Ultrahigh Current Density Nitrogen Ion Implantation-- Effects on the Microstructure and High Cycle Fatigue Properties

离子注入是最有前途的现代表面改性方法之一。为了实现低成本的离子注入，一种独特的宽束(直径10厘米)科罗拉多州立大学已经开发出超高电流密度(高达1500微安/平方厘米，而传统的6微安/平方厘米)离子注入机。首席调查员将研究高电流密度离子注入的影响。在高电流密度下，1018马氏体钢和许多其他合金的块体在高电流密度下能达到高温，但注入时间短，对块体(注入区下)硬度或块体组织没有影响。PI将研究高电流密度离子注入的下列方面：a)基于注入时间和温度以及钢的合金含量的钢的允许电流密度，b)通过电子金相比较低电流密度和高电流密度下氮离子注入α-铁所形成的硬氮化物相，以及c)在常规低电流密度(10微安/平方厘米)和CSU高电流密度(1500微安/平方厘米)氮离子注入下的高周疲劳抗力的比较。等电点在高电流密度下观察到氮离子的范围增加了四倍，从而对表面滑移有更大的抑制作用。滑移滞后可以延缓高周疲劳裂纹的萌生，提高疲劳寿命。

One of the most promising modern processes for surface modification is ion implantation. In order to achieve low cost ion implantation, a unique broad beam (10 cm.dia.) ultrahigh current density (up to 1500 Micro A/Square cm compared to conventional 6 Micro A/Square cm) ion implanter has been developed at the Colorado State University. The Principal Investigator will study the effects of high current density ion implantation. High temperatures are reached at high current densities, but the short implantation time produced no change in the bulk (beneath implanted zone) hardness or bulk microstructure in blocks of 1018 martensitic steel and many other alloys following high current density ion implantation. The PI will investigate the following aspects of high current density ion implantation: a) Permissible current densities for steels based on the time and temperature of implantation and the alloy content of steels, b) Comparison of the hard nitride phases formed due to nitrogen ion implantation in alpha-iron at low and high current densities by electron metallography, and c) Comparison of high cycle fatigue resistance of alpha-iron subjected to conventional low current density (10 Micro A/Square cm) and the CSU high current density (1500 Micro A/Square cm) nitrogen ion implantation. The PI has observed a four fold increase in the range of nitrogen ions at high current densities, resulting in a greater retardation of surface slip. Slip retardation would delay crack initiation in high cycle fatigue and increase fatigue life.