Trying out spraying modes and properties of wear-resistant flame Al<Subscript>2</Subscript>O<Subscript>3</Subscript>–TiO<Subscript>2</Subscript> coatings fabricated using a flexible cord material

Samples of Al₂O₃–TiO₂ coatings are fabricated by the flame spraying of a flexible cord. The influence of process parameters and composition of the sprayed material on the structure, composition, and mechanical properties of coatings is investigated. It is shown that an increase in the spraying distance and feed rate of the sprayed material leads to a decrease in their density. An increase in the concentration of the low-melting TiO₂ component predetermines a decrease in the coating porosity and has no significant effect on the coating hardness. Being subjected to measuring scratching, Al₂O₃–TiO₂ flame coatings formed with minimal porosity (Π = 3.2%) are characterized by cohesion fracture behavior and no substrate opening under an indenter load of up to 90 N. The friction factor of coatings under study varies from 0.2 to 0.78 after 2800 counterbody revolutions (44 m of the friction path). This is associated with the accumulation of fatigue cracks in the coating material and its subsequent cohesive fracture by the formation of large fragments serving as an abrasive.     

超声辅助电沉积Ni-Co/ZrO_2复合镀层的性能研究

采用超声辅助电沉积方法将Ni-Co/ZrO_2纳米复合镀层电镀到铜板表面。在不同纳米粒子添加量下,通过线性扫描伏安(LSV)和交流阻抗(EIS)对电沉积过程进行电化学表征,通过SEM、EDS对镀层的组成和表面形貌进行研究,并分别利用显微硬度计和摩擦磨损试验仪对复合镀层的力学性能和摩擦磨损性能进行表征。结果表明,超声的引入能够有效降低镀液中颗粒的团聚量,提高镀层中纳米粒子的复合量,从而改善复合电沉积过程以及镀层性能。在纳米粒子浓度为10g/L时,镀层的表面形貌、摩擦性能和硬度等性能最优。     

Evaluation of Abrasive Wear Resistance of Al<Subscript>2</Subscript>O<Subscript>3</Subscript>/7075 Composite by Taguchi Experimental Design Technique

Two-body abrasive wear resistance of 7075 Al-alloy reinforced with 20 wt% Al₂O₃ particles has been studied with reference to unreinforced base alloy by design of experimental technique. Taguchi L₉ orthogonal array and analysis of variance techniques considering four factors, i.e., load, size of SiC abrasive particle, velocity and sliding distance, each at three different levels, have been employed. The experimental results reveal that wear resistance of composite is far superior than that of the unreinforced base alloy under any given test condition. In general, the most dominating factor is found to be the size of abrasive particle followed by load for both base alloy and composite. The confirmation tests reveal the accuracy level ±?5.52 and ±?6.06% for base alloy and composite, respectively. Mechanism of abrasive wear and the difference of wear response of base alloy and composite are discussed via characterizations of worn surface and generated wear debris.     

Hardness,adhesion strength,and tribological properties of adaptive nanostructured ion-plasma vacuum-arc coatings (Ti,Al)N–Mo<Subscript>2</Subscript>N

The properties of nanostructured multilayered coatings of the composition (Ti,Al)N–Mo₂N, which were fabricated by the ion-plasma vacuum-arc deposition (arc-PVD), are investigated. The thickness of coating layers is comparable with the grain size, which is about 30–50 nm. The coating hardness reaches 40 GPa with relative plastic deformation work of about 60%. It is established by measuring scratching that the cohesion destruction character of the coating occurs exclusively according to the plastic deformation mechanism, which evidences its high fracture toughness. The local coating attrition to the substrate takes place under a load on the order of 75 N. The coating friction coefficient in testing conditions according to the “pin-on-disc” layout using the Al₂O₃ counterbody under a load of 5 N is 0.35 and 0.50 at temperatures of 20 and 500°C, respectively. The coating is almost unworn because of the formation of MoO₃ oxide (the Magneli phase) operating as the solid lubricant in the friction zone. An increase in the friction coefficient and noticeable wear are observed with the further increase in the testing temperature, which is associated with the sublimation intensification of MoO₃ from the working surfaces and lowering its operational efficiency as the lubricant.     

