Acta Metall Sin  2017, Vol. 53 Issue (10): 1385-1392    DOI: 10.11900/0412.1961.2017.00255
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Plastic Deformation Behavior of Biomedical Ti-24Nb-4Zr-8Sn Single Crystal Alloy
Jinrui ZHANG1,2, Yanwei ZHANG3, Yulin HAO1(), Shujun LI1, Rui YANG1
1 Shenyang National Laboratory for Materials Science, Institute of Metal Research, Chinese Academy of Sciences, Shenyang 110016, China
2 School of Materials Science and Engineering, University of Science and Technology of China, Shenyang 110016, China
3 Life Management Technology Center, Suzhou Nuclear Power Research Institute, Suzhou 215004, China
Abstract

Excellent corrosion resistance, good biocompatibility and relatively low elastic modulus make Ti and Ti alloys fulfill the property requirements in the biomedical field better than other competing materials such as stainless steels. Even so, there still exist some problems to be solved such as the biological toxicity of some alloy elements and the so-called stress shielding effect caused by higher elastic modulus than that of human bone. In response to these issues, several metastable β-type Ti alloys were developed with the advantage of nontoxicity and a much lower elastic modulus. Ti-24Nb-4Zr-8Sn (mass fraction, %, abbreviated Ti2448) alloy is a multifunctional biomedical Ti alloy with high strength and low elastic modulus, which makes it show great application prospect in the field of body implant. It put up obvious nonlinear elasticity and highly localized plastic deformation behavior. Study on deformation behavior of single crystal can help to understand the deformation mechanism of polycrystalline alloy. In this work, Ti2448 single crystal alloy along three different orientations were prepared by optical floating zone method. The plastic deformation behaviors of them under tensile stress were investigated in terms of mechanical properties, slip system and fracture morphology. Results show that Ti2448 single crystal shows obvious anisotropy, the tensile strengths along <100>, <110> and <111> orientations are 650, 642 and 889 MPa, respectively, while the elongations are about 73%, 22% and 13%, respectively. The main plastic deformation mechanism of Ti2448 single crystal alloy is by slip. The appearance of slip bands and its direction relationship with crystal orientation were detailed observed. Under tensile stress, the operated slip systems for <100>, <110> and <111> orientation single crystals are (112)[111]/(112)[111]/(112)[111]/(112)[111], (211)[111]/(211)[111] and (211)[111], respectively. This is in accordance with the law of critical shearing stress. SEM analyses show a fracture surface shape of rectangle, duckbilled and triangle for the <100>, <110> and <111> orientation single crystals, respectively. The intersection angle between fracture surface and loading direction is all about 55 degree, and a lot of dimple was detected that show ductile fracture mode.

 ZTFLH: TG146.2
Fund: Supported by National Natural Science Foundation of China (Nos.51571190, 51271180, 51631007 and 51527801), National High Technology Research and Development Program of China (No.2015AA033702) and National Key Research and Development Program of China (Nos.2016YFC1102600 and 2017YFC1104903)
 Table 1  Correspondence relationships between tensile sample and crystal direction index of Ti2448 single crystal alloy along different orientations Table 2  Uniaxial tensile properties of Ti2448 single crystal alloy along different orientations Table 3  Slip systems with the maximum Schmid factor under tensile stress of Ti2448 single crystal alloy along different orientations Fig.1  Identification of operated slip systems under tensile stress of Ti2448 single crystal along <100> orientation, with slip traces of (0$\overline{1}$0) plane (a), (010) plane (b), (100) plane (c) and schematic diagram (d) Fig.2  Identification of operated slip systems under tensile stress of Ti2448 single crystal along <110> orientation, with slip traces of (100) plane (a), ($\overline{1}$00) plane (b), (0$\overline{1}$1) plane (c) and schematic diagram (d) Fig.3  Identification of operated slip systems under tensile stress of Ti2448 single crystal along <111> orientation, with slip traces of (211) plane (a, b), (01$\overline{1}$) plane (c) and schematic diagram (d) Fig.4  Side-view SEM images of tensile samples after fracture of Ti2448 single crystal alloy along <100> (a), <110> (b) and <111> (c) orientations Fig.5  SEM images of macrostructures on fracture shape of tensile samples of Ti2448 single crystal alloy along <100> (a), <110> (b) and <111> (c) orientations Fig.6  SEM images of microstructures on fracture surfaces of tensile samples of Ti2448 single crystal alloy along <100> (a), <110> (b) and <111> (c) orientations