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关键词： Nb-16Si二元合金   激光熔化沉积   激光功率   原位反应   显微组织  

摘要： 以平均粒径约80μm的纯Nb和纯Si粉末为原料,采用500W、750W、1000W和1500W功率的激光束为热源,通过双通道同轴送粉激光熔化沉积(Laser melting deposition,LMD)技术制备了四种Nb-16Si二元合金。利用扫描电子显微镜(Scanning electron microscope,SEM)、X射线能量色散谱仪(Energy dispersive spectrometer,EDS)以及X射线衍射仪(X-raydiffraction,XRD)等手段分析了沉积态合金的宏微观组织演变与维氏硬度。结果表明,随LMD激光功率由500W增至1500W,沉积试样表面形貌逐渐趋于光滑,相对密度由91.1%增至98.5%。激光功率对沉积态Nb-16Si合金相组成无明显影响,在高能激光束的作用下,纯Nb粉末与纯Si粉末发生原位反应,直接合成了室温亚稳态的Nb3Si相和NbSS(Niobium solid solution,NbSS)相。激光功率强烈影响Nb-16Si合金的显微组织形貌,随激光功率的增加,合金中先共晶NbSS相由枝晶状逐渐转变为细小等轴状,其平均尺寸由约50μm细化至1μm左右,合金中NbSS+Nb3Si共晶组织形态由细小的层片状共晶,逐渐转变为纳米级的NbSS相弥散分布在Nb3Si基体上的不规则共晶。随激光功率增加,合金的维氏硬度由605HV逐渐增加至898HV。

关键词： gas-phase alloying   Mg-Zn alloy   heat treatment   Ringer’s solution   electrochemical behavior  

摘要： Mg-Zn binary alloys fabricated by the gas-phase alloying technique under vacuum condition were investigated in the state of initial state and after heat treatment for the microstructure and electrochemical *** from the traditional Mg-Zn alloys preparation methods,alloys prepared by gas-phase alloying have a large number of intermetallic compounds,such as MgZn,Mg7Zn3 and *** solution treatment,the boundary of the eutectic disappeared and the size ofα-Mg increased from 100μm to 150μ*** the same time,the value of the resistance of charge transfer increased,which indicates that the resistance of the charge transfer and the corrosion resistance of the alloys *** artificial aging treatment,the distribution ofα-Mg was more uniform and its size was reduced to about 50μm,and there was new eutectic structure *** newly formed eutectic structure forms galvanic cells with the alloy matrix,which makes the corrosion resistance of the alloy weaken.

关键词： Al-Sc合金   挤压变形   拉拔变形   热处理   力学性能   电导率  

摘要： 研究了Al-x Sc(x=0、0.10%、0.45%、0.70%)合金在挤压变形、拉拔变形和热处理过程中的力学性能和导电性能的变化。结果表明,铸态Al-Sc二元合金的强度都随Sc含量的增加而增加,而电导率逐渐降低。挤压变形后,Al-Sc合金的晶粒均有所细化,屈服和抗拉强度大幅提升,塑性略有下降;拉拔变形后,加工硬化使各Al-Sc合金的强度进一步提高,伸长率大幅降至1%左右;经过400℃保温2 min+300℃保温150 min的热处理后,Al-Sc合金的伸长率大幅提升,纯铝和Al-0.1%Sc合金的强度降低,然而添加0.45%和0.70%Sc的合金强度却有所升高,这主要是由于热处理后含Sc第二相析出导致的。两种变形过程对Al-Sc合金电导率的影响很小,热处理可通过分解铝钪固溶体大幅提高Al-Sc合金的电导率。最终制备的Al-0.45%Sc合金屈服强度,伸长率和电导率分别为210 MPa,7.2%,34.8×10^6S/m,兼具良好的力学性能和导电性能。

关键词： 垃圾分类   环保意识   垃圾处理   文明素质   素材运用   材料作文  

摘要： [2020年高考作文备考试题]阅读下面的文字,根据要求作文。材料1:2019年7月1日,《上海市生活垃圾管理条例》正式施行,开启了生活"垃圾强制分类"时代。按照总体部署,继上海之后,北京等45座城市也将跟进实施生活垃圾强制分类。

关键词： 等离子喷涂   Fe-Cr-Ni-C涂层   摩擦   摩擦学行为  

摘要： 通过等离子喷涂工艺在内燃机用GH4169合金表面上制得Fe-Cr-Ni-C与Fe-Cr-Ni两种涂层,采用实验测试的方式分析其组织和摩擦性能。研究结果表明:Fe-Cr-Ni-C涂层硬度以及结合强度优于Fe-Cr-Ni-C涂层,其硬度为536 HV,结合强度38.63MPa。在涂层中产生了完全熔融与部分熔融的两种区域,熔化区具备致密组织结构以及很高的硬度,部分熔融区能够对熔化区脆性得到有效改善。涂层摩擦系数均随温度的上升而减小,Fe-Cr-Ni-C涂层比Fe-Cr-Ni更低。Fe-Cr-Ni-C涂层具有比Fe-Cr-Ni更小的磨损率,并且当温度升高后,两种涂层都发生了磨损率减小,温度到达900℃时,两种涂层获得最小磨损率。在室温下Fe-Cr-Ni涂层形成了比Fe-Cr-Ni-C涂层更多的磨粒,发生了磨粒磨损,在Fe-Cr-Ni-C涂层的磨损区域产生了层状结构薄片,呈现剥落磨损特征。温度900℃时,在Fe-Cr-Ni涂层的磨损表面存在许多断裂的润滑膜,发生塑性变形。