Influence of Ni Content on the Microstructure and Dry Sliding Wear Properties of Cr<Subscript>13</Subscript>Ni<Subscript>5</Subscript>Si<Subscript>2</Subscript>/<Emphasis Type="Italic">γ</Emphasis> Intermetallic Alloys

The effect of Ni content on microstructure, hardness, and wear resistance was studied for the Cr₁₃Ni₅Si₂-base intermetallic alloys toughened by Ni-base solid solution (γ). Volume fraction and microhardness of the Cr₁₃Ni₅Si₂ primary dendrite as well as the average hardness of the Cr₁₃Ni₅Si₂/γ alloy decrease with the increasing Ni content. The Cr₁₃Ni₅Si₂/γ alloys have excellent wear resistance under dry sliding wear test conditions, which increases under high contact load wear conditions and decreases under low contact load wear test conditions with the increasing Ni content. The high wear resistance is due to the combination of high toughness of γ and high hardness of Cr₁₃Ni₅Si₂ and formation of a transferred cover layer on the worn surface during wear process. The wear rate of the Cr₁₃Ni₅Si₂/γ alloy is governed by the slow process of microspalling or pullout of the cracked Cr₁₃Ni₅Si₂ primary dendrites. The Cr₁₃Ni₅Si₂/γ alloys have extremely low load sensitivity of wear and the load-sensitivity coefficient of wear decreases drastically as the Ni content increases.     

Enhancement of Tribological Properties of Al 6060 by Spray Coated TiO<Subscript>2</Subscript> Nanoparticle

Al 6060 alloy was coated with TiO₂ by spray pyrolysis technique at 400 °C using Titanium isopropoxide as precursor. The adhesion of the coating with the alloy was enhanced by annealing at 450 °C for 1 h which increased the hardness by 50%. Dry sliding wear resistance was experimented based on Taguchi’s L₂₇ array using pin-on-disc tribometer by varying parameters such as applied load (15, 25 and 35 N), sliding distance (500, 1000 and 1500 m) and sliding velocity (1.5, 2.5 and 3.5 m/s). Analysis of Variance predicted the major influence by load, followed by velocity and distance. Trend depicted an increase in wear rate with load and distance, whereas with velocity it decreased initially and then increased. Optimum condition for maximum wear resistance was determined from the Signal-to-Noise ratio. Experimental results were validated using regression equation with an error less than 3%. Scanning Electron Microscope analysis of the worn surfaces had revealed more defoilage and lay-off as the applied load was increased.     

α″ Martensite and Amorphous Phase Transformation Mechanism in TiNbTaZr Alloy Incorporated with TiO<Subscript>2</Subscript> Particles During Friction Stir Processing

This work studied the formation of the α″ martensite and amorphous phases of TiNbTaZr alloy incorporated with TiO₂ particles during friction stir processing. Formation of the amorphous phase in the top surface mainly results from the dissolution of oxygen, rearrangement of the lattice structure, and dislocations. High-stress stemming caused by dislocations and high-stress concentrations at crystal–amorphous interfaces promote the formation of α″ martensite. Meanwhile, an α″ martensitic transformation is hindered by oxygen diffusion from TiO₂ to the matrix, thereby increasing resistance to shear.     

Ni–ZrO2 Composite Coating by Electro-Co-Deposition

In the present investigation Ni–ZrO₂ metal matrix composite coatings were prepared on steel substrate using watt’s type solution through electro-co-deposition process with different weight percentages of zirconia powder dispersed in the bath. In the coating, nickel is present with faceted appearance along with ZrO₂. The microhardness and wear resistance of the coatings increase with increasing weight percentage of particles content in the coating. The hardness of the resultant coatings was found to be 325 VHN for pure Ni coating whereas 401VHN for Ni–ZrO₂ (15 g/l ZrO₂) coating depending on the particle volume in the Ni matrix. The results also showed that the wear resistance of the composite coatings was improved as compared to unreinforced Ni deposited material. Strengthening of the coating was attributed to the ZrO₂ dispersion and partially favorable texture.     

Investigation of Tribological Behavior of Ceramic–Graphene Composite Coating Produced by Plasma Electrolytic Oxidation

Plasma electrolyte oxidation coatings were formed on AZ31 magnesium alloy in the phosphate electrolyte containing 0 and 5 g L^?1 graphenes at different process times. The composition and microstructure of the coatings were analyzed by scanning electron microscope (SEM) equipped with energy dispersive X-ray spectrometer and X-ray diffraction (XRD). The SEM images showed that by increasing the coating time, the number of coating pores decreased whereas the diameter of coating pores increased. Furthermore, the diameter and number of pores related to ceramic–graphene composite coatings were lower than ceramic ones. XRD analysis indicated that major constituents of coatings were MgO and Mg₃(PO₄)₂. The pin-on-disk sliding tests revealed that the wear loss and coefficient of friction of ceramic–graphene composite coatings were lower than simple ones.     

