The chemical composition, microstructure, strength, and thermal stability of polymer-derived Sylramic ^(TM)SiC{ }^{\mathrm{TM}} \mathrm{SiC} fibers fabricated by Dow Corning and COI Ceramics, Inc., and nitrogen-treated Sylramic ^(TM)SiC{ }^{\mathrm{TM}} \mathrm{SiC} fibers, referred to as Sylramic ^(TM)-iBN{ }^{\mathrm{TM}}-\mathrm{iBN} and Super Sylramic ^(TM)-iBN{ }^{\mathrm{TM}}-\mathrm{iBN} SiC fibers, were investigated and compared. The baseline Sylramic ^(TM)SiC{ }^{\mathrm{TM}} \mathrm{SiC} fibers fabricated by both vendors as well as the nitrogen-treated Sylramic ^(TM)SiC{ }^{\mathrm{TM}} \mathrm{SiC} fibers are composed mostly of beta-SiC(∼97wt%)\beta-\mathrm{SiC}(\sim 97 \mathrm{wt} \%) with small amounts of TiB_(2)(∼2wt%)\mathrm{TiB}_{2}(\sim 2 \mathrm{wt} \%), amorphous carbon ( ∼1wt%\sim 1 \mathrm{wt} \% ) and trace amounts of B_(4)C\mathrm{B}_{4} \mathrm{C}. Most of the amorphous carbon is segregated at the core/interior of the fibers. Both baseline and nitrogen-treated Sylramic ^(TM){ }^{\mathrm{TM}} SiC fibers have similar grain size and pore size distribution, except for a thin layer of in-situ grown crystalline BN (30-70 nm) on the surface of Sylramic ^(TM)-iBN{ }^{\mathrm{TM}}-\mathrm{iBN} and Super Sylramic ^(TM){ }^{\mathrm{TM}}-iBN fibers. Wide variation in strength within a batch as well as between batches is observed in both baseline and nitrogen-treated Sylramic ^(TM)SiC{ }^{\mathrm{TM}} \mathrm{SiC} fibers but both types of fibers are microstructurally stable at temperatures to 1800^(@)C1800{ }^{\circ} \mathrm{C} in argon and nitrogen environments compared to Nicalon ^(TM)-S{ }^{\mathrm{TM}}-\mathrm{S} and Tyranno®-SA SiC fibers. Under the same creep condition, Super Sylramic ^(TM)-iBN{ }^{\mathrm{TM}}-\mathrm{iBN} fibers show better creep resistance compared to Sylramic ^(TM){ }^{\mathrm{TM}}, Sylramic ^(TM)-iBN{ }^{\mathrm{TM}}-\mathrm{iBN}, HiNicalon ^("TM ")-S{ }^{\text {TM }}-S, and Tyranno ^(®){ }^{\circledR}-SA fibers. Possible reasons for strength variability and the mechanism of in-situ BN formation on Sylramic ^(TM)SiC{ }^{\mathrm{TM}} \mathrm{SiC} fibers are discussed. 聚合物衍生的 Sylramic 的化学成分、微观结构、强度和热稳定性 ^(TM)SiC{ }^{\mathrm{TM}} \mathrm{SiC} 由 Dow Corning 和 COI Ceramics, Inc. 制造的纤维以及经过氮化处理的 Sylramic ^(TM)SiC{ }^{\mathrm{TM}} \mathrm{SiC} 纤维，称为 Sylramic ^(TM)-iBN{ }^{\mathrm{TM}}-\mathrm{iBN} 和超级系统 ^(TM)-iBN{ }^{\mathrm{TM}}-\mathrm{iBN} 对 SiC 纤维进行了研究和比较。基线 Syramic ^(TM)SiC{ }^{\mathrm{TM}} \mathrm{SiC} 两家供应商制造的纤维以及经过氮化处理的 Sylramic ^(TM)SiC{ }^{\mathrm{TM}} \mathrm{SiC} 纤维主要由 beta-SiC(∼97wt%)\beta-\mathrm{SiC}(\sim 97 \mathrm{wt} \%) 与少量的 TiB_(2)(∼2wt%)\mathrm{TiB}_{2}(\sim 2 \mathrm{wt} \%) ，无定形碳（ ∼1wt%\sim 1 \mathrm{wt} \% ）和微量的 B_(4)C\mathrm{B}_{4} \mathrm{C} 。大多数无定形碳偏析在纤维的芯/内部。基线和氮处理的Sylramic ^(TM){ }^{\mathrm{TM}} SiC纤维具有相似的晶粒尺寸和孔径分布，除了Sylramic表面上的一薄层原位生长的晶体BN（30-70 nm） ^(TM)-iBN{ }^{\mathrm{TM}}-\mathrm{iBN} 和超级系统 ^(TM){ }^{\mathrm{TM}} -iBN纤维。在基线和氮处理的 Sylramic 中观察到批次内以及批次之间的强度差异很大 ^(TM)SiC{ }^{\mathrm{TM}} \mathrm{SiC} 纤维，但两种类型的纤维在一定温度下微观结构均稳定 1800^(@)C1800{ }^{\circ} \mathrm{C} 与尼卡龙相比，在氩气和氮气环境中 ^(TM)-S{ }^{\mathrm{TM}}-\mathrm{S} 和 Tyranno®-SA 碳化硅纤维。在相同蠕变条件下，Super Sylramic ^(TM)-iBN{ }^{\mathrm{TM}}-\mathrm{iBN} 与 Sylramic 纤维相比，纤维表现出更好的抗蠕变性 ^(TM){ }^{\mathrm{TM}} , 系统 ^(TM)-iBN{ }^{\mathrm{TM}}-\mathrm{iBN} , 海尼卡隆 ^("TM ")-S{ }^{\text {TM }}-S ，和泰拉诺 ^(®){ }^{\circledR} -SA纤维。强度变异的可能原因以及 Sylramic 上原位 BN 形成的机制 ^(TM)SiC{ }^{\mathrm{TM}} \mathrm{SiC} 讨论了纤维。
1. Introduction 一、简介
For the development of next generation SiC//SiC\mathrm{SiC} / \mathrm{SiC} composites for turbine applications, small diameter SiC fibers ( < 20 mum<20 \mu \mathrm{~m} ) are required that are microstructurally stable not only during fabrication, but also during use conditions of the composites. In addition, the reinforcing fibers should also display better creep resistance and strain-to-failure capability than the composite matrix to achieve required creep and cyclic durability in the composites. A variety of polymer-derived SiC fibers with wide variation in moduli and creep resistances have been commercially produced, but none have creep resistance equivalent to or better than chemically vapor deposited (CVD) SiC, which exhibits a steady-state creep rate of 10^(-9)10^{-9} to 10^(-10)10^{-10} /s at 1400^(@)1400^{\circ} Cat stresses up to 275 MPa [1,2]. 为了下一代的发展 SiC//SiC\mathrm{SiC} / \mathrm{SiC} 用于涡轮机应用的复合材料、小直径 SiC 纤维（ < 20 mum<20 \mu \mathrm{~m} ）不仅在制造过程中而且在复合材料的使用条件下都要求微观结构稳定。此外，增强纤维还应表现出比复合材料基体更好的抗蠕变性和应变失效能力，以实现复合材料所需的蠕变和循环耐久性。各种聚合物衍生的碳化硅纤维在模量和抗蠕变性方面差异很大，但没有一种具有与化学气相沉积 (CVD) 碳化硅相当或更好的抗蠕变性，化学气相沉积 (CVD) 碳化硅的稳态蠕变速率为 10^(-9)10^{-9} 到 10^(-10)10^{-10} /秒在 1400^(@)1400^{\circ} Cat 应力高达 275 MPa [1,2]。
