Cast iron is widely used for the sliding parts of automobile parts such as cylinder bores, piston rings and break-disks. Reasons for this are ease of forming of parts with various shapes and high wear resistance. However, tribological conditions become harsher and harsher the higher is the performance of engines. In such conditions, cast iron lacks sufficient wear resistance without surface improvement.
  In this study, the surface modification of cast iron by laser melting and alloying was carried out to obtain higher wear-resistant surface; the modified microstructure was investigated and tribological properties were tested by demonstrating the tribo-system between the cylinder bore and piston ring.
  Surface modification of cast iron by laser alloying of Mo or W formed ledeburite-like matrix, martensite islands and fine MC-carbide deposits. A hardness of Hv 950-1150 was obtained. Alloying of V formed martensite matrix and fine VC-carbide deposits. A hardness of Hv 800-900 was obtained. V-alloyed cast iron with laser irradiation showed excellent tribological properties. The wear amounts of both the plate and pin were extremely low and the scuffing resistance extremely high. This is because of the high density of the VC-carbide deposits and the moderate hardness of the matrix; the relationship between these factors of the modified microstructure and the tribological properties was shown theoretically.

抄録全体を表示

  In the attempt to improve the high temperature wear resistance of white cast iron, a cermet powder layer mixed with Ni or Cr powder was inserted by a molten 27mass% Cr white cast iron, as hard facing treatment. High temperature wear resistance of the inserted layer was examined by means of high temperature compressive impact fatigue test. Effects of the testing load, waveform, frequency, and impact number in the test on the wear of the white cast iron specimen were investigated. It was found that the testing load had a major influence on the test, while the waveform and frequency had none. Secondly, the inserted layer with 50 vol.%Ni or 50 vol.%Cr powder was tested under a load of 20 kN for temperatures ranging from room temperature to 873 K. The wear resistance decreased with increasing test temperature for all inserted layers. The impact compression characteristic of the cermet layer with 50 vol.%Cr powder was the highest in the whole testing temperature range. However, the inserted layer with 50 vol.%Cr powder showed many cracks connecting with micro pores and voids after the compressive impact test. To raise the impact compression characteristic of the inserted layer, it is thus important to construct a sound inserted layer free from micro pores and voids by controlling the size and shape of the cermet powder.

抄録全体を表示

  Ni-Al intermetallic compounds were coated onto spheroidal graphite cast iron (FCD450) surface using combustion synthesis. In this paper, the phase structure and oxidation resistance of the coating layer were investigated to evaluate the influence of post-coating heat treatment on the coating layer. Post-coating heat treatment resulted in the reduction of the unreacted phase and formation of a nearly single-phase Ni₃Al. The coating layer well-adhered to the FCD450 substrate by heat treatment. Porosities, which are peculiar to combustion synthesis, were observed mainly at the surface of the coating layer. The amount of porosity decreases as the hot-press temperature rises. The oxidation resistance of the heat-treated coatings was found to improve in comparison with the coatings before heat treatment. Heat-treated coatings are superior to FCD450 in oxidation resistance. Accordingly, Ni-Al intermetallic compound coatings were confirmed to be effective in improving the oxidation resistance of the FCD450 substrate.

抄録全体を表示

  Effects of remelting by electron beam on the fatigue strength of Al-12Si-4∼19Cu-2Ni-1Mg-0.5Mn alloys cast in metal mould were investigated at 573 K and the room temperature. Remelting by electron-beam results in higher fatigue strength of Al-Si-10∼19 mass%Cu-Ni-Mg-Mn alloys than that of the 4 mass%Cu containing alloy at 573 K. On the other hand this remelting did not improve fatigue strength for these alloys at room temperature. This is because large amounts of CuAl₂ intermetallic compounds prevent fatigue crack progressing at high temperature, whereas cleavage fracture of CuAl₂ intermetallic compounds occur as the crack progresses at room temperature.

抄録全体を表示

  Bending properties of cast iron are considered to be affected by work hardening and residual stress formation in the surface layer caused by blasting to remove molding sand from the casting surface. However, the influence of the blasting on the bending properties of cast iron have yet to be investigated and very few studies have been performed on residual stress distribution in the blasted surface layer. In this present work, the residual stress distribution in a shot blasted surface layer of ferritic spheroidal graphite cast iron and the bending properties were investigated. The surface was work hardened up to 260∼290 Hv from 200 Hv by blasting and a deeper work hardened region was formed by the blasting with increasing shot size. Shot blast caused compressed residual stress in the surface layer and the maximum residual stress value was more or less the same for different shot sizes. The residual stress distributed region corresponded with the work hardened region and the region deepened with the increase of the shot size. Fractured bending deflection was very small after blasting but the bending deflection was restored to the non-blasted state by stress relief annealing.

抄録全体を表示