Propagation of fatigue crack in amorphous Fe40Ni40B20 at high-frequency loading

This work studies the fatigue crack growth in Fe40Ni40B20 metallic glass using the stressing by longitudinal ultrasonic waves of frequency 20.2 kHz. A relation between the rate of fatigue crack propagation and stress intensity factor is derived. An extremely low threshold value of the stress intensity factor, below which a fatigue crack cannot propagate, was found. Fractographic analysis of the fatigue fracture surfaces by scanning electron microscopy confirmed that no so far known mechanism of fatigue failure was present. No slip bands were observed near fatigue fracture surfaces

Magnetic properties of nanocrystalline CoFeNbB alloys

The influence of alloy composition and heat treatment on the structure and magnetic properties of rapidly quenched CoFeNbB alloys were studied. The saturation magnetization, Js, the magnetostriction constant. λs, and the Curie teniperature. Tc, of the as-quenched amorphous alloys decrease with increasing Nb or B content (3 < xNb < 7. 8 < xB < 15 at.%). Both Js, and λs, of CoFeNb7B9 show maxima at about 29 at.% of Co. The crystallization of all the alloys takes place in two steps. On the first step bcc-Fe(Co) grains develop in the amorphous matrix. With increasing Nb content their grain sizes substantially decrease. A nanocrystalline structure with the grain size of 10 - 15 nm is obtained for xNb = 7 at.%. The saturation magnetization increases on nanocrystallization. The magnetostriction constant, λs, is positive for the as-quenched as well as nanocrystalline alloys. Its magnitude first decreases and then remains constant or increases with further annealing. A slight decrease of the coercive field. Hc,, at the early stage of nanocrystallisation is followed by a subsequent gradual increase. The best soft magnetic properties were observed for the nanocrystalline Co25Fe59Nb7B9 alloy. The following parameters Js = 1.58 T. λs and Hc = 26 5 A/m. were obtained in this alloy after annealing at 600°C

Piezomagnetic Dependences on Magnetic Bias Field of Annealed at 450°C Fe-Cu-Nb-Si-B Alloy

Magnetic field dependences of the piezomagnetic dynamics, magnetomechanical coupling and elasticity moduli in the Fe$\text{}_{73.5}$Cu$\text{}_{1}$Nb$\text{}_{3}$ Si$\text{}_{13.5}$B$\text{}_{9}$ alloy in an as-quenched state and annealed in vacuum for 1 h at 450°C were investigated. The maximum value of the magnetomechanical coupling coefficient was equal to 0.15 for the as-quenched state and 0.7 after annealing at 450°C. The changes of the elasticity moduli (ΔE effect) from about 60 to 180 GPa were observed after annealing at this temperature. These changes are connected with magnetostriction (equal to 25.8×10$\text{}^{-6}$ at saturation), internal stresses, defects, mechanical, magnetic and heat treatment history

Propagation of fatigue crack in amorphous Fe40Ni40B20 at high-frequency loading

This work studies the fatigue crack growth in Fe40Ni40B20 metallic glass using the stressing by longitudinal ultrasonic waves of frequency 20.2 kHz. A relation between the rate of fatigue crack propagation and stress intensity factor is derived. An extremely low threshold value of the stress intensity factor, below which a fatigue crack cannot propagate, was found. Fractographic analysis of the fatigue fracture surfaces by scanning electron microscopy confirmed that no so far known mechanism of fatigue failure was present. No slip bands were observed near fatigue fracture surfaces