INCREASE IN MECHANICAL STRENGTH OF NI-SI-B AMORPHOUS-ALLOYS BY DISPERSION OF NANOSCALE FCC-NI PARTICLES

Ni-base amorphous alloys with the homogeneous dispersion of nanoscale fcc-Ni particles have been produced in the composition range of 5 to 14 at%Si and 7 to 15%B. The particle size and interparticle spacing are 10 and 20 nm, respectively. The alloys exhibit tensile fracture strength (sigma(f)), Young's modulus (E) and hardness (H(v)) which are higher than those of the corresponding amorphous single phase alloys, accompanying an increase in fracture elongation (epsilon(f)). The highest values of sigma(f), E, H(v) and epsilon(f) in the mixed phase state of Ni-Si-B alloys, i.e., 3400 MPa, 130 GPa, 960 and 2.7%, respectively, are found for Ni81Si10B9. Addition of Cr increased sigma(f) and epsilon(f), their highest values being 3900 MPa and 3.8%, respectively for (Ni0.81Si0.1B0.09)97Cr3. The increase in sigma(f) by the dispersion of the fcc-Ni particles is presumably because the fcc-Ni particles are higher in mechanical strength than the amorphous phase because of the absence of internal defects and can act as a barrier to suppress the shear deformation of the amorphous matrix. The increase in epsilon(f) is due to the suppression of the inhomogeneous shear deformation. The effectiveness of Cr for the increase in sigma(f) and epsilon(f) is presumably attributed to a further refinement of the fcc-Ni particle size due to the increase in glass-forming ability.