动高压加载条件下Ti-6Al-4V和Ti-47Nb合金层裂微结构特征与断裂机理

利用平板撞击实验和样品软回收技术,结合光学显微镜(OM)、扫描电子显微镜(SEM)等微观分析手段,研究了动高压加载条件下Ti-6Al-4V和Ti-47Nb 2种不同类型钛合金的层裂微结构特征与断裂机理。结果表明:Ti-6Al-4V合金的抗层裂破坏能力强于Ti-47Nb合金,其原因在于Ti-6Al-4V合金的高强度。Ti-6Al-4V合金层裂微孔洞大多在α/β两相界面处形核并沿相界扩展,而Ti-47Nb合金中的微裂纹是通过微孔洞直接连通形成。随后汇合的大空洞或大裂纹间形成的绝热剪切带(ASB)加速了试样层裂破坏的产生,Ti-6Al-4V与Ti-47Nb合金均表现出了韧性断裂特征。     

Ti-6Al-4V合金表面等离子Nb合金化工艺

采用双辉等离子表面冶金技术对Ti-6Al-4V合金进行等离子渗铌处理。研究了温度与保温时间对合金层元素含量和渗层厚度的影响,以确定最佳渗金属工艺参数。利用光学图像分析仪以及辉光放电能谱仪观察和测定合金层的金相组织、渗层厚度及成分。结果表明,在极间距和气压恒定的条件下,渗层厚度及成分与温度和保温时间有关。温度过高或保温时间过长均会在Ti-6Al-4V试样表面产生较厚的Nb沉积层。经优化工艺参数,选择850℃保温3 h渗铌,得到一定厚度且与基体为冶金结合的合金层。该合金层可以克服Ti-6Al-4V合金耐磨性差的缺点。     

铸造Ti-6Al-4V合金拉伸断裂机理研究

对铸造Ti-6Al-4V合金进行拉伸性能测试,利用KYKY-1000B扫描电子显微镜(SEM)对其断口形貌进行观测,分析其断裂机理.结果表明,铸造Ti-6Al-4V合金拉伸试样裂纹起源于心部;裂纹扩展为穿晶型,断口为准解理型,断裂机理为穿晶型脆性断裂.     

β锻造Ti-6Al-4V合金力学性能各向异性（英文）

研究β锻造Ti-6Al-4V(Ti64)合金拉伸性能和断裂韧性的各向异性。对饼材不同取向的显微组织和晶体学织构进行分析,同时研究取样方向对拉伸性能、断裂韧性的影响。结果表明,Ti64饼材原始β晶粒呈扁平状。室温下合金主要由α相构成,β锻造后β→α相变产生的多个α相变体导致α相织构强度较低。力学性能各向异性的主要影响因素为原始β晶粒形貌以及与α织构相关的滑移。采用J积分阻力曲线法测定合金的起裂韧性,并将起裂韧性KJIC分为内在韧性和外在韧性。内在断裂韧性各向异性主要与原始β晶粒对裂纹尖端塑性区范围的影响相关;外在断裂韧性主要与α片层与集束对裂纹曲折程度的影响相关。     

Nb合金层对Ti-6Al-4V合金电化学性能的影响

采用等离子合金化技术在Ti-6Al-4V合金表面制备Nb合金层。利用电化学扫描法对Nb合金层在10%H_2SO_4溶液中的腐蚀行为进行研究,并同时与Ti-6Al-4V合金基材进行对比分析。结果表明:钛合金表面Nb合金化后形成的合金层与基体结合牢固,成分梯度分布;铌合金层在10%H_2SO_4溶液中的耐蚀性较基体有所提高。     

