新型Ti-Al-Zr-Nb-Mo-Si钛合金热变形行为及基于BP神经网络模型的本构关系研究

通过热压缩模拟实验,研究了一种新型Ti-Al-Zr-Nb-Mo-Si高强度、高弹性模量钛合金在温度为950～1 150℃、应变速率为0.05～1 s~(-1)条件下的流变行为。真应力-真应变曲线表明,变形温度、应变速率对该合金的流变应力影响显著。基于实验数据,利用包含应变参量的双曲正弦型Arrhenius方程和BP人工神经网络模型分别构建了变形参数和流变应力的本构关系,并对两种模型进行了对比评价。结果表明,两种模型的平均相对误差值分别为11.21%和2.163%,整体上均可以较好地预测Ti-Al-Zr-Nb-Mo-Si钛合金热压缩流变应力;但相对传统Arrhenius方程,BP人工神经网络模型具有更高的精度和可靠性。     

Ti3Al金属间化合物超塑性的研究进展

详细的对Ti3Al金属间化合物的超塑性研究进展状况进行了总结和评述.根据现有的研究结果可知,此类合金的最佳超塑性变形温度为940～980℃,最佳超塑性变形的应变速率为10-4～10-3s-1,其最大延伸率可达1500%左右,接近于普通钛合金的超塑性水平.Ti3Al金属间化合物超塑变形的主要机制是晶界滑动,失效的主要原因是空洞的形成和连接.针对已取得的研究成果和在目前研究中仍然存在的问题,提出了一些有关Ti3Al金属间化合物超塑性研究的看法.     

基于位错密度的钛合金电辅助压缩仿真与实验验证

目的 以新型高强韧Ti?6Cr?5Mo?5V?4Al(Ti6554)近β钛合金为对象,探讨脉冲电流对材料变形行为和温度变化的影响规律,揭示Ti6554钛合金在不同电流密度下的位错密度演化规律。方法 对材料进行不同电流密度、占空比、应变速率条件下的电辅助压缩实验,建立考虑位错密度的修正电塑性本构模型,基于ABAQUS进行UMAT子程序开发,建立电?热?力三场耦合有限元模型,模拟Ti6554钛合金电辅助压缩变形过程,并进行实验验证。结果 随着电流密度和占空比增大流动应力减小,随着应变速率增大流动应力也增大;电辅助压缩实验结果与模拟结果相比的平均误差为6.31%,验证了模型的有效性;通过子程序状态变量输出位错密度的变化发现,电流密度为15.92、23.88、27.87、31.88、39.81 A/mm²的位错密度分别下降了15.34%、55.63%、68.23%、83.84%、89.13%,表明位错密度随电流密度的增大而降低。结论 建立了基于位错密度的电塑性本构模型和电-热-力多场耦合的有限元模型,能够模拟Ti6554钛合金的电压缩变形行为,并且表征了位错增殖、位错湮灭及动态回复,获得了其位错密度的演化规律。     

线间距对SLM成形钛合金Ti–6Al–4V力学性能的影响研究

目的 探究选区激光熔化技术工艺参数线间距对钛合金Ti–6Al–4V增材试件力学性能的影响。方法 通过SLM成形技术,以钛合金粉末为原材料、以线间距为变量制备增材成形试件,通过拉伸试验、断口形貌分析以及表面硬度测量获取不同线间距工艺参数条件下钛合金成形试件力学性能表现较好的较优解。结果 不同线间距条件下成形试件拉伸曲线差异较大,线间距为0.05 mm和0.10 mm时,成形试件拉伸曲线表现较好,成形试件断口组织撕裂均具有连续性,韧窝结构明显,具有一定塑性。试件成形过程受氧化影响,其拉伸性能与硬度性能表现不一致。结论 试验最终工艺参数如下:曝光时间为80 μs、点间距为40 μm、线间距为0.05 mm,SLM成形试件获得了较高的表面硬度,试件断口组织撕裂连续性较为明显,韧窝结构较大,断口界面缺陷较少,力学性能较优。     

激光冲击处理对Ti6Al4V力学性能的影响

通过对钛合金Ti6Al4V的激光冲击处理,研究了激光冲击处理工艺对钛合金Ti6Al4V力学性能的影响.实验表明:激光冲击处理能有效提升Ti6Al4V的力学性能,在激光功率密度由1.15GW/cm2增加到2.31GW/cm2过程中,其冲击波峰值压力线性增加,表面最大残余压应力也相应增大,最高达-264MPa,表面硬化层的显微硬度高达510Hv,硬化层深度约为0.25mm,经过激光冲击处理后硬度相对于原始钛板提高了64%,随着激光能量的增加,冲击区域的抗拉强度极大增强,塑性降低.     

