The influence of nano-scale Al2O3 on the mechanical properties of Ti(C,N)-based ceramets and toughening mechanisms of micro/nano-scale composite ceramets were studied in this paper. The major toughening mechanisms such as the transformation of fracture mode, the change of the microstructure, occurrence of the multi-crack etc. were also analyzed.

Advanced Ti(C, N) matrix cermet tool materials with higher mechanical properties are successfully developed by dispersing nano-scale Al2O3 powder into the micro-scale Ti(C, N) matrix and Ni-Mo bonding phases powder. The effect of the content of nano-scale alumina on the microstructure and mechanical properties of micro-scale Ti(C, N) matrix cermet tool materials are investigated. The research results show that a type of Ti(C, N) matrix cermet tool material has the most optimal flexural strength of 900MPa, Vickers hardness of 17.4GPa and fracture toughness of 9.95MPa.m(1/2) when the content of nano-scale alumina is 12% in term of mass. It is found from the microstructure analysis that the main reason of the mechanical properties improvement is the grain fining effect caused by nano-scale Al2O3.

The effect of sintering temperature on mechanical properties and microstructure of rare earth oxides toughened Ti(C,N) ceramic cutting tool materials was investigated. The results showed that the mechanical properties of Ti(C,N) based ceramics were greatly influenced by sintering temperature. As a result, both of the density and mechanical properties of the materials sintered at 1350 and 1400 are worse than those sintered at 1450 and 1500. Low sintering temperature results in low density and degraded mechanical properties, but too high sintering temperature results in the precipitation of bond metal and thus reduces its fracture toughness. Intergranular fracture mode of the material is mainly observed.

The research status quo of the ceramet cutting tool materials is investigated and surveyed systematically. The principles for designing ceramet materials and the strengthening and toughening mechanisms of ceramet materials are introduced. The research direction of ceramet materials is finally pointed out for instructing new ceramic material design.

The phase stability of zirconia ceramics doped with stabilizers plays an important role in obtaining metastable tetragonal phase and phase transformation toughening.The effects of stabilizers on the stability of zirconia doped with single or multi-stabilizers(Y_2O_3,MgO,CeO_2) and the research of some new stabilizers(Nb_2O_5,Ta_2O_5,La_2O_3 and so on) over the last few years are reviewed.

The composite ceramic material ZrO2/Al2O3 has been successfully developed to produce scissors for textile. It is found from the microstructure and the mechanical properties that the grain size decreases and the content of t-ZrO2 increases with the increase of the alumina content, which is beneficial to the improvement of the fracture toughness and transverse rupture strength of the ZrO2/Al2O3 ceramics. The optimization of the mechanical property of ZrO2/Al2O3 is obtained as the alumina content is about 20% in term of mass.

Hot-pressing liquid phase sintering technique was used to fabricate Ti(C_ 0.7 N_ 0.3 ) based cermet tool materials with the addition of two kinds of rare earth oxides. The effect of rare earth oxides on the microstructure and mechanical properties of the tool materials was investigated. The results showed that the mechanical properties of the materials were greatly influenced by the process because of the addition of rare earth oxides. When hot-pressed at 1400?℃ and 25?MPa for 30min, the mechanical properties were greatly decreased, while the fracture toughness can be improved when hot-pressed at 1450?℃ and 25?MPa for 30min.

对比研究了SiC微粉和纳米Al2O3粉末的液相分散效果及其与不同分散剂及介质、PH值的关系,优化了制备低固相含量稳定悬浮液的最佳工艺参数,其研究结果对纳米复合陶瓷材料的制备有一定的指导意义.

In order to improve the wear resistance of traditional coating tools, two kinds of advanced cutting tools which can be re-ground have been developed with ceramic-coated powders by the sol-gel and hot pressing technology. A suitable set of coating and sintering technology was optimized. The titanium matrix coating tools XFTC1 fabricated from TiC powders coated with double phase alumina-silicon dioxide sol and XFTC2 fabricated from TiC powders coated with single phase silicon dioxide sol are prepared. A scanning electron microscope (SEM) observation reveals that in general the matrix (TiC) grains are uniformly coated with the alumina or alumina-silicon dioxide ceramic and the microstructure of the new tool materials is more homogeneous than that of conventionally made ceramics. The tests of mechanical properties and wear resistance in machining are finally conducted. It is shown that when compared with a hard coated carbide tool, the new material XFTC1 with double phase alumina-silicon dioxide coating exhibits a superior ability in maintaining the wear resistance during the entire tool-life. When machining a mild carbon steel the new tool materials can increase the tool-life by up to 100% as compared to ceramic tool materials that has the same matrix but fabricated in the conventional way, while the fracture toughness and flexural strength are improved by up to 69-86% and 5-15% respectively.

