中国有色金属学报

文章编号:1004-0609(2010)S1-s0930-07

组合思想在钛合金研究中的应用与钛合金组合芯片的表征

秦冬阳,卢亚锋

(西北有色金属研究院,西安 710016)

摘 要:

综述组合思想在二元和多元钛合金体系中的应用。对于某个确定的钛合金系,组合方法能全面地研究其中的相变规律和组分对合金力学性能的影响。以组合思想为指导,选择Ti-Al-V系和Ti-Al-V-Cr-Mo 2个典型合金体系,利用IM100旋转多靶离子束沉积系统制备出合金元素含量梯度变化的钛合金组合芯片,通过X射线衍射仪(XRD)、原子力显微镜(AFM)、X线光电子谱仪(XPS)表征薄膜态样品库的存在相、形貌和表面元素的化学状态。利用纳米压痕测试钛合金薄膜的硬度,并从Ti-Al-V系和Ti-Al-V-Cr-Mo系中发现2个力学性能最佳的合金组分。

关键词:

钛合金相变薄膜组合方法组合材料芯片技术

中图分类号:TF 804.3       文献标志码:A

Application of COMBI in study of titanium alloys and characterization of titanium combinatorial libraries

QIN Dong-yang, LU Ya-feng

( Northwest Institute for Non-ferrous Metal Research, Xi’an 710016, China)

Abstract: The application of the combinatorial material chip technology (COMBI) which is widely used in research of titanium alloys was summarized. For a multi-element titanium alloy system, it is possible to explore the relationship between alloying element contents and mechanical properties. On the basis of this method, two typical material chips of titanium alloys such as Ti-Al-V and Ti-Al-V-Cr-Mo system were fabricated by an ion beam sputtering method in the form of combinatorial material chip. The phase transformations of the samples in the libraries were identified by XRD. The morphology of samples were observed by the atomic force microscope (AFM). The chemical states of the elements in the libraries were characterized by X-ray photoelectron spectrocopy (XPS). The nanoindentation experiments were carried out to extract the hardness of the films. Furthermore, the composition with the highest hardness in each library were selected.

Key words: titanium alloys; phase transformations; thin films; combinatorial methods; combinatorial material chip technology (COMBI)

组合思想可以研究一种或多种元素的含量变化对材料体系相变规律和力学性能的影响。组合材料方法现已经应用于高温超导材料[1]、铁电/介电材料[2-3]、发光材料[4-8]、磁阻材料[9-10]和钛铝合金[11-12]等研究领域。组合思想在钛合金研究中也有着充分地体现,鉴于钛合金相变的多样性与复杂性,组合思想能够系统地分析钛合金中相变和组织的特点。

