纳米CeO2对激光熔覆Fe/Cr3C2复合涂层组织与磨损性能的影响

采用扫描电镜(SEM)、能谱分析仪(EDS)、X射线衍射仪(XRD)、显微硬度仪及滑动磨损试验,研究了1%纳米CeO_2(质量分数)对低碳钢表面激光熔覆Fe/Cr_3C_2复合涂层的组织结构和耐磨性能的影响。结果表明,Fe+Cr_3C_2+1%CeO_2复合涂层的主要组成相是α-Fe、γ-Fe、Cr_3C_2、Cr_(23)C_6及Cr_7C_3等化合物相;加入1%纳米CeO_2后,复合涂层组织明显细化,未熔Cr_3C_2数量显著减少,初生碳化物由粗大杆状向块状转变,数量增加,分布均匀,有效抑制和消除了裂纹的形成;复合涂层硬度和耐磨性能显著提高,Fe+30%Cr_3C_2+1%CeO_2涂层截面显微硬度提高105HV,增幅达到15.4%,且涂层沿深度方向硬度分布均匀性得到明显改善。     

Q235低碳钢表面等离子熔覆TiB2-TiC/Fe复合涂层及耐磨性

采用等离子熔覆技术,以Fe55、Ti、B₄C混合粉末为原料,在Q235低碳钢表面获得了TiB₂-TiC/Fe复合涂层,并分析了涂层的物相组成、组织结构,测试了显微硬度和摩擦磨损性能,探讨了其磨损机制。TiB₂-TiC/Fe复合涂层的主要物相为TiB₂、TiC、α-Fe,其中TiB₂呈多边形和矩形,TiC则呈不规则块状;随着原始粉末中Ti、B₄C含量的增加,TiB₂、TiC尺寸逐渐增大,TiB₂-TiC/Fe涂层与基体之间结合紧密,呈冶金结合;随着TiB₂-TiC/Fe复合涂层陶瓷相含量的增加,涂层硬度和耐磨性显著提高,当陶瓷相含量增加到一定程度（35wt%）时,涂层耐磨性能有所降低,TiB₂-TiC/Fe复合涂层的磨损方式主要是磨粒磨损和剥层磨损。Ti+B₄C陶瓷相含量为30wt%的等离子熔覆涂层耐磨性能较好,约为Q235钢基体的7倍,当Ti+B₄C含量持续增加时,TiB₂、TiC尺寸增大、缺陷增多,最终使TiB₂-TiC/Fe复合涂层耐磨性降低。     

Influence of SiC, Si3N4 and Al2O3 particles on the structure and properties of electrodeposited Ni

The structure and properties of electrodeposited nickel composites reinforced with inert particles like SiC, Si₃N₄ and Al₂O₃ were compared. A comparison was made with respect to structure, morphology, microhardness and tribological behaviour. The coatings were characterized with optical microscopy, Scanning electron microscopy (SEM), Energy dispersive X-ray analysis (EDX) and X-ray diffraction (XRD) technique. The cross-sectional microscopy studies revealed that the particles were uniformly distributed in all the composites. However, a difference in the surface morphology was revealed from SEM studies. The microhardness studies revealed that Si₃N₄ reinforced composite showed higher hardness compared to SiC and Al₂O₃ composite. This was attributed to the reduced crystallite size of Ni — 12 nm compared to 16 nm (SiC) and 23 nm (Al₂O₃) in the composite coating. The tribological performance of these coatings studied using a Pin-on-disk wear tester, revealed that Si₃N₄ reinforced composite exhibited better wear resistance compared to SiC and Al₂O₃ composites. However, no significant variation in the coefficient of friction was observed for all the three composites.     

Laser cladding composite coatings by Ni–Cr–Ti–B4C with different process parameters

To investigate the effect of laser process parameters on microstructure and properties of composite coating, the composite coatings were manufactured by laser cladding Ni–Cr–Ti–B₄C mixed powder on Q235 mild steel with different process parameters. The coatings are bonded with the substrate by remarkable metallurgical binding without cracks and pores. The composite coatings are consisted of in situ synthesized solid solution Ni–Cr–Fe, intermetallic compound (IMC) Ni₃Ti, Cr₂Ti, and ceramic reinforcements TiB₂, TiC. Results of scanning electron microscopy (SEM) revealed that the ceramic reinforcements became coarser with higher specific energy (E_s). There were independent ceramics TiB₂, TiC, eutectic ceramic TiB₂–TiC in coatings, and eutectic alloy–ceramic was detected. Compared with the substrate, the microhardness of coatings was increased significantly, and the maximum microhardness of coatings was approximately five times as high as the substrate. The wear resistance of coatings was improved dramatically than the substrate. Compared to the coatings with lower E_s, higher E_s led to lower microhardness and worse wear resistance ascribing to more Fe diffused into the coating from the substrate.     

