Characterizations of cold-sprayed Nickel-Alumina composite coating with relatively large Nickel-coated Alumina powder

Previous studies have shown that the fabrication of metal matrix composites (MMCs) by cold spraying is effective and promising. When light materials, such as SiC and Al₂O₃, were used as reinforcements, it was diffcuclt to obtain a high volume fraction of hard phase in the composite just through the simple powder mixture. Therefore, in this study, a Ni-coated Al₂O₃ powder, which was produced through hydrothermal hydrogen reduction method, was employed aiming at increasing the volume fraction of ceramic particles in the deposited composite coating. It was found that a dense Ni-Al₂O₃ composite coating could be deposited with the Ni-coated Al₂O₃ powder under the present spray conditions. X-ray diffraction analysis indicated that the composite coating had the same phase structures as the feedstock. The volume fraction of Al₂O₃ in the composite was about 29 ± 6 vol.%, which is less than that in the feedstock (nominal: 40-45 vol.%) due to the rebound of some Al₂O₃ particulates upon kinetic impacting. The microhardness of the composite coating was about 173 ± 33Hv_0.2.     

原位自生TiAl3增强Al基复合材料的组织结构及形成机理研究

采用冷喷涂技术沉积Ti-80Al（wt.%）复合涂层,通过热处理获得了原位自生TiAl3金属间化合物颗粒增强Al基复合材料涂层。采用SEM、EDS和XRD等分析了冷喷涂Ti/Al复合涂层在不同热处理温度下的组织结构演变规律及Ti、Al粒子间原位扩散反应过程,并对TiAl3金属间化合物的形成机理进行了探讨。结果表明,冷喷涂Ti/Al复合涂层组织致密,其相结构与喷涂粉末完全相同,450℃热处理后涂层局部区域发生Ti、Al间的固态扩散反应,并在Ti、Al粒子界面原位形成TiAl3金属间化合物,随着热处理温度升高,TiAl3金属间化合物的含量显著增加,600℃热处理后,Ti/Al复合涂层中的Ti粒子全部转变为TiAl3金属间化合物,获得原位自生TiAl3颗粒增强的Al基复合材料.     

等离子喷涂WC-12Co/NiCrAl复合涂层的摩擦磨损特性

以NiCrAl涂层为粘结层,用等离子喷涂工艺在TC4钛合金表面制备了WC-12Co/NiCrAl复合涂层。通过扫描电镜(SEM)、能谱仪(EDS)、X射线衍射仪(XRD)和显微硬度仪等手段分析了涂层微观形貌、化学成分和显微硬度,并用磨损试验考察了WC-12Co/NiCrAl复合涂层的摩擦磨损特性。结果表明:WC-12Co涂层表面未熔颗粒较多,涂层截面孔隙率为10.2%;WC发生部分分解,出现W2C、Co6W6C等新相;涂层与基体结合界面为机械结合+局部微冶金结合方式;显微硬度为双态Weibull分布,呈现不同位置结构的差异化。WC-12Co涂层表现出良好的减摩及耐磨性能,同载荷下摩擦因数低于基体,磨损失重为基体的1/10,磨粒磨损是其主要磨损机制。     

纳米氧化镧增强Mo-Si-B合金多重强化效果分析

结合机械合金化和热压烧结技术制备的多相Mo-12Si-8.5B合金是由钼固溶体（α-Mo）和金属间化合物（Mo3Si和Mo5SiB2）组成的复合材料。合金的微观组织是Mo3Si和Mo5SiB2以颗粒形态弥散分布在具有连续结构α-Mo基体的晶粒内和晶界处。纳米尺度的La2O3颗粒主要分布在Mo-12Si-8.5B合金中α-Mo相的晶粒内,部分存在于Mo3Si和Mo5SiB2颗粒内。纳米La2O3颗粒的掺杂同时细化了α-Mo基体的晶粒和Mo3Si与Mo5SiB2相的颗粒从而使合金具有细小的微观组织,合金内α-Mo、Mo3Si和Mo5SiB2相的平均晶粒或颗粒尺寸均小于1μm。结合微观组织观察及力学性能试验结果,对Mo-12Si-8.5B合金中存在的细晶强化、固溶强化和颗粒强化多重强化效果的耦合作用进行了量化分析。     