Ti(C, N) based ceramic tool materials in the Ti (C0.7N0.3)-(Ni-Co)-Cr3C2-VC system have been made by hot-pressing technology, their mechanical properties and fracture morphologies have been studied under three different fabrication conditions. The results show that the mechanical properties are significantly influenced by fabrication conditions, and the main fracture mode is intergranular fracture.

The employment of ceramic material simulation design methods can eliminate the disadvantage of traditional ceramic material developing methods of being time-consuming, laborious and high cost. Three simulation methods of artificial neural network, regression analysis and pattern recognition, and their application to ceramic material simulation design were presented in this paper. The problems existing in ceramic material simulation were proposed finally.

Nano-scale ceramic materials are very suitable to be used as the high speed cutting tool owing to their excellent properties. The incorporation of nano-scale second phase, such as SiC and Ti(CxN1-x) particles, into a ceramic matrix can lead to an improvement in mechanical properties, which is contributed to a change in microstructure. However, the differences between nano-scale ceramic materials and monoclinic ceramic materials can be found through fabricating these two kinds of materials. Firstly the changes in microstructure that will affect the mechanical properties of the nano-scale ceramic materials are investigated as the nano-ceramic tools are compared with the monolithic ceramic tools. Secondly the effect of microstructure on the mechanical properties is discussed. Finally the microstructure formation mechanism of nano-ceramic materials is given on the bases of some hypotheses.

The mechanical properties of nano-scale composite ceramics are related to a great deal of factors. Many of these factors such as the grain size of raw powders, content of nano-scale powders, additives, microstructure, fabricating and heat treatment technology are summarized in the present paper. And the problems to be solved and the future research direction are pointed out.

In this paper, 3mol% yttria-stabilized tetragonal zirconia polycrystal (3Y-TZP) and TiN/3Y-TZP(adding TiN particles to 3Y-TZP) composites were fabricated by hot-pressing technique. Phase composition, microstructure and mechanical properties of the composites were investigated. It is shown that the flexural strength, fracture toughness and Vickers hardness of TiN/3Y-TZP was significantly improved by the addition of TiN particles compared with 3Y-TZP. The flexural strength of ZYT2 (20wt% TiN addition) is 1318 MPa. The fracture toughness of ZYT4 (40wt% TiN addition) is 16.8MPa·m1/2. The toughening and strengthening mechanisms were analyzed. The XRD results show that the additing of TiN can hinder the transformation from tetragonal phase to monoclinic phase of 3Y-TZP during fabrication process.

The stochastic characteristics of ceramic tool mechanical properties have an important effect on a tool's stochastic fracture characteristics. In this paper, these tool stochastic characteristics and their relationship to tool fracture are studied using a reliability theory. It is found that the stochastic characteristics of tool mechanical properties and the tool fracture obey Weibull distributions. The fracture probability of cutting tool caused by the interfacial bonding strength and the other mechanical properties are different. The tool fracture probability caused by mechanical load is higher than that by thermal load or mechanical-thermal load in milling operations. It is shown that the stochastic fracture characteristics of the ceramic tool is caused by the synthetic action of the stochastic characteristics of tool mechanical properties including interfacial bonding strength.

纳米复合陶瓷材料可以极大地提高抗弯强度和断裂韧性.综述了目前相关的增韧补强机理的研究情况,主要包括基体晶粒的细化及由沿晶断裂向穿晶断裂模式的转变,热处理对微裂纹的愈合作用;指出了研究中尚需解决的问题.

An advanced self-toughening silicon nitride ceramic tool YL16A has been developed by adding proper additive Y2O3-La2O3 into the alpha phase silicon nitride and using the hot press fabrication technology. It is found from a scanning electron microscope (SEM) observation that the self-toughening mechanisms of the new ceramic tool material are columnar grain bridge and pullout similar as the whisker reinforcing mechanisms. Some alpha-Si3N4 grains are converted into columnar beta-Si3N4 grains with a high aspect ratio, and improve the fracture toughness of the new silicon nitride ceramic tool. The tests of mechanical properties, and wear and fracture resistance in machining are finally conducted. It is shown that the wear resistance of YL16A is almost the same as that of a commercially available alumina matrix ceramic tool SG4 and the fracture resistance of YL16A is markedly stronger than that of SG4. The new self-toughening ceramic tool YL16A can increase the tool-life by fracture by about 388% as compared to SG4 when intermittent cutting a quenched mild carbon steel. While the fracture toughness of the new ceramic tool is improved by up to 112-130% compared with other two general ceramic tool materials.

Nano-scale ceramic composites may be used as advanced cutting tool materials for their high flexural strength and fracture toughness.The strengthening and toughening mechanisms are caused by matrix grain fining,and the transition from the intergranular to the transgranular fracture mode as well as crack healing after anneal-ing treatment.Ac cording to the strengthening and toughening mechanisms and the experimental study,the main factors affecting the mechani cal properties of the nano-scale ceramic composites are dis cussed,which may be helpful for fabricating the novel nano-scale ceramic tool materials.