EFFECT OF ALLOY ELEMENTS ON QUASIEQUILIBRIUM MICROSTRUCTURE IN Fe-Mn-Ni-Cr STEELS

The microstructures of Fe-Mn-Ni-Cr steels with medium carbon and the effect of alloy ele-ments on them have been investigated by means of X-ray diffraction quantitative phase ana-lyses,metallography and hardness tests.The volume fraction of martensite in steels quenchedat 1100℃ can be expressed as:f_M~(1100)=162.643-15.482Mn-7.36Ni-4.286(Cr+Mo+V)Based on this expression,the quasi-equilibrium microstructure diagram has been obtained.Itis shown that the effect of Mn on the austenite stability is greater than that of Ni.The equiva-lent [Ni]=2.104Mn+Ni and equivalent [Cr]=Cr+Mo+V.The driving force for martensite transformation at M_s point has been calculated to hedrastically decreased by element Mn.     

QUASI-EQUILIBRIUM MICROSTRUCTURES AND EFFECT OF ALLOY ELEMENTS IN Fe-Mn-Ni-Cr STEELS

本文利用X射线定量相分析及金相观察和硬度测试,考察了中碳Fe-Mn-Ni-Cr钢的组织及合金元素的作用。建立了经1100℃淬火后的马氏体体积分数与合金成分的定量关系式; f_M~(1100)=162.643-15.482Mn-7.36Ni-4.286(Cr+Mo+V)并在此基础上给出了亚平衡组织图。结果表明,Mn稳定奥氏体的作用大于Ni的作用。Ni和Cr当量分别以[Ni]=2.104Mn+Ni,[Cr]=Cr+Mo+V表示。计算了M_S点处的马氏体相变驱动力,指出Mn具有强烈降低相变驱动力的作用。     

硼对快凝Ni3Al组织结构及力学性能的影响

本文通过快凝及加硼合金化的方法改善金属间化合物Ni_3Al的韧性。实验表明:加入0.5-1.4at.-％的硼对Ni_3Al的塑性提高最有利。结构分析表明:在含1.37at.-％硼的Ni_3Al中,硼以Ni_(23)B_6弥散相及晶界偏聚方式存在;当硼量增至2.22at.-％时,硼以粗大的Ni_(23)B_6及NiB_(12)相在晶界处析出。无硼的Ni_3Al晶界为大角度晶界;当硼加至1.37at.-％时,Ni_3Al晶界以位错排列成亚晶界,以小角晶界形式存在。     

Zr,Cr和B对Ni3Al合金组织和力学性能的影响

本文研究了含Zr(0—0.6at.-％),Cr(0—7.7at.-％)和B(0—2.22at.-％)的Ni_3Al合金的组织和室温至1050℃拉伸性能。结果表明,Ni_3Al合金的屈服强度随温度升高而增加,表现出反常的温度关系。到达峰值后,随温度升高,屈服强度降低。Zr和Zr+Cr在整个试验温度范围都增加Ni_3Al合金的屈服强度,并改善高温抗张强度和塑性。硼增加Ni_3Al合金的抗张强度和屈服强度,同时改善塑性。但当硼含量超过1.37at.-％时,则降低强度和塑性。当硼含量超过溶解度极限时,Ni_3Al合金中形成岛状和球状的Ni_(20)Al_3B_6和Ni_3Al的共晶组织,对强度和塑性都是有害的。     

半固态A356合金微观组织特征对充型能力的影响

采用电磁搅拌法制备了具有不同微观组织特征的半固态A356合金浆料,用图像分析软件对浇注前浆料金相试样的初生相微观组织特征进行了测定,利用间接挤压铸造方法铸造阿基米德螺旋线试样,以挤压成形后的螺旋线试样长度衡量充型能力,通过多元回归,建立了半固态A356合金初生相微观组织特征与充型长度之间的数学表达式。结果表明:半固态浆料充型能力不仅与初生相微观组织特征参数有关,微观组织特征参数的交互作用对充型能力的影响也较大。利用该表达式可以对半固态浆料充型能力进行预测,进而指导半固态浆料制备参数设计、间接挤压铸造工艺设计和缺陷预测。     