Cold-sprayed copper and tantalum coatings — Detailed FESEM and TEM analysis

In cold spraying, a high level of plastic deformation and adiabatic shear instability are required for the tight bonding between powder particles and thus, formation of a dense microstructure. Cold-sprayed copper and tantalum coatings have fully dense structures according to microscopic evaluations and corrosion tests, indicating coatings' impermeability. Actually, denseness, i.e., existing through-porosity is a crucial coating characteristic which is reflected to the structural properties. In this study, the microstructure and fracture behavior are characterized using a field-emission scanning electron microscope (FESEM) and the inter-particle structures with a transmission electron microscope (TEM). Furthermore, a long-time impermeable behavior of these coatings was performed with open-cell potential measurements. Cold-sprayed copper and tantalum coatings possessed highly and localized deformed micro- and grain structures with high amount of dislocations and shear bands in their structures. Additionally, metal-metal particle bonds were attained as an important factor in the tight particle bonding. Moreover, partly ductile fracture behavior and material jets due to the thermal softening were observed from the fracture surfaces.     

真空扩散原位合成NiCoCrAlY涂层及其抗氧化性能

采用机械混合的方法将Ni,Co,Cr,Al,Y的单质粉末按照4∶2∶1.5∶1∶0.03的比例机械混合4h后,利用低压冷喷涂设备(GDU-3-15)在310S不锈钢基体表面沉积厚度为160 μm的混合粉体涂层,将制备好的样品置于真空管式炉(TL1700)中进行热扩散原位合成合金涂层.采用扫描电子显微镜(SEM)、能谱仪...     

0Cr18Ni9材料紧固件制作工艺探讨

0Cr1 8 Ni9材料高强度系列紧固件力学性能要求很高 ,要求采用超低温奥氏体不锈钢制作 ,固溶状态使用。一般生产工艺根本无法达到技术条件要求。我们通过反复试验 ,力求通过强化工艺使该材料达到要求的力学性能 ,现已摸索出两种强化工艺 ,可以达到该材料技术要求的强度 ,从而解决该系列紧固件制造的难题。     

Thermal conductivity of plasma-sprayed W/SiC composite for high-temperature energy applications

W/SiC metal matrix composites were produced by gas tunnel type plasma spraying (GTPS) using a mixture of 12 wt.% SiC-88 wt.% W feedstock powder. This work aimed at the optimization of the plasma gun current for deposition of a W/SiC composite with fine microstructure on AISI 304 substrate. Characterization of deposits was performed in order to assess microstructure, micro-hardness, thermal diffusivity and thermal conductivity. WO₃ was detected in the composite deposits, which indicated that the tungsten partially oxidized during plasma spraying. Also, the deposit composite was dense and nearly free of pores due to the little mismatch between the coefficient of thermal expansion (CTE) for W and SiC. Microhardness values gradually decreased as a function of input current due to the formation of WO₃ and the decomposition of SiC particles in high temperature flame region. The thermal conductivity as high as ∼ 59 W/mK was obtained at gun current 80 A. It was found that both tungsten oxide and structure imperfections have a significant influence on the thermal conductivity and mechanical properties.     

Tensile properties and strengthening mechanisms of Mo-Si alloy

Pure Mo and Mo-Si alloys with different silicon content were fabricated by powder-metallurgical and thermo-mechanical processing. Tensile properties of the pure Mo and Mo-Si alloys were measured at room temperature and the fracture surface was analyzed after test. The results indicate that Si can effectively reduced the grain size and improve the yield strength of Mo-Si alloys. With the decrease in grain size, the dominant fracture morphology is changed from intergranular to transgranular. The strengthening mechanisms were discussed and the yield strength was analyzed described with respect to grain size, solid solution hardening and Mo₃Si particle strengthening. Calculations show that the yield strength of Mo-Si alloys is governed by grain size.     

反应热压法制备Al2O3/NiCrAl复合材料及功能梯度材料

采用NiO、Al和Cr粉末反应热压制备了Al2O3/NiCrAl复合材料,NiCrAl合金由NiO还原出来的Ni与添加的Cr和Al反应形成.制备了不同Al2O3含量的Al2O3/NiCrAl复合材料,并以Al2O3体积分数分别为25%、52.2%和75%的Al2O3/NiCrAl复合材料为过渡层制备了Y稳定氧化锆(YSZ)到NiCrAl合金的功能梯度材料.X射线衍射分析、金相观察、硬度测量和热循环冲击实验结果表明:用该方法制备的复合材料由Al2O3陶瓷相和(Ni,Cr,Al)固溶体组成,而Al2O3颗粒由NiO与Al原位反应形成,尺寸细小,呈弥散分布.该功能梯度材料经从室温到1 000℃空气中10次热循环后未发现有裂纹,表明该方法制备的材料陶瓷相与合金相有良好的相容性、较高的结合强度、良好的耐高温抗氧化及热循环冲击性能.     

