High-temperature Mechanical Properties and Dynamic Recrystallization Mechanism of in situ Silicide-reinforced MoNbTaTiVSi Refractory High-entropy Alloy Composite

The hypoeutectic composite material composed of BCC phase and in situ precipitated Ti_(5)Si_(3) was prepared by adding Si into MoNbTaTiV high-entropy alloy.The obvious oriented in situ Ti_(5)Si_(3) phase formed eutectic phase with BCC phase in the inter-dendritic area,which leads to excellent properties of the composite.The alloy exhibits ultra-high yield stress of 718 MPa at 1200℃ and obvious compression plasticity.After reaching the maximum strength,dynamic recovery(DRV)and dynamic recrystallization(DRX)caused soften phenomena.The DRX mechanism of the dual-phase eutectic structure is analyzed by electron backscatter diffraction.The DRX of the BCC phase conforms to the discontinuous DRX and continuous DRX mechanisms,while the Ti_(5)Si_(3) phase has a geometric DRX mechanism in addition to the above two mechanisms.The high performance of this composite has enough potential high-temperature applications such as nuclear and aero engine.

Deformation behaviors and processing maps of CNTs/Al alloy composite fabricated by flake powder metallurgy

Deformation behaviors of CNTs/Al alloy composite fabricated by the method of flake powder metallurgy were investigated by hot compression tests, which were performed in the temperature range of 300?550 °C and strain rate range of 0.001? 10 s?1 with Gleeble?3500 thermal simulator system. Processing maps of the CNTs/Al alloy at different strains were calculated to study the optimum processing domain. Microstructures before and after hot compressions were characterized by electron backscattered diffraction (EBSD) method. Stress?strain curves indicate that the flow stress increases with the increase of strain rate and the decrease of temperature. The processing maps of the CNTs/Al alloy at different strains show that the optimum processing domain is 500?550 °C, 10 s?1 for hot working. EBSD analysis demonstrates that fully dynamic recrystallization occurs in the optimum processing domain (high strainrate 10 s?1), whereas the main soften mechanism is dynamic recovery at low strain rate (0.001 s?1).

Evolution of microstructure, phase composition, and tensile properties of severely cold deformed titanium metastable β alloy in rapid continuous heating

Influence of severe cold deformation of titanium alloy Ti-1.5%A1-6.8%Mo-4.5%Fe in metastable β condition on the evolution of phase composition, microstructure, and tensile properties during continuous rapid heating was studied. As-deformed alloy was characterized by quasi-amorphous single-phase β condition with an abnormal temperature dependence of electric resistance that was normalized after 48 h exposure at room temperature as a result of isothermal ω phase precipitation. Subsequent rapid heating with a rate of 5 ℃/s caused recovery and recrystallization. Tensile properties of the alloy after different treatments were determined and discussed.

Comparative study on high temperature deformation behavior and processing maps of Mg-4Zn-1RE-0.5Zr alloy with and without in-situ sub-micron sized TiB2 reinforcement

Mg-4Zn-1RE-0.5Zr (ZE41) Mg alloy is extensively used in the aerospace and automobile industries.In order to improve the applicability and performance,this alloy was engineered with in-situ Ti B2reinforcement to form Ti B2/ZE41 composite.The high temperature deformation behavior and manufacturability of the newly developed Ti B2/ZE41 composite and the parent ZE41 Mg alloy were studied via establishing constitutive modeling of flow stress,deformation activation energy and processing map over a temperature range of 250℃-450℃ and strain rate range of 0.001 s-1-10 s-1.The predicted flow stress behavior of both materials were found to be well consistent with the experimental values.A significant improvement in activation energy was found in Ti B2/ZE41 composite (171.54 k J/mol) as compared to the ZE41 alloy (148.15 k J/mol) due to the dispersed strengthening of in-situ Ti B2particles.The processing maps were developed via dynamic material modeling.A wider workability domain and higher peak efficiency (45%) were observed in Ti B2/ZE41 composite as compared to ZE41 alloy (41%).The Dynamic recrystallization is found to be the dominating deformation mechanism for both materials;however,particle stimulated nucleation was found to be an additional mode of deformation in Ti B2/ZE41 composite.The twinning and stress induced cracks were observed in both the materials at low temperature and high strain rate.A narrow range of instability zone is found in the present Ti B2/ZE41 composite among the existing published literature on Mg based composites.The detailed microstructural characterization was carried out in both workability and instability domains to establish the governing deformation mechanisms.

冷轧变形铝锡复合材料的再结晶

基于冷轧变形铝锡合金再结晶过程中硬度变化的敏感性,比较研究了Al-10Sn和TiB2/Al-10Sn复合轴瓦材料的再结晶动力学。通过硬度-时间软化曲线,计算了两种材料的再结晶激活能,比较了两种材料的再结晶组织。结果表明,TiB2颗粒的存在提高了材料再结晶温度约50℃,使材料的热稳定性提高。Al-10Sn和TiB2/Al-10Sn的再结晶激活能分别为83.16kJ/mol和92.98kJ/mol。

镁合金复合变形过程中的动态再结晶及微观组织演变规律研究

对挤压态AZ31镁合金进行了压痕-压平复合变形工艺实验研究,分析了复合变形工艺参数对镁合金动态再结晶组织及孪晶组织的影响规律。研究结果表明,经过复合变形后,AZ31镁合金的微观组织呈现孪晶组织和动态再结晶组织。复合变形系数和变形温度对镁合金微观组织影响明显。随着复合变形系数的增大和变形温度的提高,动态再结晶体积分数随之增大,动态再结晶组织逐渐增多,最后覆盖原始孪晶组织,得到分布均匀且细小的等轴晶,有效改善了镁合金材料的组织性能。

