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.     

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。     

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.     

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。     

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.     

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.     

Correlation of microstructure and high temperature oxidation resistance of plasma sprayed NiCrAl, NiCrAlY, and TiAlO composite coatings on Ti−6Al−4V

In the present study Ni−18Cr−6Al, Ni−22Cr−10Al−1Y and TiAlO composite powders were coated on Ti−6Al−4V substrates by atmospheric plasma spraying, and the coated specimens were evaluated by isothermal and cyclic oxidation resistance tests at 800°C. The oxidation kinetics of the plasma sprayed NiCrAl, NiCrAlY, and TiAlO composite coated specimens obey a parabolic rate law. The oxidation resistance of the plasma sprayed NiCrAl and NiCrAlY coatings is superior to that of plasma sprayed TiAlO composite coating. The best oxidation resistance was observed in the plasma sprayed NiCrAlY coatings. This is mainly attributed to the formation of Y−Al−O complex oxides and Ni₃Al with higher thermal stability on the coatings.     

大气等离子喷涂NiCr/Cr3C2复合涂层的性能

采用化工冶金包覆、固相合金化和喷雾造粒技术制备了NiCr/Cr₃C₂复合粉体,并采用大气等离子喷涂技术制备了NiCr/Cr₃C₂复合涂层,采用SEM、显微硬度计、万能试验机和马弗炉对粉体和涂层的显微结构、涂层的显微硬度、结合强度和氧化性能进行了分析。结果显示:NiCr/Cr₃C₂涂层呈典型的层状结构,各层间结合良好,结合强度为(27.4±5) MPa,涂层显微硬度约850 HV0.2,为结合层显微硬度的2.7倍,涂层为典型的脆性断裂,断裂的位置发生在涂层的层与层之间。NiCr/Cr₃C₂涂层850 ℃氧化动力学曲线基本符合抛物线氧化规律。在氧化过程中涂层表面生产了氧化膜,且氧化膜会发生脱落,同时涂层内部出现了偏析现象,析出了金属Cr。     

爆炸喷涂WC-Co/CoMoCrSi复合涂层的组织与性能

为了提高CoMoCrSi涂层的结合强度和力学性能,采用爆炸喷涂技术制备了WC-12Co涂层作为过渡层的WC-Co/CoMoCrSi复合涂层,借助SEM和EDS等手段分析了涂层截面组织形貌和化学元素组成,采用显微硬度计、万能拉伸机及销盘式摩擦磨损试验机等研究了涂层的力学及摩擦磨损性能。结果表明：在氧燃充枪比为60%的喷涂参数下,制备WC-Co/CoMoCrSi复合涂层平均结合强度高达66 MPa,涂层截面组织致密、均匀,孔隙率小于0.6%,平均显微硬度为667 HV0.1,复合涂层摩擦因数0.53~0.56,具有优异的耐磨性能。     

电热线爆定向喷涂制备stellite/WC复合涂层的特性

利用电热线爆定向喷涂方法在45钢基体上制备了stellite/WC复合涂层,运用扫描电镜及能谱分析对复合涂层的形貌、微观结构以及涂层的基体结合机理进行了分析,利用纳米硬度计测量了复合涂层的硬度和弹性模量.结果表明:涂层致密,无层状结构出现;喷涂过程中涂层颗粒在基体上的快速凝固使得涂层晶粒细小均匀,晶粒为200～500 nm;涂层与基体界面发生了元素扩散现象,为扩散-冶金结合;涂层硬度的最大值为18.6 GPa,模量的最大值为310 GPa,硬度和模量沿横截面都呈现先增加而后减小的变化趋势.     

高速电弧喷涂FeAlCrNi/Cr3C2复合涂层的摩擦学特性

使用T11以及THT07—135型高温磨损试验机对高速电孤喷涂（HVAS）FeAlCrNi／Cr3C2复合涂层进行了滑动摩擦磨损特性的研究,并用SEM,TEM,X－ray等手段观察分析了磨痕的形貌和成分、涂层截面的组织和相结构。结果表明：FeAlCrNi／Cr3C2复合涂层具有典型的层状结构且有较高的结合强度和硬度;在常温和高温下,涂层的摩擦系数在开始阶段存在“跑合”现象;随着温度的升高,涂层的摩擦系数降低,耐磨损性能提高;剥层磨损是FeAlCrNi／C邙2复合涂层的主要磨损形式;Cr3C2增强相的加入,大大提高了涂层的耐磨损性能。     

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.     

Effects of plasma-sprayed NiCrAl/ZrO2 intermediate on the combination ability of coatings

A NiCrAl/ZrO₂ composite coating was deposited on the surface of metal carrier FeCrAl alloy by a plasma-spray technique. After static-state oxidation at 800°C, the transitions in structure and composition of the coating was analyzed by XRD, SEM and EDX. The results showed that the surface phases of the as-sprayed coating were mainly composed of Ni and ZrO₂. When the oxidation time was extended from 8 to 50 h, NiO crystallites were formed and these grew coarse on the coating surface, and alloy elements were diffused between the NiCrAl/ZrO₂ coating and the FeCrAl substrate. With the pretreatment, an intermediate coating was prepared with a coarse and porous structure, high cohesive strength and high heat resistance. These developed properties could provide high geometric surface area for a catalytic γ-Al₂O₃ washcoat, and enhance the adhesive strength between ceramic washcoat and metal substrate so as to extend the lifetime of the washcoat.     

