Self-lubricating Ceramic Tool Material Research Articles

Self-lubricating ceramic tool materials synergistically toughened by nano-coated particles and silicon carbide whiskers

Nano-coated particles and whiskers were used as reinforcing additives for ceramic tool materials to take advantage of synergistic toughening and enhancement mechanisms. An Al2O3/TiC/CaF2@SiO2/SiCw ceramic tool material was fabricated by hot-pressing. Self-lubricating ceramic tool materials toughened by nano CaF2@SiO2 coated particles and SiC whiskers were studied. When the addition content of nano CaF2@SiO2 coated particles was 10 vol% and the content of SiC whiskers was 20 vol%, ceramic tool materials with the best comprehensive properties were obtained. The results showed that the hardness of the ceramic tool material was 16.52 GPa, the flexural strength was 698 MPa, and the fracture toughness was 6.89 MPa m1/2. Compared with the ceramic tool material with 10 vol% nano CaF2 particles and 20 vol% SiC whiskers, the above properties were improved by 7.06%, 31.74% and 19.06%, respectively. The SiC whiskers played a toughening role, while nano CaF2@SiO2 coated particles reduced the porosity, the compactness and also filled between the grain boundaries of the ceramic tool materials during sintering. This improved the interfacial bonding between ceramic grains, which increased the incidence of transgranular fracture in the ceramic tool materials.

Mechanical properties, microstructure and crack healing ability of Al2O3/TiC/TiB2/h-BN@Al2O3 self-lubricating ceramic tool material

To prepare a self-lubricating ceramic tool with excellent mechanical properties and crack healing ability, the h-BN@Al2O3 solid lubricant with a core-shell structure was prepared by the heterogeneous nucleation method, and was added into Al2O3/TiC ceramic matrix together with TiB2. Examination of the micro-morphology and phase composition of h-BN@Al2O3 found that the surface of the solid lubricant h-BN was coated with Al(OH)3 at first, and after calcination at 1200 °C, a dense and uniform Al2O3 shell was formed. At the same time, the effects of the h-BN@Al2O3 addition on the ceramic tool material were studied. The mechanical properties of the ceramic tool material with h-BN@Al2O3 were improved relative to than those with h-BN. The optimal content of h-BN@Al2O3 solid lubricant was 5 vol%. In the friction and wear test, h-BN in h-BN@Al2O3 particles can be stripped to form a solid lubricating film on the material surface, which plays a good role in reducing wear and resisting wear. The crack healing ability of the self-lubricating ceramic tool material was studied by prefabricating cracks with a length of 400 μm on the surface. After a heat treatment at 700 °C for 60 min, the surface cracks of the ceramic tool material were completely healed, and the flexural strength was restored to 90% of that of the smooth samples. The oxidation of TiB2 and h-BN in ceramic tool materials is the main reason for crack healing.

Preparation of nano - coating powder CaF2@Al(OH)3 and its application in Al2O3/Ti(C,N) self-lubricating ceramic tool materials

Nano CaF2 particles of different sizes were prepared by direct precipitation. The diameters of nano CaF2 particles prepared in mixed solvent can reach 5–7 nm, and can be effectively dispersed. The surface of nano CaF2 was modified and coated by heterogeneous nucleation method. A shell layer of Al(OH)3 was coated on the surface of nano CaF2, and the structure and coating mechanism of the coated powder were analyzed. Under varying preparation conditions, the surface morphology of CaF2@Al(OH)3 was analyzed using TEM and SEM. The results showed that the coating powder showed good dispersion in mixed solvents, and the particle size of the composite powder was about 20 nm. Self-lubricating ceramic tool materials were prepared by adding coating particles to the Al2O3/Ti(C,N) matrix. The coating powder shell and the matrix material melt during sintering, so that CaF2 forms nanostructures in the particles. thereby improving the mechanical properties of the material. Cutting experiments show that the addition of coating particles can effectively reduce the temperature, cutting force and friction coefficient in the cutting process of the tool, thus improving the cutting performance of the tool material.

Investigation of Al2O3/TiB2 ceramic cutting tool materials with the addition of core–shell structured Ni–B coated CaF2

AbstractAl2O3 based self-lubricating ceramic tool materials with the addition of CaF2@Ni–B were prepared using the vacuum hot-pressing technique. The microstructure, mechanical properties and cutting performance of the material with different contents of CaF2@Ni–B were studied. Compared to its counterpart tool material without CaF2@Ni–B, the fracture toughness and flexural strength of the Al2O3/TiB2/(CaF2@Ni–B) self-lubricating ceramic tool materials increased by 40.5 % and 10.1 %, and the tool life increased by 25 %.