组合思想在多个钛合金体系中都有着充分的体现。在Ti-Al系中,HAN等[12]利用薄膜法,在500 ℃的单晶(100)Si基片上利用磁控溅射方法沉积了1 μm厚的梯度Ti-Al薄膜,并用纳米压痕系统地对薄膜的力学性能进行了表征,并分析了Al含量的变化对体系的相变影响。BANERJEE[13]通过粉末激光沉积技术,制备出梯度Ti-V合金,并研究了其组织与力学性能的特点。在Ti-Mo体系中,COLLINS[14]利用粉末激光沉积技术,制备出梯度Ti-Mo合金,分析了Mo含量对体系相变与力学性能的影响。NILSON[15]研究了铸造态二元Ti-xMo合金的相组成。在Ti-Ta体系中,ZHOU[16]研究了淬火态Ti-xTa(x=10%, 20%, 30%, 40%, 50%, 60%, 70%和80%)合金的相组成和力学性能特点。NAG[17]利用粉末激光成型法,制备了Ta含量梯度变化的Ti-Ta合金,研究了Ta含量的变化对合金组织与力学性能的影响。另外,MARDARE[18]利用组合方法,通过离子束多靶共溅射技术制备Ta元素梯度变化、厚度为300 nm的Ti-Ta薄膜,随后研究了合金薄膜的耐蚀性。Ti-Cr系和Ti-Cr-Zr系钛合金是目前应用较广的人造牙齿材料,TAKEMOTO[19]研究了铸造态Ti-xCr(x=0%,5%,10%,15%和20%)合金在口腔环境中的腐蚀机理和耐蚀性能。HOA[20]研究了铸造态Ti-xCr(x=0%,5%,10%,15%, 20%,25%和30%)合金的弯曲强度特点。CHENG[21]研究了Ti-10Zr-xCr (x=1%,3%,5%,7%和10%)铸造合金的力学性能和相组成。HOA[22]研究了Ti-10Zr-xCr (x=1%,3%,5%,7%和10%)铸造合金的耐磨性。Ti-Nb-Zr-Ta系合金是目前被认为最具医用前景的合金体系之一[17],目前,Ti-35Nb-7Zr-5Ta[23]合金已经成功研发。BANERJEE[24]利用激光粉末法,研究了Ti-Nb-Zr-Ta四元合金体系中Nb含量和α相的体积分数对合金力学性能的影响,预测出合金成分为Ti-32Nb-10Zr-5Ta,且如果通过合适的热处理制度将α相体积分数控制在20%,具有强度和弹性模量的最佳匹配。SAKAGUCHI[25]和SAHA[26]研究了Nb和Ta含量对Ti-Nb-Zr-Ta四元合金相变规律、弹性模量和变形机制的影响,通过成分调整,在合金体系中成分为Ti-30Nb-5Zr-15Ta淬火态合金的弹性模量低至68.8 GPa。

组合思想已经应用于钛合金研究领域,并取得了大量研究成果,但多数研究者每次制备单个试样,仍以传统的熔炼方式研发钛合金。组合材料芯片技术能够摆脱传统的材料研究方法,其最大的优势在于每次制备大量的样品,构成样品库,样品库中的试样为薄膜形式,这种研究方法大幅度地提高了研发效率和发现性能优异钛合金的几率。

1  实验

用于制备组合材料芯片的设备是IM100离子束材料芯片沉积系统(Intematix corp),该系统在超高真空条件下通过离子束溅射方法沉积出合金元素含量梯度变化的薄膜,实验使用了单晶MgO基片。该系统主要由主体部分、真空系统、离子束溅射系统、膜厚检测系统和精确定位掩膜系统5部分组成。主体部分包括主工作腔、预备腔和可移动样品台以及电源系统。主工作腔(也就是薄膜沉积腔)与低温泵直接相连,可以获得超高真空。预备腔是送样腔,其真空度比主工作腔稍低。采用两级真空可以保证在不破坏主工作腔的真空条件下更换样品。可移动的样品台可自由伸缩于主工作腔和预备腔中,其后端连接一个MDC磁力耦合引导杆,负责取/送样品。真空系统由3级真空设备组成:机械泵、分子涡轮泵和高速低温泵。它们分别能使腔体内真空度达到10-1,10-4和10-6 Pa数量级。多靶旋转系统位于主工作腔中,可安装5个独立的3英寸靶材,靶材可以旋转,其旋转速度可调,可使离子束均匀地打在靶上。

图1所示为该系统的工作原理示意图。沉积薄膜的厚度使用石英振子膜厚测定仪检测。连续高精度移动掩膜则可用来制备连续梯度变化的材料芯片。系统工作过程中离子源的功率为30 W,高纯Ar气(纯度为99.995%)的流量为3~4 L/min。

