A transmission electron microscopy study of the mechanisms of strengthening in heat-treated Co-Cr-Mo-C alloys (original) (raw)
Related papers
Metals, 2021
The Co-Cr-Mo alloy is a biomaterial with very good corrosion resistance and wear resistance; thus, it is widely applied for knee replacements. The wear resistance is influenced by the amount of hcp phase and morphology of carbidic precipitates, which can both be altered by heat treatment. This study compares a conventional knee replacement manufactured by investment casting with a material prepared by the progressive technology of 3D printing. The first set of results shows a different response of both materials in increasing hardness with annealing at increasing temperatures up to the transformation temperature. Based on these results, solution treatment and subsequent aging at conditions to reach the maximum hardness was applied. Microstructural changes were studied thoroughly by means of optical, scanning electron and transmission electron microscopy. While increased hardness in the conventional material is caused by the precipitation of fine hard carbides combined with an increa...
Effect of alloy preheating on the mechanical properties of as-cast Co-Cr-Mo-C alloys
Metallurgical and Materials Transactions A, 1999
The effect of various alloy preheatings followed by full solid solution treatments on the resultant strength and ductility of as-cast Co-Cr-Mo-C alloys was investigated. Three preheating temperatures were evaluated: 815 ЊC, 950 ЊC, and 1100 ЊC for 4 hours and then solid solution treated at 1225 ЊC for 4 hours. Tensile and compressive tests were carried out on the heat-treated alloys. It was found that the strength and ductility of the heat-treated alloys exhibited significant improvements over the as-cast condition. In particular, optimum ductility of the heat-treated alloys and alloy strength were promoted by preheating at 815 ЊC. A relatively fine grained structure coupled with a uniform distribution of second-phase particles promoted homogeneous plastic deformation in the bulk. Fractographic observations indicated that the exhibited ductility was associated with the development of numerous plastic bands combined with band interlockings. Alloy preheats at 950 ЊC and 1100 ЊC prior to solutionizing lead to inferior strength and ductility. Although preheating at 1100 ЊC led to slight improvements, in both cases, the fracture path was dominated by the presence of continuous carbide films surrounding the dendritic grains. Hence, less than optimum combinations of strength and ductility were achieved by the heat treatments at the higher temperatures.
Microstructural effects on the wear resistance of wrought and as-cast Co-Cr-Mo-C implant alloys
Journal of Biomedical Materials Research Part A, 2005
The tribological behavior of two cobalt-base alloys-an as-cast high-carbon and a wrought low-carbon Co alloy-that are used as hip implant materials is examined in this work. This work discusses the experimental results of cobalt-cobalt wear pairs, in wrought and as-cast conditions, where the amount of hexagonal phase is systematically modified through an isothermal aging treatment. Fully FCC and HCP Co alloys are tested versus alloys with various volume fractions of HCP phase (0.05 to 1.0 vol-ume fractions). Preliminary results indicate that Co-Cr-Mo/Co-Cr-Mo alloy pairs both possessing an HCP matrix microstructure tend to exhibit outstanding wear properties.
Materials Science and Engineering: A, 2010
The present study was undertaken to investigate the effects of isothermal aging (at 850 • C for 4, 8, 16 and 24 h) and strain-induced transformation (engineering strains of 10% and 20%) followed by isothermal aging (at 850 • C for 4, 8 and 16 h) on the microstructural evolution of a Co-28Cr-5Mo-0.3C alloy. The obtained results showed that isothermal aging at 850 • C resulted in the formation of lamellar-type carbides at the grain boundaries. Moreover, X-ray diffraction analysis indicated that isothermal aging of solution treated specimens at 850 • C for 24 h did not lead to complete fcc phase transformation to hcp one. In contrast with the isothermally aged specimens, applying plastic deformation to the solutionized samples accelerated the completion and saturation of fcc(metastable) → hcp transformation after 8 h aging at 850 • C. In addition, the X-ray diffraction results indicated that implementing isothermal aging of the strain-induced specimens at the higher aging time (16 h) caused the formation of (1 1 1) fcc and (2 0 0) fcc diffraction peaks again. Also, the strain-induced specimens followed by isothermal aging showed higher amount of microhardness as compared with the other specimens aged solely.
