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.
Effect of temperature on the microstructure and tensile properties of micro-crack free hastelloy X produced by selective laser melting
Abstract The high-temperature behaviour of micro-crack free Hastelloy X produced by SLM has been studied. The microstructure and mechanical behaviour of as-built parts and heat-treated (at 1177 and 800 °C) parts were investigated. Quasi-static tensile tests were performed at room temperature and elevated temperatures (650, 750 and 850 °C) for the three heat treatment conditions. In order to better understand the tensile test performance, the microstructure evolution of as-built samples as function of temperature was studied using confocal scanning laser microscopy (CSLM). CSLM allows in situ observation of the microstructure evolution while the sample temperature is increased. During tensile testing, a significant decrease in tensile strain was observed at a testing temperature of 750 °C that was attributed to the precipitation of carbides and Mo-rich intermetallic phases, as observed during and after CSLM. The samples heated at 1177 °C showed less carbide formation due to their more homogeneous starting microstructure, which resulted in a tensile ductility increase as compared to the as-built and 800 °C heat-treated samples.
Stress-induced precipitation of fine gamma '-phase and thermodynamics analysis
The microstructures of a single crystal Ni-base superalloy with [001] orientation were observed by means of TEM. Results showed that the fine gamma' particles were precipitated in the gamma matrix channels during the tensile deformation of the alloy. Thermodynamics analysis indicated that the solubility of elements M(Al,Ta) within the gamma matrix may be changed when the alloy was deformed by the external applied stress. The tensile stress reduced the solubility of elements Al and Ta so as to occur the over-saturation and agglomeration of them, which promoted the precipitation of fine gamma'-phase in the gamma matrix.