Correlation of microstructure and abrasive and sliding wear resistance of (TiC,SiC)/Ti-6Al-4V surface composites fabricated by high-energy electron-beam irradiation

This study is concerned with the correlation of microstructure and abrasive and sliding wear resistance of (TiC,SiC)/Ti-6Al-4V surface composites fabricated by high-energy electron-beam irradiation. The mixtures of TiC, SiC, Ti + SiC, or TiC+SiC powders and CaF₂ flux were deposited on a Ti-6Al-4V substrate, and then an electron beam was irradiated on these mixtures. The surface composite layers of 1.2 to 2.1 mm in thickness were homogeneously formed without defects and contained a large amount (30 to 66 vol pct) of hard precipitates such as TiC and Ti₅Si₃ in the martensitic matrix. This microstructural modification, including the formation of hard precipitates in the surface composite layer, improved the hardness and abrasive wear resistance. Particularly in the surface composite fabricated with TiC + SiC powders, the abrasive wear resistance was greatly enhanced to a level 25 times higher than that of the Ti alloy substrate because of the precipitation of 66 vol pct of TiC and Ti₅Si₃ in the hardened martensitic matrix. During the sliding wear process, hard and coarse TiC and Ti₅Si₃ precipitates fell off from the matrix, and their wear debris worked as abrasive particles, thereby reducing the sliding wear resistance. On the other hand, needle-shaped Ti₅Si₃ particles, which did not play a significant role in enhancing abrasive wear resistance, lowered the friction coefficient and, accordingly, decelerated the sliding wear, because they played more of the role of solid lubricants than as abrasive particles after they fell off from the matrix. These findings indicated that high-energy electron-beam irradiation was useful for the development of Ti-based surface composites with improved abrasive and sliding wear resistance, although the abrasive and sliding-wear data should be interpreted by different wear mechanisms.     

Correlation of microstructure with the hardness and wear resistance of (TiC,SiC)/Ti-6Al-4V surface composites fabricated by high-energy electron-beam irradiation

The correlation of microstructure with the hardness and wear resistance of (TiC,SiC)/Ti-6Al-4V surface composites fabricated by high-energy electron-beam irradiation was investigated in this study. The mixtures of TiC, SiC, or TiC + SiC powders and CaF₂ flux were placed on a Ti-6Al-4V substrate, and then an electron beam was irradiated on these mixtures using an electron-beam accelerator. The surface composite layers of 1.2 to 2.1 mm in thickness were formed without defects and contained a large amount (up to 66 vol pct) of precipitates such as TiC and Ti₅Si₃ in the martensitic matrix. This microstructural modification, including the formation of hard precipitates and a hardened matrix in the surface composite layer, improved the hardness and wear resistance. Particularly in the surface composite fabricated with TiC + SiC powders, the wear resistance was greatly enhanced to a level 25 times higher than that of the Ti alloy substrate, because 66 vol pct of TiC and Ti₅Si₃ was precipitated homogeneously in the hardened martensitic matrix. These findings suggested that high-energy electron-beam irradiation was useful for the development of Ti-based surface composites with improved hardness and wear properties.     

High-temperature interactions of refractory metal matrices with selected ceramic reinforcements

Interdiffusion and reactions occurring at high temperatures between refractory metals (Nb and Ta) and ceramic materials (SiC and A1₂O₃) have been investigated. Diffusion couples were fabricated by depositing Nb and Ta films of ~l-μm thickness onto polished ceramic substrates. These diffusion couples were vacuum annealed at high temperatures for various times. Interfacial reactions were evaluated using optical metallography, Auger electron spectroscopy (AES), scanning electron microscopy (SEM), and transmission electron microscopy (TEM). Kinetic studies in the 800 °C to 1200 °C temperature range for the Nb/SiC system indicated that Nb₂C initially forms, followed by the more stable NbC_xSi_y phase. In some instances, layered structures containing the phases NbC, Nb₂C, and NbC_xSi_y, were observed. The activation energies of formation for the NbC_x and NbC_xSi_y, phases were determined from these measurements. Results from the Ta/SiC system were found to be similar to those from the Nb/SiC system. In both Nb/Al₂O₃ and Ta/Al₂O₃ diffusion couples, annealing for up to 4 hours in the 1100 °C to 1200 °C range did not result in any significant reactions. These results suggest that A1₂O₃ may be a promising diffusion barrier between Nb and Ta metal matrices and SiC ceramic reinforcements. formerly with Lockheed Research and Development Division, is Senior Member of Technical Staff, Sandia National Laboratories, Albuquerque, NM 87185     

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。     

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.     

