两相钛合金热加工中初生带状α相形态演变（英文）

为实现钛合金初生带状α相的球化,以具有这种组织的TA15钛合金为对象,研究其在热加工中的组织演变。结果表明:带状α相形态演变的机理与片层组织球化机理相同。由于带状α相尺寸较大,界面分离和末端物质迁移机制较粗化更为重要。带状α相在退火中较为稳定,主要原因是:内部晶界的几何取向不利于球化、带状组织的宽度较大和α粒子几何稳定性高。预变形和低速变形通过以下方式加速球化:直接改变α相的几何形状、通过增加大角度晶界以及相界的面积促进界面分离和末端物质迁移、通过形成位错结构促进粗化。采用大预变形结合高温退火是球化带状α相的有效途径。

在β锻TA15两相钛合金中的变形带（英文）

为了研究在β锻TA15两相钛合金中的变形带,在Gleeble 3500热模拟实验机上进行热模拟压缩试验,同时通过光学显微镜(OM)和电子背散射衍射(EBSD)对显微组织进行研究。研究发现:在TA15钛合金β变形中,变形带在温度高达0.7T_m(T_m为熔点)时仍是重要的组织细化机制。变形带的边界可以是尖锐或者连续变化的。尖锐的变形带界面能够阻碍不连续动态再结晶形核,从而抑制再结晶的发生,而连续变化的界面是连续动态再结晶产生之处。变形带在高应变速率和初始粗晶组织中更加明显。分裂后的晶粒宽度对应变速率敏感,但受温度和初始晶粒尺寸影响较小。多向锻造产生交织的变形带可用于细化小型锻件的组织。

钛合金等温局部加载复杂热变形历史下的三态组织预测（英文）

建立钛合金等温局部加载三态组织预测模型,以实现三态组织参数与性能的定量调控。逐工步的TA15钛合金等温局部加载实验表明,三态组织形成中存在4个重要组织演化现象:条状α相的生成、各组成相含量变化、条状α相取向变化及条状α相的球化。基于实验结果,总结了工艺条件对上述4种组织演化现象的定量影响规律,在此基础上建立了联系三态组织参数(等轴α相含量、条状α相含量、条状α相取向分布混乱度指数、条状α相的球化分数)与成形条件的三态组织预测模型。然后,将组织模型嵌入有限元模拟软件,建立了基于有限元的等温局部加载三态组织预测模型。通过实验组织观测验证了模型的可靠性与准确性,说明本文作者建立的三态组织模型及其与有限元模型的集成可以有效地预测TA15钛合金等温局部加载三态组织参数。

Direct preparation of semi-solid billets by the semi-solid isothermal heat treatment for commercial cold-rolled ZL104 aluminum alloy

Semi-solid isothermal heat treatment was proposed to directly process cold-rolled ZL104 aluminum alloys and obtain semi-solid bil-lets.The effects of two process parameters,namely,temperature and processing time,on the microstructure and hardness of the resulting bil-lets were also experimentally examined.Average grain size(AGS)increased and the shape factor(SF)of the grain improved as the process temperature increased.The SF of the grain also increased with increasing processing time,and the AGS was augmented when the processing time was prolonged from 5 to 20 min at 570℃.The hardness of the aluminum alloy decreased because of the increase in AGS with increasing temperature and processing time.The optimal temperature and time for the preparation of semi-solid ZL104 aluminum alloys were 570℃and 5 min,respectively.Under optimal process parameters,the AGS,SF,and hardness of the resulting alloy were 35.88μm,0.81,and 55.24 MPa,respectively.The Lifshitz-Slyozov-Wagner relationship was analyzed to determine the coarsening rate constant at 570℃,and a rate constant of 1357.2μm3/s was obtained.

Phase fraction evolution in hot working of a two-phase titanium alloy： experiment and modeling

In the present work, the coupled effects of initial structure and processing parameters on microstructure of a two-phase titanium alloy were investigated to predict the microstructural evolution in multiple hot working. It is found that microstructure with different constituent phases can be obtained by regulating the initial structure and hot working conditions. The variation of deformation degree and cooling rate can change the morphology of the con- stituent phases, but do not alter the phase fraction. The phase transformation during heating and holding determi- nes the phase fraction for a certain initial structure. ^--at-~3 transformation occurs during heating and holding. [3 to ct transformation leads to a significant increase in content and size of lamellar ~. The ct to [3 transformation occurs simultaneously in equiaxed at and lamellar ct. The thickness of lamellar ~t increases with temperature, which is caused by the vanishing of fine a lamellae due to phase transformation and coarsening by termination migration. By assuming a quasi-equilibrium phase transformation in heating and holding, a modeling approach is proposed for predicting microstructural evolution. The three stages of phase transformation are modeled separately and combined to predict the variation of phase fraction with temperature. Model predictions agree well with the experimental results.

Quantitative analysis of microstructure evolution induced by temperature rise during(α＋β) deformation of TA15 titanium alloy

Temperature rise is a significant factor influencing microstructure during（α＋β） deformation of TA15 titanium alloy.An experiment was designed to explore microstructure evolution induced by temperature rise due to deformation heat.The experiment was carried out in（α＋β） phase field at typical temperature rise rates.The microstructures of the alloy under different temperature rise rates were observed by scanning electron microscopy（SEM）.It is found that the dissolution rate of primary equiaxed a phase increases with the increase in both temperature and temperature rise rate.In the same temperature range,the higher the temperature rise rate is,the larger the final content and grain size of primary equiaxed a phase are due to less dissolution time.To quantitatively depict the evolution behavior of primary equiaxed a phase under any temperature rise rates,the dissolution kinetics of primary equiaxed a phase were well described by a diffusion model.The model predictions,including content and grain size of primary equiaxed a phase,are in good agreement with experimental observations.The work provides an important basis for the prediction and control of microstructure during hot working of titanium alloy.