宽温域环境下不同纤维织物/聚酰亚胺复合材料的摩擦学性能研究

Tribological Properties of Polyimide Composites Filled with Different Fiber Fabrics in a Wide Temperature Range

目的 研究高温条件下聚合物织物复合材料的摩擦学性能。方法 分别制备碳纤维织物及芳纶纤维织物/聚酰亚胺复合材料及纯聚酰亚胺(CF-PI、AF-PI及PI),对比研究2种织物复合材料与聚酰亚胺的热力学性能,以及在25、50、100、150、200℃下的摩擦学性能。结果 AF-PI的热稳定性低于CF-PI,其中CF-PI热失质量稳定在800℃左右,AF-PI的热失质量稳定在700℃左右。同时,2种织物复合材料的拉伸强度均高于纯PI,且CF-PI的拉伸强度要高于AF-PI。断面形貌分析发现,CF-PI为脆性断裂,AF-PI为韧性断裂。摩擦实验结果表明,25℃时,AF-PI的摩擦系数和磨损率较低,更适用于室温环境,而CF-PI在200℃时具有较好的耐磨性,其磨损率为1.48×10–4 mm^(3)/(N·m)。结论 转移膜结构和化学状态分析证实,由于CF-PI与GCr15之间较强的界面作用,室温条件下对摩后,轴承钢表面更易发生摩擦氧化。高温条件下,由于金属–有机螯合物的形成,提高了转移膜的结构稳定性,CF-PI表现出优异的摩擦学性能,然而200℃时,由于AF-PI的力学性能降低,材料被磨穿,转移膜的结构被破坏,导致了金属之间的摩擦,发生了严重的摩擦氧化。

Polymer fabric composites are reinforced with fiber fabric with polymer as matrix.Compared with pure polymers,fabric composites can greatly improve the mechanical properties and service life of the materials.However,researches on the tribological properties of polymer fabric composites mostly focus on dry friction and lubrication,and there are few reports on them in high temperature environment.Therefore,to study the tribological properties of polyimide composites at high temperature,carbon fiber fabric impregnated with polyimide(CF-PI),aramid fabric impregnated with polyimide(AF-PI)and pure polyimide(PI)were prepared by a two-step method with 4.4'-diaminodiphenyl ether(ODA)and 3.3'-4.4'-biphenyltetracarboxylic acid(BPDA)as monomers.The tribological properties of these composites in a wide temperature range were investigated,and the wear mechanism and the formation mechanism of the tribofilm were discussed.Firstly,the prepared polyamide acid(PAA)solution was evenly coated on the fabric surface(the mass fraction of fiber fabric was controlled at 60%),and placed on a constant temperature heating table at 80℃for 6 hours to evaporate all the solvent.Then it was put into a tubular furnace and kept at 100,200,250 and 280℃for 1 h respectively to make PAA imide into PI,subsequently the CF-PI and AF-PIcomposites were obtained(the prepared method of CF-PI was the same with that of AF-PI).The structures of the samples were characterized by Fourier Transform Infrared Spectroscopy(FT-IR,Nicole 8700),the result of which confirmed that the materials were successfully prepared.Thermogravimetric Analyzer(TGAQ500)and Universal Testing Machine(WDW-100)were used to characterize the thermodynamic properties of the samples.The results showed that the thermal stability of CF-PI was better than that of AF-PI.The decomposition temperature of CF-PI steadied at about 800℃,and that of AF-PI was stable at about 700℃.The tensile strength of CF-PI and AF-PI was higher than that of PI owing to the reinforcing effect of fiber fabric.Nevertheless,the tensile strength of CF-PI was greater than that of AF-PI,probably because that the higher tensile strength of carbon fiber fabric than that of aramid fiber fabric.The tribological properties of all the samples were studied at high/low temperature with vacuum tribology tester.The friction pair was ball-on-disk contact and the upper sample wasϕ6.0 mm bearing steel ball(GCr15),the lower test plate wasϕ32.0 mm×10.0 mm fabric surface.The tribological properties of the materials at 25,50,100,150 and 200℃were investigated,respectively.The loading force was set as 50.0 N,the rotating speed was 200 r/min and the sliding time lasted for 1.0 h.Tribological results showed that the AF-PI displayed the lowest friction coefficient and wear rate at 25℃,so it is more suitable to be used at room temperature.CF-PI exhibited excellent wear resistance at 200℃.The wear rate was 1.48´10-4 mm^(3)/(N×m).The structure and chemical state of the tribofilm showed that the steel counterpart was apt to oxidize during the sliding process at room temperature due to the strong interfacial interaction between CF-PI and GCr15.At high temperature,the formation of a metal-organic chelate on the counterpart enhanced the robustness of the tribofilm,which endowed CF-PI with excellent tribological properties.Regarding AF-PI,the decreased mechanical performance at 200℃caused the direct sliding between metals,which destroyed the tribofilm structure and accelerated tribo-oxidation.