Search

Compairing the literature values of fracture toughness of various materials revealed that the value of the same kind of material scatters largely, depending on the authors or measuring ways, but that the temperature dependence is very small and almost common, particularly in the range RT through 1, 200 °C, for most ceramics in spite of the large scattering in the absolute value. The temperature coefficient, (-(dKIc/dT)/KIc(RT)), is(-2. 1-1.6)10-5/K for SiC ceramics, and(0-1.3)10-4/K for Si3N4. The unexpectedly small temperature dependence was explained on the basis of the dependence of the surface free energy, rs.which was found to be approximated by the empirical formular (-(dγs/dT)/γso = 1/(2.1Tm) ; Tm is melting or sublimation point ) and that of Young's modulus, E. On this basis, the value of KIc at 1, 600 °C is expected not to be less than 70% of the value at RT, if the material is not affected by low heat resistant boundary material. Furthermore, the literature values are found to be 2 to 6 times larger than the ideal value calculated from (2γsE)1/2. This large value is related to the generation of rough fractured surface.

Significance of the constitutional size in the composites having the constitution of nanometer size (Nano-Composites) was emphasized. Every Nano-Composite should have two critical values, the upper limit and the lower limit, for the dimension of the constitution to posses the distinguishable property as Nano-Composite. The critical values depend on the property expected for the composite. The values were estimated or re-viewed on various basis which are thought to be useful for each property, such as cata-lytic activity, magnetism, optical property as well as mechanical one. For examples: The range of the binding force acting across the surface of solids was estimated from the surface free energy and the ideal strength, which gives the critical value in general expression for the constitutional dimension and also for one basic aspect of catalitic activity. The values are about 7 nm(Si3N4), 4 nm(SiC), 4 nm (Al), 2 nm(Fe), 2 nm(W) and 3 nm(Pt). The value is very small for oxides, 0.5 nm(Al2O3) and 0.4 nm(MgO) probably due to screening effect on the surface. As to magnetic properties, 100 mn for super paramagnetism's occurrence and 20 nm for making the originally hard magnetic material soft one. Optically, the value is about 50 nm for reflective intex change. Mechanically, it is about 100 nm for strengthning or restricting dislocation movement. Some improved properties, which could be expected or have been realized, are described in the relation with the critical values.

Originally incompatible blends of SAN 30% and PC 70% were extruded with extremely high shear rate up to 107 s-1 as a typical example of the blends. The.blends are of binary systems microscopically in the first run of extruding, where SAN is present as small spherical particles in PC matrix. The apparent volume fraction of the spherical SAN estimated from the microscopic photographs decreases with the shear rate. The fraction is decreased also with the repeated runs. The blend appears uniform or structureless at the fifth run. Dynamic loss tangent gives two peaks corresponding to T ?? of SAN and PC, respectively. The latter shifts to lower temperatures with the number of extruding run. It is considered that some of SAN is mixed with PC in a compatible form. The pulsed NMR analysis supports the conclusion.

The critical grain size, below which the properties of the composites could be much different from those of the conventional composites, was estimated on the basis of the ideal strength and the specific surface energy. It is about 2nm-4nm for normal metal (Fe, Co), less than 1nm for oxides (Al2O3, MgO), and about 10nm for Si3N4, which suggests Si3N4 is one of the most advantageous materials for Nanometer Composites.

