Date on Master's Thesis/Doctoral Dissertation
Starr, Thomas L.
This research was performed to establish the feasibility of using Direct Metal Deposition (DMD) technology to deposit nickel powder to a nickel substrate. The substrate is electrodeposited pure nickel, and the material to be deposited is Metco 56C-NS Nickel powder which is 99.5% nickel and 0.5% trace elements. The DMD process is a form of laser welding; metallica powder is fed into and melted by a high power C02 later, which also melts the substrate. As the melted substrate and power re-crystallize, they form a metallurgical bond, as opposed to the mechanical bond created in a normal welding process. The DMD equipment adds material to the substrate in layers; each previously added layer becomes the substrate for the subsequent layer. The process has a variety of parameters that affect the quality of the deposited material. Gas flow rates, laser power, and traverse rate are a few of the most important factors that affect the quality. Historically nickel has been hard to weld; it tends to have significant porosity and cracking in the welding area. In industry this is corrected by adding a small amount of a different element. The element added depends on the nickel alloy that is being welded. In applications dealing with pure nickel, literature suggests that titanium be added to the weld filler to reduce the tendency to be porous and crack. The addition of titanium to nickel powder was evaluated in this research, since it is suggested to significantly improve the quality of the DMD process. These experiments tested various levels of gas flow rates, laser power, traverse rate, and several levels of added titanium. These factors were evaluated to find which factors have the most significant affect on quality. The quality was determined by mechanical testing, visual inspection, and microstructure inspection. When the significant factors were determined, values were found that gave the highest Rockwell hardness. These factors were evaluated to determine how similar the deposited material performed and matched the original nickel substrate. From the results of the experiment, it is concluded that nickel powder can be deposited on a nickel substrate with a quality suitable of for industrial applications. The mechanical properties of the deposited nickel were lower than those of the original substrate, but the quality of the material was high. Subsequent processing, such as heat treatment, may be able to make the properties more similar. It was found that titanium was necessary for the deposition to be fully dense. Pure nickel was too porous to be used for industrial application. It is recommended that more research be completed in finding how post processing would affect the properties of the welded material. Additional knowledge would be gained by using deposited nickel in an industrial application and finding if the difference in properties affects the process. Results from real world evaluation would determine where future research should be directed.
Gravatte, Steven James, "Optimization of process parameters for direct metal deposition of nickel." (2005). Electronic Theses and Dissertations. Paper 525.