Effect of silicon content on the microstructure and properties of Fe–Cr–C hardfacing alloys

In this study, the surface of St52 steel was alloyed with preplaced powders 55Fe39Cr6C, 49Fe39Cr6C6Si, and 45Fe39Cr6C10Si using a tungsten-inert gas as the heat source. Following surface alloying, conventional characterization techniques, such as optical microscopy, scanning electron microscopy, and X-ray diffraction were employed to study the microstructure of the alloyed surface. Microhardness measurements were performed across the alloyed zone. Room-temperature dry sliding wear tests were used to compare the coatings in terms of their tribological behavior. It was found that the as-deposited coatings contained higher volume fractions of carbides (Cr₇C₃). The presence of 6%Si in the preplaced powders caused an increase in microhardness and wear resistance.     

Dry sliding wear behaviour of AA 6351-ZrB2 in situ composite at room temperature

In the present work, AA 6351-xZrB₂ [x = 0, 3, 6 and 9 weight percentage (wt.%)] in situ composites have been prepared by the reaction of mixture of K₂ZrF₆ and KBF₄ with molten aluminium alloy at a reaction temperature of 850 °C. The in situ prepared composites were characterized by using scanning electron microscope (SEM), X-ray diffractometer (XRD), and microhardness analysis. The sliding wear properties of the prepared composite at room temperature were estimated by a pin-on-disc wear testing equipment using the composite material; the pins were machined according to standard sizes, and the tests were conducted as per the standards recommended by the ASTM G99-95a designation of different weighing percentage at room temperature. The wear characteristics of the composite in the as-cast, the solutionized and the solutionized-aged conditions were studied by conducting sliding wear test at the load of 9.81 N. The results indicated that the wear rate was decreased with an increase in the weight percentage of ZrB₂ and the wear resistance was increased with an increase in the fraction of ZrB₂ particulates in composite before and after heat treatment.     

Composite crystal Sr8/7TiSy with y = 2.84-2.97

Sr_8/7TiS_y (y=2.84-2.97) has been prepared by controlling the partial pressure of sulfur. The XRD and the ED patterns could not be indexed because of incommensurate structures; they were, therefore, indexed by four-dimensional formalism with simple lattice parameters of A, C_Ti and C_Sr in a hexagonal setting. However, a commensurate structure was obtained at y=2.84 in Sr_8/7TiS_y, the XRD and ED patterns of which were indexed by three- and four-dimensional formalisms. The sulfides, including incommensurate and commensurate structures, could be regarded as a single phase with a homogeneity range of sulfur of y=2.84-2.97, when the four-dimensional formalism was used. On the other hand, from the viewpoint of three-dimensional formalism, the structure contains two penetrating hexagonal subcells. The lattice parameter “a” in hexagonal setting is common to both subcells, while c is given by c=pC_Ti=qC_Sr, where p and q are integers, and C_Ti and C_Sr are the periodicities in c-direction of the two subcells, respectively. Hence, there is an infinite number of the structures in the composition range of y=2.84-2.97 in Sr_8/7TiS_y.     

Microstructure of Fe-TiC surface composite produced by cast-sintering

Fe-TiC surface composite was prepared in situ on a surface of cast steel by means of cast-sintering technique. The microstructure of this material was investigated by means of SEM, electron probe and XRD. Results show that the TiC and (Fe,Cr)₇C₃ carbides in an iron matrix were achieved on the surface of cast steel during cast-sintering. From the top surface of sample to that of the master-steel, the concentration of Ti, Cr and Ni as well as the quantity of both TiC and (Fe,Cr)₇C₃ carbides decreased gradually, and the morphology of (Fe,Cr)₇C₃ transforms from strip-chunky into make-and-break reticulation. There was an excellent metallurgy-bond between the surface composite layer and the master-steel.     

