The Composite Strengthen Of Ti17 Alloy By The Electrical Discharge Surface Strengthening And IBED Technology

Wear resistance deficiency restrict extensive applications of titanium alloy in aviation industry and the others industry sectors. The composite strengthened layer formed on the surface of titanium alloy by electrical discharge surface strengthening and IBED is an innovational technology to improve wear resistance of titanium alloy. Titanium alloy Til7 was surface strengthened by adopting graphite, hard alloy YG-8, CoCrMo alloy, silicon bronze and tin bronze as electrodes on electrical discharge strengthening equipment. The properties of surface strengthened layers were measured. Based on testing results, two kinds of optimum strengthened layer were selected to deposited silicon bronze by IBED to formed composite strengthened layer on the surface of titanium alloy Ti17. SEM, XRD and glow discharge spectrometer were employed to analyze micro-structure, phase and composition distribution of the strengthened layers. Micro-hardness of strengthened layers was measured on micro-hardness instrument. Wear resistance of strengthened layers was evaluated on the two kinds of wear testing machine. In the air, the thermal fatigue tests were carried out on the thermal fatigue apparatus heated by ray radiation.After five kinds of electrodes have strengthened titanium alloy Ti17, metallurgical bonding are obtained between strengthened layer and substrate material, however, the strengthened layer is a bit thin. In addition, micro-crackles and micro-pores exist on strengthened layer;electrodes materials and substrate Ti17 material elements distribute in gradient along strengthening layer depth direction. Strengthened layers are mainly composed of compounds obtained from the reactions between electrode and substrate material. The micro-hardness of strengthen layer by graphite electrodes is maximum, whose value is 858HV. While the micro-hardness of strengthen layer by silicon bronze electrodes is minimum, whose value is 493 HV. Wear resistance of strengthen layer by silicon bronze electrode, using 180μF and 60V electrical parameter, is the best, whose worn weight loss is only one fortieth of the non-strengthened specimen during the same period.Micro-crackles and micro-pores exist in the base coat of electrical discharge surfacestrengthened, after composite strengthening, microstructure of copper film of depositedl-2um. Wear resistance of composite strengthen layer by silicon bronze electrode, using 180uFand 60V electrical parameter and IBED silicon bronze, is the best, whose worn volume is only one thirtieth of the non-strengthened Til7 specimen. After the thermal fatigue in 25°C~500°C, the amount and size of micro-crackles were increased in the strengthened layer, and silicon bronze deposition layers was oxidized, however, composite strengthened layers weren't break off. Damage evaluated by the relative change of electrical resistance of the specimen with composite strengthened layer was a bit higher than Til7 specimen without composite strengthened layer, in other words, thermal fatigue property of Til7 titanium alloy has a little change after composite strengthening.