Papers by Keyword: Cermet

Abstract: Cermet includes the excellent properties of ceramic materials and the advantages of metal materials, so it is an important new engineering material. In this paper, Al₂O₃-Al cermet is prepared using different molding process via the powder metallurgy method to study the properties of Al₂O₃-Al cermet. The conclusion are shown the increasing density of Al₂O₃-Al cermet is not obvious with increasing the forming pressure of cermet body during the initial and late processing, but the increasing density is more obvious under the forming pressure for 20-30MPa. The density of cermet materials are increased with prolonging holding pressure time, the initial increase speed is faster, and the later growth rate becomes weaker. When the molding pressure is 30MPa, the holding time is 10min, the sintering temperature is 900°C, the holding time is 1h, the prepared Al₂O₃-Al cermet adding sintering aids has a coated microstructure, which indicates that the large number of particles is migrated on the grain boundary. The sample density is 2.26g/cm³, the density is highest, the distribution of Al₂O₃ and Al phase is the most uniform. The buried sintering method is more suitable for the preparation of Al₂O₃-Al cermet composites than the nudity sintering method.

Abstract: NbC-xTi (C_0.7N_0.3)-10Ni-7.5VC (vol%) based cermets with 0, 5, 10, 15 or 25 vol% Ti (C_0.7N_0.3) were prepared by conventional pressureles liquid phase sintering at 1420°C in vacuum. Detailed microstructural investigation was performed by SEM, EPMA and XRD analysis. Sintering results indicated that the partial replacement of NbC by Ti (C_0.7N_0.3) had a significant effect on the carbide grain growth, microstructure, hardness as well as fracture toughness of the fully densified NbC-based cermets. The Ti (C_0.7N_0.3)-free NbC cermet was composed of homogeneous cubic (Nb,V)C solid solution grains, whereas core-rim structured NbC grains were observed in cermets with Ti (C_0.7N_0.3) addition. All sintered cermets with  15 vol% Ti (C_0.7N_0.3) were composed of a fcc solid solution Ni binder and a cubic core-rim solid solution (Nb,V,Ti)C phase with a Nb-rich core and a Ti-rich rim. 3.8 vol% of residual pristine Ti (C_0.7N_0.3) was present in the cermets with 25 vol% Ti (C_0.7N_0.3) addition. The 15 vol% Ti (C_0.7N_0.3) starting powder based cermet exhibited the finest average NbC grain size of 1.48 μm, with a core-rim structure and an interesting combination of hardness (1486 kg/mm²) and fracture toughness (8.7 MPa.m^1/2).

Abstract: Cutting performance of reaming alloy gray cast iron HT250 using carbide, cermet and CBN reamers was studied. Experiments were conducted under constant cutting parameters and cooling strategy. Tool life, hole diameter, spindle power, surface roughness and tool wear were analyzed. The hole diameter and spindle power would keep steady when reaming with carbide reamer after 400 holes to the tool life of 1050 holes. But holes diameter reduced and spindle power increased with the number of machined holes increasing during the whole tool life when using cermet or CBN reamer. The surface roughness Rz of the holes reamed by carbide reamer was within the tolerance, although it was worse than that reamed by cermet and CBN reamer. It can be summarized that the carbide was the most suitable material for reaming alloy gray cast iron because of the longest tool life, steady hole diameter and spindle power, qualified surface roughness. After machining, crater wear and clearance wear were produced on the cermet and CBN reamer, which were caused by abrasive wear. In addition, flaking and breakages appeared on the edge of cermet reamer, which were not found on CBN reamer. However, the clearance wear of carbide reamer was smaller than that of CBN reamer, and built up edge was found along the cutting edge.

Abstract: Friction stir welding is a novel and promising joining process and most common welding tool failure is transformation of geometry caused by wear. In our point of view, this is adhesion wear. The lathe testing of adhesion wear was conducted to compare wear resistance of following materials: Co-25wt%Cr, TiC-25wt%Ni/Mo and WC-6wt%Co. According to characteristics of investigated materials, they are capable to become alternatives for conventional frictional stir welding (FSW) tool materials. Adhesive wear tests were performed by turning aluminium alloy AW6082-T6 at low speed – travel length, turning speed and feed rate were selected to simulate FSW conditions. The adhesive wear was determined as the change of the geometry of the cutting edges of the tool measured using SEM images. Most promising tool material in terms of adhesion wear resistance is WC-Co hardmetal. The two main stages of wear were distinguished: at first, the appearance of intensive adhesion wear followed by steady state wear. Surface fatigue wear complements development of the adhesive wear.

