Pulvermetallurgische Erzeugung von SiC‐ und Al2O3‐verstärkten Al‐Cu‐Legierungen

Powder metallurgical fabrication of SiC and Al₂O₃ reinforced Al‐Cu alloys Based on metallographic studies the states of composite powder formation during high‐energy ball milling will be discussed. Spherical powder of aluminium alloy AA2017 was used as feedstock material for the matrix. SiC and Al₂O₃ powders of submicron and micron grain size (<2 μm) were chosen as reinforcement particles with contents of 5 and 15 vol.‐% respectively. The milling duration amounted to a maximum of 4 hours. The abrasion of the surface of the steel balls, the rotor and the vessel is indicated by the content of ferrous particles in the powder. High‐energy ball milling leads to satisfying particle dispersion for both types of reinforcement particles. Further improvements are intended. The microstructure of compact material obtained by hot isostatic pressing and extrusion was studied in detail by scanning and transmission electron microscopy. For both types of reinforcement the microstructure of composites is similar. The microporosity is low. The interface between reinforcement particles and matrix is free of brittle phases and microcracks. In the case of SiC reinforcement particles, a small interface interaction is detectable which implies a good embedding of reinforcement particles. High‐energy ball milling under air‐atmosphere leads to the formation of the spinel phase MgAl₂O₄ during the subsequent powder‐metallurgical processing. Because of the size, rate and dispersion of the spinel particles, an additional reinforcement effect is expected.     

Microstructure and abrasive wear behaviour of B<Subscript>4</Subscript>C particle reinforced 2014 Al matrix composites

In this study, the microstructure and abrasive wear properties of varying volume fraction of particles up to 12% B₄C particle reinforced 2014 aluminium alloy metal matrix composites produced by stircasting method was investigated. The density, porosity and hardness of composites were also examined. Wear behaviour of B₄C particle reinforced aluminium alloy composites was investigated by a block-on-disc abrasion test apparatus where the samples slid against the abrasive suspension mixture (contained 10 vol.% SiC particles and 90 vol.% oil) at room conditions. Wear tests performed under 92 N against the abrasive suspension mixture with a novel three body abrasive. For wear behaviour, the volume loss and specific rate of the samples have been measured and the effects of sliding time and the content of B₄C particles on the abrasive wear properties of the composites have been evaluated. The dominant wear mechanisms were identified using SEM. Microscopic observation of the microstructures revealed that dispersion of B₄C particles was generally uniform while increasing volume fraction led to agglomeration of the particles and porosity. The density of the composite decreased with increasing reinforcement volume fraction but the porosity and hardness increased with increasing particle content. Moreover, the specific wear rate of composite decreased with increasing particle volume fraction. The wear resistance of the composite was found to be considerably higher than that of the matrix alloy and increased with increasing particle content.     

Electroless Ni‐P coating on Cu substrate with strike nickel activation and its corrosion resistance

Electroless Ni‐P coating was successfully deposited on Cu substrate by strike nickel activation process. The specific pretreatment steps were discussed. The surface and cross‐section morphologies, phosphorus content, adhesive force, and corrosion resistance were characterized for electroless Ni‐P coating. Scanning electron microscopy shows the compact surface. Energy dispersed X‐ray shows the 11.4% phosphorus content. Adhesive test shows the qualified adhesion of electroless Ni‐P coating to substrate. Porosity test shows pores free of the coating, and immersion test in 10% HCl solution indicates the better corrosion resistance of electroless Ni‐P coating in protecting Cu substrate from the corrosion of Cl ions. Thus, strike nickel activation pretreatment is suitable for electroless Ni‐P coating on Cu substrate.     

Microstructural evolution in ultrasonically processed in situ AZ91 matrix composites and their mechanical and wear behavior

AZ91 alloy matrix composites reinforced with phases formed in situ from the addition of Si particles were fabricated by solidification under ultrasonic vibrations. Application of high-intensity ultrasonic field to the melt resulted in optimized size, morphology and distribution of in situ formed Mg₂Si particles. The amount of Mg₂Si particles increased, its size was refined and the distribution became uniform. Heterogeneous nucleation from the addition of silicon particles and enhanced nucleation from rapid cooling refined the grain size of the matrix in the composites. Hardness and ultimate compressive strength of the composites increased as compared to that of the cast AZ91 alloy. Composites exhibited improved sliding wear behavior of under varying normal loads. Identified dominant wear mechanism at lower sliding velocities is abrasion. Improvement in mechanical and sliding wear properties of the composites is attributed to the refinement of both matrix and reinforcement phases and improved dispersion of the reinforcement under ultrasonic vibrations.     