The first generation of small diameter polymer-derived SiC fibers was based on melt spinnable polycarbosilane (PCS) and polytitanocarbosilane (PTC) polymer compositions that were developed by 第一代小直径聚合物衍生的 SiC 纤维基于可熔融纺丝的聚碳硅烷 (PCS) 和聚钛碳硅烷 (PTC) 聚合物组合物，这些聚合物组合物由
Yajima et al. in the early 1970 s [3,4]. In the 1980 s, these fibers were commercially produced by Nippon Carbon and Ube companies, Tokyo, Japan as CG Nicalon ^("TM "){ }^{\text {TM }} and Tyranno ^(®){ }^{\circledR} LoxM SiC fibers, respectively and are essentially composed of silicon oxycarbide (SIOC) phase [5-9]. However, this phase at temperatures > 1000^(@)C>1000^{\circ} \mathrm{C} decomposed and caused significant loss in strength as well as modulus [10-12]. 矢岛等人。 20 世纪 70 年代初 [3,4]。 20 世纪 80 年代，这些纤维由日本东京的 Nippon Carbon 和 Ube 公司进行商业化生产，名称为 CG Nicalon ^("TM "){ }^{\text {TM }} 和泰拉诺 ^(®){ }^{\circledR} LoxM SiC 纤维分别主要由碳氧化硅 (SIOC) 相组成 [5-9]。然而，这个阶段在温度 > 1000^(@)C>1000^{\circ} \mathrm{C} 分解并导致强度和模量显着损失[10-12]。
To reduce silicon oxycarbide phase and improve thermal stability, the spun PCS and PTC precursor fibers were cured in the electron beam, pyrolyzed under anaerobic conditions, and then densified in a controlled environment [13-15]. The resulting fibers consists of beta\beta-SiC crystallites, free-carbon aggregates, and a poorly organized intergranular phase of silicon and carbon atoms [16,17][16,17]. This led to commercialization of second generation SiC fibers, Hi-Nicalon ^(TM){ }^{\mathrm{TM}} and Tyranno ^(®){ }^{\circledR} LoxE. Although, the second generation SiC fibers exhibited slightly better thermal stability than the first generation SiC fibers, they still degraded in strength and showed poor creep resistance at temperatures > 1300^(@)C>1300^{\circ} \mathrm{C} due to residual SiOC and free-carbon phases [18,19][18,19]. 为了减少碳氧化硅相并提高热稳定性，纺成的PCS和PTC前体纤维在电子束中固化，在厌氧条件下热解，然后在受控环境中致密化[13-15]。所得纤维由以下组成 beta\beta -SiC 微晶、游离碳聚集体以及组织不良的硅和碳原子晶间相 [16,17][16,17] 。这导致了第二代 SiC 纤维 Hi-Nicalon 的商业化 ^(TM){ }^{\mathrm{TM}} 和泰拉诺 ^(®){ }^{\circledR} 洛克斯E。尽管第二代SiC纤维的热稳定性比第一代SiC纤维稍好，但它们的强度仍然下降，并且在一定温度下的抗蠕变性较差 > 1300^(@)C>1300^{\circ} \mathrm{C} 由于残留的 SiOC 和游离碳相 [18,19][18,19] 。
To develop fully crystalline, near stoichiometric, creep resistant polymer-derived SiC fibers, different processing routes were followed after spinning PCS and PTC polymer and curing the polymer fiber either by electron beam irradiation or by a combination of oxidizing and reducing environments to significantly reduce or completely eliminate SiOC phase and excess carbon. This effort resulted in the development of third generation SiC fibers such as Hi-Nicalon ^(TM)-S{ }^{\mathrm{TM}}-\mathrm{S} from Nippon Carbon, Sylramic ^(TM){ }^{\mathrm{TM}} from Dow Corning, and Tyranno®-SA from Ube Industries. 为了开发完全结晶、接近化学计量、抗蠕变的聚合物衍生 SiC 纤维，在纺丝 PCS 和 PTC 聚合物并通过电子束辐照或通过氧化和还原环境的组合来固化聚合物纤维后，采用了不同的加工路线，以显着减少或减少彻底消除SiOC相和多余的碳。这项努力促成了第三代 SiC 纤维的开发，例如 Hi-Nicalon ^(TM)-S{ }^{\mathrm{TM}}-\mathrm{S} 来自 Nippon Carbon、Sylramic ^(TM){ }^{\mathrm{TM}} 来自道康宁 (Dow Corning) 的Tyranno®-SA，以及来自宇部兴产 (Ube Industries) 的 Tyranno®-SA。
Nippon Carbon used the first two processing steps similar to those of Hi-Nicalon ^("TM "){ }^{\text {TM }} SiC fibers (i.e., spinning of PCS polymer into fibers and curing the fibers in electron beam radiation), but then the fiber was heat treated in a hydrogen environment to reduce the carbon content from a C//Si\mathrm{C} / \mathrm{Si} atomic ratio from 1.39 to 1.05 near stoichiometric ratio and further sintered at higher temperatures to achieve polycrystalline ceramic fibers [20,21]. Nippon Carbon 使用了与 Hi-Nicalon 类似的前两个处理步骤 ^("TM "){ }^{\text {TM }} SiC纤维（即将PCS聚合物纺成纤维并在电子束辐射下固化纤维），但随后将纤维在氢气环境中进行热处理以减少碳含量 C//Si\mathrm{C} / \mathrm{Si} 原子比从1.39到1.05接近化学计量比并进一步在更高温度下烧结以获得多晶陶瓷纤维[20,21]。
