High Wear-Resistant Aluminum Matrix Composite Layer Fabricated by MIG Welding with Lateral B<Subscript>4</Subscript>C Powder Injection

In this work, a low-cost technique combining MIG welding and lateral powder injection was developed to fabricate B₄C particles-reinforced aluminum matrix composite (AMC) layer on a T6 heat-treated 7075 aluminum alloy (AA7075-T6) substrate. The AMC layer was 6-7 mm thick and well bonded to the substrate. The B₄C particles were dispersed throughout the AMC layer with an average content of approximately 7 vol.%. No significant reaction products existed either at the particle–matrix interface or in the Al-matrix. In pin-on-disk dry sliding wear tests against Al₂O₃ grinding wheels, the AMC layer exhibited excellent wear resistance with volume wear rate approximately 1/10-3/10 that of the quenched AISI 1045 steel and only approximately 2-7% that of the AA7075-T6 alloy under the same wear conditions. A small addition of ceramic particles can greatly improve wear resistance, suggesting that this technique has good prospects for a wide variety of applications.     

Synthesis of V8C7–Cr3C2 nanocomposite via a novel in-situ precursor method

V₈C₇–Cr₃C₂ nanocomposite has been synthesized by a novel in-situ precursor method, and the raw materials are ammonium vanadate (NH₄VO₃), ammonium dichromate ((NH₄)₂Cr₂O₇) and glucose (C₆H₁₂O₆). The products were characterized by thermogravimetric and differential scanning calorimetry (TG-DSC), X-ray diffractometry (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and X-ray photoelectron spectroscopy (XPS) techniques. The results show that V₈C₇–Cr₃C₂ nanocomposite with an average crystallite size of 31.5 nm can be synthesized at 900 °C for 1 h. The powders show good dispersion and are mainly composed of spherical or nearly spherical particles with a mean diameter of about 100 nm. The weight loss ratio of the precursor throughout the reaction process reaches 70 wt.%, and it changes rapidly before 400 °C (about 35 wt.%). Four endothermic peaks and three exothermic peaks occur during the reaction. The surface of the specimen is mainly composed of V, Cr, C and O four elements. The synthesis temperature of V₈C₇–Cr₃C₂ nanocomposite by the method (900 °C) is 500 °C lower than that of the conventional method (1400 °C).     

In situ synthesis of V8C7 nanopowders from a new precursor

Vanadium carbide (V₈C₇) nanopowders were prepared through simultaneous thermal decomposition and carbothermal reduction of the precursor VOC₂O₄/sucrose in vacuum. The products were characterized by X-ray diffractometer (XRD) and transmission electron microscopy (TEM) techniques. The thermolysis process of the precursor has been investigated by themogravimetric analysis and differential thermal analysis (TG-DSC). The results showed that the pure V₈C₇ powders can be obtained at 950 °C for 30 min and the particle size is in the range from 30 to 50 nm with good dispersion. The effects of experimental parameters and reaction mechanism have been explored. The lower synthesis temperature and shorter reaction time were attributed to take the quadrivalence vanadium as a reactant, as well as carbon source and vanadium source intimate contact in the precursor. This facile and quickly synthetic strategy may open a new route to the preparation of other carbide nanomaterials.     

Microstructure and Dry Sliding Wear Behavior of Fe-Based (Cr, Fe)7C3 Composite Coating Fabricated by PTA Welding Process

Using Cr₃C₂ and Fe-CrNiBSi powder blends as raw materials, an α-Fe matrix composite coating reinforced by in situ (Cr, Fe)₇C₃ rods, with a thickness of about 3.6 mm, was fabricated on the surface of AISI A36 low carbon steel by means of plasma-transferred arc welding. The results of microstructural analysis show that in the coating, a large number of carbides, (Cr, Fe)₇C₃, in rod shape grow, and radiate around some half-dissolved Cr₃C₂ particles. The results of dry sliding wear tests at loads 100, 200, and 300 N show that the wear resistances of (Cr, Fe)₇C₃-reinforced coating, respectively, are about 6.9, 14.9, and 17 times higher than that of nonreinforced pure Fe-CrNiBSi alloy coating; the average value and fluctuation range of friction coefficient (FC) of (Cr, Fe)₇C₃-reinforced coating are less than those of pure Fe-CrNiBSi alloy coating; the main wear mechanisms of pure Fe-CrNiBSi alloy coating are ploughing, deformation, and adhesive wear, whereas those of (Cr, Fe)₇C₃-reinforced coating are microcutting, abrasive, and oxidation wear; the cracks on surfaces of (Cr, Fe)₇C₃ rods increased with the increasing loads; and the matrix α-Fe can prevent them from extending further in the composite coating.     

