在K38G高温合金基体上分别设计涂覆了75%搪瓷釉+25%Al₂O₃ (E25A)和70%搪瓷釉+20%Al₂O₃+10%NiCrAlY (E20A10M) 2种搪瓷基复合涂层,对比研究了2种搪瓷基复合涂层在900 ℃下模拟燃气热冲击条件下的防护机制。热冲击的火焰采用C₃H₈+O₂混合气体产生,喷射到试样涂层表面的压力为0.4 MPa,火焰喷射到试样涂层达到900 ℃后保持15 s,而后空气中冷却120 s为一个热冲击循环周期。结果表明,经燃气冲击150 cyc后,2种涂层与合金基体界面结合牢固,表现出优异的抗界面剥落能力。其中,E25A涂层热冲击前后的涂层组织结构无明显变化,表面完好,Al₂O₃第二相的加入提高了搪瓷的高温稳定性;而E20A10M涂层热冲击后表面产生了孔洞、开裂,发生了轻微的表层剥离。金属粉与搪瓷的界面反应Cr_(NiCrAlY)+ZnO_(enamel)→CrO_(interface)+Zn↑,致使涂层表面鼓包,在燃气切应力和界面热应力作用下,表层金属颗粒以及搪瓷发生剥离。

High-temperature-resistant enamel coatings have been reported to be applied in non-critical hot end components of aero-engine and gas turbine recently. Although the enamel with a series of excellent properties can be as high-temperature-resistant coating material under appropriate condition, its lower soft point and inherent brittleness limit their use in broader application under severe service condition. Enamel-based composite coatings (an enamel matrix with the addition of ceramic particles and/or metal platelets) can remarkably increase the properties of the enamel coating and their protection mechanism under dynamic thermal shock needs further investigation. In this work, two kinds of enamel-based composite coatings, 70%enamel+25%Al₂O₃ and 70%enamel+20%Al₂O₃+10%NiCrAlY (mass fraction, %) abbreviated to E25A and E20A10M respectively, were designed and fired on K38G superalloy substrate, and their protection mechanism was comparatively studied at 900 ℃ under the simulated combusting gas shock. The thermal shock fire was produced by the mixture gas of C₃H₈+O₂ and its ejecting pressure on the coating surface was 0.4 MPa. After the temperature has been stable at 900 ℃, samples were hold for 15 s and then cooling down in air for 120 s, constituting a thermal shock cycle. Results indicated that, after 150 cyc of thermal shock, both the coatings bond well with the alloy substrate, thus shows high resistance to spallation along interface. For the E25A coating, its microstructure had no obvious change after thermal shock and the surface is still intact. The addition of secondary phase Al₂O₃ increases the stability of enamel at high temperature. With regard to the E20A10M coating, holes and cracks form consecutively, and peeling off occurs at surface after thermal shock. Interfacial reaction between the NiCrAlY particles and enamel following Cr_(NiCrAlY)+ZnO_(enamel)→CrO_(interface)+Zn↑ results in the formation of enamel swelling, which then, under the synergistic effect of combusting gas shear stress and interface thermal stress, leads to the peeling off of enamel and metal inclusions at surface.