Influence of CaF2@Al2O3 on the friction and wear properties of Al2O3/Ti(C,N)/CaF2@Al2O3 self-lubricating ceramic tool

Abstract The Al2O3/Ti(C,N)/CaF2@Al2O3 self-lubricating ceramic tool materials with different CaF2@Al2O3 content were designed. The influence of CaF2@Al2O3 on the friction and wear properties of Al2O3/Ti(C,N)/CaF2@Al2O3 self-lubricating ceramic tool materials were studied. The results show that CaF2 as the core in Al2O3/Ti(C,N)/CaF2@Al2O3 self-lubricating ceramic tool material make the tool material have good lubricating ability, and Al2O3 as the shell will improve the wear resistance of the tool material. The friction coefficient of the Al2O3/Ti(C,N)/CaF2@Al2O3 self-lubricating ceramic tool materials with 10 vol% of CaF2@Al2O3 was 0.301, which was 90% lower than that of the tool material without CaF2@Al2O3. With the increasing of CaF2@Al2O3 content, the friction coefficient decreased, but the wear rate decreased at first and then increased a certain period later.

Preparation of Al<sub>2</sub>O<sub>3</sub> Based Nano-Micro Composite Gradient Self-Lubricating Ceramic Tool Materials

Aiming at the low mechanical property of existing self-lubricating ceramic cutting tool material, a new Al2O3 based nanomicro composite gradient self-lubricating ceramic tool material was developed by applying the design concept of nanomicro composite. The self-lubricating ceramics was composed of ceramic matrix and self-lubricating component, and was prepared by hot pressing technology at a hot-pressing temperature of 1650°C, pressure of 30MPa, and duration of 15min. The model of gradient ceramic tool material is symmetrical composition distribution, and the compositional distribution n and layer number are 1.8 and 7, respectively. The result shows that the interfaces between layers are bonded well and no cracks or defects can be observed. Compare with the homogeneous material, the flexural strength, hardness and fracture toughness of Al2O3 based graded material increase by 74%, 5.2% and 3.9%, respectively.

Finite element design and fabrication of Al2O3/TiC/CaF2 gradient self-lubricating ceramic tool material

Based on the idea of a functionally gradient material, the gradient self-lubricating ceramic tools were designed to solve the problem that the antifriction property and wear resistance of self-lubricating ceramic tools cannot be simultaneously considered. Physical, composition distribution, and micromechanical models were established. The finite element method was used to analyze the residual thermal stress of symmetrically distributed gradient ceramic tools with different compositional distribution exponent (n) values. When n=1.8, the stress gradient was small and the lowest value of the maximum Von Mises stress was obtained. An Al2O3/TiC/CaF2 gradient self-lubricating ceramic tool material with good mechanical properties was then fabricated by hot-pressing technique according to the optimum design results. Residual stresses were calculated by indentation crack method. Results showed that in the gradient self-lubricating ceramic tool material, compressive stresses were formed in the surface layers, whereas tensile stresses were formed in the middle layer, which were consistent with FEM-calculated findings.

Development of Multicomponent Graded Self-lubricating Ceramic Cutting Tool Materials

Aiming at the problem that homogeneous self-lubricating ceramic cutting tool materials are not available to possess rational combination of antifriction and antiwear properties, a graded self-lubricating ceramic cutting tool material is developed by applying the design concept of functionally graded materials. The new type of self-lubricating cutting tool material is characterized by the solid lubricant's decreasing distribution from the outer layers to the inner layers and the residual compressive stresses existing in the surface layers. A multicomponent distribution model is proposed. According to the model, Al2O3/TiC/CaF2 graded self-lubricating ceramic cutting tool material is compositionally designed and then is prepared by using the process of laminated padding and hot press in vacuum. The microstructure of the graded self-lubricating ceramic cutting tool material changes in accordance with the compositional distribution. Residual compressive stresses are formed in the surface layers. Compared with the corresponding homogeneous material, flexural strength, hardness and fracture toughness of the Al2O3/TiC/CaF2 graded self-lubricating ceramic cutting tool material are increased by 21%, 16% and 5.9%, respectively. The flexural strength is increased mainly because CaF2 in the material decreases from the surface layers to the middle layer. The improvement in the hardness and fracture toughness is attributed to the residual compressive stresses in the surface layers. Dry cutting tests are carried out on 45 steel with Al2O3/TiC/CaF2 graded self-lubricating ceramic cutting tool and the corresponding homogeneous cutting tool. Results show that wear resistance of the graded cutting tool is superior to that of the homogeneous cutting tool.

