Fe-C-Cr基多元高熵结构合金凝固路径与碳化物析出行为研究

The Fe-C-Cr based alloys have been widely used at wear-resistant parts in steel company, mineral plants, and others. In all industrial fields, the improvement of abrasion wear-resistance, especially, high performance of roll materials as rolling tool, has been strongly required due to its short working life. In the present project, thanks to the merits of high-entropy alloys that the mutually competitive growth of elements eliminates the formation of large-sized intermetallic phases, the technique of high-entropy microstructure alloying is adopted. Several strong carbide-forming elements are planned to be added simultaneously into the alloy to form the high-entropy microstructure. The finer carbides are expected to benefit the wear resistance of the material. The influences of solidification microstructures, the amount, size and morphologies of the carbides on the wear resistance of the alloys are investigated through both modeling and experiments. The present project focuses on the study of the solidification path, the microsegregation and the morphologies of matrix and carbides in Fe-C-Cr-∑Xi（Xi chosen as Ti,V,Mo,W) alloy system. Combining with the thermodynamic equilibrium calculations, the para-equilibrium microsegregation model together with the finite-diffusion microsegregation model will be developed to predict the solidification path of the multicomponent / multi-phase alloy system. The advantage of the former is to predict the total- range solidification path varying from the liquid state to the room temperature, and the merit of latter is the reflection of the effects of solute finite diffusion in different level in solid and liquid phases. The prediction of solidification morphologies especially those of carbides with faceted microstructure are expected through coupling the finite diffusion microsegregation model with macroscopic transport (Finite -Volume method) and the nucleation and grain growth procedure (Cellular Automaton method). With the help of solidification experiments, chemical analysis, erosion experiments and hardness tests, the nature of carbides precipitation and its influence on the wear resistance will be quantitively analyzed. The results and corresponding mechanics will be a helpful tool to accurately predict the precipitation of phases in multicomponent alloy system.

Fe-C-Cr基合金作为耐磨材料被广泛用于钢铁厂、矿山机械的易磨损部位，提高其耐磨性能和使用寿命，是当前迫切需要解决的问题。借鉴高熵合金元素间制约扩散以避免大尺寸金属间相生长的理念，本研究拟采取多元高熵合金化手段，同时添加几种强碳化物形成元素来形成高熵结构，以细化碳化物晶粒，提高合金耐磨性能。利用数值和实验手段考察合金基体和碳化物形态、分布对其强度、硬度及耐磨性的影响，拟建立与热力学计算相结合的类平衡模型预测液相-室温全程凝固路径、以及有限扩散的微观偏析模型反映溶质有限扩散影响，结合描述碳化物形貌的组织预测模型，预测Fe-C-Cr-ΣXi(Xi=Ti,V,Mo,W)多元合金系包括碳化物在内的凝固路径，预测机体及以小平面晶生长的碳化物形貌。结合DSC及凝固实验、成分检测、硬度检测、耐磨实验等手段，最终阐明Fe-C-Cr基多元高熵结构合金中碳化物析出机制及性状对合金硬度及耐磨性影响的定量规律。

Fe-C-Cr基合金作为耐磨材料被广泛应用于钢铁厂、矿山机械的易磨损部位，材料的大量磨损消耗直接与合金中碳化物与基体结构缺陷密切相关。为此，需系统研究合金凝固路径、成分分布和合金相形成机制，并通过合金元素间制约扩散来细化碳化物晶粒，提高合金耐磨性能。本研究采用多元合金化手段，通过同时添加几种强碳化物形成元素来获得高硬度碳化物，并控制其数量、形态及分布来提高合金的硬度和耐磨性能，结合数值和实验手段考察合金基体和碳化物形态、分布对其强度、硬度的影响。本研究建立了与热力学计算相结合的偏平衡结合近平衡模型预测液相-室温全程凝固路径，考察了溶质不同扩散特性的影响，合理阐释了包晶、共析过程固-固转变机制及碳化物析出规律。通过Fe-C-Cr-V-Mo-W-Co-Ni合金高温DSC及凝固实验、成分检测、硬度检测并结合凝固路径预测，获得了添加碳化物组成元素C, V, W, Ti, Cr, Mo等以及添加基体改善元素Co, Ni等对凝固过程中MC，M7C3, M6C，M2C, M3C型碳化物析出性状影响规律，获得了碳化物种类及数量对合金硬度影响规律。耦合全程凝固路径建立连续介质模型，获得了Fe-C-Cr 基多元合金铸锭成分分布。建立了描述枝晶及小面晶生长的碳化物形貌的组织预测模型，明确球墨铸铁（Fe-C-Si合金）中奥氏体与石墨、Fe-C-Cr-Ti合金中奥氏体与M7C3碳化物、奥氏体与TiC碳化物协同生长机制、形貌演变及分布特性。最终阐明Fe-C-Cr基多元合金中碳化物析出机制及性状对合金硬度及耐磨性影响的定量规律。研究结果为提高Fe-C-Cr基合金最终耐磨性能和使用寿命提供理论依据。