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Real-time Spectrographic analysis of melt pool composition for the generation of accurate functionally graded materials

Final Activity Report Summary - RETISPAN (Real-Time spectrographic analysis of melt pool composition for the generation of accurate functionally graded materials)

The control of the complex nature of the direct laser deposition (DLD) process is currently under investigation by many research groups worldwide. The fellow investigations allow the development of a non-contact composition monitoring technique for the DLD process. Current state-of-art was expanded via developed spectroscopic analysis of the melt pool composition at host institutions.

The in situ application of spectroscopy is potentially a powerful tool to obtain information about the composition created during the DLD process. Identification of elements by spectra lines can determine in real-time how the melt pool composition has been changed by laser irradiation. The work reported here centres on studies performed with different solid state and CO2 laser systems to investigate the feasibility of applying real-time spectroscopy and fast digital imaging to the DLD process. Initial work proved that the recorded signal analysis was correlated to the composition during laser irradiation of a number of pure metal powders, e.g.: Ti, Cr, Mn, Co, Ni, Cu, Zn, Nb, Mo, Sn, Fe. Several complex phase metal alloys have also been studied, e.g.: INCONEL 625, Durit PTA, Stellite 21, 316L. The coaxial and side powder nozzles were applied.

High-speed imaging has also been utilised to analyse metal vapour formation above the melt pool. The metal vapour gradient intensity was processed in different wavelength regions, i.e. the image can be processed in three various colours zone (RGB), than can separate the metal vapour from molten metal. The 'plume thickness' (cross-sections method) was also determined.

The fellow work shows that the size and shape of the melt pool of the deposited layer can be successfully gathered from the process. The RGB contour profiles and numerical cross-section method via Matlab programs gives opportunities for determining the melt pool dimensions. This collected data can be used in a feedback control technique for control of mixing of dissimilar materials, or for control of dilution of base materials. So far, this is very unique method, and a review of the current state-of the art in the research field has failed to show any similar research efforts. The proposed method exploited into DLD technique is very novel aspect for process analysis. The work performed proved that in-situ spectroscopy along with high speed imaging has the potential to be successfully used for process control.

The composition recorded from the emission lines is correlated with the known spectroscopic material database. The Fraunhofer IWS has also recently developed a heat sensitive camera base system (E-MAQs), which is currently under investigation to measure and control the DLD process. The host efforts and fellow work meet project expectation and gives fruitful results in state-of-art DLD process control.

The results obtained so far are very promising for various industrial applications, e.g. application of corrosion resistant alloys (stainless steel) to carbon steel. It is expected that a single monitoring system would be able to detect and indicate unwanted variations in composition. Additionally development of spectroscopic analysis for the real-time monitoring composition of the melt pool, will allow the generation of accurate functionally graded materials (FGMs). This data has confirmed the feasibility of applying spectroscopy using the low cost portable spectrometer for in situ melt pool measurements.

The development of experimental equipment using a return host E-MAQs is expected to yield more quantitative results with potential for further publications within the project timescales. The fellow made a valuable contribution to the study of DLD different type of materials, including aerospace and biomedical alloys, which is important research towards achieving a non-contact method of DLD composition control. The DLD process is potentially of significant value to industry sectors such as aerospace, aeronautical, medical, automotive, and microelectronics. The research project of the fellow was innovative and in an expanding area of research, which indicates that his research will be of significant importance for European countries.