Ube Industries explored the potential of controlling the chemistry of the PCS by grafting a metal into its chemical structure and developed a polyaluminocarbosilane, synthesized by reaction of aluminum acetylacetonate with PCS. The addition of aluminum in the PCS chains is considered to help the cross-linking of the polymeric fibers and also plays an important role as a sintering aid [22,23]. By this route, amorphous SiAlCO fibers are obtained after spinning polymer polyaluminocarbosilane, curing the green fibers in air, and pyrolyzing the fibers at temperatures to 1300^(@)C1300^{\circ} \mathrm{C} under inert gas. The resulting ceramic SiAlCO fibers are densified by sintering at temperatures > 1700^(@)C>1700{ }^{\circ} \mathrm{C}. Additions of aluminum claimed to favor formation of a smooth surface and densified SiC during the sintering process [24]. This fiber is commercialized as Tyranno®-SA3 SiC fibers. 宇部工业公司探索了通过将金属接枝到其化学结构中来控制 PCS 化学的潜力，并开发了一种聚铝碳硅烷，该聚铝碳硅烷是通过乙酰丙酮铝与 PCS 反应合成的。在PCS链中添加铝被认为有助于聚合物纤维的交联，并且作为烧结助剂也发挥着重要作用[22,23]。通过该路线，将聚合物聚铝碳硅烷纺丝，在空气中固化绿色纤维，并在一定温度下热解纤维，得到非晶态 SiAlCO 纤维。 1300^(@)C1300^{\circ} \mathrm{C} 在惰性气体下。所得陶瓷 SiAlCO 纤维通过在一定温度下烧结而致密化 > 1700^(@)C>1700{ }^{\circ} \mathrm{C} 。据称，添加铝有利于在烧结过程中形成光滑的表面和致密的 SiC [24]。这种纤维作为 Tyranno®-SA3 SiC 纤维进行商业化。
Dow Corning, in the late 1980s, used commercially available Tyr-anno®-LoxM SiC fibers from Ube Industries as a precursor for fabrication of fully crystalline, near stoichiometric SiC fiber. Dow Corning fabricated the SiC fiber by a batch process of deoxidation of Tyranno®LoxM SiC fiber in B_(2)O_(3)\mathrm{B}_{2} \mathrm{O}_{3} and an argon environment, and then sintering the fiber in an argon environment at ∼1800^(@)C\sim 1800^{\circ} \mathrm{C} [25]. This fiber is fully crystalline, near stoichiometric SiC , and contains minor phases of TiB_(2)\mathrm{TiB}_{2} and carbon. Dow Corning later commercialized this fiber as Sylramic ^(TM){ }^{\mathrm{TM}} SiC fiber. This fiber is currently fabricated by COI Ceramics, Inc. (henceforth COIC). To improve their environmental stability and creep resistance, these fibers were heat treated in a nitrogen environment at 1800^(@)C1800^{\circ} \mathrm{C} to create a thin layer of in-situ BN coating on the fiber surface [26]. The in-situ BN coating can be created by heat treating Sylramic ^(TM){ }^{\mathrm{TM}} fibers either in 0.1MN//m^(2)0.1 \mathrm{MN} / \mathrm{m}^{2} flowing N_(2)\mathrm{N}_{2} gas or in 3.52MN//m^(2)3.52 \mathrm{MN} / \mathrm{m}^{2} static N_(2)\mathrm{N}_{2}. Although the mechanism of the in-situ BN formation on the fiber surface is not clearly known, it is hypothesized that as-fabricated Sylramic ^(TM){ }^{\mathrm{TM}} fiber contains excess free boron, and when the fiber is heat treated at high temperatures in a N_(2)\mathrm{N}_{2} environment, the excess boron migrates to the fiber surface and reacts with N_(2)\mathrm{N}_{2} to form a BN coating [26] 道康宁公司在 20 世纪 80 年代末使用宇部工业公司 (Ube Industries) 的市售 Tyr-anno®-LoxM SiC 纤维作为制造全结晶、接近化学计量的 SiC 纤维的前体。道康宁通过 Tyranno®LoxM SiC 纤维的间歇脱氧工艺制造了 SiC 纤维。 B_(2)O_(3)\mathrm{B}_{2} \mathrm{O}_{3} 和氩气环境，然后在氩气环境中在 ∼1800^(@)C\sim 1800^{\circ} \mathrm{C} [25]。这种纤维是完全结晶的，接近化学计量的 SiC，并含有少量的相 TiB_(2)\mathrm{TiB}_{2} 和碳。道康宁后来将这种纤维商业化，命名为 Sylramic ^(TM){ }^{\mathrm{TM}} 碳化硅纤维。这种纤维目前由 COI Ceramics, Inc.（以下简称 COIC）制造。为了提高其环境稳定性和抗蠕变性，这些纤维在氮气环境中进行了热处理 1800^(@)C1800^{\circ} \mathrm{C} 在纤维表面形成一层薄薄的原位 BN 涂层 [26]。原位 BN 涂层可通过热处理 Sylramic 形成 ^(TM){ }^{\mathrm{TM}} 纤维要么在 0.1MN//m^(2)0.1 \mathrm{MN} / \mathrm{m}^{2} 流动的 N_(2)\mathrm{N}_{2} 气体或在 3.52MN//m^(2)3.52 \mathrm{MN} / \mathrm{m}^{2} 静止的 N_(2)\mathrm{N}_{2} 。尽管纤维表面上原位 BN 形成的机制尚不清楚，但假设所制造的 Sylramic ^(TM){ }^{\mathrm{TM}} 纤维含有过量的游离硼，当纤维在高温下进行热处理时 N_(2)\mathrm{N}_{2} 环境中，多余的硼迁移到纤维表面并与 N_(2)\mathrm{N}_{2} 形成BN涂层[26]
The chemical composition, microstructure, strength, and creep resistance of as-fabricated and heat-treated Hi-Nicalon ^(TM)-S{ }^{\mathrm{TM}}-\mathrm{S} and Tyr-anno®-SA SiC fibers have been investigated [27-35]. Similarly, the strength and creep resistance of Dow Corning as-fabricated Sylramic ^(TM){ }^{\mathrm{TM}} SiC and nitrogen-treated Sylramic ^(TM){ }^{\mathrm{TM}} SiC fibers, referred to as Sylramic ^(TM)-iBN{ }^{\mathrm{TM}}-\mathrm{iBN} fibers have been studied [36-40]. However, untreated and nitrogen-treated Sylramic ^(TM){ }^{\mathrm{TM}} SiC fibers have not been fully characterized. Currently, there is significant variation in the strength of Sylramic ^(TM)SiC{ }^{\mathrm{TM}} \mathrm{SiC} fibers fabricated by COIC from batch-to-batch and within a batch. It is not clear whether this variability is caused by manufacturing issues at the current vendor or preexisted even when the fibers were fabricated by Dow Corning. Therefore, understanding the source of strength variability and improving strength of these fibers is critical for development of ceramic matrix composites (CMCs). In addition, nitrogen-treated Sylramic ^("TM "){ }^{\text {TM }} SiC fibers show potential for development of CMCs at temperatures to 1482^(@)C1482^{\circ} \mathrm{C} compared to other third generation SiC fibers, but the mechanism for in-situ BN formation and thermal stability of nitrogen-treated Sylramic ^("TM "){ }^{\text {TM }} SiC fibers are unknown [38,39][38,39]. Also if in-situ BN coating on Sylramic ^("TM "){ }^{\text {TM }} SiC fibers can be grown to thickness 制造和热处理后的 Hi-Nicalon 的化学成分、微观结构、强度和抗蠕变性 ^(TM)-S{ }^{\mathrm{TM}}-\mathrm{S} 和 Tyr-anno®-SA SiC 纤维已得到研究 [27-35]。