表面粗糙度对钛合金超声波喷丸强化影响的有限元分析

探究超声波喷丸强化工艺对不同初始粗糙度的材料表面塑性应变、喷丸覆盖率以及残余应力及表面位移场影响的变化规律。以TC4(Ti6Al4V)钛合金材料为研究对象,基于有限元仿真软件ABAQUS构建超声波喷丸工艺的三维有限元模型,研究粗糙度对材料表面超声波喷丸强化效果的影响。结果表明:降低表面初始粗糙度,可以提高达到工艺要求覆盖率的速度和表面发生塑性变形的程度,增加亚表面残余压应力层的深度及对应层深的残余压应力值。     

应变速率循环法构建TC4-DT钛合金本构方程

采用应变速率循环法在超塑拉伸机上对TC4-DT钛合金进行三组高温超塑性拉伸实验,变形温度为850~890℃,应变速率为3.3×10-5~3.3×10-3s-1。通过对拉伸实验数据的分析计算出TC4-DT钛合金动态再结晶激活能,并利用Arrhenius模型构建TC4-DT高温条件下的超塑性本构方程。结果表明:TC4-DT钛合金的流动应力对变形温度较为敏感,随着温度的升高,流变应力逐渐减小,软化机制愈发明显,870℃附近的超塑性较好,伸长率达到554%。     

金属间化合物的组织超塑性行为

综述了金属间化合物的组织超塑性行为的最新进展状况,介绍了镍基（Ni3Al,Ni3Si,NiAl）、钛基（TiAl,Ti3Al）、铁基（Fe3Al,F3Al和Fe3Si）和钴基（Co3Ti）金属间化合物的粗晶和细晶组织的超塑性行为（CSS and FSS）,着重于微观组织的分析以及变形机制的阐述,讨论了动态再结晶（DRX）在超塑性变形中的作用;传统的动态再结晶（DRX）是细晶结构金属间化合物超塑性变形的一种有效的协调机制。而连续的动态再结晶（CRX）是粗晶结构金属间化合物超塑性变形的主要机制。还展望了金属间化合物超塑性的研究方向。     

Ti6Al4V高速干滑动摩擦磨损特性研究

对Ti6Al4V合金在高速干滑动摩擦条件下进行了系统的磨损性能测试,研究了载荷和速度对Ti6Al4V合金的摩擦磨损机制的影响,对Ti6Al4V合金的磨损表面、纵剖面进行了显微分析及X-衍射分析,实验结果表明,Ti6Al4V合金的磨损率和摩擦表面温度随着载荷和速度的升高而增加,摩擦表面的温度最高达到1044℃,磨损表面出现"蘑菇头"的磨损现象,表面出现裂纹及剥落坑,表层及次表层出现裂纹,组织变得粗大,磨损纵剖面析出Ti3O,Ti6O,VO0.53,VN等化合物.     

TC18钛合金的超塑性行为与变形机制

通过高温拉伸实验研究TC18钛合金在温度为720~950℃,初始应变速率为6.7×10~(-5)~3.3×10~(-1)s~(-1)时的超塑性拉伸行为和变形机制。结果表明:TC18钛合金在最佳超塑性变形条件下(890℃,3.3×10~(-4)s~(-1)),最大伸长率为470%,峰值应力为17.93MPa,晶粒大小均匀。在相变点Tβ(872℃)以下拉伸,伸长率先升高后下降,在温度为830℃,初始应变速率为3.3×10~(-4)s~(-1)时取得极大值373%,峰值应力为31.45MPa。TC18钛合金在两相区的超塑性变形机制为晶粒转动与晶界滑移,变形协调机制为晶内位错滑移与攀移;在单相区的超塑性变形机制为晶内位错运动,变形协调机制为动态回复和动态再结晶。     