Ti-6Al-4V激光冲击强化及其微结构响应分析

使用Nd³⁺:YAG脉冲激光器产生的脉冲能量为12.5 J,频率10 Hz,波长1064 nm的脉冲激光研究了强激光冲击下的Ti-6Al-4V合金表面响应,用SEM和TEM及IFFT方法分析了激光冲击强化造成的微结构响应.结果表明,激光冲击可使Ti -6Al- 4V合金表面硬度增加80%以上,残余压应力达到500 MPa以上.在激光冲击产生的超高能量和超高应变率作用下,具有α/β两相结构的Ti-6Al-4V合金的激光冲击强化效应表现出明显的择优倾向.在较低冲击能量下,β相优先获得形变强化;在较高的冲击能量下,α和β相才能同时获得相当的形变强化,且优先强化相出现过饱和强化现象.位错增殖是冲击强化的主要微观机制,增殖形式多为定向发射和位错偶极子,α和β相则以半共格方式协调形变;在冲击强化区域内呈现应变屏蔽现象,其源于形变缺陷的自组织,是材料在激光冲击形变时的微观约束条件和激光冲击单点累积形变方式以及α/β两相的相间强度与结构差异共同作用所致.     

铸造Ti-6Al-4V钛合金疲劳裂纹扩展特性的研究

按照GB6398-1986试验标准,采用紧凑拉伸试样(CT)测定了铸造Ti-6Al-4V钛合金疲劳裂纹扩展速率da/dN,采用扫描电镜(SEM)等现代技术对断口形貌进行观察,分析了不同应力比(R值)条件下的疲劳裂纹扩展特性。结果表明,应力比R对铸造Ti-6Al-4V钛合金的裂纹扩展速率影响较大,应力比R越大,裂纹扩展速率越大。在裂纹预裂区和快速扩展区的断裂机理主要是以微区解理断裂为主,稳态扩展区主要是以疲劳条带扩展机制为主,同时也存在微区解理断裂机制。     

电子束焊接Ti-6Al-4V接头断裂行为机制

研究了电子束焊接Ti-6Al-4V接头组织结构形态对断裂行为机制的影响。焊缝组织为大量柱状晶和等轴晶以及少量的板条马氏体,粗大的针状α+β相和马氏体α'相呈现出多向短针状,焊缝晶粒尺寸为200~350 μm,焊缝区的显微硬度值达到536 HV,焊缝晶粒粗大严重增加了组织的脆性,使其断裂易发生在焊缝区域。焊缝内部的部分微气孔充当着裂纹的起始源,同时由于气孔分布的不均匀性使其断裂裂纹的扩展路径为非直线分支型。由于α/β两相的线膨胀系数的差异,焊缝中存在的两相交错结构,亦使其断裂发生在α/β界面附近处。层错结构的存在造成强烈的位错塞积产生微孔,成为新的裂纹开裂源。     

Taylor杆冲击条件下Ti-6Al-4V合金的动态断裂

通过Taylor杆冲击实验（撞击速度范围为145-306m/s）研究Ti-6Al-4V合金在高应变率加载条件下的动态断裂行为。研究表明：该合金的临界破碎速度为217-236m/s;当撞击速度增大至260m/s时,试样断口表面除平面区及韧窝区外,还存在明显的熔化区域,试样头部端面裂纹分布呈现出自组织特征;试样撞击端面具有圆弧状头部的特殊裂纹,且未在裂纹前端发现变形组织及绝热剪切带;这类特殊的裂纹也是由于绝热剪切带而形成的,沿两最大剪应力方向形核、扩展,并最终相交形成三维＂交错屋脊＂状结构。     

钛和Ti-6Al-4V合金的高能金离子注入

20 稀有金属快报 2002年第12期 钛通常为密排六方(hcp)α相，在1155K以上α相就转变成体心立方的β相。在1155K和高能压力下，α相也能转变成简单六方的ω相。据报道，利用高能离子注入就可以得到ω相。离子注入可以提高钛的表面硬度，从而提高其表面的耐磨性。墨西哥学者利用9MeV的高能金离子对钛和Ti-6Al-4V进行了注入，并影响到金属表层下15m组织结构。 试验所用钛的纯度为99.6%，主要杂质为铝、铬、锰、镍、钒。试样取自经675℃退火的φ9.5mm钛棒，经X射线衍射证实其结构为hcp(a=0.2950nm, c=0.4686nm)；在光学显微镜和SEM下，试…     