Microstructural characterization of as-cast biocompatible Co–Cr–Mo alloys
Materials Characterization, 2011
The microstructure of a cobalt-base alloy (Co-Cr-Mo) obtained by the investment casting process was studied. This alloy complies with the ASTM F75 standard and is widely used in the manufacturing of orthopedic implants because of its high strength, good corrosion resistance and excellent biocompatibility properties. This work focuses on the resulting microstructures arising from samples poured under industrial environment conditions, of three different Co-Cr-Mo alloys. For this purpose, we used: 1) an alloy built up from commercial purity constituents, 2) a remelted alloy and 3) a certified alloy for comparison.
Microstructural Characterization of Co-Cr-Mo-W Alloy as Casting for Odontological Application
Interest in the analysis and material characterization is rising due to the necessity of the adequate material selection based on system performance in study. The analysis and knowledge of the microstructure and the mechanical properties of any material are of utmost importance since it aims primarily to estimate the performance during the material life span, minimizing the possibility of degradation and undesirable flaws during product utilization. Co-Cr-MoW alloys have been well accepted in odontology as prosthesis material, due to its high mechanical resistance, good corrosion resistance and exceptional biocompatibility properties. This study aims to characterize the microstructure of a cobalt based alloy (Co-Cr-MoW) obtained through vacuum casting process. Optical microscopy, electronic sweeping microscopy and X-ray were employed and Vickers hardness test with loads of 100 gf, 500 gf and 1000 gf during 10 s. Microstructure casting is characterized by a Co-fcc dendritic matrix with a secondary phase, as well as M 23 C 6 precipitate carbides in the interdendritics zones and grain boundaries. The precipitation of carbides represents the main device of strengthening in the cast state for these types of alloys and is also responsible for its lower mechanical properties. The material attained hardness between 25 and 35 HRC, meeting the ASTM F75 standards.
Microstructural Characterisation of Co-Cr-Mo Casting Dental Alloys
Advances in Science and Technology Research Journal
Metal biomaterials, including casting alloys, are the largest group of biomaterials used in den-tal prosthetics and maxillofacial surgery. Despite the scientific reports on the harmful effects of certain metals on living organisms, and due to the absence of non-metallic substitute materials ex-
Phase transformations in a wrought Co-Cr-Mo-C alloy
Metallurgical Transactions A, 1982
The effect of heat treatment on microstructure has been studied in a Co-Cr-Mo-C alloy using transmission electron microscopy. Isothermal aging treatments at 750 ~ were found to promote a two stage fcc ~ hcp transformation, coincident with a discontinuous precipitation of M23C 6 carbides. The variation in morphology of the carbides associated with the fcc ~ hcp transition is discussed in terms of the nature of the fcc/hcp interface.
2011
Dedication: This research project is dedicated to all who have supported the development of dentaltechnology in Ghana. il ABSTRACT ln this age of technological advancement in dentistry, the traditional method of manufacturing removable partial denture frameworks could be supplemented with rapid manufactured (RM) denture frameworks when the technology is fully developed. The RM technology has the potential to provide a better corrosion resistance, accuracy, high strength and density, reduce time and labour and eventually provide low cost restorations compared to the traditional 'lost wax technique' which is considered laborious and time consuming. However, fundamental independent tests including tensile and corrosion tests must be completed to move current researches from a proof of concept stage towards rn vivo pertormance studies if patients' safety is to be guaranteed. At the time of the presenl in vitro study, no published literature was found to have made a comparison between cast and RM dental alloys to investigate their tensile and corrosion properties. Test specimens and procedures used in this project were in accordance with BS EN ISO 22674:2006 for dental metallic restorations' During the corrosion test, electrobrightened and highly polished samples of an RM cobalt-chromium alloy were compared with those manufactured with a cast cobalt-chromium alloy. An RM as-received heat and non-heat treated cobaltchromium samples were also compared. The samples were immersed in artificial saliva (0.1M saline lactic acid) with pH 2.3+0.1 at a temperature of 37+0.1'C for 1 , 4, 7, 14, 21, 28, 35 and 42 days. The analytes were verif ied qualitatively for cobalt, chromium and molybdenum and quantitatively for released metal ions using an atomic absorption spectrometer. Results from the tests showed that the RM alloy had better ductility, modulus of elasticity, resilience, toughness and corrosion resistant properties. ln addition, surprisingly, electrobrightened samples released fewer metal ions than polished samples. RM as-received heattreated specimens released more metal ions than the non-heat treated as-received samples. The pedormance of the RM alloy has been largely linked to the manufacturing technique. Futther studies are recommended.