烧结温度对反应烧结碳化硅组织与性能的影响

本文研究了1450、1550、1650℃不同烧结温度制备的反应烧结SiC材料的密度、硬度、抗弯强度、显微组织、显微硬度及断裂行为。结果表明:烧结温度对材料密度影响较小。低温反应烧结的SiC晶粒的晶体结构不够完整,存在亚晶界等缺陷,晶粒强度较低,烧结材料的硬度和抗弯强度较低。高温反应烧结的SiC晶粒的晶体结构完整性增加,晶粒强度较高,烧结材料的硬度和抗弯强度较高。因此为了提高反应烧结碳化硅的力学性能,应该适当提高烧结温度或延长烧结时间。     

烧结温度对碳化硅陶瓷力学性能的影响

采用硼、碳助剂无压烧结制备碳化硅陶瓷。针对烧结温度与碳化硅烧结体密度、抗弯强度以及硬度之间的关系进行了试验研究,并对不同温度下制备的烧结体进行了显微结构形貌观察和XRD图谱分析。结果表明,烧结温度在2190～2220℃范围内可以制备密度高、力学性能好的碳化硅陶瓷。其相对密度超过96%;抗弯强度接近400MPa;维氏硬度23GPa以上。在试验温度范围内,密度与抗弯强度之间的关系近似为线性关系,密度越高抗弯强度和硬度性能越好。     

Investigation into the Structure Formation and Properties of Materials in the Copper–Titanium Disilicide System

The structure formation and properties during infiltration, free sintering, and spark-plasma sintering in Cu–(12.5–37.5 vol %) powder materials Ti₃SiC₂ are investigated by electron microscopy, X-ray phase analysis, and energy-dispersion analysis. The independence of the phase composition of composite materials (CMs) on the sintering method and temperature in a range of 900–1200°C is established. The peculiarities of formation of the CM structure during sintering are the intercalation of silicon from titanium carbosilicide and the formation of a carbon solid solution based on Ti₅Si₃(C) titanium disilicide, small amounts of titanium carbide, silicon carbide, and TiSi₂ silicide. An increase in Ti₃SiC₂ in the CM certainly lowers electrical conductivity, but considerably increases the hardness, strength, and electroerosion wear resistance of CM electrodes for electroerosion broaching.     

镍磷合金碳化硅复合镀层的制备与磨损性能研究

采取化学沉积方法，获得镍磷合金碳化硅复合材料镀层，研究了复合镀层的构成与磨损性能。研究结果表明，镍磷合金中加入碳化硅，不会影响其组织结构，但会显著地提高硬度和耐磨性；复合镀层经过热处理，组织结构发生变化；６７３Ｋ／１ｈ处理后，硬度与耐磨性最高，较镍磷合金镀层具有更高的硬化性能。     

Obtaining and investigating wear resistance of a composite material based on titanium carbosilicide

A composite material (CM) based on titanium carbosilicide with a titanium carbide content of 50% possessing a microcrystalline structure is obtained by mechanosynthesis in a planetary mill with subsequent hot pressing. The highly nonequilibrium structure of the powder material, which forms due to the high-energy treatment, makes it possible to obtain material with a relative density of 96% at a hot-pressing temperature of 1400°C and a pressure of 20 MPa. Comparative tests of the CM and silicon carbide for wear resistance under different conditions are carried out. The CM based on titanium carbosilicide showed less wear of the counterbody and a lower friction coefficient in all cases. However, in tests using an abrasive medium, wear of the composite material itself is observed.     

Investigation of thermal oxidation resistance of nanopowders of refractory carbides and borides

Thermal oxidation resistance in air of nanopowders of carbides and borides of vanadium, titanium, chromium, and zirconium, as well as silicon carbide, is investigated. It is found that, at the temperature of onset of oxidation in air, they are arranged into the following series: carbides TiC (548 K), VC and Cr₃(C_0.80N_0.20)₂ (553 K), ZrC (560 K), and SiC (905–913 K), and borides VB₂ (620 K), TiB₂ (643 K), CrB₂ (763 K), and ZrB₂ (823 K). The results of investigation allow one to recommend nanopowders of carbides and borides for use as strengthening phases of composition coatings that operate in oxidizing media at temperatures no higher than the onset of oxidation. Nanopowders of chromium and zirconium borides and silicon carbide can be considered as equivalent substitutes for diamond nanopowders in composition coatings.     

