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In the present work, a wall-structured nickel-aluminum bronze (NAB) alloy was fabricated via electron beam directed energy deposition (EB-DED) additive manufacturing with a single-pass multi-layer deposition strategy. A comprehensive comparative analysis of microstructure, mechanical properties, and corrosion resistance was conducted against a conventionally cast NAB alloy. The inherent rapid solidification and cyclic thermal processing of the EB-DED technique profoundly influenced the microstructural evolution of the NAB alloy. The as-deposited NAB alloy exhibited a fine-grained microstructure, devoid of the martensitic β′ phase, accompanied by the spheroidization of partial κIII precipitates, and a homogeneous distribution of alloying elements. These distinctive microstructural attributes synergistically enhanced the strength, hardness, and toughness of the NAB alloy, conferring superior mechanical properties compared to its cast counterpart. Furthermore, the as-deposited alloy demonstrated remarkable corrosion resistance in a 3.5 wt% NaCl solution, significantly outperforming the cast alloy. The underlying mechanisms governing the structure-property relationships were elucidated. This comprehensive investigation provided insights into the unique characteristics and potential applications of EB-DED fabricated NAB alloys, positioning them as promising candidates for high-performance components subjected to severe mechanical and corrosive service conditions.

In general, the Ti–6.5Al–2Zr–1Mo–1V (TA15) components fabricated via laser powder bed fusion (L-PBF) exhibit high strength and low ductility. Herein, we report a novel approach to enhance the comprehensive mechanical properties of L-PBF TA15 alloy by adjusting the laser power. Samples processed using the optimal laser power exhibit a grid structure of alternating wide and narrow prior-β grains (PBGs), the inside of which is composed of a fully martensitic microstructure. The paper discusses in detail the alterations in the microstructure of samples processed at both low and high laser powers, clarifying the relationship between microstructure and mechanical properties. Thinner martensite contributes to higher strength, while a homogenous microstructure improves ductility. These findings provide valuable insights for controlling microstructure and achieving strength-ductility synergy in L-PBF additive manufacturing of titanium alloys.

Herein, we investigate the influence of heat treatment on microstructure and thermo-physical properties of Al-50wt%Si alloy fabricated by selective laser melting (SLM). Microstructure characterizations reveal that SLM and heat-treated Al-50wt%Si alloys are all characterized by the primary Si and eutectic structure consisting of dominant Al matrix and tiny eutectic Si. However, the size of primary Si monotonously increases with increasing the heat treatment holding time at 550 °C. In addition, the SLM Al-50wt%Si alloy displays a highest coefficient of thermal expansion (CTE) among all examined alloys. As the heat treatment holding time increases, the Si precipitates from the Al(Si)-supersaturated solid solution, leading to the formation of a skeleton-like Si phase, which effectively alleviates the thermal expansion. Furthermore, the SLM Al-50wt%Si alloy exhibits a lowest coefficient of thermal conductivity (CTC), since the significantly increased size of primary Si with increasing the heat treatment holding time leads to a substantial reduction in the number of grain boundaries, which severely restricts the scattering of heat transfer phonons. Moreover, theoretical models are employed to calculate the CTE and CTC. Results indicate that the Schapery lower model provides a better prediction of CTE, and the actual CTC values of Al-50wt%Si alloys after heat treatment are closer to theoretical values. These findings can provide new insights into designing Al matrix composites with low CTE and high CTC through microstructural optimization.

Titanium/steel multi-material, given full play to their superiorities, has tremendous value for parts exposed to complexity service environments, yet invariably, its common joining techniques are lack of design freedom. To this end, we employ electron beam freeform fabrication (EBF3) to successfully prepare this multi-material system for the first time, whose interfacial microstructure and property are systematically investigated. Applying Cu as an interlayer, instead of causing extensive cracking and delamination at the interface of Ti64/316L, can effectively suppress the formation of continuous Fe–Ti intermetallic compounds (IMCs), and thus improve the strength of Ti64/Cu/316L interfaces. For the Cu/316L interface, besides the characteristic spherical Cu-rich and Fe-rich solid solutions, a few Fe–Ti IMCs appear within the Fe-rich solid solutions owing to the long-range diffusion of minor Ti atoms. Correspondingly, the dendritic Cu-rich solid solutions can also be found at the Ti64/Cu interface, which is regarded as a critical interface due to the concomitant of complex Cu–Ti IMCs. These Cu–Ti IMCs have less negative effect on the Ti64/Cu interface property relative to Fe–Ti IMCs, and the local strain produced by the deformed α-Ti near the interface and Cu-rich solid solutions can effectively relieve the concentration of residual stress. Consequently, the Ti64/Cu interface exhibits maximum micro-hardness to 490 HV and superior shear strength to 196.5 ± 2.2 MPa, which was attributed to the reinforcement for the tip of keyhole molten pool, as well as the synergy between Cu-rich solid solution and interdendritic Cu–Ti IMCs.