Sliding wear behaviors of electrodeposited nickel composite coatings containing micrometer and nanometer La2O3 particles

Micrometer and nanometer La₂O₃ particles were codeposited with nickel by electroplating from a nickel sulfamate bath. The wear behaviors of the composite coatings were evaluated sliding against AISI 1045 steel under non-lubricated conditions. It was found that the incorporation of the La₂O₃ particles enhances the microhardness and wear resistance of Ni coatings. The wear resistance of the Ni composite coating containing nano-sized La₂O₃ particles is higher than that of the Ni composite coating containing micro-sized La₂O₃ particles. The codeposition of the smaller nanometer La₂O₃ particles with Ni effectively reduces the size of Ni crystals and significantly increases the hardness of the composite coatings, resulting in significantly improved wear resistance of the nano-sized La₂O₃/Ni composite coating.     

Synthesis and characterization of functionally graded nickel‐nickel coated ZrO2 composite coating

Electroless‐nickel plated ZrO₂ (NCZ) particles have been used to produce a functionally graded nickel‐electroless‐nickel plated ZrO₂ composite coating. So, electroless‐nickel plated ZrO₂ particles concentration was continuously increased from 0 to an optimum value in the electroplating bath (Watt's bath). The substrate was ST37 steel and the thickness of the coating was approximately 50 μm. Also a uniformly distributed nickel‐electroless‐nickel plated ZrO₂ composite coating has been manufactured as comparison. The composite coatings were characterized by scanning electron microscopy and energy‐dispersive X‐ray spectroscopy. Structure and phase composition were identified by X‐ray diffraction analysis. Microhardness of the coatings was evaluated by employing a Vickers instrument. Three‐point bend test was carried out to compare the adhesion strength of the coatings. Dry sliding wear tests were performed using a pin‐on‐disk wear apparatus. The electrochemical behavior of the coatings was studied by electrochemical impedance spectroscopy. The microhardness measurements showed that, with increasing the co‐electrodeposited electroless‐nickel plated ZrO₂ particle content in the nickel matrix, the microhardness increases from interface towards the surface of the functionally graded composite coating. Bend, wear and electrochemical test results confirmed that the functionally graded composite coating has higher adhesion, wear resistance and corrosion resistance as compared with the uniformly distributed coating. This has been attributed to lower mechanical mismatch between coating and substrate in functionally graded composite coating with respect to the uniformly distributed one.     

Tribologische Modelluntersuchungen an metallischen Werkstoffen für Formeinsätze zum Mikro‐Pulverspritzgießen mit ZrO2‐Formmasse

Tribological studies on metallic materials used as mould inserts in micro powder injection moulding (microPIM) with zirconia feedstock Wear behaviour of steel X38CrMoV5‐1 and C 45E, electroplated nickel and brass Cu63Zn37 used as mould inserts in micro powder injection moulding (microPIM) was studied in two different laboratory tribometers. Using an abrasive wheel test with 220 mesh flint the volumetric wear increased with decreasing hardness from steel to nickel and brass. Experiments using a laboratory tester simulating powder injection moulding with zirconia feedstock at 170 and 190°C showed contrary results. Volumetric wear of the softer materials nickel and brass was significantly lower than that of steel X38CrMoV5‐1 and C 45E. The presented results indicate that in micro powder injection moulding wear behaviour can depend more on microstructural parameters like homogeneity or the ability of work‐hardening and deformation but on hardness of the materials.     

Exposing {001} Crystal Plane on Hexagonal Ni‐MOF with Surface‐Grown Cross‐Linked Mesh‐Structures for Electrochemical Energy Storage

Hexagonal nickel‐organic framework (Ni‐MOF) [Ni(NO₃)₂·6H₂O, 1,3,5‐benzenetricarboxylic acid, 4‐4′‐bipyridine] is fabricated through a one‐step solvothermal method. The {001} crystal plane is exposed to the largest hexagonal surface, which is an ideal structure for electron transport and ion diffusion. Compared with the surrounding rectangular crystal surface, the ion diffusion length through the {001} crystal plane is the shortest. In addition, the cross‐linked porous mesh structures growing on the {001} crystal plane strengthen the mixing with conductive carbon, inducing preferable conductivity, as well as increasing the area of ion contact and the number of active sites. These advantages enable the hexagonal Ni‐MOF to exhibit excellent electrochemical performance as supercapacitor electrode materials. In a three‐electrode cell, specific capacitance of hexagonal Ni‐MOF in the 3.0 m KOH electrolyte is 977.04 F g^?1 and remains at the initial value of 92.34% after 5,000 cycles. When the hexagonal Ni‐MOF and activated carbon are assembled into aqueous devices, the electrochemical performance remains effective.     