The codeposition of alumina and titania with copper

The codeposition of Al₂O₃ and TiO₂ from the acid copper electrolyte was investigated with respect to solution pH, particle concentration in the electrolyte, addition agents and the nature of the crystalline phase of the oxide particles. The incorporation of oxides was found possible without the need of addition agents, provided the oxide particles are of the favorable crystalline form as α-Al₂O₃ and rutile TiO₂. A technique is reported whereby the γ-Al₂O₃ particles are partially transformed to the α-form making the oxide suitable for codeposition.     

电弧喷涂含陶瓷颗粒铝基复合涂层的微结构和性能

采用5052半硬铝带分别包覆Al_2O_3、SiC、B_4C、TiC陶瓷颗粒制备的粉芯丝材进行电弧喷涂试验,制备了含陶瓷颗粒的铝基复合涂层。利用光学显微镜、XRD分析了涂层的微观组织和相结构,测试了复合涂层的显微硬度、耐磨性及耐腐蚀性。研究结果表明,制备的铝基复合涂层中含有一定数量的未熔陶瓷颗粒,涂层较为致密,无明显缺陷。含陶瓷铝基涂层的物相主要由Al和所添加的陶瓷相构成,其中在含B_4C陶瓷涂层中还存在Al_3BC、Al_4C_3和AlB_2等新相。陶瓷颗粒的加入有利于提高铝基复合涂层的显微硬度,其中B_4C的加入使涂层中基体相显微硬度提高了1.5倍,这是由于B_4C陶瓷和Al反应生成Al_3BC、Al_4C_3和AlB_2硬质相。复合涂层的耐磨性均优于纯铝涂层,摩擦磨损的形式主要为粘着磨损。动电位极化腐蚀试验表明,含SiC和TiC陶瓷涂层具有较低的腐蚀电流,耐蚀性较好,含SiC陶瓷的复合涂层出现了明显的钝化现象。     

Wettability of Mn<Subscript>x</Subscript>Si<Subscript>y</Subscript>O<Subscript>z</Subscript> by Liquid Zn-Al Alloys

The wettability of Mn_xSi_yO_z by liquid Zn-Al alloys was investigated to obtain basic information on the coating properties of high-strength steels with surface oxides in the hot-dip galvanizing process. In this study, the contact angles of liquid Zn-Al alloys (Al concentrations were 0.12 and 0.23 wt pct) on four different Mn_xSi_yO_z oxides, namely MnO, MnSiO₃, Mn₂SiO₄, and SiO₂, were measured with the dispensed drop method. The contact angle did not change across time. With an increasing Al concentration, the contact angle was slightly decreased for MnO and Mn₂SiO₄, but there was no change for MnSiO₃ and SiO₂. With an increasing SiO₂ content, the contact angle gradually increased by 54 wt pct to form MnSiO₃, and for pure SiO₂ substrate, the contact angle decreased again. Consequently, the MnSiO₃ substrate showed the worst wettability among the four tested oxide substrates.     

Surface Treatment of S355JR Carbon Steel Surfaces with ZrB<Subscript>2</Subscript> Nanocrystals by CO<Subscript>2</Subscript> Laser

To improve mechanical properties of S2355JR carbon steel, pre-synthesized ZrB₂ nanocrystals were used to coat the metal surface by laser cladding using 2000 W CO₂ laser. ZrB₂ nanocrystals were synthesized by mechanochemical process. The effect of laser power on the coating layers was examined for optimizing the most effective coating conditions. Microstructural studies were carried out using optical microscope, scanning electron microscope and X-ray diffraction to analyze phase structures of the coated layers. Mechanical characteristics of the laser coated layers were evaluated by studying microhardness, wear and scratch resistance properties. Maximum hardness of the coated layers was observed while cladding with 75 and 125 W laser powers, when other processing parameters and conditions were kept at optimum levels. EDS analysis of these laser cladded layers indicated the formation of complex boro-nitrides, nitrides and carbides of Zr and Fe that contributed to vast increase in hardness of the laser-clad coating on S2355JR steel. Depending upon the laser powers used, the thickness of the coated layers was found to be in the range of 15–37 µm. The wear and micro-scratch tests results revealed significant improvement in wear properties.     

