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非晶AlNiZr合金成分的优化

2021-09-09张志彬周志丹

河北科技大学学报 2021年4期

张志彬 周志丹

摘 要:為了解决铝基非晶合金在形成过程中容易析出α-Al晶体导致玻璃形成能力较低且不易评估的问题,设计了简单易行的玻璃形成能力评估方法,对非晶AlNiZr合金成分进行优化。首先,制备9种不同组分的AlNiZr合金铸锭;然后,在相同制备条件下,用单辊甩带法制备不同组分的合金薄带;最后,采用X射线衍射仪对薄带进行XRD表征,基于XRD结果拟合计算合金薄带的非晶含量。结果表明:在合金组分Al100-x-yNixZry中,随着Ni含量的增加玻璃形成能力提高,随着Zr含量的增加玻璃形能力成降低;当Zr含量为3%时,进一步增加Ni含量达到20%和25%,合金的玻璃形成能力降低,Al82Ni15Zr3具有更好的玻璃形成能力。通过对非晶AlNiZr合金成分的优化,可以为不含稀土元素的铝基合金的玻璃形成能力评估提供新的方法,拓展其在设备防护领域的应用空间。

关键词:非晶、微晶金属材料;铝基合金;非晶合金;玻璃形成能力;组分优化;非晶含量

中图分类号:TG139+.8;TB31   文献标识码:A

doi:10.7535/hbkd.2021yx04011

收稿日期:2021-05-24;修回日期:2021-06-19;责任编辑:张士莹

基金项目:国家重点研发计划项目(2018YFC1902400)

第一作者简介:张志彬(1982—),男,河北邢台人,高级工程师,博士,主要从事铝基非晶材料及应用基础研究工作。

E-mail:eacbia@163.com

张志彬,周志丹.非晶AlNiZr合金成分的优化[J].河北科技大学学报,2021,42(4):410-414.ZHANG Zhibin,ZHOU Zhidan.Composition optimization of amorphous AlNiZr alloys[J].Journal of Hebei University of Science and Technology,2021,42(4):410-414.

Composition optimization of amorphous AlNiZr alloys

ZHANG Zhibin,ZHOU Zhidan

(National Innovation Institute of Defense Technology,Academy of Military Sciences of PLA,Beijing 100071,China)

Abstract:In order to solve the problem that the glass forming ability of Al-based amorphous alloy is not easy to be evaluated because of the easy precipitation of α-Al crystal in the glass forming process,a simple and feasible glass forming ability evaluation scheme was designedto optimize the composition of amorphous AlNiZr alloy.Firstly,nine kinds of AlNiZr alloy ingots with different compositions were prepared; Then,under the same preparation conditions,the alloy ribbons with different compositions were prepared by single-roll strip casting method; Finally,the ribbons were characterized by XRD,and the amorphous content of alloy ribbon was calculated based on the XRD results.The results show that the glass-forming ability of Al100-x-yNixZryincreases with the increase of Ni content and decreases with the increase of Zr content; When the Zr content is 3% and the Ni content is further increased to 20% and 25%,the glass-forming ability of the alloy is reduced,and Al82Ni15Zr3 alloy has better glass-forming ability.By optimizing the compositions of amorphous AlNiZr alloy,a new evaluation scheme of glass-forming ability can be provided for the Al-based alloy without rare earth elements,and its application space in the field of equipment protection can be expanded.

Keywords:

amorphous and microcrystalline metal materials;Al-based alloy;amorphous alloy;glass-forming ability;component optimization;amorphous content

与传统合金相比,非晶合金没有晶界,不存在孪晶和位错等缺陷,因此具有较好的强度和耐腐蚀性能[1-4]。近30年来,非晶合金的应用得到了飞速发展[5-9]。在工业化应用领域推广较好的是铁基非晶合金[10],这主要得益于其高饱和磁感应强度、高磁导率、高玻璃形成能力,以及制备成本低等优势。铝基非晶合金具有较高的强度质量比,在航空航天领域应用前景广阔[11-12]。然而,铝基非晶合金的玻璃形成能力较差,非晶态制备困难,严重制约了其发展进程。

