Warm bending mechanism of extrados and intrados of large diameter thin-walled CP-Ti tubes

In order to develop the warming bending technology of the large diameter thin-walled（LDTW） commercial pure titanium alloy CP-Ti tubes, the warm bending mechanism of the extrados and intrados of LDTW CP-Ti tubes was researched. By EBSD analysis and Vickers hardness test, the changes of microstructure and strength of the tubes at different bending temperatures of 293, 423 and 573 K, were analyzed. The results show： 1） The extrados of the bent tube deforms mainly by slip, along with few twinning, and the preferred orientation is similar to that of the initial tube; the intrados of the bent tube experiences compression deformation mainly by {1 012} tensile twinning, and the twinning makes the preferred orientation of wall materials change sharply. 2） The Vickers hardness values of both the extrados and intrados of the samples after bending increase greatly; the Vickers hardness values of the intrados are much higher than those of the extrados, and Vickers hardness values of the RD-TD planes are always higher than those of the RD-LD planes, which are related to the different deformation mechanisms.

Experimental and numerical investigations of interface properties of Ti6Al4V/CP-Ti/Copper composite plate prepared by explosive welding

Explosive welding technique is widely used in many industries.This technique is useful to weld different kinds of metal alloys that are not easily welded by any other welding methods.Interlayer plays an important role to improve the welding quality and control energy loss during the collision process.In this paper,the Ti6Al4V plate was welded with a copper plate in the presence of a commercially pure titanium interlayer.Microstructure details of welded composite plate were observed through optical and scanning electron microscope.Interlayer-base plate interface morphology showed a wavy structure with solid melted regions inside the vortices.Moreover,the energy dispersive spectroscopy analysis in the interlayer-base interface reveals that there are some identified regions of different kinds of chemical equilibrium phases of CueTi,i.e.CuTi,Cu_(2)Ti,CuTi_(2),Cu_(4)Ti,etc.To study the mechanical properties of composite plates,mechanical tests were conducted,including the tensile test,bending test,shear test and Vickers hardness test.Numerical simulation of explosive welding process was performed with coupled Smooth Particle Hydrodynamic method,Euler and Arbitrary Lagrangian-Eulerian method.The multi-physics process of explosive welding,including detonation,jetting and interface morphology,was observed with simulation.Moreover,simulated plastic strain,temperature and pressure profiles were analysed to understand the welding conditions.Simulated results show that the interlayer base plate interface was created due to the high plastic deformation and localized melting of the parent plates.At the collision point,both alloys behave like fluids,resulting in the formation of a wavy morphology with vortices,which is in good agreement with the experimental results.

Influence of flash trap profiles on joint properties of friction welded CP-Ti tube to 304L stainless steel tube plate using external tool

Titanium tube and stainless steel tube plate were welded by an innovative friction welding of tube to tube plate using an external tool (FWTPET). Copper was used as an interlayer for joining the dissimilar materials and also to minimize the effect of intermetallics formed at the joint interface. The process parameters that govern FWTPET process are plunge rate, rotational speed, plunge depth, axial load and flash trap profile. Among them, the flash trap profile of the tube has a significant influence on the joint integrity. Various flash trap profiles like vertical slots, holes, zig-zag holes, and petals were made on the titanium tube welded to the stainless steel tube plate. Macroscopic and microscopic studies reveal defect-free joints. The presence of copper interlayer and intermetallics was evident from X-ray diffraction (XRD), scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS) studies. The microhardness survey was presented across and along the interface. A novel test procedure called “plunge shear test” was developed to evaluate the joint properties of the welded joints. The highest shear fracture load of 31.58 kN was observed on the sample having petals as flash trap profile. The sheared surfaces were further characterized using SEM for fractography.

