基于位错密度理论的Q550D钢动态软化及加工硬化行为

针对Q550D超低碳贝氏体钢,通过热压缩实验建立了应变硬化曲线。并通过分析临界应变与峰值应变的关系、稳态流变应力和动态回复应力与峰值应力的关系,建立了位错密度模型。将位错密度模型和元胞自动机法相结合,对Q550D钢热变形行为进行了数值分析。结果表明,在相同的形变量下,应变速率较大时,位错密度高,动态再结晶形核率大,晶粒尺寸小。并且,模拟结果与实验结果吻合,说明计算模型具有较高的精度。

Q550D超低碳贝氏体钢的微观组织模拟

利用Q550D超低碳贝氏体钢的热压缩试验数据建立了动态再结晶模型及元胞自动机模型,通过有限元软件DEFORM-3D对试样热变形过程的微观组织演变过程进行了模拟.结果表明:在变形温度为1 150°C条件下,当应变速率为0.05s-1时,热变形过程中的试样微观组织发生了动态再结晶现象,晶粒尺寸得到细化;在变形温度为1 050°C条件下,当应变速率不断增大时,奥氏体动态再结晶的晶粒尺寸减小;模拟结果与试验结果较吻合.

TC21钛合金β锻动态再结晶行为及晶粒尺寸预测

采用Gleeble-3500热模拟实验机对TC21钛合金进行等温恒应变速率的热模拟压缩实验,研究其在变形温度960℃-1020℃,应变速率0.001s-1、0.01s-1、0.1s-1、1s-1条件下的动态再结晶行为。结果表明,TC21钛合金在变形过程中存在动态回复、动态再结晶现象。当温度一定时,在应变速率≤0.1s-1情况下,随着应变速率的降低,动态再结晶晶粒尺寸变大;在应变速率为1s-1时,变形过程几乎只发生动态回复;当应变速率一定时,随着温度的升高,动态再结晶晶粒尺寸变大。根据流动应力与变形温度和应变速率之间的关系,得到了TC21钛合金动态再结晶激活能Q=258.6kJ/mol;通过对热模拟实验数据的分析计算,建立了动态再结晶演化模型。依据所建模型,并基于DEFORM-3D软件预测了975℃热变形后的晶粒尺寸和动态再结晶体积分数,晶粒尺寸相对误差在±10%以内,较好的验证了模型的准确性。

TC21钛合金的等温转变行为

针对TC21钛合金,采用JMat Pro软件模拟计算得到该合金的等温转变曲线(TTT),同时采用膨胀法及金相法绘测其TTT曲线进行对比验证。模拟计算结果表明,在温度800~875℃析出α相速度最快。实验结果表明,由于TC21钛合金β→α相转变时相变体积效应小,膨胀法无法测得等温转变开始时间;金相法能较准确的绘测出等温转变曲线,表明在温度800~840℃左右其次生α相析出速度最快,也就是TTT曲线鼻尖位置,β→α相转变对温度敏感性高,淬火及退火时效时在此温度区间的停留时间不能过长,在低温时析出次生α相的速度最慢;JMat Pro软件模拟计算结果和实验绘制得到的TTT曲线吻合得较好。

TC21钛合金时效析出α相的长大动力学

为研究TC21钛合金时效时析出α相的长大动力学,采用JMatPro软件模拟计算得到了钛合金时效相平衡时α相和β相的化学成分与时效温度的关系,计算得到了在500~900℃下等温时效时析出α相的长大速率与温度的关系式,并进行了试验验证。结果表明:在750℃以下等温时效时,析出α相的长大速率较慢,时效温度高于800℃时,长大速率随温度升高而迅速增加,这是由合金元素的扩散系数随温度的变化而决定的;试验得到的TC21钛合金在900℃等温时效时析出α相的长大速率与模拟计算得到的结果一致,析出α相的生长速率随温度升高不断增大。

Mechanical and tribological behaviors of graphene/Inconel 718 composites

Graphene/Inconel 718 composites were innovatively synthesized through selective laser melting,and the mechanical and tribological performances of the grapheme-reinforced Inconel 718 matrix composites were evaluated.The composite microstructures were characterized by XRD,SEM and Raman spectroscopy.The results show that selective laser melting is a viable method to fabricate Inconel 718 matrix composite and the addition of graphene nanoplatelets leads to a significant strengthening of Inconel 718 alloy,as well as the improvement of tribological performance.The yield strength and ultimate tensile strength of 1.0%graphene/Inconel 718 composites(mass fraction)are 42%and 53%higher than those of pure material,and the friction coefficient and wear rate are 22.4%and 66.8%lower than those of pure material.The decrease of fraction coefficient and wear rate is attributed to the improved hardness of composites and the formation of graphene nanoplatelet protective layer on the worn surfaces.

Base material location dependence of corrosion response in friction-stir-welded dissimilar 2024-to-5083 aluminum alloy joints

The effects of the base material(BM)location on the mechanical properties and the exfoliation corrosion performance of friction-stir-welded(FSWed)dissimilar 2024-to-5083 aluminum alloy joints were investigated.Scanning electron microscopy(SEM),electron backscatter diffraction(EBSD),transmission electron microscopy(TEM),tensile tests and electrochemical experiments were conducted.The results revealed that the BM location had little effect on the tensile properties of the joints.The grain orientation spread(GOS)value of 2024 alloy side was lower than that of 5083 alloy side.Intergranular corrosion occurred mainly on the 2024 alloy side,while the grain interior of the 5083 alloy side was corroded due to the higher GOS value and dislocation density.The FSWed dissimilar joints with a superior exfoliation corrosion resistance could be achieved when the 5083 aluminum alloy with better corrosion performance was positioned on the retreating side.

40Cr钢奥氏体动态再结晶过程数值模拟

采用数值模拟研究了40Cr钢奥氏体热变形行为。通过JMatPro软件得到本构关系曲线,建立了动态再结晶模型。在Deform-3D平台上将动态再结晶模型和元胞自动机模型结合起来,对40Cr钢高温压缩过程进行模拟仿真。结果表明,40Cr钢平均晶粒尺寸随着压缩变形量的增加而不断变小。当真应变为1时,在大变形区的晶粒尺寸为10.1μm,和相关试验对比误差在±10%以内。元胞自动机模拟可视化再现了动态再结晶过程。