Microstructure characteristics of SiC particle-reinforced aluminum matrix composites by plasma spraying

Aluminum with 55 and 75 vol.% SiC powders were ball milled as plasma spray feedstock. The feedstock was deposited onto a graphite substrate to form a freestanding composite by air plasma spraying. The microstructure characteristics of the sprayed composite were investigated by x-ray diffraction, scanning electron microscopy, and transmission electron microscopy. The SiC volume fraction and porosity in the sprayed composites depend on plasma spray conditions. The silicon phase was formed in the sprayed composites in some plasma spray conditions, and its amount was related to the input of electrical power into the plasma spray. The mechanism of silicon formation was studied. In the sprayed composites, no reaction products could be observed in the Al/SiC interface. Impurity materials from ball media, stainless steel, and ZrO₂ reacted with aluminum and silicon to form complex compounds during plasma spray deposition.     

Microstructure Characteristics of SiC Particle-Reinforced Aluminum Matrix Composites Coatings by Cold Spraying

A dense Al/SiCp composite coating with high volume fraction(60%)of nano SiCp reinforcement was fabricated by cold spraying of ball-milled Al-60SiCp composite powder.The morphologies evolution of the Al-60SiCp composite powder during ball milling and the microstructure and microhardness of the cold-sprayed Al-60SiCp composite coating were investigated.The results show that Al particles undergone fracture deformation and nano SiC particles are uniformly distributed in soft Al matrix after ball milling.A dense Al-60SiCp composite coating can be fabricated by cold spraying of ball milled composite powder.Nano SiC particles in the cold-sprayed Al-60SiCp composites coating exhibit a reasonably uniform distribution.The Hv0.5 microhardness of the Al-60SiCp composite coating is reached up to(5.30±0.53)GPa due to the enhancement of SiC particles,compared to(0.34±0.03)GPa for the pure Al bulk.     

Amorphization of ZrO2 + CeO2 Powders Through Mechanical Milling for the Use of Kinetic Spray

The coating formation in a kinetic spray process mainly depends on the impact of inflight particles at a high velocity. The plastic deformation at the impact interface would disrupt the native oxide scale on the particle and the substrate to generate the intimate contact of the atomic structures. Accordingly, it poses a challenge in producing ceramic coating during kinetic spray because of the lack of plasticity of ceramic powders at room temperature. In this study, we proposed to prepare ZrO₂ ceramic coatings using partially amorphized powder with nanometer size in the kinetic spray process. To prepare the powder for the use of the kinetic spray, the amorphization and grain refinement of ZrO₂ powder in mechanical ball milling were studied. The results showed that the amorphization and grain refinement were improved because of the formation of solid solution when the CeO₂ agent was added. Subsequently, a nearly spherical powder was achieved via spray drying using the milled powders. The plasticity of the milled powders was tested in the kinetic spray process using Nitrogen as process gas. A dense ZrO₂-CeO₂ coating with a thickness of 50 μm was formed, whereas spraying milled ZrO₂ powder can only lead to an inhomogeneous dispersion of the destructible particles on the surface of the substrate.     

Microstructure and Mechanical Behavior of Microwave Sintered Cu<Subscript>50</Subscript>Ti<Subscript>50</Subscript> Amorphous Alloy Reinforced Al Metal Matrix Composites

In the present work, Al metal matrix composites reinforced with Cu-based (Cu₅₀Ti₅₀) amorphous alloy particles synthesized by ball milling followed by a microwave sintering process were studied. The amorphous powders of Cu₅₀Ti₅₀ produced by ball milling were used to reinforce the aluminum matrix. They were examined by x-ray diffraction (XRD), scanning electron microscopy (SEM), microhardness and compression testing. The analysis of XRD patterns of the samples containing 5 vol.%, 10 vol.% and 15 vol.% Cu₅₀Ti₅₀ indicates the presence of Al and Cu₅₀Ti₅₀ peaks. SEM images of the sintered composites show the uniform distribution of reinforced particles within the matrix. Mechanical properties of the composites were found to increase with an increasing volume fraction of Cu₅₀Ti₅₀ reinforcement particles. The hardness and compressive strength were enhanced to 89 Hv and 449 MPa, respectively, for the Al-15 vol.% Cu₅₀Ti₅₀ composites.     

