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1.
Tharaka Chandanayaka Fardad Azarmi 《Journal of Materials Engineering and Performance》2014,23(5):1815-1822
In the present study, cold spraying technique was used to fabricate a metal matrix composite (MMC) that consists of Ni matrix and 20 vol.% Ni3Al particles at two different particle sizes as reinforcement. This study intends to investigate the effect of reinforcement particle size on microstructural and mechanical properties of cold sprayed MMCs. Two different Ni3Al powders with nominal particle size of ?45 to +5 and +45 to 100 μm were used as reinforcement in this study. Cold sprayed Ni-Ni3Al samples were subjected to the microstructural observation and characterization prior to any mechanical testing. Then, samples were tested using nano-indentation, Knoop hardness, Vickers hardness, and Resonance frequency to evaluate their mechanical properties. No significant changes were observed in microstructural characteristics due to different particle sizes. The results obtained from a variety of mechanical testings indicated that the increasing reinforcement particle size resulted in the slight reduction of mechanical properties such as elastic modulus and hardness in cold sprayed MMCs. The mechanical interlock between deposited particles defines the bonding strength in cold sprayed samples. Small size particles have a higher velocity and impact resulting in stronger interlock between deformed particles. 相似文献
2.
A promising Ni(Al)-Cr2O3-Ag-CNT-WS2 self-lubricating wear-resistant coating was deposited via atmospheric plasma spray of Ni(Al), nano Cr2O3, nano silver and nano WS2 powders, and CNTs. Feedstock powders with various compositions prepared by spray drying were plasma sprayed onto carbon steel substrates. The tribological properties of coatings were tested by a high temperature tribometer in a dry environment from room temperature to 400 °C, and in a natural humid environment at room temperature. It was found that all nanocomposite coatings have better frictional behavior compared with pure Ni(Al) and Ni(Al)-Cr2O3 coatings; the specimen containing aproximately 7 vol.% Ag, CNT, and WS2 had the best frictional performance. The average room temperature friction coefficient of this coating was 0.36 in humid atmosphere, 0.32 in dry atmosphere, and about 0.3 at high temperature. 相似文献
3.
In the present work, two different methods were used to study the effect of mechanical activation on aluminothermic reduction of MoO3. In the first method, a stoichiometric amount of Al + MoO3 and 20% weight percent of aluminum oxide (as the heat absorber) was mixed and mechanically activated by milling process in a planetary ball mill under argon atmosphere. XRD patterns and SEM micrographs of the activated samples indicated that aluminothermic reduction of MoO3 was done in the milling media after 5 h and increasing the milling time, decreased the remaining non reacted Al and MoO3. In the second method, as received MoO3, was mechanically activated in different times in the range of 3 to 24 h. The effect of mechanical activation on molybdenum trioxide grain size was analyzed by Williamson-Hall method, and it was shown that, by increasing the activation time, the grain size and internal strain was reduced and increased, respectively. In the next step, the activated MoO3 powders were mixed with stoichiometric amount of Al and 20 wt% Al2O3 (as the heat absorber) and shaped in the form of cylindrical samples of 10 mm in diameter and height of 15–20 mm by applying 70 MPa uniaxial pressure. Aluminothermic reaction was initiated in the prepared pellets by using conventional microwave oven. The XRD patterns of the combustion products showed that, by mechanical activation of MoO3, the undesired phases of molybdenum dioxide (MoO2) and aluminum molybdate Al2(MoO4)3 was decreased. The aluminothermic reduction of activated MoO3 also was studied by non-isothermal Differential Scanning Calorimetry (DSC) with heating rate of 10 °C min−1 under argon atmosphere. The results showed that by mechanically activating MoO3 for 24 h, the ignition temperature of reduction reaction decreased from 910 to 780 °C and the practical efficiency of the reaction increased from 82.9% (for the nonactivated MoO3) to 92.5%. The comparing results between the milling mixture and the milling molybdenum trioxide indicated that the reaction in mixture cannot be completed during milling and a small amount of Al and MoO3 remained in the activated powder. But for the activated MoO3, and after igniting in a conventional microwave oven the desired reaction went to completion. 相似文献
4.
