脉冲频率和热输入对电弧增材制造TC4形貌和组织的影响

粗大β柱状晶导致的各项异性是电弧增材制造TC4合金面临的主要问题。为解决上述问题,采用不同的脉冲频率和热输入成形了多组试样,并结合有限元分析,重点研究了热输入和脉冲频率对成形TC4合金形貌和组织的影响。结果表明:随着脉冲频率增加,试样宽度先快速减小,随后略有增加,β晶粒由柱状晶转变为等轴晶,并且得到细化,但α相没有显著变化;提高热输入有利于获得等轴晶,但会增加试样的宽度,还会导致α相变得粗大。试样的宽度由熔池的尺寸决定,主要与平均热输入和峰值阶段输入的热量相关。提高脉冲频率能破碎树枝晶,降低温度梯度,有利于增加形核率,提高热输入也能降低温度梯度,因此能够获得等轴晶。α相形貌主要与相变时的冷却速度相关,降低热输入能增大冷却速度,细化α相。     

新型Al-5Nb-RE-B合金组织和细化效果研究

采用熔体反应制备了组织均匀的Al-5Nb-RE-B中间合金,研究了该中间合金对A356铝合金的细化效果。结果表面,添加1 wt.%的Al-5Nb-RE-B中间合金后,A356铝合金的晶粒度从原来的800um细化为200um。不同冷速下的研究结果表明,Al-5Nb-RE-B中间合金具有较低的冷速敏感性。     

慢速搅拌摩擦加工对工业纯钛摩擦磨损性能的影响

目的利用慢速搅拌摩擦加工,获得工业纯钛细晶组织,提高其耐磨性能。方法采用慢速搅拌摩擦加工对TA2工业纯钛退火板材进行表面处理,获得细晶结构。使用EBSD技术和显微硬度检测仪对表面微观结构及力学性能进行表征。采用球盘式摩擦磨损试验仪对搅拌摩擦加工前后的样品进行摩擦磨损性能测试,计算磨损率,并使用SEM及EDS分析磨痕特征。结果搅拌摩擦加工处理后,工业纯钛晶粒尺寸显著细化,小角度晶界比例较高,加工硬化程度高。搅拌摩擦加工样品氧化磨损较为严重,粘着磨损程度减小。搅拌摩擦加工后,样品主要磨损方式由粘着磨损和二体磨损转变为氧化磨损和三体磨损。经过180 r/min、25 mm/min处理的工业纯钛磨损率仅为未加工样品的1/4左右。结论慢速搅拌摩擦加工可同时提高工业纯钛表面硬度及耐磨损性能,较小的晶粒尺寸及合适的加工硬化程度可减轻粘着磨损和磨粒磨损。     

Effect of Zr Addition on the Grain Refinement Mechanism of Mg-Gd-Er AlloysEI北大核心CSCD

In recent years, Zr is widely used as an important additive element in magnesium alloys containing rare earth (RE), to improve the mechanical properties of Mg-RE alloys such as strength, ductility, creep resistance and corrosion resistance property. Heterogeneous nucleation mechanism and peritectic reaction mechanism are recognized as the main grain refining mechanisms. Whereas, during the solidification process, the melt wetting angle and nucleation energy are important factors which influence the nucleation. In this work, the effect of Zr on the solidification microstructure of the Mg-Gd-Er alloy was analyzed by using OM and EBSD; the undercooling of alloy melts was tested by using DSC; and the Mg/Zr interface relationship and interfacial energy were investigated by using HRTEM. Moreover, the effects of Zr on the wetting angle and nucleation activation energy of the Mg-11Gd-2Er and Mg-11Gd-2Er-0.4Zr alloys were investigated; the refinement mechanism of Zr on the alloys was discussed. The results indicates that the addition of Zr element can significantly refine the grain, and the grain size decreased from 1000 mm to 50 mu m. Compared with the Zr-free alloy, the nucleation wetting angle of the present alloy melt decreased from 18.3 degrees to 11.1 degrees, and the activation energy of nucleation decreased by 44.4%. The (1010) plane of Mg was completely coherent with the (1100) plane of Zr, reducing the interfacial energy between the (1010) Mg and the (1100) Zr. The grain refinement of Mg-Gd-Er alloy was ascribed to the decrease of melt wetting angle and the fully coherent interface relationship between Mg and Zr.     