Ti-22Al-24Nb-0.5Y合金流变行为及BP神经网络高温本构模型

利用Gleeble-3500热模拟试验机进行等温恒应变热压缩实验,以实验获得的数据为基础,研究Ti-22Al-24Nb-0.5Y合金流变行为,通过正交实验对影响合金的流变应力因素进行分析,并建立基于BP神经网络的合金高温本构关系模型。结果表明:影响合金流变应力的主要因素依次为应变速率、变形温度和应变量;Ti-22Al-24Nb-0.5Y合金在热变形时的流变应力对应变速率和变形温度都较为敏感。当变形温度较低,应变速率较高时,合金变形呈流变软化特征,当变形温度较高,应变速率较低时,合金变形趋向于稳态流动;利用BP神经网络建立的合金高温本构关系模型,具有较高的精度,其相关性系数达到0.9949,平均相对误差在3.23%,预测值偏差在10%以内的数据点达98.79%,该预测模型可作为Ti2AlNb基合金塑性成形过程有限元模拟的本构关系。     

Superplastic deformation characteristics of two microduplex titanium alloys

A comparison of the superplastic deformation behaviour of Ti-6Al-4V (wt%) between 760 and 940‡ C and Ti-6Al-2Sn-4Zr-2Mo between 820 and 970‡ C has been carried out on sheet materials possessing similar as-received microstructures. High tensile elongations were obtained with maximum values being recorded at 880‡ C for Ti-6Al-4V (Ti-6/4) and at 940‡ C for Ti-6Al-2Sn-4Zr-2Mo (Ti-6/2/4/2), under which conditions both alloys possessed aΒ phase proportion of approximately 0.40. For a given deformation temperature the Ti-6/4 alloy had a slightly lower flow stress than the Ti-6/2/4/2, and this was attributed to the lowerΒ phase proportion in the latter alloy. However, at the respective optimum deformation temperatures the Ti-6/2/4/2 alloy had the lower flow stress. The results show that suitably processed Ti-6/2/4/2 alloy is capable of withstanding substantial superplastic strains at relatively low flow stresses, although the optimum deformation temperature is higher for this alloy than for Ti-6/4 material possessing a similar microstructure.     

Research Progress of Advanced Titanium Alloys in Korea

A brief review of some research works for the advanced titanium alloys carried out at the Center for Advanced Aerospace Materials (CAAM) and Korea Institute of Machinery and Materials (KIMM) has\break been described. New titanium alloys having superior superplastic characteristics as compared to the conventional Ti-6Al-4V alloy has been developed and the fatigue crack propagation behavior of a gamma TiAl alloy has been investigated. Current status of titanium research and developments in Korea is also briefly described.     

Finite Element Simulations of Four-holes Indirect Extrusion Processes of Seamless Tube

Finite element simulations are performed to investigate the plastic deformation behavior of Ti-6Al-4V titanium alloy during its indirect extrusion through a four-hole die. The simulations assume the die, mandrel and container to be rigid bodies and ignore the temperature change induced during the extrusion process. Under various extrusion conditions, the present numerical analysis investigates the effective stress and profile of product at the exit. The relative influences of the friction factors, the temperature of billet and the eccentricity of four-hole displacement are systematically examined. The simulations focus specifically on the effects of the friction factor, billet temperature and eccentricity ratio of the four-hole die on the maximum load and effective stress induced within the billet and the taper angle of the extruded tubes. The simulation results provide a useful insight into the optimal processing conditions for the four-hole indirect extrusion of seamless titanium alloy tubes.     

增材制造Ti-6Al-4V合金组织调控研究现状

增材制造技术可实现复杂钛合金零件的快速成形,制造的Ti-6Al-4V合金具有较高的强度以及优异的高温性能,被广泛应用于航空、医疗等各大领域。综述了金属增材制造的典型工艺,分析了Ti-6Al-4V合金的相变特征,总结了选区激光熔化制造Ti-6Al-4V的力学性能和组织调控方法,着重分析了热处理温度、冷却速率、变质处理以及超声冲击等对合金组织的影响;展望了增材制造Ti-6Al-4V合金的主要发展方向。     

TI-6Al-4V合金置氢-除氢组织与力学性能

为研究除氢处理对置氢钛合金组织与性能的影响,对Ti-6Al-4V合金在不同参数条件下进行了置氢与除氢处理,采用光学显微镜分析了置氢-除氢处理过程中Ti-6Al-4V合金微观组织的演化规律,通过室温拉伸试验研究了置氢-除氢处理后Ti-6Al-4V合金的力学性能,探讨了Ti-6Al-4V合金置氢-除氢组织与力学性能之间的相...     

