The surface of AISI 1045 steel was coated using the flame spray technique. Iron-based superalloy (Fe16Mo2C0.25Mn) powders were used as matrix material and a mixture of mechanically alloyed 10 wt.-% Fe16Mo2C0.25Mn and 90 wt.-% Al2O3–3TiO2 powders was used as reinforcing material. The mechanical alloying process was performed by milling with an attritor for 60 hours. The coating material comprised of a mixture of the matrix (Fe16Mo2C0.25Mn) powder and mechanically alloyed reinforcing powders at varying rates of 5, 10 and 15 %, respectively. The microstructure, microhardness, adhesive wear behaviors and the coefficients of friction of the coated specimens were examined. It was observed that defects increased and cracks formed on the interface, depending on the increase in the reinforcing ratio. It was determined that the coefficient of friction and wear loss increased by the increasing load in all specimens. The minimum wear loss was observed for the specimen with 10 % reinforcement and the maximum wear loss was observed for the specimen with 15 % reinforcement. The highest average coefficient of friction by the applied load was obtained for the coating with 10 % reinforcement and the lowest average coefficient of friction was obtained for the specimen with 5 % reinforcement.
Las aleaciones de aluminio de la serie 6xxx son propensas a agrietarse cuando se sueldan por fusión sin un metal de relleno adecuado. Alternativamente, estas aleaciones se pueden soldar mediante soldadura por fricción rotatoria, un proceso de soldadura en estado sólido, que no utiliza otro material. Sin embargo, el uso de los parámetros correctos para el proceso de soldadura por fricción giratoria es clave para obtener buenas soldaduras. En este estudio, la aleación de aluminio 6060 fue soldada por fricción rotatoria utilizando diferentes velocidades de rotación, y se estudiaron los efectos de las velocidades de rotación en las propiedades mecánicas de dichas soldaduras. Las muestras se caracterizaron utilizando microscopía electrónica de barrido, se analizaron realizando un mapeo elemental utilizando espectroscopía de rayos X por dispersión de energía, y se caracterizaron mecánicamente realizando microdurezas y ensayos de tracción. Entre las muestras estudiadas, la muestra soldada con la velocidad de rotación de 1700 rpm resultó ser mucho mejor que las demás en términos de resistencia mecánica. En las observaciones realizadas bajo el microscopio, a diferencia de la soldadura por fusión, no se notó agrietamiento u otros defectos de soldadura o macro segregación en la muestra soldada a la velocidad de 1700 rpm.
When extended distally due to higher loading in the posterior region implant-supported bar-retained overdentures with cantilever bar extension exhibit greater bending moments on the implants closest to the cantilever bar and increased stresses in the overdenture components. In this study, a new abutment-bar structure connection was introduced to minimize undesired bending moments and reduce the resulting stresses by increasing the rotational mobility of the bar structure on the abutments. Copings of the bar structure were modified to have two spherical surfaces, sharing the same center, located at the centroid of the top surface of the coping screw head. The new connection design was applied to a four implant-supported mandibular overdenture to create a modified overdenture. Both the classical and modified models had bar structures with cantilever extensions in the first and second molar areas, and were analyzed for deformation and stress distribution using finite element analysis, which was also conducted for both the overdenture models without cantilever bar extensions. Real-scale prototypes of both models with cantilever extensions were manufactured, assembled on implants embedded in polyurethane blocks, and subjected to fatigue testing. Both models’ implants were subjected to pull-out testing. The new connection design increased the rotational mobility of the bar structure, minimized the bending moment effects, and reduced the stress levels in the peri-implant bone and overdenture components, whether cantilevered or not. Our results verify the effects of rotational mobility of the bar structure on the abutments and validates the importance of the abutment-bar connection geometry as a design parameter.
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