High Temperature Sliding Wear of Spray-Formed Solid-Lubricated Aluminum Matrix Composites

The present work describes the tribological study of the aluminum metal matrix composite manufactured by the spray atomization and deposition technique. The immiscible element Sn is added in the Al-Si alloy in different proportion to see its effect on wear behavior. The economical mineral zircon sand (8 vol.%) of size range 63-90 μm has been used as ceramic reinforcement. The microstructural features showed that Sn and reinforced particles were homogeneously dispersed in the matrix phase. The wear experiments were conducted at high temperature on pin-on-disk wear testing machine. The wear debris and worn surfaces are analyzed with the help of scanning electron microscope equipped with energy-dispersive spectroscopy facility. The Al-Si-10Sn/ZrSiO₄ composite offers higher wear resistance as compared to base alloy and other composites irrespective of the high temperature conditions of wear tests.     

M7C3的形态分布对铁基复合层耐磨性能的影响

研究了在电磁搅拌的作用下,硬质相M7C3(主要是(Fe, Cr)7C3和Cr7C3)的数量和形态分布对堆焊层金属耐磨性的影响规律.对堆焊试件进行耐磨、硬度试验,并采用SEM,XRD对堆焊进行显微组织和成分分析.发现随着磁场参数的改变,硬质相M7C3由杂乱无章的分布逐渐转变为较规则的六方块状分布,堆焊层金属的耐磨性也随之增强;当磁场电流为3A,磁场频率为10Hz时,堆焊层金属的性能达到最佳状态,此时堆焊层中硬质相(M7C3)均成较规则的六方块状分布.结果表明,在适当的磁场参数作用下,硬质相(M7C3)成较规则的六方块状分布可以显著的提高堆焊层金属的耐磨性.     

Effect of Nd2O3 Additive on Microstructure and Tribological Properties of Plasma-Sprayed NiCr-Cr2O3 Composite Coatings

Four types of NiCr-Cr₂O₃ composite coatings doped with different mass fraction of Nd₂O₃ were deposited by atmospheric plasma spraying. The microstructure and phase composition of as-sprayed coatings were analyzed by scanning electron microscope (SEM) and X-ray diffraction (XRD). Furthermore, their friction and wear behaviors at 20 and 600 °C under unlubricated condition were evaluated using CSM high temperature tribometer. The results showed that Nd₂O₃ could refine microstructure of NiCr-Cr₂O₃ composite coating and make Cr₂O₃ distribution more uniform in the coating, which leads to the increase of average microhardness. In addition, NiCr-Cr₂O₃ composite coatings doped with Nd₂O₃ had better wear resistance than that without Nd₂O₃ at experimental temperatures. Especially, the coating containing 8 wt.% Nd₂O₃ showed the best wear resistance at 20 and 600 °C, which was attributed to the refined microstructure and improved microhardness. At 20 °C, the wear mechanism of the coating was abrasive wear, brittle fracture and splat detachment. At 600 °C, the wear mechanism was adhesion wear and plastic deformation.     

Influence of Martensite Volume Fraction on Impact Properties of Triple Phase (TP) Steels

Ferrite-bainite-martensite triple phase (TP) microstructures with different volume fractions of martensite were obtained by changing heat treatment time during austempering at 300 °C. Room temperature impact properties of TP steels with different martensite volume fractions (V _M) were determined by means of Charpy impact testing. The effects of test temperature on impact properties were also investigated for two selected microstructures containing 0 (the DP steel) and 8.5 vol.% martensite. Test results showed reduction in toughness with increasing V _M in TP steels. Fracture toughness values for the DP and TP steels with 8.5 vol.% martensite were obtained from correlation between fracture toughness and the Charpy impact energy. Fractography of Charpy specimens confirmed decrease in TP steels’ toughness with increasing V _M by considering and comparing radial marks and crack initiation regions at the fracture surfaces of the studied steels.     

Properties and Tribological Performance of Vanadium Carbide Coatings on AISI 52100 Steel Deposited by Thermoreactive Diffusion

Vanadium carbide coatings were formed on AISI 52100 steel specimens by thermoreactive diffusion and characterized using nanoindentation, x-ray diffraction, and chemical analysis. The deposition process formed a 4-µm coating of vanadium carbide (V₄C₃) with an average grain size of 33 nm and a [200] crystallographic texture. The hardness and elastic modulus of the coatings were determined to be 35 ± 7.5 GPa and 334 ± 67 GPa, respectively. Friction and wear of the coatings were examined in reciprocating sliding contact against tungsten carbide (WC) balls in dry and in an abrasive environment. It was determined that in the abrasive environment, the V₄C₃ coating provided wear protection comparable to WC.     

