稀土对机械镀无结晶形成过程及镀层性能的影响

采用机械镀方法制备了锌基稀土无结晶镀层,用扫描电子显微镜(SEM)、X射线荧光光谱分析(XRF)等研究了稀土添加对机械镀无结晶镀层形成过程及镀层特性的影响.结果表明,稀土金属盐复合添加剂能影响无结晶镀层形成时金属微粉的集聚、吸附和沉积特性,使金属粉趋于面状吸附一沉积,改善了镀层的形成条件.机械镀锌基稀土合金镀层外观平整、光亮,密度、显微硬度、耐腐蚀性和电化学特性明显优于传统机械镀锌层.     

机械镀合金镀层的研究进展

首先,概述了近年来国内外对机械镀合金层研究的发展历程,指出不同种类机械镀合金层在湿式与干式工艺中的研究难点,湿式机械镀研究主要集中于镀层形成机理、锌基复合镀层及表面活化剂等,干式机械镀主要集中于镀层的合金化及镀层合金材料的配制方面。其次,分析了2种不同工艺下合金镀层的形成机理及合金镀层的防腐机理,湿式镀层由金属粉依靠表面活性剂和沉积促进剂在先导金属的作用下稳定持续形成,从而在基体表面形成防腐屏障;干式镀层依靠合金包覆的丸粒高速喷射冲击基体而形成,合金层和其表面的氧化膜作为防护层。最后,基于合金镀层优良的耐蚀性能和机械镀工艺特点,给出了研究发展以合金粉为原料的湿式机械镀的倡议,并从活化与沉积稳定性、绿色与复合化、产业标准化等方向,提出了机械镀合金镀层在防腐材料领域的发展趋势及研究建议。     

钛材表面无氢式一次性形成金属碳化物新方法

发明了1种能够在钛材表面无氢式一次性形成金属碳化物的三栅极离子渗镀新方法。系统工作时所产生的等离子从空隙处直接奔向工件待处理表面，从而无氢式一次性在金属材料表面形成由镀层、或扩散层或渗镀层构成的金属碳化物表面改性合金层。利用该方法在纯钛(TA2)基材表面进行了一次性无氢式渗碳和C，Mo共渗的试验。试样的x射线衍射分析(XRD)、辉光放电分析(GDA)等测试结果表明，在钛基表面形成了具有金属碳化物及碳扩散次层的渗镀合金层，渗镀成分呈现明显的梯度分布，厚度在20μm以上，最高硬度可达13000MPa。     

空心玻璃微珠表面化学镀镍磷合金

以胶态钯为活化液对空心玻璃微珠表面化学镀镍工艺进行了研究.通过环境扫描电镜(ESEM)和能谱分析(EDS)分别对微珠镀镍前后的形貌进行了观察、对镀层成分进行了测试,并对微珠施镀装置进行了设计.结果表明:利用该工艺可在微珠表面形成光滑、均匀的Ni-P镀层,且在微珠间无散落的镀层金属颗粒存在;采用液体搅拌促进镀液循环,有利于微珠的悬浮和分散,并提高镀液的稳定性,为空心玻璃微珠表面的金属化提供了一个简单易行的工艺.     

Ni-SiC纳米复合镀层的耐高温氧化性能

研究了电镀工艺条件对Ni-SiC纳米复合镀层耐高温氧化性能的影响规律.研究表明,经800℃,1.5h灼烧,随着镀层中SiC复合量的增加,复合镀试片总增重略降后上升至最大,后又再下降,对基底金属Fe的耐高温氧化的保护作用先增后减.最佳工艺条件下获得的纳米复合镀试片总增重比Watts镀试片减少1/4,镀层本身的耐高温氧化性能有所增强,而源自基底金属Fe的氧化增重减少近2/3,对基底金属的保护作用明显增强;显微硬度测试表明,灼烧后镀层表面形貌发生了很大的变化,原来结晶细小的蜂窝状结构消失,结晶粗大的瘤状突起明显增多,但显微硬度没有发生明显变化.     

金刚石表面镀镍工艺研究

研究金刚石表面镀Ni工艺,金刚石经粗化处理后,首先以氯化钯对其表面活化,进行化学镀Ni形成金属表层,然后以滚镀方式在其表面进行电镀加厚,镀Ni层使金刚石强度提高,磨削性能得到改善。讨论了各工艺因素对镀层质量指标的影响。     

机械镀的现状及发展

机械镀是在非冶金和非电解结晶的条件下形成镀层，具备低成本、低能耗、无工业污染和镀后无氢脆，耐腐蚀性好，设备投资低等优点。在工业应用中，薄层镀应改善外观，厚层镀应提高结合强度，以期接近电镀和热镀产品的使用功能。由于镀层的厚度范围较宽，且能按防腐蚀要求灵活调整，为合金化镀层的发展提供了简便的条件，在镀层防腐功能和成本控制上形成优势，在市场竞争中具有潜力。     