Calciothermic reduction of titanium oxide in molten CaCl<Subscript>2</Subscript>

Titanium oxides were reduced to metallic titanium using the liquid calcium floating on the molten CaCl₂. A part of Ca dissolved into CaCl₂ and reacted with TiO₂ settled below CaCl₂. The by-product CaO also dissolved by about 20 mol pct into CaCl₂, which was effective in reducing the oxygen concentration in the obtained Ti particles. The compositional region in the Ca-CaCl₂-CaO system was examined for the less oxygen contamination in Ti and the better handling in leaching. A large amount of the residual calcium oxidized the titanium powder in leaching. The metallic Ti powder less than 1000 mass ppm oxygen could be obtained only for 3.6 ks using 5 to 7 mol pct Ca-CaCl₂ at 1173 K. The powder was slightly sintered like sponge, and contained approximately 1500 ppm Ca. The anatase phae, the intermediate product in the refining process of TiO₂, could be also supplied as raw material as well as rutile.     

Solid-state reactions during heating mechanically milled Al/TiO<Subscript>2</Subscript> composite powders

Solid-state reactions between Al and TiO₂ during heating high-energy mechanically milled Al/TiO₂ composite powders have been investigated by using a combination of thermal analysis, X-ray diffraction (XRD), and various microstructural characterization techniques. When the TiO₂ particles and their interparticle spacing in the Al/TiO₂ composite powder particles are sufficiently large, the reaction between Al and TiO₂ proceeds by two steps. The low-temperature step is an interfacial reaction, which starts at a temperature close to 660 °C. The high-temperature step is a reaction facilitated by bulk diffusion and starts at a temperature above 820 °C. The first phase formed from the reaction is always Al₃Ti irrespective of the starting powder composition or milling time. Al₂O₃ is difficult to form at temperatures below 800 °C. The formation of the α-Ti(Al,O) phase proceeds slowly and requires either continuous heating to a temperature above 1000 °C or holding at a temperature close to 1000 °C for a period of time. Mechanical milling of the Al/TiO₂ powder enhances the interfacial reaction between Al and TiO₂. This enhancement is originated from the establishment and refinement of Al/TiO₂ composite microstructure.     

Effects of Ni60WC25 powder content on the microstructure and wear properties of WC<Subscript>p</Subscript> reinforced surface metal matrix composites

The vacuum evaporative pattern casting technique was used to fabricate WC_p reinforced surface metal matrix composites in order to study the effects of Ni60WC25 powder content on the microstructure and wear properties of it. The results showed that the Ni60WC25 powders weakened the stability of WC particles and reacted with metal matrix at the interfacial regions in the composite. Diffusion kinetics and Gibbs free energy were calculated from the interactions between WC particles and matrix. It was found that adding 35 vol% Ni60WC25 alloy powder to composites led to the formation of Fe₃W₃C phases and complete dissolution of WC particles. The wear properties of composites with different Ni60WC25 alloy powder content were tested by the MLD-10 type tester. WC particles and Fe₃W₃C phases could protect the matrix and the matrix could support WC particles and Fe₃W₃C phases during wear processing.     

Correlation of microstructure and wear resistance of Al2O3-TiO2 coatings plasma sprayed with nanopowders

Correlation of microstructure and wear resistance of Al₂O₃-TiO₂ coatings plasma sprayed with nanopowders was investigated in this study. Four kinds of nanostructured Al₂O₃-13 wt pct TiO₂ coatings were fabricated by varying plasma-spraying parameters and were compared with an Al₂O₃-13 wt pct TiO₂ coating fabricated with conventional powders. The nanostructured coatings showed a bimodal microstructure composed of fully melted regions of γ-Al₂O₃ and partially melted regions, while the conventional coating mostly consisted of fully melted γ-Al₂O₃, together with some TiO₂-rich regions and unmelted Al₂O₃ powders. The wear test results revealed that the wear resistance of the nanostructured coatings was 3 or 4 times better than that of the conventional coating, because the preferential delamination seriously occurred along TiO₂-rich regions in the conventional coating. In the nanostructured coatings, TiO₂ was homogeneously dispersed inside splats and around, thereby leading to higher splat bonding strength and to better wear resistance over the conventional coating.     

