SiCf/SiC复合材料用B-N-Si新型界面相的高通量制备与性能研究
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High-throughput Screening of a Novel B-N-Si Interphase for Continuous SiC Fiber Reinforced SiC Ceramic Matrix Composites
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通讯作者: 张 洁,研究员,jiezhang@imr.ac.cn,研究方向为极端环境陶瓷涂层应用基础
收稿日期: 2025-11-26 修回日期: 2026-01-09
| 基金资助: |
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Corresponding authors: ZHANG Jie, Tel:
Received: 2025-11-26 Revised: 2026-01-09
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作者简介 About authors
雷一明,男,1992年生,博士
连续碳化硅纤维增强碳化硅陶瓷基复合材料(SiCf/SiC)中,界面相通常对载荷传递、界面解离及纤维保护起着关键作用,进而决定了复合材料的力学性能、热力学稳定性及耐腐蚀性。针对热解碳和六方氮化硼等传统界面相高温水蒸气氧化性能较差的瓶颈,本研究聚焦B-N-Si新型界面相。采用高通量组合材料芯片制备及表征技术,系统研究了Si含量对其结构、力学性能以及抗高温水蒸气氧化性能的影响。结果表明,在室温沉积的B-N-Si薄膜均为非晶结构,且掺杂的硅原子倾向于取代硼原子形成Si-N键。Si含量(原子分数)为7.57%~19.66%的薄膜均满足裂纹偏转的力学判据,具有理想的增韧潜力;Si含量高于11.76%的薄膜在900 ℃、90%H2O-10%O2条件下因氧化生成B2O3‧SiO2玻璃相而膨胀,具有优异的自愈合能力和抗氧化性能。
关键词:
Continuous SiC fiber reinforced SiC ceramic matrix composites are promising high-temperature structural materials for aerospace applications, whose performance is strongly influenced by the interphase between the fiber and the matrix. Although traditional interphases such as pyrolytic carbon and hexagonal boron nitride possess a layered structure, the resistance against high-temperature steam oxidation is relatively poor. This work focused on the B-N-Si ternary system as a novel interphase candidate. The effect of Si content on the structure, mechanical properties, and high-temperature water vapor oxidation behavior of B-N-Si interphase material were systematically investigated by means of high-throughput fabrication and characterization technique. The results showed that all B-N-Si coatings deposited at room temperature exhibited an amorphous structure, with silicon atoms preferentially replacing boron atoms and forming Si-N bonds. When silicon content was in the range of 7.57%-19.66% (atomic fraction), all coatings satisfied the mechanical requirements for crack deflection. Moreover, when the silicon content exceeds 11.76%, the coatings could swell up after oxidation at 900 oC in a 90%H2O-10%O2 atmosphere due to the formation of B2O3·SiO2 glass phase, exhibiting remarkable self-healing capability and oxidation resistance.
Keywords:
本文引用格式
雷一明, 石金瑜, 吕熙睿, 张洁, 王京阳.
LEI Yiming, SHI Jinyu, LV Xirui, ZHANG Jie, WANG Jingyang.