电刷镀机械研磨复合沉积试验研究

在电刷镀过程中引入机械研磨，形成复合作用下的电化学沉积镀层。相对于常规电刷镀工艺进行的对比性试验表明：复合方式对改善电刷镀层的孔隙率、表面粗糙度及镀层内部的应力状态都有明显的效果。     

微粉金刚石表面镀钛对钎焊磨具性能的影响

在微粉金刚石磨具的制备过程中,金刚石热损伤和磨粒与结合剂间界面特性是影响磨具性能的主要因素。利用电铸与钎焊相结合的工艺把表面镀钛和未镀钛两种微粉金刚石磨料制备成磨具,并将其用于氧化铝陶瓷的磨削试验。通过对钎焊后金刚石磨粒与钎料的界面分析,磨削力、磨粒脱落率以及工件表面粗糙度的比较,探讨磨粒表面镀钛对钎焊微粉金刚石磨具性能的影响。结果表明,镀钛微粉金刚石表面镀层在钎焊过程中对微粉金刚石起到包裹隔离的作用,可以降低微粉金刚石的热损伤和石墨化;在利用两种钎焊微粉金刚石磨具磨削氧化铝陶瓷时,镀钛微粉金刚石磨具的磨削力较小,磨料的脱落率也较少,且工件表面粗糙度值更低。综合比较,磨粒表面镀钛后,可以减弱微粉金刚石的热损伤,提高磨具的磨削性能。     

热处理温度对镁合金表面化学镀Ni-P合金结构和性能的影响

镁合金直接化学镀工艺中热处理温度是影响镀层质量的最重要因素之一,本文利用扫描电镜观察镀层的表面形貌确定了最佳镀液温度。将试样在不同的温度下进行热处理,用X射线衍射仪分析不同热处理温度下的晶化程度,从而确定镀层的结晶温度,并用显微硬度仪测量镀层显微硬度。     

RHEOLOGY FEATURE OF SIMPLE METAL MELT

The rheology feature of Sb, Bi melt and alloys was studied using coaxial cylinder high-temperature viscometer. The results showed that the curve of torsion-rotational speed for Sb melt presents a linear relation in all measured temperature ranges, whereas for the Bi melt, the curve presents obvious non-Newtonian feature within the low temperature range and at relative high shear stress. The rheology feature of Sb80Bi20 and Sb20Bi80 alloy melts was well correlated with that of Sb and Bi, respectively. It is considered that the rheology behavior of Sb melt plays a crucial role in Sb80Bi20 alloy and that of Bi melt plays a crucial role in Sb20Bi80 alloy.     

Microstructures and Mechanical Properties of a Newly Developed Austenitic Heat Resistant Steel

The effect of heat treatment on the microstructures and mechanical properties of a newly developed austenitic heat resistant steel(named as T8 alloy) for ultra-supercritical applications have been studied. Results show that the main phases in the alloy after solution treatment are γ and primary MX. Subsequent aging treatment causes the precipitation of M_(23)C_6 carbides along the grain boundaries and a small number of nanoscale MX inside the grains. In addition, with increasing the aging temperature and time, the morphology of M_(23)C_6 carbides changes from semi-continuous chain to continuous network.Compared with a commercial HR3C alloy, T8 alloy has comparable tensile strength, but higher stress rupture strength. The dominant cracking mechanism of the alloy during tensile test at room temperature is transgranular, while at high temperature, intergranular cracking becomes the main cracking mode, which may be caused by the precipitation of continuous M_(23)C_6 carbides along the grain boundaries. Typical intergranular cracking is the dominant cracking mode of the alloy at all stress rupture tests.     

The 15th Global Foundry Sourcing Conference 2014held in Qingdao China

Organized by Suppliers China Co., Ltd and co-organized by the National Technical Committee 54 on Foundry of Standardization Administration of China, the 15th Global Foundry Sourcing Conference 2014 （hereinafter referred to as FSC 2014） was successfully held on Sep. 23rd in Grand Regency Hotel, Qingdao. More than 500 delegates from home and abroad attended this conference, including over 130 purchasers from 20 countries and 380 domestic and foreign suppliers.     

LASER CLADDED TiCN COATINGS ON THE SURFACE OF TITANIUM

Laser cladded coatings of TiCN were produced on the surface of titanium. To obtain the optimal techniques, several conditions were tested by varying the laser scanning rate. The choice of shielding gas was also studied. The cladded coatings were then evaluated from the surface mechanics point of view based on their microhardness. The microstructure of some interesting samples was investigated by optical micrographs (OM). The results showed that under the condition of fixed pulse frequency and pulse width, the laser scanning rate and the shielding gas are the main factors influencing the components of coatings. TiCN coatings were decompounded and oxidized during the cladding process in the condition of no shielding gas of N2. X-ray diffraction results indicated that the composite coatings composed of TiCN, TiC, Ti2N, and TiO2 were produced using appropriate techniques. The results indicated that the best condition in terms of the surface microhardness is obtained when the scanning rate is 1.5mm / s, the pulse frequency is 15Hz, the pulse width is 3.0ms, and N2 is chosen as the shielding gas. The microhardness of the composite coatings is about 1331kg · mm - 2, which is about 4 times that of the substrate. The optical micrographs indicated that the cladding zone is made up of TiCN, TiO2, and some interdendritic Ti, but the diffusion zone mainly consists of the dendrites phase, and the cladded depth is about 80m, which is more than 2 times that of the laser nitrided sample. There were no microcracks or air bubbles in the cladded sample, which was cladded using the above optimal techniques.     

