Formation Mechanism And Control Of Checkered Morphology Defects For K423A Whole Structure Investment Castings

During the production process of the Ni-base superalloy investment castings, some unavoidable impurity elements are present due to the complex processes of nickel-based superalloy materials used in the castings, while the casting has a complex vane structure and high manufacturing precision, resulting in a lower ratio of finished products. Analyzing the causing and influence factors of checkered morphology defects and exploring the effective ways to eliminate the defects are meaningful for obtaining high quality Ni-based superalloy investment castings.The fluorescence detection, 3D super-depth microscopy, scanning electron microscopy and energy dispersive spectroscopy were used to study the appearance, texture and composition of the checkered morphology defects on K423 A investment castings. The experimental results showed that the checkered morphology defects were not flaw. It was caused in the chemical reaction of SiO2 in the shell surface material and alloy liquid at high temperature. At the same time, the distribution law and appearance characteristics of checkered morphology defects of the K423 A whole structure investment castings were obtained. It was found that the checkered morphology defects were more sensitive to temperature. In the high temperature area of the semifinished product, the probability of checkered morphology defects greatly increased, and the change in heat dissipation conditions could effectively control the formation of checkered morphology defects;The chemical milling process was applied to the control of the checkered morphology defects The K423 A casting was cut into small specimens and the chemical milling fluid was prepared according to certain process to study the changes of the specimen surface with different temperatures and time of chemical milling. The experimental results showed that the chemical milling process had an ideal effect to control checkered morphology defects, the quality of the specimen surface after chemical milling was greatly improved with significantly reduced checkered morphology defects, and the most suitable chemical milling temperature for the nickel-based superalloy K423 A was 55-60℃. The laser remelting process was applied to the control of checkered morphology defects. Different laser technology parameters were set to study the control effect of the laser remelting process on checkered morphology defects. The experimental results indicated that the laser remelting process greatly changed the surface appearance of the specimen, while the surface composition of the sample underwent certain changes. The laser power is the biggest influencing factor, surface crazing defects disappeared under the effect of the laser, but a large number of tiny flaws appeared on the specimen surface, therefore to get the specimen with better surface quality, a more suitable combination of laser parameters needs to be found.Through the research of checkered morphology defects, the formation mechanism was studied, the casting process was optimized, provided theoretical guidance and technical supports.