Rapid consolidation of nanostructured WC-FeAl hard composites by high-frequency induction heating and its mechanical properties

In the case of cemented WC, Co or Ni is added as a binder for the formation of composite structures. However, the toxic behavior of both Co and Ni and their cancerogenic classification in Europe and the US, the high cost of Co or Ni, the low hardness and the low corrosion resistance of the WC-Ni and WC-Co cermets have generated interest in recent years for alternative binder phases. In this study, FeAl was used as a novel binder and consolidated by the high-frequency induction sintering (HFIS) method. The advantage of this process is not only rapid densification to near theoretical density but also the prohibition of grain growth in nano-structured materials. Dense WC-FeAl with a relative density of up to 98% was obtained within two minutes by HFIS under a pressure of 80 MPa. The effect of FeAl addition on mechanical properties, consolidation and microstructure of WC was evaluated.     

Rapid sintering of ultra fine WC and WC-Co hard materials by high-frequency induction heated sintering and their mechanical properties

Using a high-frequency induction heated sintering (HFIHS) method, the densification of binderless WC and WC-x wt.%Co (x=8, 10, 12) hard materials were accomplished using an ultra fine powder of WC and WC-Co. The advantages of this process are that it allows very quick densification close to the theoretical density and prohibits grain growth in nano-structured materials. Nearly fully dense WC and WC-Co with a relative density of up to 99.9% could be obtained with a simultaneous application of 60 MPa pressure and induced current (within 2 min) without a significant change in grain size. The average grain size of WC was approximately 270 nm for WC-x wt.%Co. The hardness and fracture toughness of the dense WC and WC-Co composites produced by HFIHS were investigated.     

The mechanical properties of nanostructured materials

In this paper, the state-of-the-art progress in research on novel mechanical properties of nanocrystalline materials and carbon nanotubes is reviewed. There is evidence that the relation between the strength of nanocrystalline materials and grain size does not observe the classic Hall-Petch plot. Lowtemperature and high-strain rate superplasticity have been found in some nanocrystalline materials. Theoretical prediction and experimental data indicate that carbon nanotubes are materials with high stiffness, high strength, great toughness, and low density. There are already some application examples for novel mechanical properties of nanocrystalline materials and carbon nanotubes. For more information, contact P.K. Liaw, University of Tennessee at Knoxville, Materials Science and Engineering Department, 427-B Dougherty Engineering Building, Knoxville, Tennessee 37996; (865) 974-6356; fax (865) 974-4115; e-mail pliaw@utk.edu.     

Comparison of sintering behavior and mechanical properties between WC−8Co and WC−8Ni hard materials produced by high-frequency induction heating sintering

The sintering behavior and mechanical properties of WC-Co and WC-Ni hard materials produced by high-frequency induction-heating sintering (HFIHS) were compared using ultra fine WC, WC-Co, and WC-Ni powders. HFIHS allows very quick densification to near theoretical density and prohibits grain growth in nano-structured materials. Highly dense WC, WC-Co, and WC-Ni with a relative density of up to 99.2% could be obtained with simultaneous application of 60 MPa pressure and induced current within 2 min without significant change in grain size. The hardness and fracture toughness of the dense WC, WC-Co, and WC-Ni composites produced by HFIHS were also investigated.     

Spark plasma sintering consolidation of nanostructured TiC prepared by mechanical alloying

Spark plasma sintering technique was used for the consolidation of nanostructured titanium carbide synthesized by mechanical alloying in order to avoid any important grain growth of the compact materials. The TiC phase was obtained after about 2 h of mechanical alloying. Towards the end of the milling process (20 h), the nanocrystalline powders reached a critical size value of less than 5 nm. Some physical and mechanical properties of the consolidated carbide were reported as a function of the starting grain size powders obtained after different mechanical alloying durations. The crystalline grain size of the bulk samples was found to be increased to a maximum of 120 nm and 91 nm for carbides mechanically alloyed for 2 h and 20 h respectively. The Vickers hardness showed to be improved to about 2700 Hv for a maximum density of 95.1% of the bulk material.     