早在1965年,PREDECKI等[13]首次制备了非晶态的Al-Si合金,随后又开发了一系列的二元铝基非晶合金,如Al-Ge,Al-Cr和Al-Cu[14]等。然而受当时技术制约,非晶合金中会含有部分晶体相。1981年,INOUE等[15]和SUZUKI等[16]在二元铝基非晶基础上,添加元素制备了完全非晶的Al-(Fe,Co)-B和Al-Fe-(Si,Ge)三元铝基非晶合金,但这2种合金具有较大脆性,当时并未引起人们的足够重视。直至1987年,研究人员才制备出具有高韧性的Al-Ni-Si非晶合金[17]。随后,铝基非晶合金引起了国际社会的广泛关注,各国学者陆续制备了拉伸强度高达1 000 MPa、具有较高比强度和韧性的铝基非晶合金[18-23]。由于制备过程中铝基非晶合金容易析出α-Al晶体,因而大大降低了其玻璃形成能力[24-26]。为了提高铝基合金的玻璃形成能力,科研人员进行了大量工作,如在二元铝基合金中掺入稀土元素等[27-29]。随着深入研究不同元素对铝基合金玻璃形成能力的影响,铝基合金组分也从三元扩展到了五元。目前所报道的玻璃形成能力最高的铝基合金组分是Al-Ni-Y-Co-La五元合金,其全非晶棒材的直径可达2.5 mm[30]。含有稀土的多元铝基合金能够提高玻璃形成能力,但是其组分复杂,且含量不易控制。近年来,随着稀土元素在电池、半导体和军工领域的广泛应用,提升了含有稀土元素铝基非晶合金的制备成本。有研究表明:铝基非晶合金中,含有部分纳米晶能够在保持合金韧性的同时,增加合金的硬度[15,31];通过热喷涂技术,可以较容易制备含有纳米晶的铝基非晶涂层[32-36]。对于金属涂层形态而言,其厚度往往只有几百微米,突破了块体非晶合金中尺寸的限制,弱化了对合金玻璃形成能力的要求。不少学者在探究铝基非晶合金在表面防护领域的应用中,选择了不含稀土元素的三元组分[26,32,34]。然而,不含稀土元素铝基合金的玻璃形成能力差,很难用常规方法测量其玻璃转变温度(Tg),三元铝基合金中各元素对合金玻璃形成能力影响的相关研究也较少。

笔者以Al-Ni-Zr合金为研究体系,设计不同的合金组分,通过单辊法制备合金薄带,根据薄带的非晶含量评估不同组分合金的玻璃形成能力,分析Ni元素和Zr元素对Al-Ni-Zr合金的影响。

1 实验部分

1.1 主要材料与设备

单质Al,Ni和Zr,纯度≥99.95%(质量分数,下同),北京普瑞新材科技有限公司提供。

旋转式真空铜模熔铸系统,型号NMS-DRⅡ,成都中科新材料科技有限公司提供;真空熔体超速急冷系统,型号为NMS-GPⅡ,成都中科新材料科技有限公司提供;X射线衍射仪,D8型號,德国布鲁克AXS公司提供;机械泵;分子泵。

1.2 制备合金铸锭

采用单质Al,Ni和Zr,通过真空电弧熔炼制备Al100-x-yNixZry(x=5,10和15,y=3,6和9;x=20和25,y=3;若不特别说明,分子式下标均指代原子数)组分的合金锭。熔炼设备采用旋转式真空铜模熔铸系统,熔炼前打开循环水冷系统维持腔体温度为15~20 ℃,清理铜坩埚、炉内壁和钨极杂质,将单质去皮后按照设计组分配比置于坩埚中,其中将低密度的Al单质放置在底层。关闭炉门,先后用机械泵和分子泵抽真空,炉内真空度低于3×10-3 Pa时再充入氩气,重复抽真空步骤以确保炉内无氧气及其他杂质。开始熔炼后,先小电流引弧,随后增大电流熔化金属单质,于熔融状态下开启磁力搅拌,迅速实现合金化。熔液凝固后通过翻面进行重熔,再次合金化。反复5次合金化过程,制得均匀的母合金锭。

1.3 制备合金薄带

采用真空熔体超速急冷系统,通过单辊甩带法制备铝基合金薄带。清理炉腔并抛光铜辊,直至表面光滑如镜面,随后将去除表面氧化皮的合金锭破碎后进行清洗。称取约3 g,置于底部孔径为0.9 mm的石英管中,将石英管置于铜线圈中,距离铜辊0.02 mm,关闭炉门。预热扩散泵,依次进行抽低真空和高真空操作,使炉内真空度达到5×10-3 Pa,随后充入氩气,重复抽真空操作确保炉腔内无杂质气体。随后缓慢充入氩气,调整石英管内、外压差为0.02 Pa。进入甩带阶段,打开电机,将铜辊转速调至38 m/s,打开整流器,调节电流为46 A,通过铜线圈加热合金。待合金熔化后,打开电磁阀将熔融合金喷射到高速旋转的铜辊表面,熔液快速凝固并被甩出形成合金薄带。