铌在集装箱用特种槽钢中的应用

本文介绍了含铌集装箱用特种槽钢的化学成分、金相组织及力学性能 ,观察并分析了铌的碳、氮化物析出特点     

Microstructure and wear properties of aluminum/aluminum-silicon composite coatings prepared by cold spraying

Composite coatings containing aluminum and aluminum-11.6 wt.% silicon eutectic alloy phases of varying compositions were fabricated using cold spraying. Coating contained a uniform distribution of the two phases. The hardness of the coatings increased as the volume fraction of Al-Si in the coating increased. The length to width ratio of the splats was found to be larger for Al particles compared to Al-Si particles. Dry sliding ball-on-plate wear tests indicated that the wear volume loss was similar for the Al and Al/Al-Si composite coatings in spite of the increase in microhardness. This discrepancy is explained by the inter-splat delamination mechanism. The coefficient of friction of aluminum coating reduced on Al-Si addition.     

Mechanical properties of cold-sprayed and thermally sprayed copper coatings

The present investigation compares the mechanical properties of cold-sprayed and thermally sprayed copper coatings. The mechanical properties of the Cu-coatings are determined by in plane tensile test using micro-flat tensile specimen technique. A deeper view into the type of obtained defects, their stability and their influence on coating performance, is supplied by subsequent failure analyses and the comparison to annealed copper coatings. The results demonstrate that cold-sprayed coatings, processed with helium as propellant gas, show similar performance as highly deformed bulk copper sheets and respective changes in properties after annealing. In the as-sprayed condition, cold-sprayed coatings processed with nitrogen and thermally sprayed coatings show rather brittle behavior. Whereas subsequent annealing can improve the properties of the cold-sprayed coating, processed with nitrogen, such heat treatments have only minor influence on the tensile properties of thermally sprayed copper coatings. The investigation of failure modes for the as-sprayed states and after different heat treatments provided further information concerning particle–particle bonding and the effect of oxides on mechanical properties.     

亚晶及析出相强化对Al-Zn-Mg-Cu合金性能的影响

采用金相显微镜、XRD物相分析、透射电镜观察和力学性能测试,研究了真空感应熔炼水冷铜模铸造下Al-8.2Zn-2.05Mg（10Zn-2.5Mg,12Zn-3Mg）-2.2Cu-0.1Mn-0.25Zr合金析出相的强化效应,以及第1种合金在形变热处理工艺下引入的亚晶强化效应。结果表明,3种合金在T6（120℃时效24h）状态下均析出了均匀弥散的强化相η′,此时析出相强化起主导作用。随着Zn、Mg含量的提高,析出强化相的数量逐渐增多,析出相强化效应增大,3种合金的抗拉强度分别为646.2、697.4和732.5MPa,伸长率分别为13.0%、10.6%和7.1%,抗拉强度与其析出相强化效应对应;采用120℃预时效12h+120℃温变形30%+120℃终时效10h的形变热处理工艺可使Al-8.2Zn-2.05Mg-2.2Cu-0.1Mn-0.25Zr合金获得亚晶组织,此时合金为亚晶强化与析出相强化共同作用的强化机制,合金的抗拉强度达到752.3MPa,伸长率为6.7%;亚晶内析出均匀弥散强化相提高合金性能,比单一增加析出相数量效果更好。     

Mechanical property of Fe-base metallic glass coating formed by gas tunnel type plasma spraying

Metallic glass has excellent functions such as high toughness and corrosion resistance. Therefore it is one of the most attractive materials, and many researchers have conducted various developmental research works. However, the metallic glass material is expensive and a composite material is preferred for the industrial application. Thermal spraying method is one of potential candidates to produce metallic glass composites. The gas tunnel type plasma system, which has high energy density and efficiency, is useful for smart plasma processing to obtain high quality ceramic coatings such as alumina (Al₂O₃) and zirconia (ZrO₂) coatings. Also, the gas tunnel type plasma spraying can produce metallic glass coatings. In this study, the Fe-base metallic glass coatings were formed on the stainless-steel substrate by the gas tunnel type plasma spraying, and the microstructure and mechanical property were investigated. The Fe-base metallic glass coatings of about 200 μm in thickness were dense with a Vickers hardness of about Hv = 1100 at plasma current of 300 A. The abrasive wear resistance of Fe-base metallic glass coating was higher than the SUS substrate.     

