【摘要】：高熵合金是一種新型金屬材料,具有獨(dú)特的結(jié)構(gòu)和優(yōu)異的性能,因此受到廣泛的關(guān)注。本課題用真空電弧熔煉法制備了含有難熔金屬元素的CuYZr/Al,Ti,Hf、CuxYxZrTiHf(x=0.6,1.0,摩爾比)和AlxHfNbTiZr(x=0、0.5、0.75、1.0、1.25和1.5,摩爾比)系列高熵合金。較為系統(tǒng)地分析了這些高熵合金的物相結(jié)構(gòu)和組織形貌,測試了熱學(xué)參數(shù)、力學(xué)性能、海水耐蝕性等性能,探討了合金成分對高熵合金結(jié)構(gòu)和各項性能的影響機(jī)制。主要研究結(jié)果如下:1.三種CuYZr/Al,Ti,Hf高熵合金的主要結(jié)構(gòu)都由密排六方(HCP1)樹枝晶和存在于枝晶間的體心立方(BCC)結(jié)構(gòu)CuY型化合物相組成。特別地,富Hf的HCP2固溶體相和少量非晶相分別出現(xiàn)在CuYZrAlHf和CuYZrAlTi高熵合金中。Hf、Ti和Zr元素集中分布在HCP1和HCP2固溶體中,這表明HCP結(jié)構(gòu)元素能促進(jìn)高熵合金中HCP固溶體的形成。CuYZrTiHf高熵合金的壓縮屈服強(qiáng)度為1340 MPa,斷裂方式為塑性斷裂;而CuYZrAlHf和CuYZrAlTi高熵合金具有更高的強(qiáng)度和硬度,斷裂方式為脆性斷裂。富Hf-HCP2相和非晶相的存在能阻礙位錯運(yùn)動,起到明顯強(qiáng)化作用,大幅降低了CuYZrAlHf和CuYZrAlTi合金的塑性。海水溶液中的電化學(xué)腐蝕測試表明,三種合金枝晶間的CuY型化合物發(fā)生了明顯的腐蝕,而HCP樹枝晶耐蝕性良好。此外,CuYZrAlTi合金具有較好的耐點(diǎn)蝕性。2.鑄態(tài)CuxYxZrTiHf高熵合金由HCP固溶體相和位于枝晶間的CuY化合物相組成。通過同時改變Cu、Y兩種元素的含量,能夠調(diào)節(jié)這兩種物相在高熵合金中的體積分?jǐn)?shù)。其中,Cu0.6Y0.6ZrTiHf合金的HCP相體積分?jǐn)?shù)增多,CuY相明顯減少。兩種合金在1400℃以下沒有出現(xiàn)熔化現(xiàn)象。Cu0.6Y0.6ZrTiHf高熵合金的塑性較好,但硬度和壓縮強(qiáng)度略低于CuYZrTiHf合金。CuY化合物和HCP固溶體的體積分?jǐn)?shù)主要決定了高熵合金力學(xué)性能的差異。海水耐蝕性測試表明,Cu0.6Y0.6ZrTiHf合金出現(xiàn)了二次鈍化行為,具有較好的局部耐點(diǎn)蝕性。對Cu0.6Y0.6ZrTiHf和CuYZrTiHf合金樣品進(jìn)行緩慢預(yù)形變(變形量10%)后,其強(qiáng)度和硬度都有小幅提升,但后者的塑性大幅下降。此外,預(yù)形變顯著改善了這兩種合金的海水耐蝕性。3.在AlxHfNbTiZr高熵合金(簡稱為Alx)中,Al0和Al0.5高熵合金由單一的無序BCC固溶體組成。除無序固溶體外,Al0.75~Al1.5高熵合金中新生成了有序BCC固溶體,且這兩相的晶格常數(shù)很接近。較低的混合焓和價電子濃度有助于AlxHfNbTiZr高熵合金中有序固溶體的形成。在1400℃以下,AlxHfNbTiZr高熵合金未出現(xiàn)熔化現(xiàn)象。Al添加導(dǎo)致了高熵合金力學(xué)性能的顯著變化。隨著Al含量升高,脆硬的有序BCC相增多,合金的強(qiáng)度、硬度大幅提高,塑性變形能力明顯下降。AlxHfNbTiZr高熵合金的強(qiáng)化機(jī)制有固溶強(qiáng)化、有序固溶體強(qiáng)化和細(xì)晶強(qiáng)化。Al添加有效降低了高熵合金的密度,提升了強(qiáng)度,從而大幅提升了合金的比強(qiáng)度。Al0合金具有良好的海水耐蝕性。Al添加后,合金的鈍化區(qū)寬度減小,其表面發(fā)生了明顯的點(diǎn)蝕現(xiàn)象,海水耐蝕性下降。
[Abstract]:High entropy alloy is a new metal material with unique structure and excellent properties. In this paper, a series of high entropy alloys containing refractory metal elements, CuYZr/Al,Ti,Hf,CuxYxZrTiHf (x = 0.6N, 1.0, mole ratio) and AlxHfNbTiZr (x = 0. 5, 0. 75, 0. 05), were prepared by vacuum arc melting (VARF). The phase structure and microstructure of these high entropy alloys were systematically analyzed. The thermal parameters, mechanical properties and corrosion resistance of seawater were tested. The mechanism of the effect of alloy composition on the structure and properties of high entropy alloys was discussed. The main results are as follows: 1. The main structures of the three kinds of CuYZr/Al,Ti,Hf high entropy alloys are composed of dense hexagonal (HCP1) dendrites and bulk centered cubic (BCC) (BCC) structure CuY compounds which exist between dendrites. In particular, Hf rich HCP2 solid solution phase and a small amount of amorphous phase appear in CuYZrAlHf and CuYZrAlTi high entropy alloys respectively. Hf,Ti and Zr elements are concentrated in HCP1 and HCP2 solid solution. The results show that HCP structure element can promote the formation of HCP solid solution in high entropy alloy. The compressive yield strength of CuYZrTiHf high entropy alloy is 1340 MPa, and the fracture mode is plastic fracture. CuYZrAlHf and CuYZrAlTi high entropy alloys have higher strength and hardness, and the fracture mode is brittle fracture. The existence of rich Hf-HCP2 phase and amorphous phase can hinder dislocation movement, play an obvious strengthening role, and greatly reduce the plasticity of CuYZrAlHf and CuYZrAlTi alloys. The electrochemical corrosion test in aqueous solution shows that the CuY type compounds of three kinds of alloy dendrites are obviously corroded, while the HCP dendrites have good corrosion resistance. In addition, CuYZrAlTi alloy has good pitting corrosion resistance. The as-cast CuxYxZrTiHf high entropy alloy consists of HCP solid solution phase and CuY compound phase located between dendrites. By changing the content of Cu,Y two elements at the same time, the volume fraction of these two phases in high entropy alloy can be adjusted. The volume fraction of HCP phase increases and CuY phase decreases obviously in Cu0.6Y0.6ZrTiHf alloy. The two alloys have no melting phenomenon below 1400 鈩，

本文編號：2349180