关键词： Fe-Cr-B-C堆焊合金   焊接热输入   焊缝组织   性能  

摘要： 为了研究焊接热输入对高硼铁基堆焊合金组织结构及力学性能的影响,利用CO2/MAG焊,采用FeCr-C-B系金属粉芯焊丝制备高硼铁基堆焊合金,利用力学试验机、硬度仪、光学显微镜、扫描电镜及X射线衍射仪等研究了堆焊合金的组织形貌、力学性能及析出相的变化。结果表明:高硼铁基堆焊合金由(Fe,Cr)、(Fe,Cr)2B和(Fe,Cr)3(C,B)相组成,随着热输入的增加,初晶(Fe,Cr)和(Fe,Cr)2B体积分数增加,(Fe,Cr)3(C,B)相减少,堆焊合金的冲击韧性增加,当热输入为220.8 k J/m时冲击功达到最大298 J;堆焊合金的宏观硬度取决于(Fe,Cr)、(Fe,Cr)2B和(Fe,Cr)3(C,B)的体积分数,当热输入为220.8 k J/m时获得堆焊合金的最小洛氏硬度59 HRC。

关键词： 自保护药芯焊丝   明弧堆焊   Fe-Cr-C-B-W合金   组织及性能  

摘要： 采用自保护药芯焊丝明弧堆焊技术制备五组不同钨含量的Fe-Cr-C-B-W合金.借助金相显微镜、扫描电子显微镜、X射线衍射仪、洛氏硬度计和磨损试验机分析堆焊合金的组织及性能.结果表明,合金的显微组织由马氏体、残余奥氏体、M7(C,B)3,M3(C,B),Fe3W3C和WC组成.大部分钨元素被迁移到晶界生成了比WC稳定性更好的Fe3W3C缺碳复合相,堆焊层中没有典型的初生WC硬质相颗粒生成.随着钨添加量的增多,共晶硬质相M7(C,B)3,M3(C,B)和Fe3W3C随之增多,间距减小,呈连续网状均匀分布.当钨的添加量为12%时,堆焊层的耐磨性达到最佳.

关键词： as-cast fine grain ingot of GH4720Li alloy   homogenization heat treatment   microstructure evolution   hot workability  

摘要： GH4720Li was Ni-Cr-Co base precipitation strengthened superalloy and widely used for high performance applications such as disks and blades of either aircraft engines or land-based gas turbines attributing to its excellent properties including resistance to creep and fatigue, together with corrosion, fracture and microstructural stability for the intended applications. Compared with the double-melting process (vacuum induction melting (VIM)+electroslag remelting (ESR) or VIM+vacuum arc remelting (VAR), a triple-melting process (VIM+ESR+VAR) can eliminate the segregation coefficient of the alloying elements and reduce the content of impurity elements, while the ingot fabricated by the triple-melting process also exhibited lots of shortcomings, such as the coarse grains, dendritic structure, microstructure defects and high forging temperature. The as-cast fine grain ingot prepared by grain refining casting process can eliminate the microscopic shrinkage, reduce the differences among three crystalline regions and improve the hot workability as a result. However, it was hardly to avoid the microstructure defects by simply improving the casting process attributing to its large number of alloying elements. Therefore, the homogenization treatment was always performed on the superalloy ingot. In this work, the optimized homogenization parameter was identified according to the investigation on the microstructure evolution under various homogenization treatment conditions and hot workability of as-cast fine grain ingot after homogenization treatment. The relationships of one-stage as well as two-stage homogenization treatment parameters and segregation coefficient as well as volume fraction of eutectic phase were investigated indepth. The hot workability of the homogenized samples under various conditions was also analyzed with the help of hot compression tests. Experimental results revealed that the increased homogenization treatment temperature and extended holding time wer

关键词： 7175铝合金   均匀化   显微组织  

摘要： 采用DTA热分析仪、光学显微镜和扫描电镜(SEM)等分析仪器,研究了7175铝合金铸锭组织及均匀化工艺。结果表明,7175合金的铸态凝固组织由α(Al)+S相+T相非平衡共晶相组成;当均匀化温度在440℃时,合金中枝晶组织部分消失,低熔点相溶解不充分,当均匀化温度在460℃时出现过热组织。调整为阶段均匀化440℃×12 h+460℃×8 h处理后,合金晶界处的共晶组织基本消除,第二相尺寸降低至30μm以下,含铜相基本全部回溶,均匀化效果良好。

关键词： 3003铝合金   均匀化退火   显微组织   成分偏析   Al6Mn相  

摘要： 采用光学显微镜(0M)、扫描电子显微镜(SEM)、透射电子显微镜(TEM)结合能谱分析(EDX)技术,研究了3003铝合金圆铸锭不同部位的铸态显微组织以及均匀化退火温度和时间对组织的影响.研究结果表明:受冷却速度的影响,铸锭心部的晶粒尺寸和枝晶臂间距比铸锭边部的粗大;呈点状的Al(Mn,Fe)和Al(Mn,Fe,Si)金属间化合物在晶界上大量富集;经过均匀化处理后,合金的组织得到明显改善,Mn偏析得以消除,但均匀化处理未能使富集在晶界上的金属间化合物完全溶解.3003铝合金铸锭的最佳均匀化退火工艺为605℃13h.