涡轮叶片低压等离子喷涂NiCoCrAlYTa涂层未熔颗粒尺寸超标研究

Study of Unmolten Particle Size Exceedance in Low Pressure Plasma Sprayed NiCoCrAlYTa Coatings on Turbine Blades

摘要:

航空发动机燃烧室、叶片、涡轮外环等热端部件的工作环境恶劣，除需承受高温环境外，还需经受高温燃气引起的腐蚀和浸蚀，因此部件高温防护涂层的应用至关重要。防护涂层不仅能提升部件的耐温能力，还能延长其服役时间，进而提高发动机的整体性能。NiCoCrAlYTa涂层是一种典型的高温防护涂层，在1 050 ℃下具有良好的服役性能。这是由于Ta和Y等元素对Al₂O₃氧化膜选择性生成具有促进作用，使得NiCoCrAlYTa涂层在高温下能形成完整的Al₂O₃膜，从而具有良好抗氧化和抗热腐蚀性能。采用低压等离子喷涂技术，在高温合金上制备NiCoCrAlYTa涂层，该涂层具有结构致密、元素分布均匀、孔隙率低，以及能显著提高基体的疲劳极限和出色的高温服役性能等优点，已成为涡轴发动机热端部件，特别是涡轮叶片的首选涂层。但是，低压等离子喷涂NiCoCrAlYTa涂层存在厚度分布不易调控、未熔颗粒尺寸易超标等问题，尤其是未熔颗粒会导致涂层性能下降及抗氧化、抗腐蚀能力降低，使叶片使用寿命缩短。在某型发动机涡轮叶片涂层试制中发生批次性未熔颗粒尺寸超标问题，以此批次涂层叶片为研究对象，通过对未熔颗粒形成进行分析、原因排查和复现验证，确定是真空舱体中的NiCoCrAlYTa粉尘在喷涂时进入涂层中，导致涂层的未熔颗粒尺寸超标。针对问题原因，通过采取强化转移弧清理，可有效避免粉尘污染带来的未熔颗粒尺寸超标问题，获得符合技术质量要求的涂层。该研究为低压等离子喷涂涂层未熔颗粒尺寸超标问题的处置提供了工程经验。

Abstract:

Aero-engine combustion chambers， blades， turbine outer rings and other hot-end components operate in harsh environments. In addition to being subjected to high temperature environments， these components are also subjected to corrosion and leaching caused by high temperature gases， so the application of high temperature protective coatings is critical. Protective coatings not only improve the temperature resistance of components， but also extend their service life， which in turn improves the overall performance of the engine. NiCoCrAlYTa coating is a typical high-temperature protective coating， demonstrating excellent oxidation and corrosion resistance at 1 050 ℃. Since elements such as Ta and Y have a promoting effect on the selective generation of Al₂O₃ oxide film， the NiCoCrAlYTa coating can form a complete Al₂O₃ film at high temperatures， resulting in good oxidation and thermal corrosion resistance. NiCoCrAlYTa coatings prepared on high-temperature alloys using low-pressure plasma spraying technology have the advantages of dense structure， uniform elemental distribution， low porosity， as well as significantly improving the fatigue limit of the substrate and excellent high-temperature service performance， which has become the coating of choice for the hot-end components of turboshaft engines， especially the turbine blades. However， the low-pressure plasma sprayed NiCoCrAlYTa coating has problems such as the thickness distribution is not easy to be regulated and the size of the unmelted particles exceeds the standard. Especially， the unmelted particles will lead to the decrease of coating performance and the reduction of oxidation and corrosion resistance， which will shorten the service life of the blade. The problem of batch size exceedance of unmelted particles occurred in the trial production of a turbine blade coating for a certain type of engine. Through the analysis of the unmolten particles in the spraying process， it is determined by exclusion and reproduction verification that the NiCoCrAlYTa dust in the vacuum chamber enters the coating during spraying， leading to the exceeding of the size of the unmelted particles in the coating. To address the cause of the problem， by adopting enhanced transfer arc cleaning， the problem of exceeding the size of unmelted particles caused by dust contamination can be effectively avoided， and coatings that meet the technical quality requirements can be obtained. This study provides engineering experience for the disposal of low pressure plasma spraying coatings with excessive size of unmelted particles.