2Nb alloy experience compositional loss when operating above 650°C, limiting their service temperature to that threshold and preventing them from performing effectively at higher temperatures. To address this issue, a dense Ti2AlNb/Ti-48Al-2Cr-2Nb composite material was fabricated using a mixture of Ti2AlNb and Ti-48Al-2Cr-2Nb powders, along with process optimisation. Additionally, the evolution of microstructure, phase composition, and phase distribution of the composite material was studied, as well as the mechanisms by which microstructural features and phase distribution influence its mechanical properties. The research findings indicate that the optimal process for samples with different Ti2AlNb content achieved a density exceeding 98%. As the amount of Ti2AlNb increased, the microstructure transitioned from fine equiaxed grains to coarse dendrites, and the phase composition shifted from a dominance of the γ phase to a predominance of the B2 phase. The higher levels of α2 phase and O phase in the composite material increased its room-temperature tensile strength by 11% and high-temperature tensile strength by 32%, while the elevated B2 phase content resulted in higher yield strength. Grain size, microstructural uniformity, Nb and O phase content, along with the activity of the B2 phase at high temperatures, contributed to a creep behaviour characterised by resistance to deformation failure, thereby enhancing the material's damage tolerance.

Fig 1. Microstructure and phase composition and distribution of samples with different doping levels of Ti2AlNb: (a) none doping; (b) 10% Ti2AlNb doping; (c) 20% Ti2AlNb doping; (d) 30% Ti2AlNb doping

Fig 2. Display of formed workpieces in relevant application cases

In this work, ultra-low dilution rate Inconel 625 coatings with a thickness of approximately 534.4 μm were prepared by high-speed laser cladding technique on the Q245R steel. The XRD and TEM results shown that the Inconel 625 coatings are mainly composed of the Nb and Mo-enriched laves phase with hexagonal close-packed (HCP) structure and the γ-Ni phase with face-centered-cubic (FCC) structure. The cellular crystal, column crystal and equiaxed dendritic crystal were observed in the bottom, middle and top of the Inconel 625 coatings from SEM results, respectively, as shown in Fig. 3. The wear resistance and corrosion resistance of Q245R steel are significantly improved by high-speed laser cladding Inconel 625 coatings. In addition, the low dilution rate is beneficial for improving the wear and corrosion resistance of high-speed laser cladding Inconel 625 coatings. These findings may provide a method to design the wear and corrosion resistance of coatings on steels surface.

Fig 3. (a) Cross-sectional FESEM images of Inconel 625 coatings; Bottom to top views of Inconel 625 coatings: (b) Bottom zone; (c) Middle zone; (d) Top zone

Phase identification for Inconel 625 coating was carried out by using TEM and the results are shown in Fig. 4. Fig. 4a shows the bright field image for an area with coexisting phases. Figs. 4b and 4c display the selected area diffraction patterns for the phase A and phase B in Fig. 4(a), respectively. As shown in Fig. 4b and 4c, the phases A and B shows the characteristics of γ-Ni phase with FCC structure and lavas phase with HCP structure. The chemical composition of lavas phase (phase B) was analyzed by EDS and the results are listed in Table 1. From Table 1, it can be found that the laves phase is rich in Nb and Mo. Fig. 4d shows the bright field image for an area with the interface between Inconel 625 coatings and Q245R steel substrate. Figs. 4e and 4f display the selected area diffraction patterns for the phase C and phase D in Fig. 4d, respectively. As shown in Fig. 4e and 4f, the phases C and D shows the characteristics of α-Fe phase with BCC structure and γ-Ni phase with FCC structure.

Fig 4. TEM image of Inconel 625 coatings (S6): (a) Top view; (b, c) Selected area diffraction patterns for phase A and B corresponding to (a); (d) Bottom to top views; (e, f) Selected area diffraction patterns for phase C and D corresponding to (d)

Table 1. EDS results of lavas phase 

Fig 5. Display of formed workpieces in relevant application cases