Mitigating Inhomogeneity and Tailoring the Microstructure of Selective Laser Melted Titanium Orthorhombic Alloy by Heat Treatment, Hot Isostatic Pressing, and Multiple Laser Exposures

Titanium orthorhombic alloys based on intermetallic Ti2AlNb-phase are attractive materials for lightweight high-temperature applications. However, conventional manufacturing of Ti2AlNb-based alloys is costly and labor-consuming. Additive Manufacturing is an attractive way of producing parts from Ti2AlNb-based alloys. High-temperature substrate preheating during Selective Laser Melting is required to obtain crack-free intermetallic alloys. Due to the nature of substrate preheating, the temperature profile along the build height might be uneven leading to inhomogeneous microstructure and defects. The microstructural homogeneity of the alloy along the build direction was evaluated. The feasibility of mitigating the microstructural inhomogeneity was investigated by fabricating Ti2AlNb-alloy samples with graded microstructure and subjecting them to annealing. Hot isostatic pressing allowed us to achieve a homogeneous microstructure, eliminate residual micro defects, and improve mechanical properties with tensile strength reaching 1027 MPa and 860 MPa at room temperature and 650 °C, correspondingly. Annealing of the microstructurally graded alloy at 1050 °C allowed us to obtain a homogeneous B2 + O microstructure with a uniform microhardness distribution. The results of the study showed that the microstructural inhomogeneity of the titanium orthorhombic alloy obtained by SLM can be mitigated by annealing or hot isostatic pressing. Additionally, it was shown that by applying multiple-laser exposure for processing each layer it is possible to locally tailor the phase volume and morphology and achieve microstructure and properties similar to the Ti2AlNb-alloy obtained at higher preheating temperatures.

Characterization of Thermally Sprayed Coated GT Components Made of 3D Printing Based Selective Laser Melting Processed Inconel Alloy 718

Functional requirements like higher strength, resistance, and shielding from chemical reactions, degradation, etc., of the base metal are achieved by modifying their exposed surfaces using TBC (thermal barrier coating). Modified outer surface of components in the GT (gas turbine) improves the performance by the increase of inlet temperature, enhancing longer life and providing many interrelated surfaces to withstand severe working conditions. This work is based on characteristic (mechanical, thermal, and tribology) evaluation of TBC-coated GT components made of Inconel 718 manufactured from traditional and 3-D printing-based selective laser melting (SLM) process and compared. TBCs comprising bond coat and top ceramic oxide coat were deposited by High-Velocity Oxy-Fuel and Atmospheric Plasma Spraying techniques, respectively. Characteristics evaluated by varying coating thickness, standoff distance, substrate preheating, Input torch power, etc., revealed that characteristics of substrates manufactured from SLM methods improved significantly except porosity and average surface roughness. These improvements are essential for embedding sensors, thin films, etc., in TBCs for continuous monitoring of outputs.

Comparison of Substrate Preheating on Mechanical and Microstructural Properties of Hybrid Specimens Fabricated by Laser Metal Deposition 316 L with Different Wrought Steel Substrate

The combination of additive manufacturing and conventional metal forming processes provides the possibility for improvements of forming efficiency and flexibility. Substrate preheating is an implementable technique to improve the interface adhesion properties of the hybrid forming method. The present experiment investigates the adhesion of additive manufactured 316 L steel on P20 and 1045 steel substrates under two substrate temperatures, and the geometrical characterization, interfacial microstructure and mechanical property of the hybrid specimens were compared. As a result, it was found that the ratio of deposition height to the width was reduced and the width was increased under substrate preheating. Tensile results show that the ultimate strength of 1045 and 316 L hybrid specimens was obviously increased, while the properties of hybrid specimens P20 and 316 L were similar, under different substrate temperature conditions. For the hybrid specimens with the metallurgically bonding characteristic, the tensile properties can reach the level of 316 L depositioned specimens fabricated by laser metal deposition (LMD). Furthermore, substrate preheating had little effect on the microstructure of the laser metal deposition zone, and significant influence on the microstructure of the heat affected zone, which was reflected in the difference of the hardness distribution.

Wear Resistance Enhancement of Al6061 Alloy Surface Layer by Laser Dispersed Carbide Powders

In this paper, results of the experimental study on improving wear resistance in sliding friction of Al-based alloy are presented. The technique used involves the formation of a metal matrix composite (MMC) in the alloy surface layer by laser dispersion of carbide powders such as WC, TiC and SiC. For WC and TiC MMC surface coatings fabricated under conditions typical for most of the technologically relevant solid-state lasers (wavelength range of 0.8–1.1 μm), the nearly inversely proportional dependence of the required laser energy density on the powder mass density is observed. Highly homogenous distribution of powder particle content (up to 40%) in the MMC surface coatings of a thickness between 0.8 and 1.6 mm obtained by multiple scanning is observed in the cross-section of specimens processed within a rather narrow parameter window. Tribological tests and comparison to untreated material reveal wear resistance increases by five- and ten-fold, observed in samples with laser-dispersed TiC and WC powders, respectively. Results indicate that substantial modification and reinforcement of the surface layer can be achieved in Al alloy in a one-step process without substrate preheating.