Effects of SiC Volume Fraction and Particle Size on the Deposition Behavior and Mechanical Properties of Cold-Sprayed AZ91D/SiCp Composite Coatings

AZ91D/SiC_p composite coatings were fabricated on AZ31 magnesium alloy substrates using cold spraying. The effects of SiC volume fraction and particle size on the deposition behavior, microhardness, and bonding strength of coatings were studied. The mean sizes of SiC particles tested were 4, 14, and 27 μm. The results show that fine SiC particles (d _0.5 = 4 μm) are difficult to be deposited due to the bow shock effect. The volume fraction of SiC particles in composite coatings increases with the increasing SiC particle size. The microhardness and bonding strength of composite coatings also show increases compared with AZ91D coatings. The volume fractions of SiC particles in the original powder were set at 15, 30, 45, and 60 vol.%. The corresponding contents in composite coatings are increased to 19, 27, 37, and 51 vol.%, respectively. The microhardness of composite coatings also increases as the volume fraction of SiC particles increases.     

Characterization of Microstructure and Wear Resistance of PEO Coatings Containing Various Microparticles on Ti6Al4V Alloy

Titania-based composite coatings were prepared by plasma electrolytic oxidation (PEO) treatment of Ti6Al4V alloy in electrolyte with α-Al₂O₃, Cr₂O₃ or h-BN microparticles in suspension. The microstructure, composition of PEO composite coatings were analyzed by SEM, EDS and XRD. The wear resistance of composite ceramic coatings was studied by ball-on-disk wear test at ambient temperature and 300 °C. The results showed that the addition of microparticles accelerated the growth rate of PEO coating and changed the microstructure and composition of PEO coating. PEO coating was porous and mainly composed of rutile-TiO₂, anatase-TiO₂ and Al₂TiO₅. PEO/α-Al₂O₃ (Cr₂O₃ or h-BN) composite coating only had small micropores and appeared some α-Al₂O₃ (Cr₂O₃ or h-BN) phase. Besides, the addition of α-Al₂O₃ (Cr₂O₃ or h-BN) microparticles greatly improved the wear resistance of PEO coating. At ambient temperature, abrasive wear dominated the wear behavior of PEO coating, but abrasive wear and adhesive peel simultaneously happened at 300 °C. Whether at ambient temperature or 300 °C, PEO composite coating had better wear resistance than PEO coating. Besides, PEO/h-BN composite coating outperformed other composite coatings regardless of the temperature.     

Effect of Submicron and Nano SiC Particles on Erosion Wear and Scratch Behavior of Plasma-Sprayed Al2O3/8YSZ Coatings

This paper reports studies into the effect of submicron and nano SiC particles on microstructure, phase composition, hardness, erosion wear, and scratch behavior of Al₂O₃-20wt.%8YSZ (ZrO₂ + 8 wt.% Y₂O₃) coatings fabricated by atmospheric plasma spraying. The failure mode of erosion wear and scratch for coatings was established and analyzed. The hardness, density, erosion wear, and anti-scratch resistance of coatings fabricated from plasma treating feedstocks were higher than that of coatings made from sintering feedstocks. The erosion wear rate of coatings with SiC was evidently decreased, and there was some small debris on worn surface with characteristic of translamellar fracture. The spallation, fracture, plough, and cracking were main failure mechanism for coatings. In the scratch process, the critical load of coating with SiC was increased. The crack growth resistance of coatings was analyzed from crack length at end of scratch test.     

Designed fabrication of hard CrCr2O3Cr7C3 nanocomposite coatings for anti-wear application

Nanocrystalline CrCr₂O₃Cr₇C₃ composite coatings were fabricated by electrodeposition followed by thermal treatment. The structures of coatings were investigated using high-resolution transmission electron microscopy and X-ray diffraction analysis. The composition, elemental chemical state, mechanical properties and wear resistance of coatings were determined using energy dispersive X-ray spectroscopy, X-ray photoelectron spectroscopy, nanoindentation and oscillating friction-wear testing, respectively. Wear tracks were observed by scanning electron microscopy. The results show that the as-deposited coating exhibits amorphous structure. The subsequent thermal treatment at 600 °C induces the crystallization and the generation of nanoscale Cr₂O₃ and Cr₇C₃ particles in the Cr-matrix, which results in the hardness of the coating increasing to 21 GPa with slight increase in elastic modulus. Owing to the compromise between high hardness and low elastic modulus, the obtained CrCr₂O₃Cr₇C₃ composite coating exhibits excellent wear resistance.     

