热变形参数对TA15合金组织的影响及其相变动力学

采用Gleeble-1500热模拟机单道次热压缩变形实验和元胞自动机方法观察模拟了TA15在变形温度为750~1100℃、应变速率为0.01~1s-1范围内的微观组织变化,研究了不同变形参数对等温热压缩过程中微观组织和性能的影响;根据元胞自动机模拟结果,计算其相变动力学。热压缩实验结果表明,该合金属于温度敏感型和应变速率敏感型合金,随着温度的升高或应变速率的降低,β相含量增加;元胞自动机模拟结果表明,相变动力学Avrami指数n在2.0~3.0之间。     

基于摩擦修正的 TA15 钛合金热变形行为及加工图

目的采用Gleeble-3500热模拟实验机,研究TA15钛合金在变形温度为900~1050℃、应变速率为0.01~1 s-1条件下的热压缩流变行为及变形组织。方法采用一种简单有效的方法修正了TA15钛合金热压缩实验中摩擦引起的误差;计算出了TA15钛合金的应力指数和热变形激活能,建立了含有Z参数的双曲正弦函数形式本构方程;基于Murty准则,建立了其加工图。结果TA15钛合金的热压缩流变行为可采用含有Z参数的双曲正弦函数形式本构方程来描述,其平均变形激活能为625.884 kJ/mol;通过分析热加工图,确定了最优热变形工艺参数为:T=950℃,ε=0.01 s-1。结论研究结果可为TA15钛合金的塑性变形数值模拟提供基础,对合理制定热加工工艺具有重要指导意义。     

钛合金热变形机制及微观组织演变规律的研究进展

综述了当前国内外钛合金在热加工过程中的变形机制及微观组织演变规律方面的研究成果.主要讨论了α,α β和β钛合金在β区、α区或α β两相区热变形的流变曲线特征,应力指数和变形激活能参数,α相和β相的变形方式、再结晶和回复以及α β两相组织的球化等组织演变机制及规律.     

初始组织特征对2E12铝合金热变形行为的影响

制备了富含大量共晶组织、过饱和固溶体以及富含粗大析出相3种典型组织特征的2E12合金。结合热模拟实验和显微组织观察,针对3种合金铸锭在变形温度为340~490℃、应变速率为0.001~10s-1下的变形行为开展研究。结果表明:组织特征对合金的热变形行为有显著影响。在3种合金中,富含粗大析出相合金的峰值应力较高而富含大量共晶组织合金的峰值应力较低。3种合金的流变应力均可用双曲正弦本构关系来描述。3种合金的变形激活能分别为178.6,222.1,154.9kJ/mol。利用加工图确定热变形的流变失稳区,富含粗大析出相合金具有较大的可加工范围而富含大量共晶组织合金的可加工范围最小。     

热变形参数对TC21钛合金微观组织的影响

通过在Gleeble-1500D型热模拟试验机上进行的等温恒应变速率压缩试验和金相及透射分析,研究了变形温度和应变速率对TC21钛合金热变形后微观组织的影响.结果表明:变形温度和应变速率对TC21钛合金的变形组织有着显著的影响.在两相区,随着变形温度的升高,组织中初生α相含量减少,β相含量增加;在应变速率为0.01 s-1、变形温度为860和890 ℃时,初生α相发生了再结晶.随着应变速率的增加,马氏体条变窄,当应变速率较低时(0.01 s-1),组织中观察了再结晶晶粒.     

TA15钛合金β热变形对组织特征参数的影响规律研究

研究了TA15钛合金β区变形时变形温度、变形量、变形速率、冷却条件等热工艺参量对β晶粒尺寸D,α集束尺寸d,α片厚b的影响.结果表明:随变形温度增加,D,d,b呈现峰谷值变化,1050℃温度时,D,d最小,b最大,1050℃以上,温度增加,D,d增大,b减小;随变形量增加,D,d,b均下降;变形速率增加,D,d减小,b稍有增加;变形后水淬大于空冷的D,而d,b则相反.     