图1  IM100离子束材料芯片沉积系统工作原理示意图

Fig.1  Schematic diagram of IM100 ion beam sputtering deposition system

用于离子束溅射的Ti、Al、V、Cr和Mo高纯度金属靶材购买于阿法埃莎(天津)化学有限公司,选用纯度分别为99.995%、99.999%、99.5%、99.991%和99.95%。单晶(100)MgO基片。基片首先在沸腾的碱性溶液中清洗20 min,然后在丙酮溶液中清洗,再经过去离子水反复冲洗后用红外灯烘干备用。在沉积过程中Ti、Al、V、Cr和Mo的沉积速率分别为0.05、0.04、0.05、0.07和0.05 nm/s。制备出的多层单质金属薄膜在KTL-1600管式氩气保护退火退火炉中完成合金化,高纯Ar气(纯度为99.995%)的流量为48 L/min。

利用理学D/max2500强力转靶全自动X射线衍射仪分析了样品库中的相组成,采取间断扫描的方式,X射线源为Cu Kα1、管电压为40 kV,管电流200 mA。利用PHI-5300 X射线光电子能谱仪(XPS)表征了样品库表面元素的化学状态,X射线源为Mg Kα。利用MTS-XP型纳米压痕仪测试了材料芯片的硬度,实验中采用玻氏压针(Berkovich tip)、连续刚度法(CSM)测量技术、应力加载速率为0.05 /s、泊松比为0.25、每个试样测试10个点、点间距大于50 μm。实验利用SPI3800-SPA-400型原子力显微镜观察了样品库的形貌。实验利用JSM6760型扫描电镜中的EDS附件测试了样品的成分。

图2所示为Ti-Al-V系样品库的示意图。其中每个正方形代表一种组分不同、面积相同(6.25 mm× 6.25 mm)的钛合金薄膜。样品库的名义成分为Ti-(2%~8%)Al-(3%~10%)V,Al含量在Al元素含量坐标轴方向上梯度增加、V含量在V元素含量坐标轴方向上梯度增加。每个样品钛沉积的厚度均为200 nm,Al和V的沉积厚度由其名义成分决定。

图2  Ti-Al-V系样品库示意图

Fig.2  Schematic diagram of Ti-Al-V library

Ti-Al-V-Cr-Mo样品库中合金元素含量的变化规律如图3所示,其中每个正方形代表一种组分不同、面积相同(6.25 mm×6.25 mm)的钛合金薄膜。体系中的名义成分为Ti-(2%~6%)Al-(4%~10%)V-(1%~5%)Cr- (3%~10%)Mo,目的是在Mo含量变化范围较大的条件下,研究样品库内合金元素的变化对相变的影响。

2  结果与讨论

为了证明合金化后样品成分与名义成分的一致性,表1列出Ti-Al-V系经合金化退火后的4个样品

图3  Ti-Al-V系样品库示意图

Fig.3  Scheme of Ti-Al-V library

的EDS测试成分和名义成分。样品中EDS测出V元素的含量与名义成分基本一致,Al元素的含量存在着一定的差别,这是由于EDS对薄膜样品中原子量较小的Al元素测试不精确性造成的。但是EDS测试出的不同样品中Al元素含量的变化规律与名义成分中Al元素的变化规律一致。

表1  Ti-Al-V系4个样品经合金化退火后EDS测试成分和名义成分

Table 1  Normal composition and tested composition of samples in Ti-Al-V library

Ti和V都是较为活泼的金属元素,利用XPS方法分析了薄膜表面的样品库表面元素的化学状态。图4所示为合金化退火后Ti-5V-6Al试样Ti和V的窄能量范围谱。由图4可以看出,Ti和V元素都发生了化学位移,电子结合能较单质状态相比都增大,其中Ti元素以+4价存在;V元素以+5价存在,说明样品的表面存在着TiO2和V2O5,但在XRD衍射谱中未发现TiO2和V2O5相的衍射峰,说明样品库在合金化退火中发生微弱的氧化,不会影响后续力学性能的测试。这种微弱的氧化是由于合金化退火升温过程中吸附在样品库表面的氧原子脱离薄膜表面,而扩散泵的工作参数恒定使其不能在短时间内使系统的真空度维持在10-3 Pa,此时系统的真空度仅为10-1 Pa,在高温条件下O与Ti和V形成氧化物。