Nanostructured severe plastic deformation processed titanium for orthodontic mini-implants

Titanium mini-implants have been successfully used as anchorage devices in Orthodontics. Commercially pure titanium (cpTi) was recently replaced by Ti-6Al-4 V alloy as the mini-implant material base due to the higher strength properties of the alloy. However, the lower corrosion resistance and the lower biocompatibility have been lowering the success rate of Ti-6Al-4 V mini-implants. Nanostructured titanium (nTi) is commercially pure titanium that was nanostructured by a specific technique of severe plastic deformation. It is bioinert, does not contain potentially toxic or allergic additives, and has higher specific strength properties than any other titanium applied in medical implants. The higher strength properties associated to the higher biocompatibility make nTi potentially useful for orthodontic mini-implant applications, theoretically overcoming cpTi and Ti-6Al-4 V mini-implants. The purposes of the this work were to process nTi, to mechanically compare cpTi, Ti-6Al-4 V, and nTi mini-implants by torque test, and to evaluate both the surface morphology and the fracture surface characteristics of them by SEM. Torque test results showed significant increase in the maximum torque resistance of nTi mini-implants when compared to cpTi mini-implants, and no statistical difference between Ti-6Al-4 V and nTi mini-implants. SEM analysis demonstrated smooth surface morphology and transgranular fracture aspect for nTi mini-implants. Since nanostructured titanium mini-implants have mechanical properties comparable to titanium alloy mini-implants, and biocompatibility comparable to commercially pure titanium mini-implants, it is suggestive that nanostructured titanium can replace Ti-6Al-4 V alloy as the material base for mini-implants.     

FABRICATION AND EVALUATION OF SUPERPLASTICALLY FORMED/WELD BRAZED CORRUGATED COMPRESSION PANELS WITH BEADED WEBS

A study was made to investigate the feasibility of superplastically forming corrugated panels with beaded webs and to demonstrate the structural integrity of these panels by testing. The test panels in the study consisted of superplastically formed titanium alloy Ti-6Al-4V half-hat elements that were joined by weld-brazing to titanium alloy Ti-6Al-4V caps to form either single-corrugation compression panels or multiple-corrugation compression panels. Stretching and subsequent thinning of the titanium sheet during superplastic forming was reduced by approximately 35 percent with a shallow half-hat die concept instead of a deep die concept and resulted in a more uniform thickness across the beaded webs. The completed panels were tested in end compression at room temperature and the results compared with analysis. The heavily loaded panels failed at loads approaching the yield strength of the titanium material. At maximum load, the caps wrinkled locally accompanied with separation of the weld-braze joint in the wrinkle. None of the panels tested, however, failed catastrophically in the weld-braze joint. Experimental test results were in good agreement with structural analysis of the panels.     

Interface contribution to the SiC-titanium and SiC-aluminium tensile strength prediction

Fragmentation tests of single SiC filaments embedded in an aluminium (1050 and 5083 alloys) or a titanium (Ti-6Al-4V) matrix have been analysed in an effort to obtain the interface contribution in terms that could be incorporated into a tensile fracture model for unidirectional composites. Depending on the matrix, two regimes of interfacial stress transfer can be distinguished within the whole range of tested temperatures. For the SCS2/5083 system, plastic deformation of the alloy limits the stress transfer, and the interface contribution thus finds its expression in the shear stress of the matrix. for the SCS6/Ti-6Al-4V system, friction is the leading process and the interface contribution strongly depends on the stress state around the fibre. Assuming a temperature dependent compressive radial stress up to 925C, an effective transfer shear stress may be easily calculated for unidirectional SCS6/Ti-6Al-4V composites.     

On flow stress anisotropy in Ti-6Al-4V alloy sheet during superplastic deformation

The anisotropy of flow stress in a cold rolled sheet of Ti-6Al-4V alloy has been observed during superplastic deformation at 850 °C. At this temperature, the alloy has duplex microstructure with almost equiaxed grains of the alpha and beta phases. The maximum value of flow stress has been established for the rolling direction and minimum—for the transverse one. Also, the anisotropy of crystallographic texture weakening in the alpha phase has been observed. However, it has been demonstrated that texture in the alpha phase cannot be responsible for the observed anisotropic behavior. Texture in the beta phase is the suggested reason for the flow-stress anisotropy during superplastic deformation.