Titanium matrix composites (TMCs) have long been recognized for their exceptional properties, making them invaluable in various industries, including aerospace, automotive, and biomedical fields. TMCs owe their popularity to attributes such as high strength-to-weight ratios, superior mechanical properties, biocompatibility, and osseointegration. Among the various materials used as reinforcement in TMCs, Titanium Carbide (TiC) stands out due to its remarkable properties, including high hardness, thermal stability, and good compatibility with titanium matrices. However, the success of TMCs depends significantly on the morphology, size, and dispersion of the reinforcement particles within the matrix. In particular, nanoscale reinforcement with uniform dispersion offers the potential to substantially enhance the mechanical properties of TMCs by increasing the interfacial area and interfacial adhesion between the reinforcement and the matrix. Traditional manufacturing techniques for TMCs, such as powder metallurgy and casting, have faced challenges in achieving optimal dispersion, especially when dealing with nanoscale reinforcements. These conventional methods often result in uneven distribution, leading to suboptimal mechanical properties.
Laser powder bed fusion (LPBF) has emerged as a promising additive manufacturing (AM) technique capable of producing near-net-shape 3D objects with complex geometries, high precision, and excellent mechanical properties. However, previous attempts to fabricate TiC/TMCs using LPBF encountered obstacles related to the uniform dispersion of reinforcement particles and the impact on the spherical shape and flowability of titanium powder, affecting densification levels and mechanical properties. To address these challenges, Associate Professor Wenhou Wei and graduate students Yong Yang and Jiyuan Zhang from the Chongqing Institute of Green and Intelligent Technology at the Chinese Academy of Sciences developed an innovative method for in-situ AM of TMCs using methane (CH4) gas and spherical Ti6Al4V powder based on gas–liquid reactions. This groundbreaking approach aims to achieve excellent dispersion and strong bonding of nanoscale TiC reinforcement with the Ti matrix in a composite structure through a fast AM process.
The authors found the XRD patterns confirmed the successful synthesis of TiC reinforcement in the TMCs fabricated using this novel method. The intensity of TiC diffraction peaks increases with higher CH4 concentration, indicating an enhanced TiC phase formation due to increased C atoms/ions supply for in-situ reactions. When they conducted microstructural analysis it showed that the TiC particles are uniformly distributed in the Ti6Al4V matrix, with a significant presence of nanoscale TiC particles in samples fabricated with lower CH4 concentrations. This excellent dispersion is attributed to the high diffusivity and good dispersity of the gaseous carbon source. Furthermore, the TiC reinforcement maintained its fine dispersion and ultrafine grain size due to the molecular-level size of the gaseous feedstock. The interface between TiC and the matrix remains clean, contributing to strong interfacial bonding. EBSD analyses demonstrated that the prior β grains in the TMCs are refined, resulting in a more uniform distribution of acicular α’ martensites. This grain refinement is attributed to the “pinning” effect of TiC precipitates, hindering grain growth in the Ti matrix.
The research team found the microhardness of the TMCs is higher than that of the monolithic Ti6Al4V alloy, with the highest microhardness achieved at a 19 vol% CH4 concentration. This improvement can be attributed to the dispersion strengthening and precipitation hardening effects of TiC in the Ti6Al4V matrix. However, excessive TiC content beyond a certain point leads to decreased microhardness due to the presence of brittle TiC particles.
Compressive tests revealed that the TMCs exhibit higher compressive yield strength and ultimate compressive strength than the monolithic Ti6Al4V alloy. The strengthening effect is mainly attributed to grain refinement in the Ti matrix and the dispersion strengthening of uniformly distributed TiC particles. An optimal combination of high strength and high plasticity is achieved in TMCs with moderate TiC content. Moreover, the TMCs showed improved wear resistance compared to the monolithic Ti6Al4V alloy, with the best wear resistance achieved in samples with an appropriate amount of TiC reinforcement. Excessive TiC content results in impaired wear resistance due to the presence of brittle TiC particles.
In conclusion, the innovative in-situ AM method for fabricating TiC/TMCs using methane gas and spherical Ti6Al4V powder represents an advancement in its manufacturing technology. This approach overcomes the limitations of traditional manufacturing techniques and previous LPBF methods, ensuring excellent dispersion, clean interfaces, and strong interfacial bonding of nanoscale TiC reinforcement with the Ti matrix. Associate Professor Wenhou Wei research not only opens new possibilities for the fabrication of advanced TMCs but also underscores the importance of innovative manufacturing techniques in enhancing material performance for critical applications in aerospace, automotive, and biomedical fields.
Yong Yang, Jiyuan Zhang, Wenhou Wei, Microstructure and mechanical properties of TiC/ Ti6Al4V nanocomposites fabricated by gas–liquid reaction laser powder bed fusion, Materials Science and Engineering: A, Volume 869, 2023, 144829,