Journal Bearings

WC-Co cemented carbides exhibit high hardness, high transverse rupture strength, and excellent fracture toughness ¹1Unresolved citation key: tianOptimizationMechanicalProperties2020

These materials consist of a matrix of hard faceted WC grains embedded in a tough Co rich binder that exists for a defined range of C and W contents. ²2Unresolved citation key: layMorphologyWCGrains2008

A homogeneous microstructure where the WC grains have a fine and tight size distribution is required to develop high hardness and sufficient toughness. ²2Unresolved citation key: layMorphologyWCGrains2008

However, tungsten carbide grains grow during liquid phase sintering, and the increased grain size strongly affects the mechanical properties of the alloy. Therefore control of microstructure is important to produce highly qualified carbide tools. ³3Unresolved citation key: kishinoComputationalStudyGrain2002

Studies have shown that the addition of the Cr can improve oxidation resistance and inhibit grain growth while the addition of Ni into the cobalt matrix can improve ductility and oxidation/corrosion resistance, compared to traditional Co bonded grades. ⁴4Unresolved citation key: aristizabalLiquidPhaseSintering2010⁵5Unresolved citation key: aristizabalComparisonOxidationBehaviour2011

Co-Cr system, as described by Wang et al is the most reliable one. ⁶6Unresolved citation key: wangThermodynamicAnalysisTopologically2019

Markström et al. [16], Sato et al. [17] and Wang et al. [6] have assessed the Co–W system.

There are many factors influencing microstructure and properties of cemented carbides, such as composition, sintering time and temperature as well as the solubilities of doping carbides in carbide and binder phase. Sintering temperature and composition, which can be predicted by thermodynamic calculations, have a large influence on the microstructure and properties of cemented carbides [[22], [23], [24]]. Thermodynamic calculations were carried out by using Thermo-Calc software [25] according to a thermodynamic database of CSUTDCC1 [26]. The purpose of the calculation is to design appropriate amount of Cr addition and predict the optimum sintering temperature. The maximum addition of Cr in the WC-10 wt% Co cemented carbides is 0.98 wt% at 1100 °C based on the thermodynamic database CSUTDCC1 [26]. When the Cr amount exceeds the solubility limit, M7C3 phase will precipitate. To avoid the formation of unwanted phase, M6C or graphite, the carbon content in cemented carbides was carefully controlled based on thermodynamic calculations. The Cr content has a significant effect on the complete liquefaction temperature based on thermodynamic database CSUTDCC1 [26], as shown in Fig. 1. And based on the paper [19], a good agreement is obtained between calculation and DTA experiment with respect to the complete liquefaction temperature. Consequently, optimization of sintering process parameters can be given an accurate guidance by thermodynamic calculations. ¹1Unresolved citation key: tianOptimizationMechanicalProperties2020

The grain growth in liquid phase sintered materials, which is generally understood as a solution/re-precipitation process called Ostwald ripening, has often been studied from a theoretical point of view [4], [5], [6], [7], [8], [9]. Most of studies assume that carbide grains are completely surrounded by a liquid phase. These classical theories of Ostwald ripening are not sufficient to explain the grain growth mechanism in cemented carbides [10], [11], [12], [13], [14], especially in the case of low binder content which is popular for industrial applications. Because in that case WC grains are not completely surrounded by a binder phase, but contact with neighboring grains. Simulation techniques seem useful to examine the effects of both solid/liquid and solid/solid interface on grain growth behavior. ³3Unresolved citation key: kishinoComputationalStudyGrain2002

CALPHAD - Computer Coupling of Phase Diagrams and Thermochemistry

https://calphad.org/ https://www.sciencedirect.com/journal/calphad

The design of industrial processes requires reliable thermodynamic data. CALPHAD (Computer Coupling of Phase Diagrams and Thermochemistry) aims to promote computational thermodynamics through development of models to represent thermodynamic properties for various phases which permit prediction of properties of multicomponent systems from those of binary and ternary subsystems, critical assessment of data and their incorporation into self-consistent databases, development of software to optimize and derive thermodynamic parameters and the development and use of databanks for calculations to improve understanding of various industrial and technological processes. This work is disseminated through the CALPHAD journal and its annual conference. Contributions of high quality in these and related fields, especially the fields of first-principles calculations, experimental measurements of thermochemical and phase equilibrium data, phase transformations, and the process and materials designs that the CALPHAD works are based on or used for, are welcome.

Related

• Bearings — the rolling-element counterpart
• Lubrication — hydrodynamic film theory
• Tribology — the wear modes
• Gears — journal bearings on gear shafts