同样，道康宁制造的 Sylramic 的强度和抗蠕变性 ^(TM){ }^{\mathrm{TM}} SiC 和氮化处理的 Syramic ^(TM){ }^{\mathrm{TM}} SiC纤维，简称Sylramic ^(TM)-iBN{ }^{\mathrm{TM}}-\mathrm{iBN} 纤维已被研究[36-40]。然而，未经处理和氮处理的Sylramic ^(TM){ }^{\mathrm{TM}} SiC 纤维尚未完全表征。目前，Sylramic的强度存在显着差异 ^(TM)SiC{ }^{\mathrm{TM}} \mathrm{SiC} COIC 在批次间和批次内制造的纤维。目前尚不清楚这种变化是由当前供应商的制造问题引起的，还是在纤维由道康宁公司制造时就已经存在了。因此，了解强度变异的来源并提高这些纤维的强度对于陶瓷基复合材料（CMC）的开发至关重要。此外，经过氮处理的Sylramic ^("TM "){ }^{\text {TM }} SiC 纤维显示出在以下温度下开发 CMC 的潜力： 1482^(@)C1482^{\circ} \mathrm{C} 与其他第三代 SiC 纤维相比，但氮化处理的 Sylramic 的原位 BN 形成机制和热稳定性 ^("TM "){ }^{\text {TM }} SiC纤维尚不清楚 [38,39][38,39] 。另外，如果在 Sylramic 上进行原位 BN 涂层 ^("TM "){ }^{\text {TM }} SiC 纤维可以生长至一定厚度 ∼0.5 mum\sim 0.5 \mu \mathrm{~m} by controlling the heat-treatment conditions, then the need for deposition of additional chemical vapor infiltration (CVI) BN coating during fabrication of composites can be avoided. ∼0.5 mum\sim 0.5 \mu \mathrm{~m} 通过控制热处理条件，可以避免在复合材料制造过程中沉积额外的化学气相渗透（CVI）BN涂层。
The objectives of this study are several: first, to compare the composition, microstructure, and strength of Sylramic ^(TM)SiC{ }^{\mathrm{TM}} \mathrm{SiC} fibers as fabricated by Dow Corning and COIC, and nitrogen-treated Sylramic ^(TM){ }^{\mathrm{TM}} SiC fibers; second, to determine factors controlling strength variability between batches as well as within the batch of Sylramic ^(TM)SiC{ }^{\mathrm{TM}} \mathrm{SiC} fibers fabricated by COIC; third, to study the possible mechanism of in-situ BN formation; and lastly, to measure creep resistance and thermal stability of nitrogen-treated Sylramic ^(TM)SiC{ }^{\mathrm{TM}} \mathrm{SiC} fibers. 这项研究的目的有几个：首先，比较 Sylramic 的成分、微观结构和强度 ^(TM)SiC{ }^{\mathrm{TM}} \mathrm{SiC} 由 Dow Corning 和 COIC 制造的纤维以及经过氮化处理的 Sylramic ^(TM){ }^{\mathrm{TM}} 碳化硅纤维；其次，确定控制批次之间以及批次内 Sylramic 强度变异性的因素 ^(TM)SiC{ }^{\mathrm{TM}} \mathrm{SiC} COIC制造的纤维；第三，研究原位BN形成的可能机制；最后，测量经过氮化处理的 Sylramic 的抗蠕变性和热稳定性 ^(TM)SiC{ }^{\mathrm{TM}} \mathrm{SiC} 纤维。
2. Material and characterization methods 2 材料及表征方法
2.1. Material and fiber heat-treatment 2.1.材料和纤维热处理
Several batches of Sylramic ^("TM "){ }^{\text {TM }} SiC fibers were purchased from two different fiber vendors: Dow Corning, Midland, MI and COIC, Long Beach, CA. The as-fabricated fiber tows had a polyvinyl alcohol (PVA) sizing. For brevity, these fibers are referred to as Sylramic ^("TM "){ }^{\text {TM }} fibers from now on. For all characterization work, the as-fabricated fiber tows were heat treated in argon at 1100^(@)C1100^{\circ} \mathrm{C} for 2 h to remove PVA sizing, and for tow strength measurement, desized tows were resized with uniform layer of PVA. 多批次Sylramic ^("TM "){ }^{\text {TM }} SiC 纤维购自两个不同的纤维供应商：密歇根州米德兰的道康宁公司和加利福尼亚州长滩的 COIC。制成的纤维丝束具有聚乙烯醇（PVA）浆料。为简便起见，这些纤维被称为 Sylramic ^("TM "){ }^{\text {TM }} 纤维从现在开始。对于所有表征工作，将制造好的纤维束在氩气中进行热处理，温度为 1100^(@)C1100^{\circ} \mathrm{C} 2小时以除去PVA浆料，并且为了测量丝束强度，将退浆的丝束用均匀的PVA层重新上浆。
To create a thin layer of in-situ BN coating on fiber surface, ∼1.3m\sim 1.3 \mathrm{~m} Sylramic ^(TM){ }^{\mathrm{TM}} fiber tow was wrapped on a graphite mandrel, and then heat treated in a graphite-lined furnace in 0.1MN//m^(2)0.1 \mathrm{MN} / \mathrm{m}^{2} flowing N_(2)\mathrm{N}_{2} gas or in a hot isostatic press (HIP) under 3.52MN//m^(2)3.52 \mathrm{MN} / \mathrm{m}^{2} static N_(2)\mathrm{N}_{2} gas at 1800^(@)C1800^{\circ} \mathrm{C} for 1 hh as described in the patent [26]. Henceforth, the Sylramic ^("TM "){ }^{\text {TM }} fibers heat treated in 0.1MN//m^(2)0.1 \mathrm{MN} / \mathrm{m}^{2} flowing N_(2)\mathrm{N}_{2} gas, and 3.52MN//m^(2)3.52 \mathrm{MN} / \mathrm{m}^{2} static N_(2)\mathrm{N}_{2} are referred to as Sylramic ^(TM)-iBN{ }^{\mathrm{TM}}-\mathrm{iBN} and Super Sylramic ^(TM)-iBN{ }^{\mathrm{TM}}-\mathrm{iBN} fibers, respectively. A section of the heat-treated fiber tow was cut for individual fiber filament diameter and strength measurements and microstructural characterization, and the rest of the tow was resized for tow strength measurements. 