Nanostructured coatings produced by plasma spraying

雾化Fe-18mass%Cr-2mass%B合金粉末是低压等离子喷涂到钢基体上，以产生具有非常细的硼化物沉淀的高性能涂层。基材要么是水冷的，要么是不冷却的。在后一种情况下，根据衬底预热的条件，衬底温度为1133K或1293K。研究了涂层的结构和力学性能。所得结果如下：(1)涂层的结构：在水冷基底上形成的涂层由非晶相和铁氧体组成。在1073K热处理时，非晶态相分解生成非平衡态Fe_3B，在更高热处理温度下出现（Cr, Fe）_2B。在使用预热基底喷涂的情况下，涂层的成分是亚微米尺寸的铁氧体和（Cr, Fe）_2B。随着喷涂过程中基材温度的升高，组成涂层的扁平颗粒之间的凝聚力增加，涂层的孔隙率降低。(2)涂层性能：水冷基底上涂层硬度高，但抗拉强度不高，约为0.67GPa。由于非晶相的消失，在预热基底上涂层的线束减小。这些涂层的抗拉强度高达1.4GPa，这是由于极细的硼化物析出物的分散和扁平颗粒之间的凝聚力的提高。在1473K下热处理后，涂层中硼化物颗粒粗化到0.9μm左右，涂层软化。而该涂层的抗拉强度为0.9GPa，延伸率约为10%，是目前工作中耐磨性最好的涂层。

Atomized Fe-18mass%Cr-2mass%B alloy powder is low-pressure plasma sprayed onto steel substrates to produce high performance coatings having very fine boride precipitates. The substrate is either water cooled or not cooled. In the latter case, the substrate temperature is 1133K or 1293K depending on the condition of the substrate preheating. The structures and the mechanical properties of the coatings are examined. The results obtained are as follows.(1) Structures of the coatings :The coating formed on the water-cooled substrate consists of an amorphous phase and ferrite. The amorphous phase decomposes on heat treatment at 1073K to form non-equilibrium Fe_3B, and (Cr, Fe)_2B appears at higher heat treatment temperatures. In the case of spraying using preheated substrates, the constituents of the coatings are ferrite and (Cr, Fe)_2B of submicrometer size. As the substrate temperature during spraying becomes higher, the cohesion between flattened particles composing the coatings increases and the porosity of the coatings decreases.(2) Properties of the coatings :While the coating on the water-cooled substrate has a high hardness, its tensile strength is not so high and is about 0.67GPa. The harness decreases in the case of the coatings on preheated substrates due to the disappearance of the amorphous phase. The tensile strength of these coatings is as high as 1.4GPa, which is attributed to the dispersion of very fine boride precipitates and to the improved cohesion between the flattened particles. When this coating is heat treated at 1473K, the boride particles coarsen to a size of about 0.9μm and the coating softens. This coating, however, has a tensile strength of 0.9GPa with the elongation of about 10% and the best wear resistance in the present work.