鈷基高溫合金碳化物演變及相關性能研究
發(fā)布時間：2018-08-18 12:51
【摘要】：鈷基高溫合金因其具有較高的熔化溫度、優(yōu)異的抗熱疲勞以及抗熱腐蝕性能,廣泛應用于航空發(fā)動機中導向葉片材料。熱疲勞是導向葉片最主要的失效形式之一。熱疲勞裂紋主要萌生于碳化物和晶界處,并且會沿著碳化物和晶界擴展。為了提高合金的熱疲勞性能,需要探索改善碳化物和晶界形態(tài)的途徑。熱處理是影響碳化物類型、形貌、尺寸以及分布的重要手段。本文重點研究了熱處理條件下DD640M和DD6509兩種鈷基高溫合金碳化物組織演變規(guī)律及其對熱疲勞行為的影響,并關注了相應條件下合金持久性能的變化規(guī)律。另外,為避免晶界對碳化物演變產(chǎn)生影響,合金應用單晶凝固技術制備。同時,晶界的消除也有利于合金熱疲勞性能的提高。本研究為鈷基高溫合金的發(fā)展和應用提供理論基礎。DD640M合金的鑄態(tài)組織為粗大的富Cr網(wǎng)狀M_7C_3和富Ta、Zr的骨架狀MC的兩種共晶碳化物。在1140～1260℃/4h熱處理過程中,隨著溫度升高初生碳化物的數(shù)量和尺寸逐漸減小。另外,熱處理過程中發(fā)生了 M_7C_3→M23C6反應以及MC碳化物的蛻化。本研究中首次揭示M_7C_3碳化物以原位方式向M23C6碳化物發(fā)生轉變。M23C6碳化物在M_7C_3碳化物和基體界面處形核并朝著M_7C_3碳化物長大。初生MC碳化物在熱處理過程中發(fā)生蛻化釋放大量的W和Ti,溫度較低時分解形成M6C碳化物,溫度較高時則僅以固溶形式發(fā)生蛻化。DD6509合金的鑄態(tài)組織為粗大的富Ta骨架狀MC和富Cr不規(guī)則塊狀M23C6兩種共晶碳化物。在1260～1330℃/4h熱處理過程中,初生碳化物逐漸發(fā)生溶解。初生M23C6碳化物在1300℃/4h熱處理時完全溶解到基體中,另外,高溫下部分骨架狀MC碳化物分解成顆粒狀。固溶處理促進DD640M和DD6509合金在1000～1200℃時效條件下析出更均勻更細小的二次碳化物。DD640M合金基體中只析出二次M23C6碳化物;DD6509合金中析出二次MC和M23C6碳化物,其中二次MC碳化物分布在基體中而二次M23C6碳化物分布在碳化物周圍。DD640M合金初生M_7C_3共晶碳化物在1280℃發(fā)生熔化,重凝組織為片層更細的M23C6共晶碳化物。M_7C_3共晶碳化物的熔化過程為M_7C_3碳化物先轉變成M23C6碳化物再發(fā)生熔化。初生MC共晶碳化物在1320℃發(fā)生熔化,重凝后形成骨架更細的MC共晶碳化物。DD6509合金中初生M23C6共晶碳化物熔化發(fā)生在1335℃以及MC共晶碳化物熔化發(fā)生在1340℃。本研究首次關注了鈷基高溫合金中初生共晶碳化物的熔化現(xiàn)象,為優(yōu)化鈷基高溫合金的化學成分以及微觀組織提供借鑒。采用合適的熱處理方法可有效改善DD640M和DD6509合金的熱疲勞性能。其中,DD640M 和 DD6509 合金分別在 1260℃/24h 和 1330℃/24h+1100℃/100h熱處理后熱疲勞性能提高最為明顯。熱處理使得合金中碳化物更加彌散和細化,減緩熱疲勞裂紋萌生與擴展,從而提高合金熱疲勞性能。DD640M和DD6509合金高溫固溶處理后持久壽命均有提高,其緣于熱處理后獲得良好的組織穩(wěn)定性、細小MC碳化物以及過飽和固溶體。DD640M合金鑄態(tài)樣品在高溫持久過程中發(fā)生了 M_7C_3→M23C6, M23C6→M6C和MC→M23C6轉變。熱處理使得鈷基高溫合金熱疲勞性能和持久性能均得到顯著提高,這改變了熱處理對鈷基高溫合金性能影響有限的認識,鈷基高溫合金熱處理應該得到應有的重視。兩種合金的成分差異影響合金碳化物組織的組成和穩(wěn)定性。DD6509合金的熱疲勞性能和高溫持久性能均優(yōu)于DD640M合金,歸因于DD6509合金更加穩(wěn)定的碳化物組織、較高的碳化物含量和二次MC碳化物的析出。
[Abstract]:Cobalt-based superalloys are widely used in aero-engine guide vanes because of their high melting temperature, excellent thermal fatigue resistance and thermal corrosion resistance. Thermal fatigue is one of the most important failure modes of guide vanes. In order to improve the thermal fatigue properties of alloys, it is necessary to explore ways to improve the carbide and grain boundary morphology. Heat treatment is an important means to influence the type, morphology, size and distribution of carbides. In addition, in order to avoid the effect of grain boundary on carbide evolution, the alloy was prepared by single crystal solidification technique. At the same time, the elimination of grain boundary was beneficial to the improvement of thermal fatigue properties of the alloy. The as-cast microstructure of the alloy is two kinds of eutectic carbides with thick Cr-rich reticulate M_7C_3 and rich Ta, Zr skeleton MC. The amount and size of primary carbides decrease gradually with the increase of temperature during the heat treatment process from 114 to 1260 c/4h. In addition, the reaction of M_7C_3 M23C_6 and the decay of MC carbides occur during the heat treatment. M23C6 carbides nucleate at the interface between M 7C 3 carbides and matrix