Reactive spraying of nickel-aluminide coatings 总被引:2,自引:0,他引:2
S. C. Deevi V. K. Sikka C. J. Swindeman R. D. Seals 《Journal of Thermal Spray Technology》1997,6(3):335-344
Reactive spraying of nickel aluminides was accomplished via reaction synthesis techniques in which nickel and aluminum powders
were fed through a direct- current plasma torch onto carbon steel substrates. The as- sprayed coatings obtained by reactive
spraying were characterized by x- ray diffraction and microscopic techniques. Reactive spraying of nickel and aluminum resulted
in coatings consisting of Ni, Al, Ni
3Al, NiAl3, Ni5Al3, NiAl, and Al2O3, depending on the experimental conditions. Nickel aluminide phases observed in plasma spray depositions were compared with
the phases obtained by combustion synthesis techniques, and the formation of phases in reactive spraying was attributed to
the exothermic reaction between splats of aluminum and nickel. Primary and secondary reactions leading to the formation of
nickel aluminides were also examined. The splat thickness and the reaction layer suppressed the formation of desired equilibrium
phases such as Ni3Al and NiAl. As- sprayed coatings were annealed to enhance the diffusional reactions between the product phases and aluminum
and nickel. Coatings obtained by reactive spraying of elemental powders were compared with as- sprayed and annealed coatings
obtained with a bond coat material in which nickel was deposited onto aluminum particles. 相似文献
5.
Ha Yong Lee Young Ho Yu Young Cheol Lee Young Pyo Hong Kyung Hyun Ko 《Journal of Thermal Spray Technology》2004,13(2):184-189
Al + SiC, Al + Al2O3 composites as well as pure Al, SiC, and Al2O3 coatings were prepared on Si substrates by the cold gas dynamic spray process (CGDS or cold spray). The powder composition
of metal (Al) and ceramic (SiC, Al2O3) was varied into 1:1 and 10:1 wt.%, respectively. The propellant gas was air heated up to 330 °C and the gas pressure was
fixed at 0.7 MPa. SiC and Al2O3 have been successfully sprayed producing coatings with more than 50 μm in thickness with the incorporation of Al as a binder.
Also, hard ceramic particles showed peening effects on the coating surfaces. In the case of pure Al metal coating, there was
no crater formation on hard Si substrates. However, when Al mixed with SiC and Al2O3, craters were observed and their quantities and sizes depended on the composition, aggregation and size of raw materials. 相似文献
6.
《Intermetallics》2015
Metal-based reactive composites are high energy-density materials that have potential uses as multifunctional energetics. However, when composed of micron size particles they can be difficult to ignite and have slow reaction rates. Recent work has shown that mechanically activated (MA) materials can have increased ignition sensitivity and reaction rate, yet the role of microstructure refinement (i.e., mechanical activation duration) in controlling combustion behavior is not well understood. In this work, the combustion velocities and flame temperatures were measured for equiatomic MA Ni/Al reactive powders produced using different milling durations in a two-step dry/wet milling process. For MA Ni/Al pellets pressed to 70% of the theoretical maximum density, it was shown that the combustion velocities increase as the milling time increases from ∼9.4 cm/s at 25% of the critical reaction milling time (tcr) to ∼20 cm/s at a milling time of 97% tcr. For the cases considered, the average maximum flame temperatures were measured to be ∼1873 ± 30 K for samples milled for 25% tcr to 1786 ± 30 K at 97% tcr. It was also found that hydrocarbon contaminants are milled into the MA Ni/Al composite particles during the wet milling step and result in expansion of the pellets during combustion. Differential scanning calorimetry coupled with Fourier transform infrared spectroscopy showed that the release of hydrocarbon contaminants occurs at a temperature of ∼630 K. It was also shown that the concentration of hydrocarbon contamination decreased as the dry milling times increased, which suggests particle structure and mechanical property evolution during initial dry milling also affects contamination during subsequent wet milling. 相似文献
7.
Mohammed Shahien Motohiro Yamada Toshiaki Yasui Masahiro Fukumoto 《Journal of Thermal Spray Technology》2011,20(1-2):205-212
Reactive plasma spray is the key to fabricating aluminum nitride (AlN) thermally sprayed coatings. It was possible to fabricate AlN/Al composite coatings using atmospheric plasma spray process through plasma nitriding of Al powders (Al 30 ??m). The nitriding reaction and the AlN content could be improved by controlling the spray distance and the feedstock powder particle size. Increasing the spray distance and/or using smaller particle size of Al powders improved the in-flight nitriding reaction. However, it was difficult to fabricate thick and dense AlN coatings with an increase in the spray distance and/or when using fine particles. Thus, the coatings thickness was suppressed because of the complete nitriding of some particles (formation of AlN particles) during flight, which prevents the particle deposition. Furthermore, the excessive vaporization of Al fine particles (due to increased particle temperature) decreased the deposition efficiency. To fabricate thick AlN coatings in the reactive plasma spray process, improving the nitriding reaction of the large Al particles at short spray distance is required to decrease the vaporization of Al particles during flight. This study investigated the influence of adding ammonium chloride (NH4Cl) powders on the nitriding process of large Al powders and on the microstructure of the fabricated coatings. It was possible to fabricate thick AlN coatings at 100 mm spray distance with small addition of NH4Cl powders to the Al feedstock powders (30 ??m). Addition of NH4Cl to the starting Al powders promoted the formation of AlN through changing the reaction path to vapor-phase nitridation chlorination-nitridation sequences as confirmed by the thermodynamic analysis of possible intermediate reactions. This changes the nitriding reaction to a mild way, so it is more controlled with no explosive mode and with relatively low heating rates. Thus, NH4Cl acts as a catalyst, nitrogen source, and diluent agent. Furthermore, the evolved gases from the sublimation or decomposition of NH4Cl can prevent the Al particles coalescing after melting. 相似文献
8.
