Recently, Professor Yuan Songmei’s Team from the School of Mechanical Engineering and Automation at Beihang University has published an article, titled "How does ultrasonic cutting affect the macroscopic deformation and microstructure evolution of fibre-reinforced titanium matrix composites?" in International Journal of Machine Tools and Manufacture (DOI: 10.1016/j.ijmachtools.2024.104245). Wang Liyu, a doctoral student in the School of Mechanical Engineering and Automation, is the first author of the paper, and Professor Yuan Songmei is the corresponding author.

Continuous silicon carbide (SiC) fibre-reinforced titanium (Ti) matrix composites (SiCf/Ti) possess exceptional properties, making them promising for aerospace applications. Continuous SiC fibres significantly enhance the axial tensile strength of SiCf/Ti compared to traditional Ti alloys. To utilise this material fully, its axial dimensions are fixed during manufacturing, but the outer Ti matrix layer must be thinned to meet structural accuracy requirements. Thinning often leads to interfacial cracking and fibre breakage owing to machining stress, which presents a major challenge in manufacturing. The deformation mechanism during thinning is unclear and the lack of low-stress thinning methods significantly limits the potential applications of SiCf/Ti.

Fig. 1. The production process flowchart for SiCf/Ti structural components

The research investigates the macroscopic deformation and microstructural evolution of SiCf/Ti under ultrasonic cutting (UC) through orthogonal experiments. Compared with conventional cutting (CC), UC reduces cutting force by 20 % and surface residual stress by 60 %, while increasing subsurface residual stress and nano-hardness. The acoustic softening effect in UC reduces cutting force and surface stress, while high-frequency stress waves elevate subsurface stress. Digital image correlation (DIC) analysis reveals that the combined effects of loading and unloading cycles during UC produce an elastic recovery strain, reducing the overall deformation in SiCf/Ti during machining. Additionally, UC promotes grain refinement in the outer Ti layer of SiCf/Ti and induces a stress concentration at the α-Ti and β-Ti interface, facilitating the transformation of α-Ti to β-Ti. The presence of SiC fibres amplifies the effects of the ultrasonic energy, accelerating dislocation diffusion and annihilation, promoting dynamic recrystallisation, and reducing the dislocation density between the fibres. Moreover, UC homogenises and realigns the stress field at the SiCf/Ti interface, making the composition and structure of the interface more uniform and reducing interfacial damage.

Fig 2: Near-machined surface matrix, inter-fibre matrix, and interface above and between the fibres in the SiCf/Ti subsurface under CC and UC

Fig 3: Subsurface microstructural variation of SiCf/Ti under CC and UC

This study contributes to an enhanced understanding of the macroscopic deformation and microstructural evolution of SiCf/Ti during ultrasonic thinning and provides insights into the low-stress machining of SiCf/Ti and other fibre-reinforced metal matrix composites, paving the way for broader applications of SiCf/Ti in advanced structural components.

This work was supported by the National Natural Science Foundation of China and the Postdoctoral Fellowship Program of CPSF.

Link to the original article: https://www.sciencedirect.com/science/article/pii/S0890695524001317

Editor: Lyu Xingyun