Ti-6Al-4V合金高温氧化行为及显微组织研究

分析了Ti-6Al-4V合金在900 _oC,930 _oC,960 _oC温度下的氧化行为及表层显微组织变化。在0.5-24 h时间内,氧化层不断增厚,越靠近表面氧化层越疏松。氧含量在氧化层/富氧层界面的5 μm内发生急剧下降,进入富氧层后缓慢下降直到稳定。氧化层中以TiO₂为主,同时也出现了Al₂O₃。富氧层中的a相含量远远高于基体内部,其晶粒尺寸也发生长大。富氧层深度与热暴露时间的关系可用对数函数描述,通过线性回归分析计算出了O在富氧层中的扩散激活能为206 kJ/mol。     

Turning characteristics of titanium alloy Ti-6Al-4V with high-pressure cutting fluid

This study investigates the effect of high-pressure cutting fluid on the turning characteristics of Ti-6Al-4V alloy. A noncoated carbide tool was used to measure the cutting temperature using a tool-work thermocouple technique, and the cutting characteristics were evaluated with respect to the cutting temperature, chip breakability, and tool wear. Furthermore, the viability of TiAlN/AlCr₂O₃-coated tool was examined. The coolant jet when placed towards the cutting zone on the rake face is effective in reducing the cutting temperature because of the reduction in the chip-tool contact length. Based on this result, tools with a textured rake face were examined.     

Dynamics of chip formation during orthogonal cutting of titanium alloy Ti-6Al-4V

Polished and etched disks of titanium alloy Ti-6Al-4V were machined in a series of continuous and interrupted orthogonal cutting tests on a specially adapted lathe. A high-speed imaging system with a microscope lens and strobed copper-vapour laser illumination system enabled direct observation of the chip formation zone at a recording rate of 24,000 frames/s. The chip formation cycle was recorded for cutting speeds from 4 to 140 m/min. Segmented chips were observed throughout. Image analysis of the recorded video sequences examined the resulting chip segment geometry, the segmentation frequency and the critical strain required to initiate shear band formation.     

Ti-42Al-8Nb合金氧化膜的XPS研究

以Ti-42Al-8Nb(at%)合金为研究对象,将其置于900℃空气气氛中氧化20 h,重点采用XPS手段对合金表面氧化膜结构、相组成及成分分布进行了分析。结果表明:合金经20 h氧化后,XRD结果显示氧化膜主要由Al_2O_3和Ti O_2混合物组成,而经XPS结果分析可知氧化膜最外层只有Ti O_2一种物质,次外层由Al2O3、3种不同价态的Ti氧化物及少量Ti N组成,且沿基体到外表层的方向,Ti的高价氧化物含量逐渐增多,最外表面只有Ti O_2,另外2种低价Ti氧化物含量为零,说明整个系统通过O原子的溶解、扩散完成氧化过程,导致氧化反应随时间和样品深度发生阶段性变化,从而使氧化膜沿深度方向表现出物质种类及其含量的不同。     

细晶Ti-6Al-4V宽幅板材的超塑性变形机理及组织演变

通过恒应变速率拉伸试验,在1103~1223 K温度范围、3.2×10-4~1×10-2s-1应变速率范围内,研究了Ti-6Al-4V宽幅板材的超塑性,在实验中获得了100%-604%的延伸率。分析了组织演变和变形机理,结果表明,其主要变形机理为晶界滑移,以晶内位错运动和β相的晶内滑移为协调机制。实验中还发现在低温下变形时,Ti-6Al-4V宽幅板材存在各向异性,当在高温下变形时,各向异性不太明显。     

Compression fatigue behavior of Ti-6Al-4V mesh arrays fabricated by electron beam melting

