Effect of plastic bending on high temperature creep resistance of molybdenum single crystals

Using molybdenum single crystals, it is shown how plastic bending multiplies the high-temperature strength of products for pipelines and tube shells of small diameter (10-30 mm), which are subjected to high internal pressure. It is very convenient to do this when the plastic bending process is included in the manufacturing technology of such products, for example, in the form of spiral winding a strip into a pipe. It has been established that during 1000 h, the creep rate of a pre-bent Mo single crystals at 1633 K and an applied stress of 10 MPa permanently decreases by 4-5 orders of magnitude as compared to an unstrengthened single crystal. Using light microscopy, X-ray diffractometry, and transmission electron microscopy, changes in the dislocation structure and the mechanism leading to such strengthening have been found. During the creep test, the edge components of dislocations are depleted and disappear, and the cross slip of screw dislocations is blocked by numerous loops and helicoids that were formed under bending and transformed during the creep process. As a result, dislocation creep gradually turns into diffusion creep during one test. It is safe to assume that similar effects will be observed in polycrystals when the dominant texture direction will correspond to the required bending axis.