Ideal Strength, aid as a function of temperature was found to be approximated by the following formula:σid≥σid=∫TxT3αE/(1-2μ)dT=3αE(Tx-T)/(1-2μ)where Tx stands for the minimum value of transformation points (melting, sublimation, solid to solid, and brittle to ductile), and α, E, μ respectively for the coefficient of linear thermal expansion, Young's modulus and Poisson's ratio. The formula's error is less than 20%, expressed in the term of error compared with whisker's strength at RT. It was also compared with literature data on high temperature strength of sapphire monofilament, which proved the compatibility of the formula.σid is estimated as 9 GPa for SiC and 3.5 GPa for Si3N4 at 1, 400°C, 1 GPa at 2, 200°C for SiC, and 1 GPa at 1, 700°C for Si3N4. These values prove the usefulness of the materials as high temperature gas turbine components. The formula tells also us that the ideal strength can be well approximated by a straight line regardless of material.The Young's modulus plotted against temperature can be converted to Young's modulus plotted against strain, e, by using e=3∫α/(1-2μ)dT, which can not be given directly from experimental measurement due to the occurrence of fracture in the material. The tangent of the curve for MgO was proved to agree well with the value given by a classical solid state theory. The range of binding force acting across material surface was estimated by using the ideal strength, giving 0.5-1 nm for SiC and Si3N4 and 0.1-0.5 nm for MgO and Al2O3. The allowable atomic distance difference between neighboring layerd material in coherently multilayered films, which has no defect was also estimated to be less than 3% from the ideal fracture strain.

In the present study, we investigated deposition of diamond films on both Si substrates pre-treated with diamond powder by an ultrasonic vibrator and also further ion-implanted. The pre-treatment with diamond powders increased a density of diamond nucleation on Si substrate by five-order of magnitude against to the untreated substrate. 280keV Ar+ ion implantation at 90K to the pre-treated substrate significantly reduced the density of the diamond nucleation while the implantation at 773K scarcely affected the density. It is proposed that healing of micro-flaws, which are thought to work as the nucleation sites, is an important mechanism to reduce the diamond nucleation density by ion implantation.

Masao Kohzaki, Shoji Noda. Haruo Doi and Osami Kamigaito : Improvement of The Tribological Properties of Ceramics by Si Film Deposition and Ion Irradiation.We studied the tribological properties of surface modified SiC ceramics with a pin-on-disk friction and wear tester in an ambient atmosphere without oil lubrication. The friction coefficient between Si film deposited SiC(Si/SiC) and a diamond pin was about 0.05, which was smaller than one half of that between SiC and a diamond pin. The low friction state of Si/SiC lasted for 40 hours when the Si/SiC was irradiated with Ar+ ions. Ar+ ion irradiation was also effective for reducing the wear. Effectively no wear was detected in Si/SiC irradiated to the dose over 5 × 1015 ions/cm2.

Silicon nitride ceramics were implanted with 200 KeV Cr+ ions and then oxidized at temperatures from 1273 to 1473 K in air. The oxidation scales were examined by RBS, XRD and SEM methods. At temperatures up to 1373 K, in the Cr+-implanted ceramics, the implanted Cr atoms were predominantly oxidized to Cr2O3, which resulted in a reduction of the oxidation of Si4N4 to SiO2, and then the diffusion of impurity cations through the grain boundary to the surface oxide (SiO2) was also retarded. For the oxidation at 1473 K, there was little difference in oxidation behavior between the implanted specimen and the unimplanted one. But the preoxidation at 1273 K of the implanted specimen was found to give the implanted specimen a little better resistivity against the oxidation at 1473 K.

Crystalline phase transformation from α-phase to ω-phase(high pressure phase) was found to occur in Zr thin film on sapphire when it was irradiated with N+ or Ar+ions at low temperature. Ion irradiation at ambient temperature caused only grain growth of the α-phase. The ω-phase formation is tentatively attributed to crystal growth in collision cascade under large compressive stress which was generated by preceding irradiation.

Sapphire plates whose strength was degraded previously by Vickers indentation were irradiated with 300 keV Ni+ or 400 keV Mn+ ions, and the strength recovery was studied as a function of ion dose. Also the strength degradation by Vickers indentation in sapphire plates irradiated previously with 400 keV Mn+ ions to the dose of 5×1017 ions/cm2 was studied to evaluate the resistivity to the crack initiation due to point contact stresses.The strength of sapphire plates which were degraded previously to about 50% of the original strength was recovered to about 90% of the original strength of the sapphire by Ni+ or Mn+ ions irradiation of the dose of 5×1017 ions/cm2.The crack initiation by Vickers indentation was largely retarded by ion irradiation to the sapphire specimen. The retardation was attributed to the presence of amorphous layer made by Mn+ ions irradiation.

