Papers by Keyword: Cobalt Base Alloys

Abstract: Due to high wear resistance, Cobalt-based alloys, such as Stellite12 (52Co30Cr8.5W), have presently been used as materials for hardfacing in several applications. Thermowell, a protecting part for thermocouple in petrochemical production, is also coated by Stellite12. Because of high deposition rate, the flux-core arc welding (FCAW) method was selected to be hardfacing process in the research. However, their welding parameters should be exactly controlled in order to obtain desired properties, depending on the microstructure of this material. The objective of this experiment is to study the influence of the FCAW parameters on the erosion resistance of AISI 304 (Fe-18Cr-8Ni-0.06C) welded by the cobalt base alloy filler, Stellite12 (Co-30Cr-8.5W-1.5C) as the hardfacing layer. The studied parameters were welding speed in the range of 2.1-8.5 mm s^-1, and wire feed speed in the range of 42.3-67.7 mm s^-1, leading to different heat inputs and cooling rates. The erosion resistance was investigated by using solid particle erosion test rig at ambient temperature. Surface characterization was then carried out by SEM equipped EDX and XRD. The results showed the relationship between erosion resistance and microstructure in welding and HAZ zone. The erosion resistance was depended on the formation of interdendritic phase in the welding zone. According to the surface examination, it was found that the formation of interdendritic, including size and shape played an important role on the erosion resistance. The heat input and cooling rate concerned with welding parameters was further discussed with the erosion behavior in this research.Keywords Stellite12, Cobalt base alloys, Flux-core arc welding, FCAW, Erosion-resistance

Abstract: In order to understand the problems that arising during machining and contribute to find the best way to produce medical prosthesis, an experimental milling analysis was conducted in Ti-6Al-4V and Co-28Cr-6Mo alloys. The thermal gradient and the cutting forces created on the surface during the machining were evaluated for different cutting speeds. Moreover, the roughness and Vickers hardness were evaluated. Based on the results obtained, it is possible to conclude that the difficult to cut of Co-28Cr-6Mo alloy is higher than Ti-6Al-4V alloy.

Abstract: Two different techniques were used to promote a bioactive surface on a cobalt base alloy: i) the cobalt alloy melt was cast into wollastonite-coated cavities of an investment mold, or ii) wollasonite-encapsulated as-cast samples were heat treated at 1220°C for 1 h, this is the typical treatment performed to this alloy for improving its mechanical behavior. In vitro bioactivity was assessed by immersing samples in a simulated body fluid for 21 days. Potentially bioactive layers were obtained in both of the cases. A thicker apatite layer was formed on the samples obtained by investment casting. However, since the heat treatment needs to be performed, the heat treatment method is also a promising technique for promoting the bone-bonding ability of this Co alloy.

Abstract: The effects of tensile deformation on the amount of hcp phase formed during a 3 hour isothermal aging at 800 °C is studied using in-situ X-ray diffraction and scanning electron microscopy. It is shown that the start of the isothermal martensitic transformation during aging of this material is delayed by prior plastic deformation. Nevertheless, the total amount of hcp phase present in the microstructure at the beginning of aging increases at a continuously decreasing rate due to stress-assisted transformation. This behavior is attributed to the relieving of internal stresses produced by plastic deformation prior to aging. Finally, during the last stage of aging, the amount of hcp phase in the microstructure increases as a result of isothermal martensitic transformation. It is suggested that the presence of mechanically-induced hcp phase during aging inhibits the thermally activated nucleation process that leads to the isothermal martensitic transformation.

Abstract: Wollastonite ceramics was used in a biomimetic method to promote apatite formation on a Co-Cr-Mo alloy (ASTM F-75). The metallic samples were initially chemically treated in a 5M NaOH aqueous solution. The treated samples were immersed for 7 days in SBF on a bed of wollastonite and then immersed 7 or 14 days in 1.5SBF. For comparative purposes no wollastonite was used during the first 7 days in some tests. A homogeneous bonelike apatite layer was formed on the samples immersed in SBF on the wollastonite bed. The morphology and the Ca/P ratio of the layer were closely similar to those observed on the existing bioactive systems. A thinner homogeneous bonelike apatite layer was formed on the samples immersed in SBF and 1.5SBF without using wollastonite. However, the morphology and the Ca/P ratio of this layer differs slightly to that observed on the existing bioactive systems. The immersion of the samples during the first days in SBF on a wollastonite bed improves significantly the quality and thickness of the bonelike apatite layer.