Effect of metallurgical structure and properties on adhesion and friction behavior of cobalt alloys

The metallurgical structure and some of the mechanical properties of two cobalt alloys, cobalt-50% iron and cobalt-25% molybdenum-10% chromium, were determined under various heat treated conditions. The mechanical properties of the bcc disordered Co-50Fe alloy, which was found to be very brittle, indicated an exceedingly low fracture strength, low hardness, and very weak grain boundary strength. Ordering by suitable heat treatment only produced a more brittle material with a lower fracture strength and a slightly higher hardness value. Work hardening was found to produce a finer grain structure and a greater grain boundary strength. Tensile properties were examined. It was found that the Co-25Mo-10Cr alloy was difficult to place in the alpha Co solid solution condition, which limited the ability to use precipitation as a hardening reaction. Over two hundred adhesion cycles from zero contact load, to maximum load, to fracture were conducted between couples for each of the above alloys in an ultrahigh vacuum system which would permit the sample surfaces to be cleaned of all contaminant layers. In the Co-50Fe case, the calculated fracture stress from the adhesion tests showed values in the range of 80 to 150 k.s.i., which is about ten times greater than the values from tension tests

Adiabatic kinetic studies of the cytidine/acetic anhydride reaction by utilizing temperature versus time data

It is possible to predict the kinetics of a reaction by using temperature versus time data under adiabatic conditions. This method was used for the cytidine/acetic anhydride reaction using a RC1 Mettler Reaction Calorimeter. The authenticity of the experimental adiabatic system was verified by determining the kinetic parameters of a known reaction (hydrolysis of acetic anhydride) and comparing them to literature values. For example, the average experimental activation energy, heat of reaction, and ln k0 values for the hydrolysis of acetic anhydride were 11.2 ±.5 kcal/gmole, -14.4 ± .2 kcal/gmole, and 12.74 ± .94 sec-1, respectfully, while the average literature values were 12.0 ± 2.4 kcal/gmole, -14.3 ± .3 kcal/qmole, and 11.56 ± 1.47 sec-1, respectfully. The reaction was first order. The cytidine/acetic anhydride reaction (unknown system) was subjected to the same adiabatic analysis and the average experimental activation energy, heat of reaction, and ln k0 values were 13.3 ± .2 kcal/gmole, -10.5 ± .1 kcal/gmole, and 15.68 ± .34 L/(gmole sec), respectfully. To further verify the results for the unknown system,three isothernal runs were executed and sanples were analyzed for concentration by High Pressure Liquid Chronatography (HPLC). The concentration-time data were analyzed and an Arrhenius Plot was constructed yielding an activation energy of 13.2 kcal/ginole and a ln k0 value of 15.14 L/(gTnole sec). The reaction was second order

A new density-dependent mixing rule for equations of state

A general procedure for the development of density-dependent mixing rules is demonstrated. This method is used to obtain a density-dependent local-composition mixing rule based on an extention of the work of Knox et al (1984). The resulting expression is tested with the Soave-Redlich-Kwong equation of state. Results for normal and cryogenic vapor-liquid systems for both one-parameter and three-parameter versions of the mixing rule are compared with results using the classical mixing rules

Aplicação de cavacos de titânio para produção de revestimentos resistentes ao desgaste

Equipments of the sugar-cane plants and mineral extraction are submitted to severe abrasive wear conditions. Welded hardfacing are usually applied to repair that kind of damage where commercial chromium/carbon-rich welding consumables have usually been employed. In the present work was investigated the microstructure of experimental hardfacings made by addition of residues (chips) collected from machining of ASTM F67 (unalloyed Ti, grade 4) alloy. Mixtures with different carbide-formers (Cr/Nb ferro-alloys) were also tested. Two layers of pure chips (Ti), chips plus Fe-Cr (Ti-Cr), and chips plus Fe-Nb (Ti-Nb) were applied on low-carbon steel specimens by GTAW/TIG process. The microstructure of hardfacing layers was observed by optical and scanning electron microscopy (SEM) equipped with EDS microanalysis. The microstructural characterization has determined that carbide distributions change significantly with the chemical nature of the hardfacing. SEM observations coupled with EDS microanalysis have confirmed the formation of complex carbides within metal weld, whose stoichiometry was determined by X-rays diffraction (XRD) analysis. Mixed carbides MC-type and some cementite have been found. As a result it was suggested that using of ASTM F67 chips as carbide formers for composition of welding consumables can contribute to improve wear resistance of hardfacings, if compared with traditional chromium-based hardfacings.Equipamentos usados nas usinas sucroalcooleiras e de extração mineral são submetidos a condições severas de desgaste abrasivo. Revestimentos duros são usualmente aplicados para reparar este tipo de dano, sendo bastante empregados consumíveis de soldagem contendo altos teores de cromo e carbono. No presente trabalho visa investigar a microestrutura de revestimentos duros formados com a fusão de cavacos de titânio puro ASTM F67 grau 4, material usado na fabricação de implantes odontológicos. Misturas com diferentes formadores de carbonetos (Fe-Cr e Fe-Nb como aditivos) também foram testadas. Revestimentos feitos com duas camadas de cavacos puros (Ti), cavacos com Fe-Cr (Ti-Cr) e cavacos com Fe-Nb (Ti-Nb) foram depositadas sobre peças de aço-carbono por soldagem TIG/GTAW. A microestrutura das camadas foi observada com microscópio óptico e por microscópio eletrônico de varredura equipado com microanálise. A caracterização microestrutural revelou que a distribuição de carbonetos varia significativamente com a natureza química dos aditivos usados. A microanálise mostrou que houve a formação de carbonetos com composição química complexa no seio do metal de solda, cuja estequiometria foi determinada com análise por difração de raios-X. Carbonetos mistos do tipo MC e cementita foram identificados. Os resultados apresentados indicam que a aplicação de cavacos de titânio ASTM F67, como insumo para formação de carbonetos, pode contribuir para melhorar a resistência ao desgaste em comparação aos tradicionais revestimentos duros com carbonetos de cromo.Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)UNESP PPGEMAutocam Medical, Gerência de ProdutosUniversidade Estadual PaulistaUNESP PPGEMUniversidade Estadual Paulist

Molecular dynamics simulation of nanoindentation of Fe₃C and tetrahedral Fe₄C

Study of nanomechanical response of iron carbides is important because presence of iron carbides greatly influences the performance and longevity of steel components. This work contributes to the literature by exploring nanoindentation of Fe3C and tetrahedral-Fe4C using molecular dynamics simulation. The chemical interactions of iron and carbon were described through an analytical bond order inter-atomic potential (ABOP) energy function. The indentations were performed at an indentation speed of 50 m/s and a repeat trial was performed at 5 m/s. Load–displacement (P–h) curve for both these carbides showed residual indentation depth and maximum indentation depth (hf/hmax) ratio to be higher than 0.7 i.e. a circumstance where Oliver and Pharr method was not appropriate to be applied to evaluate the material properties. Alternate evaluation revealed Fe3C to be much harder than Fe4C. Gibbs free energy of formation and radial distribution function, coupled with state of the average local temperature and von Mises stresses indicate the formation of a new phase of iron-carbide. Formation of this newer phase was found to be due to deviatoric strain rather than the high temperature induced in the substrate during nanoindentation