在合金化退火过程中薄膜试样发生结晶与合金元素扩散化等变化,合金化退火后的表面形貌与沉积态相比会发生明显的变化,同时合金化退火条件也会影响着薄膜表面的形貌。实验利用原子力显微镜和扫描电子显微镜观察了样品库中部分样品的表面形貌。

图5所示为名义成分为Ti-5V-xAl(x=3%,5%,6%和8%)样品经550 ℃合金化退火后原子力显微镜像。样品的晶粒形状均为颗粒状,但是晶粒尺寸和均匀性有一定的区别。名义成分为Ti-5V-6Al的试样的晶粒尺寸最小,直径约为50 nm;其他名义成分试样晶粒尺寸接近,在100~200 nm之间,但是成分为Ti-5V-5Al试样的晶粒尺寸最均匀。

图6所示为名义成分为Ti-3Al-3Mo-xV-yCr(x=2%, 5%, 7%和10%;y=1%, 2%, 4%, 5%)样品经600 ℃合金化退火后的原子力显微镜像。由图6可看出,除了Ti-3Al-5V-2Cr-3Mo合金薄膜的组织为大小均一的三


图4  合金化退火后Ti-5V-6Al试样Ti和V的XPS谱

Fig.4  XPS spectrum of Ti and V of Ti-5V-6Al sample after annealing: (a) Ti2p; (b) V2p

图5  Ti-5V-xAl合金样品经550 ℃合金化退火后的AFM像

Fig.5  AFM images of Ti-5V-xAl alloys annealed at 550 ℃ for 1 h: (a) Ti-5V-3Al; (b) Ti-5V-5Al; (c) Ti-5V-6Al; (d) Ti-5V-8Al

图6  Ti-3Al-3Mo-2V-1Cr, Ti-3Al-3Mo-5V-2Cr, Ti-3Al-3Mo-7V-4Cr和Ti-3Al-3Mo-10V-5Cr薄膜经600 ℃合金化退火后的AFM像

Fig.6  AFM images of Ti-3Al-3Mo-2V-1Cr(a), Ti-3Al-3Mo-5V-2Cr(b), Ti-3Al-3Mo-7V-4Cr(c) and Ti-3Al-3Mo-10V-5Cr(d) samples annealed at 600 ℃ for 1 h

角形晶粒之外,其他样品的晶粒形状均为颗粒状。

从上述分析可以得出以下结论:

1) 合金化制度对样品库的形貌影响较大,合金化退火温度的升高会使晶粒尺寸增大。

2) 钛合金薄膜的形貌与传统块状钛合金的形貌有所差别。传统钛合金在高温β相区缓冷后会得到片层状的α相组织,经过变形热处理的钛合金的组织随着后续热处理制度的不同α相的形状变化较多,但是本实验以钛合金薄膜为研究对象,观察到得薄膜的形貌主要以等轴颗粒状为主,少数试样中出现了三角形颗组织。

3) 传统钛合金中α相和β相的形貌有所差别,α相以单一或多种形态分布在β相基体上,本实验目前状态下无法从形貌来区别α相和β相,α相和β相可以通过XRD等晶面衍射的方法来鉴定。

Ti-Al-V系样品库中成分为Ti-5Al-2V的样品经合金化处理炉冷后的XRD谱如图7所示。由图7可看出,在室温条件下出现β相证明V与钛形成了固溶体,样品库中存在少量Al单质说明Al没有完全固溶在Ti中,仍有部分以Al单质的形式存在。与后续高温合金化处理的XRD谱相比,Ti-Al-V系样品库的衍射峰的强度较弱,峰宽较大,虽然Al和V已经扩散较为充分,但薄膜结晶化程度不好。图8所示为Ti-3Al-3Mo-xV- yCr(x=2%, 5%, 7%, 10%;y=1%, 2%, 4%, 5%)样品合金化处理后的XRD谱。从图8中可以看出,随着系统中Mo含量的增加,α相的衍射峰减少,强度减弱;β的衍射峰数量曾多,强度增加;合金系中Mo含量最高的钛合金薄膜以单相β钛合金的形式存在。