热变形对轴承钢G80T晶粒细化行为的影响

利用Gleeble-3800热模拟变形试验机,对高温轴承钢G80T的动态再结晶行为及相关力学性能进行了研究。通过对该钢在1 050℃下以10s-1的变形速率进行0%~70%的不同形变量的单道次压缩,研究了不同形变量下热变形钢的微观组织结构及硬度。结果表明:当形变量在20%时,无动态再结晶发生;当形变量达到40%时,热变形组织出现了部分的再结晶晶粒;随着形变量的进一步加大,再结晶晶粒数目增多,形变量达到60%后,形变组织形成了平均晶粒尺寸为2.8μm的完全再结晶组织。同时由于形变和晶粒尺寸大幅度细化,钢中的碳化物也随着形变量的增加而逐步减少。通过对压缩应力-应变曲线软化行为的分析,认为该钢的再结晶属于动态再结晶;在1 050℃进行60%的形变可以实现该钢的完全动态再结晶,将平均晶粒尺寸从原始的22μm细化到2.8μm,同时将钢的硬度从820 HV提高到895 HV。研究结果表明,动态再结晶是细化高温轴承钢G80T晶粒尺寸和提高性能的一种有效措施。     

相比例对高压扭转Ti-6Al-4V合金晶粒细化及显微硬度的影响

冷轧态Ti-6Al-4V(TC4)合金经两种不同热处理制度处理之后,分别得到70%的等轴α相和30%的α+β片层组织(TC4-1)与25%的等轴α相和75%的α+β片层组织(TC4-2).等轴α相的晶粒尺寸分别为7.0±2μm和9.5±1.5μm.在室温下进行高压扭转,扭转过程中施加6.0 GPa的压力,扭转速度为1 r/min,分别扭转了1/4、5、10和20圈.随着扭转圈数和片层组织的增加,组织更为均匀.经20圈扭转变形后,TC4-1和TC4-2中的晶粒尺寸分别为115±30 nm和75±15 nm.随着片层组织的增加,显微硬度值显著升高.同时探讨了相比例对晶粒细化机制的影响.     

少量硼对钛合金组织影响的研究进展

硼作为一种显著影响钛合金组织的元素,已经在钛合金应用研究领域引起材料工作者的广泛关注。国内外近几年的研究工作主要围绕少量硼对钛合金的晶粒尺寸、组织稳定性以及相变点的影响展开。对含硼钛合金研究的最新进展进行了综述,分析了硼显著改变钛合金组织的机理,并提出了当前研究存在的不足以及今后潜在的发展方向。     

An ultrahigh strength steel with ultrafine-grained microstructure produced through intercritical deformation and partitioning process

In this work, a novel design scheme in which deformation-induced ferrite transformation (DIFT) was applied to produce fine-grained steel and the quenching is controlled by quenching and partitioning (Q&P) process has led to the development of a new kind of steel. This steel possesses excellent mechanical properties and the ductility can be further improved without compromising strength because the refined microstructure contains martensite, retained austenite and deformation-induced ferrite. The highest elongation of 15% allied with strength of 1700 MPa is obtained through hot deformation followed by Q&P treatment at 300 °C. The microstructure evolutions are discussed in terms of the current knowledge of the Q&P process and the experimental observations. The results show that the designed multiphase steels are a promising candidate for the development of the third generation of advanced high strength steels.     

Relationships of diboride phases in Al–Ti(Zr)–B alloys

Abstract

The relationships of diboride phases in Al–Ti(Zr)–B alloys with a variable Ti/B ratio close to the stoichiometry of TiB₂ were studied. The formation of diboride solid solutions was confirmed. A grain refinement mechanism is proposed as that diboride particles in the Al–Ti–B master alloys reacting with aluminium upon adding into an aluminium melt and release titanium into the melt through forming a (Ti,Al)B₂ solid solution and maintain a thin dynamic Ti rich layer on the surfaces of the (Ti,Al)B₂ particles, which nucleates α-Al grains in solidification. The poisoning effect of zirconium on grain refinement of aluminium by Al–Ti–B master alloys is also discussed.     

基于Sobel算子的医学图像边缘检测研究

边缘检测是图像处理过程的关键技术.由于医学图像的特殊性,检测边缘的准确性对疾病的诊断和治疗有着重大的影响.针对传统Sobel算法存在定位不精确、提取边缘较粗等不足,提出了一种改进算法.算法在传统Sobel算子模板基础上增加了45°方向和135°方向两个模板,提高了边缘定位的精度,采取局部梯度均值作为阈值对初始梯度图像进行局部梯度筛选,局部弱边缘得到增强,然后对处理后梯度图像进行细化和提取,得到边缘图像.实验证明,算法获取的图像边缘与传统Sobel算法相比,具有定位准确、边连续性好和边缘较细等优点,在医学图像处理中具有一定的实用性.