Evaluation of Chill Cast Co-Cr Alloys for Biomedical Applications

Abstract

Binary Co-Cr alloys containing various Cr contents were vacuum induction melted and cast into wedge-shaped copper molds. It was intended to develop a microstructure (1) free from interdendritic segregation and porosity; (2) having minimal intermetallic precipitates; and (3) suitable for biomedical applications. The resultant microstructures were evaluated from sections obtained longitudinally and centrally in the plane normal to the diverging wedge faces. All ingots showed a dendritic microstructure with some characteristic features. For instance, in Co-20-30 wt. % Cr alloys, the chilled cast microstructures consisted of columnar dendrites without interdendritic segregation, a minimum of intermetallic precipitates, and the presence of a predominantly athermal HCP ε-martensite (>80 vol. %). In addition, the metastable FCC γ-Co phase was identified by X-ray diffraction and scanning electron microscopy. In the case of 35-44 wt. % Cr cobalt alloys, a eutectic constituent including the σ-phase were found to develop in the interdendritic regions. From this work, a Co-20 wt. % Cr alloy was chosen for further investigation after heat treating below the γ/ε transition temperature. The resultant tensile strength and ductility were further improved after applying a heat treatment at 730 • C for 30 min, obtaining values of elongation of 26% as compared with 2.55 < 5 of elongation in the as cast condition. Also, the alloy corrosion resistance in artificial saliva was investigated. It was found that the exhibited corrosion rates for the as-cast and heat-treated conditions are between those reported for other similar systems.

Volatilization Behavior of β-Type Ti-Mo Alloy Manufactured by Electron Beam Melting

“…Furthermore, the interdendritic segregation was observed between the adjacent column grains, as shown in Figure 6c. The composition in the solid phase was not diffused homogeneously due to the high cooling speed during the solidification process [39]. In addition, some small pores, characterized by the black points, were observed in some grains (Figure 6a,b).…”

The Effect of Cyclic Solution Heat Treatment on the Martensitic Phase Transformation and Grain Refinement of Co-Cr-Mo Dental Alloy

“…At 0.8 V, the current density starts to increase sharply which is related to the passive-transpassive oxidation. The reaction of Cr2O3 with hydrogen reactivates the anodic dissolution of passive layer leading to oxide layer breakdown (Cr2O3 + 6H + → 2Cr 3+ + 3H2O) [26,27]. Figure 12 shows the Tafel plot curves of the samples subjected to different thermal treatment conditions in the 3.5 wt.%.…”

“…Therefore, cyclic solution treatment is proposed as an effective method to enhance the surface characteristics and biocompatibility of the Co-Cr-Mo implant alloy. It was shown that the protective oxide layer in Co-Cr-Mo alloy in simulated physiological solution (SPS) at E < 0.3 V consists mainly of Cr 2 O 3 and the fraction of CoO increased with potential and, in the region from 0.5 to 0.7 V, the fractions of Cr and Co were found to be approximately the same [26]. Generally, all thermally treated samples showed lower corrosion current density and higher polarization resistance as compared to the as-cast sample.…”

The Effect of Rapid Solidification on Microstructure and Corrosion of Advanced Biomaterial Co-Cr-Mo-C Alloy

“…Co-based alloys are increasingly being used in biomedical application for their biocompatibility, excellent corrosion resistance, and mechanical and wear properties [1,2]. Solidified microstructures of as-cast cobalt alloys is mainly FCC dendritic structure in presence of segregation, and second phase precipitates within the matrix and along the interdendritic regions [3]. Since the introduction of Co-based alloys as prosthesis material, a considerable amount of research has been done on examining the possibility of enhancing mechanical properties and biocompatibility of this alloy by modifying the microstructure [1,[3][4][5][6].Overall, Co-Cr-Mo-C alloys made by investment casting are showing poor ductility, high shrinkage porosity, interdendritic segregation, and intermetallic compounds brittleness.…”

“…Solidified microstructures of as-cast cobalt alloys is mainly FCC dendritic structure in presence of segregation, and second phase precipitates within the matrix and along the interdendritic regions [3]. Since the introduction of Co-based alloys as prosthesis material, a considerable amount of research has been done on examining the possibility of enhancing mechanical properties and biocompatibility of this alloy by modifying the microstructure [1,[3][4][5][6].Overall, Co-Cr-Mo-C alloys made by investment casting are showing poor ductility, high shrinkage porosity, interdendritic segregation, and intermetallic compounds brittleness. Thus, to improve alloy performance for high lifetime service in biomedical applications, modifications in alloy design and casting technology have taken place [7].…”