磁控溅射C靶电流对Cr/C和Cr/C/N复合镀层组织和性能的影响

利用控溅射技术,通过改变溅射C靶电流工艺参数,在45#钢上制备出Cr/C和Cr/C/N复合镀层.用能谱仪(EDS),X射线衍射仪(XRD)、扫描电子显微镜(SEM)检测镀层的微观组织;用HX-1000型维氏显微硬度计、球-盘摩擦磨损试验机(POD)、光学显微镜(OM)测试镀层的力学性能.结果表明:随C靶电流增加,镀层微...     

Microstructure and mechanical characteristics of iron-based coating prepared by plasma transferred arc cladding process

This paper investigated the effect of electromagnetic stirring (EMS) on the microstructure and abrasive wear behavior of iron-based coatings. A series of coatings were prepared by using plasma transferred arc cladding (PTAC) process. The phase and structure of the coatings were characterized by means of SEM, EDXA and X-ray diffraction. The microstructure of the coatings was mainly γ-Fe matrix and (Cr, Fe)₇C₃ carbide reinforced phases. Without EMS, the average size of (Cr, Fe)₇C₃ carbide was about 73 μm, while that of the carbide reached a minimum value of about 20 μm with stirring current of 3 A. The mechanical properties, especially wear resistance, were analyzed in detail. The results showed that the microstructure of the coating plays an important role on abrasive mechanism and the main mechanism is micro-cutting. When the stirring current is 3 A, the coating exhibits excellent wear resistance, which contributes to the good microstructures that hexagonal (Cr, Fe)₇C₃ carbide with the highest volume fraction are uniformly distributed in the matrix. The microhardness of the coatings increase at first, and then decrease as a function of stirring current. The maximum microhardness value of the coating is about 1050 HV.     

Temperature compensated Sr2Al2SiO7 ceramic for microwave applications

The Sr–Gehlenite (Sr₂Al₂SiO₇) ceramic has been prepared by the conventional solid-state ceramic route. Phase pure Sr₂Al₂SiO₇ (SAS) ceramic sintered at 1525 °C for 4 h has ?_r = 7.2 and Q_u × f = 33,000 GHz. The SAS showed large negative τ_f of −37.0 ppm/ °C. A low value of τ_f was achieved by preparing SAS–CaTiO₃ composite. The composite with 0.04 volume fractions (V_f) CaTiO₃ sintered at 1500 °C for 4 h showed good microwave dielectric properties: ?_r = 8.6, Q_u × f = 20,400 GHz and τ_f = +8.5 ppm/°C.     

Microstructure and properties of in situ nanostructured ceramic matrix composite coating prepared by plasma spraying

In situ nanostructured ceramic matrix composite coating toughened by metallic phase was fabricated by reactive plasma spraying micro-sized Al–Fe₂O₃ composite powders. The microstructure of the composite coating was characterized by X-ray diffraction, scanning electron microscopy, and transmission electron microscopy, respectively. The adhesive strength, microhardness, toughness, and wear resistance of the composite coating were explored. The results indicated that the composite coating exhibited dense microstructure with a lot of spherical α-Fe and γ-Al₂O₃ nano-sized grains embedded within the equiaxed and columnar FeAl₂O₄ nano-grains matrix. The adhesive strength, toughness, and wear resistance of the composite coating were significantly enhanced despite its lower microhardness compared with the micro-sized Al₂O₃ coating, which were attributed to the inclusion of ductile metallic phase Fe in the composite coating and the nanostructure of the composite coating.     

TiC as heterogeneous nuclei of the (Fe, Mn)3C and austenite intergrowth eutectic in austenite steel matrix wear resistant composite

By calculation of thermodynamics, analysis of crystal structure and study of transmission electron microscope (TEM), scanning electron microscope (SEM) and electron probe microanalyzer (EPMA), it has been discovered that TiC is formed preferentially between austenite dendrites at the end of the solidification to act as heterogeneous nuclei for the crystallization of the (Fe, Mn)₃C (cementite) and γ₂-Fe (austenite) intergrowth eutectic in the austenite steel matrix wear resistant composite.     

