High strength-toughness difficult-to-cut materials represented by titanium alloy and superalloy, exhibiting excellent properties, such as high-temperature strength, impact resistance, and great creep resistant performance, have opened up the increasing application as key materials of complex components in high thrust-to-weight ratio of modern aero-engine. Grinding process has become the major method to achieve the final forming surface of components. Compared to the problems, such as severe tool wear, low machining efficiency, and poor quality stability with conventional abrasive grinding wheels, the cubic boron nitride (CBN) superabrasive grinding wheel exhibiting unique advantages in the grinding of high strength-toughness difficult-to-cut materials. However, the grinding process is also facing the similar challenges, and then the root cause of these problems is the poor wear resistance and sharpening ability of traditional CBN abrasive wheels and thus the sharpness and tool life of CBN grinding wheel are not stable. The reason can be explained that these CBN grains possess anisotropic crystalline property, leading to the unfavorable macrofracture along the cleavage plane. In this case, the grinding performance and stability of CBN grains, as well as the surface precision and sharpness state of corresponding sintered wheels are severely affected, which restricts the improvement of machining efficiency. In order to improve the grinding performance of CBN grains, a new-type aggregated CBN grains coupled with great wear resistance and sharpening ability is proposed by employing cold press forming and high vacuum liquid-phase sintering techniques. In this work, the comparative grinding trials with a single grain for both aggregated and monocrystalline CBN grains were performed to study the grain wear behavior and material removal characteristics in grinding of Ti-6Al-4V alloys, in terms of the worn grain and grinding scratch morphologies. The strong bonding interface between metallic phases and Ti-coated CBN particles inside aggregated CBN grains was achieved through the diffusion of active Ti elements and thus new compounds (i.e. TiB2, TiB and TiN) were formed on the surface of CBN particles under high-temperature liquid phase sintering conditions. Here, the sintering process was optimized as 800 ℃ for 10 min considering the grain strength. In addition, the as-sintered aggregated CBN grain had better wear resistance and more sharper cutting edges due to the existence of multiple micro-grains and the associate surrounding metallic materials compared to the other one. In addition, aggregated CBN grains possessed a higher grinding efficiency as well as a higher and more stable material removal volumes in basis of the calculation of the volumetric pile-up ratio of each scratch and the wear loss of reconstructed grains in machining of Ti-6Al-4V alloys. Moreover, steady micro- and multi-wear stages are provided by the combination of various wear patterns (i.g. microfracture, chip adhesion, and partial macrofracture) of CBN particles, which attributes to the improvement of grinding performance of aggregated CBN grains. Furthermore, the good consistency of groove profiles in a single scratch can be also observed for aggregated CBN grains, whereas the grooves scratched by monocrystalline CBN grains decrease significantly due to the appearance of grain macrofractures along the cleavage plane. In this case, the developed aggregated CBN grains exhibit the better grinding performance and quality compared with traditional monocrystalline CBN grains. © 2023 Chongqing Wujiu Periodicals Press. All rights reserved.