Nb47Ti合金热变形行为及微观组织

目的 研究Nb47Ti合金在变形温度为600～750℃、应变速率为0.001～1s?1条件下的热变形行为和微观组织。方法 采用Gleeble-3500型热/力模拟试验机进行等温恒应变速率压缩实验,获得Nb47Ti合金热变形的真应力应变曲线,并利用EBSD技术手段分析热变形后的微观组织。结果 Nb47Ti合金在变形温度小于650℃、应变速率小于0.1s?1下热变形的真应力-应变曲线为动态再结晶型曲线,变形温度大于等于700℃时呈现为动态回复型曲线;峰值应力随变形温度的升高和应变速率的减小而减小;在变形温度为650℃、应变速率为0.001 s?1下热变形组织以再结晶晶粒和亚晶粒为主,随着应变速率的增大,动态再结晶晶粒不断减少,而亚晶粒和变形晶粒增多,晶粒得到显著细化。当应变速率为0.1 s?1时,随着变形温度的增加,晶粒尺寸增大,变形温度升高至750℃,热变形组织中亚晶粒所占比例高达50.5%。结论 Nb47Ti合金是温度和正应变速率敏感材料,随变形温度的升高和应变速率的增大,变形过程中动态回复软化机制更为显著,低温、高应变速率下变形获得的再结晶晶粒尺寸小。     

NiPt15合金热变形行为及微观组织演变规律

本研究采用Gleeble-3500热模拟机对NiPt15合金高温热变形过程进行研究,设定NiPt15合金变形温度为950～1150℃,变形速率为0.01～3 s-1.通过分析热变形过程中NiPt15合金在不同条件下的真应力-应变曲线,建立了双曲正弦型Arrhenius本构关系模型,并拟合模型各参数对合金变形量的依赖性.通过对热变形组织及显微硬度的表征,研究试样各区域热变形组织的差异,分析温度、变形速率、lnZ对动态再结晶及材料维氏硬度的影响.结果表明:NiPt15合金真应力-应变曲线包括三种不同变化趋势,各变形速率下对应的趋势变化临界温度值不同;应变激活能不大于476.85 kJ/mol;升高温度并且降低变形速率能提高再结晶比例至完全动态再结晶,形核机制为非连续性动态再结晶,主要以晶界弓出和反复生成孪晶为再结晶晶粒提供形核位置;当lnZ小于38.89时,晶粒尺寸与lnZ呈负相关性,当lnZ大于38.89时,晶粒尺寸与lnZ关系不明显;硬度与lnZ在本次实验条件下呈正相关性.     

变形温度对TA15合金组织和性能的影响

研究了变形温度对原始坯料为片状组织的TA15合金显微组织和性能的影响.随着变形温度(1030～930℃)的降低,合金的室温抗拉强度、延伸率及断面收缩率均增加.β区变形的镦粗试样为片状组织,在剧烈变形区和自由变形区,1080℃变形时β晶粒的动态再结晶程度比1030℃高.两相区变形镦粗试样的显微组织为过渡型组织,难变形区和剧烈变形区及自由变形区组织差别较大.     

GH4049合金的热变形行为及组织演变

在Gleeble-1500热模拟机上进行GH4049合金的热压缩实验,获得合金在温度为1090~1180℃、应变速率为0.1~50s-1条件下的应力-应变曲线。对峰值应力进行线性回归获得合金在不同变形条件下的材料常数,通过非线性回归建立合金的热变形本构方程。结果表明:随着变形温度升高,动态再结晶更加充分,晶粒尺寸变大;随着应变速率增加,晶粒组织趋于均匀,晶粒尺寸先减小后增大。     

Microstructure evolution of the transitional region in isothermal local loading of TA15 titanium alloy