Microstructures, strengthening mechanisms and fracture behavior of Cu-Ag alloys processed by high-pressure torsion

Disks of a eutectic Cu-Ag alloy were processed by high-pressure torsion (HPT) up to 20 revolutions to reveal the microstructural evolution and mechanical properties. Both the Cu and Ag phases were thinned continuously with increasing numbers of revolutions. After 20 revolutions, the alternating Cu and Ag phases were significantly refined and became fibrous with dimensions as thin as 5 nm. The strain hardening behavior of the Cu-Ag alloy was characterized after different numbers of HPT revolutions, and a saturation microhardness was attained. It is shown that the tensile fracture mode changed from necking to fully brittle shearing with increasing numbers of revolutions, and some shear offsets with sizes of ∼5-20 μm were observed on the fracture surfaces. Based on the abnormal saturation microhardness value of the eutectic alloy, the strengthening mechanisms of various Cu-Ag alloys are discussed.     

Carbon nanotube reinforced aluminum composite coating via cold spraying

Multiwalled carbon nanotube (CNT) reinforced aluminum nanocomposite coatings were prepared using cold gas kinetic spraying. Spray drying was used to obtain a good dispersion of the nanotubes in micron-sized gas atomized Al-Si eutectic powders. Spray dried powders containing 5 wt.% CNT were blended with pure aluminum powder to give overall nominal CNT compositions of 0.5 wt.% and 1 wt.% respectively. Cold spraying resulted in coatings of the order of 500 μm in thickness. Fracture surfaces of deposits show that the nanotubes were uniformly distributed in the matrix. Nanotubes were shorter in length as they fractured due to impact and shearing between Al-Si particles and the Al matrix during the deposition process. Nanoindentation shows a distribution in the elastic modulus values from 40-229 GPa which is attributed to microstructural heterogeneity of the coatings that comprise the following: pure Al, Al-Si eutectic, porosity and CNTs.     

热处理对机械合金化Ni/Ti冷喷涂层金属间化合物形成的影响

选择了三种球磨时间制备的Ni/Ti机械合金化粉末,通过冷喷涂制备了不同结构的Ni/Ti涂层.涂层组织结构采用扫描电镜(SEM)和X射线衍射(XRD)进行了表征分析.试验发现,随着粉末球磨时间的增加,热处理后的冷喷涂合金转变为金属间化合物的温度下降,涂层的组成相由Ni3Ti,B2-NiTi和Ti2Ni逐渐变成Ni3Ti和Ti2Ni;随着热处理温度的增加,涂层组织中不同成分的金属间化合物的相对量会发生一定改变.结果表明,热处理过程中形成的B2-NiTi金属间化合物在冷却时表现出较高的稳定性.     

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.     

hBN含量对等离子喷涂NiCr/Cr_3C_2-hBN复合涂层力学性能的影响

采用化工冶金包覆、喷雾造粒和固相合金化技术以Cr3C2和hBN为核心制备了NiCr/Cr3C2-h BN复合粉体,并用等离子喷涂技术制备了NiCr/Cr3C2-hBN涂层,研究了涂层的显微结构、物相组成、显微硬度和结合强度。研究结果表明,等离子喷涂NiCr/Cr3C2-h BN复合涂层呈典型的层状结构,各层之间结合良好。涂层的显微硬度和结合强度均随hBN含量的增加逐渐降低,当hBN含量为20%时,涂层的显微硬度和结合强度分别为NiCr/Cr3C2涂层的66%和50%。涂层断裂位置发生在涂层内部,为典型的脆性断裂。     

Microstructure evolution of cold-sprayed coating during deposition and through post-spraying heat treatment

The microstructural features of cold-sprayed coatings were investigated using Cu, Ti and Zn feedstocks by optical microscopy, scanning electron microscopy and transmission electron microscopy to reveal the microstructure evolution mechanisms in cold spray. Four typical effects including tamping, refinement, impact-induced fusion and annealing were examined on microstrueture. It is found that the microstructure of cold spray coating is remarkably influenced by spray materials. Ti coatings consist of evident porous layer and Cu coatings present a limited porous layer only near the surface. It is clear that the successive tamping effect and dynamic refinement of grains significantly influence the microstructure evolution of cold-sprayed coating. The tamping effect leads to the densification of porous coating layer gradually and the refinement effect leads to the formation of fine microstructure. It is considered that the large difference in the formation of porous layer is attributed to the dynamic impact pressure and hardenability of materials. It is also found that the impact-induced fusion during deposition of Zn coating can also modify the interfacial microstructure between particles in cold spray coating. Moreover, the nanocrystalline phase can be formed at the interfaces among particles resulting from the localized melting of the interfaces and tamping effect. Furthermore, the annealing treatment can modify the microstructure and property of a cold-sprayed coating.     

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160μm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(EDS)、X射线衍射仪(XRD)、显微硬度计等方法对喷涂态及扩散合成的NiCoCrAlY合金涂层的显微组织、物相组成、显微硬度等进行对比研究。结果表明:冷喷涂制备的NiCoCrAlY混合粉体涂层主要以单质元素混合存在,经过1100℃, 4 h真空扩散后,涂层中发生了元素的扩散和冶金反应,涂层与基体间有扩散现象发生,形成明显的冶金结合;氧化实验表明,原位扩散合成的NiCoCrAlY涂层的试样氧化增重明显低于纯基体试样,能对基体起到很好的保护作用,有效地保护了基体不被快速氧化。