材料期刊网

通过在粉末法渗硼过程中施加交流电场,对45钢进行中低温粉末法渗硼,研究交流电场增强中低温粉末法渗硼特性.结果表明,位于交流电场平行电极间不同位置处试样渗硼效果一致.施加适当的交流电场,可显著增加中低温(450～800℃)下的渗硼速度,硼化物层厚度与渗硼温度呈线性关系.交流电场增强渗硼渗层的形貌与常规渗硼的相似,呈锯齿状垂直楔入基体,其厚度与渗硼时间关系曲线呈抛物线型.采用交流电场易于获得单一Fe2B相渗层.在800℃渗硼时,交流电场增强渗硼的硼化物层厚度随电场电流增加而增加.交流电场的促渗作用是电场强化试样内的扩散、渗剂中的反应与扩散及提高渗罐内的实际温度等的综合结果.

Conventional pack boriding (CPB) has shortcomings of high processing temperature and long process duration for producing boride coating with an effective thickness.Alternating current field enhanced pack boriding (ACFEPB) is a new approach for overcoming those shortcomings in CPB.In the present work,ACFEPB was carried out on a 45 medium carbon steel at low and medium temperatures (450～800 ℃) by applying a 50 Hz alternating current field (ACF) during the pack boriding for revealing effects of ACF on the treatment.Understanding characterization of the ACFEPB better will lay a good foundation for investigating the mechanism of the ACF on the boriding and optimizing the new process.Experimental results showed that nearly same thick boride coatings were obtained in target surface of samples located in different positions right between the parallel ACF electrodes,while less thick boride coatings were found in samples not within the region.All ACFEPB samples' boride coatings were thicker than that of corresponding CPB,which demonstrated that applying an appropriate ACF could notably enhance the boriding.A linear relation was shown in the profile of ACFEPB coating thickness vs the boriding temperature.The coating thickness of the ACFEPB at 800 ℃ increased with the increase of the ACF current.And the coating thickness vs the boriding time exhibited a parabolic character.Morphology similar to the CPB coat-ing was presented in the ACFEPB coating.The saw-tooth shaped boride penetrated perpendicularly to the substrate.However,fewer or no FeB phase was found in ACFEPB coating when comparing with CPB coating treated at same temperature with same duration.More micro-porosities were found in the near surface zone of single Fe2B phase coating by ACFEPB,which was an indication that more vacancies moved from the substrate to the near surface region.Although a temperature rise caused by the ACF was detected in the sample during the boriding,the heating effect of the ACF to the sample and the boriding media was not the main reason for ACF's enhancing effect to boriding.The ACF' s electro-magnetic effect should be the main factor for the enhancement.The ACF induced current would lead more vacancies in the treated sample,which promoted the diffusion in the substrate.The ACF should also intensify chemical reactions and diffusions in the boriding media with the energy from the ACF and the ACF's electro-magnetic stirring effect.More active boron-containing species formed and moved to the sample's surface to accelerate the formation of borides.