The microstructure of the transitional region determines the performance of TA15 component under isothermal local loading forming. To understand the characteristic of microstructure evolution in transitional region, a set of analogue experiments for isothermal local loading were designed and carried out to investigate the microstructure development under different temperatures and complex strain path. It is found that the isothermal local loading does not change the microstructural composition of TA15 alloy with initially equiaxed microstructure in the transitional region, though a small fraction of lamellar α phases appear at temperatures above 950 °C due to reheating and small deformation in the second loading step. Recrystallization takes place in the β matrix but not in the primary equiaxed α phases. The β grains are fine and equiaxed irrespective of strain path due to recrystallization. The existence of lamellar α refines the β grains. Kinked and disordered primary equiaxed α phases are produced under complex strain path. The grain size of primary equiaxed α phases increases slightly due to static coarsening and strain induced grain growth in multi-heat processing. The volume fraction of primary equiaxed α phases is not influenced by strain path but determined by working temperature.     

基于修正的Arrhennius方程钛合金高温本构方程研究

为了更准确地描述钛合金的高温变形行为,对Arrhennius方程进行修正得到钛合金高温本构方程.通过对一种新型钛合金在热模拟试验机上进行恒应变速率等温压缩实验,研究其在700~1 000℃、应变速率0.01~10 s-1条件下的热变形行为,分析了材料的真实应力-真实应变曲线.采用最小二乘拟合的数据回归处理,得到该钛合金在α+β双相区和β单相区的热变形激活能,并通过引入温度变量,获得了Arrhennius方程参数A随温度变化的函数关系,建立了该材料的高温流变应力本构方程.实验结果表明,随着变形增加,流变应力开始急剧增加,随后出现软化并趋于稳态,同时峰值应力对于温度和应变速率具有很强的敏感性.通过在Arrhenius方程中引入温度变量,有利于提高本构方程的准确性.     

Microstructure and mechanical properties of TA15 titanium alloy under multi-step local loading forming

In this paper six different local loading processes were proposed to study the effects of local loading conditions (temperature, deformation degree, loading pass, heats, cooling modes and heat treatment) on the microstructure and mechanical properties of TA15 titanium alloy workpieces including room and high temperature tensile properties, impact property, fracture toughness and high temperature duration property.It is found that it is better to finish the local loading forming in one heating time, if multi-fire forging needed the optimal forging technique as follows: adopting conventional forging (950 °C) at first and then following near-beta forging to control the proportion of the equiaxed primary α phase and the transformed β phase, allocating deformation degree of each loading pass rationally and using WQ cooling mode. Thus the workpiece with good compositive mechanical properties can be obtained.     

高纯钛热变形的本构模型及微观组织演变

利用轴对称单向压缩法研究了纯钛在变形温度从723~873 K范围内、应变速率从0.001~1 s-1下的热压缩行为,并通过背散射电子衍射技术对不同热变形条件下的微观组织进行表征。研究结果表明,高温轴对称单向压缩下的纯钛经历从应变硬化阶段到稳态变形阶段的过程,在低的应变速率条件下材料流变应力出现平台,高的应变速率条件下,流变应力随变形过程逐渐增加。该合金流变应力的大小受变形温度、应变速率的强烈影响,随变形温度升高而降低,随应变速率提高而增大,高纯钛是一种具有正应变速率敏感性的材料。该合金高温流变应力σ可采用ZenerHollomon参数的函数来描述,函数表达式中参数A、α和n的值分别为1.84×1024s-1、0.013 MPa-1、12.66,其热变形激活能Q为415.69 k J/mol。不同Z参数条件下微观组织对比分析表明在高的Z参数条件下,材料未发生动态再结晶,在低的Z参数条件下,材料发生明显的动态再结晶,在Z值介于两者之间时材料发生部分再结晶。     

BT20合金高温变形行为的研究

为实现BT20合金锻造的数值模拟和合理制定其热成形工艺参数,利用Thermecmastor-Z型热模拟试验机对该材料在热成形条件下的变形抗力进行了研究,考察了变形温度、应变速率及变形程度与变形抗力之间的关系,并利用冶金学方法对其进行了分析.结果表明,应变速率和变形温度的变化强烈影响着合金流变应力的大小,流变应力随变形温度升高而降低,随应变速率提高而增大.通过真实σ-ε曲线,回归出可综合反映锻造热力参数对材料成形性能影响的本构方程.     