Development of nonoxide ceramics based on silicon carbide and nitride

Research on nonoxide ceramics based on silicon carbide and nitride is reviewed along with related technological developments. The role of I. N. Frantsevich in initiating the development of such materials is shown. Three main stages in the development of the ceramics are distinguished. The relationship between the physical properties and applications of ceramics based on SiC and Si₃N₄.Institute of Materials Sciences, Ukranian Academy of Sciences, Kiev. Translated from Poroshkovaya Matallurgiya, Nos. 7/8(380), pp. 24–32, July–August, 1995.     

Wear-Resistant Layered Electrospark Coatings Based on ZrB2

We have studied the composition and tribological parameters (coefficient of friction and wear rate) of coatings obtained in electrospark alloying (ESA) of steel 45 with the composite ceramic ZrB₂ – SiC – B₄C based on zirconium diboride. We have shown that layer-by-layer electrospark alloying using Ti – Al – N composites to form an undercoat reduces the coefficient of friction of the coating down to 0.12-0.20 while maintaining a rather low wear level (7-11 μm/km). We have analyzed the effect of the composition of the secondary structures which are formed during tribo-oxidation under dry friction conditions.     

The effect of production conditions on the structure formation and on the electrical conductivity of hotpressed materials in the system nitride-silicon carbide

Conclusions n materials of the system Si₃N₄-SiC are hot-pressed, there occur processes of carbidization of Si₃N₄ and of reduction of the surface film of SiO₂ accompanied by weight loss and increased concentration of SiC. The degree of such physicochemical transformations is well correlated with the magnitude of the specific weight losses. The electrical conductivity of the investigated materials is basically determined by the content of the conducting phase SiC in the initial charge; however, when the concentration of the introduced silicon carbide is low, then the amount of secondary SiC forming in hot pressing plays a considerable role.Translated from Poroshkovaya Metallurgiya, No. 2(290), pp. 51–54, February, 1987.     

Dry friction and wear of alloys of diboride-nitride systems at normal temperatures

Conclusions A study was made of the room-temperature dry friction and wear of alloys of the systems ZrB₂-ZrN and HfB₂- HfN in air. It was found that all the materials investigated possess high wear resistance. The lowest values of coefficient of friction (0.3–0.4) and increased wear resistance at a sliding speed of 1 m/sec are exhibited by composites based on hafnium diboride and those containing 40–70 mole % zirconium nitride.Translated from Poroshkovaya Metallurgiya, No. 7 (103), pp. 63–67, July, 1971.     

Influence of the Composition and Structure of B4C - Al2O3 Ceramic on the Tribotechnical Characteristics in Friction Against Steel

The morphology and phase composition of friction surfaces and the tribotechnical properties of the (B₄C - Al₂O₃)-steel 45 system are studied under dry friction at various sliding velocities and contact loads. We have found that fine-grained secondary structures are formed on the friction surfaces. The morphology and phase composition of these structures depend on the ceramic composition and on the test conditions. A comprehensive investigation of friction surfaces, using x-ray, electron-diffraction electron-probe, and electron-microscopy analysis, has shown that the structure and morphology of the secondary phases determine the tribotechnical properties of ceramic-steel couples. The maximum wear resistance of B₄C ceramics containing 5-20 mass% Al₂O₃ is determined by the formation of dense secondary-phase thin films on the friction surface. __________ Translated from Poroshkovaya Metallurgiya, Nos. 5–6(443), pp. 49–59, May–June, 2005.     

Microstructure and sliding-wear behavior of tungsten-reinforced W-Ni-Si metal-silicide <Emphasis Type="Italic">in-situ</Emphasis> composites