Effects of various sintering methods on microstructure and mechanical properties of CP-Ti powder consolidations

Effects of various sintering methods such as spark plasma sintering(SPS), hot pressing(HP) and electric resistance sintering(ERS) on the microstructure and mechanical properties of commercial pure titanium(CP-Ti) powder consolidations with particle size of <147 μm, <74 μm and <43 μm were studied. The smaller particle powders are densified to proceed at a higher rate. Dense titanium with relative density up to 99% is found to take place at 850 °C under 30 MPa of SPS and HP condition. However, in case of ERS, CP-Ti powders were densified almost at 950 °C under 30 MPa. The microstructure of sintered titanium is composed of equiaxed grains at 850-950 °C. The yield strength of sintered body composed of <43 μm powder is 858 MPa by using SPS at 850 °C under 30 MPa. When there is a higher content of small particle, the higher yield strength value is obtained both by using SPS and HP. However, when ERS is introduced, the highest yield strength is 441 MPa at 950 °C under 30 MPa, which shows much lower values than those by SPS and HP methods. ERS method takes much less sintering time compared with SPS and HP. Nevertheless, higher sintering temperature results in lower strength and elongation because of brittle fracture.

CP-Ti激光焊接接头组织与性能研究

采用光学显微镜等观察和测试CP-Ti激光焊接头组织和硬度,对比接头在酸性、中性和碱性环境中的耐腐蚀性能。结果表明:接头各区域组织均为α相,其中焊缝中的α晶呈针状、锯齿状和板条状3种形貌,在热影响区则为锯齿状。硬度测试表明,焊缝为接头硬度值最高区域,显微硬度达到210 HV,热影响区次之,约为165 HV。接头在酸性环境中的耐蚀性最差,表现为其电流密度、腐蚀速率均高于碱性和中性环境中的。

CP-Ti在含氟离子硝酸中电化学腐蚀行为

采用开路电位(OCP)、动电位极化曲线(PPC)、电化学阻抗谱(EIS) 3种电化学测试手段对工业纯钛(CP-Ti)在含氟离子硝酸溶液中的电化学腐蚀行为进行研究。结果表明:随着硝酸溶液中氟离子浓度的增加,CP-Ti耐蚀性变差;影响CP-Ti耐蚀性转变的临界氟离子浓度为1. 25 mmol/L;氟离子与CP-Ti表面的氧化膜发生反应,致使均匀、致密的氧化膜溶解转变为多孔膜,降低了CP-Ti的耐蚀性。

CP-Ti棒材加热拉压不对称变形研究

近年来,随着国民经济的发展和国防工业建设的突飞猛进,高性能、轻量化高端精密构件的技术性需求日益增加。CP-Ti是一种新型结构材料,具有密度小、比强度高、抗蚀抗疲劳等优异的综合性能,能够满足新型飞机研制对机身减重、提高飞行机动性等方面的需求,在航空、航天、汽车、造船等行业获得日益广泛的应用,其中钛产量中约70%用于航空宇航工业。然而CP-Ti在室温下塑性变形过程中存在变形抗力大、延伸率很低、材料流动性差以及成形质量差等问题,如何提高CP-Ti的塑性成形能力成为其塑性变形过程研究中亟待解决的问题。本文选取CP-Ti棒材,通过对棒材试样进行不同温度、速率的单向拉压试验,获得其真应力-真应变曲线,并分析其在拉压加载下的硬化关系。

室温动态等径角挤压CP-Ti的变形孪晶研究

室温下运用动态等径角挤压(D-ECAP)技术实现了工业纯钛(CP-Ti)在L型模具内的高应变率剪切变形,结合电子背散射衍射(EBSD)技术研究了CP-Ti动态剧烈塑性变形过程中的孪生行为。结果表明,D-ECAP变形在CP-Ti中激发了大量的一次{1122}和{1012}孪晶,同时生成了少量的一次{1121}、{1011}、{1123}和{1124}孪晶。在单个晶粒内部,一次{1122}压缩孪晶和一次{1012}拉伸孪晶分别存在四种和两种孪晶变体,以一次{1122}压缩孪晶和一次{1012}拉伸孪晶为基体可进一步激发二次{1122}-{1121}、{1122}-{1012}和{1012}-{1122}孪晶以及三次{1122}-{1012}-{1122}和{1012}-{1122}-{1012}孪晶,其中二次{1122}-{1012}和{1012}-{1122}孪晶均存在两种孪晶变体。