MICROSTRUCTURE AND MECHANICAL PROPERTIES OF Mg-Li ALLOY WITH Ca ADDITION

Mg-9wt%Li-2wt%Zn alloy was prepared and studied in this article. The addition of Ca to the alloy from 0.1wt% to 1wt% can refine the α-Mg and the best effect of refinement occurs when Ca content is 0.4wt%-0.5wt%. The billets can be rolled to thin sheets at room temperature, from which it is obvious that the addition of Ca improves alloys ormalin. while it decreases with the excess addition of Ca. The results also show that the ultimate tensile strength （UTS） and yield strength （YS） of the alloy with lwt% Ca may rise by 28% and 25%, respectively, however, the elongation decreases. It is clarified that the adsorption of proper Ca on the grain boundaries refines α-Mg and improves the tensile properties, but the presence of excess Ca and stable Ca2Mg6Zn3phase worsens the elongation.     

New inverse method for identification of constitutive parameters

A new inverse method by coupling iSIGHT and ABAQUS was proposed to determine the constitutive parameters of Al2O3sf/LY12 composite deforming at elevated temperature. It combined the merits of the f＇mite element simulation and optimization technique. The direct model was simulated with finite element code ABAQUS. The inverse problem associated with the identification of the constitutive parameters was expressed as a least square optimization problem. The direct simulation and the parameters optimization were implemented in iSIGHT integrated environment. The aim was to match the output of the direct simulation with the experiment data. The capability of the proposed inverse method was demonstrated through the identification of constitutive parameters of Al2O3sf/LY12 composite. The proposed new inverse method is also applicable to other parameters identification which is hardly determined through experiments or direct analytical method.     

Unique microstructure and property of a 2024 aluminum alloy subjected to upsetting extrusion multiple processing

The microstructure and hardness of a 2024 aluminum alloy subjected to multi-pass upsetting extrusion at ambient temperature were studied. Experimental results indicated that with the number of upsetting extrusion passes increasing, the grains of the alloy are gradually refined and the hardness increases correspondingly. After ten passes of upsetting extrusion processing, the grain size decreases to less than 200 nm in diameter and the sample maintains its original shape, while the hardness is double owing to equal-axial ultrafine grains and work hardening effect caused by large plastic deformation.     

胫骨的层状微结构研究

利用扫描电镜对胫骨的微结构进行观察，结果显示胫骨是一种由羟基磷灰石和胶原蛋白组成的生物层状陶瓷复合材料，其增强相羟基磷灰石在骨中占较大比例，并平行于骨的表面以层状的形式排列。观察也显示这些羟基磷灰石层又是由许多羟基磷灰石片所组成，这些羟基磷灰石片具有长而薄的形状，也以平行的方式整齐排列。基于在胫骨中观察到的羟基磷灰石片的微结构特征，通过微结构模型分析及实验，研究了这种微结构的最大拔出力。结果表明：羟基磷灰石片长而薄的形状以及层状排列方式增加了其最大拔出力，进而提高了骨的断裂韧性。     

Structure and blood compatibility of tetrahedral amorphous hydrogenated carbon formed by a magnetic-field-filter plasma stream

Tetrahedral amorphous hydrogenated carbon (ta-C:H) films with various substrate bias voltages were prepared using a magnetic-field-filter plasma stream deposition system. The microstructural and optical properties were studied using ellipsometric spectra. The refractive index n of each sample was obtained by simulating their ellipsometric spectral using Tauc-Lorentz oscillator model, and then the relative sp³ C ratio of each sample was calculated using Bruggeman effective medium approximation. The sp³ C fraction of each sample was quantified by using electron energy-loss spectroscopy (EELS). The blood compatibility of the samples was evaluated by tests of platelet adhesion, kinetic clotting time and thrombin time. The quantity and morphology of the adherent platelets on the surface of these samples were investigated using scanning electron microscopy. Results show that the spectroscopic ellipsometry is a helpful method to evaluate the sp³ carbon fraction of the carbon films. The substrate bias voltage has an obvious effect on sp³ content and blood compatibility of ta-C:H films. The sample prepared with substrate bias voltage of − 20 V showed the best blood compatibility. A simple bio-physical hypothetical model was proposed to explain the experiment results.