Porous sintered bearings are of a metal structure containing a multitude of pores that are connected with each other and also with the surface. The pore volume incorporated in the bearings varies from about 10 to 40 vol%. This pore volume serves as strage for a fluid lubricant with which the part has been impregnated during its manufacture. In most applications, the lubrication is produced within the bearing itself.
This report is containing an outline of sintered porous bearings and introductions of writer's researches on the bearings and then, some suggestions on the progress of the bearings, in conformity with the writer's research life for about fifty long years.

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Fine-grained AZ91, ZK61 and WE56 magnesium alloys were processed by a powder metallurgy (P/M) method and mechanical properties of the P/M Mg alloys were investigated by tensile tests. The P/M Mg alloys showed high strength at room temperature and high-strain-rate superplasticity at elevated temperature. These excellent mechanical properties of the P/M Mg alloys are attributed to fine grain sizes less than 1μm.

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The forsterite-based ceramics doped with CaTiO₃ and MgAl₂O₄ was developed to decrease the temperature dependence of dielectric permittivity. Doping of CaTiO₃ into forsterite decreased the temperature coefficient of relative permittivity, TCε, and changed the sign of TCε. When 6mol% and 20mol% of CaTiO₃ was doped, the values of TCε were 104 and-129 ppm/K, respectively. However, the values of tan6 increased to 1.8×10^-3, and 3.6×10^-3, respectively, because of the nucleation of titanite crystals with larger dielectric loss. Further addition of MgAl₂O₄ lowered the value of tanδ as low as 4×10^-4. The decrease in tand may be attributed to the decomposition of titanite crystals by the reaction between spinel and titanite.

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The tool life in turning of the sintered steels becomes shorter than that in turning of the melted steels such as carbon steels. In order to clarify the effective tool materials for the turning of the sintered stainless steel, the tool wear is experimentally investigated. The sintered stainless steel was turned with the various tool materials at the cutting speed from 1.67m/s to 5 m/s. The main results obtained are as follows: (1) In the conventional tool materials, the cemented carbide tool (coated by TiVN PVD) is the most effective tool material for the turning of the sintered stainless steel. (2) In the three kinds of CBN tools, the tool wear of the CBN tool with TiN binder increases slower than those of the CBN tool with Al₂O₃, TiC binder. (3) The CBN tool with TiN binder gets a better surface finish than the CBN tool with Al₂O₃ binder. Therefore, the CBN tool with TiN binder is the most effective tool material for the turning of the sintered stainless steel.

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Heat generation, piezoelectric property and fracture of PZT ceramics were investigated applying a large pulsed input power. Heat generation in low-Q_m material was larger than in high-Q_m one. Nonlinear phenomena were revealed in low-Q_m material at high voltage power. The values of k₃₁ were roughly constant, Q_m values decreased with increasing driving time. Applying a pulsed input power, however a fracture was suppressed in low-Q_m material.

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In the preparation of magnetite sintered body which is the ferrite magnetic material, there are problems such as a high temperature at 1500°C, sintering under decompression or vacuum. Therefore, in this study, magnetite powder derived from the oxalic acid iron by the liquid phase sedimentation using iron chloride and ammonium oxalate was sythesized. Subsequently, a small amount of boric acid [H₃BO₃] was added to the powder, and magnetite powder compact was produced. Examination of the sintering condition by TMA and preparation of the sintered body under a CO₂ atmosphere using horizontal electric furnace were carried out, and effect of additives on the characteristics of the sintered body was investigated in detail.

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Amorphous Se_100-xTe_x powders (x=0, 5, 10, 15 and 20) have been produced by mechanical alloying (MA). The time-of-flight neutron scattering measurement was employed in order to elucidate the short range structures for these powders. Well-resolved first peak in radial distribution functions can be decomposed into two Gaussian peaks, which correspond to the Se-Se and Se-Te correlation. The coordination number teaches us that amorphous Se has a lot of dangling bonds due to broken of Se-Se bond by milling. However, the compositional changes of the coordination numbers of Se-Se and Se-Te pairs for Se-Te powders imply that Te atoms are bonded to the edge of Se chain molecules and the twofold chain structure is built up with increasing Te content.

