Al-C和Al-Ti-C中间合金对AZ91合金晶粒的细化

制备出两种用于AZ91合金晶粒细化的Al-C和Al-Ti-C中间合金.结果表明:这两种中间合金对AZ91合金均有良好的晶粒细化作用.向AZ91合金中加入1%的Al-C中间合金可使晶粒由原来的约130μm减小至65μm左右;向AZ91合金中加入1%的Al-TI-C中间合金可使晶粒由原来的约130μm减小至45μm左右.然而,两种中间合金添加量分别大于1%时,晶粒尺寸没有进一步的变化.分析认为:Al-C和Al-Ti-C中间合金起晶粒细化作用的分别是Al4C3相和Al4C3和TiC复合相.     

Mn、Fe对AZ91D镁合金中Al4C3细化效率的影响

采用OM、SEM、EDS等测试手段研究了Mn、Fe对Al4C3细化AZ91D镁合金显微组织的影响.结果表明,经0.6%Al4C3细化后,基体合金的平均晶粒尺寸由360μm减小至215μm.在此基础上,将基体合金的Mn含量由0.23%增至0.5%,可使合金的平均晶粒尺寸进一步降至130μm.继续增加Mn量至0.7%时,其晶粒尺寸变化不大.当基体合金中Fe含量由0.0021%增至0.1%时,晶粒尺寸由215μm减小至123μm.Mn、Fe对AZ91D合金中Al4C3细化效率的影响机制可能是,三者共同作用形成的Al-C-O-Mn-Fe复杂颗粒可作为α-Mg晶粒的异质核心.     

C2 Cl6对AZ91镁合金显微组织及力学性能的影响

使用光学显微镜（OM）、X射线衍射仪（XRD）和扫描电镜（SEM），研究了C2Cl6对AZ91镁合金铸态显微组织与力学性能的影响，并利用Imagetool软件测量了晶粒尺寸和晶粒面积。结果表明，少量的C2Cl6（0．3％-0．8％）对α-Mg晶粒有明显地细化作用，平均晶粒尺寸由106μm降至约53μm，晶粒面积也明显减小，C2Cl6的最佳加入量为0．3％。而且，C2Cl6加入导致β-Mg17Al12相弥散细小。此外，显微组织的改善导致合金的力学性能明显提高。     

C2Cl6变质剂对铸造AZ91镁合金化学成分、组织和力学性能的影响

在加入与不加入C2Cl6两种不同工艺条件下,对铸造AZ91镁合金的化学成分、组织和力学性能进行了研究对比.结果表明,C2Cl6可使AZ91镁合金的晶粒得到明显细化,从而使合金的力学性能得到提高.     

新型Al-Ca-C中间合金对AZ91合金的细化作用

以Al粉、CaC2粉为原料,采用粉末冶金及原位合成法制备了一种新型Al-Ca-C中间合金用于AZ91合金的晶粒细化,Al-Ca-C中间合金中含有Al4C3、CaAl2、CaAl4相.试验表明,该中间合金对AZ91镁合金有良好的晶粒细化作用.当加入1.0％的Al-Ca-C中间合金时,AZ91合金的晶粒尺寸由原来的120～150 μm减小到40～50 μm.分析认为镁合金的细化机理为,Al4C3充当了α-Mg的异质形核核心,熔体中Ca与C原子则由于成分过冷进一步促进了晶粒细化.     

熔体处理及电磁搅拌对AZ91D合金组织的影响

利用金相显微分析等手段，研究了熔体处理及电磁搅拌对AZ91D合金组织的影响。结果表明，C粉对AZ91D合金晶粒具有明显的细化作用，优于C2Cl6和Al—10Sr间合金，无水FeCl3、Al-5Ti—B测效果甚微。熔体处理与电磁搅拌复合作用使AZ91D合金晶粒转化为均匀细小的类球状半固态组织，作用优于单纯的电磁搅拌。     

MgCO3对AZ91D镁合金晶粒细化效果的研究

研究了MgCO3对AZ91D镁合金的组织的影响.利用光学显微镜和扫描电子显微镜及其电子探针观察发现,MgCO3加入使得AZ91D镁合金的二次枝晶臂间距与晶粒尺寸显著减小,主要机理是MgCO3加入后反应生成了Al4C3、Al4C3颗粒可以作为Mg的结晶核心.通过在不同温度添加不同含量的MgCO3,在790℃时添加1.0%的MgCO3使AZ91D镁合金达到最佳细化效果.对于AZ91D合金而言,MgCO3是一种良好的晶粒细化剂.     

Mn-30Al中间合金对镁合金的晶粒细化

采用真空淬火炉制备出含ε-AlMn相的Mn-30Al中间合金和含γ_2-Al_8Mn_5相的Mn-30Al中间合金,观察了两种中间合金的组织,并探讨ε-AlMn相、γ_2-Al_8Mn_5相、Mn和Al对镁合金的晶粒细化效果.试验表明,相比添加Mn、Al,含γ_2-Al_8Mn_5相的Mn-30Al中间合金对AZ31镁合金存在一定的细化效果,含ε-AlMn相的Mn-30Al中间合金对AZ31镁合金具有更好的细化效果.当含ε-AlMn相的Mn-30Al中间合金添加量为0.4%时,AZ31镁合金的晶粒尺寸由原来的898μm减小至320 μm,Mg-Zn合金晶粒尺寸由原来的320 μm减小至180μm.通过面错配度计算,ε-AlMn可以成为初生α-Mg晶粒的良好异质形核核心.     

