Abstract
The authors have studied the tensile strength, rotational bending fatigue strength and Charpy impact property of the joints of spheroidal graphite cast iron bonded by diffusion bonding and found that the properties of the joints were comparable to the base metal. In this study, spheroidal graphite cast irons were bonded by diffusion bonding and the effects of nickel foil as an insert metal on the torsional fatigue strength of the joints have been investigated. Main results are as follows ;
(1) For the directly bonded specimens after ferritizing, an S-N curve could not be obtained because of large scatters of the fatigue lives at a given stress amplitude due to the presence of fine precipitates of graphite on the interface. However, no failure was occurred for specimens tested for 107 cycles at stress amplitudes below 160 MPa.
(2) When the specimens bonded with insert metal of a 10μm thick nickel foil were ferritized, the torsional fatigue limit was 170 MPa, which was lower by 20 MPa than that of the base metal. The difference in fatigue strength at the cycles between 10% and 90% of the failure probability was about 38 MPa ; this is higher by about 16 MPa than that of the base metal.
(3) The torsional fatigue limit of the joints having a ferrite and pearlite structure bonded with insert metal of a 10μm thick nickel foil was 210 MPa which was lower by 10 MPa than that of the base metal. However, the difference in fatigue strength at the cycles between 10% and 90% of the failure probability was nearly equal to that of the base metal.
(4) The torsional fatigue limit of the joints bonded using a 10μm thick nickel foil increased with increase in the tensile strength of the joints and was about 43% of the tensile strength.
