中文摘要：

针对具有特殊非线弹性变形行为的高强度低模量Ti-24Nb-4Zr-8Sn（质量分数,%,简称Ti2448）医用钛合金,采用光学浮区生长法制备出3种典型取向的低指数单晶,研究其塑性变形行为。结果表明,Ti2448单晶合金的室温拉伸性能表现出明显的各向异性,〈100〉取向、〈110〉取向和〈111〉取向单晶的抗拉强度分别为650、642和889 MPa,延伸率分别约为73%、22%和13%;单晶合金的室温拉伸塑性变形机制以滑移为主,〈100〉取向单晶开动的滑移系统为（112）[111]、（112）[111]、（112）[111]和（112）[111],〈110〉取向单晶开动的滑移系统为（211）[111]和（211）[111],〈111〉取向单晶开动的滑移系统为（211）[111];〈100〉取向、〈110〉取向和〈111〉取向单晶合金的拉伸样品断口形状分别呈现矩形状、鸭嘴状和三角状,断裂面与拉伸方向的夹角均约为55°,断口均呈现韧性断裂特征。

英文摘要：

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 bio-logical 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 b-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