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The effects of the addition of boron (B) and silicon (Si) on mechanical properties of P/M SUS630 stainless steels were investigated. As a result, the addition of B is effective to the densification of microstructure, and the maximum relative sintered density (98.2%) is obtained in the P/M steel with 0.2mass%B sintered at 1573 K. By the simultaneous addition of B and Si, the sintering temperature obtained the maximum density is lower than that of the single addition of B about 50 K. The addition of Si is effective to obtain high strength and hardness. This may be due to the solid solution strengthening by Si to the matrix. But the excessive addition of Si (over 2 mass%) makes the P/M steels brittle. Tensile strength and Rockwell hardness of P/M steels with 0.2mass%B and lmass%Si, which was sintered at 1523 K and heat treated, were 1230MPa and 43HRC respectively. These values of the P/M steel are similar to those of wrought SUS630 steel. On the other hand, the ductility was not improved by the addition B and Si. This result may be due to grain coarsening, precipitation of borides and hardening of matrix by Si during liquid phase sintering.

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The influence of the raw powder characteristics and compacting condition on the solid-state synthesis of Mg₂Si from elemental Mg-Si mixture powder has been examined by thermal analysis using DSC thermogram. The Mg₂Si synthesis progresses at the lower temperature range when employing the fine Mg powder, because of the increase in the contacting area between the Mg and Si particles. In employing fine Si powder, the endothermic heat due to the appearance of liquid phase of Mg at 920 K decreases remarkably. MgO film, covering the Mg powder surface, prevents the Mg₂Si synthesis due to its thermal stability, however SiO₂ surface film is not so effective because of the deoxidization by Mg during heating. Concerning the effect of the compaction pressure, when the hard Si particles are embedded in the Mg powder after compacting the mixture powder, the mechanical breakage of the thermally stable MgO surface film occurs. Therefore, the enlargement of the contacting clean area between Mg and Si particles causes the progress of the Mg₂Si synthesis at the lower temperature.

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In order to control the primary recrystallization textures of pure molybdenum (pure Mo) and molybdenum-0.5mass% Ti-0.1%Zr-0.5%C alloy (TZM alloy) sheets, the effects of heating rates during annealing on the development of recrystallization texture were investigated by means of X-ray diffraction and line broadening techniques. Recrystallization at a rapid heating rate produces a texture which is substantially similar to the rolling texture in both pure Mo and TZM alloy sheets, i.e. a ({100} <011>+{111} <uvw>+{211} <011>) type texture. While recrystallzation at a slow heating rate produces a texture which is significantly different from the rolling texture in both sheets, i.e. a strong {111} <112> type texture. Changes in the primary recrystallization textures of both molybdenum sheets which were brought about at different heating rates are considered mainly to arise as a result of the difference in the orientation dependence of degree of recovery for the deformed fine structures (potential nuclei of recrystallization).

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A lithium-manganese spinet was synthesized by hydrothermal method in mixed lithium-alkaline aqueous solution. It was confirmed that the mixed lithium-alkaline aqueous solution dissolved with Li-salt (LiC1, Li₂SO₄, LiNO₃) and ROH (LiOH, NaOH, KOH) was excellent reaction environment for hydrothermal synthesis. The obtained lithium-manganese spinet showed analogous electrochemical behavior to the calcined spinet.

