采用超音速火焰喷涂技术(HVOF)在3种丙烷流量(30,36和42 L/min)下将机械球磨后的TiB2-25 Ni颗粒沉积在Q235钢表面上获得不同涂层,将涂层在600℃(50次、100次、150次)和800℃工况下进行热震试验,研究涂层的抗热震性能.采用扫描电镜(SEM)表征热震后涂层的表面和截面形貌以分析热震后的裂纹产生和扩展情况,通过X射线衍射技术(XRD)分析热震后涂层的物相演变规律.研究结果发现,3种涂层在600℃热震条件下随着热震循环次数的增加,涂层中裂纹扩展的愈加严重,且在热震150次后出现了纵向和横向裂纹,并且以丙烷流量为36 L/min时涂层失效最快.通过在800℃涂层热震后发现,涂层失效更快,涂层热震循环次数明显降低,并且在涂层表面出现了明显的网状式裂纹,在涂层截面中裂纹扩展的更为强烈,并延伸至涂层和基体的界面处,从而导致腐蚀介质(水或空气)进入至裂纹中使基体腐蚀,在交界处产生了明显的腐蚀产物.通过对涂层在不同热震条件后的XRD分析发现,3种涂层的主要物相仍然是TiB2和Ni,热震后涂层表面氧化物增多.
Different coatings were prepared on Q235 steel substrate surface used mechanical milling TiB2-25Ni particles as raw materials by high velocity oxygen fuel (HVOF) under three kinds of propane flows(30,36 and 42 L/min),the thermal shock property of the coatings at 600 ℃ (50 cycles,100 cycles and 150 cycles) and 800 ℃ was tested.The surface and cross-sectional morphology of the coatings after thermal shock test were studied by scanning electron microscopy (SEM) to analyze the crack generation and propagation,and the composition transformation of the coatings was analyzed by X-ray diffraction analysis (XRD).The results show that with increasing the thermal shock cycles,the propagating cracks of the three kinds of the coatings are worse at 600 ℃,and there are longitudinal and transverse cracks appeare in the coatings,especially the coating with propane flow rate of 36 L/min is the worst among the three coatings.The thermal shock cycles are obviously decreased and the coatings are invalid faster under 800 ℃ conditions,meanwhile,there are a network of cracks appear on the surface of the coatings,and the cracks propagate into the interface of the coating and substrate,it can lead to the substrate corroded by the corrosion medium (i.e.water,air) to form metallic oxide.By investigating the phase composition of the three coatings after thermal shock,the main composition of the coatings is TiB2 and Ni,and the metallic oxides increase after thermal shock test.
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