Matsuo Miyazaki

Fabrication of tungsten/copper graded material

Abstract A tungsten/copper graded materials is developed as a new material against plasma, ion beams, electron beams, etc. The fabrication process of the tungsten/copper graded material is newly established by sintering and an infiltration technique. It is very useful for combining two materials with a considerable difference in melting point, such as a combination of tungsten and copper. In this paper, the process conditions for preparing the tungsten/copper graded material is established. The ability to reduce thermal stresses in the tungsten/copper graded material is confirmed by heat-cycle testing in comparison with a tungsten-to-copper lamination prepared by brazing.

Strength Properties of Yttrium-Oxide-Dispersed Tungsten Alloy.

The microstructure of an yttrium-oxide-dispersed tungsten alloy, newly developed, was investigated by examining the effect of sintering temperature on the particle size of yttrium oxide and the crystal size of tungsten. Also, it was confirmed that the bending strength of yttrium-oxide-dispersed tungsten alloy was affected by the sintering temperature in comparison with a sintered tungsten sample. The residual stress, induced by the coefficient of thermal expansion mismatch, is analyzed for the tungsten matrix composite with a particle of yttrium oxide using the finite element method. Because of the high residual stress, particles of yttrium oxide become crack initiation sites under the fabrication process. Finally, it is also shown that the bending strength of yttrium-oxide-dispersed tungsten alloy can be estimated simply by the fracture mechanics approach, based on the assumption of a flaw introduction effect by the yttrium oxide dispersed.

Development of Integral High-Pressure—Low-Pressure Combination Rotor Forgings

Integral high pressure (HP)-low pressure (LP) combination rotor forgings for single-cylinder turbines used under the steam condition over 773 K require good toughness and elevated temperature strength. Conventional Ni-Cr-Mo-V or Cr-Mo-V steel forgings are undesirable from the viewpoint of material properties. We developed integral HP-LP combination rotor forgings by alloy modifications (niobium and nickel addition) based upon Cr-Mo-V steel and the application of differential heat treatment. An actual dimensional prototype sample forging (1650 mm in diameter) was manufactured and evaluated. The forging exhibited high quality, and superior creep rupture strength at the HP zone and excellent toughness at the LP zone were obtained simultaneously. These developed rotor forgings have been applied for several turbine units of about the 100-MW class.