The design freedom of powder bed fusion process selective laser melting(SLM)enables flexibility to manufacture customized,geometrically complex medical implants directly from the CAD models.Cobased alloys have adequat...The design freedom of powder bed fusion process selective laser melting(SLM)enables flexibility to manufacture customized,geometrically complex medical implants directly from the CAD models.Cobased alloys have adequate wear and corrosion resistance,fatigue strength,and biocompatibility,which enables the alloys to be widely used in medical devices.This work aims to investigate the evolution of microstructures and their influence on tribological property of CoCrMo alloy processed by SLM and aging heat treatment.The results showed that very weak<110>texture along the building direction and microsegregation along cellular boundaries were produced.The presence of high residual stress and fine cellular dendrite structure has a pronounced hardening effect on the as-SLM and aging-treated alloys at moderate temperatures.Furthermore,the hexagonalεphase transformed from theγmatrix during SLM became significant after subsequent aging at moderate temperatures,which further increased the nanohardness and scratch resistance.High temperature(1150℃)heating caused homogenized recrystallization microstructure free of residual stress andεphase,which sharply decreased the hardness and scratch resistance.The material parallel to the building direction exhibited improved tribological property in both SLMed and aging-treated alloy than that of the material perpendicular to the building direction.The anisotropy in frictional performance may be considered when designing CoCrMo dental implants using laser additive manufacturing.展开更多
The failure of thin film-substrate structure occurs mainly at the thin film or the interface. However, the characterizing and estimating methods of failure stress in thin film are neither uniform nor effective because...The failure of thin film-substrate structure occurs mainly at the thin film or the interface. However, the characterizing and estimating methods of failure stress in thin film are neither uniform nor effective because there are some complex effects of such as size, interface and stress state on the failure behavior of thin film-substrate structure. Based on the scanning electron microscope (SEM) in-situ in- vestigation on the failure models of the Cu thin film-substrate structure and the nano scratched testing results, the failure stresses in different thicknesses of the Cu film-substrate were characterized, which were compared and confirmed by other methods, such as Stoney formula and other empiric equations. These results indicate that the novel estimating method of failure stress in thin film based on the critical wavelength of surface unstable analysis is better than other methods. The main reason is that the novel estimating method of failure stress in meso thickness film fully considered the effect factors of free surface unstable behavior and elastic anisotropy of thin film. Therefore, the novel estimating method of failure stress assists people to understand the critical interfacial strength and to set up the failure criterion of thin film-substrate structure.展开更多
基金the Key R&D Plan of the Ministry of Science and Technology(No.2018YFB1105900)the Shandong Province Key R&D Project(No.2018GGX103017)the Zibo City and SDUT Integration Project(No.2018ZBXC154)。
文摘The design freedom of powder bed fusion process selective laser melting(SLM)enables flexibility to manufacture customized,geometrically complex medical implants directly from the CAD models.Cobased alloys have adequate wear and corrosion resistance,fatigue strength,and biocompatibility,which enables the alloys to be widely used in medical devices.This work aims to investigate the evolution of microstructures and their influence on tribological property of CoCrMo alloy processed by SLM and aging heat treatment.The results showed that very weak<110>texture along the building direction and microsegregation along cellular boundaries were produced.The presence of high residual stress and fine cellular dendrite structure has a pronounced hardening effect on the as-SLM and aging-treated alloys at moderate temperatures.Furthermore,the hexagonalεphase transformed from theγmatrix during SLM became significant after subsequent aging at moderate temperatures,which further increased the nanohardness and scratch resistance.High temperature(1150℃)heating caused homogenized recrystallization microstructure free of residual stress andεphase,which sharply decreased the hardness and scratch resistance.The material parallel to the building direction exhibited improved tribological property in both SLMed and aging-treated alloy than that of the material perpendicular to the building direction.The anisotropy in frictional performance may be considered when designing CoCrMo dental implants using laser additive manufacturing.
基金Supported by the National Natural Science Foundation of China (Grant No. 10772091) National Basic Research Program of China (Grant Nos. 2004CB619304-5, 2007CB936803)
文摘The failure of thin film-substrate structure occurs mainly at the thin film or the interface. However, the characterizing and estimating methods of failure stress in thin film are neither uniform nor effective because there are some complex effects of such as size, interface and stress state on the failure behavior of thin film-substrate structure. Based on the scanning electron microscope (SEM) in-situ in- vestigation on the failure models of the Cu thin film-substrate structure and the nano scratched testing results, the failure stresses in different thicknesses of the Cu film-substrate were characterized, which were compared and confirmed by other methods, such as Stoney formula and other empiric equations. These results indicate that the novel estimating method of failure stress in thin film based on the critical wavelength of surface unstable analysis is better than other methods. The main reason is that the novel estimating method of failure stress in meso thickness film fully considered the effect factors of free surface unstable behavior and elastic anisotropy of thin film. Therefore, the novel estimating method of failure stress assists people to understand the critical interfacial strength and to set up the failure criterion of thin film-substrate structure.