为了在纤维表面形成一薄层原位 BN 涂层， ∼1.3m\sim 1.3 \mathrm{~m} 西拉米克 ^(TM){ }^{\mathrm{TM}} 将纤维丝束缠绕在石墨芯轴上，然后在石墨衬里的炉中进行热处理 0.1MN//m^(2)0.1 \mathrm{MN} / \mathrm{m}^{2} 流动的 N_(2)\mathrm{N}_{2} 气体或在热等静压机 (HIP) 中 3.52MN//m^(2)3.52 \mathrm{MN} / \mathrm{m}^{2} 静止的 N_(2)\mathrm{N}_{2} 气体在 1800^(@)C1800^{\circ} \mathrm{C} 为 1 hh 如专利[26]中所述。从此以后，Sylramic ^("TM "){ }^{\text {TM }} 纤维经过热处理 0.1MN//m^(2)0.1 \mathrm{MN} / \mathrm{m}^{2} 流动的 N_(2)\mathrm{N}_{2} 气体，以及 3.52MN//m^(2)3.52 \mathrm{MN} / \mathrm{m}^{2} 静止的 N_(2)\mathrm{N}_{2} 被称为Sylramic ^(TM)-iBN{ }^{\mathrm{TM}}-\mathrm{iBN} 和超级系统 ^(TM)-iBN{ }^{\mathrm{TM}}-\mathrm{iBN} 纤维，分别。切割经过热处理的纤维丝束的一部分，用于单根纤维丝直径和强度测量以及微观结构表征，并且调整丝束的其余部分的尺寸以用于丝束强度测量。
To establish the influence of exposure time and N_(2)\mathrm{N}_{2} gas over pressure on the thickness of in-situ grown BN coating, some batches of COICfabricated Sylramic ^(TM){ }^{\mathrm{TM}} fibers were heat treated at 1800^(@)C1800^{\circ} \mathrm{C} for up to 10 h in 0.1MN//m^(2)0.1 \mathrm{MN} / \mathrm{m}^{2} flowing N_(2)\mathrm{N}_{2} and other batches were heat treated at 1800 ^(@)C{ }^{\circ} \mathrm{C} for 1 h in N_(2)\mathrm{N}_{2} pressure up to 10MN//m^(2)10 \mathrm{MN} / \mathrm{m}^{2}. 确定曝光时间和 N_(2)\mathrm{N}_{2} 气体超压对原位生长BN涂层厚度的影响，COIC部分批次生产的Sylramic ^(TM){ }^{\mathrm{TM}} 纤维在以下温度下进行热处理 1800^(@)C1800^{\circ} \mathrm{C} 长达 10 小时 0.1MN//m^(2)0.1 \mathrm{MN} / \mathrm{m}^{2} 流动的 N_(2)\mathrm{N}_{2} 其余批次均经过1800℃热处理 ^(@)C{ }^{\circ} \mathrm{C} 1小时内 N_(2)\mathrm{N}_{2} 压力高达 10MN//m^(2)10 \mathrm{MN} / \mathrm{m}^{2} 。
To determine their thermal and microstructural stability, Sylramic ^(TM){ }^{\mathrm{TM}}-iBN fibers were heat treated between 1400 and 1800^(@)C1800{ }^{\circ} \mathrm{C} at 100 ^(@)C{ }^{\circ} \mathrm{C} intervals for 10 h either in 0.1MN//m^(2)0.1 \mathrm{MN} / \mathrm{m}^{2} flowing N_(2)\mathrm{N}_{2} or in 3.52MN//m^(2)3.52 \mathrm{MN} / \mathrm{m}^{2} static N_(2)\mathrm{N}_{2}. For comparison purposes, Hi-Nicalon ^(TM)-S{ }^{\mathrm{TM}}-\mathrm{S} and Tyranno®-SA fibers were also heat treated under the same temperature and exposure conditions as Sylramic ^(TM)-iBN{ }^{\mathrm{TM}}-\mathrm{iBN} fibers, but in 0.1MN//m^(2)0.1 \mathrm{MN} / \mathrm{m}^{2} flowing argon. 为了确定它们的热稳定性和微观结构稳定性，Sylramic ^(TM){ }^{\mathrm{TM}} -iBN 纤维在 1400 至 1400 之间进行热处理 1800^(@)C1800{ }^{\circ} \mathrm{C} 100 时 ^(@)C{ }^{\circ} \mathrm{C} 间隔 10 小时 0.1MN//m^(2)0.1 \mathrm{MN} / \mathrm{m}^{2} 流动的 N_(2)\mathrm{N}_{2} 或在 3.52MN//m^(2)3.52 \mathrm{MN} / \mathrm{m}^{2} 静止的 N_(2)\mathrm{N}_{2} 。出于比较目的，Hi-Nicalon ^(TM)-S{ }^{\mathrm{TM}}-\mathrm{S} 和 Tyranno®-SA 纤维也在与 Sylramic 相同的温度和暴露条件下进行了热处理 ^(TM)-iBN{ }^{\mathrm{TM}}-\mathrm{iBN} 纤维，但在 0.1MN//m^(2)0.1 \mathrm{MN} / \mathrm{m}^{2} 流动的氩气。
The scanning electron microscopy (SEM), elemental chemical analysis, Auger electron spectroscopy (AES), x-ray diffraction (XRD), electron probe microanalysis (EPMA), Raman microspectroscopy (RMS), and diameter and individual single filament strength measurements were performed on desized single filaments or tows. Whereas for tow strength measurements, as-fabricated and heat-treated fiber tows were resized with PVA. For microstructural analysis, grain size measurement, EPMA, and RMS desized fiber tows were first coated with a thin layer of carbon and then with a layer of electroplated nickel to aid in metallographic preparation. The coated tow was cut transverse to the axis of the tow. Each piece was mounted in a metallographic mold and infiltrated with epoxy. The cross section of the coated fiber tow was ground and polished according to standard metallographic procedure. Before SEM and EPMA analysis, the mounted and polished specimens were coated with a thin layer of C to prevent charging during analysis. 进行了扫描电子显微镜（SEM）、元素化学分析、俄歇电子能谱（AES）、X射线衍射（XRD）、电子探针微量分析（EPMA）、拉曼显微光谱（RMS）以及直径和单个单丝强度测量在退浆的单丝或丝束上。而对于丝束强度测量，用 PVA 调整了制造和热处理后的纤维丝束的尺寸。对于微观结构分析、晶粒尺寸测量、EPMA 和 RMS 退浆纤维束，首先涂覆一层薄薄的碳，然后涂覆一层电镀镍以辅助金相制备。横向于丝束的轴线切割涂覆的丝束。每个部件都安装在金相模具中并用环氧树脂渗透。根据标准金相程序对涂覆纤维束的横截面进行研磨和抛光。在进行 SEM 和 EPMA 分析之前，在安装和抛光的样品上涂上一层薄薄的 C，以防止分析过程中带电。
The diameter variation, morphology, microstructure of the fibers were characterized by a high resolution Hitachi SEM (Model Hitachi S- 通过高分辨率日立 SEM（日立 S-型）对纤维的直径变化、形态、微观结构进行了表征。