W-Ni-Si metal-silicide-matrix in-situ composites reinforced by tungsten primary grains were fabricated using a water-cooled copper-mold laser-melting furnace by the LASMELT process. Main constitutional phases of the W/W-Ni-Si in-situ composites are the tungsten primary phase, peritectic W₂Ni₃Si, and the remaining W₂Ni₃Si/Ni₃₁Si₁₂ eutectics, depending on the alloy compositions. The sliding-wear resistance of the W/W-Ni-Si intermetallic composites was evaluated at room temperature and 600 °C. Wear mechanisms of the W/W₂Ni₃Si in-situ composites were discussed based on morphology observations of the worn surface and wear debris. Results show that the W/W-Ni-Si composites have excellent wear resistance under both room- and high-temperature sliding-wear-test conditions, because of the high yield strength and toughness of the tungsten-reinforcing phase and the high hardness and the covalent-dominated intermetallic atomic bonds of the W₂Ni₃Si and Ni₃₁Si₁₂ metal silicides. Tungsten-reinforcing grains played the dominant role in resisting abrasive-wear attacks of microcutting, plowing, and brittle spalling during the sliding-wear process, while the W₂Ni₃Si and Ni₃₁Si₁₂ metal silicides are responsible for the excellent adhesive wear resistance.     

Effect of microstructure (particulate size and volume fraction) and counterface material on the sliding wear resistance of particulate-reinforced aluminum matrix composites

The effects of microstructure (namely, particulate volume fraction and particulate size) and the counterface materials on the dry-sliding wear resistance of the aluminum matrix composites 2014A1-SiC and 6061Al-Al₂O₃ were studied. Experiments were performed within a load range of 0.9 to 350 N at a constant sliding velocity of 0.2 ms^-1. Two types of counterface materials, SAE 52100 bearing steel and mullite, were used. At low loads, where particles act as loadbearing constituents, the wear resistance of the 2014A1 reinforced with 15.8 μm diameter SiC was superior to that of the alloy with the same volume fraction of SiC but with 2.4 μm diameter. The wear rates of the composites worn against a steel slider were lower compared with those worn against a mullite slider because of the formation of iron-rich layers that act asin situ solid lubricants in the former case. With increasing the applied load, SiC and A1₂O₃ particles fractured and the wear rates of the composites increased to levels comparable to those of unreinforced matrix alloys. The transition to this regime was delayed to higher loads in the composites with a higher volume percentage of particles. Concurrent with particle fracture, large strains and strain gradients were generated within the aluminum layers adjacent to contact surfaces. This led to the subsurface crack growth and delamination. Because the particles and interfaces provided preferential sites for subsurface crack initiation and growth and because of the propensity of the broken particles to act as third-body abrasive elements at the contact surfaces, no improvement of the wear resistance was observed in the composites in this regime relative to unreinforced aluminum alloys. A second transition, to severe wear, occurred at higher loads when the contact surface temperature exceeded a critical value. The transition loads (and temperatures) were higher in the composites. The alloys with higher volume fraction of reinforcement provided better resistance to severe wear. Wearing the materials against a mullite counterface, which has a smaller thermal conductivity than a counterface made of steel, led to the occurrence of severe wear at lower loads.     

Formation of highly porous ceramic based on silicon nitride

The formation of the structure of a porous ceramic based on Si₃N₄ has been investigated. It has been found that the structure can be controlled over a wide range of porosities. Materials based on a consisting of a single fraction silicon nitride of grain size 3–5 μm, with the addition of a fine-grained pore agent have most uniform, hard, and developed porous structure. A comparative evaluation of the properties of material based on SiC and Si₃N₄ showed that silicon nitride materials of the same porosity are stronger and that small micropores can be formed in them. That is of fundamental importance in the development of materials—catalyst carriers for chemical production and various kinds of filtering devices. With the results of the investigations general technological recommendations can be made for producing ceramics with specific structures.     

Hard plasma chemical coatings based on silicon carbon nitride

Silicon carbon nitride (SiCN) coatings deposited on a silicon substrate are produced by plasma-enhanced chemical vapor deposition (PECVD) using methyltrichlorosilane (MTCS), nitrogen, and hydrogen as starting materials. The coatings are characterized with AFM, XRD, and FTIR. Their mechanical properties are determined with nanoindentation. The abrasion wear resistance is examined using a ball-on-plane (calowear) test and adhesion to the base using a scratch test. The x-ray diffraction indicates that the coatings produced at moderate F_N are nanostructured and represent β-C₃N₄ crystallites embedded into the amorphous a-SiCN matrix. The coatings deposited at a higher nitrogen flow rate are amorphous. The nanostructure is supposed to result from an increase in hardness (25 GPa) and Young’s modulus (above 200 GPa). The tribological tests have revealed that the friction coefficients of the coatings containing nitrogen are two to three times smaller than those based on SiC and deposited on a silicon substrate. The ball-on-plane tests show that the nanostructured coatings also exhibit the highest abrasive wear resistance. These findings demonstrate that the SiCN films deposited using MTCS show good mechanical and tribological properties and can be used as wear-resistant coatings.     