Magnetic and transport properties of La0.3Ca0.7Mn0.9T0.1O3 (T = Cr, Fe, and W)

We have carried out structural, magnetic and magneto transport measurements of the electron-doped manganite La_0.3Ca_0.7MnO₃ substituted with 10% of Cr, Fe and W on the Mn site. The substitution by Cr, Fe and W suppresses the charge order transition present at 260 K in the parent compound. All the samples show a semiconducting behavior. Whereas the parent compound does not show any magneto resistance (MR) even in a field of 14 T, a maximum MR of 6% in 5 T at 25 K is observed for the Cr substituted sample that is attributed to a spin-cluster glass like states induced by Cr. The Fe and W substituted samples showed a MR of 1.5 and 3%, respectively which may be attributed to a smaller number of FM domains/spin-clusters and to an increase in anti-ferromagnetic interaction.     

Wear behavior of TiB<Subscript>2</Subscript> inoculated 20Cr–3Mo–4C high chromium white cast irons

FeTi, B₂O₃, Al, and FeW particulates, approximately 40–60 μm in size, were mixed in stoichiometric ratio and sintered at 1,200 °C. The sintered particulates were added as 5 wt% to molten high chromium white cast iron over 50 C-deg above the melting temperature, and stirred at 1,000 rpm. The samples were investigated in three groups: (1) high Cr white cast iron inoculated by the particulates sintered from Al–FeTi–B₂O₃ particulates; (2) high Cr white cast iron inoculated by the sintered particulates derived from Al–FeTi, B₂O₃, and FeW particulates; and (3) specimens of the second group that were subsequently homogenized. The microhardness of ceramic particulates was measured as 2,800–3,400 HV₁₀. The effect of sintered particulate volume fraction on the abrasive wear resistance of the high chromium white cast iron was determined. The wear resistance and hardness of the composites improved significantly as a result of particulate inoculation. The application of the homogenization heat treatment to the inoculated samples produced a microstructure having homogeneously distributed particulates.     

Effects of aging treatment on microstructure and tribological properties of nickel-based high-temperature self-lubrication wear resistant composite coatings by laser cladding

The NiCr/Cr₃C₂–WS₂ high-temperature self-lubrication wear resistant composite coatings were fabricated on substrate of a hot-rolled AISI304 austenitic stainless steel by laser cladding. The high-temperature phase stability of the composite coatings was evaluated by aging at 600 °C for 10 h, 30 h, 50 h, and the microstructures of the as-laser clad and aged coatings were examined by means of XRD, SEM, EDS, respectively. The sliding wear resistance of the as-laser clad and aged coatings was evaluated at 600 °C. The results show that NiCr/Cr₃C₂–WS₂ composite coating has excellent high-temperature phase stability, the γ-(Fe,Ni)/Cr₇C₃ eutectic phases, Cr₇C₃ and (Cr,W)C hard phases, CrS/WS₂ mixed solid lubricant phases all existed in the as-laser clad and aged coatings. The volume fraction of eutectic phases decreased gradually with the increasing of aged time due to their dissolution. The microhardness of the aged coating decreased slightly after aging the coating 50 h at 600 °C due to the dissolution of the eutectic phases and notable breaking or granulation of the Cr₇C₃ hard phase, but the tribological properties were not significantly affected by aging treatment.     

Lamellar Fe/Al2O3 catalyst for high-yield production of multi-walled carbon nanotubes bundles

The lamellar Fe/Al₂O₃ catalysts were prepared by sol-gel method, and then with these prepared catalysts, carbon nanotubes (CNTs) were synthesized by catalytic chemical vapor deposition (CCVD) method using C₂H₂ as precursor. The as-prepared CNTs and Fe/Al₂O₃ catalysts were characterized by X-ray diffraction, field emission scanning electron microscopy, transmission electron microscopy, high-resolution transmission electron microscopy and Raman spectrum. The results proved that the as-prepared CNTs actually existed in bundles. And the growth of CNTs bundles should be attributed to the lamellar catalysts, which supported the bottom growth mechanism of CNTs. The transition metal of Mo was not introduced in catalysts to produce CNTs bundles, which was different with others’ results.     

