Microstructural evolution of TiAl base alloy during three-stepped thermo-mechanical treatment

ＴｉＡｌｂａｓｅａｌｌｏｙｓｈａｖｅｂｅｉｎｇｃｏｎｓｉｄｅｒｅｄａｓｐｒｏｍｉｓｉｎｇｈｉｇｈｔｅｍｐｅｒａｔｕｒｅｓｔｒｕｃｔｕｒａｌｍａｔｅｒｉａｌｓ.Ｂｅｉｎｇｓｔｕｄｉｅｄｆｏｒｎｅａｒｌｙ 2 0ｙｅａｒｓ,ｔｈｅｆｕｎｄａｍｅｎｔａｌｏｆＴｉＡｌｂａｓｅａｌｌｏｙｓｈａｖｅｂｅｅｎｕｎｄｅｒｓｔｏｏｄ(ｍｏｒｅｃｌｅａｒｌｙ) ,ａｎｄｔｈｅｉｒｍｅｃｈａｎｉｃａｌｐｒｏｐｅｒｔｉｅｓ ,ｅｓｐｅ ｃｉａｌｌｙｔｈｅｒｏｏｍｔｅｍｐｅｒａｔｕｒｅｄｕｃｔｉｌｉｔｙ ,ｈａｖｅｂｅｅｎｇｒｅａｔｌ…     

Densification behavior of high Nb containing TiAl alloys through reactive hot pressing

Densification behavior of high Nb containing TiAl alloys through reactive hot pressing was investigated. The results showed that the density of the sample hot pressed at 1400°C could reach a near full density of 98.37%. However, the densification abnormality was observed at 1500°C. The diffusion of elemental Nb during microstructural evolution is an important aspect affecting densification, which will form pore nests. With the increase of hot pressing temperature, the diffusion of Nb becomes more adequate. HIP （Hot isostatic pressing） treatment can only decrease porosity to some extent, but cannot eliminate it completely.     

Effects of HIPing pressure on microstructures and properties of TiAl alloy

ＴｉＡｌａｌｌｏｙｉｓａｃａｎｄｉｄａｔｅｍａｔｅｒｉａｌｆｏｒａｄｖａｎｃｅｄａｅｒｏｓｐａｃｅａｉｒｆｒａｍｅｂｅｃａｕｓｅｏｆｉｔｓｌｏｗｄｅｎｓｉｔｙ ,ｇｏｏｄｏｘｉｄａ ｔｉｏｎｒｅｓｉｓｔａｎｃｅａｎｄｈｉｇｈｍｅｃｈａｎｉｃａｌｓｔｒｅｎｇｔｈａｔｈｉｇｈｔｅｍ ｐｅｒａｔｕｒｅ.Ｈｏｗｅｖｅｒ,ｉｔｓｌｏｗｅｒｔｅｎｓｉｌｅｄｕｃｔｉｌｉｔｙａｔａｍｂｉｅｎｔｔｅｍｐｅｒａｔｕｒｅｉｓｈｉｎｄｅｒｉｎｇｉｔｆｒｏｍｂｅｉｎｇｗｉｄｅｌｙｕｓｅｄ[1,2 ] .Ｔｏｉｍｐｒｏｖｅｔｈｅｓｅｍｅ…     

Flow stress behavior of Al-Cu-Li-Zr alloy containing Sc during hot compression deformation

The flow stress behavior of Al-3.5Cu-1.5Li-0.25（Sc＋Zr） alloy during hot compression deformation was studied by isothermal compression test using Gleeble-1500 thermal-mechanical simulator. Compression tests were preformed in the temperature range of 653-773 K and in the strain rate range of 0.001-10 s^-1 up to a true plastic strain of 0.7. The results indicate that the flow stress of the alloy increases with increasing strain rate at a given temperature,and decreases with increasing temperature at a given imposed strain rate. The relationship between the flow stress and the strain rate and the temperature was derived by analyzing the experimental data. The flow stress is in a hyperbolic sine relationship with the strain rate,and in an Arrhenius relationship with the temperature,which imply that the process of plastic deformation at an elevated temperature for this material is thermally activated. The flow stress of the alloy during the elevated temperature deformation can be represented by a Zener-Hollomon parameter with the inclusion of the Arrhenius term. The values of n,α and A in the analytical expressions of flow stress σ are fitted to be 5.62,0.019 MPa^-1 and 1.51×10^16 s^-1,respectively. The hot deformation activation energy is 240.85 kJ/mol.     

7050铝合金热挤压成形过程的有限元模拟

针对传统工程机械用销轴数量多、重量大、工况差等不足,以7050高强轻质铝合金代替传统钢质材料,采用DEFORM-3D有限元分析软件,对7050铝合金热挤压成形过程进行有限元数值模拟,分析了挤压载荷、金属流动速率、等效应变、等效应力和温度场等参量的变化规律。结果表明,销轴的热挤压变形过程可分为4个阶段,即挤压填充阶段、开始挤出阶段、稳定挤压阶段和终了挤压阶段;工件内部等效应变分布横向均匀性较好,除了尾部变形不均匀外,其他部位应变分布基本一致;在挤压凹模模口处形成死区,工件内部等效应力达到最大值。     

TC11合金的新型本构关系

ＴＣ１１合金的新型本构关系刘东，罗子健所谓本构关系，指一种材料的流动应力与应变速率、变形温度和变形程度的关系．实质上，本构关系表示材料对热力参数变化的动态响应．因此，建立本构关系是制定材料塑性加工工艺、对材料塑性加工过程进行数值模拟的基础性工作．由于...     