不同搅拌时间对半固态铝合金坯料制备的影响

ADC12铝合金用机械搅拌方法进行加工能细化晶粒,获得半固态铝合金坯料;本文通过改变搅拌时间制备半固态铝合金,并观察其微观组织、检测其硬度,以寻求最佳的搅拌时间工艺参数取值范围。对试验结果分析后得出：在搅拌温度为580℃、搅拌速度330r／min,固定不变时,搅拌时间25min左右半固态铝合金的金相组织和硬度为最佳。     

一种由MCNP设计,通过SPS加热轧制备的新型辐射屏蔽复合材料

本研究旨在设计和制备一种新型的中子和γ射线辐射屏蔽复合材料。基于蒙特卡罗模拟,含不同W质量分数(40~70%)的新型(W+B)/6061Al复合材料首次采用球磨法和SPS加热轧制法制备,并对其组织和力学性能进行了研究。实验结果显示,轧制之后,W和B颗粒均匀分布于基体中,而且W/Al界面以固溶体的形式呈现出良好的冶金结合。复合材料的物相主要包括W和Al。EBSD结果表明,W颗粒具有促进动态再结晶(DRX)成核、限制晶粒长大和降低6061Al基体织构的作用。拉伸试验表明,W含量为50 wt.%的复合材料强度最高,塑性较好。结合模拟结果,该组分的复合材料性能达到了实际应用要求。(W+B)/6061Al复合材料的强化机理包括位错强化和载荷传递效应。     

混杂增强AZ91镁合金基复合材料

采用挤压铸造成形法 ,成功地制备了具有不同含量与粒度的石墨颗粒与氧化铝短纤维混杂增强的镁合金基复合材料。对制备工艺、复合材料的显微组织及性能进行了研究 ,结果表明 ,增强相在复合材料中分布均匀 ,基体和增强相界面结合紧密 ,无明显铸造缺陷。复合材料的硬度随石墨含量的增加而降低 ,随石墨颗粒尺寸的细化而增大。     

Hardfacing of AISI304 steel: fabrication of oxide-boride-nitride ceramic matrix composite layer by laser-assisted high temperature chemical reaction

Composition, structure and properties of the products of self-propagating high-temperature synthesis (SHS) are characterised by some distinctive features. High heating rate, fast cooling after rapid completion of the reactions and steep temperature gradients make SHS very effective in producing in situ composites with ceramic reinforcements. In the present work, hardfacing of AISI304 substrates has been done by fabricating a hard ternary ceramic matrix composite layer of Al₂O₃–TiB₂–TiN by laser surface treatment at different scan speeds. The formation of the surface layer is due to laser-triggered SHS followed by laser melting. A mixture of Al, TiO₂ and hBN has been used as a precursor for the SHS reaction. The study of the microstructure of the as-fabricated composite layer reveals the co-existence of TiB₂ and TiN phases in the nanometric size range in Al₂O₃ matrix. The presence of all the phases has been confirmed by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), high resolution transmission electron microscopy (HRTEM) and Raman spectroscopy. The average grain sizes were calculated for the reinforcing phases and found to be 36 and 66?nm for TiB₂ and TiN, respectively, for the ceramic layer fabricated with a scan speed of 10?mm?s^?1, whereas 21 and 53?nm have been observed for TiB₂ and TiN, respectively, for the ceramic layer fabricated with the scan speed of 5?mm?s^?1. The understanding of the chemical synthesis in the SHS reaction mentioned here and the process of development of the reinforced composite in the fabrication of the hardfaced layer over steel surface will be immensely helpful in the discernment of the mechanical properties and, thus, finding the target area for the usage of this product. The virtues of the process and formation of the hard composite are reflected well in the microhardness achieved in the fabricated layers, as it is significantly higher than that of the substrate (AISI304 steel). In addition, indentation with a Berkovich tip in a nano-indentation set-up helped in further evaluation of the composite’s hardness and elastic modulus. The property spectrum of the composite, as reported here, indicates its suitability in various wear-intensive applications.