高能球磨时间对CNTs/Al5083纳米晶粉体微观组织及性能的影响

采用机械合金化法制备出2wt%CNTs/Al5083纳米晶复合粉体,研究了高能球磨时间对CNTs/Al5083纳米晶粉体性能的影响。利用XRD、SEM和TEM对该复合粉体的形貌及显微组织进行观察。结果表明,延长球磨时间可改善CNTs在Al5083粉末中的分散性,并使CNTs逐渐嵌入到金属粉末中,同时使复合粉体的晶粒细化。在球磨2.5 h时,晶粒尺寸达到46.4nm。另外,2.5h的球磨时间,会破坏CNTs的结构,同时诱发动态再结晶,使晶粒变粗,不利于粉末烧结。

微量Ti·Gd对银的组织和再结晶特性的影响

采用硬度法、金相、Ｘ－ｒａｙ衍射、透射电镜和能谱分析等手段研究了Ａｇ－Ｔｉ（００５～０６１ｗｔ％Ｔｉ，下同）和Ａｇ－Ｔｉ－Ｇｄ（０５１～１３ｗｔ％Ｔｉ，００９～０４６ｗｔ％Ｇｄ，下同）合金的组织、再结晶特性和相结构。结果表明：微量Ｔｉ及Ｔｉ＋Ｇｄ加入Ａｇ中，有效细化晶粒，提高晶粒组织稳定性，再结晶温度相应提高１００～１５０℃和２５０℃；作者还确认了某些二相合金和三相合金；最后探讨了微量元素的作用机理。

Effects of Cr and Al Contents on the Preparation of SiC Fiber-Reinforced NiCrAl Alloy Matrix Composite

In this work,the effects of Cr and Al contents on the preparation of SiC fiber-reinforced NiCrAl alloy matrix composites(SiCf/Ni-20Cr-5Al,SiCf/Ni-15Cr-5Al,SiCf/Ni-10Cr-5Al and SiCf/Ni-10Cr-3Al)were thoroughly discussed.The composites were prepared by vacuum hot pressing process using matrix-coated fibers.It was found that Cr solute atoms played a significant role in retarding the recrystallization of NiCrAl alloy matrix,and the Al elements in the form of γ'-Ni3Al phase had a suppression effect on the plastic flow of the matrix.Therefore,the reduction in Cr and Al contents was conductive to the recrystallization and plastic flow of NiCrAl alloy matrix,thereby reduced the size and number of micro-voids in the composite.In addition,this work provides some guidance for designing and manufacturing reasonable SiC fiber-reinforced Ni alloy matrix composites.

优化合金成分与生产工艺,控制电池锌饼的合适硬度

结合四轮轮带式连铸连轧生产线生产电池锌饼卷坯的特点,阐述合金成分与生产工艺对电池锌饼硬度的影响,指出生产合适电池锌饼硬度最优化的合金化学成分与生产工艺条件。

镁铝轻质复合板多层挤压复合工艺

采用挤压工艺对AZ31镁合金板和6061铝合金板进行多层挤压复合,结合扫描电镜、能谱分析仪、金相显微镜、EBSD以及万能拉伸试验机等分析手段,研究了不同坯料层数对AZ31/6061复合板的微观组织及力学性能的影响。实验结果表明:复合板镁合金侧中存在大量的细小再结晶晶粒和少量变形组织,复合板铝合金侧的晶粒呈现典型的带状结构,且周围有大量细小再结晶晶粒生成;此外,复合板中Mg/Al界面具有良好的冶金结合,且有不同厚度的界面反应层生成,其中P1板的界面反应层以Mg_2Al_3为主,P2板靠近镁合金侧有Mg_(17)Al_(12)生成,靠近铝合金层有Mg_2Al_3生成。

Fe基非晶合金增强1060铝基多层复合材料的组织与性能

采用累积叠轧焊+中间退火法复合轧制1060Al/Fe基非晶多层铝合金复合板材。利用光学显微镜、扫描电镜、X-衍射分析仪以及拉伸试验机分析Al基复合材料的微观组织结构变化、断口形貌、物相组成以及力学性能。结果表明:Fe基非晶复合材料的增强体在300℃中间退火过程中发生部分晶化,在累积变形轧制过程中发生破碎,并随着变形道次的增加,破碎程度随之增大;复合板前6道次的累积轧制变形出现了明显的加工软化现象,并且随着变形道次的增加,其加工软化的效果愈明显;随着累积轧制变形道次增加,Al基复合材料的力学性能发生了明显的变化,第2道次轧制变形后屈服强度与抗拉强度达到了最大值为140 MPa和156 MPa,伸长率为5. 53%,达到最佳综合性能。

短切碳纤维/AZ91D镁合金复合材料高温变形动态再结晶行为

在变形温度为340~400℃、应变速率为0.001~0.1s-1、最大真应变为0.7的条件下,采用等温压缩实验研究了短切碳纤维(CFs)/AZ91D复合材料和AZ91D镁合金的动态再结晶行为。结果表明:CFs/AZ91D复合材料和AZ91D镁合金在高温压缩过程中均发生了显著的动态再结晶;CFs极大地促进了AZ91D基体的动态再结晶过程,减小了动态再结晶临界应变并细化了再结晶晶粒组织;AZ91D镁合金动态再结晶体积分数随应变量增加表现为典型的"S"型变化曲线,而CFs/AZ91D复合材料则呈现出快速增长-缓慢增长-趋于平稳的非线性变化规律。根据实验结果分别建立了CFs/AZ91D复合材料和AZ91D镁合金的动态再结晶临界应变模型和动力学模型,在此基础上分析了二者高温变形动态再结晶行为的差异。