Microstructure and abrasive wear performance of chromium carbide reinforced Ni3Al matrix composite coating

A Ni-Al-Cr₃C₂ welding wire was produced by metal-powder-core technique. When the welding wires were welded on the surface of carbon steel, under the effect of the physical heat of arc, Ni reacted with Al to form Ni₃Al and carbide particles reinforced Ni₃Al matrix composite was formed. Cr₃C₂ was decomposed during welding and dispersed Cr₇C₃ with stripe shape formed, which strengthened the matrix significantly. The Cr₇C₃-Ni₃Al interface has broadened into a zone of interdiffusion and a new phase M₂₃C₆, which indicates that a good bond has been formed. The pin-abrasion wear test showed that the abrasion resistance of Cr₇C₃/Ni₃Al composite is six times higher than that of Stellite12 alloy at room temperature. The good wear resistance of Cr₇C₃/Ni₃Al composite coating can be attributed to large volume fraction of carbides, high hardness, and good phases interface bond.     

The High-Temperature Wear and Oxidation Behavior of CrC-Based HVOF Coatings

Three commercially available chromium carbide-based powders with different kinds of matrix (Cr₃C₂-25%NiCr; Cr₃C₂-25%CoNiCrAlY and Cr₃C₂-50%NiCrMoNb) were deposited by an HVOF JP-5000 spraying gun, evaluated and compared. The influence of heat treatment on the microstructure and properties, as well as the oxidation resistance in a hot steam environment (p = 24 MPa; T = 609 °C), was evaluated by SEM and XRD with respect to their potential application in the steam power industry. The sliding wear resistance measured at room and elevated (T = 600 °C) temperatures according to ASTM G-133. For all three kinds of chromium carbide-based coatings, the precipitation of secondary carbides from the supersaturated matrix was observed during the heat treatment. For Cr₃C₂-25%NiCr coating annealed in hot steam environment as well as for Cr₃C₂-25%CoNiCrAlY coating in both environments, the inner carbide oxidation was recorded. The sliding wear resistance was found equal at room temperature, regardless of the matrix composition and content, while at elevated temperatures, the higher wear was measured, varying in dependence on the matrix composition and content. The chromium carbide-based coating with modified matrix composition Cr₃C₂-50%NiCrMoNb is suitable to replace the Cr₃C₂-25%NiCr coating in a hot steam environment to eliminate the risk of failure caused by inner carbide oxidation.     

Effects of Boron Carbide Content on the Microstructure and Properties of Atmospheric Plasma-Sprayed NiCoCrAlY/Al2O3-B4C Composite Coatings

NiCoCrAlY/Al₂O₃ and NiCoCrAlY/B₄C composite powders were prepared with hydrogen reduction and solid state alloying process. NiCoCrAlY/Al₂O₃-B₄C composite coatings with different contents of B₄C were prepared by atmospheric plasma spray technology. The microstructures, mechanical properties, and tribological properties of the composite coatings with different B₄C contents were systematically investigated. The results show that the microhardness of the composite coatings increases, while the tensile strength of the composite coatings decreases, with the increase of B₄C contents. The wear volume of the composite coatings decreases from room temperature to 800 °C with the increase of B₄C contents. Abrasion wear is the main wear mechanism of the NiCoCrAlY/Al₂O₃-B₄C composite coating from room temperature to 800 °C.     

Effect of surface Cr/C infiltration on microstructure,mechanical properties and wear resistance of high chromium cast iron

A new type of high chromium cast iron (HCCI) was prepared, and its microstructure, mechanical properties, and abrasion resistance were investigated systematically. Results showed that after surface carburizing and chromizing, the microstructure of HCCI mainly consists of martensite, boride (M₂B), and carbide (M₇C₃), accompanied with a large amount of secondary precipitations M₂₃C₆. Moreover, the morphology and hardness of the carbide and boride in HCCI change little, while the volume fraction of carbide and boride increases from 16.23% to 23.16%. This effectively increases the surface hardness of HCCI from 64.53±0.50 HRC to 66.58±0.50 HRC, with the result that the surface of HCCI possesses a better abrasion resistance compared to the center position. Furthermore, the wear mechanism of HCCI changes from micro-plowing to micro-cutting with the increase of surface hardness.

     

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.     

Synthesis and thermal expansion of 4J36/ZrW<Subscript>2</Subscript>O<Subscript>8</Subscript> composites

Gas atomized 4J36 alloy powder was milled for 72 h then mixed with ZrW₂O₈ powder and sintered at 600°C for 4 h under argon atmosphere. 4J36/ZrW₂O₈ composites containing 10 vol.%, 20 vol.%, 30 vol.%, and 40 vol.% ZrW₂O₈ were fabricated, the relative density of which ranged from 70% to 80%. Thermal expansion coefficients of the composites decreased as the amount of ZrW₂O₈ increased, in agreement with the rule of the mixture. The coefficient of thermal expansion of the 4J36/40 vol.%ZrW₂O₈ composite in 25–100°C is 0.55 × 10⁻⁶/°C.