冷喷涂SiC/Al纳米复合涂层的组织结构与性能

为制备基体相晶粒细小、增强相均匀分布的SiC/Al纳米复合涂层,以Al、SiC为原料,采用高能球磨法获得SiC颗粒弥散分布的纳米晶Al基复合材料粉末,利用冷喷涂技术低温成型制备了SiC/Al纳米复合涂层,分析了SiC含量对复合涂层相结构、晶粒尺寸、微观结构、硬度及磨损性能的影响规律。结果表明：冷喷涂可实现球磨纳米晶复合粉末结构的原位移植,所制备SiC/Al纳米复合涂层组织致密,微米及亚微米级SiC弥散分布在纳米晶Al（约80 nm）基体之上;SiC颗粒对Al基体有明显强化作用,冷喷涂SiC/Al纳米复合涂层的硬度随SiC体积分数的增加而显著增加,50% SiC/Al纳米复合涂层的硬度高达515 HV_0.3,约为Al块材的13倍;冷喷涂SiC/Al纳米复合涂层的耐磨损性能随着SiC含量增加而显著提高,涂层磨损失效机制为磨粒对基体的切削犁沟变形。     

Properties and fast low-temperature consolidation of nanocrystalline Ni-ZrO2 composites by high-frequency induction heated sintering

Nanopowders of Ni and ZrO₂ (11 nm and 90 nm, respectively) were synthesized from NiO and Zr by high energy ball milling. A highly dense nanostructured 2Ni-ZrO₂ composite was consolidated at low temperature by high-frequency induction heat sintering within 2 min of the mechanical synthesis of the powders (Ni-ZrO₂) with horizontal milled NiO + Zr powders under 500 MPa pressure. This process allows very quick densification to near theoretical density and prohibits grain growth in nano-structured materials. The grain sizes of Ni and ZrO₂ in the composite were calculated. Finally, the average hardness and fracture toughness values of nanostructured 2Ni-ZrO₂ composites were investigated.     

Fabrication and Properties of Thermal Sprayed AlSi-Based Coatings from Nanocomposite Powders

AlSi-based nanocomposite powders (where nanoparticles were TiO₂, ZrO₂, and Al₂O₃ and the amount of reinforcement was 2.5, 5, and 10 wt.%) were made by ball milling and then thermal sprayed using low velocity oxy-fuel technique. The AlSi-based nanocomposite powders had nanosized ceramic reinforcement adhered to the surface of the powders after ball milling. The AlSi-based coatings had the typical thermal spray microstructure where lamellae, oxide layers, unmelted particles, and pores could be seen. Submicron second phase in the form of agglomerates, molten splats, or unmelted particles between AlSi lamellae could be observed as well. Hardness and porosity of the coatings increased when more ceramic second phase particles (harder than AlSi) were added. Sliding wear tests were carried out in pin-on-disk geometry. The wear tracks of AlSi and AlSi-based coatings show plastic deformation as the main material removal mechanism during the sliding wear test. The sliding wear rate of the coatings decreased as more second phase ceramic particles were added. It was due to an increase in the hardness and a decrease in the friction coefficient of the coatings.     

Plasma Spray Coatings of Ni-Al-SiC Composite

Ni-Al-SiC powder mixture containing 12 wt.% SiC was prepared by conventional ball milling. Morphological and microstructural investigations showed that powder particles after 15 h of milling time had the optimum characteristics with respect to their size and microstructure. X-ray diffraction patterns of powder particles included only the elemental Ni, Al, and SiC peaks without any traces of oxides or intermetallic phases. The powder mixture was then deposited onto a steel substrate by atmospheric plasma spray (APS) process under different conditions. The results showed that under APS conditions used here, the coatings were composed of various intermetallics including Ni-Al and Ni₂Al₃. The mean hardness of coating was found to be about 567 HV. It was also found that by increasing current density of APS, the coating/substrate adhesive strength was increased.     

纳米晶W粉和W-Ni-Fe预合金粉的制备

采用高能球磨法制备纳米晶W粉和W-Ni-Fe预合金粉，研究了不同的球磨材质包括硬质合金球(CCB)、钨球(TAB)和球磨转速、球料比及球磨时间等条件对球磨后粉末性能的影响。利用XRD，TEM和EDX分析球磨后粉末的晶粒尺寸、晶格畸变、形貌、结构变化及颗粒成分变化。结果表明：高能球磨法可制得10nm～80nm的W粉和W-Ni-Fe预合金粉，纳米级颗粒含量达80％以上。相同材质的钨球制得的纳米粉末综合性能较好。球磨过程中，粉末保持颗粒状结构，纳米级粉末颗粒形状最终趋于等轴化。     

Mechanical alloying of platinum with 5% ZrO2 nanoparticles for glass making tools

Synthesis and characterization of mechanically alloyed Pt–5%ZrO₂ (volume fraction) for structural components in the glass industry were described. Zirconia (ZrO₂) nanoparticles (<100 nm) were produced by the electrical explosion of zirconium (Zr) wires, and blended with platinum (Pt) powders (<44 μm) for 2–72 h in ambient atmosphere. The Pt particle size followed the typical decreasing trend of the normal ball milling process up to 48 h, but particle agglomeration was observed at 72 h. The grain size evolution was similar to that of the particle size, dropping down to around 50 nm at 48 h. The root mean square strain of the Pt crystallites showed the opposite behavior, maximizing at 48 h with a subsequent relaxation process. For the 48 h ball milled powders, spark plasma sintering was carried out to form a bulk disk. The measured mass loss of the sintered bulk sample shows a decent thermal stability despite its relatively low density.     

