稀土对等离子体电解渗碳层组织结构和性能的影响

Effect of Rare Earths on Microstructure and Properties of Plasma Electrolytic Carburized Layer

目的研究稀土对液相等离子体电解渗碳层组织结构和性能的影响。方法将稀土LaCl_(3)·7H_(2)O和CeCl_(3)·7H_(2)O添加到电解液中,在17-4PH不锈钢表面制备有无稀土添加的液相等离子体电解渗碳层。通过扫描电子显微镜、金相显微镜、X射线衍射仪分析渗层的表面形貌、截面组织和相结构,利用维氏硬度计、洛氏硬度计和摩擦磨损试验机评价渗层的硬度、塑韧性和耐磨性。结果渗碳层主要由碳化物、“膨胀”α相和少量铁氧化物组成,稀土LaCl_(3)·7H_(2)O和CeCl_(3)·7H_(2)O均可以促进等离子体电解渗碳层表面碳化物的生成,且稀土CeCl_(3)·7H_(2)O可以有效抑制渗层表面铁氧化物的生成。添加稀土LaCl_(3)·7H_(2)O和CeCl_(3)·7H_(2)O后,渗层表面多孔化合物层厚度由20μm分别减小至15μm和8μm,致密层+扩散层的厚度从20μm分别增加至46μm和45μm。添加稀土LaCl_(3)·7H_(2)O和CeCl_(3)·7H_(2)O后,渗层的有效硬化层厚度可达70μm,是不加稀土时的3倍以上,截面硬度呈梯度分布。添加稀土LaCl_(3)·7H_(2)O和CeCl_(3)·7H_(2)O后,渗层表面洛氏压痕附近的径向裂纹出现了明显的偏转。添加稀土LaCl_(3)·7H_(2)O可使摩擦前期摩擦因数显著降低至0.14,磨痕宽度减至534μm,主要发生氧化磨损、化合物层剥落和磨粒磨损,而添加稀土CeCl_(3)·7H_(2)O可使摩擦因数一直维持在0.21左右,磨痕宽度显著减少至226μm,主要发生轻微的磨粒磨损。结论稀土LaCl_(3)·7H_(2)O和CeCl_(3)·7H_(2)O均可以改善渗层表面质量,提高等离子体电解渗碳层的耐磨性,且稀土CeCl_(3)·7H_(2)O的效果更显著。

To study the effect of rare earths on the microstructure and properties of liquid plasma electrolytic carburized layer,in this paper,the rare earths LaCl_(3)·7H_(2)O and CeCl_(3)·7H_(2)O were added to the electrolyte,and the liquid plasma electrolytic carburized layer with or without rare earths addition was prepared on the surface of 17-4PH stainless steel.The surface morphology,cross-sectional structure and phase structure of the infiltrated layer were analyzed by scanning electron microscope,metallographic microscope and X-ray diffractometer.The hardness,toughness and wear resistance of the infiltrated layer were evaluated by Vickers hardness tester,Rockwell hardness tester and friction and wear tester.The results show that the carburized layer is mainly composed of carbides,expansive“α”phase and a small amount of iron oxides.Both LaCl_(3)·7H_(2)O and CeCl_(3)·7H_(2)O can promote the formation of carbides on the surface of the plasma electrolytic carburized layer,and CeCl_(3)·7H_(2)O can effectively inhibit the formation of iron oxides on the surface of the carburized layer.After adding rare earths LaCl_(3)·7H_(2)O and CeCl_(3)·7H_(2)O,the thickness of the porous compound layer on the surface of the infiltration layer decreased from 20μm to 15μm and 8μm respectively,and the total thickness of the dense layer+diffuse layer increased from 20μm to 46μm and 45μm respectively.The thickness of the infiltration layer increased,the surface roughness decreased and the compactness increased.After adding rare earths LaCl_(3)·7H_(2)O and CeCl_(3)·7H_(2)O,the effective hardened layer thickness of the layer can reach 70μm,which is more than 3 times that without rare earths,and the cross-section hardness is gradient distribution.After adding rare earths LaCl_(3)·7H_(2)O and CeCl_(3)·7H_(2)O,the radial cracks near the Rockwell indentation on the surface of the carburized layer appeared obvious deflection,which alleviated the decrease of toughness after plasma electrolytic carburizing.The addition of rare earths LaCl_(3)·7H_(2)O can significantly reduce the friction coefficient to 0.14 at the early stage of friction,and the width of wear scar is reduced to 534μm,which mainly occurs oxidative wear,compound layer spalling and abrasive wear.The addition of rare earths CeCl_(3)·7H_(2)O can maintain the friction coefficient at about 0.21,and the width of wear scar is signi ficantly reduced to 226μm,which mainly occurs slight abrasive wear.Both rare earths LaCl_(3)·7H_(2)O and CeCl_(3)·7H_(2)O can increase the thickness of the infiltration layer,improve the surface quality of the infiltration layer,and improve the hardness and wear resistance.Among them,the effect of rare earths CeCl_(3)·7H_(2)O on improving the surface quality of the infiltration layer and improving the wear resistance is more significant.