钛合金表面Ti/TiB_2仿生多层膜的断裂韧性

Fracture Toughness of Ti/TiB_2 Bionic Multilayers on the Surface of Titanium Alloy

根据贝壳珍珠层的结构特点,以金属Ti层为软质层,对TiB_2陶瓷薄膜进行仿生增韧处理,并通过压痕法研究了Ti/Ti B_2仿生多层膜的断裂韧性。结果表明:随着调制比Λ(t_(TiB_2):t_(Ti))的增大,多层膜的断裂韧性先增大而后减小,当Λ为5时,多层膜的断裂韧度达到最大值(KIC=2.68 MPa·m^(1/2))。对于相同厚度的Ti B_2单层膜而言,断裂韧度值仅为0.76MPa·m^(1/2),也就是说,Ti/Ti B_2仿生多层膜可有效提高陶瓷层的断裂韧性。沉积在Ti6Al4V基体上的多层膜在断裂过程中进行能量释放以径向裂纹为主,以环形裂纹为辅。由于多层膜中Ti子层的周期性引入,有效缓解了Ti B_2薄膜的内应力;当裂纹扩展至Ti子层时,Ti层可对裂纹尖端起到很好的钝化作用,使裂纹扩展方向发生偏转。此外,多层膜的界面增多,也相应增大了裂纹扩展的阻力,提高了多层膜的断裂韧性。

To enhance the fracture toughness of TiB2 ceramic film, Ti/TiB2 bionic multilayers were formed by period intervention of Ti layer which was abstracted into a soft layer inspired by the structural of nacre. An improved indentation method was proposed to characterize the fracture toughness（KIC） of the Ti/TiB2 bionic multilayers. The results show that the KIC of the multilayers strongly depends on the modulation ratios（Λ, the ratio of TiB2 to Ti thickness is denoted as t_（TiB2）：t_（Ti））. With the increase of modulation ratio, the KIC of the multilayers increases first, gets a maximum of 2.68 MPa·m^1/2 at Λ=5, and decreases subsequently. For the same thickness of TiB2 monolayer, the KIC is only 0.76 MPa·m^1/2; that is, the fracture toughness of the ceramic film can be enhanced effectively via formation of Ti/TiB2 multilayers. The fracture energy is released mainly in the form of radial cracks, and partly in the form of annular cracks of the multilayers deposited on the substrate of Ti6Al4 V alloy. The stress of the TiB2 ceramic film can be effectively alleviated due to the periodic insertion of Ti sublayer in the multilayers. Passivation effect may occur at the crack tip, which leads to a path deflection of the crack propagation, as a result, improving the fracture toughness of the multilayers. Furthermore, the extra interface in the multilayers increases the resistance of crack growth and thus enhances the fracture toughness.