SiC对AZ91D镁合金晶粒细化效果的影响

研究了SiC对AZ91D镁合金组织的影响.通过在不同温度添加不同含量的Mg-SiC混合粉末,在760～780 ℃、SiC含量为0.20%时,AZ91D镁合金晶粒达到75 μm.利用光学显微镜和扫描电子显微镜及其电子探针观察发现,Mg-SiC混合粉末的加入使得AZ91D镁合金的晶粒尺寸显著减小,这是因为Mg-SiC混合粉末加入后反应生成了少量的Al4C3,Al4C3颗粒可以作为α-Mg的结晶核心,同时SiC颗粒本身也可以作为α-Mg的异质结晶核心.对于AZ91D合金而言,Mg-SiC混合粉末是一种良好的晶粒细化剂.     

SiC颗粒参与下快冷镁合金异质形核与高温晶粒长大

采用铜模喷铸与高温退火相结合,研究快冷AZ91+Si C合金组织细化与高温晶粒长大,揭示Si C颗粒对亚快速凝固镁合金异质形核及热稳定性的影响。结果表明:Si C可促进亚快速凝固过程中异质形核,阻碍凝固界面迁移,显著细化喷铸合金组织。400℃等温退火后,组织从枝晶向等轴晶转变并发生明显晶粒长大,快冷AZ91合金保温8 h后平均晶粒尺寸达78μm。添加2%Si C后,晶粒长大得到有效控制,8 h退火处理后平均晶粒尺寸仅为22μm。Si C的存在提高了基体中晶格畸变,退火组织中析出层片状与粒状共存的沉淀相。晶粒细化及Si C的添加提高了快冷镁合金显微硬度。随退火时间延长,合金硬度下降。沉淀相的析出导致AZ91+2%Si C合金硬度增加,最高可达111HV,比AZ91合金的硬度提高63.2%。     

High temperature naphthenic acid corrosion and sulphidic corrosion of Q235 and 5Cr1/2Mo steels in synthetic refining media

The corrosion of Q235 and 5Cr1/2Mo steels in synthetic refining media containing naphthenic acid and/or sulphur compounds was studied to evaluate naphthenic acid corrosion (NAC), sulphidic corrosion (SC), and their interaction. Corrosion dependencies on the test duration, temperature, total acid number (TAN) and content of sulphur compound were assessed. Specimens after NAC and SC tests were characterized by SEM/EDX, and XRD. It is found that in liquid phase of media containing only naphthenic acid and at temperature about 230 °C, 5Cr1/2Mo and Q235 steels have almost the same NAC rate, and above 230 °C, 5Cr1/2Mo has a higher NAC rate than Q235 has due to the higher NAC activation energy (63.2 kJ mol⁻¹) of 5Cr1/2Mo than that of Q235 (54.0 kJ mol⁻¹), indicating that increasing temperature accelerates NAC rate of 5Cr1/2Mo more than that of Q235. In oil containing only dimethyl disulphide, the growth of SC film follows parabolic kinetics, and the film of Q235 grows faster than that of 5Cr1/2Mo while SC rate of Q235 is higher than that of 5Cr1/2Mo. In oil containing both naphthenic acid and dimethyl disulphide, 5Cr1/2Mo has a lower corrosion rate than Q235 has. On the basis of “naphthenic acid corrosion index” (NACI), the benefits of 5Cr1/2Mo over Q235 should ascribe to that the pseudo-passive film for 5Cr1/2Mo has better NAC resistance than that for Q235. This is close related to the existing of additional chromium sulphide (Cr₅S₈) on the pseudo-passive film of 5Cr1/2Mo, in contrast with the pyrrhotite (Fe₇S₈) and troilite (FeS) on the film of Q235.     

Effects of particle angular velocity and friction force on erosion enhanced corrosion of 304 stainless steel

Erosion enhanced corrosion of 304 stainless steel was studied by single particle impingement. Velocities of the particles before and after impact were measured by a high speed camera. Impact and rebound dynamics of particles were used as a benchmark in analyzing the difference in the magnitude of current transients that were caused by passive film breakdown. Friction force and the effective path in which it acts on the surface showed significant influence on the extent of depassivation of the surface; however, the pre-impact angular velocity of the particles did not show a significant influence on the magnitude of current transients.     