Aspects of the metrology of contiguity measurements in WC based hard materials

Contiguity is thought to be of significant importance regarding the properties of WC–Co hardmetals and other multiphase hard materials. Contiguity is an estimate of the degree of contact between adjacent grains in two phase materials. It is straightforward to define and, in principle, relatively easy to measure. However, published values of contiguity, generally expressed as a function of the volume fraction of the Co phase in WC–Co, show considerable scatter. Possible reasons for this scatter are discussed; in particular various aspects of the measurement process are examined in order to recommend suitable measurement metrology that will contribute to minimising uncertainties in the measurement process. Furthermore, the consequences of uncertainty in contiguity measurements for the use of published models relating contiguity to microstructural variables is also discussed.     

Influence of alloy ingredients on mechanical properties of ternary boride hard alloy clad materials

Using Mo, B-Fe alloy and Fe powders as raw materials, and adding C, Cr and Ni ingredients, respectively, or C, Cr and Ni mixed powders, ternary boride hard alloy clad materials was prepared on Q235 steel substrate by means of in-situ reaction and vacuum liquid phase sintering technology. The influence of alloy ingredients on the mechanical properties of ternary boride hard alloy clad materials was investigated. The results indicate that a mixture of 0.8% C, 5% Cr and 2% Ni ingredients gives a ternary boride hard alloy clad material with optimal mechanical properties, such as high transverse rupture strength, high hardness and good wear resistance.     

A comparison between magnetic properties and grain size for WC/Co hard materials containing additives of Cr and V

The magnetic properties of cemented carbides are often used as an indirect measure of the microstructure. For this purpose, models relating coercive force with WC-grain size have been developed. In this study, it is investigated how well magnetic models describe the microstructure of cemented carbides (WC/Co) for samples containing different kinds of commonly used grain growth inhibitors, varying carbon content, and cooling conditions. We found that small amount of V (0.2 wt%) and Cr (0.4 wt%) influence the magnetic properties differently. Even so, commonly applied models relating magnetic properties with WC-grain size may be applied, but the importance to account for variation in saturation magnetisation in the analysis is stressed.     

Preparation of bulk ultrafine-grained and nanostructured Zn,Al and their alloys by in situ consolidation of powders during mechanical attrition

Bulk ultrafine-grained (UFG) or nanostructured Zn, Al and their alloys were produced via in situ consolidation of powders by mechanical attrition (MA) at room temperature. In situ consolidation of metal powders during MA may be a promising method to produce bulk UFG or nanostructured materials with full density and less contamination.     

碳纳米管/聚酰亚胺纳米复合材料的制备及动态力学性能和介电性能

依次用混强酸和SOCl2对多壁碳纳米管(MWNTs)进行改性,解决其在有机溶剂的溶解性和在基体聚酰亚胺中分散性问题,并采用光电子能谱(XPS)和透射电镜(TEM)对改性前后的MWNTs进行表征.以4,4'-二氨基二苯醚(ODA)和3,3',4,4'-二苯甲酮四羧酸二酐(BTDA)为原料,以原位聚合法将改性碳纳米管掺杂聚酰亚胺(PI),制备MWNTs/PI纳米复合材料.通过热重分析(TGA)、动态力学分析(DMA)和电容测试对材料的热性能、动态力学和介电性能进行表征.结果表明:加入MWNTs后,材料仍有很好的热稳定性,材料的动态力学性能随MWNTs增加而增强,在50℃和10%(质量分数)MWNTs时储能模量为2.307 GPa,比纯聚酰亚胺(PI)提高23.1%;材料的介电常数随着MWNTs含量的增加明显提高,在IMHz和10%时介电常数为66.7,是纯PI的18.6倍.制备的碳纳米管/聚酰亚胺材料是一种具有优良的热学、动态力学力学和介电性能性能的纳米复合材料.     

