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超声表面滚压对氢化钛烧结纯钛显微组织及性能的影响

Effect of ultrasonic surface rolling process on microstructure and properties of hydride sintered pure titanium

  • 摘要: 采用超声表面滚压技术对氢化钛烧结纯钛进行表面强化,并借助X射线衍射、电子背散射衍射、扫描电镜和透射电镜分析滚压后纯钛的微观组织演化及性能影响。结果表明,滚压后组织呈梯度变化,最外表面晶粒为等轴纳米晶,尺寸约100 nm;随距表面距离增大,晶体组织依次为块状晶、层片状组织及等轴粗晶,塑性变形层厚度可达400 μm。滚压后表面硬度提高了36%,表面粗糙度显著降低,滚压后引发的晶粒细化和残余应力有助于产生致密的钝化膜,提高了耐腐蚀性能。滚压后抗拉强度和屈服强度为640 MPa、485 MPa,分别提高了32%和27%,但延伸率有所下降,断口形貌总体仍表现为韧性断裂。

     

    Abstract: Surface hardening of the pure titanium sintered by titanium hydride was treated by ultrasonic surface rolling process (USRP) in this paper, and the effects of USRP on the microstructure evolution and properties of the hydride sintered pure titanium were investigated by X-ray diffraction (XRD), electron back scattering diffraction (EBSD), scanning electron microscope (SEM), and transmission electron microscope (TEM). The results demonstrate that a gradient microstructure is present after USRP with the static load of 600 N, the outermost layer of the deformed microstructure displays the equiaxial nanocrystals, and the average grain size of the fine grains is about 100 nm. As the distance from the surface increases, the crystal structure shows the massive crystal, lamellar structure, and equiaxed coarse crystal in turn, and the average thickness of the deformation layer is about 400 μm. The surface roughness, grain refinement, and high surface compressive residual stress caused by rolling synergistically help to form a dense and stable passive film on the deformation layer, which could improve the corrosion resistance effectively. In addition, taking advantages of the microstructure evolution, the ultimate tensile strength and yield strength are 640.57 MPa and 485.29 MPa, increased by 32.43% and 27.57%, respectively. Meanwhile, the surface hardness is increased by 36% for the USRP treated titanium alloy. However, the introduction of deformation layer leads to a decrease of uniform elongation, while the fracture morphology indicates a ductile failure.

     

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