A comparative Study on the Wear Behavior of Al2O3 and SiC Coated Ti-6Al-4V Alloy Developed Using Plasma Spraying Technique

This paper reports the wear characteristics of the ceramic coatings made with Al₂O₃ and also with SiC which were performed using atmospheric plasma spraying technique on the Ti-6Al-4V biomedical alloy with the aim of improving their tribological behavior. The wear behavior of the coatings was evaluated using reciprocatory wear tester with coated substrate as the flat and alumina ball as a friction partner in simulated body fluid (Hank’s solution) environment. The microstructure and phase composition of the ceramic powders and as-sprayed coatings have been characterized using scanning electron microscope and X-ray diffractometer. Porosity, microhardness, adhesion strength and roughness of the coatings were measured as they have a bearing on wear and friction behavior. The results indicate that plasma sprayed Al₂O₃ coating exhibits higher wear resistance compared to that of plasma sprayed SiC coating. The higher wear resistance of Al₂O₃ coating is attributed to the improved melting and spreading of the alumina particles onto the substrate yielding increasingly bonded splats, resulting in compact and dense microstructure with lower porosity and higher microhardness.     

Preparation and performance of electrodeposited Ni-TiB2-Sm2O3 composite coatings

Sm₂O₃ and TiB₂ were used as codeposited particles in electrodeposition Ni-TiB₂-Sm₂O₃ composite coatings to improve its performance. Ni-TiB₂-Sm₂O₃ composite coatings were electrodeposited in the nickel sulfate, hexadecylpyridinium bromide and cetyltrimethylammonium bromide solution containing TiB₂ and Sm₂O₃ particles. The content of codeposited Sm₂O₃ in the composite coating was controlled by changing the concentrations of Sm₂O₃ particles in the solution. The composite coatings were characterized with X-ray diffraction (XRD) and inductively coupled plasma-atomic emission spectrometer (ICP-AES). The effects of Sm₂O₃ content on microhardness, wear weight loss and friction coefficient of composite coatings were investigated, respectively. The microhardness of the Ni-TiB₂-Sm₂O₃ composite coatings was 19.35%, 16.58%, 2.03% higher than that of the Ni coating, Ni-Sm₂O₃ and Ni-TiB₂ composite coatings, respectively. The wear weight loss of the Ni-TiB₂-Sm₂O₃ composite coatings was 7, 2.33, 1.22 times lower than that of the Ni coating, Ni-Sm₂O₃ and Ni-TiB₂ composite coatings, respectively. The friction coefficient of the Ni coating, Ni-Sm₂O₃, Ni-TiB₂ and Ni-TiB₂-Sm₂O₃ composite coatings were 0.712, 0.649, 0.850 and 0.788, respectively. The loading-bearing capacity and the wear-reducing effect of the Sm₂O₃ particles were closely related to the content of Sm₂O₃ particles in the composite coatings.     

Characterization and tribological behavior of cast In-Situ Al (Mg,Mo)-Al2O3 (MoO3) composite

Aluminum alloy—based cast in-situ composite has been synthesized by dispersion of externally added molybdenum trioxide particles (MoO₃) in molten aluminum at the processing temperature of 850 °C. During processing, the displacement reaction between molten aluminum and MoO₃ particles results in formation of alumina particles in situ and also releases molybdenum into molten aluminum. A part of this molybdenum forms solid solution with aluminum and the remaining part reacts with aluminum to form intermetallic phase Mo(Al_1−x Fe _x )₁₂ of different morphologies. Magnesium (Mg) is added to the melt in order to help wetting of alumina particles generated in situ, by oxidation of molten aluminum by molybdenum trioxide, and helps to retain these particles inside the melt. The mechanical properties of the cast in-situ composite, as indicated by ultimate tensile stress, yield stress, percentage elongation, and hardness, are relatively higher than those observed either in cast commercial aluminum or in cast Al-Mo alloy. The wear and friction of the resulting cast in-situ Al(Mg,Mo)-Al₂O₃(MoO₃) composites have been investigated using a pin-on-disc wear testing machine under dry sliding conditions at different normal loads of 9.8N, 14.7N, 19.6N, 24.5N, 29.4N, 34.3N, and 39.2 N and a constant sliding speed of 1.05 m/s. The results of the current investigation indicate that the cumulative volume loss and wear rate of cast in-situ composites are significantly lower than those observed either in cast commercial aluminum or in cast Al-Mo alloy, under similar load and sliding conditions. Beyond about 30 to 35 N loads, there appears to be a higher rate of increase in the wear rate in the cast in-situ composite as well as in cast commercial aluminum and cast Al-Mo alloy. For a given normal load, the coefficient of friction of cast in-situ composite is significantly lower than those observed either in cast commercial aluminum or in cast Al-Mo alloy. The coefficient of friction of cast in-situ composite increases gradually with increasing normal load while those observed in cast commercial aluminum or in cast Al-Mo alloy remain more or less the same. Beyond a critical normal load of about 30 to 35 N, the coefficient of friction decreases with increasing normal load in all the three materials.