Preparation of TiB<sub>2</sub>/WC/h-BN Micro-Nano Composite Gradient Self-Lubricating Ceramic Tool Material

TiB2/WC/h-BN micro-nano composite gradient self-lubricating ceramic tool material was prepared by vacuum hot-pressing technique. The mechanical properties were tested and compared. The best flexural strength, fracture toughness and Vickers hardness of the tool material were 678MPa, 4.75MPa·m1/2 and 15.1GPa, respectively. The microstructure was analyzed by thermal field emission scanning electron microscope (SEM). TiB2 nanoparticles were obviously observed in the ceramic matrix. It suggested that the developed TiB2/WC/h-BN micro-nano composite gradient self-lubricating ceramic tool materials will have potential application in dry machining.

Effects of Nano-Al<sub>2</sub>O<sub>3</sub> on the Mechanical Property and Microstructure of Nano-Micro Composite Self-Lubricating Ceramic Tool Material

A new nanomicro composite self-lubricating ceramic tool material was prepared with vacuum hot pressing technique. The effect of nanoAl2O3 powders on the microstructure and mechanical properties of nanomicro composite self-lubricating ceramic tool material was investigated. With the increase of nanoAl2O3 content, the hardness and fracture toughness first up then down. When the nanoAl2O3 content is 4 vol.%, the flexural strength, hardness and fracture toughness reaches 562 MPa, 8.46 MPa·m1/2 and 18.95 GPa, respectively. The microstructure and mechanical property of nanomicro composite self-lubricating ceramic tool material can be improved by the grain refinement strengthening of nanoAl2O3.

The Design of Self-Lubricating Ceramic Tool Material

Chemical compatibility of self-lubricating ceramic tool materials, such as Al2O3/TiC/MoS2, Al2O3/TiC/h-BN, Al2O3/TiC/CaF2, were analyzed and calculated, and the results were verified by X-ray diffraction patterns. The optimal volume content of solid lubricant was calculated by the thermal stress theory under specific condition. The results show that under high temperature, there were some reactions in Al2O3/TiC/MoS2 and Al2O3/TiC/h-BN, while there were no reactions in Al2O3/TiC/CaF2. To Al2O3/TiC/CaF2, the optimal volume content of CaF2 is 25.1% under specific condition.

Research and Application of Finite Element Method on the Simulation of Graded Self-Lubricating Ceramic Tools

The introduction and application of common finite element method (FEM) about the modern metal cutting theory research was stated emphatically. Graded self-lubricating ceramic tool materials was briefly introduced, and problems existed about simulating the metal cutting process using FEM are pointed out and discussed in this study.

Development of Al<sub>2</sub>O<sub>3</sub>/TiC/CaF<sub>2</sub> Graded Self-Lubricating Ceramic Cutting Tool Materials

The design concept of functionally graded materials was first introduced into the development of self-lubricating ceramic cutting tool materials. An Al2O3/TiC/CaF2graded self-lubricating ceramic cutting tool material was designed and fabricated. Mechanical properties were evaluated by comparing with those of Al2O3/TiC/CaF2homogeneous self-lubricating ceramic cutting tool material. The results showed that the Al2O3/TiC/CaF2graded self-lubricating ceramic cutting tool material had superior performance to the counterpart. Graded self-lubricating ceramic cutting tool materials are bound to have promising prospect in the field of high speed dry machining.

State of the Art of Graded Self-Lubricating Ceramic Cutting Tool Materials

In this paper, the effects of addition of solid lubricants on mechanical properties, tribological properties and cutting performance of ceramic cutting tool materials were analyzed. The problem that existing homogeneous self-lubricating ceramic cutting tool materials were not available to possess rational combination of antifriction and antiwear properties was pointed out. The main methods to acquire graded self-lubricating materials were discussed. The design concept and research prospect of graded self-lubricating ceramic cutting tool materials were proposed, which would have promising applications in the field of high speed cutting.

Mechanical Properties and Microstructure of Self-Lubricating Ceramic Cutting Tool Materials

Al2O3/TiC ceramic tool materials with the addition of solid lubricants such as BN and CaF2 were produced by hot pressing. Effect of the solid lubricants on the microstructure and mechanical properties has been studied. Results showed that AlN phase resulted from the reaction of Al2O3 with BN was formed in Al2O3/TiC/BN composite after sintering. Significant micro-cracks resulted from the residual stress owing to the difference in the thermal expansion coefficient were found on the polished surface, and caused large mechanical properties degradation. While Al2O3/TiC/CaF2 composite showed higher flexural strength, fracture toughness, and hardness compared with that of Al2O3/TiC/BN composite owing its porosity absent and finer microstructure.