微量B,Mg对TiAl金属间化合物热变形行为的影响

在１２７３～１５２３Ｋ的温度和１０－３～１００ｓ－１的应变速率范围内研究了微量元素Ｂ，Ｍｇ对固溶有Ｃｒ，Ｖ合金元素的ＴｉＡｌ金属间化合物热变形性能的影响，计算并建立了相应的热变形方程和热加工图，确定了实验合金的动态再结晶峰应力．结果表明：Ｂ，Ｍｇ的加入提高了ＴｉＡｌＣｒＶ合金的形变激活能，尤其是Ｍｇ的加入能显著改善ＴｉＡｌＣｒＶ金属间化合物的热加工性能．     

Effects of strain rate on dislocation for TA15 alloy during hot compressive deformation

The effects of strain rate on the dislocation type and dislocation configure of TA15 alloy were investigated.The experimental results show that the operating dislocation type changes from c type to c and a+ c type with increasing strain rate under the deformation condition of 900℃,60% strain.Under the condition of 900℃,60% strain and 0.001/s strain rate,lots of orientate dislocation cellular configurations and sub-grains,many dislocations pile up before sub boundary.When the strain rate increases to 0.1/s,some dislocations exhibit curved and dislocation tangles and pile-ups can be found,suggesting more dislocations and much stronger interactions among dislocations.     

Al-1Mn-1Mg合金热变形过程中的动态软化行为研究

研究了Al-1Mn-1Mg合金不同变形下的流变应力曲线和微观结构特征,探讨了该铝材在热变形过程中的动态软化行为。结果表明,应变速率为0.1 s-1时,若变形温度较低,则发生了动态回复;若变形温度高于723 K,产生明显的动态再结晶;变形温度为673 K时,在低应变速率条件下,产生动态再结晶,应变速率高于0.1 s-1,软化过程具有动态回复和动态再结晶的混合特征。当应变速率高于5.0 s-1时,产生几何动态再结晶。     

Al-Mg-Si合金热压缩变形的流变应力方程

为了给制定和优化热加工工艺参数提供理论依据,采用Gleeble-1500热模拟机研究了含锆Al-Mg-Si合金在变形温度为653~803 K、变形速率为0.01~10s^-1条件下的热压缩变形的流变应力行为,并通过回归法建立材料变形的流变应力数学模型.结果表明：该合金为正应变速率敏感材料,真应力-真应变曲线存在明显的稳态流变特征;流变应力随着变形速率的增加以及变形温度的降低而增加;在较低变形温度条件下,真应力〖CDF*3〗真应变曲线为动态回复曲线;在较高变形温度条件下真应力-真应变曲线为动态再结晶曲线.该合金流变应力σ可用包含Arrhenius项的Zener Hollomon参数的函数来描述,式中A、α和n的值分别为1.89×10¹⁰s^-1、0.024MPa^-1和7.46,热变形激活能Q为166.85kJ/mol.     

Preparation of TiAl/Ti2AlC Composites with Ti/Al/C Powders by In-situ Hot Pressing

TiAl/Ti2AlC composites were prepared by in-situ hot pressing of TilAl/C powders mixtures and sintered at different temperatures were investigated by X- ray diffraction （ XRD ） of samples. The reaction procedure of Ti-Al-C system could be divided into three stnges. Below 900℃ , Ti reacts with Al to form TiAl intermetallics ; above 900 ℃ , C reacts with remain Ti to form TiC triggered by the exothermal reaction of Ti and Al ; TiAl reacts with TiC to produce dense TiAl/Ti2AlC compasites.In the holding stage, ternary Ti2AlC develops to layered polycrystal and composites pyknosis in the meanwhile. The mechanism of synthesis and microstructure was especially discussed.     

Constitutive behavior of Ni-Ti shape memory alloy under hot compression

Constitutive behavior of nickel-titanium shape memory alloy (Ni-Ti SMA) under hot deformation was investigated by means of the compression tests and the linear fitting method. Based on the true stress-strain curves of Ni-Ti SMA under compression at the strain rates of 0.001-1s -1 and at the temperatures ranging from 600 to 1 000℃, the constitutive equation of Ni-Ti SMA with respect to the Zener-Hollomon parameter was established according to the high stress level and the low stress level at various temperatures so as to more accurately describe the deformation behavior of Ni-Ti SMA during hot working. Dynamic recovery and dynamic recrystallization of Ni-Ti SMA occur under hot compression, which lays the theoretical foundation for understanding the constitutive behavior of Ni-Ti SMA.     