图7  Ti-5Al-2V薄膜合金化处理后的XRD谱

Fig.7  XRD pattern of Ti-5Al-2V thin films after alloying

图8  Ti-Al-V-Cr-Mo(Ⅰ)样品库中4个样品合金化处理后的XRD衍射谱

Fig.8  XRD patterns of four samples in Ti-Al-V-Cr-Mo (Ⅰ) library: (a) Ti-3Al-10V-5Cr-3Mo; (b) Ti-3Al-7V-4Cr-3Mo; (c) Ti-3Al-5V-2Cr-3Mo; (d) Ti-3Al-2V-1Cr-3Mo

纳米压痕系统可以表征出薄膜的硬度和模量,但是容易受到基片力学性能的影响[26]。对于一个合金体系,本实验假设基片对样品库中所有样品的影响程度相同,这样就可以利用纳米压痕系统表征出样品库力学性能的变化趋势。图9所示为Ti-3Al-5V-2Cr-3Mo试样的硬度—深度曲线。样品库中所有样品的硬度—深度曲线都与其类似,由于曲线光滑、连续,证明压头压入过程中薄膜没有发生断裂。试验测得的2个样品库的硬度如图10所示。由图10可看出,在2个合金体系中,成分为Ti-5V-5Al和Ti-3Al-3Mo-5V-2Cr的合金具有最高的硬度。Ti-5V-Al[26]薄膜具有最高的硬度是由于组织的均一性引起的,而Ti-3Al-5V-2Cr-3Mo合金薄膜大小均一的三角形晶粒是其硬度提高的主要原因。另外Ti-3Al-5V-2Cr-3Mo

图9  Ti-3Al-5V-2Cr-3Mo试样的硬度—深度曲线

Fig.9  Hardness—depth curve of Ti-3Al-5V-2Cr-3Mo thin films

图10  Ti-Al-V和Ti-Al-V-Cr-Mo(Ⅰ)样品库中部分样品的显微硬度

Fig.10  Microhardnesses of samples in Ti-Al-V(a) and Ti-Al-V-Cr-Mo(Ⅰ)(b) libraries

合金薄膜的硬度高于Ti-5V-AlTi-3Al- 5V-2Cr-3Mo合金薄膜的,这是由于Cr和Mo的固溶强化效应引起的。本实验测定的2个样品库中部分样品的硬度高于HAN等[12]测定的Ti-Al薄膜的硬度,其中V,Cr和Mo的固溶强化作用是主要原因。

3  结论

实验利用组合材料芯片技术,制备出了Ti-Al-V系和Ti-Al-V-Cr-Mo系样品库,在样品库经合金化后,分析了样品库相变规律,确定出了Ti-5V-5Al和Ti-3Al-3Mo-5V-2Cr 2种具有最佳力学性能的合金组分,完成了一种新的钛合金设计流程。

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[12] HAN S M, SHAH R, BANERJEE R. Combinatorial studies of mechanical properties of Ti-Al thin films using nanoindentation[J]. Acta Materialia, 2005, 53: 2059-2066.

[13] BANERJEE R. Microstructural evolution in laser deposited compositionally graded α/β titanium-vanadium alloys[J]. Acta Materialia, 2003, 51: 3277-3282.

[14] COLLINS P C. Laser deposition of compositionally graded titanium-vanadium and titanium-molybdenum alloys[J]. Materials Science and Engineering A, 2003, 352: 118-125.

[15] NILSON T C, OLIVEIRA. Development of Ti-Mo alloys for biomedical applications: Microstructure and electrochemical characterization[J]. Materials Science and Engineering A, 2007, 452: 727-731.

