Fractographic study on fatigue crack initiation and early crack growth processes for pure titanium implanted with nitrogen ions with variable notch radii

摘要

The aim of this work was to study fractographically the fatigue crack initiation and early crack growth mechanism for pure titanium metal implanted with nitrogen ions while varying the notch radii. A maximum surface roughness, R_(max) and the factual dimensions, D, were calculated from the fatigue fracture surface and were related to crack initiation and early crack growth patterns. The main results obtained are summarized as follow; (1) When crack length is <1mm, R_(max) decreased by D increased with decreasing notch radius. (2) When crack length is > 1mm, the tendency of R_(max) and D were to keep close to constant values. These constant values were about 0.1mm and 1.2, respectively. (3) The second type of early crack growth easily occurred when the value of D was high.