Comparison of Fatigue Properties for Alloy EP708 Specimens Prepared by Selective Laser Melting and Hot Rolling

Structure and fatigue resistance tests of EP708 alloy specimens prepared by selective laser melting (SLM) and subjected to strengthening heat treatment and hot isostatic pressing (HIP), combined with heat treatment compared with hot-rolled heat-treated specimens, are studied. It is shown that the use of the HIP process significantly reduces specimen porosity obtained by the SLM method for EP708 alloy, and it also increases cyclic endurance. Test specimens prepared by the SLM method, after heat treatment and after HIP and heat treatment, as well as those hot-rolled and heat-treated, withstand 2·10⁶ cycles during the first stage of loading at 340 MPa. With a subsequent increase in the load to 380 MPa, the best cyclic durability is shown by specimens in a hot-rolled heat-treated condition. In this case, specimens after HIP and heat treatment show a reduction of twice the cycle time from the hot-rolled specimens, and the specimens obtained by the SLP method given heat treatment have an operating cycle an order of magnitude lower than for hot-rolled specimens. The SLM-specimens after HIP and heat treatment have characteristics comparable with hot-rolled heat-treated specimens for fatigue resistance required by the standard documents for products made of alloy EP708.