【摘要】：TiAl金屬間化合物合金具有高的比強(qiáng)度、比彈性模量以及優(yōu)異的高溫力學(xué)性能,是一種具有巨大發(fā)展?jié)摿Φ暮教旌娇沼眯滦透邷亟Y(jié)構(gòu)材料。但TiAl室溫塑性差、脆性大、室溫延伸率不足3%、機(jī)加難度大等固有屬性使其成形工藝異常復(fù)雜與困難,是TiAl尚未獲得大量應(yīng)用的主要障礙。為克服TiAl合金成形工藝的不足,本文以現(xiàn)階段應(yīng)用最為廣泛的Ti4822合金(Ti-48Al-2Cr-2Nb,at%)為基礎(chǔ),開展了TiAl合金的激光沉積制造(LDM)工藝研究,分析不同激光沉積制造工藝參數(shù)條件下TiAl合金的顯微組織與力學(xué)性能,以及后續(xù)熱處理工藝參數(shù)對成形后TiAl合金顯微組織與力學(xué)性能的影響。研究發(fā)現(xiàn),經(jīng)LDM工藝制備的TiAl合金顯微組織特征為等軸狀初生晶粒內(nèi)包含有大量層片狀的γ、α2和微量層片狀B2相;掃描速度恒定,隨著激光功率的增加,初生等軸晶晶粒尺寸逐漸增大,晶內(nèi)的α2和B2相含量逐漸增加,γ相含量降低,合金顯微硬度逐漸增大;激光功率恒定,隨著掃描速度的增加,初生等軸晶晶粒尺寸逐漸減小,晶內(nèi)的α2和B2相含量逐漸減少,γ相含量增加,合金顯微硬度逐漸增大。經(jīng)綜合分析認(rèn)為激光功率1200W、掃描速度7mm/s為優(yōu)佳的TiAl合金LDM工藝參數(shù)。熱處理后的TiAl合金顯微組織以γ和α2相為主,同時(shí)包含微量B2相。1260℃固溶處理后獲得雙態(tài)組織,由塊狀γ以及層片狀間隔分布的γ+α2混合組織構(gòu)成,XRD譜線中,γ相衍射峰強(qiáng)度和比例略高于α2相,二者體積分?jǐn)?shù)基本相當(dāng);1330℃固溶處理后,合金形成近片層組織,主要由層片狀γ+α2構(gòu)成,XRD譜線中γ衍射峰強(qiáng)度和比例較高,體積分?jǐn)?shù)明顯高于α2;1350℃固溶處理后同樣獲得近片層組織,由層片狀γ+α2構(gòu)成,組織內(nèi)γ相衍射峰強(qiáng)度和比例高于α2相,其α2相比例高于1330℃熱處理的TiAl合金。隨著熱處理溫度的升高TiAl合金顯微硬度逐漸減小。經(jīng)熱等靜壓再經(jīng)同上熱處理后,TiAl合金組織中以γ和α2為主,B2相微量,顯微組織類型基本相同。在XRD譜線中,隨固溶溫度升高,γ相衍射峰強(qiáng)度和比例增加,α2衍射峰強(qiáng)度和比例減小,表明γ相含量隨固溶溫度增加逐漸增大,α2含量隨固溶溫度增加而減小,B2相含量微量。經(jīng)(熱等靜壓+熱處理)與熱處理相比,合金組織結(jié)構(gòu)沒有明顯改變,組織內(nèi)的層片尺寸明顯有增大。熱等靜壓后隨著熱處理溫度的升高TiAl合金顯微硬度逐漸減小,硬度值略大于同等熱處理溫度而未經(jīng)熱等靜壓的樣品。
[Abstract]:Because of its high specific strength, specific elastic modulus and excellent mechanical properties at high temperature, TiAl intermetallic alloy is a new type of high-temperature structural material for aerospace and aeronautics with great potential for development. However, the inherent properties of TiAl, such as poor plasticity at room temperature, high brittleness, less than 3% elongation at room temperature, and so on, make its forming process extremely complex and difficult, which is the main obstacle to the large-scale application of TiAl. In order to overcome the deficiency of forming process of TiAl alloy, the laser deposition process of Ti4822 alloy (Ti-48Al-2Cr-2Nb,at%) was studied on the basis of Ti4822 alloy (Ti-48Al-2Cr-2Nb,at%), which is the most widely used alloy at present, and the laser deposition technology of (LDM) alloy was studied in this paper. The microstructure and mechanical properties of TiAl alloy under different laser deposition process parameters and the influence of heat treatment parameters on the microstructure and mechanical properties of formed TiAl alloy were analyzed. It is found that the microstructure of TiAl alloy prepared by LDM process is characterized by a large number of lamellar 緯, 偽 2 and micro lamellar B2 phases in equiaxed primary grains. The scanning velocity is constant. With the increase of laser power, the grain size of primary equiaxed crystal increases gradually, the contents of 偽 _ 2 and B _ 2 phases increase gradually, and the content of 緯 phase decreases, and the microhardness of the alloy increases gradually. The laser power is constant, with the increase of scanning speed, the grain size of primary equiaxed crystal decreases gradually, the content of 偽 _ 2 and B _ 2 phase decreases, the content of 緯 phase increases, and the microhardness of the alloy increases gradually. Comprehensive analysis shows that laser power 1200 W and scanning speed 7mm/s are the best technological parameters of TiAl alloy LDM. After heat treatment, the microstructure of TiAl alloy consists mainly of 緯 and 偽 2 phases, and contains a small amount of B 2 phase. After solution treatment at 1260 鈩，

本文編號：2434898