and grow towards M 7C 3 carbides. Primary MC carbides decay and release large amounts of W and Ti during heat treatment, and decompose to form M6C carbides at lower temperatures, but only solid solution at higher temperatures. The as-cast microstructure of DD6509 alloy is composed of coarse Ta-rich skeleton MC and Cr-rich irregular block M23C6 eutectic carbides. Primary carbides dissolve gradually during heat treatment at 1260-1330 c/4h. Primary M23C6 carbides dissolve completely into the matrix at 1300 c/4h, and some skeleton MCs at high temperature. Solid solution treatment promotes the precipitation of more homogeneous and finer secondary carbides in DD640M and DD6509 alloys at 1000-1200 C. Only secondary M23C6 carbides are precipitated in DD640M alloy matrix; secondary MC and M23C6 carbides are precipitated in DD6509 alloy matrix, and secondary MC carbides are distributed in matrix while secondary M23C6 carbides are precipitated in DDD6509 alloy matrix. The primary M_7C_3 eutectic carbide of DD640M alloy melts at 1280 C, and the recrystallized structure is M23C_6 eutectic carbide with finer lamellar structure. The melting process of M_7C_3 eutectic carbide is that M_7C_3 carbide first transforms into M23C_6 carbide and then melts. The primary MC eutectic carbide melts at 1320 C and then re-solidifies. MC eutectic carbides with finer skeleton. Melting of primary M23C6 eutectic carbides in DD6509 alloy occurred at 1335 C and melting of MC eutectic carbides occurred at 1340 C. The melting phenomenon of primary eutectic carbides in cobalt-based superalloys was studied for the first time in this study, which provided a reference for optimizing the chemical composition and microstructure of cobalt-based superalloys. Thermal fatigue properties of DD640M and DD6509 alloys can be effectively improved by proper heat treatment. Thermal fatigue properties of DD640M and DD6509 alloys are improved most obviously after heat treatment at 1260 c/24h and 1330 c/24h + 1100 c/100h, respectively. The rupture life of DD640M and DD6509 alloys after high temperature solid solution treatment is improved because of their good microstructure stability, fine MC carbides and supersaturated solid solution. As-cast samples of DD640M alloy occur M_C_3_M23C6, M23C6_M6;MC and MC_M23C during high temperature rupture. 6 transformation. The thermal fatigue and rupture properties of Co-based superalloys have been significantly improved by heat treatment, which changes the understanding that heat treatment has limited effect on the properties of Co-based superalloys. The heat treatment of Co-based superalloys should be given due attention. The composition difference between the two alloys affects the composition and stability of the carbides. The thermal fatigue properties and high temperature rupture properties of alloy DD6509 are superior to those of DD640M alloy, which is attributed to the more stable carbide structure, higher carbide content and secondary MC carbide precipitation.
