Han Lian Liu

Microstructure and Mechanical Properties of Ti(C,N)-TiB2-WC Composite Ceramic Tool Materials

Ti (C,N)-TiB2-WC composite ceramic tool materials with sintering aids such as Ni and Mo were fabricated at a temperature of 1550 °C for 1h sintering duration time in vacuum by a hot-press technique. The microstructure and mechanical properties were investigated. The composite ceramic tool materials were analyzed by means of scanning electron microscope (SEM), X-ray diffraction (XRD) and energy dispersive spectrometry (EDS). The main phases were composed of Ti (C, N), TiB2, WC and MoC, which indicated that no severe chemical reactions occurred in the composite. The flexural strength, fracture toughness and hardness of Ti (C,N)- 20 wt.%TiB2-WC ceramic material were 795.7 MPa, 6.4 MPa·m1/2 and 19.2 GPa respectively.

Study on the Multi-Scale Nanocomposite Ceramic Tool Material

An advanced ceramic cutting tool material was developed by means of micro-scale SiC particle cooperating with nano-scale SiC particle dispersion. With the optimal dispersing and fabricating technology, this multi-scale nanocomposite may get both higher flexural strength and fracture toughness than that of the single-scale composite. The improved mechanical properties may be mainly attributed to the inter/intragranular microstructure with a lot of micro-scale SiC particles located on the grain boundary and a few nano-scale SiC particles located in the matrix grain. Because of the thermal expansion mismatch between SiC and Al2O3 resulting in the compressive stress on the SiC/Al2O3 interface, the interface bonding strength between Al2O3 and SiC was reinforced, which can compel the crack propagating into the relatively weak matrix when meeting the SiC particle on the boundary; while the alumina grain boundary is not the same strong as the SiC/Al2O3 interface and the Al2O3 grain, therefore the crack propagates sometimes along the Al2O3 grain boundaries and sometimes through the grains, when reaching to the nano-scale SiC particle inside the matrix, the crack was pinned and then deflected to the sub-grainboundaries. These coexisting transgranular and intergranular fracture mode induced by micro-scale and nano-scale SiC and the fining of matrix grain derived from the nano-scale SiC resulted in the remarkable strengthening and toughening effect.

A study on the development of a composite ceramic tool ZrO2/(W, Ti)C and its cutting performance

Abstract An experimental investigation is carried out to fabricate a new ceramic tool ZrO2/(W, Ti)C by the hot pressing method and to study the effects of (W, Ti)C on the microphotograph of crystal particles, the phase transition and the mechanical properties of the new ceramic tool. Scanning electron microscope (SEM) observation reveals that the densification degree of the material ZrO2/(W, Ti)C may be improved and that the microstructure of the new ceramic tool material is more homogeneous as a result of the proper addition of the powder (W, Ti)C. Tests of the mechanical properties and wear resistance in machining are conducted. It is found that the fracture toughness of the developed ceramic tool is the highest when the content of powder (W, Ti)C is 45% in terms of volume due to the highest content of tetragonal zirconia. It is also shown that when machining a carbon tool steel the new tool material can increase the tool-life as compared to other ceramic tool materials that have the same matrix but were fabricated without (W, Ti)C, while the fracture toughness is improved by up to 38.8%. When compared with a conventional ceramic tool, the new ceramic tool material exhibit superior ability in maintaining wear resistance during the entire tool-life.

Study on the Microstructure and Mechanical Properties of TiB2-Ti(C,N) Composite Ceramic Tool Materials

TiB2-Ti(C, N)-(Ni, Mo) composite ceramic tool materials were fabricated by the hot-press sintering technology. The effects of the content of Ti(C, N) on the microstructure and mechanical properties were investigated by XRD and SEM observations. It is shown that the grain size of the composites is small, the fracture surface is irregularity, the grain boundaries of TiB2 and Ti(C, N) are connected tightly, and a new crystalline phase of MoNi is formed. A small amount of Ti(C, N) is decomposed into TiN, and the decomposition of Ti(C, N) is intensified as the content of Ti(C, N) is increased during the sintering process. The fracture pattern is the combination of the intergranular mode and transgranular mode. It is found that the flexural strength and fracture toughness of TiB2-Ti(C, N)-(Ni, Mo) composites increase consistently owning to the addition of Ti(C, N), the maximum resultant mechanical properties of TiB2-Ti(C, N)-(Ni, Mo) composites are 1019.53MPa for the flexural strength, 6.89MPa•m1/2 for the fracture toughness and 23.65GPa for Vickers hardness.

Effect of TiN Addition on Microstructure and Mechanical Properties of Zirconia Matrix Ceramic Tool Material

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.

New Thought for Designing the Multi-Phase and Multi-Scale Nanocomposite Ceramic Tool Materials

The new thought for designing the multi-phase and multi-scale nanocomposites was proposed to improve the comprehensive mechanical properties. Multi-phase and multi-scale particles are added to the matrix, and one of the additives is nano-scale particle, thus the comprehensive mechanical properties can be improved by the synergic effects of micro-scale toughening, nano-scale strengthening and mutual benefit between multi-phases. The ideal microstructure of multi-phase and multi-scale nanocomposites was designed. With this microstructure, the trans/intergranular fracture modes can be formed, which will consume more fracture energy during the crack propagation, therefore, both the flexural strength and fracture toughness can be improved. An advanced ceramic tool material has been fabricated based on this new thought.

