Ultra-high cycle fatigue behaviour of warm compaction Fe–Cu–Ni–Mo–C sintered material

• We designed axial ultrasonic fatigue testing specimen of Fe–2Cu–2Ni–1Mo–1C.
• We studied ultra-high cycle fatigue behaviours by ultrasonic resonance system.
• Ultrasonic fatigue fracture of sintered steels was analysed.
• Crack source is located at different place under different cycle range.
• There is no obvious relationship between facet size and fatigue cycles.

The present work studied the ultra-high cycle fatigue behaviours of Fe–2Cu–2Ni–1Mo–1C sintered steels. The partially pre-alloyed material was fabricated by die-wall lubricated warm compaction; its mechanical properties, such as hardness and tensile strength, were measured. In addition, axial ultrasonic fatigue testing specimens were designed using the finite element method. The results indicated that fatigue failure appeared after more than 107 stress-cycles and that a fatigue limit existed. The fatigue strengths were 392, 249 and 159 MPa for the corresponding conditions of 105, 107 and 109 cycles, respectively. The fatigue crack sources were located at non-metallic inclusions or voids near the surface under high cycle conditions but move to the internal sites under ultra-high cycle conditions. With an increase in the number fatigue cycles the stress intensity range factor gradually reduced.