1.4 样品表征

用X射线衍射仪分析薄带的相组成,仪器以CuKα为射线源,步长为0.02°,扫描速率为2°/min。依据基于薄带的XRD衍射图谱,拟合计算非晶含量[37],此方法在非晶涂层领域应用广泛[32,38-40]。

2 结果与讨论

图1所示为薄带的XRD衍射图。

图1 a)为Ni固定为5%时,不同Zr含量(3%,6%和9%)的铝基合金薄带的XRD衍射图。从图1 a)可以看出:各合金均由复杂晶体相组成,几乎不含非晶相;当Zr含量为9%时,由于含量较高,存在明显的Zr偏析,因此Al10Ni5Zr9合金中有Zr单质相,此外合金中还有α-Al,Al3Ni,Al9.83Zr0.17和Al3Zr相;当Zr含量降至6%时,合金中的Zr单质相消失,合金相的组成为α-Al和Al3Ni相;当Zr含量为3%时,晶体峰开始宽化,说明合金开始具有非晶化的倾向,主要相的组成为α-Al,Al3Ni和少量Al2NiZr6。图1 b)为Ni含量为10%的合金薄带的XRD衍射图。可以看出:Zr含量为9%时,合金有明显的α-Al相和少量Al3Ni相,另外在42°附近有一个较小的“馒头峰”,该峰是非晶相的特征。对比Zr含量为6%和3%合金薄带的XRD图谱可知,随着Zr含量的减少,晶体特征峰强度减弱,而非晶的“馒头峰”更加凸显。图1 c)为Ni固定为15%时的合金薄带的XRD衍射图。当Zr含量为9%时,相较相同Zr含量而Ni为10%时的XRD衍射图,合金的非晶特征更为明显;当Zr含量降至6%时,合金XRD图谱中的晶体特征峰基本消失,只有较明显的非晶峰;Zr含量进一步降低至3%时,除了没有晶体峰以外,其代表非晶相的“馒头峰”显得更加宽泛。

依据图1中的XRD图谱,通过拟合计算,可以得到不同组分的合金薄带的非晶含量,如图2所示。

相同条件下制备的铝基合金薄带,非晶含量越高则表示玻璃形成能力越强。在图2所示的合金组分的范围内,随着Ni含量的增加,玻璃形成能力增大。随着Zr含量的升高,玻璃形成能力降低。由此可知,Al82Ni15Zr3组分合金的玻璃形成能力较高。为进一步优化合金组分,可以增加Ni含量或者减少Zr含量。由于Zr含量已经很少,进一步优化的空间很小,因此确定Zr的最佳含量为3%。可以通过进一步增加Ni含量来比较其合金薄带的非晶含量。

图3所示为Zr含量为3%,Ni含量为15%,20%和25%时的合金薄带的XRD衍射图。

从图3可以看出,当Ni含量为20%时,合金XRD图中开始有出现晶体峰的倾向。当Ni含量增至25%时,从对应的XRD衍射图可以看出,合金已经没有非晶特征,合金存在Ni元素偏析且存在其他合金化合物,如Al3Ni和NiZr2等。当Ni含量大于15%时,合金的玻璃形成能力开始下降,由此可以确定具有最大玻璃形成能力的合金组分为Al82Ni15Zr3。

3 结 语

1)以Al-Ni-Zr为研究体系,针对AlNiZr合金玻璃形成能力不易评估的问题,设计了简单的玻璃形成能力评估方法,对比了不同组分AlNiZr合金的玻璃形成能力。

2)通过对9组合金组分进行研究,得出了Ni和Zr元素对合金的影响:随着Ni含量的逐步增加,合金的玻璃形成能力越来越大;随着Zr含量的增加,合金的玻璃形成能力越来越小。

3)固定Zr含量为3%,当Ni含量超过15%后,合金的玻璃形成能力开始减小。通过优化可知,具有最佳玻璃形成能力的合金组分为Al82Ni15Zr3。

4)本文为不含稀土元素的铝基合金的玻璃形成能力评估提供了新方法,该方法也有望应用于Zr基、Fe基等其他体系合金玻璃形成能力的评估中。在今后的工作中,可以基于AlNiZr合金组分,加入其他元素的微合金,探寻具有更高玻璃形成能力的多元铝基非晶合金。

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