Improving tribological properties of CP-Ti by in-situ fabrication of Ti-WC surface composite using a pinless WC-Co stirring tool

A surface Ti-WC composite was fabricated on CP-Ti by surface friction stirring(SFS)using a pinless WC-Cotool at a processing window of 800−2500 r/min and 8−50 mm/min.At 1600 r/min-50 mm/min,a defect-free compositelayer with an average hardness of~HV 1170 is formed.The hardness was increased by WC and TiN reinforcingparticles,dissolved Co atoms in Ti,and the formation of ultrafine grains.WC particles were incorporated into the Tisubstrate owing to the intense frictional interaction/heating at the tool-plate interface(~1000℃),which led to strengthloss and wear of the tool.The Williamson-Hall analysis of the XRD peaks of the SFSed sample confirmed a significantlysmall crystallite size(~100 nm).Wear tests showed that the wear resistance of the composite structure was about 4.5times higher than that of the CP-Ti.Friction analysis revealed a significant reduction in average value and fluctuations ofthe friction coefficient.

Microstructural Evolution of Infrared Brazed CP-Ti Using Ti-Cu-Ni Brazes

Microstructural evolution of infrared vacuum brazed CP-Ti using two Ti-based braze alloys,Ti-15Cu-15Ni and Ti-15Cu-25Ni,has been investigated.The infrared brazed joint consisted of eutectic Ti 2 Cu/Ti 2 Ni intermetallic compounds and Ti-rich matrix.The eutectic Ti 2 Cu/Ti 2 Ni intermetallic compounds disappeared from the joint after being annealed at 900 C for 1 h.In contrast,the depletion rate of both Cu and Ni from the braze alloy into CP-Ti substrate at 750 C annealing was greatly decreased as compared with that annealed at 900 C.Blocky Ti 2 Cu/Ti 2 Ni phases were observed even if the specimen was annealed at 750 C for 15 h.Because the Ni content of the Ti-15Cu-25Ni braze alloy is much higher than that of the Ti-15Cu-15Ni alloy,the amount of eutectic Ti 2 Cu/Ti 2 Ni phases in Ti-15Cu-25Ni brazed joint is more than that in Ti-15Ci-15Ni brazed joint.However,similar microstructural evolution can be obtained from the infrared brazed joint annealed at various temperatures and/or time for both filler metals.

The Effects of Aging Time on the Structural and Electrochemical Properties of Composite Coatings on CP-Ti Substrate

TiO2-SiO2 composite films were produced on commercially pure titanium （CP-Ti） substrate by a sol-gel method to in- vestigate the behavior of sol aging time and its potential effects on the structural and electrochemical properties of composite coatings. Anatase-TiO2 and quartz-SiO2 peaks were observed on all composite coated samples according to XRD results. It was observed that the average grain size increased with sol aging time. Also, the average smallest grain size was seen at composite coatings prepared from unaged sol according to the width of the peaks. Electrochemical behavior of coated samples was mainly investigated by potentiodynamic polarization and Electrochemical Impedance Spectroscopy （EIS） in Simulated Body Fluid （SBF） solution. In corrosion tests, the composite coatings showed better anti-corrosion behavior than that of uncoated samples. In addition, the corrosion properties of the composite films were considerably affected by sol aging time. Corrosion resistance of coatings decreased with increasing aging time and the best result was obtained from composite coatings prepared from unaged sol.