Abstract: Present paper discusses the influence of spark plasma sintering (SPS) on the microstructure and perfomances of chromium carbide based cermets. The effect of SPS parameters (temperature, pressure) is discussed. It is shown that SPS enables to produce more fine grained chromium carbide based cermets compared to conventional liquid phase sintering. Hardness and fracture toughness are exhibited.

Abstract: In this paper, Fe/SiO₂ composites with different Fe content were prepared through pressureless sinter in weakly reductive atmosphere after high energy ball milling. The electrical properties including ac conductivity, permittivity were investigated in detail. The results showed that the frequency dispersions of ac conductivity follow the power law, indicating the hoping conduction behavior. The real part of permittivity for composites increased with higher Fe content, which was attributed to the more interface between Fe and SiO₂. Besides, Debye-like dielectric relaxations were observed, and the Debye-like loss peak appeared blue shift as increasing the Fe content.

Abstract: Amorphous embedded nickel-silica composites can be directly obtained by Polymeric Precursor Method when the polymeric precursor is pyrolysed in controlled atmosphere. The metallic particles dispersion into the matrix composite is very important to material applications, but the resistance against the oxidation under extreme conditions is also required. In this work, nickel-silica nanocomposite sample was synthesized for containing amorphous carbon as matrix interphase through the direct route based on the Polymeric Precursor Method. The composite sample was obtained by pyrolysis of polymeric precursor at 600 oC for 1 hour under nitrogen flow and then submitted to oxidation in oxygen flow at 400 oC up to 7 hours. It was observed by Transmission Electron Microscopy the metallic nickel nanoparticles present high dispersion into matrix composite. However, in spite of the border of the composite particles are easily oxidized and originate nickel oxide phase, as proven by X-Ray Diffraction, the amorphous carbon phase acts as protective phase for the majority of the composite sample. By Nitrogen Adsorption-Desorption Isotherms at 77 K it was demonstrated the carbon phase also preserves significantly the mesoporous nature of the composite under oxidation process.

Abstract: Iron-based sintered materials are fabricated via the process of compacting iron powder by using die, sintering in 1100 to 1300°C, and quenching or sizing. These materials are used as variable valve system and oil pump system in automobiles. Recently, the severe requirement for complication and high precision shape of them has increased the products machined by turning and drilling. In general, it is more difficult to machine the sintered materials than the steel. However, the quantitative evaluations and the mechanisms of those are ambiguous, then there is a few suggestion for improvement of the machining. In this study, we will report the machinability of sintered materials by compare with that of steel materials, and the improvement of machinability of sintered materials.

Abstract: In this study, a series of ZrB₂-ZrC_x-Zr cermets were prepared by reactive hot-pressing of Zr + B₄C powder mixtures at different temperatures between 1400°C and 1900°C. The microstructure of the resulting cermets was characterized by field emission scanning electron microscopy. The strength and fracture toughness of the cermets were measured by four-point bending test at room temperature. The results showed that the strength and fracture toughness dependend on the amount of excess Zr and sintering temperature as well. In addition, the crack propagation behavior of the cermets was examined under indent cracking. The cracks induced by indenter directly propagated in the samples with less than 16 vol% Zr. For comparison, the multiple cracking behavior was observed for the samples with equal to or greater than 16% Zr. Furthermore, the effects of compositions and sintering temperatures on the microstructure and the mechanical properties of the cermets were discussed.

Abstract: In cermet coatings with both ceramic and metal present, these can have very different corrosion potentials. Therefore, determination of the corrosion behaviour performance and its mechanism is crucial, especially in very acidic and alkaline environment. A conventional high velocity oxy-fuel (HVOF) tungsten carbide (WC)-Co coatings and a weld overlay tungsten carbide-nickel alloy cermet with carbide size of ~0.3-5 mm and ~50-140 mm respectively are used. Potentiodynamic tests are carried out in acidic and alkaline electrolytes: 0.5 M sulphuric acid, pH 0.45 and bentonite drilling fluid, pH 10.45. The behaviour of both coating types tested were pH dependent. The HVOF coating showed preferential dissolution of the binder in both electrolytes, with material loss being approximately twice as severe in the 0.5 M sulphuric acid compared to the alkaline drilling fluid. For the weld overlay coatings, with the larger carbide particles, the Ni₃B phase in the binder was preferentially removed in the acidic electrolyte whereas the Ni rich dendritic phase underwent preferential dissolution in the alkaline environment.