Optimization of the process of manufacture of diamond-containing composite materials based on titanium carbide-steel alloys

Conclusions A study was made of the conditions of production of tungsten-free composite materials by sintering in a high-pressure chamber and in vacuum. Good-quality nonporous specimens of titanium carbide-steel materials cannot be produced by hot pressing in graphite dies. The hardness of materials sintered in a HPC is higher (81–86 HRA) than that of materials sintered in vacuum (75–82 HRA.). Heat treatment slightly lowers it (to 77–85 HRA). The highest wear resistance is exhibited by vacuum-sintered materials. In alloys sintered in a HPC a directional orientation of the steel binder with titanium carbide grain inclusions was observed. In service tests the properties of composition diamond-containing materials based on titanium carbide-steel alloys were found to match those of Tvesal alloys-diamond-containing composites based on a tungsten-group hard metal.Translated from Poroshkovaya Metallurgiya, No. 7 (259), pp. 21–25, July, 1984.     

Structure and Tribological Properties of B83 Babbit–Based Composite Rods and the Coatings Produced from Them by Arc Surfacing

Surfacing composite rods based on a B83 babbit alloy reinforced by silicon carbide and boron carbide particles are fabricated by extrusion. The structure and the tribological properties of the rods are studied. Extrusion allowed us to introduce and to uniformly distribute reinforcing fillers and to change the size and the morphology of the intermetallic phases in the matrix alloy. The wear resistance of the rods made of the B83 babbit + 5 wt % SiC composite material is shown to be higher than that of commercial B83 alloy samples by a factor of 1.2. Arc surfacing is used to deposit antifriction coatings, which are made of the surfacing composite rods based on B83 babbit reinforced by boron carbide or silicon carbide particles, onto steel substrates. The deposited layers exhibit good adhesion to the substrates: the melting line is continuous and does not contain discontinuities. The structure and the tribological properties of the deposited coatings are studied. The wear resistance of the composite coatings is higher than that of the B83 alloy–based coating by 30%.     

SPS-assisted Synthesis of SICp reinforced high entropy alloys: reactivity of SIC and effects of pre-mechanical alloying and post-annealing treatment

In this work a traditional high entropy alloy (FeCoNiCrAl) was reinforced by uniformly distributed reactive silicon carbide (SiC) particles by a powder metallurgy synthetic route, using as precursors simply mixed powders or mechanically prealloyed ones. The reactive sintering produced a single isomorphic BCC structure. The sample microstructure resulted equiassic, more homogenous in samples based on prealloyed powders. The instability of SiC in the presence of metal precursors resulted in the formation of more stable carbides and silicides, as well as in carbon diffusion in the high entropy alloy matrix and partially unreacted SiC particles. The formation of these newly formed fine precipitates, as well as the presence of residual SiC were useful to increase the hardness of the alloy.     

Laser Alloyed Coatings of TiB2/Graphite on 9Cr18 Stainless Steel Surface

 Modified coatings including carbide of iron, nickel, chromium, silicon, and titanium are obtained on 9Cr18 stainless steel surface by laser alloying. The processing method, the microstructure, the interface, the tribological properties, and the forming mechanisms of the coatings are analyzed. The results show that the microstructure of the alloyed coatings is mainly irregular FeC crystals. Carbides of chromium and iron are around the FeC crystals. Small granular TiC disperses in the alloyed coatings. The microhardness of the alloyed coatings is greatly improved because of the occurrence of carbide with high hardness. At the same time, the wear resistance of the alloyed coatings are higher than that of 9Cr18 stainless steel.     

Wear of tungstenless hard alloys based on SHS-titanium carbide

The structure, porosity, strength, and wear resistance of tungstenless hard alloys based on titanium carbide are investigated. Titanium carbide is produced by self-propagating high-temperature synthesis (SHS). The strength of this alloy and normal hard alloy of similar composition is about the same, but SHS alloy exhibits higher wear resistance. The use of SHS titanium carbide alloyed with molybdenum results in an increase in strength. Addition of molybdenum to the nickel binder results in a twofold increase in wear resistance.Institute of Structural Microkinetics, Russian Academy of Sciences, Chernogolovka. Translated from Poroshkovaya Metallurgiya, Nos. 1/2(383), pp. 61–64, January–February, 1996. Original article submitted April 13, 1994.     