Dual-wire-fed electron beam directed energy deposition (EB-DED) is a highly efficient technique for additive manufacturing (AM) of TiAl alloys, but research into the evolution of microstructure and mechanical properties within the melt pool is limited. Experimental and numerical simulations are used together to study the evolution along the vertical direction within the TiAl alloy melt pool. The chemical composition, microstructure and microhardness in the top region (TR), middle region (MR) and bottom region (BR) within the melt pool were characterized and comparatively analysed. The results showed that the Al content decreased from 52 at. % to 49 at. % from the top to the bottom, the grain size increased and then decreased, and the grain aspect ratio increased from 1 to over 3. The decreasing size factor and increasing shape factor result in variations in grain size and shape. The improvement in microhardness from 226 HV0.5 to 280 HV0.5 was quantitatively analysed as being mainly due to the reduction in Al content. The results of this study are of paramount importance in facilitating the use of the dual-wire-fed EB-DED technique for the production of high performance TiAl alloy components.

Investigation about how to enhance the corrosion properties of Ti alloys is essential to their actual applications in corrosive environments. Herein, the specific influences of Zr content on the corrosion behavior of Ti-6Al-3Nb-xZr-1Mo alloys (x = 2, 6, 10, 20 and 40 wt%) are systematically investigated using microstructure characterization, electrochemical and weight loss measurements. The results signify that all investigated alloys are composed of α and β phases; however, the increase of Zr content endows alloys with the refined thickness of lamellar α phase and enhanced volume fraction of intergranular retained β phase. Meanwhile, the corrosion resistance monotonously improves along with increasing the Zr content, directly characterized by the decreased corrosion current density, improved polarization resistance as well as reduced corrosion rate. The improvement in corrosion performance is a result of the alleviated micro-galvanic corrosion formed between α and β phases, increased volume fraction of corrosion-resistant β phase and modified composition of oxide film. One should note that the corrosion mode changes from the uniform corrosion to the mixed pitting and uniform corrosion with the Zr addition up to 40 wt%. Besides, surface analysis of samples after immersion tests reveals that the lamellar α phase is more susceptible to corrosion compared to the adjacent intergranular β phase, attributed to its higher concentration of Ti and Al elements. The current findings provide data that can be referenced for designing high-corrosion resistance materials for marine, biomedical applications and hydrochloric acid industries through composition optimization.

Herein, we systematically investigate the corrosion behaviour of a wrought Ti-6Al-3Nb-2Zr-1Mo (Ti80) alloy in artificial seawater with various fluoride ion (F−) concentrations and pH values using electrochemical, static immersion measurements and surface characterizations. Results of electrochemical tests manifest that increasing the F− concentration and/or reducing pH value can deteriorate the corrosion performance of Ti80 alloy due to the dissolution of the compact passive film into the porous passive film. Besides, the electrochemical parameters obtained from polarization curves indicate that the F− concentration has few effects on the cathodic reaction but noticeable promoting effects on the anodic process, whereas the increase of pH plays a significant role in inhibiting both cathodic and anodic processes. In addition, surface characterizations reveal the preferential dissolution of the equiaxed α phase compared to the intergranular β phase, resulting from its relatively low Volta potential. We also interpret the F− concentrations and pH values dependent corrosion behaviour based on the mixed potential theory and illustrate the corrosion mechanisms associated with F− in artificial seawater. We believe that the insights into the F− concentration and pH value dependent corrosion behaviour can provide practical guidelines for the design and development of Ti alloys with high-corrosion resistance.

The addition of interstitial elements generally has a significant impact on the macroscopic performances of structural alloys. Here, we report a systematic study on the microstructure, corrosion behaviors and mechanical properties of a series of as-cast Ti-0.3Mo-0.8Ni- x C ( x = 0.09, 0.12 and 0.15 wt.%) alloys. A typical basket-weave microstructure appears in all specimens, characterized by the lamellar α -phase and intergranular retained β -phase without TiC precipitates within the prior β grain boundary. Based on the electrochemical and immersion tests, doping with C element can significantly improve the corrosion resistance of TA10 alloys; with increasing the carbon content, the passivation current density decreases from 5.750 to 4.938 μ A·cm ^−2 , the breakdown potential increases from −1.115 to −1.223 V versus SCE, the corrosion rate reduces from 15 mm/a to 7.5 mm/a. Moreover, the mechanical properties of TA10 alloys, such as the strength and hardness, can also be enhanced via C alloying. Our results indicate that the addition of interstitial elements should be a potential effective mean to accommodate the comprehensive performances of TA10 alloys.