Study of Selective Laser Melting of intermetallic TiAl powder using integral analysis

• Published in: International journal of machine tools & manufacture Vol. 129; pp. 1 - 14
• Main Authors: Doubenskaia, Maria, Domashenkov, Alexey, Smurov, Igor, Petrovskiy, Pavel
• Format: Journal Article
• Language: English
• Published: Elmsford Elsevier Ltd 01.06.2018; Elsevier BV
• Subjects: Concentration profiles; Cooling rate; Energy dispersive X ray spectroscopy; Evaporation; Experiments; Fluid mechanics; Heat treatment; Heating; Intermetallic compounds; Laser beam melting; Lasers; Mathematical models; Melting; Metallography; Metals; Monitoring; Optical diagnostics; Parametric analysis; Powder preheating; Process parameters; Scanning electron microscopy; Selective Laser Melting; SLM modelling; Spectrum analysis; Thermal emission; TiAl intermetallic; Titanium aluminides; X-ray diffraction; SLM modelling; Concentration profiles; Selective Laser Melting; Optical diagnostics; TiAl intermetallic; Powder preheating
• ISSN: 0890-6955; 1879-2170
• DOI: 10.1016/j.ijmachtools.2018.02.003

Selective laser melting (SLM) of intermetallic Ti–48Al–2Cr–2Nb powder is studied using different and complementary methods: (a) experimental parametric analysis (variation of laser power, beam scanning velocity, etc.); (b) metallography including X-ray diffraction (XRD) and energy-dispersive X-ray spectroscopy (EDS), scanning electron microscopy (SEM); (c) optical monitoring by infra-red (IR) camera, high speed pyrometer and (d) mathematical modelling. The advantage of the present approach is based on parallel application of diverse methods of analysis using the same SLM set-up and feedstock powder. Also the novelty is related to the preheating of the entire manufacturing module up to 450 °C which is applied before and during the manufacturing of the samples. XRD analysis shows domination of the α2-Ti3Al phase in the initial powder, heat treated powder before SLM and in the developed samples. Some minor peaks of γ-TiAl are identified in SLM parts. EDS analysis confirms the effect of Al evaporation, which intensifies with laser energy input. IR-camera is used for optical monitoring of a single track formation. The geometry of the thermal emission field for different processing parameters is compared with the track geometry. The intensification of hydrodynamic instabilities accompanied by material rejection from the zone of powder consolidation with beam scanning velocity is found. For the first time the evaporation of Al for elevated laser energy input is clearly detected by the IR-camera. Mathematical modelling shows that the same elementary volume of SLM sample can be remelted several times during its fabrication depending on the SLM processing parameters and beam scanning strategy. The maximum values of calculated cooling rates are in the order of 106 °C/s. For the first time the thermo-cycling during SLM parts fabrication is confirmed experimentally by pyrometer measurements. •Integral approach includes parametric analysis, metallography, optical monitoring and modelling.•The domination of α2-Ti3Al phase in the feedstock powder and SLM parts is found.•The composition of SLM track is governed by thermocapillary convection and Al evaporation.•IR-camera is used for monitoring of the SLM stability and Al evaporation.•The same elementary volume of SLM sample can be remelted several times during its fabrication.