SiC晶须含量对镁基复合材料性能影响的研究

采用加压烧结法制备镁基复合材料,研究不同含量的SiC晶须对镁基复合材料密度、硬度、抗拉强度、抗压强度、摩擦磨损等性能的影响。结果表明:镁基复合材料的致密度并不随SiC晶须质量分数的改变而发生规律性变化;材料的硬度随着晶须质量分数的增加而增大;与基体材料ZK60相比,添加SiC晶须的镁基复合材料的抗拉强度、抗压强度、弹性模量、压缩模量和伸长率都有一定提高,当SiC晶须的质量分数为20.0%时,复合材料烧结体的常温力学性能最好;通过对烧结材料磨损量变化的分析,发现当SiC晶须质量分数为10.0%时,摩擦磨损性能最好。综合比较分析,SiC晶须的质量分数为15.0%时,增韧增强效果最佳。     

Investigation of the corrosion resistance of nanopowders of refractory borides and carbides in electrolytic solutions

Solubility of nanopowders of vanadium, titanium, chromium, and zirconium borides and carbides and of silicon carbide has been studied in standard electrolytes used for nickel plating. As the objects of the investigation, nanopowders with the contents of the main phase of 92.6–95.3% and an average particle size of 35–62 nm have been used. Their corrosion resistance was estimated depending on the electrolyte acidity, temperature, and duration of the interaction. It has been established that within each group of compounds the nanopowders are close in terms of their corrosion resistance in the electrolytic solutions and are characterized by an unlimited induction period in alkaline media, except for the silicon-carbide nanopowder, which is stable in solutions of any acidity.     

Sintering Behavior of Nanocrystalline Silicon Carbide Using a Plasma Pressure Compaction System: Master Sintering Curve Analysis

Nanostructured ceramics offer significant improvements in properties over corresponding materials with larger grain sizes on the order of tens to hundreds of micrometers. Silicon carbide (SiC) samples with grain sizes on the order of 100 nm can result in improved strength, chemical resistance, thermal stability, and tailored electrical resistivity. In this study, nanocrystalline SiC was processed in a plasma pressure compaction (P²C) system at a temperature of 1973 K (1700 °C) that was much lower than the temperatures reported for other sintering techniques. Microstructure of the resulting samples was studied and the hardness and the fracture toughness were measured. The grain sizes were on the order of 700 nm, the hardness between 22 and 24 GPa, and the toughness between 5 and 6.5 MPa·m^1/2. The master sintering curve (MSC) analysis was used to model the densification behavior of SiC powder sintered by the P²C method. The apparent activation energies for three different pressures of 10, 30, and 50 MPa were obtained to be 1666, 1034, and 1162 kJ/mol, respectively. Although densification occurs via diffusion, the activation energies were higher than those associated with self-diffusion in SiC (between 570 and 920 kJ/mol). A validation study of the MSC was also conducted and the variation in observed density from the density predicted by the MSC was found to range from 1 to 10 pct.     

Production of NiAl–matrix composites by reactive sintering

Abstract

This work was devoted to the development of NiAl–matrix composite and its production by reactive sintering powder metallurgy. Various types of reinforcement (aluminium oxide, silicon and tungsten carbides, titanium silicide) were tested. The best chemical compatibility and the highest hardness and wear resistance were achieved by Al₂O₃ fibres. Electroless nickel plating pretreatment of Al₂O₃ fibres improves both distribution of fibres and hardness of the composite. However, it strongly reduces the wear resistance, probably due to phosphorus content in the nickel coating. In situ formation of NiAl–Al₂O₃ composites by reactive sintering of a pressed powder mixture of Ni, Al and NiO was unsuccessful. Only a small amount of cubic γ-Al₂O₃ was detected after reactive sintering and hence no significant hardness increase was observed.     

Correlation of abrasive wear with microstructure and mechanical properties of pressure die-cast aluminum hard-particle composite

Aluminum hard particle composites were synthesized by the solidification processing technique and the composite melt was solidified using gravity and pressure die castings. An aluminum-silicon alloy (A 332.1) has been used as the matrix and silicon carbide particles (quantity: 10 wt pct, and size: 50 to 80 μm) have been used as reinforcement for synthesis of the composite. The microstructure of the pressure die cast composite is found to be finer than those of the gravity cast ones. Additionally, the distribution of SiC particles in the Al alloy matrix is found to be more uniform in the pressure die-cast composites compared to the gravity die-cast ones. The mechanical properties such as ultimate tensile strength, hardness, and ductility are observed to be superior in the case of pressure die-cast composites compared to the gravity-cast one. The two-body abrasive wear resistance of the Al-composite is also noted to be greater in the pressure die-cast composite than in the gravity-cast one. The effects of injection pressure on the mechanical properties and wear resistance of the pressure die-cast composites are examined. It is observed that the wear resistance (inverse of wear rate), hardness, and strength of the Al-SiC composites increase with the increase in injection pressure during pressure die casting. This may be due to the finer microstructure, the absence of casting defects, and the stronger interfacial bonding between the matrix and hard dispersoid in pressure die-cast composites. The wear rate of the alloys and composites is studied as a function of their hardness, strength, and Young’s modulus. It is noted that the wear rate is primarily controlled by hardness even though other mechanical properties influence the wear behavior of the materials to some extent. An attempt is made to establish an empirical relation to correlate the wear rate of material with the mechanical properties such as hardness, ultimate tensile strength, and elongation.     