目前,SiCf/SiC复合材料的典型界面相是热解碳(PyC)和六方氮化硼(h-BN)。这两类材料的优势在于,其弱结合的层状结构使纤维/基体间的裂纹偏转从而使复合材料强韧化,但是其抗高温水蒸气氧化性能较低。PyC在较低的温度(~450 ℃)即开始氧化,使复合材料的性能严重降低[8,9]。h-BN的氧化产物(B2O3)在高温下能使裂纹自愈合,比PyC的抗氧化性能更好。但是在实际服役环境中B2O3与水蒸气发生反应生成气态产物,留下的开放通道不能阻挡水氧腐蚀介质的侵入,导致复合材料的强度降低、脆性提高[10,11]。向BN界面相中掺杂改性元素,可提高其抗氧化性能[12]。例如,在BN中掺杂7.6%~28.6% (原子分数)Si的薄膜,在1200 ℃氧气环境的质量损失比BN降低2~3个数量级[13]。在700 ℃、10%H2O-90%O2 (体积分数)混合气中,Si掺杂量为12.1%和33.7% (原子分数)的SiBN氧化10 h未发生明显的变化;而在相同的条件下BN界面相因生成挥发性气体,陶瓷基复合材料的衰退距离超过240 mm[14]。但是,掺杂元素也扰动BN的弱结合层状结构。掺杂的Si含量(原子分数)超过24.2%时界面相材料的结构由层状结构逐渐转变为具有各向同性的非晶结构,不利于裂纹偏转[15]。目前针对SiBN的高温氧化性能的表征仍局限在600~800 ℃,且缺少针对高水蒸气分压下(
1 实验方法
1.1 薄膜制备
本研究基于组合材料芯片技术获取成分梯度变化、以阵列形式排列的B-N-Si薄膜样品。组合材料芯片的制备在四靶磁控溅射制备系统上进行,四个靶材的中心聚焦在试样台的中心,靶材中心距离试样表面约为100 mm,靶材中心与试样台中心的连线与试样台所在平面的夹角为45°。溅射使用的靶材是BN靶(纯度99.9%)和Si靶(纯度99.9%),基体是直径为50 mm的圆形单晶氧化铝。溅射开始前先将设备预抽真空到1 × 10-4 Pa以降低残余气体的污染,然后通入高纯氩气和高纯氮气混合气(氮气的含量为10%)保持压强为0.44 Pa。沉积时,将BN靶与功率为200 W的射频电源连接,将Si靶与功率为15 W的直流电源连接。沉积温度为室温,溅射时间为20 h。在溅射过程中用有101个圆孔(直径3 mm)的掩模版覆盖单晶基体,以制备出101个成分呈梯度分布的薄膜试样。
1.2 性能表征
用ESCALAB250型X射线光电子能谱仪(XPS)表征薄膜中元素的化学状态,使用单色化的Al靶(能量为1486.6 eV) X射线源,功率为150 W,X射线束斑的尺寸为500 mm,刻蚀面积为2 mm × 2 mm。测试前对薄膜进行60 s的氩离子刻蚀以去除试样表面的吸附物。用试样表面的污染碳(C 1s,结合能284.6 eV)作为荷电校正标准。对XPS谱中元素峰的面积积分,计算出各元素的含量。使用Bruker AXS型微区X射线衍射仪测定薄膜的相组成,使用Co靶的Kα线作为入射线,入射束斑尺寸直径为1 mm。用Agilent G200型纳米压痕仪测试薄膜的硬度和弹性模量,试样的厚度为1.7~2.7 mm,压入深度为150 nm,忽略基体对薄膜硬度和模量的影响。每个试样测试3~5个点,取其结果的平均值。
对在单晶氧化铝基体上沉积的薄膜试样进行高温水蒸气氧化测试:将试样置于GSL1600X型高温水蒸气氧化炉中,以5 ℃·min-1的速率将温度升至900 ℃。炉腔中的水蒸气由SG-3050型相对湿度发生器产生,湿度误差为0.3%。使用高纯氧气作为载体,将水蒸气通入氧化炉,在氧化测试过程中氧化气氛为H2O-O2混合气(H2O体积的占比90%,O2体积的占比10%,记为90%H2O-10%O2)。实验装置的温度在露点以上,以防止水蒸气冷凝。因为在高温水蒸气氧化测试中氧化铝基体不氧化或挥发,观测到的厚度和形貌变化完全源于薄膜。氧化1 h后,用P-7台阶仪测试薄膜的厚度以分析厚度的变化。使用配有能谱系统的SUPRA 55型扫描电子显微镜(SEM)观察薄膜氧化后的微观形貌。
2 结果和讨论
2.1 B-N-Si组合材料芯片的相结构和化学键合
图1
图1
制备在单晶氧化铝上的组合材料芯片光学照片和Si含量分布图
Fig.1