Microstructure and Mechanical Properties of X80 Pipeline Steel Joints by Friction Stir Welding Under Various Cooling Conditions

X80 pipeline steel plates were friction stir welded(FSW) under air, water, liquid CO_2 + water, and liquid CO_2 cooling conditions, producing defect-free welds. The microstructural evolution and mechanical properties of these FSW joints were studied. Coarse granular bainite was observed in the nugget zone(NZ) under air cooling, and lath bainite and lath martensite increased signifi cantly as the cooling medium temperature reduced. In particular, under the liquid CO_2 cooling condition, a dual phase structure of lath martensite and fi ne ferrite appeared in the NZ. Compared to the case under air cooling, a strong shear texture was identifi ed in the NZs under other rapid cooling conditions, because the partial deformation at elevated temperature was retained through higher cooling rates. Under liquid CO_2 cooling, the highest transverse tensile strength and elongation of the joint reached 92% and 82% of those of the basal metal(BM), respectively, due to the weak tempering softening. A maximum impact energy of up to 93% of that of the BM was obtained in the NZ under liquid CO_2 cooling, which was attributed to the operation of the dual phase of lath martensite and fi ne ferrite.     

INDUSTRY NEWS

China Securities News reported on March 21, 2014： Guangdong Hongtu Wuhan Die Casting Co., Ltd. （Wuhan Hongtu）, a wholly owned subsidiary of Guangdong Hongtu Technology （Holdings） Co., Ltd., held a groundbreaking ceremony recently. With the registered capital of 50 million Yuan, Wuhan Hongtu has a total land area of 100,000 square meters and a plant construction area of 72,000 square meters. It is expected to have a production capacity of about 30,000 tonnes of aluminum castings annually after it is put into production.     

GROWTH MORPHOLOGIES OF A BINARY ALLOY WITH LOW ANISOTROPY IN DIRECTIONAL SOLIDIFICATION

Two new classes of growth morphologies, called doublons and seaweed, were simulated using a phase-field method. The evolution of doublon and seaweed morphologies was obtained in directional solidification. The influence of orientation and velocity on the growth morphology was investigated. It was indicated that doublons preferred growing with its crystallographic axis aligned with the heat flow direction. Seaweed, on the other hand, could be obtained by tilting the crystalline axis to 45°. Stable doublons could only exist in a range of velocity regime. Beyond this regime the patterns formed would be unstable. The simulation results agreed with the reported experimental results qualitatively.     

STUDY ON PROPERTIES OF PULSE ELECTRODEPOSITED RE-Ni-W-P-SiC COMPOSITE COATINGS

The effects of pulse frequency f and duty cycle r on the deposition rate, composition, morphology, and hardness of pulse electrodeposited RE （rare earth）-Ni-W-P-SiC composite coatings have been studied. The results indicate that pulse current can improve the deposition rate of RE-Ni-W-P-SiC composite coatings; W, P, and SiC contents in the coating decrease with the increase of pulse frequency and reach the lowest value at f = 33Hz, whereas the RE content in the composite coatings increases with the increase of pulse frequency. SiC content decreases with the increase of duty cycle, W content reaches the lowest value, and P content reaches the highest value at r = 0.4; pulse current and RE can lead to smaller size of the crystalline grains; however, the effects of different pulse frequency and duty cycle on the morphologies of RE-Ni-W-P-SiC composite coatings are not obvious. The hardness of RE-Ni-W-P-SiC composite coatings is the highest when the duty cycle is at 0.6 and 0.8 and pulse frequency is at 50Hz. At the same pulse frequency, the hardness of RE-Ni-W-P-SiC composite coatings at r= 0.8 is higher than that at r= 0.6.     

RELATIONSHIP BETWEEN J-INTEGRAL AND FRACTURE SURFACE AVERAGE PROFILE

To investigate the causes that led to the formation of cracks in materials, a novel method that only considered the fracture surfaces for determining the fracture toughness parameters of J-integral for plain strain was proposed The principle of the fracture-surface topography analysis （FRASTA） was used. In FRASTA, the fracture surfaces were scanned by laser microscope and the elevation data was recorded for analysis. The relationship between J-integral and fracture surface average profile for plain strain was deduced. It was also verified that the J-integral determined by the novel method and by the compliance method matches each other well.