This paper focuses on the compression fatigue behavior of Ti-6Al-4V mesh arrays with high porosities of ∼60-85%, which were fabricated by an additive manufacturing technique using electron beam melting. The results show that their fatigue lives are mainly determined by uniform deformation through the entire specimens, while their failures are characterized by rapid strain accumulation and a severe crush band at an angle of 45° to the cyclic loading direction. The relation between the relative fatigue strength and relative density can be evaluated by the well-known Gibson-Ashby model with the exponential factor n being 2.7, which is higher than the reported data for aluminum and nickel foams, and almost double the idealized value (n = 1.5) of a stochastic open cellular foam. The underlying mechanism of fatigue failure appears to be interaction between cyclic ratcheting and fatigue crack initiation and propagation, while the former plays a dominant role in fatigue life. TEM observations found that dislocations are generated along the interface of the α′ phase and their generation becomes more evident with an increase in the relative density. This would contribute to the retardation of cyclic ratcheting and an improvement in the fatigue strength.     

Ti-4.5Mo-5.1Al-1.8Zr-1.1Sn-2.5Cr-2.9Zn钛合金的动态力学性能及失效研究

针对近β型Ti-4.5Mo-5.1Al-1.8Zr-1.1Sn-2.5Cr-2.9Zn新型钛合金,研究了轧制及热处理2种状态下材料的动态力学性能及其失效行为。结果表明,经880℃多道次轧制,获得由β相基体及"等轴+条状"非均匀分布的α相组成的双态组织;经895℃保温0.5 h炉冷热处理后,其组织则由β相及完全等轴化的α相构成。3100～3800 s~(-1)不同应变率条件下的动态压缩试验结果表明,轧制态钛合金较热处理态钛合金的动态抗压缩强度高出200～400 MPa,最高可达2133 MPa,但其临界断裂应变则明显较低,最高仅10.8%;热处理后,虽然动态抗压缩强度有所下降,但临界断裂应变最高可达23.6%,表现出良好的强塑性匹配特性。进一步研究发现,轧制态钛合金高的位错密度及非均匀的组织分布特征,导致其在动态压缩过程中出现分叉的绝热剪切带,断口呈现出平滑区及韧窝区2种特征,表明其断裂机制为脆性断裂+韧性断裂;而热处理态钛合金断口则以韧窝区为主,表明其断裂机制为韧性断裂。相关研究为该新型合金的工程化制备及应用提供了理论及技术支撑。     

Tool development based on modelling and simulation of hot sheet metal forming of Ti-6Al-4V titanium alloy

In the aero engine industry alternative manufacturing processes for load carrying aero engine structures imply fabrication. The concept of fabrication involves simple forgings, sheet metals and small ingots of e.g. titanium alloys which are welded together and heat treated. In the concept phase of the product development process, accurate evaluations of candidate manufacturing processes with short lead times are crucial. In the design of sheet metal forming processes, the manual die try out of deep drawing tools is traditionally a time consuming, expensive and inexact process. The present work investigates the possibility to design hot forming tools, with acceptable accuracy at short lead times and with minimal need for the costly die try out, using finite element (FE) analyses of hot sheet metal forming in the titanium alloy Ti-6Al-4V. A rather straightforward and inexpensive approach of material modelling and methods for material characterisation are chosen, suitable for early evaluations in the concept phase. Numerical predictions of punch force, draw-in and shape deviation are compared with data from separate forming experiments performed at moderately elevated temperatures. The computed responses show promising agreement with experimental measurements and the predicted shape deviation is within the sheet thickness when applying an anisotropic yield criterion. Solutions for the hot forming tool concept regarding heating and regulation, insulation, blank holding and tool material selection are evaluated within the present work.     

TEM investigations on hydrogen induced phase transformation in Ti-6Al-4V alloys

The TEM and HRTEM were utilized to investigate the phase transformation of hydrogenated Ti-6Al-4V alloys (0 wtpct-0.9 wt pct H) treated by annealing and quenching from β field. The results indicate that the orthorhombic α' martensite and β phase appear progressively with the increase of hydrogen concentration. On the other hand, hydrides with sizes of 2-5 nm are observed in the specimens containing more than 0.6 wt pct hydrogen. The formation of α' and twins can be attributed to the internal stress caused by solid solution of hydrogen and hydrides precipitation.