Nucleation Crystallography of Ni Grains on CrFeNb Inoculants Investigated by Edge‐to‐Edge Matching Model in an IN718 Superalloy

In this work, the nucleation crystallography of CrFeNb intermetallic particles as a grain refiner for Ni‐based IN718 superalloys is studied using Edge‐to‐Edge Matching model. Three distinguishable orientation relationships between CrFeNb intermetallic particles and Ni grains are well predicted: , (111)_Ni 1.28° from (0004)_CrFeNb, , (111)_Ni 1.32° from _CrFeNb, and _Ni//[0001]_CrFeNb, (111)_Ni 0.72° from _CrFeNb. The results indicate that CrFeNb intermetallic particles have a strong nucleation potency as an effective grain refiner for Ni‐based superalloy and the existence of semi‐coherent interfaces between the CrFeNb intermetallic particles and Ni grains. Furthermore, the IN718 superalloy is used to experimentally validate the grain refinement effect of CrFeNb intermetallic particles, showing that its grain size is obviously refined from 8.60 to 1.23 mm. And, the corresponding heterogeneous nucleation mechanism of grain refinement at the atomic level is further identified.

     

纳米SiC浓度对Ni/纳米MoS_2基复合镀层结构和耐磨性能的影响

采用双脉冲复合电镀技术,在瓦特型镀液中,制备含纳米SiC的Ni/MoS2基复合镀层。研究纳米SiC浓度对复合镀层微观形貌、组织结构、显微硬度和摩擦性能的影响。结果表明:镀液中添加纳米SiC后,Ni/MoS2复合镀层的微观形貌产生明显的变化,随镀液中SiC浓度的增加,复合镀层表面致密度提高;镀液中纳米SiC浓度在1.0~1.5g/L时,组织由Ni+MoS2+SiC组成;纳米SiC为1.5g/L时,显微硬度达到最大,为505HV,摩擦因数为0.28,分别为纯Ni/MoS2的1.6倍和1/2。复合镀层的磨损机制以磨料磨损为主。     

2D Free‐Standing Nitrogen‐Doped Ni‐Ni3S2@Carbon Nanoplates Derived from Metal–Organic Frameworks for Enhanced Oxygen Evolution Reaction

2D metal–organic frameworks (2D MOFs) are promising templates for the fabrication of carbon supported 2D metal/metal sulfide nanocomposites. Herein, controllable synthesis of a newly developed 2D Ni‐based MOF nanoplates in well‐defined rectangle morphology is first realized via a pyridine‐assisted bottom‐up solvothermal treatment of NiSO₄ and 4,4′‐bipyridine. The thickness of the MOF nanoplates can be controlled to below 20 nm, while the lateral size can be tuned in a wide range with different amounts of pyridine. Subsequent pyrolysis treatment converts the MOF nanoplates into 2D free‐standing nitrogen‐doped Ni‐Ni₃S₂@carbon nanoplates. The obtained Ni‐Ni₃S₂ nanoparticles encapsulated in the N‐doped carbon matrix exhibits high electrocatalytic activity in oxygen evolution reaction. A low overpotential of 284.7 mV at a current density of 10 mA cm^?2 is achieved in alkaline solution, which is among the best reported performance of substrate‐free nickel sulfides based nanomaterials.     

Effect of cobalt content on microstructure and property of electroplated nickel‐cobalt alloy coatings

Nickel‐cobalt alloys were electrodeposited on copper sheets in sulfate bath containing 288.5 g/l NiSO₄·6H₂O, 30 g/l CoSO₄·7H₂O, 40 g/l HBO₃, 15 g/l NaCl and 0.08 g/l lauryl sodium sulfate. The effects of cobalt content on microstructure, microhardness, and wear resistance of electroplating nickel‐cobalt alloys were studied by using SEM and XRD techniques, and microhardness tester and wear tester. The relationship between the microhardness of nickel‐cobalt alloy coatings and heat treatment procedures was also investigated. The experimental results show that cobalt content (W_t) in coating increases with Co²⁺/(Co²⁺ + Ni²⁺)% (X) in plating solution. Fitted regression equation is as following: W_t = –0.7399 + 2.2847X – 0.0133X². The increase of cobalt content leads to that the longitudinal section morphology of coating transforms from the cone into sphericity and at last into the shape of willow leaf, and its structure transforms from face centered cubic (fcc) nickel solid solution into fcc cobalt solid solution and at last into hcp cobalt solid solution. The increase of cobalt content results in the increase of microhardness of nickel‐cobalt alloy coatings, and the hardness reaches a maximum value (363 HV) when cobalt content is 54.9%. After heat treatment at 400°C and 600°C, the microhardness of coatings begins to decrease except the coating containing 79.2% Co. Moreover, the wear resistance of electroplated coatings increases with the increase of cobalt content.     

