ICME tools for the design of cemented carbides

Abstract

Cemented carbides have often been generalized as composite materials composed of hardtungsten carbide (WC) particles embedded in a softer and tougher Cobalt-based matrix. Thisgeneralization has become less accurate over time as alternative binder systems and additionalcarbides (for instance γ-carbides) have been introduced. Such changes have always been drivenby the need to excel in heavy-duty wear applications, as well as, more recently, by the effort tominimize cemented carbide’s social and ecological impact. The development of new grades thatfulfil both goals has been traditionally addressed following a trial-and-error methodology, in whichextensive experimental work must be performed to reach a satisfactory outcome. This leads to longand expensive concept-to-application processes. A more efficient alternative to design sustainablecemented carbides with the required performance is by using the Integrated ComputationalMaterials Engineering (ICME) approach. In this approach models and databases are developed todescribe the relationships between the process-structure-properties-performance (P-S-P-P) of thematerial. These models provide valuable information on the mechanisms ruling the behavior ofthe material at each step in the P-S-P-P chain, which can be used to design new materials moreefficiently.In this work two models are developed, and validated, contributing to an ICME-based frameworkfor the design of cemented carbides. The first model addresses the relationship between the materialstructure and its hardness (property) as a function of temperature. This Hot Hardness model usesstructural information on the mean and variation of the hard phase grain size, and the volume contentof binder to accurately predict the hardness of cemented carbides in a temperature range spanningfrom room temperature up to 1000°C. In addition, the model characterizes the differentmechanisms contributing to softening at elevated temperatures during service. Specifically, theintrinsic softening of the hard phases is in this work described using a Peierls-Nabarro-basedmodel. Further, a method to describe the microstructural rearrangement at high temperatures isproposed.The second model addresses the relationship between the material processing and its structure.The Dynamic C-window model describes the precipitation of detrimental phases in cementedcarbides to redefine the compositional processability limits of these materials, known as the Cwindow.Unlike traditional methods that rely solely on thermodynamic equilibrium calculations,this model also considers the cooling rate and the initial WC grain size, which are influentialprocessing design parameters affecting the width of the C-window. In addition to define a Cwindowthat take kinetics into account, the model also gives insights into the mechanisms rulingthe microstructural evolution during cooling, as well as predicting the particle size distribution ofthe detrimental phases as a function of the considered processing parameters. The modeling resultshave been experimentally validated through the processing and microstructural characterization ofsamples with controlled processing condition. This has allowed to conclude that the C-windowcan effectively be broadened by increasing the cooling rate during processing or/and by increasingthe WC grain size when the application allows it. The implications of this observation on thepotential processing of cemented carbides with alternative binder systems are also described.

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