耐高温Si-Zr-Y复合渗层的组织形成机理及抗氧化性能研究

The Nb-Ti-Si based ultrahigh temperature alloy is a promising candidate material for structural application in the temperature range of 1200～1450℃. However, its high-temperature oxidation-resistant performance is not enough to guarantee its actual application in oxidation attacking environment. Therefore, there is an urgent requirement to prepare smart oxidation-resistant coatings on the alloy substrate. In this project, Zr films with controllable thickness will be deposited on the alloy substrate by magnetron sputtering at first, and then Si-Y co-deposition process will be conducted on the Zr deposited specimens. The Si-Zr-Y compound coatings that would utilize the joint modification effects of both refractory active element Zr and rare earth element Y sufficiently will be prepared on the Nb-Ti-Si based ultrahigh temperature alloy by this two-step process. These compound coatings are expected to be dense, contain suitable amounts of Zr and Y, possess multi-layer structure, and be bonded with substrate alloy metallurgically. The influence of the Zr film thickness and Si-Y co-deposition process parameters on the microstructure, phase constituents, the interface with the alloy substrate and its bonding strength of Si-Zr-Y compound coatings will be revealed, and the distributing characteristics of Si, Zr, Y, Nb and Ti elements in various phases in these coatings will be investigated. The microstructural formation, growth mechanisms and the joint modification effects of Zr and Y addition in the Si-Zr-Y compound coatings prepared by this two-step process will be illustrated. Both isothermal oxidation and cyclic oxidation behaviors in the temperature range of 1200～1450℃, and then the structure and anti-spallation characteristics of the scales of the selected Si-Zr-Y compound coating specimens with optimized microstructure and composition will be examined. The scale formation mechanism and retrogression process of the coatings will be revealed. We believe that the smart Zr and Y jointly modified silicide coatings that could endure even more higher temperature than 1350℃ will be prepared successfully by this magnetron sputtering and then co-deposition diffusion two-step process.

新型Nb-Ti-Si基超高温合金有潜力应用于1200～1450℃的温度范围内，但其抗氧化性能较差，迫切需要研究其表面先进高温抗氧化渗层的制备技术、组织形成机理及抗氧化性能。本项目拟采用磁控溅射Zr膜然后再Si-Y扩散共渗的两步法，在合金表面制备经高熔点活性元素Zr及稀土Y联合改性、具有多层复合结构、与基体合金冶金结合的致密Si-Zr-Y复合渗层；研究复合渗层的结构、相形成、组织形貌、致密性、与基体合金界面结构及结合强度随Zr膜厚度、Si-Y扩散共渗工艺参数的变化规律及Si,Zr,Y,Nb,Ti等元素在复合渗层各相中的分配特征，揭示两步法制备Si-Zr-Y复合渗层的生长机制、组织形成机理及Zr-Y联合改性机理。研究具有优化组织结构的Si-Zr-Y复合渗层在1200～1450℃温度范围内的恒温氧化及循环氧化动力学、氧化膜组织结构及抗剥落性能，提出该复合渗层的氧化膜组织形成机理及抗退化机制。

Nb-Si基超高温合金具有高熔点、适中的密度以及良好的室温及高温力学性能，有望应用在1200～1450℃的温度范围内，但其高温抗氧化性能较差。本项目采用先磁控溅射沉积Zr膜，然后再Si-Y扩散共渗的方法在Nb-Si基超高温合金表面成功制备了Zr-Y改性硅化物复合渗层，分析了渗层的组织结构及形成机制，揭示了沉积Zr膜的厚度(2～10μm)及Si-Y共渗温度(1150～1350℃)对所制备渗层组织的影响规律。发现在不同Zr膜厚度和Si-Y共渗温度下所制备的渗层具有相似的结构，均由ZrSi2外层，(Nb,X)Si2中间层和(Ti,Nb)5Si4内层组成，共渗层的厚度随着共渗温度的升高显著增加。ZrSi2-NbSi2复合渗层具有较好的高温抗氧化性能，氧化后在渗层表面形成了由SiO2, ZrSiO4, ZrO2, Al2O3, TiO2和Cr2O3混合组成的致密氧化膜，能够在1250℃的空气中保护基体合金100h以上。ZrSi2外层的氧化较为迅速，此阶段氧化膜的生长主要由O的内扩散控制；随着保护性内氧化膜的形成和生长，氧化膜的生长逐渐由O的内扩散占优转变为Si, Ti, Cr和Al的外扩散占优。B, Y改性硅化物渗层在1350℃热震氧化过程中，Ti、Cr、Nb等元素的外扩散明显增强，形成的氧化膜以Nb2O5、TiO2和SiO2为主，渗层可保护基体合金经受41次热震氧化。.使用不同种类催化剂(NaF、NH4F、NH4Cl、NaBr和NaCl)制备的Zr, Y改性硅化物共渗层由外至内均由(Nb,X)Si2(X表示元素Ti, Cr和Hf)外层，(Ti,Nb)5Si4过渡层及富Al, Cr和Y的(Nb,X)5Si3内层组成。采用NaF和NH4F时制备的共渗层较厚、组织致密，且采用NaF时所制备的共渗层中Zr和Y元素的含量较高。在硅化物涂层中添加少量Zr可抑制Ti的外扩散，促进形成致密连续的SiO2膜；而添加Zr过量后则不利于渗层的高温抗氧化性能。随着Zr含量的增加，氧化膜的生长以涂层中Ti的外扩散为主逐渐转变为以O的内扩散为主。.本项目执行期间，共发表学术期刊论文34篇，SCI收录29篇，EI收录33篇，JCRⅠ区及Ⅱ区论文20篇，获授权国家发明专利4项，在国际学术会议上应邀作特邀报告3次，在全国性学术会议上做特邀报告5次，培养毕业博士研究生3名，硕士研究生9名.