Friction and wear properties of Cr:(Wx,N0.1) coatings deposited by magnetron sputtering

This paper discusses the friction and wear properties of Cr:(W_x,N_0.1) coatings with different tungsten contents. The Cr:(W_x,N_0.1) coatings with x being in the range of 0-0.16 were deposited using unbalanced magnetron sputtering technology. The microstructures and mechanical properties of Cr:(W_x,N_0.1) coatings have been characterized by SEM, TEM, X-ray diffraction (XRD), nanoindentation and adhesion techniques. The tribological properties of the coatings were investigated using an oscillating friction and wear tester under dry conditions. Indexable inserts with Cr:(W_x,N_0.1) coatings were applied to turning AISI 1045 steel material by a lathe. Micron-drills with Cr:(W_x,N_0.1) coatings were adopted in the ultra high speed (10⁵ rpm) PCB through-hole drilling test. Experimental results indicate that the coating microstructure, mechanical properties and wear resistance vary according to the tungsten content. All the coatings crystallize in the BCC phase. Cr:(W_0.06,N_0.1)-coated tools showed the best wear resistance in 1045 steel turning and PCB through-hole drilling tests. The service life of Cr:(W_0.06,N_0.1)-coated tool is three times greater than that of an uncoated tool in PCB through-hole drilling test.     

304不锈钢激光原位合成自润滑涂层的宽温域摩擦学性能

由于304不锈钢在中、高温下摩擦学性能较差,制约了其在重要摩擦运动副零部件上的应用。为改善304不锈钢的摩擦学性能,以Ni60粉末为增韧相,WS2为合成润滑相的前驱化合物,TiC为高硬度耐磨相,采用高能激光束在其表面原位合成自润滑耐磨复合涂层。利用X射线衍射仪、扫描电子显微镜、显微硬度计、摩擦磨损试验机和探针式材料表面磨痕测量仪表征涂层和基体的物相、微观结构、显微硬度与表面形貌,并系统研究涂层和基体在20,300,600,800℃下的摩擦学性能及其磨损机理。结果表明:涂层主要由Cr0.19Fe0.7Ni0.11,Ti2SC,Fe2C,Cr7C3,CrS和WS2组成;涂层的平均显微硬度(302.0HV0.5)略高于基体(257.2HV0.5),但涂层上部区域的硬度(425.4HV0.5)约为基体的1.65倍;涂层在所有等温摩擦学实验中摩擦因数和磨损率均低于基体,300℃时涂层润滑效果最好,摩擦因数为0.3031,600℃时涂层耐磨效果最好,磨损率为9.699×10^-5 mm^3·N^-1·m^-1。     

Plasma- and vacuum-plasma-sprayed Cr3C2 composite coatings

Plasma- and detonation-sprayed chromium carbide-Nichrome coatings have long been used for applications requiring superior wear resistance at temperatures up to 820°C. The coatings are typically sprayed from mechanical blends of powder containing from 17 to 35 wt.% Nichrome. These coatings are susceptible to non-uniformity of microstructure because of segregation of the blended powders. Oxide formation occurs in both ambient atmosphere plasma and detonation-applied coatings.A new Cr₃C₂Nichrome composite powder was developed for application by the plasma and vacuum plasma processes. The developed material consists of 50 wt.% Cr₃C₂ clad with 50 wt.% 80-20 Nichrome. Unlike powder blends, each Cr₃C₂ powder particle is clad with an essentially continuous layer of Nichrome. The developed material is sized ?270 mesh + 5 μm.Coatings of the composite Cr₃C₂ material were sprayed using the conventional non-transferred arc plasma and the low pressure low oxygen vacuum plasma processes. These coatings were compared with coatings sprayed from a commercially available blend of 75 wt.% Cr₃C₂25wt.% Nichrome. Unlike the blend, the microstructure of both composite coatings showed Cr₃C₂ to be present as discrete second-phase particles embedded in the Nichrome matrix. The vacuum-plasma-sprayed composite coating showed no visible oxide. Macrohardness (Rockwell C hardness) and microhardness (diamond pyramid hardness for a load of 300 gf) readings of the conventionally sprayed coatings were 50 HRC and 600 HDP 300 respectively. The hardness values for the vacuum-plasma-sprayed composite were 60 HRC and 860 HDP 300. The abrasive slurry wear resistance of the conventionally sprayed composite was three times that of the blend, while the wear resistance of the vacuum-plasma-sprayed composite was four times that of the standard blend coatings.The air-plasma-sprayed composite Cr₃C₂Nichrome coatings are expected to exhibit performance characteristics comparable with similar detonation-applied coatings. The vacuum-plasma-sprayed composite coatings combine superior wear resistance with low oxide and are recommended for severe high temperature wear environments.