Microstructure and mechanical properties of nanostructured bainite weld with regeneration

Because of the brittle martensite crystalline structure, nanostructured bainitic steel is very difficult to be welded and easily form cracks in the welded joint, which limits the scope of their application. Regeneration treatment can lead to nanostructured bainite formation in the welded joints, preventing further degradation of the welded joint. Detailed changes of microstructures and mechanical properties of the weld are characterized here. Coarse inter-dendrite structures appear in the weld due to welding segregation, and are confirmed to be retained austenite by TEM. Moreover, an extraordinary combination of strength and ductility of the weld is achieved. The ultimate tensile strengths are 1913MPa and 2115MPa when regeneration temperatures are 250 °C and 230 °C. The corresponding elongations are 5.14% and 2.3%. In addition, the tension fracture behaviour and crack propagation mode of the weld are investigated.     

Microstructure and mechanical properties and of pulse plasma compacted WC - Co

Tungsten carbides-based inserts have been considered as one of the dominant hard materials in the cutting industry, receiving great interest for their excellent combination of mechanical properties. Pulse plasma compaction (PPC) process has been applied to a series of WC-Co samples with varying sintering temperature, initial particle size and sintering pressure in order to study the mechanical and microstructural behaviour. The quality of the products, as well as the mechanical properties and microstructural features this process yields, are commendable and worth looking into. A high hardness of more than 2000 HV has been achieved while a maximum fracture toughness of 15.3 MPa √ m was recorded in samples that were sintered at 1100 °C and 100 MPa. Microstructural features like grain growth and other properties are discussed with respect to the varying parameters. While grain size shows an incremental pattern with increasing temperature, it was still possible to limit them to a great extent ensuring high mechanical properties. The effect of sintering pressure in the range of 60–100 MPa, while keeping sintering temperature constant, was found to be almost negligible.     

PCBN材料的组织结构与力学性能

以CBN-TiN-Ti-Al₂O₃为初始原料,采用高温高压法在1500 ℃不同保温时间下制备PCBN材料,探讨其在不同保温时间下的物相组成、显微结构、力学性能和切削性能。结果表明:保温时间对PCBN材料物相组成无明显影响,但有助于提高其结晶度,实现其烧结均匀化和致密化;在保温时间为9.00 min时,能获得综合性能最佳的PCBN材料,其相对密度为99.1%,抗弯强度为910.9 MPa,磨耗比为7120,显微硬度为33.5 GPa;用此PCBN做成的刀具加工模具钢零件,最多可加工365个。      

High-rate mechanical properties of energetic materials

Compared to the many thousands of studies that have been performed on the energy release mechanisms of high energy materials, relatively few studies have been performed (a few hundred) into their mechanical properties. Since it is increasingly desired to model the high rate deformation of such materials, it is of great importance to gather data on their response so that predictive constitutive models can be constructed. This paper reviews the state of the art concerning what is known about the mechanical response of high energy materials. Examples of such materials are polymer bonded explosives (used in munitions), propellants (used to propel rockets), and pyrotechnics (used to initiate munitions and also in flares).     

Microstructure evolution and mechanical properties of nanocrystalline FeAl obtained by mechanical alloying and cold consolidation

In the present study high energy mechanical milling followed by cold temperature pressing consolidation has been used to obtain bulk nanocrystalline FeAl alloy. Fully dense disks with homogenous microstructure were obtained and bulk material show grain size of 40 nm. Thermal stability of the bulk material is studied by XRD and DSC techniques. Subsequent annealing at a temperature up to 480 °C for 2 h of the consolidated samples enabled supersaturated Fe(Al) solid solution to precipitate out fine metastable Al₅Fe₂, Al₁₃Fe₄ and Fe₃Al intermetallic phases. Low temperature annealing is responsible for the relaxation of the disordered structure by removing defects initially introduced by severe plastic deformation. Microhardness shows an increase with grain size reduction, as expected from Hall-Petch relationship at least down to a grain size of 74 nm, then a decrease at smallest grain sizes. This could be an indication of some softening for finest nanocrystallites. The peak hardening for the bulk nanocrystalline FeAl is detected after isochronal ageing at 480 °C.     

