本文選題：DD6單晶合金　切入點(diǎn)：中溫脆性　出處：《武漢理工大學(xué)》2015年碩士論文

【摘要】：鎳基單晶高溫合金是通過(guò)定向凝固技術(shù)制備的,它按照預(yù)定的取向生長(zhǎng)形成單一柱狀晶,完全消除了晶界,因此具有優(yōu)異的高溫強(qiáng)度、蠕變抗力和良好的抗氧化和耐腐蝕等綜合性能,被廣泛應(yīng)用于航空航天、艦船等領(lǐng)域,目前幾乎成為所有先進(jìn)航空發(fā)動(dòng)機(jī)渦輪葉片的首選材料。鎳基單晶合金優(yōu)異的力學(xué)性能與其微觀組織結(jié)構(gòu)及其演化過(guò)程是密不可分的,因此研究單晶合金特殊γ/γ′兩相共格組織結(jié)構(gòu)及其在不同溫度下的演化具有科學(xué)內(nèi)涵和工程應(yīng)用價(jià)值。本文以我國(guó)自主研制的第二代單晶合金DD6為對(duì)象開(kāi)展了實(shí)驗(yàn)研究,通過(guò)室溫、650℃、850℃和1020℃條件下的拉伸試驗(yàn)得到不同溫度下的應(yīng)力-應(yīng)變曲線和力學(xué)性能,并利用SEM、TEM和EDS等先進(jìn)微觀測(cè)試手段和對(duì)比分析方法,研究了DD6單晶合金的初始微觀組織結(jié)構(gòu)、元素分布特點(diǎn)以及其在不同溫度的組織演化特點(diǎn)和微觀變形機(jī)制,探討了合金斷裂形式和γ′相高溫筏化機(jī)理。DD6單晶合金拉伸真實(shí)應(yīng)力-應(yīng)變曲線表明,室溫時(shí)出現(xiàn)明顯的加工硬化現(xiàn)象,隨溫度升高合金動(dòng)態(tài)回復(fù)加快,而在高溫時(shí)發(fā)生動(dòng)態(tài)再結(jié)晶過(guò)程。通過(guò)力學(xué)性能測(cè)試結(jié)果可以看到,650℃時(shí)抗拉強(qiáng)度和屈服強(qiáng)度最高,分別達(dá)到1020MPa和854MPa,但此時(shí)塑性最低,斷面收縮率為2.7%,僅為室溫的1/6;隨著溫度升高,屈服強(qiáng)度顯著降低,塑性得到恢復(fù)。合金表現(xiàn)出中溫脆性現(xiàn)象,中溫位錯(cuò)發(fā)生交滑移是屈服強(qiáng)度反常溫度升高的主要原因,而動(dòng)態(tài)應(yīng)變時(shí)效(鋸齒狀屈服)和滑移面的減聚導(dǎo)致合金出現(xiàn)塑性低谷。微觀觀測(cè)結(jié)果顯示,經(jīng)標(biāo)準(zhǔn)熱處理之后DD6單晶合金組織為立方態(tài)的γ′相以共格方式鑲嵌在γ基體中,并沿100取向有序規(guī)則地排列。合金中γ′相平均尺寸為0.45μm,體積分?jǐn)?shù)達(dá)到70%左右,γ′相和γ基體晶格錯(cuò)配度為-0.45%。合金元素在兩相中分布不均勻,Co、Cr、W、Mo等合金元素主要溶入γ基體,對(duì)基體起到固溶強(qiáng)化作用;而Al、Ti與Ni形成Ni3(Al,Ti)金屬間化合物,是γ′相主要組成成分,另外Ta也是形成γ′相的重要元素。元素的定向擴(kuò)散導(dǎo)致1020℃時(shí)具有負(fù)錯(cuò)配度的DD6單晶合金γ′相發(fā)生N型筏化。DD6單晶合金室溫和650℃時(shí)變形機(jī)制為位錯(cuò)剪切γ′相,合金具有類解理或解理斷裂特征;高溫時(shí),合金變形方式為位錯(cuò)繞過(guò)γ′相,合金斷口具有大小不一的等軸韌窩,表現(xiàn)為微孔聚集型斷裂;850℃時(shí)合金變形機(jī)制為位錯(cuò)剪切γ′相向繞過(guò)γ′相轉(zhuǎn)變,合金斷口同時(shí)具有解理和韌窩斷裂特征。
[Abstract]:Nickel-based single crystal superalloy was prepared by directional solidification technique. It formed a single columnar crystal in accordance with the predetermined orientation and completely eliminated the grain boundary, so it has excellent high temperature strength.Creep resistance, good oxidation resistance and corrosion resistance are widely used in aerospace, ship and other fields. At present, they are the preferred materials for all advanced aero-engine turbine blades.The excellent mechanical properties of Ni-base single crystal alloy are closely related to its microstructure and evolution process.Therefore, it has scientific connotation and engineering application value to study the special 緯 / 緯 'two-phase coherent structure of single crystal alloy and its evolution at different temperatures.In this paper, the second generation single crystal alloy DD6, which has been developed independently in China, has been studied experimentally. The stress-strain curves and mechanical properties at different temperatures have been obtained by tensile tests at room temperature of 650 鈩，

本文編號(hào)：1719106