Design and performance evaluation of additively manufactured composite lattice structures of commercially pure Ti(CP-Ti)

Ti alloys with lattice structures are garnering more and more attention in the field of bone repair or regeneration due to their superior structural,mechanical,and biological properties.In this study,six types of composite lattice structures with different strut radius that consist of simple cubic(structure A),body-centered cubic(structure B),and edge-centered cubic(structure C)unit cells are designed.The designed structures are firstly simulated and analysed by the finite element(FE)method.Commercially pure Ti(CP-Ti)lattice structures with optimized unit cells and strut radius are then fabricated by selective laser melting(SLM),and the dimensions,microtopography,and mechanical properties are characterised.The results show that among the six types of composite lattice structures,combined BA,CA,and CB structures exhibit smaller maximum von-Mises stress,indicating that these structures have higher strength.Based on the fitting curves of stress/specific surface area versus strut radius,the optimized strut radius of BA,CA,and CB structures is 0.28,0.23,and 0.30 mm respectively.Their corresponding compressive yield strength and compressive modulus are 42.28,30.11,and 176.96 MPa,and 4.13,2.16,and 7.84 GPa,respectively.The CP-Ti with CB unit structure presents a similar strength and compressive modulus to the cortical bone,which makes it a potential candidate for subchondral bone restorations.

CP-Ti在含氟离子硝酸中表面附着物形成研究

钛具有优良的耐蚀性能,可长期工作在高浓度的沸腾硝酸介质中,是商业后处理较为理想的设备用材。采用SEM、EDS、XRD、XPS等表征手段对CP-Ti在含氟离子硝酸中试样表面出现的白色附着物进行分析,并解释其形成机理。结果表明:氟离子浓度在50μL/L以下时,CP-Ti腐蚀速率呈现由大到小并趋于稳定的规律;氟离子浓度在50μL/L及以上时,腐蚀速率呈现由大到小再变大的“v”型规律。试样表面的白色附着物的物相为TiO2,其形成机理为:先是试样表面多孔膜的形成;其次是TiO2以多孔膜上的孔为基点进行生长、脱落。

工业纯钛在120°模具中的多道次ECAP室温变形组织与性能(英文)

在室温,采用通道夹角为120°的变形模具对工业纯钛(Commercial Pure Titanium,CP-Ti)以Bc方式实施四道次ECAP(Equal Channel Angular Pressing)挤压变形,成功获得表面光滑无裂纹的变形试样。文中主要研究了工业纯钛在室温下进行ECAP多道次变形的组织结构演变,并测试了变形试样的力学性能。微观结构显示工业纯钛在室温下进行多道次ECAP变形时,只在前两道次产生了大量的变形孪晶,且随道次增加变形孪晶逐渐消失。最终获得的试样晶粒平均尺寸由最初的约28μm细化到约250nm,试样断裂强度和显微硬度分别提高到773和2486MPa,而试样仍保持较好的延伸率(可达16.8%)。

Comparison of microstructures and mechanical properties between forging and rolling processes for commercially pure titanium

In order to reveal the differences caused by forging and rolling process for titanium ingots, hot compression behavior, mechanical properties and the microstructures of forged billets and rolled ones were investigated in detail using Gleeble-1500 thermal mechanical simulator, universal testing machine and optical microscope （OM）. The compression deformation experimental data of commercially pure titanium （CP-Ti） were mapped to be a T vs lg diagram in which data fall into three distinct regions, i.e., three-stage work hardening, two-stage work hardening and flow softening, which can be separated by border lines at 17.5 and 15.4 for lg Z, where Z represents the Zener-Hollomon parameter. The deformation twin is found to have higher Z-value corresponding to the work hardening region. The differences in microstructures and mechanical properties for two kinds of billets indicate that forged billet consists of deformation twins and some twin intersections, and many twins cross the grain boundaries. However, nearly no twins can be seen in the microstructure of billet formed by rolling under optical microscope （OM）, but there are equiaxed and platelike grains. Tensile tests and Vickers hardness test indicate that yield strength, tensile strength and microhardness of the samples after forging are higher than those after rolling.

