Microstructural changes of aluminized Alloy 617 during high-temperature aging

In this study, aluminized Alloy 617 was prepared by Al-pack cementation of high temperature high Al activity process. The microstructure evolution and microstructural changes of aluminide coating were investigated after Al-pack cementation and high-temperature aging. The aluminide coating was composed of Ni-aluminide layers, such as δ-Ni₂Al₃, β-NiAl, Cr₂Al, Al_3 + xMo_1 − x, and inter-diffusion zone by pack cementation. After high-temperature aging, the aluminide coating was transformed from the δ-Ni₂Al₃ to the β-NiAl because of outward Ni diffusion from substrate. The Cr₂Al and the Al_3 + xMo_1 − x were dissolved during aging. On the other hand, the α-(Cr, Mo) particles were precipitated during aging due to the low solubility of alloying elements in the β-NiAl. The β-NiAl newly formed by the outward Ni diffusion during aging and resulted in the formation of the inter-diffusion zone. The inter-diffusion zone consisted of β-NiAl, Ni₃(Al, Ti), Cr-rich M₂₃C₆ carbide, and sigma phases.     

CQFP器件高可靠组装的实现

CQFP器件由于其卓越的高可靠性能,在军事、航空、航天领域都有着广泛的应用,但是由于该类器件自身的特点,在实际组装过程中容易出现偏离焊盘、引脚变形以及焊点开裂等问题,这些都是装配工艺必须要尽量解决和避免的问题。阐述了CQFP器件的特点,分析了影响CQFP器件组装可靠性的主要工艺环节,给出了组装的注意事项和一些具体实施方法。另外列举了CQFP器件的一些常见缺陷,对发生的原因进行了分析,并结合实际给出了有效的解决措施。     

In situ chemical vapour co-deposition of Al and Si to form diffusion coatings on TZM

Multilayer alumino-silicide and silicide coatings were formed by in situ chemical vapour co-deposition of Al and Si on TZM (Mo–0.5Ti–0.1Zr–0.02C) alloy for improving its high-temperature oxidation resistance. MoSi₂ and Mo (Si, Al)₂ layers were formed in the inner and the outer layers, respectively in the case of alumino-silicide coating. Whereas silicide coating consisted of Mo₅Si₃ and MoSi₂ phases in the inner and the outer layers, respectively. 24–100-μm thick coatings were formed by optimizing the pack mixture of Al and or Si, NH₄F and Al₂O₃ powders and conducting the experiments at 1000 °C for 8–36 h. MoSi₂ layer showed a faster growth rate and presence of columnar grains. A small weight gain at the initial stages was observed during the oxidation tests of the coated samples under continuous or cyclic heating at 1300 °C in air. Neither cracks nor peeling of the coating layers were noticed after oxidation tests.     

地下工程机电管线预埋敷设施工技术探讨

在地下工程施工中,对机电管线的预埋敷设施工技术要求严格,本文根据笔者在多个地下工程中的施工经验,对此进行一定的分析和总结。     

Study on effects of alternating current field to pack boriding of medium carbon steel

Abstract

A plain medium carbon steel was borided by alternating current field enhanced pack boriding (ACFEPB). Diffusion kinetics and case characteristics of the borided steel were investigated to understand effects of an alternating current field (ACF) on pack boriding. Conventional pack boriding (CPB) was also employed for comparison. A series of boriding were conducted at temperatures of 873, 973, 1073 and 1173 K for 1, 2, 4 and 6 h, respectively, with a fixed current of 4 A. The morphology and types of borides formed in the steel were investigated by optical microscopy and X-ray diffraction, respectively. Boride growth kinetics was analysed by measuring the average thickness of the boriding case as a function of time and temperature. The growth rate of the ACFEPB case versus time showed the same parabolic character as CPB. The parameters of the boron diffusion kinetics, D?=?D₀exp(?QR^?1T^??1), have been determined. The results showed that the ACF enhanced inter-diffusion of boron in the substrate. The value of D, diffusion coefficient, in ACFEPB was more than 4 times of that in the CPB. The activation energy Q (44·45 kJ mol^?1) of the borided steel in the ACFEPB was less than 1/4 of that (180·6 kJ mol^?1) in the CPB.     

Corrosion behaviors and contact resistances of the low-carbon steel bipolar plate with a chromized coating containing carbides and nitrides

This work improved the surface performance of low-carbon steel AISI 1020 by a reforming pack chromization process at low temperature (700 °C) and investigated the possibility that the modified steels are used as metal bipolar plates (BPP) of PEMFCs. The steel surface was activated by electrical discharge machining (EDM) with different currents before the chromizing procedure. Experimental results indicate that a dense and homogenous Cr-rich layer is formed on the EDM carbon steels by pack chromization. The chromized coating pretreated with electrical discharge currents of 2 A has the lowest corrosion current density, 5.78 × 10⁻⁸ Acm⁻², evaluated by potentiodynamic polarization in a 0.5 M H₂SO₄ solution and the smallest interfacial contact resistance (ICR), 11.8 mΩ-cm², at 140 N/cm². The carbon steel with a coating containing carbides and nitrides is promising for application as metal BPPs, and this report presents the first research in producing BPPs with carbon steels.     

基于Cape Pack的军用物资单元包装优化研究

探讨了现代后勤对军用物资单元包装的要求,介绍了Cape Pack包装决策支持软件的主要功能,提出了基于该软件对军用物资单元包装优化的设计方案,最后通过案例演示了优化设计过程并对其结果进行分析,为军用物资单元包装优化提出了新的思路。     

电动汽车用铅酸善电池智能管理系统

绍了铅酸蓄电池的特点且设计出一套完整的基于P87C591单片机的铅酸蓄电池数字智能管理系统,包括铅酸蓄电池电压、充放电电流、内阻、剩余容量及电池温度等重要参数的检测,解决了传统充电方式中电池过充放电、寿命低等缺点,具有很好的应用前景,模块实现了对动力电池的监控和保护。具有接线简单、效率高、易于与整车控制网络相兼容等优势。     

S4手机用MH/Ni电池组的研制

本文介绍了S4手机用MH/Ni电池组的研制情况,对制作工艺及其特点作了较详细的说明。电池组放电容量在800mAh以上,循环寿命超过500次,能较好地替代S4手机中的锂离子电池组。     

Influence of siliconizing on the oxidation behavior of plasma sprayed MoSi2 coating for niobium based alloy

Plasma spraying combined with halide activated pack cementation (HAPC) was used to deposit silicide coating on Nb-based alloy. X-ray diffraction (XRD) and energy disperse spectrum (EDS) indicate the formation of the siliconized NbSi₂ transition layer and the sprayed MoSi₂ outer layer. NbSi₂ layer prepared with HAPC exhibits relatively uneven surface which could promote the deposition of the sprayed MoSi₂. The coating specimen with 5 h siliconizing presented the best oxidation resistance with only 0.18% mass gain after 25 h oxidation at 1200 °C in air. The synergistic protection effect, depending on the continuous silica layer formed on the coating surface and the dispersal silica within the coating and interface, is responsible for the excellent oxidation resistance of the coating.