C／C-SiC材料的快速制备及显微结构研究

分别以碳毡和二维碳纤维为预制体，采用化学液相气化渗入法结合熔融渗硅反应法快速制备了C／C-SiC陶瓷复合材料。对这种材料的密度和气孔率进行了表征，并通过XRD，OM和SEM等方法对其相组成、显微结构和反应机理进行了研究。结果表明：不同预制体制备的C／C—SiC材料密度和气孔率分别为～2．0g／cm^3和～1．0％。其相组成包括反应生成β-SiC以及未反应的游离Si和C。C／C—SiC中纤维被环状的沉积碳包裹，生成SiC的反应只发生在Si与沉积碳之间，纤维没有损伤。Si，C和SiC各相分布和含量因预制体的不同而有明显差异。     

晶闸管整流弧焊机引弧及其数字控制设计

针对直流电焊机引弧的工作环境和特点,分析了在焊接时采用旁路引弧的方法,同时在焊接时对焊机输出的电压、电流采样,并进行数字控制运算,适时稳定地控制焊机输出的电压、电流.其实现方法是采用C8051芯片处理器控制整个焊机的性能和功能,同时通过对负载电压、电流的采样进行双闭环控制.通过理论分析,实验验证了该焊接系统能根据焊接工...     

不同成分对C/C-SiC材料摩擦磨损行为的影响与机理

采用温压-原位反应法制备C/C-SiC复合材料,研究了SiC、石墨和树脂炭成分对C/C-SiC材料摩擦磨损行为的影响及其机理.结果表明:SiC在摩擦表面摩擦膜的形成过程中起骨架作用,提高SiC的含量有利于提高摩擦系数,降低磨损率;树脂炭在材料中具有粘结各成分和提高摩擦系数的作用,但其成膜性较差,易增大磨损率;石墨粉在制动过程中起润滑作用,适量石墨粉有助于形成稳定的摩擦膜降低磨损率;摩擦表面摩擦膜的形成有利于减少C/C-SiC材料的磨损率.     

测控系统中标准键盘接口设计

通过实例对标准键盘工作原理及其与单片机测控系统的接口做了介绍 ,提供了用C51编写的读键函数get-key及应用实例.提供的接口及C51函数可直接移植到其他测控系统开发中.     

Corrosion of austenitic and ferritic-martensitic steels exposed to supercritical carbon dioxide

Supercritical carbon dioxide (S-CO₂) is a potential coolant for advanced nuclear reactors. The corrosion behavior of austenitic steels (alloys 800H and AL-6XN) and ferritic-martensitic (FM) steels (F91 and HCM12A) exposed to S-CO₂ at 650 °C and 20.7 MPa is presented in this work. Oxidation was identified as the primary corrosion phenomenon. Alloy 800H had oxidation resistance superior to AL-6XN. The FM steels were less corrosion resistant than the austenitic steels, which developed thick oxide scales that tended to exfoliate. Detailed microstructure characterization suggests the effect of alloying elements such as Al, Mo, Cr, and Ni on the oxidation of the steels.     

Effect of environmental and metallurgical factors on hydrogen induced cracking of HSLA steels

Hydrogen induced cracking (HIC) resistance of two high strength low alloy (HSLA) steel plates equivalent to API X70 grade was evaluated in various test solutions with different H₂S partial pressures and pH values. Results showed that H₂S partial pressure is the key parameter affecting HIC resistance. Hydrogen permeation rate was affected by both H₂S partial pressure and pH of test solutions, whereas the apparent hydrogen diffusivity was determined mainly by pH value in case of H₂S partial pressure less than 0.1 atm. HIC in the steels primarily nucleated at inclusions and/or clusters containing the Al and Ca oxides. HIC resistance was determined by diffusible hydrogen amount with different microstructures.     

Hydrogen embrittlement susceptibility and permeability of two ultra-high strength steels

Slow displacement rate tensile tests were carried out in a saturated H₂S solution to investigate the effect of hydrogen embrittlement on notched tensile strength (NTS) and fracture characteristics of two ultra-high strength steels (PH 13-8 Mo stainless steel and T-200 maraging steel). Hydrogen permeation properties were determined by an electrochemical permeation method. The results of permeation tests indicated that over-aged specimens showed a lower diffusivity/hydrogen flux and higher solubility than those solution-annealed. The great increase in reverted austenite (irreversible hydrogen traps) together with numerous precipitates at the expense of dislocations (reversible) in the over-aged specimen led to such a change in permeability. Ordinary tensile tests indicated that four tested specimens had roughly the same yield strength level. Hence, the hydrogen embrittlement susceptibility of the material could be related to their permeation properties. The uniform distribution of strong hydrogen traps in over-aged specimens instead of weak traps in the solution-annealed impeded the hydrogen transport toward the strained region, thus, the resistance to sulfide stress corrosion cracking was improved in over-aged specimens.     

用于单元刚度计算的矩阵类程序的设计与开发

在有限元软件开发中,程序模块的重用和执行效率是影响软件性能的两个关键问题.运用面向对象语言开发有限元软件中的单元刚度矩阵计算程序,可有效解决其重用问题;运用引用变量、内存动态分配函数--calloc函数和内联函数,可有效地提高单元矩阵计算效率,从而提高有限元软件执行效率.本文开发的单元刚度矩阵计算程序是用C 语言编写.与传统的面向过程语言编制的有限元程序相比,该法编制的程序执行速度快、重用性好,易于实现多种类型单元共存的情况,是解决大型有限元程序编制的有效方法.文中通过应用实例比较,说明了此矩阵类的高效性.