工业纯钛室温一道次ECAP加工后的组织和硬度

室温下,分别采用90°模具和120°模具对工业纯钛(CP-Ti)进行一道次等径弯曲通道变形(Equal ChannelAngular Pressing,简称ECAP),研究了其组织和硬度的变化情况。结果表明,工业纯钛经一道次ECAP变形后都形成板条状组织,硬度显著提高。90°模具挤压后试样上、下表面的硬度值稍低于试样中间的硬度值,而120°模具挤压后试样表面硬度分布较均匀。

剧烈塑性变形条件下工业纯钛晶粒细化机理研究

通过对工业纯钛表面机械研磨(SMAT)这种变形方式的结果和微观组织变化的研究,分析了工业纯钛的晶粒细化机制,讨论了其他剧烈塑性变形技术无法制备出晶粒尺寸更小的纳米晶的原因。结果表明:对于工业纯钛,SMAT这种具有高的应变速率和多方向载荷的变形方式,有利于形成细小的纳米晶;同时高应变速率增加了位错滑移的临界分切应力。

轧制变形超细晶纯钛的电化学腐蚀行为

工业纯钛经过8道次等通道弯角挤压处理后,在室温或液氮温度下进行轧制。随后以林格式人工模拟体液为腐蚀介质,对两步大变形前后纯钛的电化学腐蚀行为进行了研究。结果表明,8道次ECAE处理后获得的超细晶纯钛,较退火粗晶态具有更好的轧制变形能力。两步大变形制备超细晶纯钛不仅表现出良好的综合力学性能,而且具备优异的耐腐蚀性能。8道次ECAE处理的纯钛在室温冷轧后的耐腐蚀性较液氮温度冷轧后好,主要因为不同温度轧制织构组分改变使得平行于样品表面的晶面变为密排面或低指数晶面,比高指数晶面难溶解,呈现更优的耐腐蚀性能。

120°模具室温ECAP制备工业纯钛的压缩变形本构关系

在Gleeble-1500热模拟机上对120°模具室温Bc方式ECAP变形8道次制备的平均晶粒尺寸约为200 nm的工业纯钛进行等温变速压缩实验,研究超细晶工业纯钛在变形温度为298~673 K和应变速率为1×10-4~1×100s-1条件下的流变应力行为。结果表明：变形温度和应变速率均对流变应力具有显著影响,峰值应力随变形温度的升高和应变速率的降低而降低;流变应力在变形初期随应变的增加而增大,出现峰值后逐渐趋于平稳,呈现稳态流变特征。采用双曲正弦模型确定了超细晶工业纯钛的变形激活能Q=104.46 kJ/mol和应力指数n=23,建立了相应的变形本构关系。

反复熔铸对纯钛烤瓷合金力学性能的影响

目的 ：探讨反复熔铸对纯钛烤瓷合金力学性能的影响。方法 ：纯钛经过1-3次单纯反复熔铸后,采用拉伸实验、弯曲实验、硬度实验对各代试件的力学性能进行测试。采用SPSS13.0软件包对数据进行统计学分析。结果：经不同次数熔铸的纯钛烤瓷合金试件,其弯曲强度无显著差异。经过2次、3次熔铸的纯钛烤瓷合金试件,其弯曲模量较1次熔铸的纯钛烤瓷合金显著升高（P〈0.05）。拉伸强度、0.2%屈服强度随着熔铸次数的增加而升高（P〈0.05）。经过3次熔铸的纯钛烤瓷合金试件,其延伸率较经过1次、2次熔铸的纯钛烤瓷合金显著降低（P〈0.05）。经过3次熔铸的纯钛烤瓷合金试件,其显微硬度较经过1次、2次熔铸的纯钛烤瓷合金显著升高（P〈0.05）。结论：纯钛烤瓷合金经1~3次单纯反复熔铸后,弯曲性能、显微硬度未下降,但拉伸性能下降。