The compressive deformation behavior and deformation mechanism of Ti14 alloy in semi-solid state

The semi-solid deformation behavior of Ti14 was investigated using compression tests at deformation temperatures between 1 273 and 1 423 K with strain rate of 5×10-2s-1. Moreover, the fraction solid at different temperatures was also measured by image analysis. The results showed that the deformation temperature had strong effects on the flow stress, and the stress increased with the decrease of deformation temperature. The maximum stress depended greatly on the fraction solid, and a sharp decrease in stress occurred at a solid fraction between 0.94 and 0.98(temperature from 1 323 to 1 373 K). This decrease was related to the decrease in the amount of solid bridges between grains. Because of the partial solid/liquid segregation during deformation, the experimental strain rates were much lower than those calculated by the flow of liquid incorporating solid particles, which suggested that the main deformation mechanism between 1 323 and 1 373 K was still plastic deformation of solid particles.     

Ti-15-3合金热变形实验研究

在Cleeble-1500热模拟机上对Ti-15-3合金试样进行了热压缩试验,根据压力应变曲线研究了该合金在高温时的流动特性,由金相观察分析了热变形参数对该合金组织的影响。此研究结果对确定Ti-15-3合金锻造工艺参数提供了重要依据。     

Deformation behavior and microstructure of an Al-Zn-Mg-Cu-Zr alloy during hot deformation

The hot deformation behavior and microstructures of Al-7055 commercial alloy were investigated by axisymmetric hot compression at temperatures ranging from 300°C to 450°C and strain rates from 10-2 to 10 s-1,respectively.Microstructures of deformed 7055 alloy were investigated by transmission electron microscopy (TEM).The dependence of peak stress on deformation temperature and strain rate can be expressed by the hyperbolic-sine type equation.The hot deformation activation energy of the alloy is 146 kJ/mol....     

Ti-15-3合金高温变形的微观组织

Ti-15-3合金的组织和性能对工艺参数十分敏感，生产中不易获得组织和性能稳定一致的产品，通过在Gleeble-1500型热加工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、变形程度和变形速率对Ti-15-3合金热变形的显微组织的影响，分析表明，Ti-15-3合金高温变形时容易发生动态回复，高温大变形下低速变形时有发生少量的再结晶，这些研究对于制定该合金合理的热变形工艺，保证产品的质量和提高使用性能具有重要的理论价值和实际意义。     

热连轧工艺对GH4648合金棒材组织与性能的影响

研究了连轧生产线生产的GH4648合金热轧棒材的组织与性能.采用热连轧过程的自动化控制系统调整棒材的轧制速度、保持稳定的终轧温度,从而获得晶粒组织均匀、α-Cr相形态与分布合理的热轧棒材.与传统的横列式轧机相比,工艺更稳定、可控,热轧棒材的组织稳定、性能提高.     

Hot compressive deformation behavior and constitutive relationship of Al-Zn-Mg-Zr alloy with trace amounts of Sc

Abstract： The hot deformation behaviors of AI-Zn-Mg-Sc-Zr alloy were investigated in a temperature range of 340-500℃ and a strain rate range of 0.001-10 s 1 using uniaxial compression test on Gleeble-1500 thermal simulation machine. The results show that the flow stress increases with increasing strain and tends to be constant after a peak value. The flow stress increases with increasing strain rate and decreases with increasing deformation temperature. The phenomenon of dynamic recovery and dynamic recrystallization can be observed by microstructural evolutions. Based on the hyperbolic Arrhenius-type equation, the true stress-true strain data from the tests were employed to establish the constitutive equation considering the effect of the true strain on material constants （α, β, Q, n and A）, which reveals the dependence of the flow stress on strain, strain rate and deformation temperature. The predicted stress-strain curves are in good agreement with experimental results, which confirms that the developed constitutive equations are suitable to research the hot deformation behaviors of Al-Zn-Mg-Sc-Zr alloy.     

Determination of stacking fault energies in a high-Nb TiAl alloy at 298 K and 1273 K

The stacking fault energies of Ti-46A1-8.5Nb-0.2W alloy at 298 K and 1273 K were determined. The principle for the determination of the stacking fault energies is based on the fact that the stacking fault energy and the elastic interaction energy acting on the dissociated partial dislocations are equal. After the compress deformations with the strain of 0.2% at 298 K and 1273 K, and water quench to maintain the dislocation structures deformed at 1273 K, the dissociation distances between two partial dislocations were determined by weak beam transmission electron microscopy (WBTEM) technique. Based on these dissociation distances and the corresponding calculation method, the stacking fault energies were determined to be 77-81 mJ/m^2 at 298 K and to be 57-60mJ/m^2 at 1273 K respectively.     

铝铜合金热裂倾向分析研究

用ＺＸＤ合金铸造性能多功能测试仪，对含量不同的铝铜合金热裂倾向进行测试．实验结果表明：铝铜合金热裂倾向主要表现在铝铜合金凝固末期阶段；当铜含量在６％时热裂倾向最大．对铝铜合金热裂断口观察表明：其热裂呈典型的脆性断裂．分析得出在铝铜合金凝固过程中合金抵抗热裂纹形成的能力取决于试样表面已凝固壳层的强度、跨越断面枝晶的强度以及断面枝晶与其晶间液体之间的吸咐力三者的综合效应的结论．