[16] ZHOU Ying-long. Effects of Ta content on Young’s modulus and tensile properties of binary Ti-Ta alloys for biomedical applications[J]. Materials Science and Engineering A, 2004, 371: 283-290.

[17] NAG S. A novel combinatorial approach for understanding microstructural evolution and its relationship to mechanical properties in metallic biomaterials[J]. Acta Biomaterialia, 2007, 3: 369-376.

[18] MARDARE A I. A combinatorial passivation study of Ta-Ti alloys[J]. Corrosion Science, 2009, 51: 1519-1527.

[19] TAKEMOTOA S. Corrosion mechanism of Ti-Cr alloys in solution containing fluoride[J]. Dental Materials, 2009, 25: 467-472.

[20] HOA W F. Mechanical properties and deformation behavior of cast binary Ti-Cr alloys[J]. Journal of Alloys and Compounds, 2009, 468: 533-538.

[21] CHENGA C H. Effects of chromium addition on structure and mechanical properties of Ti-10Zr alloy[J]. Journal of Alloys and Compounds, 2009, 484: 524-528.

[22] HOA W F. Effects of Cr addition on grindability of cast Ti-10Zr based alloys[J]. Materials Chemistry and Physics, 2010, 121: 465-471.

[23] AHMED T A, LONG M, SILVERSTRI J, RUIZ C, RACK H J. A new low modulus biocompatible titanium alloy[J]. Titanium 95’: Sci Technol, 1996: 1760-1767.

[24] BANERJEE R. A novel combinatorial approach to the development of beta titanium alloys for orthopaedic implants[J]. Materials Science and Engineering C, 2005, 25: 282-289.

[25] SAKAGUCHI N. Effect of Ta content on mechanical properties of Ti-30Nb-Xta-5Zr[J]. Materials Science and Engineering C, 2005, 25: 370-376.

[26] SAHA R. Effects of substrate on the determination of thin film mechanical properties by nanoindention[J]. Acta Materialia, 2002, 50: 23-38.

(编辑 陈爱华)

基金项目:国家科技支撑计划项目(2007BAE07B03)

通信作者:秦冬阳;电话:029-86231078;E-mail: qindongyang19831205@126.com


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[12] HAN S M, SHAH R, BANERJEE R. Combinatorial studies of mechanical properties of Ti-Al thin films using nanoindentation[J]. Acta Materialia, 2005, 53: 2059-2066.

[13] BANERJEE R. Microstructural evolution in laser deposited compositionally graded α/β titanium-vanadium alloys[J]. Acta Materialia, 2003, 51: 3277-3282.

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[16] ZHOU Ying-long. Effects of Ta content on Young’s modulus and tensile properties of binary Ti-Ta alloys for biomedical applications[J]. Materials Science and Engineering A, 2004, 371: 283-290.

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[18] MARDARE A I. A combinatorial passivation study of Ta-Ti alloys[J]. Corrosion Science, 2009, 51: 1519-1527.

[19] TAKEMOTOA S. Corrosion mechanism of Ti-Cr alloys in solution containing fluoride[J]. Dental Materials, 2009, 25: 467-472.

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[21] CHENGA C H. Effects of chromium addition on structure and mechanical properties of Ti-10Zr alloy[J]. Journal of Alloys and Compounds, 2009, 484: 524-528.

[22] HOA W F. Effects of Cr addition on grindability of cast Ti-10Zr based alloys[J]. Materials Chemistry and Physics, 2010, 121: 465-471.

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[24] BANERJEE R. A novel combinatorial approach to the development of beta titanium alloys for orthopaedic implants[J]. Materials Science and Engineering C, 2005, 25: 282-289.

[25] SAKAGUCHI N. Effect of Ta content on mechanical properties of Ti-30Nb-Xta-5Zr[J]. Materials Science and Engineering C, 2005, 25: 370-376.

[26] SAHA R. Effects of substrate on the determination of thin film mechanical properties by nanoindention[J]. Acta Materialia, 2002, 50: 23-38.