Optical photograph of the combinatorial material chip fabricated on a single crystal alumina substrate (a) and corresponding Si content distribution map (b)
对B-N-Si薄膜试样进行XPS分析以明确其中各元素的键合状态,图2给出了5种代表性薄膜的XPS谱。从N 1s谱(图2a)可以看出,随着Si含量的提高XPS峰的峰位由397.4 eV移至397.2 eV。其原因是,B-N-Si体系的N-B键和N-Si键对应的结合能分别为398.3 eV和397.4 eV[21],表明随着Si含量的提高N-Si键的占比随之提高,使XPS峰的峰位移向低能方向。如图2b所示,Si 2p的峰位介于101.2~101.4 eV之间,对应Si-N键;且随着Si含量的提高,Si-N键对应的XPS峰强度随之提高。图2c给出了B 1s谱,其中位于190.2 eV的峰对应B-N键;随着Si含量的提高B-N键的结合能不变,表明Si的加入并未影响B原子的化学环境。基于以上结果可以判定,掺杂的Si原子更倾向于取代BN中的B原子形成Si-N键。模拟计算结果[14]表明:含量为3.0%~11.1%的Si原子会占据BN晶格中B原子的位置,固溶在层状BN结构中;随着Si含量的进一步提高,非晶结构中会出现Si3B x N4-x 构型,使B-N-Si薄膜由层状结构转变为各向同性的非晶结构。Si3B x N4-x 构型中的Si-N键的键长随着Si含量的提高而增大,对应结合能的降低,使Si 2p的峰位移向低能方向。掺杂在B-N-Si薄膜中的Si会优先固溶在BN晶格中B原子的位置,且随着掺杂Si含量的提高非晶结构中Si3B x N4-x 构型的比例随之提高。
图2
图2
不同Si含量样品的XPS图谱
Fig.2
XPS spectra of the B-N-Si coatings with different Si contents (a) N 1s, (b) Si 2p, (c) B 1s
2.2 B-N-Si组合材料芯片的力学性能
图3给出了B-N-Si薄膜的硬度和模量与Si含量的关系。可以看出,薄膜的硬度范围为8.0~9.9 GPa,弹性模量的范围为119.8~150.2 GPa。在BN中掺杂少量Si时,薄膜的模量迅速减小,因为Si破坏了B-N的强键结合;Si含量为9.65%~15.97%的薄膜,其硬度和模量的变化很小;Si含量超过15.97%的薄膜硬度和模量再次出现降低的趋势,可归因于低模量Si3B x N4-x 构型占比的提高。一般来说,从基体扩展到纤维的裂纹,其尖端存在径向和轴向两个方向的应力场。当径向应力的最大值达到界面分层所需的强度而轴向应力最大值还未达到纤维的强度时,裂纹将在界面偏转。Pompidou和Lamon[22]进行有限元模拟得到了径向最大应力值与轴向最大应力值的比值(
图3
图3
B-N-Si薄膜的硬度和模量与Si含量的关系
Fig.3
Hardness and modulus of B-N-Si coatings as a function of Si content
图4
2.3 B-N-Si组合材料芯片的高温水蒸气氧化行为
在服役环境中,提高界面相抗高温水蒸气氧化性能的关键在于提高反应产物的自愈合能力。为实现对B-N-Si界面相连续组分高温氧化性能的高通量评价,并建立材料组分与高温水蒸气氧化性能之间的映射关联,本文发展了基于静态高温水蒸气氧化和离位厚度测量的高温水蒸气氧化测试方法。如图5所示,制备态薄膜各成分样本的厚度为1.7~2.7 μm。随着Si含量的提高厚度随之减小,这可归因于溅射过程中BN靶的功率(200 W)远比Si靶的功率(15 W)高,导致接近BN靶成分点处的沉积速率较高。将薄膜在900 ℃、90%H2O-10%O2条件下氧化1 h,则各成分点的厚度增大到2.3~3.1 μm。Si含量为7.57%的薄膜氧化后厚度减小;Si含量超过8.22%时,氧化后的薄膜呈现增厚趋势,且随着Si含量的提高,厚度增长率由8.5%逐渐提高到84.9%。