Effect of milling and reinforcement on mechanical properties of nanostructured magnesium composite

Recycled Mg chips were used to synthesize nanostructured Mg composite of Mg–5 wt%Al reinforced with x wt% (x = 1, 2 and 5) in-situ formed AlN powder. Mechanical milling was employed to produce the composite powder of crystalline size 30–43 nm. The mechanically milled (MMed) powders were subjected to uniaxial pressing, sintering and hot extrusion processes to produce bulk solid samples. After sintering at 400 °C and hot extrusion at 350 °C, the crystalline size of the composite samples still remains in nanometer range from 52 to 84 nm. The effect of milling and the percentage of reinforced AlN on the mechanical properties such as tensile strength and ductility were discussed with the general explanation of deformation mechanisms involved.     

羟基磷灰石-氧化锆复合材料的致密化及其力学性能

在无压条件下,采用添加CaF2法制备了羟基磷灰石-氧化锆致密材料,并研究了CaF2含量对HA-ZrO2材料的致密化、微观结构和力学性能的影响.结果显示:在HA-ZrO2(10%～40%,质量分数,下同)复合材料中添加CaF2,使HA变成了分解温度高的氟部分取代羟基的磷灰石FHA,材料的密度和力学性能(抗弯强度和断裂韧性)明显提高;加入6%(质量分数)CaF2经1 350℃烧结4 h后,HA-ZrO2(10%～40%)的相对密度均达到95%,抗弯强度达到100～120 MPa,断裂韧性提高到1.2～1.6 MPa·m1/2;随ZrO2含量的升高,HA-ZrO2致密度有所下降;而当CaF2含量为6%,ZrO2含量高于40%时,HA-ZrO2复合材料中形成α-Ca3(PO4)2、HA/ZrO2固溶体或立方氧化锆,导致复合材料的力学性能下降.     

Nanoporous materials and their adsorption properties

Principal regularities of forming microporous adsorbents with different surface composition, in particular, active coals, zeolites, silica gels, alumina gels, fullerenes, and carbon nanotubes are considered. The data on the structure-energetecal characteristics of the adsorbents and systems are correlated. Principal characteristic features of the microporous adsorbents deformation during CO₂,CH₄, Ar, N₂, and Xe adsorption in a 177.65–393 K temperature range at the pressures of up to 7.0 MPa are studied by example of the AUK microporous carbonaceous adsorbent and the NaX zeolite. An analysis of the adsorption deformation of the microporous adsorbents as a function of the adsorption amount, temperature, and physicochemical properties of adsorbed gas is presented. Based on the analysis of benzene adsorption isotherms for the C60 and C70 fullerenes, a suggestion is advanced on the formation of fullerene-benzene adsorption complexes comprising on average three fullerene and two benzene molecules; their characteristic energy comes to E _o ～ 25 kJ/mol. It is shown, by using the adsorption and SEM data that the cuminol adsorption at the nanotubes yields supramolecular complexes in which the cumene molecules act as coordinating ones. By using the micropore bulk filling theory, the hydrogen adsorption is calculated for model supramolecular systems in which the carbon nanotubes are bundled up, with leaving gaps between the bundles.     

Thermodynamics of nanostructured materials

Published data on the influence of the effective nanoparticle size and the atomicity of clusters on the physicochemical properties of substances are considered. An interpretation is suggested for the analytical relations of the first and second laws of thermodynamics considered with conversion of the substance and the dependence of the chemical potential of reagents on the effective nanoparticle size taken into account.