Y_2O_3含量对38CrMoAl钢表面激光合金化WC/Ni金属陶瓷组织与性能的影响

采用激光合金化技术,在38CrMoAl钢表面制备不同Y_2O_3含量的WC/Ni合金化层。利用X射线衍射仪(XRD)、扫描电镜(SEM)、电子探针(EPMA)、显微硬度计和摩擦磨损试验机,系统研究合金化层的相组成、显微组织、显微硬度及摩擦磨损性能随Y_2O_3含量的变化规律。结果表明:不同Y_2O_3含量的合金化层皆是由γ-(Fe,Ni)、基体马氏体、M3C及WC相组成,其中纳米WC颗粒主要分布在合金化层上部的枝晶间,而微米WC颗粒则分布于合金化层底部边缘区,且在颗粒边缘形成有明显的外延生长层。随着Y_2O_3含量的增加,具有亚共晶形貌特征的凝固组织逐渐细化,γ-(Fe,Ni)和M3C数量增多,基体马氏体数量略有减少。但当Y_2O_3含量(质量分数,下同)超过1.0%时,凝固组织开始有所粗化。随Y_2O_3含量增加,合金化层硬度呈先增后降、摩擦因数和磨损失重呈先减后增的变化趋势。当Y_2O_3含量为1.0%时,合金化层硬度(781HV0.2)最高,为基体的2.4倍;摩擦因数和磨损失重最小,分别为基体的17%和8.9%。     

Investigation of corrosion and mechanical properties of Al–Cu–SiC–xNi composite alloys

In this study, dry sliding wear behavior and corrosion resistance of Al–Cu–SiC–xNi (x: 0, 0.5, 1, 1.5 wt.%) composites were investigated. Effect of nickel content on the microstructure and hardness of the alloys was also studied. Wear tests were conducted using a ball on disc wear test device. Corrosion behavior of Al–Cu–SiC–xNi composite alloys in 3.5% NaCl solution was investigated by using potentiodynamic polarization, impedance spectroscopy and cronoamperometric methods. The results showed that the hardness of the composite alloy increases with increasing nickel content. Maximum wear resistance is reported with the addition of 1 wt.%Ni. It was determined that corrosion resistance of Al–Cu–SiC composite alloys improved with increasing nickel content in the alloy.     

Regulating Surface and Grain‐Boundary Structures of Ni‐Rich Layered Cathodes for Ultrahigh Cycle Stability

The wide applications of Ni‐rich LiNi_1‐x‐yCo_xMn_yO₂ cathodes are severely limited by capacity fading and voltage fading during the cycling process resulting from the pulverization of particles, interfacial side reactions, and phase transformation. The canonical surface modification approach can improve the stability to a certain extent; however, it fails to resolve the key bottlenecks. The preparation of Li(Ni_0.4Co_0.2Mn_0.4)_1‐xTi_xO₂ on the surface of LiNi_0.8Co_0.1Mn_0.1O₂ particles with a coprecipitation method is reported. After sintering, Ti diffuses into the interior and mainly distributes along surface and grain boundaries. A strong surface and grain boundary strengthening are simultaneously achieved. The pristine particles are fully pulverized into first particles due to mechanical instability and high strains, which results in serious capacity fading. In contrast, the strong surface and the grain boundary strengthening can maintain the structural integrity, and therefore significantly improve the cycle stability. A general and simple strategy for the design of high‐performance Ni‐rich LiNi_1‐x‐yCo_xMn_yO₂ cathode is provided and is applicable to surface modification and grain‐boundary regulation of other advanced cathodes for batteries.     

Untersuchungen zum Elektronenstrahl‐Randschichtumschmelzen einer sprühkompaktierten übereutektischen eisenhaltigen Al‐Si‐Legierung

The present study shows the influence of two different electron beam deflection techniques on surface deformation, microstructure and hardness after an electron beam surface remelting of a spray‐formed hypereutectic aluminium alloy (AlSi17Fe5Cu4Mg). Due to the specific rapid heating and cooling rates on the one hand and the high content of alloying elements on the other hand, the surface microstructure was modified by phase formation, grain refinement and an oversaturation of aluminium solid solution. As a result the hardness was threefold increased (284 HV 0.1) compared to the untreated base material (104 HV 0.1). This hardness increase was significantly higher than the level of the conventional heat treatment (e. g. age hardening approx. 170 HV 0.1). The remelting process largely influenced the wear behaviour under abrasive (scratch test) and abrasive‐adhesive (pin‐on‐disc test) load conditions. Remelted surface layers generated by meander deflection technique showed the most improvement regarding their wear performance.     