4700) equipped with a field emission gun. For fiber diameter measurements, the fiber tows from different batches were desized at 1000^(@)C1000^{\circ} \mathrm{C} for 2 h in vacuum and then examined in SEM after using standard specimen preparation procedure. From each fiber tow, the diameters of 20-30 individual fibers and in total ∼200\sim 200 single filaments from different fiber batches were examined 4700）配备场发射枪。为了测量纤维直径，不同批次的纤维束在以下温度下退浆： 1000^(@)C1000^{\circ} \mathrm{C} 在真空中放置 2 小时，然后使用标准样品制备程序在 SEM 中进行检查。每个纤维束中 20-30 根单纤维的直径以及总直径 ∼200\sim 200 检查来自不同纤维批次的单丝
Chemical analysis of bulk fiber samples for minor constituents B and Ti , and trace impurities such as Ca,Fe\mathrm{Ca}, \mathrm{Fe}, and Ni , were performed by inductively coupled plasma optical emission spectroscopy (ICP-OES), on a Varian Vista-PRO® model in the axial viewing configuration. The fiber samples were dissolved in a Parr Instrument Company, model 4746 acid digestion bomb with hydrofluoric, nitric, and sulfuric acids at 230^(@)C230{ }^{\circ} \mathrm{C}. Carbon, nitrogen, and oxygen were determined by combustion analysis on a LECO Corporation, CS-444-LS for total C and a LECO TC-436 for N and O . 对散装纤维样品进行化学分析，了解微量成分 B 和 Ti 以及微量杂质，例如 Ca,Fe\mathrm{Ca}, \mathrm{Fe} 和 Ni 是通过电感耦合等离子体发射光谱 (ICP-OES) 在轴向观察配置的 Varian Vista-PRO® 模型上进行的。将纤维样品溶解在 Parr Instrument Company 4746 型酸消解弹中，用氢氟酸、硝酸和硫酸溶解。 230^(@)C230{ }^{\circ} \mathrm{C} 。碳、氮和氧通过 LECO Corporation 的燃烧分析测定，CS-444-LS 测定总 C，LECO TC-436 测定 N 和 O。
The crystalline phases present in the fibers were studied by XRD using a Bruker D8 ADVANCE diffractometer using CuKalpha\mathrm{Cu} \mathrm{K} \alpha radiation with a Ni Kbeta\mathrm{K} \beta filter and a Bruker LYNXEYE linear position sensitive detector. For XRD, the desized fiber tows were ground in an agate mortar and pestle, and the resulting powder was analyzed. 使用 Bruker D8 ADVANCE 衍射仪通过 XRD 研究了纤维中存在的晶相 CuKalpha\mathrm{Cu} \mathrm{K} \alpha Ni 辐射 Kbeta\mathrm{K} \beta 滤波器和 Bruker LYNXEYE 线性位置敏感探测器。对于 XRD，将退浆的纤维束在玛瑙研钵和研杵中研磨，并对所得粉末进行分析。
AES was used to determine the elemental composition at the fiber surface. The analysis was performed on a flattened tow whose top and bottom ends were supported in a steel fixture. AES measurements were performed in a scanning microprobe (Model PHI-680) equipped with a field emission gun and an Ar ion sputtering gun for depth profiling. The variation of the intensities (peak area mode) of the Auger electron peaks (the KLL-transition for all elements) as a function of the sputtering time was used to plot the semi-quantitative composition-depth profile from the fiber surface. A Ta_(2)O_(5)\mathrm{Ta}_{2} \mathrm{O}_{5} reference was used to measure the sputtering rate. AES 用于测定纤维表面的元素组成。分析是在扁平丝束上进行的，丝束的顶端和底端由钢夹具支撑。 AES 测量在配备场发射枪和 Ar 离子溅射枪的扫描微探针（型号 PHI-680）中进行，用于深度剖析。俄歇电子峰（所有元素的 KLL 跃迁）强度（峰面积模式）随溅射时间的变化用于绘制纤维表面的半定量成分深度分布。一个 Ta_(2)O_(5)\mathrm{Ta}_{2} \mathrm{O}_{5} 使用参考来测量溅射速率。
EPMA was conducted in a JEOL Ltd. electron probe micro analyzer (Model JXA-8200) equipped with a tungsten filament gun. EPMA measurements were performed in the wavelength dispersion mode, with a thallium acid phthalate (TAP) crystal analyzer for Si-K®, Ni-L®, and FeL ®, Al-K®, a lithium fluoride (LIF) crystal analyzer for Ti-K®, and an artificial layered dispersive element (LDE) (with a high signal/noise intensity ratio) for B-K®\mathrm{B}-\mathrm{K} \circledR, N-K®,C-K®\mathrm{N}-\mathrm{K} ®, \mathrm{C}-\mathrm{K} \circledR, and O-K®\mathrm{O}-\mathrm{K} \circledR. Monocrystalline SiC and BN,Ti,Fe,Ni\mathrm{BN}, \mathrm{Ti}, \mathrm{Fe}, \mathrm{Ni}, and SiO_(2)\mathrm{SiO}_{2} from a C. M. Taylor Company 203 multielement standard were used as standards. The microprobe analyses were performed as line scan measurements along the diameter of the fiber. The electron beam was focused on a single point (point mode), allowing a spatial resolution of 1 to several mum^(3)\mu \mathrm{m}^{3}, depending on the X-ray emitting volume and therefore the composition of the samples. EPMA在配备钨丝枪的JEOL Ltd.电子探针微量分析仪（型号JXA-8200）中进行。 EPMA 测量在波长色散模式下进行，使用邻苯二甲酸铊 (TAP) 晶体分析仪测量 Si-K®、Ni-L® 和 FeL®、Al-K®，使用氟化锂 (LIF) 晶体分析仪测量 Ti -K® 和人工层状色散元件 (LDE)（具有高信号/噪声强度比） B-K®\mathrm{B}-\mathrm{K} \circledR , N-K®,C-K®\mathrm{N}-\mathrm{K} ®, \mathrm{C}-\mathrm{K} \circledR ， 和 O-K®\mathrm{O}-\mathrm{K} \circledR 。单晶碳化硅和 BN,Ti,Fe,Ni\mathrm{BN}, \mathrm{Ti}, \mathrm{Fe}, \mathrm{Ni} ， 和 SiO_(2)\mathrm{SiO}_{2} 使用来自CM Taylor Company 203多元素标准品作为标准品。微探针分析是沿纤维直径进行线扫描测量。电子束聚焦在一个点上（点模式），允许空间分辨率为 1 到几个 mum^(3)\mu \mathrm{m}^{3} ，取决于 X 射线发射体积以及样品的成分。