因为氧化引起的尺寸变化为微米量级,而试样的直径为3 mm,故直径的变化可忽略不计。因为薄膜在氧化过程中完全消耗,氧化前后厚度的变化直接反映了氧化物与原始薄膜的体积比,表明氧化层厚度的增加对应了薄膜氧化后体积的膨胀。根据B-N-Si薄膜的体积变化率,计算出Si含量为8.22%~19.66%的薄膜中金属离子体积与金属原子体积之比值(Pilling-Bedworth Ratio, PBR)为1.085~1.849。这表明,Si含量为8.22%~19.66%成分点薄膜的PBR均大于1,生长过程中的氧化膜处于压应力状态,有助于封闭其中的裂纹和孔洞,从而提高反应产物的自愈合能力。
图5
图5
B-N-Si薄膜在900 ℃、90%H2O-10%O2条件下氧化前后的厚度变化
Fig.5
Thickness change of B-N-Si coatings before and after oxidation in 90%H2O-10%O2 at 900 oC
图6给出了薄膜氧化后的典型形貌。从图6a和b可以看出,Si含量较低(7.57%和8.22%)的薄膜,部分表面剥落。随着Si含量提高到11.76% (图6c),氧化后的薄膜保持完好,未观察到剥落现象,且表面生成了大量突起的岛状产物。能谱分析结果表明,Si元素聚集在岛状产物中。同时,随着Si含量的进一步提高,薄膜表面的岛状产物密度随之提高,但是尺寸减小。因为氧化环境为900 ℃、90%H2O-10%O2,薄膜的氧化产物仍以B2O3和SiO2为主[23]。高温水蒸气腐蚀过程中,B-N-Si薄膜厚度的减小可以归因于B2O3和NO2的挥发,而厚度的增大则源于硼硅酸玻璃B2O3‧SiO2生成引起的体积膨胀。纯BN氧化后产生的B2O3在900 ℃干燥环境中才会挥发,但是其与水蒸气在600 ℃就发生反应生成气体产物[24]。与纯BN相比,B-N-Si体系中SiO2的形成不仅提高了氧化产物的热稳定性,还生成了粘度适中的硼硅酸玻璃增强了薄膜的保护性。B2O3的挥发在薄膜表面残留孔洞,且B2O3‧SiO2氧化产物的粘度随着B2O3含量的降低而提高,Si含量的提高更有利于玻璃相流动性的提高,进而使自愈合能力提高[25]。当B-N-Si薄膜中Si含量大于11.76%时,氧化物层的粘度适中,能在高温下保持较高的流动性,从而形成光滑的表面。
图6
图6
Si含量为7.57%、8.22%、11.76%和17.44%的B-N-Si薄膜在900 ℃、90%H2O-10%O2条件下氧化后的表面形貌
Fig.6
Surface morphologies of B-N-Si coatings with Si content of 7.57% (a), 8.22% (b), 11.76% (c) and 17.44% (d) after oxidation in 90%H2O-10%O2 at 900 oC
SiCf/SiC复合材料作为航空发动机的热端部件服役时,由于燃料的燃烧气体产物中含有5%~10%水蒸气,基体材料可能发生高温水蒸气氧化。为了降低高温水蒸气对SiCf/SiC复合材料的影响,使用BN基界面相可利用氧化产生的体积膨胀和氧化物与基体的粘附实现裂纹自愈合。在高温水蒸气环境中BN基界面相的体积变化,主要受氧化和氧化产物挥发的影响。其中界面相的氧化,主要受氧通过界面相生成氧化物的扩散速率控制;而氧化产物的挥发,则主要受水蒸气分压和扩散通道宽度(即界面相厚度)的影响。例如,界面相厚度小于0.17 μm的SiCf/BN/SiC复合材料在1000 ℃、水分压
3 结论
(1) 在室温沉积的B-N-Si薄膜均具有非晶结构,掺杂的Si原子倾向于取代B原子形成Si-N键。
(2) Si含量为7.57%~19.66%的薄膜均满足裂纹偏转的力学判据,具有理想的增韧潜力。
(3) B-N-Si薄膜的抗高温水蒸气氧化性能依赖于Si含量:低Si含量的薄膜因B2O3挥发而失效;Si含量高于11.76%的薄膜,在900 ℃、90%H2O-10%O2条件下氧化后因生成B2O3‧SiO2玻璃相而体积膨胀,使其具有优异的自愈合性能和抗氧化性能。
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