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A high-energy-ball-milling process was applied to the synthesis of the Rb₄Cu₁₆I₇Cl₁₃ crystalline phase, which was known to show high Cu⁺ ion conductivity 3.4×10¹Sm^-1 at room temperature. CuCI, Cul, and RbCl were used as raw materials for the mechanical synthesis of the Rb₄Cu₁₆I₇Cl₁₃ phase. The ball mill treatment of the mixture of the raw materials more than l0h led to the formation of the Rb₄Cu₁₆I₇Cl₁₃ crystalline phase. The obtained Rb₄Cu₁₆I₇Cl₁₃ crystals showed high ion conductivity more than 10¹ Sm^-1 at room temperature, and the conductivity increased with an increase in milling time and reached a constant value of 1.8 x 10¹ Sm^-1 at 298 K for the sample ball-milled more than 20 h. The electronic polarization measurements with Wagner's methods suggested that main carrier of the electronic conduction of the ball-milled sample was positive hale and that the hale conductivity was 1.2×10^-11 Sm^-1 at 273 K. These measurements indicated that the Cu⁺ ion transport number of the sample was almost unity.

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Recently, a number of amorphous alloys having a temperature range of supercooled liquid above 50K before crystallization and high glass-forming ability have been discovered. The new amorphous alloys are called "bulk metallic glasses". Such metallic glasses can be fabricated from the melt in a bulk form with a thickness of-10mm at slow cooling rates of the order of 1-100 K/s. The metallic glasses, moreover, exhibit useful properties such as high strength and high stiffness at ambient temperature. We have found that the metallic glasses exhibited high-strain-rate superplasticity at temperatures above the glass transition temperature. The superplasticity inherent in the supercooled liquid seems to give a unique approach for the synthesis of bulk metallic glasses by powder metallurgy processing. We, therefore, tried to consolidate the metallic glass powders using the superplasticity. We consequently succeeded in synthesis of bulk metallic glasses with the same tensile strength as the cast bulk glassy alloy and melt-spun metallic glass ribbon. Recently, the bulk metallic glasses produced by extrusion of gas-atomized glass powders have been commercially used as a face material of newly designed "iron"-type and "patter"-type golf club heads.

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The imide powders of Si-C-N-H system were formed by liquid phase reaction in SiCl₄-CH₃SiC1₃-NH₃ or SiCl₄-(C₂H₅)₂NH system in n-hexane and decomposed at 900°C in vacuum to amorphous powder of Si-C-N system. The powders were heat-treated in N₂ at 1400-1800°C. Si₃N₄ was crystallized above 1500°C and SiC was formed at higher temperatures. The formation temperature of SiC lowered with an increase of the carbon content in the synthesis system. The SEM-EDX indicated that the detected carbon content was small, when Si₃N₄ phase was predominant, and increased according to SiC formation at high temperatures. This means that carbon may be included inside Si₃N₄ particles, reacting with Si₃N₄ to form SiC at higher temperatures. This results suggests that Si₃N₄-SiC composite can be fabricated from the Si-C-N amorphous powder by optimizing starting materials and heat treatment condition.

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Fe₆₅Co₁₀Ga₅P₁₂C₄B₄ glassy alloy powders were produced by high pressure Ar gas atomization of Fe₆₅Co₁₀Ga₅P₁₂C₄B₄ alloy ingot prepared by induction melting. The glass transition temperature (T_g), supercooled liquid region (ΔT_x(=T_x-T_g)) of the glassy alloy powders are 730K and 50K. The glassy alloy powders have ferromagnetism with a Curie temperature (T_c) of 640 K and exhibits saturation magnetization (I_s) of 1.18 T. No appreciable difference in the thermal stability and magnetic properties is seen between the glassy alloy powders and the melt-spun ribbon. By spark-plasma-sintering (SPS) these glassy alloy powders under the pressure of 80 MPa and at the temperature of 723 K below T_g, a bulk glassy Fe₆₅Co₁₀Ga₅P₁₂C₄B₄ alloy with a size of 20 mm in diameter and 5 mm in thickness was synthesized. Its relative density was about 96%. There was also no appreciable difference in the thermal stability between the bulk glassy alloy and the glassy alloy powders. This bulk glassy alloy exhibited saturation magnetization (I_s) of 1.19 T and coercivity (H_c) of 115 A/m.

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