Kerstin-Raffaela Donner Frank Gaertner Thomas Klassen 《Journal of Thermal Spray Technology》2011,20(1-2):299-306
A successful combination of insulating substrates with conducting metal coatings produced by cold spraying could open new industrial application areas like the fabrication of power electronic components. For minimizing the number of industrial process steps, insulating ceramic layers should ideally be processed by thermal spray techniques. Thus, this study investigates the impact behavior and coating formation of ductile metallic feedstock powders onto brittle ceramic coatings. With respect to high electrical conductivity of the metallic lines and good electrical insulation of the ceramic interlayer, copper was cold gas sprayed on previously thermally sprayed Al2O3 coatings. Successful cold coating formation requires different strategies for the activation of the ceramic layer to increase adhesion and to avoid brittle failure. These both can be achieved either by applying a bondcoat on the ceramic layer or using heated substrates during the cold spray process. 相似文献
9.
《Intermetallics》2014
Mechanically alloyed nanocrystalline Al63Ni37 powder with a metastable structure of NiAl intermetallic phase was mixed with 30 vol.% of Al powder. This powder mixture was consolidated under the pressure of 7.7 GPa at 600, 700, 800 and 1000 °C for 15 and 180 s. During the consolidation, in all cases, the metastable NiAl phase transformed into the equilibrium Al3Ni2 intermetallic. Moreover, a solid-state reaction between the intermetallic matrix and Al occurred, yielding an Al3Ni phase. Progress of this reaction depended on the consolidation temperature and temperature exposure time, thus Al3Ni2–Al, Al3Ni2–Al–Al3Ni or Al3Ni2–Al3Ni composites were produced by hot-pressing with various parameters. The mean crystallite size of the Al3Ni2 intermetallic matrix in the composites is 39–67 nm, depending on consolidation parameters. The composites hardness is in the range of 6.02–7.51 GPa. 相似文献
10.
《Intermetallics》2014
Ti–48Al–6Nb (at.%) porous alloys are fabricated by elemental powder metallurgy to study the pore formation and propagation mechanism. Reactive diffusion, pore formation process, and pore characteristics of the porous TiAl–Nb alloys are investigated at different temperatures. It is found that the porous alloys exhibit a uniform, maze-like network skeleton, viz., a typical α2-TiAl3/γ-TiAl fully lamellar microstructure. The reactive diffusivities between Ti and Al powders are dominant during the Ti–Al–Nb powder sintering. Gas release during sintering also plays an important role in the pore propagation and the compact expanding process. In addition, a pore-formation model is proposed to interpret the growth mechanism of pores and skeletons. 相似文献
11.
Influence of the Spray Angle on the Characteristics of Atmospheric Plasma Sprayed Hard Material Based Coatings 总被引:1,自引:0,他引:1
Wolfgang Tillmann Evelina Vogli Benjamin Krebs 《Journal of Thermal Spray Technology》2008,17(5-6):948-955
This paper presents an investigation of the influence of the spray angle on thermally sprayed coatings. Spray beads were manufactured with different spray angles between 90 and 20° by means of atmospheric plasma spraying (APS) on heat-treated mild steel (1.0503). WC-12Co and Cr3C2-10(Ni20Cr) powders were employed as feedstock materials. Every spray bead was characterized by a Gaussian fit. This opens the opportunity to analyze the influence of the spray angle on coating properties. Furthermore, metallographic studies of the surface roughness, porosity, hardness, and morphology were carried out and the deposition efficiency as well as the tensile strength was measured. The thermally sprayed coatings show a clear dependence on the spray angle. A decrease in spray angle changes the thickness, width, and form of the spray beads. The coatings become rougher and their quality decreases. 相似文献
12.
