不同强度岩石的破坏过程及声发射数值模拟

采用FLAC模拟了初始内聚力及内摩擦角对具有随机材料缺陷单轴平面应变压缩岩样破坏过程及声发射的影响;采用编写的若干FISH函数规定随机缺陷及统计发生破坏的单元数目.密实的岩石服从莫尔-库仑剪破坏与拉破坏复合的破坏准则,破坏之后呈现应变软化-理想塑性行为;缺陷在破坏之后经历理想塑性行为.随着密实岩石强度参数的提高,从应力峰值到残余应力的应力降、轴向应变增量提高,贯通试样的剪切带出现滞后,试样内部最终发生破坏的单元数降低.对于密实岩石强度参数高的试样,缺陷全部发生破坏之后,密实岩石没有立即发生破坏;应力峰值被达到之后,破坏的单元数增长不大.在加载过程中,声发射数有显著增加的三个区段.区段1、2及区段3的绝大部分位于峰前.在区段3的峰前阶段,声发射数的增加源于缺陷的长大、聚结、传播和竞争.强度参数越高,区段3越长,区段3的峰值越低.这表明当密实岩石的强度参数较高时,密实岩石单元破坏相继发生,破坏过程持续得较长.     

Effect of reduction temperature on some properties of ultrafine iron powders and hot-forged specimens

Conclusions A study was made of the processing properties of a reduced ultrafine electrolytic iron powder. The key parameter determining these properties is powder reduction temperature, which controls also the density of finished parts. An investigation into the process of structure formation during the heating of compacts for hot forging demonstrated the feasibility of producing -Fe of grain size 1 m or less. The principal parameters determining the conditions of production of an ultrafine -Fe grain are compact heating temperature and rate and duration of holding at the heating temperature. It is shown that ultrafine iron powders can be employed for manufacturing high-strength ultrafine-grained materials.Translated from Poroshkovaya Metallurgiya, No. 4(280), pp. 1–7, April, 1986.     

Mechanochemical synthesis of nanodimensional ferrite powders from salt systems

Nanodimensional spherical powders of oxide cubic ferrimagnets are obtained by mechanochemical synthesis. Their phase composition, morphology, dispersity, specific surface, and magnetic properties are determined. It is established that the synthesized ferrites are nanodimensional powders with a highly developed surface (S = 100?160 m²/g), and their magnetic characteristics substantially differ from those for bulk ferrites. As the structural element is reduced from 1000 to ～3–16 nm, ferrimagnets acquire the properties of cluster spin glass with a high blocking temperature.     

Manufacture of magnetic cores from various iron powders

Conclusions Coercive force measurements were made on grades PZh4M3, PZhCh3SV, PZhCh3MV, NC 100.24, PZhR(0) and PZhÉ iron powders and magnetic cores heat treated in the temperature range 750–1200°C. Iron powders of large specific surface are characterized by greater coercive forces compared with powders of small specific surface. Grades PZhCh3SV, PZhCh3MV, NC 100.24, and PZhR(0) iron powders are suitable for the manufacture of magnetic cores after they have been alloyed with elements decreasing internal stresses in alloys. Sintered magnetic cores from PZhÉ electrolytic iron powder meet all the requirements of TU 16-538.225-74 without alloying. The properties of grades EMP300M, PM282N, KiP 270.MS, and SC 100.26 iron powders were assessed. KiP 270.MS and SC 100.26 powders possess the same properties as PZhCh3SV, PZhCh3MV, and NC 100.24 powders, but in grade SC 100.26 powder high oxygen contents are not permissible. Consequently, magnetic cores made from this powder will exhibit high coercivity. Grades EMP300M and PZhR(0) iron powders are similar in all their properties, and the magnetic characteristics of cores made from them will therefore also be comparable. Grade PM282N iron powder is produced by the electrolysis of solutions and characterized by a dendritic particle shape. Owing to the large specific surface of the particles of this powder, its coercive force will be 25–30 A/m greater than that of PZhÉ. In the manufacture of magnetic cores from this powder recourse must therefore be had to alloying with silicon in order to decrease their coercivity.Translated from Poroshkovaya Metallurgiya, No. 6(234), pp. 73–78, June, 1982.     

Permanent magnets from fine iron and iron-cobalt alloy powders

Conclusions It has been established that, to obtain the optimum, magnetic properties in isotropic materials from fine iron and iron-cobalt alloy powders, the powders should be heat-treated for 4 h at a temperature of 280°C and compacted under a pressure of 15–16 kbar. Heat treatment tends to destroy dendritic axes of the second and third orders on the powder particles, heal structural defects, and increase the flowability of particles during pressing, thereby ultimately improving the magnetic properties of the resultant components. The maximum magnetic energy is 4.6 kJ/m³ for isotropic magnets from iron powders and 8.6 kJ/m³ for magnets from iron-cobalt alloy powders.Translated from Poroshkovaya Metallurgiya, No. 10 (142), pp. 61–63, October, 1974.     

Ni-Co合金粉末的热压显微组织与力学性能研究

研究了Co含量(质量分数)分别为10%、20%、30%、40%、50%的Ni-Co合金粉末在不同热压温度下的显微组织与力学性能.研究结果表明:采用共沉淀-还原法制备的Ni-Co合金粉末烧结活性高,在700℃下就能热压致密化;在700℃至800℃之间热压时,晶粒长大较明显,热压温度超过800℃后,晶粒长大趋势减缓;随热压温度升高,Ni-Co合金综合力学性能下降,在700℃的热压温度下能获得最佳的综合力学性能;随Co含量增加,合金综合力学性能增强,Co含量增加到30%后,力学性能增强趋势减缓.700℃热压时含30%Co、40%Co、50% Co的Ni-Co合金的抗弯强度分别为1188.7 MPa、1220.5 MPa、1227.1 MPa.     

Recrystallization of electrolytic iron powders

Translated from Poroshkovaya Metallurgiya, No. 2, pp. 4–5, February, 1991.     

铜包铁粉的应用及制备

铜包铁粉是一种将铜包在铁粉表面形成包覆层的复合粉末,被用来改善铜铁混合粉末组织不均、成分偏析等问题。本文综述了铜包铁粉的应用及制备方法,介绍了机械球磨涂覆法、置换镀铜法、化学镀铜法等铜包铁粉制备技术的基本原理及研究进展,总结了铜包铁粉制备过程中存在的问题,并展望了铜包铁粉的发展方向。