Zr-2.5Nb合金不同工艺预生膜的显微组织和摩擦磨损性能研究

Study on Microstructure and Friction and Wear Properties of Pre-formed Films of Zr-2.5Nb Alloy Prepared by Different Processes

摘要:

微动磨损是限制重水堆用压力管寿命的主要原因之一。为提高重水堆用Zr-2.5Nb压力管的服役可靠性，本文通过三种工艺在Zr-2.5Nb合金表面制备了约1μm厚的预生氧化膜，并研究了其力学性能与显微组织的关系。三种预氧化处理工艺分别为在400 ℃、10.3 MPa除氧过热蒸汽、300 μg/kg溶解氧过热蒸汽以及400 ℃、2 MPa低压蒸汽中氧化24 h。结果表明，Zr-2.5Nb合金由α-Zr和β-Zr双相组成，α-Zr和β-Zr的形貌均呈长条状，β-Zr连续分布在α-Zr晶界处。不同预氧化条件下生成的膜显微结构存在差异:除氧条件下的预生膜中的微裂纹相对较多，其柱状晶尺寸较为短小并且排列杂乱；溶解氧条件下的预生膜最致密，缺陷最少，而低压条件下的预生膜厚度虽最大，但孔隙和裂纹相对更多。与原始合金相比，预生膜使合金纳米硬度提高了50%~180%，硬度/模量比值（H/E）提高了约56%~81%，磨损率降低了31%~44%，预生膜显著提高了合金表面的硬度和耐磨损性能，使磨损机制由严重的磨粒磨损转变为轻微黏着磨损。其中，溶解氧条件下制得的预生膜最为致密，硬度提升效果最突出，这是因为预生膜的强化作用与其显微形貌密切相关。致密完好的氧化膜不仅硬度更高，且与金属基体结合更牢固，不易在局部受力时剥落或开裂。

Abstract:

Micro-motion wear is one of the primary factors limiting the service life of pressure tubes used in heavy-water reactors. To enhance the operational reliability of Zr-2.5Nb pressure tubes for heavy-water reactors, this study prepared a pre-formed film approximately 1 μm thick on the surface of Zr-2.5Nb alloy using three different processes and investigated the relationship between its mechanical properties and microstructure. The three pre-oxidation treatment processes were carried out for 24 hours at 400 °C: one in deoxidized superheated steam at 10.3 MPa; one in superheated steam with 300 μg/kg of dissolved oxygen; and one in low-pressure steam at 2 MPa.The results indicate that the Zr-2.5Nb alloy consists of α-Zr and β-Zr phases, with both α-Zr and β-Zr exhibiting elongated morphologies, and β-Zr continuously distributed at the α-Zr grain boundaries.The microstructures of the films formed under different pre-oxidation conditions exhibit differences: the pre-formed film under deoxidized conditions contains relatively more microcracks, with shorter and more randomly arranged columnar grains; the pre-formed film under dissolved oxygen conditions is the most dense with the fewest defects, while the pre-formed film under low-pressure conditions has the greatest thickness but relatively more pores and cracks.Compared with the original alloy, the pre-formed film increased the nano-hardness of the alloy by 50%–180%, improved the hardness-to-modulus ratio (H/E) by approximately 56%–81%, and reduced the wear rate by 31%–44%. The pre-formed film significantly enhanced the surface hardness and wear resistance of the alloy, transforming the wear mechanism from severe abrasive wear to mild adhesive wear.Among these, the pre-formed film produced under dissolved oxygen conditions is the most dense and exhibits the most pronounced hardness enhancement. This is because the strengthening effect of the pre-formed film is closely related to its microstructure. A dense and intact oxide film not only has higher hardness but also adheres more firmly to the metal substrate, making it less prone to peeling or cracking under localized stress.