Synergistically toughening effect of SiC whiskers and nanoparticles in Al2O3-based composite ceramic cutting tool material

In recent decades, many additives with different characteristics have been applied to strengthen and toughen Al2O3-based ceramic cutting tool materials. Among them, SiC whiskers and SiC nanoparticles showed excellent performance in improving the material properties. While no attempts have been made to add SiC whiskers and SiC nanoparticles together into the ceramic matrix and the synergistically toughening effects of them have not been studied. An Al2O3-SiCw-SiCnp advanced ceramic cutting tool material is fabricated by adding both one-dimensional SiC whiskers and zero-dimensional SiC nanoparticles into the Al2O3 matrix with an effective dispersing and mixing process. The composites with 25 vol% SiC whiskers and 25 vol% SiC nanoparticles alone are also investegated for comparison purposes. Results show that the Al2O3-SiCw-SiCnp composite with both 20 vol% SiC whiskers and 5 vol% SiC nanoparticles additives have much improved mechanical properties. The flexural strength of Al2O3-SiCw-SiCnp is 730±95 MPa and fracture toughness is 5.6±0.6 MPa·m1/2. The toughening and strengthening mechanisms of SiC whiskers and nanoparticles are studied when they are added either individually or in combination. It is indicated that when SiC whiskers and nanoparticles are added together, the grains are further refined and homogenized, so that the microstructure and fracture mode ratio is modified. The SiC nanoparticles are found helpful to enhance the toughening effects of the SiC whiskers. The proposed research helps to enrich the types of ceramic cutting tool and is benefit to expand the application range of ceramic cutting tool.

In-situ fabricated TiB2 particle-whisker synergistically toughened Ti(C, N)-based ceramic cutting tool material

The mechanical properties of ceramic cutting tool materials can be modified by introducing proper content of nanoparticles or whiskers. However, the process of adding whiskers or nanoparticles has the disadvantages of high cost and health hazard as well as the agglomeration; although a new in-situ two-step sintering process can solve the above problems to some extent, yet the problems of low conversion ratio of the raw materials and the abnormal grain growth exist in this process. In this paper, an in-situ one-step synthesis technology is proposed, which means the growth of whiskers or nanoparticles and the sintering of the compact can be accomplished by one time in furnace. A kind of Ti(C, N)-based ceramic cutting tool material synergistically toughened by TiB2 particles and whiskers is fabricated with this new process. The phase compositions, relationships between microstructure and mechanical properties as well as the toughening mechanisms are analyzed by means of X-ray diffraction (XRD) and scanning electron microscopy (SEM). The composite which is sintered under a pressure of 32 MPa at a temperature of 1700°C in vacuum holding for 60 min can get the optimal mechanical properties. Its flexural strength, fracture toughness and Vickers hardness are 540 MPa, 7.81 MPa · m1/2 and 20.42 GPa, respectively. The composite has relatively high density, and the in-situ synthesized TiB2 whiskers have good surface integrity, which is beneficial for the improvement of the fracture toughness. It is concluded that the main toughening mechanisms of the present composite are whiskers pulling-out and crack deflection induced by whiskers, crack bridging by whiskers/particles and multi-scale particles synergistically toughening. This study proposes an in-situ one-step synthesis technology which can be well used for fabricating particles and whiskers synergistically toughened ceramic tool materials.

Influence of Cobalt Additive on Mechanical Properties and Residual Stress of Al2O3-TiC Ceramic Cutting Tool Material

Cobalt additive was added into the Al2O3-TiC composite to improve the mechanical properties. The microstructure and fracture mode of composite tool materials Al2O3-TiC and Al2O3-TiC-Co were investigated, emphasizing on the difference of thermal residual stress distribution with added cobalt. The interfacial thermal stress and the stress distribution in each phase were worked out according to thermoelasticity theory. The results demonstrated that cobalt could strengthen the interfacial bonding strength of ceramic grains and influence the residual stress distribution in Al2O3 matrix, which change the fracture mode and lead to the flexural and irregular crack propagation path.

The Effects of MgO Content on the Mechanical Properties and Microstructures of Al 2 O 3 -TiN-TiC Ceramic Materials

Al2O3-TiN-TiC ceramic materials with different MgO content were fabricated by hot-pressing technique. The MgO volume percent was varied from 0vol% to 5vol%. The mechanical properties such as flexural strength, Vickers hardness and fracture toughness were tested. The phase composition of the sintered body was analyzed by XRD while the microstures of the sintering body were observed by OM (Optical Microscope) and SEM. The effects of MgO content on the mechanical properties and microstructures of Al2O3-TiN-TiC were investigated. The results shows that the addition of MgO can change the phase composition of the sintered ceramic materials which displayed with diverse solid solutions and intermetallic compounds. Meanwhile the new sintering products changed the the microstructure morphology which made the crack path complex and affected the mechanical properties.