共查询到20条相似文献,搜索用时 109 毫秒
1.
热处理是机械加工中保证产品质量、提高零件使用寿命的重要工艺之一。本文介绍了热处理的三要素、热处理的种类及其适用条件。举例分析了可以通过不同的热处理工艺,使工件达到所需要的状态,以满足其使用性能和要求。 相似文献
2.
为满足激光热处理工艺对数控编程的要求,本文介绍了一种基于AutoCAD的图形自动编程方法,用AutoCAD自带的Visual LISP编程语言实现了对复杂轮廓工件的激光热处理. 相似文献
3.
4.
5.
本文对LEC不掺杂SI-GaAs的热处理特性进行了实验研究和分析。结果表明,As、Ga原子从表面挥发及缺陷的内扩散引起表面热蚀和热致导电层的形成。文章讨论了它们对注入层激活行为的影响。指出,采用本文设计的高温快速热处理结合压盖、InAs作过砷压源技术,可以获得满足注硅材料退火要求的SI-GaAs热处理特性。 相似文献
6.
7.
8.
传统燃气炉对设备进行热处理时,炉内温度的是工作人员凭经验控制燃气炉的进气量来实现,因此炉内温度常常不能满足工艺要求,造成热处理效果不理想。本文提出采用AT89S52单片机来实现对燃气炉内温度的自动控制。由此构成的可控型燃气炉对设备进行热处理时,处理效果更能符合工艺的要求。 相似文献
9.
10.
运用差分法建立了圆柱体表面激光产生热场的计算,对不同的激光分布进行了模拟研究,给出了不同尺寸圆柱形物体的热场模拟.结果表明,激光在圆柱体上产生的热场与激光强度分布、圆柱体半径大小有关,在圆柱体半径较小时,激光热处理的自冷却条件不成立,因此,如果对圆柱表面进行热处理,必须注意有临界尺寸效应,超过该临界尺寸,可以进行激光自冷却热处理,小于该临界尺寸不能用激光自淬火热处理,必须加以辅助冷却;同样,对于管状物体也必须注意热处理时自淬火条件是否满足,否则,必须采取辅助冷却手段,以便获得适当的淬火层.
在模拟的同时,用相关尺寸的圆柱形和圆管形试样进行了热处理研究,试验结果和模拟结果进行了比较,充分肯定了模拟结果的正确性.同时,从模拟结果和实验结果的误差分布可以看出,激光热处理时,如果吸收层的不稳定会带来模拟和试验控制的困难,因此,除了研究模拟问题外,必须解决激光在试样表面的稳定吸收问题,否则,模拟结果和实验结果是不可预计的.(PE4) 相似文献
11.
对用液相外延(Liquid Phase Epitaxy,LPE)方法生长的碲镉汞(HgCdTe)材料进行了闭管富汞热处理,并研究了不同的热处理时间和热处理温度对其电学性能的影响.通过对HgCdTe材料进行富汞热处理可以有效降低材料内的缺陷尺寸、密度以及位错密度,并可完成材料由p型到n型的转变.工艺中,低温热处理对HgC... 相似文献
12.
高Al、Ti含量的定向凝固镍基高温合金在传统的修复过程中由于较大的热输入,存在严重的热裂倾向。利用激光热量集中、能量输入小的特点,可以有效控制修复过程中的热输入,从而减小铸造基体的晶界液化和开裂倾向。在优选参数下,可以获得无裂纹的修复组织,并可实现定向凝固组织的连续生长。对修复组织进行热处理,结果表明热处理过程不会促使裂纹产生,也不会影响熔覆层组织的定向凝固特征,但对于其内部γ′相的析出行为及形貌有较大影响,从而影响了沉积层的力学性能。对沉积层的拉伸性能测试表明,无论在常温还是高温(900 ℃)下,沉积层的拉伸性能都达到了铸造基体拉伸性能的80%以上,而且均为塑性断裂,一定程度上满足了实际修复需求。 相似文献
13.
14.
