An investigation into laser deposition of machining chips and characteristics of the final clad

摘要

Laser metal deposition is an additive manufacturing technique to build fully dense structures with a strong metallurgical bonding with the underlying material. Spherical gas-atomised metal powders are principally used as build material which is a costly option and restricts its application on a wide scale. On the other hand, nonspherical particles produced by machining are much cheaper to produce and readily available as waste swarf which should be recycled. The use of machined particles as a viable form of build material for laser direct metal deposition has not been explored previously and is the subject of the investigations reported in this thesis.;In the first work, samples of carbon steel machining swarf in three size ranges were laser deposited to build thin walls. The produced walls exhibited fine martensitic microstructure with minimal porosity. As general trends, individual deposition tracks were found to be lower, and wider with an increase of particle size. 50% reduction in hardness was observed when using coarser particle size. This work was extended so as to build U-shaped structures with variable laser power in contrast to the previous work which was done with one set of processing parameter values. The microstructure observed was similar to that of the previous work. However, hardness has found to increase with decrease in laser power.;After successful deposition and encouraging results from the process, machining swarf of Inconel 617 was used to produce corrosion resistant layers on a mild steel substrate. A Design of Experiment methodology was used to analyse the relationship between the processing parameters and the coated layer characteristics. The layer thickness and hardness were found to increase with the mass feed rate whilst an increase in laser power produced the opposite result. All layers had a predominantly dendritic microstructure and displayed remarkably higher corrosion resistance than the mild steel sample. The work was expanded to investigate the surface characteristics and corrosion resistance in a harsh corrosive environment, using different pH brine solutions. In this investigation, four layers were produced with two laser power and mass feed rate values. Accounting for all measurements, Inconel 617 swarf built layers provided very good corrosion protection and confirmed the viability of using this method as a low-cost corrosion protection for both mild and harsh environments.;Since the investigations authored above were confined to swarf alone, the final chapter examines the comparison of stainless steel 316L thin wall structures produced with swarf and gas-atomised powder using similar processing conditions. The build materials performed similarly, but walls made from swarf were slightly shorter with a coarser microstructure and had poorer corrosion resistance than the powder equivalents.;The results of these investigations confirm the feasibility of machining swarf as an alternative viable option. However, further research will help to explore its full potential.