Fiber orientation induced during injection mold filling of fiber filled thermoplastics causes material properties to be anisotropic and molded parts to warp. Predicting fiber orientation is important for parts and mold designs to produce sound molded parts. A computer program has been developed to predict planar fiber orientation in thin walled molded parts by using Folgar and Tucker's orientation model for concentrated suspensions. Computed result was compared with experimental one for an injection molded square plate of glass fiber reinforced polypropylene.

400KeV Ag+ ions were irradiated to the (100) surfaces of 9.5m% Y2O3 stabilized ZrO2 with the doses ranging from 5×1015 ions/cm2 to 5×1017 ions /cm2 at room temperature in order to investigate the correlations between the state of implanted Ag and the suppression of crack initiation.1) Ag precipitated as particles in orienting the (200) face of Ag. The sizes of the Ag particles were ranging from 2nm(5×1016ions/cm2)to 11nm (5×1017ions/cm2).2) Knoop hardness of the surface of ZrO2 increased by about 20-30% by Ag+ ion-irradiation at the doses less than 5×1016ions/cm2 and decreased at the doses larger than 1×1017ions/cm2.3) Vickers indentation crack at a loads of 0.25N was completely suppressed in the surface of ZrO2 irradiated to a dose of 5×1017ions/cm2.4) The suppression of the crack initiation may be ascribed to the influence of the nanometer composite layer containing max. 23at% Ag.

Flow analysis has been studied in plastic injection molding. It can predict defects in the filling process with computer. The computer simulation has been used for mold design. This paper describes mold filling theory and our experience with a flow analysis program, "IMAP-F".

Formula to estimate the ideal strength of brittle material was derived from the consideration of the relationship between the fracture under uniform tensile stress and the transformations of the material, sublimation, melting and solid to solid transformation. The validity of the formula was examined by comparing the ideal strength with the fracture stress of whiskers. The accuracy of the formula was within ± 30% for the material whose ionicity is less than 50%. The fracture stress of the whisker whose ionicity is more than 50% is about 1/3 to 1/5 of the value given by the formula. The discrepancy in the ionic materials seems to come from the possible occurence of shear fracture in the materials. From the formula, mullite is concluded that it would have the fracture stress similar to silicon nitride.

Interface of N+ion-irradiated Zr/SiO2 was examined by the XPS method combined with Ar+ion sputteretching. The ion irradiation was found to form a diffusion layer at the interface and to generate chemical bonds like Zr-Si and Zr-O-Si in the diffusion layer. The diffusion layer was inferred to be an atomically mixed phase of Zr, Si, O, and N atoms rather than a mixed phase of Zr and SiO2.

SiC ceramics, the one deposited with niobium metal film (Nb/SiC) and Ar+ ion-irradiated Nb/SiC were subjected to a pin-on-disk friction and wear test in an ambient atmosphere with a diamond pin for 40 hours. The friction coefficient between SiC and diamond pin was about 0.1. The Nb film deposition reduced the friction coefficient and it was about 0.04 with the normal load of 1000 gf. The wear of SiC was also reduced to one seventh by the Nb deposition. The Ar+ ion-irradiated Nb/SiC was found to have very high wear resistivity and effectively no wear was detected in the samples irradiated to the doses over 5×1015 ions/cm2.

The interface of the Zr/sapphire implanted with N+ ions were examined by RBS and cross-sectional TEM observations. The ion implantation induced the interdiffusion of atoms at the interface and the clear border-line between the Zr film and sapphire was found to disappear. The thickness of the diffusion layer was estimated to be about 10 nm at the interface of the Zr/sapphire implanted with N+ ions to the dose of 2×1017/cm2.