Chemically graded Fe–Al/steel samples fabricated by laser metal deposition

By laser metal deposition (LMD) samples from Fe–28Al (at.%) have been built on iron and various steels. Chemically graded iron aluminium and Fe–28Al/steel samples were fabricated with intended concentration gradients by controlling the feed rates of the powders. All samples were subsequently heat treated at 700 °C for 1000 h to study possible reactions between Fe–28Al and the steels and the long-term stability of the composition gradients. Microstructures were characterized by scanning electron microscopy (SEM) and concentration profiles along the building direction were analysed by energy- and wavelength-dispersive spectrometry (EDS, WDS)

Growing of bulk sapphire single crystals using laser material deposition

A device to grow oxide single crystals via powder based laser additive manufacturing has been built and successfully tested. Single crystals of sapphire as demonstrator materials have been grown to prove the ability of this technique. A sapphire seed disk with a diameter of 25.4 mm is heated in a high temperature furnace up to 1550 °C. Through a hole of the furnace-lid, the seed disk is irradiated by CO2 laser radiation. Simultaneously, Al2O3 powder is fed into the furnace via ceramic tubes. The molten material solidifies on the seed material with exactly the same crystallographic orientation, thus retaining the single crystal structure. A crack free single crystal of a few millimeters in height is produced

Laser metal deposition and selective laser melting of Fe-28 at.% Al

The iron aluminide Fe3Al has been successfully processed by selective laser melting (SLM) and laser metal deposition (LMD). Process parameters have been determined by which defect free and dense (>99.5%) samples were produced. However, due to the low thermal conductivity of Fe3Al, preheating the substrate to 200 °C was necessary to prevent cracking during cooling. Microstructural characterization by electron backscatter diffraction (EBSD) showed that in spite of the high cooling rates large elongated grains grew in the building direction, more distinctive for SLM than for LMD. These grains show a continuous change in the crystallographic orientation. Evaluation of the compressive flow stress showed that the anisotropic microstructure results in anisotropic mechanical properties, depending whether the samples are loaded in building direction or perpendicular to it. The alloy shows a very high strength up to 600 °C and - concerning the coarse microstructure - becomes d uctile already at low temperatures

Investigations of laser clad, thermal sprayed and laser remelted AlSi20-coatings on magnesium alloy AZ31B under constant and cycling thermal load

Magnesium alloys need to be coated for applications exhibiting mechanical or chemical loads. Al-based coatings with Si reinforcements have proven to be a suitable coating choice to offer good wear and corrosion protection. Especially in the automotive and aviation industry, the demand for lightweight construction materials such as Mg alloys is permanently growing. In some of these applications, like engine components, in passenger cars or shell parts in jet engines, Mg parts might also be exposed to thermal shocks or elevated temperatures. Laser clad, thermal spray and laser remelted thermal spray coatings made of AlSi20 were generated on magnesium alloy AZ31B. In order to qualify these coatings for applications exhibiting thermal loads, samples were exposed to 190 °C, 300 °C and 400 °C for time periods of 3 h to 144 h. Thermal shock testing was performed in a cycling heating (200 and 300 °C) and cooling (27 °C) with a cycle length of approx. 14 s. Increasing temperature and increasing heat exposure time period led to increasing diffusion between the coating and the substrate with formation of brittle Mg2Si. This led to the formation of cracks and pores under thermal loading which consequently resulted in delamination of the coating. The laser remelted thermal spray coatings behaved similar to the as-sprayed coatings since the layers were not melted. The results show that the performance of the AlSi20 coatings depends strongly on the coating process