Metal Matrix Composites Produced by Spray Codeposition

Abstract

A new technique for producing metal matrix particulate composites, consisting of the spray deposition of the metal matrix and the particles, is described. The deposit is removed from the substrate and hot rolled to produce composite strip for examination and testing. It is shown that up to 36 vol.-% of SiC, Al₂0₃, chilled iron, graphite, and sand particles, and mixtures of these, 75–120 μm in size, can successfully be incorporated in aluminium and Al–5Si alloy matrixes. The friction properties of some of the composites were shown to be particularly promising. High coefficients of friction of ～0·6 were obtainable under dry contact conditions, and these were remarkably constant with time. The friction properties compared very favourably with conventional asbestos based and sintered friction materials which showed lower coefficients of friction that increased with time. PM/0310     

Tribological properties of metal-matrix composite materials reinforced by superelastic hard carbon particles

Metal-matrix composite materials (CMs) are synthesized from a mixture of a metal powder (Ti, Fe, Co, Ni, Cu, Al-based alloy) and fullerenes (10 wt %). The thermobaric synthesis conditions (700–1000°C, 5–8 GPa) ensure the collapse of fullerene molecules and their transformation into superelastic carbon phase particles with an indentation hardness H_IT = 10–37 GPa, an elastic modulus E_IT = 60–260 GPa, and an elastic recovery of >80% upon indentation. After reinforcing by superelastic hard carbon, the friction coefficient of CM decreases by a factor of 2–4 as compared to the friction coefficient of the matrix metal, and the abrasive wear resistance increases by a factor of 4–200. Superelastic hard carbon particles are a unique reinforcing material for an increase in the wear resistance and a simultaneous decrease in the friction coefficient of CM.     

Mechanical and tribotechnical characteristics of fine-grained hard alloys obtained by coreduction and carbidization of tungsten-cobalt oxide systems

The properties of hard alloys based on fine-grained hard-alloy mixtures, obtained by coreduction of tungsten oxide with the oxides CoO and Co₃O₄, are discussed. A linear relation is shown between the strength and the abrasive resistance: the relative abrasive resistance increased and the wear resistance under friction on steel decreased as the strength increased. Fine-grained mixtures obtained by coreduction and carbidization of WO₃ and Co₃O₄ and sintered at 1440–1450°C were found to have the best strength and abrasive resistance. Sintering after homogenizing preannealing enhances the mechanical properties of hard metals.     

High-temperature reaction between silicon carbide and nitrogen under pressure

The effects of temperature and nitrogen pressure are studied on the SiC Si₃N₄ transformation of silicon carbide powders of various phase compositions, specific surface areas, and contents of mixtures. It is shown that the degree of transformation increases with nitrogen pressure up to 10 MPa and that, in all temperature and pressure ranges of nitrogen, it is higher for bulk free powder than the preliminarily compacted material. In 30–60 min, a complete transformation of SiC into Si₃N₄ occurs under 10 MPa nitrogen pressure and at 1650–1750°C temperature.Institute of Inorganic Chemistry, Slovakian Academy of Sciences. Institute of Superhard Materials, Ukrainian Academy of Sciences, Kiev. Translated from Poroshkovaya Metallurgiya, No. 4(364), pp. 1–6, April, 1993.     

Resistive Properties of the Sintered Ceramic Composite Si3N4 - SiC

A technology has been developed for activated sintering of resistive Si₃N₄ - SiC ceramic composite. The microstructure, electrophysical properties and strength of the materials obtained have beenstudied over a wide range of concentration.     

Structure and Properties of B4C - SiC Composites

We have investigated how the composition, grain morphology, and method of preparing the starting mixture affect the processes that form the structure and phase composition of B₄C - SiC composites during hot pressing. We found that, depending on the composition of the initial powder mixtures, which is responsible for different mechanisms of consolidation of ceramic materials during hot pressing, the grain size of the main B₄C phase and its defect content as well as the nature of the SiC phase distribution within the material differ significantly. When B₄C - SiC composites with a low SiC content are made from initial B₄C - B₄Si - B - C powder mixtures those composites have a high cracking resistance because of their fine grain structure.__________Translated from Poroshkovaya Metallurgiya, Nos. 3–4(442), pp. 112–119, March–April, 2005.