Infrared dissimilar brazing of α2-Ti3Al and Ti–6Al–4V using Ti–15Cu–25Ni and Ti–15Cu–15Ni filler metals has been performed in this study. The brazed joint consists primarily of Ti-rich and Ti2Ni phases, and there is no interfacial phase among the braze alloy, α2-Ti3Al and Ti–6Al–4V substrates. The existence of the Ti2Ni intermetallic compound is detrimental to the bonding strength of the joint. The amount of Ti2Ni decreases with increasing brazing temperature and/or time due to the depletion of Ni content from the braze alloy into the Ti–6Al–4V substrate during brazing. The shear strength of the brazed joint free of the blocky Ti2Ni phase is comparable with that of the α2-Ti3Al substrate, and strong bonding can thus be obtained. 相似文献
13.
Ti46Al7Nb alloy has been used as the research substrate material for the deposition of water-based slurries containing Al and Si powders. The diffusion treatment has been carried out at 950 °C for 4 h in Ar atmosphere. The structure of the silicon-modified aluminide coatings 40 μm thick is as follows: (a) an outer zone consisting of TiAl3 phase and titanium silicides formed on the matrix grain boundaries composed of TiAl3–type Ti5Si3; (b) a middle zone containing the same phase components with the matrix TiAl3 and the silicides Ti5Si3, which formed columnar grains; (c) an inner zone, 2 μm thick, consisting of TiAl2 phase. Cyclic oxidation tests were conducted in 30 cycles (690 h at high temperature) and showed a remarkably higher oxidation resistance of the Ti46Al7Nb alloy with the protective coating in comparison with the uncoated sample. 相似文献
14.
The Protectiveness of Thermally Grown Oxides on Cold Sprayed CoNiCrAlY Bond Coat in Thermal Barrier Coating 总被引:1,自引:0,他引:1
This paper presents the results of an oxidation behavior study for a thermal barrier coating (TBC) with air plasma sprayed yttria-stabilized zirconia top coat and CoNiCrAlY bond coat deposited using low pressure plasma spray (LPPS) and cold spray (CS). The TBC is subjected to isothermal oxidation and creep tests at 900?°C and evaluated using scanning electron microscopy, energy dispersive x-ray spectrometry transmission electron microscopy and electron backscatter diffraction. The thermally grown oxide (TGO) developed in the TBC with the LPPS bond coat was composed of only ??-Al2O3 and the TGO developed in the TBC with a CS bond coat is composed of ??-Al2O3 and ??-Al2O3. Despite the presence of this metastable ?? phase, the TGO in the CS specimens exhibits a dense microstructure and lower amounts of mixed oxides. The correlation between ??-Al2O3 and the formation of mixed oxides was investigated through the measurement of ??-Al2O3 thickness ratio and mixed oxides coverage ratio. It was found that the mixed oxides coverage ratio is inversely proportional to the ??-Al2O3 thickness ratio. 相似文献
15.
《Intermetallics》2014
The effects of cold work on the microstructural evolution during aging of a solutionized alumina-forming austenitic stainless steel, Fe–20Cr–30Ni–2Nb–5Al (at.%), were investigated using scanning electron microscopy, transmission electron microscopy, and scanning transmission electron microscopy. Cold work prior to aging at either 700 °C or 800 °C facilitated the heterogeneous precipitation of both Laves phase and B2-type NiAl precipitates. While often co-located after cold work, these particles were distinct. γ′-Ni3Al precipitates were also observed in samples aged at 700 °C with 90% prior cold work. Compared to material that had not been strained, defects introduced by 50 and 90% cold work at 700 °C and 90% cold work at 800 °C not only caused a more rapid precipitation in the matrix but also an increase in the total volume fraction of precipitates as compared to material that had been simply aged. 相似文献
16.
Consolidation of Al2O3/Al Nanocomposite Powder by Cold Spray 总被引:1,自引:0,他引:1
Dominique Poirier Jean-Gabriel Legoux Robin A. L. Drew Raynald Gauvin 《Journal of Thermal Spray Technology》2011,20(1-2):275-284
While the improvement in mechanical properties of nanocomposites makes them attractive materials for structural applications, their processing still presents significant challenges. In this article, cold spray was used to consolidate milled Al and Al2O3/Al nanocomposite powders as well as the initial unmilled and unreinforced Al powder. The microstructure and nanohardness of the feedstock powders as well as those of the resulting coatings were compared. The results show that the large increase in hardness of the Al powder after mechanical milling is preserved after cold spraying. Good quality coating with low porosity is obtained from milled Al. However, the addition of Al2O3 to the Al powder during milling decreases the powder and coating nanohardness. This lower hardness is attributed to non-optimized milling parameters leading to cracked particles with insufficient Al2O3 embedding in Al. The coating produced from the milled Al2O3/Al mixture also showed lower particle cohesion and higher amount of porosity. 相似文献
17.
