Ai Xing

Thermal shock behaviors of functionally graded ceramic tool materials

Thermal shock resistance of Al2O3–TiC and Al2O3–(W, Ti)C functionally graded ceramic tool materials with symmetrical structures were evaluated by water quenching and subsequent three-point bending tests of strength diminution. Comparisons were made with the results from parallel experiments conducted using homogeneous Al2O3–TiC and Al2O3–(W, Ti)C ceramic tool materials. Functionally graded cutting ceramics exhibited both increased critical temperature difference and increased strength retention properties compared to homogeneous cutting ceramics, indicating their higher thermal shock resistance. The experimental results were discussed and rationalized in terms of microstructural observations and the calculations of one-dimensional transient temperature fields and transient thermal stress fields in case of surface cooling by using the perturbation method. It was concluded that higher thermal shock resistance could be achieved by means of varying the compositional distribution and hence the resultant distribution of thermo-mechanical properties of ceramic tool materials appropriately. # 2003 Elsevier Ltd. All rights reserved.

Wear behavior and mechanisms of alumina-based ceramic tools in machining of ferrous and non-ferrous alloys

In this paper, the machining performance and wear mechanisms of two alumina-based ceramic cutting tools (Al2O3/TiB2 and Al2O3/TiB2/SiCw) in continuous turning of hardened steel and nickel based alloy (Inconel 718) were examined. Results showed that in turning of hardened steel performed under identical conditions, Al2O3/TiB2/SiCw tool exhibited lower flank wear resistance than that of Al2O3/TiB2 tool, the mechanisms responsible for this were determined to be the strong atom bonding between SiC and Fe, and the whisker pullout from the matrix for Al2O3/TiB2/SiCw ceramic tool. In continuous turning of Inconel 718, the Al2O3/TiB2/SiCw tool showed greatly improved flank wear resistance compared to Al2O3/TiB2 tool, adhesion and abrasion wear were found to be the dominant wear mechanisms, the adhesion and diffusion of Ni, and Cr of Inconel 718 to the tool rake face may accelerate the tool wear rates.

An analysis of unsteady thermal stresses in a functionally gradient ceramic plate with symmetrical structure

Abstract The analytical formulae of one-dimensional unsteady temperature field and unsteady thermal stress field for a functionally gradient material plate with symmetrical structure were derived by using perturbation method, by which the unsteady temperature fields and unsteady thermal stress fields of an Al2O3/(W,Ti)C functionally gradient ceramic plate with symmetrical structure were calculated in case of both surface cooling and surface heating. The results obtained showed that the absolute values of thermal stresses of the functionally gradient ceramic plate are lower than those of the homogeneous ceramic plate for both surface cooling and surface heating cases. Hence an approach to improving the thermal shock resistance of ceramic tool materials i.e. using functionally gradient ceramic tool materials, was put forward and verified by intermittent turning of hardened tool steel.

A study on the wear resistance of ZrO2/Al2O3 ceramic scissors for spinning and weaving

A new kind of zirconia matrix ceramic material (ZrO2/Al2O3) has been developed with 3Y-PSZ (3 mol% Y2O3 partially stabilized ZrO2) and the additive of alumina. The wear resistance of ZYA20 (3Y-PSZ+20 wt.% Al2O3) has been experimentally investigated compared with ZYA30 (3Y-PSZ+30 wt.% Al2O3) by the wear ring-block test. It is shown that the friction coefficients of ZYA20 and ZYA30 decrease with the increment of the applied load and the wear ratios increase with the increment of the applied load. It is also found that their wear mechanisms are plastic deformation, adhesive and abrasive wear, as well as stripping. The wear resistance of ZYA20 and ZYA30 are very good at low load and ZYA20 is stronger than ZYA30.

Simulation design for the composition of zirconia composite ceramic tool

The relationship between the fracture toughness increment (ΔKIC) resulting from toughening mechanisms, such as phase transition, residual stress, geometry effect, and grain bridging, and the volume fraction of zirconia was established to simulate and design the composition of a zirconia-matrix composite tool, thereby avoiding “trial-and-error” experiments. The composition of the ZrO2/Al2O3 ceramic tool was simulated in accordance with the requirement for fracture toughness. It was shown that the simulated result was in agreement with experiment and that the established simulation model was to some extent valid in predicting the composition of the zirconia-matrix composite ceramic tool with dispersed α-Al2O3. Thus, a new type of ceramic tool material, a ZrO2/Al2O3 composite, was developed by adding α-Al2O3 to ZrO2 on the basis of the results of the computer simulation.