Increase in Mechanical Strength of Ni–Si–B Amorphous Alloys by Dispersion of Nanoscale fcc-Ni Particles

Abstract

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 (σ_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 (ε_f). The highest values of σ_f, E, H_v and ε_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 σ_f and ε_f, their highest values being 3900 MPa and 3.8%, respectively for (Ni_0.81Si_0.1B_0.09)₉₇Cr₃. The increase in σ_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 ε_f is due to the suppression of the inhomogeneous shear deformation. The effectiveness of Cr for the increase in σ_f and ε_f is presumably attributed to a further refinement of the fcc-Ni particle size due to the increase in glass-forming ability.