不銹鋼表面FeCoCrAlCuNiMox激光高熵合金化層

不銹鋼表面FeCoCrAlCuNiMox激光高熵合金化層的相演變PHASE EVOLUTION OF FeCoCrAlCuNiMox COATINGS BY LASER HIGH-ENTROPY ALLOYING ON STAINLESS STEELS

采用激光高熵合金化技術(shù)在2Cr13不銹鋼表面制備FeCoCrAlCuNiMox (x = 0, 0.5, 1) 激光高熵合金化層. 利用XRD, SEM, EDS及顯微硬度計對FeCoCrAlCuNiMox激光高熵合金化層相轉(zhuǎn)變機制、微觀組織形貌及硬度進行研究. 結(jié)果表明, 2Cr13 不銹鋼基材主元素Fe, Cr 在激光輻照條件下參與了表面合金化過程, 形成了FeCoCrAlCuNiMox激光高熵合金化層; 隨著Mo含量的增加, 合金化層相結(jié)構(gòu)逐漸由fcc+bcc雙相固溶體結(jié)構(gòu)轉(zhuǎn)變?yōu)閒cc+bcc+hcp三相共存, hcp相主要為Ni3Mo和Co7Mo6, 且Ni3Mo相含量高于Co7Mo6相, 熔池的凝固溫度在激光高熵合金化層相選擇過程中起到重要作用. 激光高熵合金化層顯微組織為典型的枝晶組織; 隨著Mo含量的增加, 枝晶內(nèi)析出塊狀Ni3Mo和Co7Mo6相. FeCoCrAlCuNiMox激光高熵合金化層的顯微硬度在390~490 HV之間, 且Mo 含量的增加顯著提高高熵合金化層的硬度.

High-entropy alloys (HEAs), defined as solid solution alloys which have at least 5 principal elements but no more than 13 elements, with concentrations of each principal element ranging from 5% to 35% in atomic fraction, are emerging as one of the hot research frontiers in the metallic materials field. The significance of HEAs originates from their various combinations of high strength, good thermal stability and excellent resistance to corrosion, wear and oxidation. HEAs exhibit simple solid solutions with bcc and/or fcc structure(s) due to the effect of high mixing entropy in the solid solution state of HEAs, which may make the HEAs with improved mechanical and physical properties. However, a small quantity of intermetallic compounds can also form in certain HEAs, indicating that the formation of simple solid solutions cannot solely depend on the high mixing entropy. Then, the theory of HEAs based on the concept of entropy-enthalpy competition to judge whether or not simple phases will form was proposed. However, even if an alloy meets these criterions, it can still contain intermetallic phases. Why and how these intermetallics form in HEAs needs much more clarification. In this work, Co-Al-Cu-Ni-Mox (x = 0, 0.5, 1) powder system with close-to-equiatomic ratios was mixed and laser surface alloyed onto 2Cr13 stainless steel substrates, and then the FeCoCrAlCuNiMox HEA coatings was obtained by reaction synthesis of Fe, Cr with Co-Al-Cu-Ni-Mox powder. The phase transition mechanism, microstructure and microhardness of FeCoCrAlCuNiMox coatings were investigated by XRD, SEM, EDS and microhardness tester. Experimental results showed that the principal element of Fe, Cr in 2Cr13 stainless steel substrate participated in surface alloying process during the laser irradiation, forming FeCoCrAlCuNiMox laser high-entropy alloying coatings. With the increase of Mo content, the crystal structures of FeCoCrAlCuNiMox laser high-entropy alloying coatings evolved from fcc+bcc two-phase solid solution to fcc+bcc solid solution with hcp phase precipitations. The hcp phases were mainly Ni3Mo and Co7Mo6, and the content of Ni3Mo phase was higher than that of Co7Mo6. The phase formation analysis indicated that besides ? and δ parameters, solidification temperature of the molten pool must be considered during the phase selection, instead of melting point as suggested previously. The microstructure of the coatings exhibited a typical dendrite structure. With the increase of Mo content, the block-shaped Ni3Mo and Co7Mo6 precipitated in the innerdendritic regions. The microhardness of the FeCoCrAlCuNiMox laser high-entropy alloying coatings was 390~490 HV, which significantly increased with the increase of Mo content.

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