Effects of the Hot Isostatic Pressing Process on Crack Healing of the Laser Repair-Welded CM247LC Superalloy
This study investigated the effects of the hot isostatic pressing process on the crack healing, microstructure, and mechanical properties of the laser repair-welded CM247LC precipitation-hardened superalloy. To ensure the strength of the repair-welded area, this study used the direct re-melting approach, and simulated the repair welding with the filler addition, which has a chemical composition matching that of the base superalloy. As expected, different types of cracks, including the solidification crack in the weld fusion zone and various types of liquidation cracks in the heat-affected zone, were observed. Through a proper hot isostatic pressing healing process, all cracks in the weld fusion zone and the heat-affected zone of the repair-welded pieces were healed. At the same time, some nano- and micro-sized carbides tended to form discontinuously along the healed crack trace. A micro-hardness test was conducted in the repair-welded area, and the results were similar to that of the as-cast material.
Induction-assisted laser welding of IN-738 nickel–base superalloy☆
Abstract Induction-assisted laser welding was performed with filler metal additions to weld IN-738, a nickel–base superalloy. IN-738 powder was added through a coaxial nozzle to the weld pool in order to reduce the weld defects, such as underfill and porosity in the welds. This was particularly important for the square-groove butt joints due to the presence and opening of gaps in the welding process. Crack-free laser welds were obtained by induction preheating at approximately 800 °C, however, some scattered pores were still observed in the welded specimen. Tensile testing indicated that the strength of the weld metal was comparable to that of the base metal at 850 °C. Stress-induced precipitation of fine γ′ particles was also observed on IN-738 specimens subjected to tensile loading. The preliminary results of this study demonstrated that the quality and performance of laser-welded IN-738 specimens were acceptable. However, more works on the process optimization are required to further improve the weld quality.
Metal forming: Industrial, mechanical computational and microstructural
Abstract In hot mechanical forming, large scale machines with varied tooling exert forces on rough feed stock under controlled temperature to produce objects of the desired shape. The plastic deformation and thermal softening are only possible through a system of internal atomistic mechanisms, both dynamic (during straining) and static (afterwards), which define the flow stresses and determine the final microstructure and properties. The objective of this paper is to explain the pertinent features of both macroscopic processing and microscopic mechanisms, in order to be able to predict both the forces and the product quality.