Wear resistance of silicon carbide and nitride based ceramic materials

Various factors that affect the nature of wear in SiC and Si₃N4₂ based ceramics have been analyzed. It is shown that adhesion, mechanochemical and diffusion interactions in the contact zone and wear due to fatigue, thermal stresses and abrasion are the predominant factors. Ceramics based on SiC and Si₃N₄ are shown to have excellent wear resistance. Poreless silicon nitride materials that have good chemical stability, heat and crack resistance appear promising as ceramic—metal friction couples and for metal machining. Silicon carbide based poreless materials are efficient ceramic—ceramic friction couples and for service under severe hydro and gas abrasive media attack.Translated from Poroshkovaya Metallurgiya, No. 5, pp. 3–8, May, 1993.     

Simultaneous co-deposition of SiC and CNT into the Ni coating

Various researches are carried out to investigate the properties of Ni-SiC and Ni-CNT composite coatings. The simultaneous effect of carbon nanotube (CNT) and silicon carbide (SiC) is not addressed in the literature. Hence, Ni-SiC and Ni-SiC-CNT nanocomposite coatings were electrodeposited on aluminium substrate in this paper. Surface hardness and elastic modulus of the coatings were measured by atomic force microscope, and X-ray diffraction technique was used to evaluate the grain size of the coatings. Pin-on-disk wear test was carried out and the frictional surfaces along with the morphology of the coatings were investigated using scanning electron microscope. Both hardness and elastic modulus of the coating increased after CNT was introduced. The results indicate that CNT improved the wear behaviour of the coating by preventing the detachment of strengthening particles from the coating and consequently decreasing its abrasive wear.     

Friction Stir Processing for Enhancement of Wear Resistance of ZM21 Magnesium Alloy

Present work pertains to surface modification of the magnesium alloy using friction stir processing (FSP). Silicon carbide and boron carbide powders are used in the friction stir processing of the ZM21 Magnesium alloy. Coating was formed by FSP of the alloy by placing the carbide powders into the holes made on the surface. Surface coating was characterized by metallography, hardness and pin-on-disc testing. Friction stir processed coating exhibited excellent wear resistance and is attributed to grain boundary pinning and dispersion hardening caused by carbide particles. Surface composite coating with boron carbide was found to possess better wear resistance than coating made with silicon carbide. This may be attributed to formation of very hard layer coating of boron carbide reinforced composite on the surface of magnesium alloy. In the present work an attempt has also been made to compare the wear behaviour of surface composite layer on ZM21 Mg alloy with that of conventionally used engineering materials such as mild steel and austenitic stainless steel. Wear data clearly shows that wear resistance of friction stir processed composite layer is better than that of mild steel and stainless steel. This work demonstrates that friction stir processing is an effective strategy for enhancement of wear resistance of magnesium alloys.     

反应温度对卤素刻蚀法制备碳化物衍生碳涂层的影响

近些年来,碳化物衍生碳以其独特的性能被广泛应用在气体存储、超级电容器、催化剂载体和摩擦涂层等方面.卤化法以成本低、制备工艺简单等特点成为制备衍生碳涂层的热点.本文以SiC陶瓷基体为前驱体,通过高温氯化处理工艺在SiC表面制备碳化物衍生碳涂层,并研究了反应温度与其摩擦学性能之间的关系.研究结果表明:在1 175℃下保温2 h所制备的SiC-CDC涂层表面光滑平整、硬度最高、且与基体的结合强度最好.此时SiC-CDC涂层的干摩擦系数最小,耐磨性最强,具有良好的摩擦学性能.氯气刻蚀反应制备SiC-CDC涂层可为工业上应用衍生碳涂层提供理论和技术支持.