Microstructure and Adhesion Strength of Ni<Subscript>3</Subscript>Ti Coating Prepared by Mechanical Alloying and HVOF

In the present work we report the development of Ni₃Ti intermetallic compound by high energy ball milling of Ni and Ti powders. The ball milled powders were taken at various intervals (4, 6, 8, 10, and 11 h) to analyze the formation of Ni _x Ti _x intermetallic compounds. The ball milled powders were analyzed using scanning electron microscopy and X-ray diffraction. The layered shaped powder particles of Ni₃Ti phase were formed after 11 h of ball milling, which was confirmed by X-ray peaks. Further High-Velocity Oxy-Fuel (HVOF) process was used to coat Ni₃Ti and Ni₃Ti + (Cr₃C₂ + 20NiCr) on MDN 420 steel. Both the coated materials displayed excellent cohesion with minimal porosity less than 2%. The tensile adhesion strength test was carried out on these coatings to check the bond strength. Out of the two the Ni₃Ti coating showed excellent bond strength of 41.04 MPa compared to that of Ni₃Ti + (Cr₃C₂ + 20NiCr) coating.     

Microstrucmral characteristics and properties in centrifugal casting of SiCp/Zl104 composite

The microstructural characteristics and Brinell hardness of a cylinder produced by centrifugal casting were investigated using 20% (volume fraction) SiC_p/Zl104 composites. Macrostructure and XRD analysis show that most of SiC particles segregate to the external circumference of the cylinder, the other SiC particles maintain in the inner circumference of the cylinder, and a free particle zone is left in the middle circumference of the cylinder. Microstructural characteristics and quantitative assessment of SiC particles show that most of congregated SiC particles in 20%SiC_p/Zl104 composites are dispersed by centrifugal force, and the other congregated SiC particles and most of alumina oxide are segregated to the inner circumference of the cylinder. The SiC particles in aluminum melt can promote the refinement of primary α(Al) during solidification, and fine primary α(Al) grains can also promote the uniform distribution of SiC particles. Brinell hardness of SiC_p/Zl104 composites is connected with not only the volume fraction of SiC particles, but also the distribution of SiC particles in matrix alloy.     

Consolidation of Al2O3/Al Nanocomposite Powder by Cold Spray

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.     

OXIDATION RESISTANCE OF NANOCRYSTAL ODS ALUMINIDE COATINGS PRODUCED BY PACK ALUMINIZING PROCESS ASSISTED BY BALL PEENING

Nanocrystal ODS （oxide dispersion strengthening） aluminide coatings were produced on a stainless steel and nickel-based superalloy by the pock aluminizing process assisted by ball peening, Pure Al powders and 1% of ultra-fine Y2O3 powders were mixed by ball milling. The ultra-fine Y2O3 powders were dispersed in Al particles. Ball peening welded the Al particles onto the substrate and accelerated the formation of aluminide coating. Nanocrystal ODS aluminide coatings were produced by the outward growth at a much low temperature （below 600℃） in a short treatment time. The effects of the operation temperature and treatment time on the formation of the coatings were analyzed. SEM （scanning electron microscope）, AFM （atomic force microscope）, EDS （energy dispersive X-ray spectroscopy）, XRF （X-ray fluorescence spectrometer） and XRD （X-ray diffraction） methods were applied to investigate the microstructure of the coatings. High-temperature oxidation tests were carried out to evaluate the oxidation resistance of the ODS aluminide coatings.     

Microstructure and transformation of Al-containing nanostructured 316L stainless steel coatings processed using spark plasma sintering

Three austenitic stainless steel alloys containing 0, 2 and 6 wt.% Al were prepared by cryomilling and spark plasma sintering. It was shown that aluminum influences the strain-induced phase transformation that occurs during milling. The milled powders consisted of finely dispersed particles with the powder particle size distribution increasing with aluminum concentration. Consolidation of the SS0Al (stainless steel containing 0 wt.% Al) powder via the spark plasma sintering (SPS) process onto a solid stainless steel substrate yields an equiaxed structure due to the original particle morphology resulting from cryomilling. The SS2Al and SS6Al SPS consolidated powder coatings exhibit a lamellar structure due to the increased aspect ratio of the particles. The degree to which the BCC structure induced during cryomilling of all three powder systems reverted to FCC was dependent upon the Al content. The SPS process was found to minimally influence the FCC recovery compared to conventional powder consolidation heat treatments. The energy supplied by the SPS process was insufficient to overcome the activation energy governing the rearrangement of dislocations required to complete the FCC recovery. The microhardness of the coatings processing using SPS was found to be highly dependent on the Al content by controlling the ratio of the BCC/FCC crystals in the formed coating.     