Li Hao Pingzhi Fan 《Wireless Communications, IEEE Transactions on》2007,6(8):2782-2787
In this paper, the inverse discrete Fourier transform (IDFT) results of oversampled Walsh Hadamard (WH) sequences and WH-based complementary (CP) sequences are derived, based on which, the peak factors (PF) of MC-CDMA signals are investigated for both the two sequence sets. The upper bounds of PF for both BPSK and QPSK modulation are presented in this paper and the PF bounds presented in B.J. Choi and L. Hanzo (2003) can be regarded as special cases of the bounds derived here. Compared with accurate computing which requires prohibitive computations, the upper bounds obtained provide a more effective way to estimate the PF of BPSK and QPSK modulated MC-CDMA signals employing WH or WH-based CP sequences. In addition, based on the IDFT properties of WH sequences, a simplified search for optimum WH subset in the context of BPSK modulation is derived. 相似文献
15.
16.
激光熔覆是一种典型的表面改性技术,已得到了广泛的应用。在激光熔覆快速冷凝过程中容易产生热应力,进而产生变形,严重时会产生裂纹、失效等缺陷。负膨胀材料是指在一定温度范围内材料体积出现热缩冷涨行为的材料,和热胀冷缩材料正好相反,负膨胀材料的发现为解决材料在受热时出现膨胀变形和失效提供了处理方法。正确的使用负膨胀材料可以抑制激光熔覆加工中的裂纹和热应力集中等缺陷,提高熔覆层的机械性能,产生热膨胀可控的材料甚至零膨胀材料。本文分析了激光熔覆中裂纹产生的机理,对负膨胀材料的种类及负膨胀的原理进行了总结,对每种负膨胀材料产生负膨胀行为的条件进行了对比和分析,负膨胀材料的膨胀系数和产生负膨胀行为的温度区间会影响在激光熔覆过程中的使用。重点对国内外已经实验验证的负膨胀材料在激光熔覆中的应用进行了总结概括,提出负膨胀材料在激光熔覆中存在的一些普遍规律,以及现阶段负膨胀材料在激光熔覆应用中的不足,对负膨胀材料在激光熔覆中的应用进行概括和展望。 相似文献
17.
《Electron Devices, IEEE Transactions on》1959,6(3):311-314
A complementary pair of medium-power high-speed switching transistors was required to satisfy the needs of an electronic switching system. Units have been designed and produced which exhibit a median cutoff frequency of 7 mc and a punch-through voltage of 70 volts. High yields have been achieved on established production lines by very close manufacturing controls of the critical alloying variables, namely, germanium wafer thickness, alloyed junction area, concentricity, mass of alloying material, alloying temperature, and special material properties such as orientation and etch-pit density. A vacuum-tight transistor structure has been designed to permit the dissipation of one-half watt of power at 25°C in free air. The structure embodies an all-copper cold-welded encapsulation for efficient heat removal. Important techniques concerning the cold-welding process will be discussed, and the particular die contour used will be illustrated in some detail. Additional cleanliness advantages are obtained by use of the cold welded seal. 相似文献
18.
In this paper, a method of constructing a sequence set similar to Walsh Hadamard (WH) codes is described. In general, two complementary sequence set of length 2 is used as a basic kernel to construct WH codes. In this work, four complementary sequence set of length 3 is used as a basic kernel. The proposed code set have a nearly non linear phase sequences with a more evenly spread frequency spectrum when compared with WH codes. It is shown that the proposed spreading codes perform comparable to WH in a Direct Sequence code division multiple access (DS-CDMA) system in an Additive White Gaussian Noise and Rayleigh channel at a reduced code length. In this work, bit error rate performance of the Underlay Cognitive Radio system implemented using DS-CDMA system is simulated. Primary and Secondary Users are distinguished by assigning spreading codes from different families and it is assumed that the channel information is known by both the Primary and Secondary User receivers. This new code set offers good performance in a Cognitive Radio Underlay system. 相似文献
19.
20.
Close-to-eutectic compositions in the Ge-Te system are analyzed and their behavior with repeated heat treatments is studied by means of differential scanning calorimetry and X-ray diffraction. It is shown that repeated heat treatment of the compositions under study leads to phase separation in the material. Assumptions are made about the nature of processes occurring in the materials subjected to heat treatment. 相似文献