EFFECT OF GROUNG SURAFACE LAYER ON BENDING STRENGTH OF STRUCTURAL CERAMICS

研究了磨削表面层对结构陶瓷（Al_2O_3、SiC、Si_3N_4和ZrO_2）抗弯强度的影响。主要结果如下。(1)产生残余压应力的塑性变形主要是由磨粒的抛光作用引起的。抛光的效果减少，在材料去除过程中的断裂幅度的增加，压缩残余应力较大的陶瓷具有较高的抗弯强度，但较小的那些具有较高的硬度在常规磨削条件下。(2)残余压应力的深度可以从球形压痕所获得的塑性变形区中估算出来，该塑性变形区与磨粒的抛光作用类似。(3)用X射线测量陶瓷的残余压应力，即使在较浅穿透的特征X射线作用下， ...更多信息 使用离子深度。这是因为X射线的有效穿透深度与压缩应力存在的深度相比不够浅。(4)陶瓷粉的抗弯强度的劣化程度取决于断裂韧性和相变能力：Si_3N_4的劣化程度较高，而ZrO_2的劣化程度较低。(5)通过在Si_3N_4中退火，降低了的抗弯强度得到了很大程度的恢复。这表明裂纹愈合效应克服了残余压应力消除的缺点。另一方面，ZrO_2的退火使研磨试样的强度下降。(6)对球形压痕的弹塑性应力场进行了有限元分析，并对压痕应力场中的裂纹进行了断裂分析，结果表明，压痕在不扩展裂纹的情况下，可以产生塑性变形。这意味着可以在不降低强度的情况下进行研磨。(7)用新方法统计得到的磨粒切削深度可用于估算磨削裂纹扩展长度和磨削残余应力。少

Effect of ground surface layr on bending strength of structural ceramics (Al_2O_3, SiC,Si_3N_4, and ZrO_2) was investigated. The main results were as follows.(1) Plastic deformation causing the compressive residual stress was mainly generated by the burnishing action of abrasive grains. The effect of burnishing diminished with an increase in the magnitude of fracture during the material removal ; the compressive residual stress was larger in the ceramics with higher bending strength but smaller in those with higher hardness under conventional grinding conditions.(2) The depth of the compressive residual stress can be estimated from the plastic deformation zone obtained by the sphere indentation which gives an analogous effect to the the burnishing action of abrasive grains.(3) The compressive residual stress of ceramics measured by X-ray is estimated to be considerably smaller than the peak stress realy existing in the surface layr even if the characteristic X-ray of shallower penetrat … More ion depth is used. This is because the effective penetration depth of the X-ray is not sufficiently shallow in comparison with the depth where compressive stress exists.(4) Deterioration of bending strength of ground ceramics varied depending upon fracture toughness and phase transformability : the deterioration was higher in Si_3N_4 but lower in ZrO_2.(5) The bending strength deteriorated was considerably recovered by annealing in Si_3N_4. This implied that crack healing effect overcame the disadvantage of elimination of compressive residual stress. On the other hand, the annealing of ZrO_2 rather deteriorated strength of ground specimen.(6) The finite element method analysis of elasto-plastic stress field in a spherical indentation and the fracture analysis of pre-existing crack in its stress field showed that plastic deformation could be caused without any crack extension. This implied that grinding could be carried out without strength deterioration.(7) Grain depth of cut which was statistically evaluated by newly developed method could be applied to estimate crack extension length and residual stress caused by grinding. Less