Cracking suppression by substrate preheating using an induction heater in directed energy deposition

Abstract

The applications of wear resistant material coatings or claddings by directed energy deposition (DED) are rapidly increasing in industrial engineering fields. DED allows us the use of non-expensive substrate materials and add functional materials such as Co-based superalloys on them. However, depending on the deposition parameters, cracks can easily occur on the workpiece. The determination of the appropriate deposition parameters is crucial because it is still difficult to predict and to control cracking. This paper discusses the effect of substrate preheating by an induction heater on the crack generation for DED of Co-based superalloys. An induction heater was adopted for its high efficiency, low waste heat and ability to quickly induce a high temperature in the workpiece directly. The material used in this study is Stellite® 1, which is widely used for die cut rolls or screw shafts. To investigate the effect of the preheating, experiments were conducted by changing the process parameters: preheating temperature and laser power. Sufficient hardness of 642 HV was obtained without cracking when the preheating temperature was 500 ℃ and the laser power was 1750 W. Although cracking did not occur when the preheating temperature or the laser power was higher, the hardness decreased. There is a trade-off between hardness and crack occurrence. This trade-off is considered to be influenced by thermal stress and the precipitation amount of chromium carbides, which are hard and brittle materials. The amount of chromium carbide precipitation is affected by the cooling rate of the deposited material. In addition, a higher cooling rate may result in greater thermal stress.