Study on plastic deformation behavior of hot splitting spinning of TA15 titanium alloy

The plastic deformation behavior of hot splitting spinning of TA15 titanium alloy is a complex metal forming problem with multi-factor coupling interactive effects. In this paper, on condition of considering various thermal effects, a three-dimensional (3D) elastic–plastic coupled thermo-mechanical finite element (FE) model of hot splitting spinning of TA15 titanium alloy is established using the dynamic, temp-disp, explicit module of FE software ABAQUS. Based on the analysis of flow behaviors of TA15 titanium alloy, the mechanism and influence of materials plastic deformation behavior during the forming process are studied. The results show that, the flow stress of TA15 titanium alloy generally decreases with the increase of deformation temperature; at the same strain rate, the higher temperature is, the lower flow stress is. The temperature distributions along the circumferential direction of disk blank are even and the temperature of plastic deformation area is about 984 °C. The heat from plastic deformation and friction at local plastic deformation area is less than the dissipated heat, so the temperature just falls into approximately 945 °C. Radial spinning force as the driving force of plastic deformation increases gradually and reaches about 35 kN at the end. The maximum value of equivalent stress is presented in fillet part between disk blank and two mandrels. The distributions of equivalent plastic strain appear the large strain gradients and the obvious characteristics of inhomogeneous deformation. When friction factor on interfaces between disk blank and dies ranges from 0.4 to 0.6, the forming quality and precision are highest.     

Microstructure evolution of different loading zones during TA15 alloy multi-cycle isothermal local forging

The microstructure evolution of the TA15 Ti-alloy in different loading zones under two kinds of multi-cycle isothermal local forging (multi-cycle local near-β forging and multi-cycle conventional forging combined with near-β heat treatment) was investigated and the mechanical properties predicted. Under the first processing route, a microstructure with small grain size was obtained with a significant difference in morphology and composition between the first and second loading zones. An equiaxial microstructure with larger size and more α-phase was obtained in the first loading zone. In the second loading zone when cooled by water after multiple forging cycles and a tri-modal microstructure (finely interlaced and disordered lamellar α, transformed β matrix, and a few equiaxed α) was obtained. The second loading zone possesses excellent room and high temperature mechanical properties. Under the second processing route, the relatively large bimodal microstructures in both loading zones are almost identical. When treated using a vacuum annealing furnace after forging, a coarse clustered lamellar secondary α-phase appeared, which has poor mechanical properties.     

The effect of heterogeneous deformation on the hot deformation of WE54 magnesium alloy

The high temperature forming behavior of WE54 magnesium alloy is studied by means of compression and tension tests. Metallographic investigation was performed to evaluate the heterogeneous deformation of the compression samples at high temperature. Dynamic recrystallization was found to be related to the amount of deformation in the various regions of the compression sample. The compression data allowed determination of the Garofalo equation describing the hot deformation behavior. The parameters n and Q, stress exponent and activation energy, of this equation were 4.4 and 237 kJ/mol respectively. This equation was used to predict the formability behavior for the hot rolling process and also to determine the maximum forming efficiency and stability of the alloy. The optimum rolling temperature was found to be 520 °C.     

Flow behavior and processing map for hot deformation of ATI425 titanium alloy

Flow behavior and processing map play important roles in the hot deformation process of titanium alloys. In this research, compression Gleeble tests have been carried out to investigate the stress–strain relationship at temperatures ranging from 700 to 1000℃ and strain rates ranging from 0.001 to 1 s~(-1) for ATI 425 titanium alloy. Arrhenius type constitutive equation was obtained to describe the compressive flow behavior with modification of additional deformation dead zone, friction model, temperature model and strain rate. The introduction of novel calculation method for value in Arrhenius equation gives more accurate fitting than traditional one. Processing maps were drawn based on the distribution of dissipator co-content, and optimized deformation temperature and strain rate range obtained. It is proven to be accurate and effective through the experimental results. The microstructure analysis shows that more dynamic recrystallization can be achieved in the area with larger value on the processing map.