【作者】 周宇；

【导师】 杨贤金；

【作者基本信息】 天津大学 ， 材料学， 2010， 博士

【摘要】 本文主要对新型医用Ti-25Nb-2Zr(at%下同)钛合金的制备,热机械加工工艺及表面生物活性进行了研究。通过DSC、金相组织、XRD、拉伸试验,显微硬度及形状记忆效应及超弹性测试对微量锆元素对Ti-25Nb合金的相变、显微组织,力学性能及形状记忆效应等性能的影响进行了考察。同时进一步研究了热处理及冷加工工艺对Ti-25Nb-2Zr合金显微组织及力学性能的影响。此外,采用普通氧化法对Ti-25Nb-2Zr合金的表面进行改性,借助SEM、EDS、XRD、XPS及FTIR对改性后的合金表面及随后经过仿生生长的合金表面进行表征。通过实验研究及理论分析,主要得出以下结论:在Ti-25Nb合金中添加微量锆元素对于降低合金的相变点,抑制相析出及细化晶粒有一定的作用:合金中每增加1at%的锆元素,合金相变点约降低10K。合金的强度随锆含量的变化呈现先增加后减小的趋势;合金的弹性模量及显微硬度随锆含量的变化趋势则与抗拉强度相反,呈现先降低后升高的趋势。合金在锆含量为3at%时获得最高770MPa的抗拉强度,在锆含量为2at%时合金具有最低62GPa的弹性模量。锆元素的添加对合金的马氏体相变温度有影响:锆含量为2at%左右的合金在室温变形能生成马氏体,故其形状记忆效应较明显。Ti-25Nb-2Zr合金在β相变点以上固溶处理,空冷后保留等轴全β相组织,合金具有较低的强度和优异的塑性。随着固溶温度的增加,合金晶粒显著粗化,导致合金的强度及塑韧性下降。合金在350℃进行时效处理,在基体中析出硬脆相ω相;在450℃左右时效,在基体中析出相。合金在经过冷加工后,发生了应力诱发马氏体相变。由于马氏体相变和加工硬化的共同作用,导致合金的强度在冷形变量较小时增加不显著。Ti-25Nb-2Zr合金在空气中氧化,在300℃～600℃的温度区间内,表面氧化物将从亚稳态氧化钛先转变为锐钛矿,最终转变为金红石。合金经空气中500℃2h氧化后,SEM及AFM观察显示合金表面粗糙度明显增加。经空气中500℃2h氧化后的合金试样置于钙磷溶液中进行浸泡,并成功的在合金表面制备了钙磷层。XRD分析显示所得的钙磷层的主要成分为羟基磷灰石。XPS及FTIR分析表明钙磷层中含有CO32-离子。更多还原

【Abstract】 This paper studied the preparation, thermal-mechanical processing technique and surface bioactivity of Ti-25Nb-2Zr (at %) alloy. The influence of small amount of Zr element to phase transformation, microstructure, mechanical properties and shape memory effect were examined by means of DCS, optical microscopy, XRD, tensile test, microhardness test, shape memory effect and superelasticity test. The relationship between microstructure, mechanical properties of Ti-25Nb-2Zr alloy and heat treatment and cold work technique was further studied. Meahwhile, the surface of Ti-25Nb-2Zr alloy was modified by oxidization in air. The surface of modified and subsequently immersed in Ca-P solution alloy were characterized by SEM, EDS, XRD, XPS and FTIR. After experiment and theoretical study, the following results are listed as follows:The addition of small amount of Zr element in Ti-25Nb alloy could lowerβtransus, prohibit precipitation of phase and refine its microstructure. Especially, the phase transformation temperature could be lowered by 10 K with addition of 1at% Zr element. The strength of Ti-25Nb alloy initially increased with increasing Zr content, and then it decreased with further addition of Zr element; while the migration trends of elastic modulus and microhardness with increasing Zr content are the opposite of that of the strength. The highest ultimate strength was obtained with 3at% Zr addition while the lowest elastic modulus was get by 2at% Zr addition. The addition of Zr element could influence the Ms of Ti-25Nb alloy. The alloys with 2at% Zr content could precipitate martensite when deformed in room temperature, so the shape memory effect of this alloy is more evident than other alloys.When Ti-25Nb-2Zr alloy was solution treated aboveβtransus, its phase structure retained fullyβphase with low strength and superior plasticity. As solution temperature rised, the microstructure get coarser which lead to the decrease of its strength and plasticity. When aged at 350℃,ωphase appeared in the the alloy; when aged at 450℃, phase emerged in the alloy. When the alloy was cold rolled, stress induced martensite transformation emerged in the alloy. Because of the co-work of martensite transformation and work hardening, the harden effect of the alloy was not obvious when the amount of cold work was small. When Ti-25Nb-2Zr alloy was oxidized in air, the surface oxide of the alloy transform first from metastable titania to anatase, then to stable rutile. When the alloy was oxided in air at 500℃for 2h, SEM and AFM observation showed that the surface roughness of the alloy increased evidently. When the specimen oxidized at 500℃for 2h was immersed in Ca-P solution, Ca-P layer was successfully prepared in the surface of the alloy. XRD analysis showed that the main content of the Ca-P layer was hydroxyapatite. XPS and FTIR analysis showed that CO32- ion existed in the Ca-P layer.更多还原