Gradient Design And Application Of Self-lubricating Ceramic Tool Material

The idea of functionally gradient material was used to design self-lubricatingceramic tools based on the problem that the antifriction property and wear resistance ofself-lubricating ceramic tools can’t be reasonably concerned simultaneously. Thegradient self-lubricating ceramic tool material was fabricated by hot-pressingtechnique according to the optimum design result, and the mechanical propertiesmicrostructure and residual stress were detailed studied.The Al₂O₃/TiC/CaF₂composites and the Al₂O₃/（W,Ti）C/CaF₂composites weredetermined based on the physical and chemical compatibility analysis, meanwhile thethermophysical properties of different layers were calculated. The physical,composition distribution and micromechanical models of gradient self-lubricatingceramic tool were established. By means of the finite element method the residualthermal stress of symmetrically distributed gradient ceramic tools with differentcompositional distribution exponent n and layers were analyzed. Results showed thatthe fabricated gradient ceramic tool material formed compressive stresses in surfacelayers, while tensile stresses were formed in the middle layer. The optimumcompositional distribution n and layer number were proposed as1.8and7, respectively.In the condition of this, the maximum radial compress stress reached117.6MPa andthe maximum Von Mises stress was119.3MPa.By means of the finite element method the residual thermal stress ofsymmetrically distributed gradient ceramic tools with different thickness, differencethermal expansion coefficient and compositional distribution exponent n, differencethermal expansion coefficient and Young’s modulus were analyzed. Results showedthat after the thicken of the first layer, the maximum radial tensile stress increased, themaximum radial compress stress decreased and the maximum Von Mises stress alsoincreased. The value of stresses according to the stress curves had a certain relativeerror with the values of finite element method, the relative error of the maximum radialcompress stress was in the range of0.5%-1.4%, and the relative error of the maximumradial tensile stress and the maximum Von Mises stress were between4.7%-8.2%,4.0%-7%, respectively. But the trend of these two methods was the same.The gradient self-lubricating ceramic tool materials with different distributionexponent n and composites were fabricated by hot-pressing technique. The mechanicalproperties of gradient self-lubricating ceramic tool materials were measured and the microstructure of gradient self-lubricating ceramic tool materials was studied. And theresidual stresses were measured by the indentation method compared to whichcalculated using the finite element method. Results showed that: to the Al₂O₃/TiC/CaF₂composites, hardness and fracture toughness were higher relatively and were12.71GPaand3.86MPa·m^1/2when distribute exponent n was1.8. And to the Al₂O₃/（W,Ti）C/CaF₂composites, hardness and fracture toughness reached15.36GPa and4.02MPa·m^1/2,experiment results coincide well with that calculated with finite element method. Thelayered architectures can be clearly seen and the interfaces are straight andwell-distinguishable, the interfaces between layers are bonded well and no cracks ordefects can be observed. The results obtained from the indentation method have asimilar trend with the finite element results; and the relative error is in the range of5.7%-12.6%. It suggests that the finite element method can effectively and efficientlybe used to calculate the residual stress of the gradient self-lubricating ceramic toolmaterial without measure by experiments.