RMS is especially suitable for detecting and investigating the structural properties of silicon carbide and free carbon containing materials. RMS analyses were conducted on polished cross sections of fiber tows using a MIRA SEM (Tescan Orsay Holding, Brno, Czech Republic) integrated with a WITec Confocal Raman Imaging system. The samples used were the same as those for EPMA. The monochromatic excitation source was the 532 nm emission line of an Nd:YAG laser. For RMS data analysis, a 2D array of Raman spectra was recorded from the specimen. All recorded spectra were background corrected to correlate the different Raman peak intensities. All spectra from an array were analyzed and for each 2D spectral array, the corresponding components were extracted. These spectra were then used for basic analysis as a color-coded distribution of elements analyzed specimen volume. Peak width and position analysis were performed using the algorithms that allow fitting one or several peaks using Lorenz curves. The result of the fit is an image displaying either a shift of Raman bands, the position of the Raman band, full width at half maximum, or the integrated intensity. RMS 特别适合检测和研究碳化硅和含游离碳材料的结构特性。使用与 WITec 共焦拉曼成像系统集成的 MIRA SEM（捷克共和国布尔诺 Tescan Orsay Holding）对纤维束的抛光横截面进行 RMS 分析。使用的样品与 EPMA 的样品相同。单色激发源是 Nd:YAG 激光器的 532 nm 发射线。对于 RMS 数据分析，记录了样本的二维拉曼光谱阵列。所有记录的光谱均经过背景校正，以关联不同的拉曼峰强度。分析了阵列中的所有光谱，并针对每个二维光谱阵列提取了相应的成分。然后将这些光谱用于基本分析，作为分析样品体积的元素的颜色编码分布。使用允许使用洛伦兹曲线拟合一个或多个峰的算法进行峰宽度和位置分析。拟合的结果是显示拉曼带偏移、拉曼带位置、半峰全宽或积分强度的图像。
Transmission electron microscopy (TEM) was conducted to determine crystalline phases in the as-fabricated Sylramic ^(TM){ }^{\mathrm{TM}} fibers, and crystallinity and thickness of in-situ BN coating on the surface of Sylramic ^(TM){ }^{\mathrm{TM}}-iBN fibers. For TEM, a fiber tow was infiltrated with conductive epoxy, followed by transversely slicing the tow specimen into thin discs by focused ion beam (FIB), and ion milling the disc with gallium ions to 进行透射电子显微镜 (TEM) 以确定所制造的 Sylramic 中的晶相 ^(TM){ }^{\mathrm{TM}} Sylramic 表面原位 BN 涂层的纤维、结晶度和厚度 ^(TM){ }^{\mathrm{TM}} -iBN纤维。对于 TEM，用导电环氧树脂渗透纤维丝束，然后通过聚焦离子束 (FIB) 将丝束样品横向切成薄盘，并用镓离子对盘进行离子铣削，以形成薄盘。
create a thin foil that is transparent to an electron beam. The thin foil was examined and analyzed using a CM 200 Phillips TEM model equipped with a LaB_(6)\mathrm{LaB}_{6} field emission gun. Attempts to conduct TEM analysis of Sylramic ^(TM){ }^{\mathrm{TM}}-iBN fiber failed due to poor retention of in-situ BN coating during preparation of thin foils. Even in some thin foils in which in-situ BN could be partially retained, its thickness and thickness variation could not be determined. To overcome this problem, thin foils of SiC//SiC\mathrm{SiC} / \mathrm{SiC} composite preform with Sylramic ^("TM "){ }^{\text {TM }}-iBN fiber fabricated by CVI were examined. The composite preforms were fabricated by first stacking 2D woven fabric of Sylramic ^(TM)-iBN{ }^{\mathrm{TM}}-\mathrm{iBN} fiber, clamping in a graphite tool to compress the fabric, and infiltrating the tooled fabric with a thin layer of CVI BN followed by ∼2-mu\sim 2-\mu m-thick CVI SiC. 创建一个对电子束透明的薄箔。使用配备有 LaB_(6)\mathrm{LaB}_{6} 场发射枪。尝试对 Sylramic 进行 TEM 分析 ^(TM){ }^{\mathrm{TM}} -iBN 纤维因薄箔制备过程中原位 BN 涂层保留不良而失败。即使在一些可以部分保留原位BN的薄箔中，也无法确定其厚度和厚度变化。为了克服这个问题，薄箔 SiC//SiC\mathrm{SiC} / \mathrm{SiC} 采用 Sylramic 的复合材料预制件 ^("TM "){ }^{\text {TM }} -对CVI制造的iBN纤维进行了检验。复合材料预成型件是通过首先堆叠 Sylramic 的 2D 机织物制成的 ^(TM)-iBN{ }^{\mathrm{TM}}-\mathrm{iBN} 纤维，夹在石墨工具中以压缩织物，并用一薄层 CVI BN 渗透到工具织物中，然后 ∼2-mu\sim 2-\mu m 厚的 CVI SiC。
2.3. Strength characterization 2.3.强度表征
To measure average tensile strength and scatter of as-fabricated Sylramic ^(TM){ }^{\mathrm{TM}} fibers, 40 individual fiber filaments and 20 tows were selected at random from each batch, and fibers from 7 to 12 batches were chosen from each vendor. The individual filament tensile strength tests were conducted on filaments extracted from the desized fiber tows, and the tow tensile strength tests were on PVA-sized tows. The handling and preparation of individual filaments and tows are essential to reduce scatter during tensile strength measurements. The as-fabricated Sylramic ^(TM){ }^{\mathrm{TM}} fiber tow has a slight twist along its length, and the surface of an individual filament within a tow is very rough and grainy. Pulling out individual filaments from the desized twisted fiber tow will cause fiber damage. Therefore, it is better to cut the fiber tow to the required length, desize the tow, lightly sonicate it either in alcohol or acetone to separate individual fiber from the tow, and then mount individual filaments for testing. Whereas, the PVA sizing applied on either Dow Corning or COIC Sylramic ^("TM "){ }^{\text {TM }} fibers is non-uniform and spotty, in some regions of the fiber tow, the PVA sizing does not even exist. In general, PVA sizing is hydrophilic and hygroscopic. These bare spots are prone for oxidation, causing individual filament to bond. Moreover, the poorly sized fiber tows also cause uneven loading during tow tensile testing. Therefore, uniform PVA sizing on fiber tow is essential before tow testing to avoid wide variation in strength. 