The wear resistance of plasma sprayed molybdenum blend coatings applicable to synchronizer rings or piston rings was investigated
in this study. Four spray powders, one of which was pure molybdenum and the others blended powders of bronze and aluminum-silicon
alloy powders mixed with molybdenum powders, were sprayed on a low-carbon steel substrate by atmospheric plasma spraying.
Microstructural analysis of the coatings showed that the phases formed during spraying were relatively homogeneously distributed
in the molybdenum matrix. The wear test results revealed that the wear rate of all the coatings increased with increasing
wear load and that the blended coatings exhibited better wear resistance than the pure molybdenum coating, although the hardness
was lower. In the pure molybdenum coatings, splats were readily fractured, or cracks were initiated between splats under high
wear loads, thereby leading to the decrease in wear resistance. On the other hand, the molybdenum coating blended with bronze
and aluminum-silicon alloy powders exhibited excellent wear resistance because hard phases such as CuAl2 and Cu9Al4 formed inside the coating. 相似文献
18.
P. E. Leger M. Sennour F. Delloro F. Borit A. Debray F. Gaslain M. Jeandin M. Ducos 《Journal of Thermal Spray Technology》2017,26(7):1445-1460
Aluminum (Al) powders with spherical and irregular particle shapes were mixed with two alumina (Al2O3) powders with either a spherical or an angular particle shape to achieve high-performance cold-sprayed coatings onto steel. Two effects of the aluminum particle shape were observed. First, coating microstructure observation showed impinging heterogeneity depending on particle shape. Second, particle jet differences depending on particle morphology were shown by velocity maps. From the latter, SEM and XRD, three effects of the alumina particle shape were also shown, i.e., higher in-flight velocity of angular particles, fragmentation of spherical hollow particles and embedding of alumina particles with aluminum. Numerical simulation of particle impacts was developed to study the densification of Al coating due to Al2O3 addition through elucidation of Al-Al2O3 interaction behavior at the scale of the coating. Al/Al and Al/Al2O3 interfaces were investigated using TEM to understand coating strengthening effects due to alumina addition at the scale of the particle. As a whole, Al and Al2O3 particle shape effects were claimed to explain coating mechanical properties, e.g., microhardness and coating–substrate bond strength. This study resulted in specifying criteria to help cold spray users in selecting powders for their applications, to meet economic and technical requirements. 相似文献
19.
C. Feng V. Guipont M. Jeandin O. Amsellem F. Pauchet R. Saenger S. Bucher C. Iacob 《Journal of Thermal Spray Technology》2012,21(3-4):561-570
In this work, the microstructures of B4C/Ni coatings by cold spray with blends or chemical vapor deposited (CVD) Ni-coated powders were investigated and compared. Powder blends with Ni powder and fine or coarse B4C powders were prepared for various B4C content ranging from 54 to 87?vol.% (equal to 25-65?wt.%). Three CVD Ni-coated B4C powder batches were also synthesized with various B4C content using the fine B4C as core particles. Ni-coated powders and both types of cold sprayed coating microstructures with blends or coated powders were investigated by optical and scanning electron microscopy. Further quantitative image analysis was carried out on scanning electron microscopy (SEM) images to measure the B4C content within the coating regarding the influence of the nominal content in the feedstock for each coating type. Both types exhibited fine fragments and unfragmented B4C, but coatings with CVD-coated powders had many more unfragmented particles. Moreover, the higher levels for both B4C (44.0?±?4.1?vol.%) and coating microhardness (429?±?41 HV0.5) were obtained in case of the CVD-coated powders. However, it was assessed that the highest microhardness was not obtained for the highest B4C content. This questionable result is discussed with regard to the fully original composite microstructure obtained from CVD Ni-coated B4C powder. 相似文献
20.
The use of Al-Al2O3 cold spray coatings to improve the surface properties of magnesium alloys 总被引:1,自引:0,他引:1
Pure Al and 6061 aluminium alloy based Al2O3 particle-reinforced composite coatings were produced on AZ91E substrates using cold spray. The strength of the coating/substrate interface in tension was found to be stronger than the coating itself. The coatings have corrosion resistance similar to that of bulk pure aluminium in both salt spray and electrochemical tests. The wear resistance of the coatings is significantly better than that of the AZ91 Mg substrate, but the significant result is that the wear rate of the coatings is several decades lower than that of various bulk Al alloys tested for comparison. The effect of post-spray heat treatment, the volume fraction of Al2O3 within the coating and of the type of Al powder used in the coatings on the corrosion and wear resistance was also discussed. 相似文献