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221.
用呋喃树脂石英砂工艺生产牵引电机换向器套筒出现变形、裂纹等铸造缺陷,是由石英砂相变膨胀引起,后用高铬刚玉砂代替石英砂得到解决. 相似文献
222.
223.
The deposition of copper by cold gas dynamic spraying has attracted much interest in recent years due to the capability to
deposit low-porosity oxide-free coatings. However, it is generally found that as-deposited copper has a signicantly greater
hardness, and potentially lower ductility, than bulk material. In this article, copper was deposited by cold spraying using
helium as the driving gas at both 298 and 523 K. Evidence is presented indicating that the material sprayed at the lower temperature
exhibits a lower dislocation density throughout the grain structure than the material sprayed at the higher temperature. The
low stacking fault energy of copper restricts recovery during annealing, and thus microstructural changes during annealing
only proceed once recrystallization begins. The material sprayed at low temperature (with the low dislocation density) exhibited
recrystallization at annealing temperatures as low as 373 K with a corresponding reduction in hardness. However, the copper
sprayed with helium at 523 K was resistant to annealing at temperatures up to 473 K where the dislocations in the structure
prevented recrystallization. However, at higher temperatures, recrystallization did proceed (with corresponding reductions
in hardness). The fracture behavior of the copper that was cold sprayed with helium at 523 K, both in the as-sprayed condition
and following annealing, was measured and explained in terms of the annealing mechanisms proposed.
The original version of this paper was published in the CD ROM Thermal Spray Connects: Explore Its Surfacing Potential, International
Thermal Spray Conference, sponsored by DVS, ASM International, and HW International Institute of Welding, Basel, Switzerland,
May 2–4, 2005, DVS-Verlag GmbH, Düsseldorf, Germany. 相似文献
224.
Calculated hardenability for improved consistency of properties in heat treatable engineering steels
W. T. Cook P. F. Morris L Woollard 《Journal of Materials Engineering and Performance》1997,6(4):443-448
Hardenability is one of the most important parameters controlling the heat treated properties of engineering steels. It affects
the consistency of response for microstructure, hardness, strength, toughness, and dimensional change (distortion). This study
illustrates that a major benefit of controlling hardenability is improving the consistency of dimensional distortion resulting
from heat treatment. To facilitate the supply of steels to hardenability limits, especially restricted hardenability, a new
technique was developed for the prediction of Jominy hardenability from chemical composition. The technique, termed the “Database
Method,” uses measured Jominy hardenability and chemical composition data, contained in a database, to calculate the hardenability
for a query composition. Using up to ten known steels, selected from the database with compositions closely matching that
of the query steel, a small adjustment is made to the measured hardenability of each known steel allowing for the small difference
in composition between the query and chosen steel. The final calculated result for the query steel is taken as the average
of the various estimates. The basis of the Database Method is explained, and the advantages are illustrated for selecting
engineering grades. 相似文献
225.
226.
冲天炉炉胆径向胀裂问题,也是一道颇有难度的课题,本文提出:用平行四边形、竖立的梯形和微凹矩形三种炉壁断面作为防止措施。 相似文献
227.
228.
Strengthening technology and mechanism for semi-solid die casting of aluminum alloy 总被引:10,自引:0,他引:10
Combined with theoretical evaluation,an optimized strengthening process for the semi-solid die castings of A356 aluminum alloy was obtained by studying the mechanical properties of castings solution treated and aged under different conditions in detail,then,the semi-solid die castings and liquid die castings were heat treated with the optimized process.The results show that the mechanical properties of semi-solid die castings of aluminum alloy are superior to those of the liquid die castings,especially the strengthening degree of heat treated semi-solid die castingsis much greater than that of liquid die castings with the tensile strength more than 330 MPa and the elongation more than 10%,and this is mainly contributed to the non-dendritic and more compact microstructure of semi-solid die castings.The strengthening mechanism of heat treatment for the semi-solid die castings of A356 aluminum alloy is due to the dispersive precipitation of the second phase(Mg2 Si) and formation of GP Zone. 相似文献
229.
变频开关电源Fuzzy-PID控制器的设计 总被引:1,自引:0,他引:1
针对感应式变频开关电源在对金属材料进行热处理过程中,负载的等效参数和谐振频率发生变化,而变频电源的输出频率不能及时调整和跟踪的问题,结合PID和Fuzzy控制技术的优点,设计Fuzzy-PID控制器对变频电源进行控制,在大偏差时用Fuzzy控制,在小偏差时用PID调节。Fuzzy-PID控制器以单片机8098为核心,采用SPWM专用芯片SA4828,实现变频开关电源的电压、电流双闭环控制,使变频电源不仅具有较快的动态响应、更小的超调,并且具有较高的稳态精度和频率跟踪控制特性。 相似文献
230.