During the sintering process of cemented carbides (e.g., WC-Co), grain growth tends to become excessive, leading to a decline in mechanical properties (e.g., reduced toughness and strength). The addition of grain growth inhibitors (GGIs) effectively suppresses grain coarsening, optimizing material performance.<\/p>\n

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Mechanisms of Grain Growth Inhibition<\/h1>\n

The grain growth inhibitors primarily influence WC grain growth through the following approaches:<\/p>\n

Solute Drag Effect<\/h2>\n

Principle:grain growth Inhibitor elements (e.g., V, Cr) dissolve into the WC or Co phase, adsorb at WC\/Co phase boundaries or WC\/WC grain boundaries, hindering atomic diffusion and grain boundary migration.<\/p>\n

Elemental Solid Solution<\/h3>\n

Inhibitors such as VC and Cr\u2083C\u2082 decompose during sintering, with V and Cr atoms dissolving into the WC lattice or Co binder phase.<\/p>\n

Example: V substitutes W sites in WC (forming (V,W)C solid solution), while Cr dissolves into the Co phase (forming (Co,Cr) solid solution).<\/p>\n

Grain Boundary Segregation<\/h3>\n

Solute atoms (e.g., V, Cr) enrich at WC grain boundaries or WC\/Co interfaces, forming a “solute atmosphere.”<\/p>\n

These segregated atoms pin grain boundaries, increasing the energy barrier for migration.<\/p>\n

Drag on Grain Boundary Movement<\/h3>\n

When grain boundaries attempt to migrate, solute atoms must move along, but their slower diffusion rate impedes boundary motion.<\/p>\n

Analogous to “viscous drag,” this suppresses WC grain coalescence and growth.<\/p>\n

Applicable grain growth Inhibitors: VC, Cr\u2083C\u2082 (primarily rely on solute drag).<\/p>\n

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Second-Phase Pinning Effect (Zener Pinning)<\/h2>\n

Principle: grain growth inhibitors form nanoscale carbide particles (e.g., (V,W)C, (Cr,W)C) that physically obstruct WC grain growth at boundaries.<\/p>\n

Nanoparticle Precipitation<\/h3>\n

During sintering, decomposed VC or Cr\u2083C\u2082 reprecipitate as nanoscale carbides (e.g., 5\u201350 nm (V,W)C particles), typically located at WC\/WC or WC\/Co interfaces.<\/p>\n

Grain Boundary Pinning<\/h3>\n

Migrating boundaries must overcome the restraint of these nanoparticles, requiring additional energy.<\/p>\n

According to the Zener equation, pinning force (F\u209a) correlates with particle volume fraction (f) and size (r). Finer, denser particles yield stronger inhibition.<\/p>\n

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Suppression of WC Dissolution-Reprecipitation<\/h2>\n

Nanoparticles hinder WC dissolution in liquid Co and redeposition, reducing Ostwald ripening (“large grains consuming small ones”).<\/p>\n

Applicable grain growth Inhibitors: VC (strongest pinning), Cr\u2083C\u2082 (moderate), TaC\/NbC (weaker).<\/p>\n

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Common Grain Growth Inhibitors and Their Characteristics<\/h1>\n\n\n\n\n\n\n\n

Mechanism<\/b><\/strong><\/td>\n	Primary Inhibitors<\/td>\n	Key Characteristics<\/td>\n<\/tr>\n
Solute Drag<\/td>\n	VC, Cr\u2083C\u2082<\/td>\n	Hinders grain boundary migration through solute atom segregation<\/td>\n<\/tr>\n
Second-Phase Pinning<\/td>\n	VC, Cr\u2083C\u2082<\/td>\n	Physically blocks grain boundaries via nanoparticle dispersion (Zener pinning)<\/td>\n<\/tr>\n
Dissolution-Reprecipitation Control<\/td>\n	VC, Cr\u2083C\u2082<\/td>\n	Reduces WC dissolution in Co binder and slows atomic diffusion<\/td>\n<\/tr>\n
Grain Boundary Energy Modification<\/td>\n	TaC, NbC<\/td>\n	Lowers grain boundary energy, enhancing high-temperature stability<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n  <\/p>\n Selection and Optimization of grain growth Inhibitors<\/h1>\n Ranking of Inhibition Effectiveness<\/h2>\n VC > Cr\u2083C\u2082 > TaC \u2248 NbC<\/p>\n