【學位授予單位】：中國科學技術大學
【學位級別】：博士
【學位授予年份】：2017
【分類號】：TG132.3
本文編號：2189526
[Abstract]:Cobalt-based superalloys are widely used in aero-engine guide vanes because of their high melting temperature, excellent thermal fatigue resistance and thermal corrosion resistance. Thermal fatigue is one of the most important failure modes of guide vanes. In order to improve the thermal fatigue properties of alloys, it is necessary to explore ways to improve the carbide and grain boundary morphology. Heat treatment is an important means to influence the type, morphology, size and distribution of carbides. In addition, in order to avoid the effect of grain boundary on carbide evolution, the alloy was prepared by single crystal solidification technique. At the same time, the elimination of grain boundary was beneficial to the improvement of thermal fatigue properties of the alloy. The as-cast microstructure of the alloy is two kinds of eutectic carbides with thick Cr-rich reticulate M_7C_3 and rich Ta, Zr skeleton MC. The amount and size of primary carbides decrease gradually with the increase of temperature during the heat treatment process from 114 to 1260 c/4h. In addition, the reaction of M_7C_3 M23C_6 and the decay of MC carbides occur during the heat treatment. M23C6 carbides nucleate at the interface between M 7C 3 carbides and matrix and grow towards M 7C 3 carbides. Primary MC carbides decay and release large amounts of W and Ti during heat treatment, and decompose to form M6C carbides at lower temperatures, but only solid solution at higher temperatures. The as-cast microstructure of DD6509 alloy is composed of coarse Ta-rich skeleton MC and Cr-rich irregular block M23C6 eutectic carbides. Primary carbides dissolve gradually during heat treatment at 1260-1330 c/4h. Primary M23C6 carbides dissolve completely into the matrix at 1300 c/4h, and some skeleton MCs at high temperature. Solid solution treatment promotes the precipitation of more homogeneous and finer secondary carbides in DD640M and DD6509 alloys at 1000-1200 C. Only secondary M23C6 carbides are precipitated in DD640M alloy matrix; secondary MC and M23C6 carbides are precipitated in DD6509 alloy matrix, and secondary MC carbides are distributed in matrix while secondary M23C6 carbides are precipitated in DDD6509 alloy matrix. The primary M_7C_3 eutectic carbide of DD640M alloy melts at 1280 C, and the recrystallized structure is M23C_6 eutectic carbide with finer lamellar structure. The melting process of M_7C_3 eutectic carbide is that M_7C_3 carbide first transforms into M23C_6 carbide and then melts. The primary MC eutectic carbide melts at 1320 C and then re-solidifies. MC eutectic carbides with finer skeleton. Melting of primary M23C6 eutectic carbides in DD6509 alloy occurred at 1335 C and melting of MC eutectic carbides occurred at 1340 C. The melting phenomenon of primary eutectic carbides in cobalt-based superalloys was studied for the first time in this study, which provided a reference for optimizing the chemical composition and microstructure of cobalt-based superalloys. Thermal fatigue properties of DD640M and DD6509 alloys can be effectively improved by proper heat treatment. Thermal fatigue properties of DD640M and DD6509 alloys are improved most obviously after heat treatment at 1260 c/24h and 1330 c/24h + 1100 c/100h, respectively. The rupture life of DD640M and DD6509 alloys after high temperature solid solution treatment is improved because of their good microstructure stability, fine MC carbides and supersaturated solid solution. As-cast samples of DD640M alloy occur M_C_3_M23C6, M23C6_M6;MC and MC_M23C during high temperature rupture. 6 transformation. The thermal fatigue and rupture properties of Co-based superalloys have been significantly improved by heat treatment, which changes the understanding that heat treatment has limited effect on the properties of Co-based superalloys. The heat treatment of Co-based superalloys should be given due attention. The composition difference between the two alloys affects the composition and stability of the carbides. The thermal fatigue properties and high temperature rupture properties of alloy DD6509 are superior to those of DD640M alloy, which is attributed to the more stable carbide structure, higher carbide content and secondary MC carbide precipitation.
【學位授予單位】：中國科學技術大學
【學位級別】：博士
【學位授予年份】：2017
【分類號】：TG132.3
【參考文獻】
相關期刊論文 前10條
1 謝君;于金江;孫曉峰;金濤;孫元;;高鎢K416B鑄造鎳基合金高溫蠕變期間碳化物演化行為[J];金屬學報;2015年04期
2 馬亞芹;于興福;孫文儒;;K417G合金γ+γ′共晶初熔特性及影響因素研究[J];鑄造;2014年02期
3 石倩穎;李相輝;鄭運榮;謝光;張健;馮強;;HRS和LMC工藝制備的兩種鎳基單晶高溫合金鑄態(tài)及固溶微孔的形成[J];金屬學報;2012年10期
4 孫躍軍;劉喜中;劉夢龍;張軍;;Co基合金的短時高溫氧化行為[J];熱加工工藝;2012年08期
5 劉海霞;司松海;司乃潮;袁婷婷;;鋁銅定向凝固合金熱疲勞應力場數(shù)值模擬[J];江蘇大學學報(自然科學版);2011年06期
6 肖旋;許輝;秦學智;郭永安;郭建亭;周蘭章;;3種鑄造鎳基高溫合金熱疲勞行為研究[J];金屬學報;2011年09期
7 夏鵬成;于金江;孫曉峰;管恒榮;胡壯麒;;DZ40M合金的熱疲勞性能[J];稀有金屬材料與工程;2011年01期
8 劉源;于金江;徐巖;孫曉峰;;單晶高溫合金的冷熱疲勞裂紋生長行為研究[J];稀有金屬材料與工程;2009年01期
9 王志輝;趙乃仁;李金國;侯貴臣;金濤;孫曉峰;胡壯麒;;熱處理工藝對SRR99鎳基單晶高溫合金組織和性能的影響[J];材料工程;2008年12期
10 ;Crack growth behavior of SRR99 single crystal superalloy under thermal fatigue[J];Rare Metals;2008年05期
相關碩士學位論文 前1條
1 王中原;GH5188合金組織與熱疲勞性能研究[D];沈陽理工大學;2012年
，本文編號：2189526
本文鏈接：http://sikaile.net/kejilunwen/jiagonggongyi/2189526.html
最近更新
教材專著
