三元稀土硅化物Gd_2PdSi_3单晶生长(英文)

采用光悬浮区熔法以3 mm/h的生长速度制备Gd2PdSi3单晶。该化合物表现为同成分熔融,其熔点在1700°C左右。与Gd2PdSi3化学计量成分相比,制备的晶体中Pd含量略低,导致了熔区内Pd的富集以及实验过程中熔区温度的降低。采用标准成分给料棒制备的单晶内含有少量定向的GdSi沉淀,可以通过退火热处理减少其含量但并不能完全消除。采用给料棒成分微调的方法制备出不含GdSi沉淀的高质量Gd2PdSi3单晶。     

‘Beautiful’ unconventional synthesis and processing technologies of superconductors and some other materials

Abstract

Superconducting materials have contributed significantly to the development of modern materials science and engineering. Specific technological solutions for their synthesis and processing helped in understanding the principles and approaches to the design, fabrication and application of many other materials. In this review, we explore the bidirectional relationship between the general and particular synthesis concepts. The analysis is mostly based on our studies where some unconventional technologies were applied to different superconductors and some other materials. These technologies include spray-frozen freeze-drying, fast pyrolysis, field-assisted sintering (or spark plasma sintering), nanoblasting, processing in high magnetic fields, methods of control of supersaturation and migration during film growth, and mechanical treatments of composite wires. The analysis provides future research directions and some key elements to define the concept of ‘beautiful’ technology in materials science. It also reconfirms the key position and importance of superconductors in the development of new materials and unconventional synthesis approaches.     

Disorder strengthening of ordered L12 alloys by face centered cubic (A1) precipitates

We present a new theory of strengthening (disorder strengthening) of a crystallographically ordered L1₂ matrix by spherical, coherent crystallographically disordered fcc (A1) precipitates. There are two versions of the theory, each involving different approximations for the length of the chord, inside the precipitate, subtended by the trailing dislocation in the super-dislocation pair. Each of these versions incorporates two other assumptions involving the statistics of dislocation-precipitate interactions, which determine the average spacing of the precipitates along the super-dislocation. All versions of the theory predict a peak-strength condition at small particle sizes, followed by an extended period of overaging in which the strength decreases slowly with increasing particle size. We compare the quantitative predictions of the theory with both computer-simulated and experimentally generated data on inverse Ni-base γ′-type superalloy matrices strengthened by γ precipitates. In all cases at least one version of the theory is in excellent agreement with the data. The predicted strengthening is significant, the order of 85–110 MPa in the computer simulated results and 40–80 MPa in model precipitation strengthened inverse superalloys containing small volume fractions (≤0.04) of γ precipitates. The results are discussed in light of the statistics of dislocation-precipitate interactions and the resistance of individual γ particles to shearing by the super-dislocation pair; this resistance depends on the ratio of maximum force required to break free of the precipitate and the line tension of the dislocation pair.     

高温服役后TP347HFG钢的组织与性能

利用金相显微镜、SEM、EDS和万能试验机分析了过热器管TP347HFG钢高温运行1.2×10⁴ h和7.5×10⁴ h后的组织与性能。结果表明,高温服役1.2×10⁴ h和7.5×10⁴ h后,TP347HFG钢仍保持明显的孪晶特征,析出的NbC有利于保持材料的组织稳定性。TP347HFG钢高温服役后力学性能能够保持稳定,随服役时间增加,强度增加而塑性变化不大。     

Precipitation Behavior of Modified as Cast High Nitrogen Super Hard High‐Speed Tool Steel

The properties of high‐speed tool steels can be improved by modifying their chemical composition or the technology of production. Nitrogen alloying is an attractive technology to enhance the mechanical and physical properties of tool steels. In this work, modified super hard high‐speed tool steel was produced through nitrogen alloying and decreasing the level of cobalt content in investigated steels. This work aims to study the effect of nitrogen as alloying element on carbides and carbo‐nitrides precipitates type, shape, and size for investigated steels. From the results obtained from Thermo‐Calc, it was concluded that nitrogen alloying produced large amount of stable austenite, also eutectic carbides precipitates (M₆C and M₇C₃) were stable at room temperature. Transmission electron microscope (TEM) images for traditional grade showed that the as cast structure contains beside the carbides network other single carbides precipitates. While on the other hand the selected area diffraction pattern (SADP) images of nitrogen alloyed grade shows fine carbides and carbo‐nitrides precipitates with more amount of retained austenite in the ferrite matrix, they showed also the presence of the eutectic precipitates as well as the dislocations.     

GH80A组织特征及平衡相析出行为的热力学计算分析

采用高分辨扫描电镜、物理化学相分析、X射线衍射等手段对实验GH80A合金热处理态的微观组织特征进行了定性和定量分析。结果表明,合金晶界分布有M7C3、M23C6两种碳化物,有效强化晶界,晶内弥散分布有γ’强化相,有效提高合金的高温强度;此外,采用Thermo-Calc热力学计算软件和Ni基数据库,对GH80A平衡析出相和非平衡凝固过程进行了模拟计算,并分析了合金元素Al、Ti对γ’相,C对MC、M7C3、M23C63种碳化物析出量和析出温度的影响。     

热暴露对航空用2E12铝合金组织演变及疲劳性能的影响

利用维氏硬度检测、疲劳性能测试、视差量热法(DSC)、透射电子显微分析(TEM)等手段,研究了航空用T3态2E12铝合金在150℃下分别暴露10 h,100 h,1000 h组织演变及疲劳寿命变化规律.结果表明:随热暴露时间的增加,合金硬度不断增大,疲劳寿命呈先增后降趋势;T3态及热暴露10 h合金中析出相由GPB区结构组成,热暴露10 h合金中GPB区发生长大,因而具有最长疲劳寿命;热暴露100 h至1000 h后,合金中析出相为S"相及S'相,析出相在晶界处析出,晶界附近形成无沉淀析出带(PFZ);由于S"相及S'相共格性较GPB区低,加之晶界处析出相易形成裂纹源,PFZ与基体协调性差等因素,热暴露100 h和1000 h后,合金疲劳寿命急剧下降.     

低碳微合金钢的组织结构对强度的影响

利用扫描电镜、透射电镜及能量损失谱仪对不同强度的低碳微合金钢的组织结构进行了观察分析。结果表明:不同强度试验钢的析出相均以大量30～80nm的球形和矩形颗粒相为主,类型相同,尺寸相近,强化效果相当;试验钢组织均为贝氏体+M/A岛,但贝氏体类型和M/A岛尺寸差别明显;具有板条贝氏体及细小M/A岛的轧态组织强度高,冲击韧性好;粒状贝氏体及粗大M/A岛组织显著降低钢的屈服强度和抗张强度。