Cr3C2-NiCr与Ni基复合涂层的制备、性能及空蚀机理

High-pressure pumps are the key equipments of sea water desalination. A great interest has been taken in cavitation erosion of high-pressure pumps. Ni-based coatings with high strength, high hardness and good toughness are widely used for cavitation erosion resistance. Nevertheless, industrial applications of these coatings have been limited by their poor interfaces in the coating. In this project, a Cr3C2-NiCr and Ni-based composite coating is prepared to improve the poor interfaces and, in turn, the cavitation erosion resistance of the coating by adding a commercial Cr3C2-NiCr powder. The optimum spray condition is obtained based on the multi-factor orthogonal array optimization. The formation law of the composite coating is discussed by changing the composition and mixed way of the feedstock powders and the corresponding properties of the coating. Cavitation erosion tests are carried out using a vibratory cavitation apparatus. The cavitation erosion resistance of the composite coating is investigated by the cavitation erosion mass loss curves and the characteristic of exfoliated particles. Cavitation erosion mechanism is revealed by comparing the transformation of microstructure and phase structure before and after the cavitation erosion tests. Damage model of cavitation erosion is attempted to be established by means of Matlab. Initiation, propagation and evolution of the poor interfaces in cavitation erosion process are explored by means of scanning electron microscopy (SEM). which gives theoretical and practice basis for improving the cavitation erosion resistance of the composite coatings.

高压泵为海水淡化的核心设备，高压泵的空蚀破坏问题在业界受到相当高的关注。强韧性好的Ni基涂层是常用的抗空蚀涂层材料之一。但Ni基涂层内部硬质小颗粒相和金属相之间的界面结合较弱，在空蚀过程中硬质颗粒极易脱落。本项目采用涂层复合技术，通过添加适量的Cr3C2-NiCr粉末，来改善Ni基涂层中的弱结合界面，从而提高涂层的抗空蚀性。 首先，采用正交优化法得到制备Cr3C2-NiCr与Ni基复合涂层的最佳工艺参数，通过改变原始配料比、粉料混合方式，来制备性能优良的复合涂层，并研究复合涂层的形成规律；采用磁致伸缩试验，给出蚀去量与空蚀时间的变化关系，并对剥落掉下的粒子进行表征，比较空蚀前后组织、性能的变化，综合评判复合涂层的抗空蚀性，探讨空蚀机理，构建空蚀损伤模型；研究涂层结合界面处空蚀坑的萌生、长大的演变规律，揭示提高复合涂层抗空蚀性的内在机制，为获取抗空蚀性能优良的复合涂层提供理论依据和实验基础。

本课题选用40%Cr3C2-NiCr/60%NiCrBSi（后称N60）、85%Cr3C2-NiCr/15%NiCrBSi（后称N15）两种不同质量配比的碳化物增强的Ni基抗空蚀HVOF复合涂层，结合空蚀、腐蚀前后涂层的形貌及单因素影响结果，研究了在3.5wt.%NaCl溶液中的抗空蚀性能和空蚀机理。发表论文6篇，专利4个，培养研究生4名。.研究中，NiCrBSi（又称Ni基涂层）和Cr3C2-NiCr涂层组织结构致密，都含有晶相和非晶相，Ni基涂层弥散分布很多新生成的亚微米级的碳化物、硼化物硬质相小颗粒。在喷涂参数相同的情况下，Ni基涂层的沉积效率低，而Cr3C2-NiCr涂层的沉积效率高。当 15%NiCrBSi与85%Cr3C2-NiCr复合后，硬度达1249HV0.1，增加18%，喷涂粉体的沉积率、涂层的厚度和孔隙率都变化不大；空蚀过程中涂层在空蚀过程中粗糙度变化小，无明显空蚀孔洞，抗空蚀性提高；当60%NiCrBSi与40%Cr3C2-NiCr复合后，喷涂粉体沉积率增加，喷涂参数相同的情况下，涂层厚度增加两倍，硬度和孔隙率增加，空蚀后试样的中心有明显的空蚀坑，呈中间向四周扩散的常规模式，空蚀严重，颗粒偏析处空蚀更为严重。在3.5wt.%NaCl溶液中，涂层的空蚀始于涂层表面的孔隙、缺陷和微裂纹处，孔是空蚀的起源，硬质相的剥落留下的孔洞会成为空蚀破坏的新诱发点。涂层的孔隙率、相组成、硬质相颗粒尺寸、涂层的内聚强度以及涂层与基体结合处的缺陷都是影响涂层抗空蚀性能的重要因素。在电解质溶液中的空蚀破坏是由腐蚀和空蚀联合造成的，其中空蚀占主导作用，腐蚀起促进作用。