Research on Milling Subsurface Layer Damages of DD5 Ni-based Single Crystal Superalloy

In order to research the milling subsurface layer damages of DD5 Ni-based single crystal superalloy, based on the directional cutting method and slot milling experiments, this paper discussed the DD5 deformation layer characteristics and recrystallization behaviors though the massive DD5 longitudinal sections micro-metallographic structures and micro-hardness tests under different milling parameters before and after heat treatments. Then the control approaches for inhibiting the deformation layer generation and development were proposed. The research results demonstrate that milling parameters, cooling methods and crystal direction conditions all influence the DD5 hardening rate largely, the hardness of the machined surface along the normal direction show the "hardening-softening-hardening"trend, which illustrate that the main reason for metamorphic layer formation is work hardening under the competition mechanism between the thermal softening and strain hardening, and the metallographic structure in this area is transformed, which improve the corrosion resistance of DD5 machined surfaces. The reasonable milling trajectory along the [110] crystal direction scheme and the water based minimum quantity lubrication adoption of cooling methods are beneficial for the inhibition of deformation layer formation. In addition, under the machining conditions designed herein, the milling processes may not provide sufficient stored energy to activate material recrystallization under the traditional and vacuum high temperature conditions to 1300℃. © 2020, Editorial Office of Journal of CIFST. All right reserved.