Bioinspired Nacre‐Like Ceramic with Nickel Inclusions Fabricated by Electroless Plating and Spark Plasma Sintering

Hybrid composites of layered brittle‐ductile constituents assembled in a brick‐and‐mortar architecture are promising for applications requiring high strength and toughness. Mostly, polymer mortars have been considered as the ductile layer in brick‐and‐mortar composites. However, low stiffness of polymers does not efficiently transfer the shear between hard ceramic bricks. Theoretical models point to metals as a more efficient mortar layer. However, infiltration of metals into ceramic scaffold is non‐trivial, given the low wetting between metals and ceramics. The authors report on an alternative approach to fabricate brick‐and‐mortar ceramic‐metal composites by using electroless plating of nickel (Ni) on alumina micro‐platelets, in which Ni‐coated micro‐platelets are subsequently aligned by a magnetic field, taking advantage of ferromagnetic properties of Ni. The assembled Ni‐coated ceramic scaffold is then sintered using spark plasma sintering (SPS) to locally create Ni mortar layers between ceramic platelets, as well as to sinter the ceramic micro‐platelets. The authors report on materials and mechanical properties of the fabricated composite. The results show that this approach is promising toward development of bioinspired ceramic‐metal composites.

     

Microstructure investigations and mechanical properties of an Al‐Al2O3 MMC produced by semi‐solid solidification

The influence of the semi‐solid solidification production parameters (shear rate and agitation time) and the concentration of reinforcing particles on the microstructure formation and mechanical properties of a 520 aluminum alloy reinforced with Al₂O₃ particles was investigated. Depending on the content of reinforcing particles and the stirring conditions different rosette structures were formed. The type of wear mechanism (delamination or adhesion) depends on the size of the rosettes and the distribution of Al₂O₃ reinforcements. Best mechanical properties were obtained for metal matrix composites reinforced with 12 wt% of Al₂O₃ stirred at a shear rate of 2100 s^–1 for 1800 s. These samples showed tensile strength and yield stress similar to the commercial A520 alloy. The hardness and wear resistance were improved by the addition of Al₂O₃ particles, meanwhile the elongation to fracture was reduced.     

Role of zirconia filler on friction and dry sliding wear behaviour of bismaleimide nanocomposites

This paper discusses the friction and dry sliding wear behaviour of nano-zirconia (nano-ZrO₂) filled bismleimide (BMI) composites. Nano-ZrO₂ filled BMI composites, containing 0.5, 1, 5 and 10 wt.% were prepared using high shear mixer. The influence of these particles on the microhardness, friction and dry sliding wear behaviour were measured with microhardness tester and pin-on-disc wear apparatus. The experimental results indicated that the frictional coefficient and specific wear rate of BMI can be reduced at rather low concentration of nano-ZrO₂. The lowest specific wear rate of 4 × 10⁻⁶ mm³/Nm was observed for 5 wt.% nano-ZrO₂ filled composite which is decreased by 78% as compared to the neat BMI. The incorporation of nano-ZrO₂ particles leads to an increased hardness of BMI and wear performance of the composites shows good correlation with the hardness up to 5 wt.% of filler loading. The results have been supplemented with scanning electron micrographs to help understand the possible wear mechanisms.     

Fabrication of composites from different carbon content ferrous powders adopting thermomechanical processes

In this research, deep consolidation technique is utilized for processing of low and high carbon content ferrous powders to manufacture composite material. High carbon content ferrous powders were used as reinforcing material. The powder particles were allowed to mix with low carbon content ferrous powders in 50:50 weight percent for fabrication of composites. The composites were heat treated at three different temperatures (i.e., 800°C, 900°C, and 1000°C). The changes in microstructure, microhardness, the grain size, and bonding among powder particles were studied. Refinement of grains was observed and this led to improved hardness enabling the processed material to be used as a suitable composite. Abrasive wear tests were carried out using a laboratory tribometer in dry reciprocating sliding contact against Sic abrasive paper. The outcomes demonstrate that the abrasive wear resistance was notably affected by the treatment temperature and hardness of the composites.