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.
Microstructure Evolution of Laser Repair Welded René 77 Nickel-Based Superalloy Cast
This study performed repair-welding tests on Rene 77 Nickel-based superalloy by adopting a Nd:YAG pulsed laser technique, coupled with Rene 41 filler wire and various welding parameters. After welding, the microstructure evolution, crack behavior and mechanical properties of the welds were determined by a combination of scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDS), transmission electron microscopy (TEM), and micro-hardness test. The experimental results showed that, due to suffering from different thermal histories during the conduction of the multi-pass welding process, the microstructures within the welds had split into six zones. In terms of cracking behavior, no cracks formed in the weld fusion zone (WFZ) or the heat-affected zone (HAZ) under appropriate welding parameters; however, setting the laser energy too high resulted in weld centerline cracking or intergranular cracking in the weld fusion zone. Moreover, various types of liquation cracks may occur at the interface between the WFZ and the HAZ.
Stereoselective interaction between the R enantiomer of warfarin and cimetidine.
The stereoselectivity of the pharmacokinetic interaction between warfarin and cimetidine was investigated in eight healthy volunteers. The warfarin enantiomers were given separately as single doses (15 mg) alone and during chronic administration of cimetidine (1 g day-1). Cimetidine did not interact with S warfarin but there was an interaction with the R enantiomer of warfarin. Cimetidine caused a significant increase in the mean plasma half-life of R warfarin (from 47.8 h to 57.8 h) and a significant decrease in its mean plasma clearance (from 2.3 to 1.7 ml h-1 kg-1) (P less than 0.02). Administration of a pharmacological dose of vitamin K1 together with the enantiomers of warfarin was necessary clinically and resulted in elevation of vitamin K1 2,3-epoxide concentrations, which were similar in each case.