Synthesis of SnFe<Subscript>2</Subscript>O<Subscript>4</Subscript> Nanomaterials Via High Energy Ball Milling of SnO (Stannous) and α-Fe<Subscript>2</Subscript>O<Subscript>3</Subscript> (Hematite) Solid Precursors

The synthesis of single phase tin-ferrite, SnFe₂O₄, from tin (II) oxide or stannous oxide (SnO), and hematite (α-Fe₂O₃) solid precursors was carried out via high energy ball milling (HEBM) under wet condition involving the addition of controlled amounts of acetone. The stoichiometric amounts of the precursor materials were ball milled continuously for up to 22 h in a Spex-8000D mill using a ball-to-powder ratio of 40:1, with hardened stainless steel balls in WC-lined jars. The time-dependent formation of the SnFe₂O₄ based on combined X-ray diffraction and room temperature Mössbauer spectroscopy (MS) measurements revealed reaction enhancements associated with particles size reduction. The 22 h milled material indicated that synthesized SnFe₂O₄ had a particle size of 10.91 nm, coercivity of 4.44 mT, magnetic saturation/remanent ratio (M _r/M _s) of 0.085, while its superparamagnetic behavior was confirmed based on the combined MS and vibrating sample magnetometer measurements.     

Properties and rapid low-temperature consolidation of nanocrystalline Fe-ZrO<Subscript>2</Subscript> composite by pulsed current activated sintering

Nanopowders of Fe and ZrO₂ were synthesized from Fe₂O₃ and Zr by high-energy ball milling. The powder sizes of Fe and ZrO₂ were 70 nm and 12 nm, respectively. Highly dense nanostructured 4/3Fe-ZrO₂ composite was consolidated by a pulsed current activated sintering method within 1 minute from the mechanically synthesized powders (Fe-ZrO₂) and horizontal milled Fe₂O₃+Zr powders under the 1 GPa pressure. The grain sizes of Fe and ZrO₂ in the composite were calculated. The average hardness and fracture toughness values of nanostuctured 4/3Fe-ZrO₂ composite were investigated.     

Property improvement of stainless-steel-base surface composites fabricated by high-energy electron-beam irradiation

This is a study on the fabrication of surface composites of SiC, TiC particulates, and AISI 304 substrate by high voltage electron beam irradiation. Using CaF₂ powders as flux, two kinds of surface composites were fabricated for a comparative analysis of the microstructural modification and mechanical properties. Through the employed process, the powders and substrate surface were melted and surface composite layers were successfully formed in both cases. In the specimen fabricated with SiC powders, a volume fraction of Cr₂₃C₆ particles (−22 vol.%) were homogeneously distributed along solidification cell boundaries. The large amount of Cr₂₃C₆ particles in combination with solid solution hardening of Si in the matrix resulted in the improved hardness and wear resistance of the surface composite layer, that are 2 to 3 times those of the substrate. In the specimen fabricated with SiC and Ti+SiC powders, TiC and Cr₂₃C₆ particles were precipitated without precipitation of SiC.     

Bulk Al/SiC nanocomposite prepared by ball milling and hot pressing method

Nano-sized Al/SiC powders were prepared by mechanical alloying method. Two sorts of SiC particle, i.e., nano-sized and popular micron-sized SiC were utilized. The particle size and microstructure of the milled powder were characterised. Effects of the particle size and agglomerate state of SiC, as well as the microstructure of Al/SiC nanocomposite were studied by SEM and TEM. The results show that nano-sized SiC particles is dispersed in aluminium uniformly after ball milled for only 2 h, whereas the similar process need about 10 h for popular micron-sized SiC particle. The bulk Al/SiC nanocomposite can be fabricated by hot pressing the nano-sized Al/SiC powders at temperature about 723 K under pressure of 100 MPa.     

Microstructure and sliding wear behavior of nanostructured Ni60-TiB2 composite coating sprayed by HVOF technique

A nanostructured Ni60-TiB₂ composite coating (Ni60 is a brand of Ni-based self-fluxing alloy with a hardness of HRC60) was sprayed on steel substrate by high velocity oxy-fuel (HVOF) process using high energy ball milled powders. Its sliding wear resistance at room-temperature was evaluated by ball-on-disc testing. For comparison, conventional Ni60-TiB₂ composite coating was prepared by HVOF using mechanically mixed Ni60 and TiB₂ powders and tested under the same conditions. The results show that the nanostructured composite coating has excellent mechanical properties and sliding wear resistance due to the microstructural homogenization and the well preserved nanostructure characteristic of the ball milled powders. Adhesive and abrasive wears are found to be responsible for the wear down mechanisms of the nanostructured Ni60-TiB₂ composite coating.