测量已制成的 Sylramic 的平均拉伸强度和分散度 ^(TM){ }^{\mathrm{TM}} 纤维，每批次随机选择 40 根单纤维长丝和 20 根丝束，每个供应商选择 7 至 12 批次纤维。单根长丝拉伸强度测试是在从退浆纤维丝束中提取的长丝上进行的，并且丝束拉伸强度测试是在PVA施胶丝束上进行的。单个长丝和丝束的处理和准备对于减少拉伸强度测量过程中的分散至关重要。预制的Sylramic ^(TM){ }^{\mathrm{TM}} 纤维丝束沿其长度方向有轻微的扭曲，丝束中单根长丝的表面非常粗糙且有颗粒状。从退浆加捻纤维束中拉出单根长丝会导致纤维损坏。因此，最好将纤维丝束切割至所需长度，对丝束退浆，在酒精或丙酮中轻轻超声处理，以将单根纤维与丝束分离，然后安装单根长丝进行测试。而 PVA 施胶剂适用于 Dow Corning 或 COIC Sylramic ^("TM "){ }^{\text {TM }} 纤维不均匀且有斑点，在纤维丝束的某些区域，PVA浆料甚至不存在。一般来说，PVA浆料具有亲水性和吸湿性。这些裸露点很容易氧化，导致单个灯丝粘合。此外，尺寸不佳的纤维丝束还会导致丝束拉伸测试过程中负载不均匀。因此，在丝束测试之前，必须对纤维丝束进行均匀的 PVA 施胶，以避免强度发生较大变化。
For tensile strength measurement of individual fiber filaments or tows, a modified version of ASTM standards D4018 and D3379 developed for testing carbon filament was used. The picture frames of size 6.35cm(L)xx5.08cm(W)xx0.08cm(T)6.35 \mathrm{~cm}(\mathrm{~L}) \times 5.08 \mathrm{~cm}(\mathrm{~W}) \times 0.08 \mathrm{~cm}(\mathrm{~T}) with an inner cavity of size 2.54 cm(L)xx2.54cm(W)xx0.08cm(T)\mathrm{cm}(\mathrm{L}) \times 2.54 \mathrm{~cm}(\mathrm{~W}) \times 0.08 \mathrm{~cm}(\mathrm{~T}) were machined from the cardboard sheet. A shallow groove was created at the centerline of the picture frame. A 5.08-cm5.08-\mathrm{cm} long individual SiC filament or tow was placed at the centerline of the cardboard picture frame. The top and bottom 1.91 cm of the fiber or the tow was bonded to the cardboard frame using a fast drying epoxy leaving a 2.54-cm2.54-\mathrm{cm} long section of the fiber or the tow in the gauge without any back support. On top of this, another picture frame coated with epoxy was placed to create a rigidized sandwich frame. Subsequently, the top and bottom 1.91 cm of frame was clamped in the grips of a table top tensile testing machine (Instron Model 5966), the side arms of the picture frame were cut using a small blow torch and the fiber/tow was tensile tested at room temperature at a crosshead rate of 1.27mm//s1.27 \mathrm{~mm} / \mathrm{s}. The strength of individual filament was calculated from the measured fracture load and calculated fiber area based on an average fiber diameter of 10 mum10 \mu \mathrm{~m} as reported by the vendor. The tow strength of the fiber was calculated from the measured fracture load and crosssectional area of the tow, which was calculated by multiplying 800 (# of fibers in a tow) and the area of the 10-mum10-\mu \mathrm{m}-diameter fiber. 为了测量单根纤维丝或丝束的拉伸强度，使用了为测试碳丝而开发的 ASTM 标准 D4018 和 D3379 的修改版本。相框尺寸 6.35cm(L)xx5.08cm(W)xx0.08cm(T)6.35 \mathrm{~cm}(\mathrm{~L}) \times 5.08 \mathrm{~cm}(\mathrm{~W}) \times 0.08 \mathrm{~cm}(\mathrm{~T}) 内腔尺寸为2.54 cm(L)xx2.54cm(W)xx0.08cm(T)\mathrm{cm}(\mathrm{L}) \times 2.54 \mathrm{~cm}(\mathrm{~W}) \times 0.08 \mathrm{~cm}(\mathrm{~T}) 由纸板加工而成。在相框的中心线上创建一个浅凹槽。一个 5.08-cm5.08-\mathrm{cm} 长的单个碳化硅丝或丝束被放置在纸板相框的中心线上。使用快干环氧树脂将纤维或丝束的顶部和底部 1.91 厘米粘合到纸板框架上，留下 2.54-cm2.54-\mathrm{cm} 测量仪中的长段纤维或丝束，没有任何背部支撑。在此之上，放置另一个涂有环氧树脂的相框以创建刚性夹层框架。随后，将框架的顶部和底部 1.91 厘米夹在台式拉伸试验机（Instron 型号 5966）的夹具中，使用小型喷灯切割相框的侧臂，并对纤维/丝束进行拉伸测试在室温下，十字头速率为 1.27mm//s1.27 \mathrm{~mm} / \mathrm{s} 。单根长丝的强度是根据测量的断裂载荷和基于平均纤维直径计算的纤维面积来计算的 10 mum10 \mu \mathrm{~m} 据供应商报告。纤维的丝束强度是根据测得的断裂载荷和丝束的横截面积来计算的，该横截面积是通过乘以 800（丝束中的纤维数）乘以丝束的面积来计算的。 10-mum10-\mu \mathrm{m} -直径纤维。
2.4. Creep testing methods 2.4.蠕变试验方法
Two different techniques were used in evaluating creep resistance of the fibers: the bend stress relaxation (BSR) and tensile creep. BSR is a qualitative test that reflects resistance of the material to primary creep. In this test, the outer surface of the fiber is subjected to a maximum 使用两种不同的技术来评估纤维的抗蠕变性：弯曲应力松弛（BSR）和拉伸蠕变。 BSR 是一项反映材料抗初次蠕变性能的定性测试。在此测试中，纤维的外表面承受最大
Corresponding author at: HX5, LLC. NASA Glenn Research Center, Materials and Structures Division, 21000 Brookpark Road, Cleveland, OH, 44135, United States. 通讯作者：HX5, LLC。 NASA 格伦研究中心，材料与结构部，21000 Brookpark Road, Cleveland, OH, 44135, United States。